Free Orthopedic MCQs 2022, Dec, 16 | 12:00 am

Orthopedic MCQS online Basic 018

AAOS BASIC SCIENCE

self Assessment 2018

Question 1 of 100 In the context of joint arthroplasty, the alpha-defensin immunoassay test is useful for the detection of

aseptic loosening.
metal corrosion.
periprosthetic infection.
bone ingrowth. Discussion: C

Alpha-defensin is a protein released by activated neutrophils in response to infection. The detection of alpha-defensin in synovial fluid is highly sensitive and specific as a marker of periprosthetic infection. Aseptic loosening and the bone ingrowth of prostheses generally are detected radiographically. Metal corrosion issues—in metal-on-metal prostheses, for example—generally are followed using blood metal ion levels.

Question 2 of 100

In posttraumatic arthritis, the initial injury stimulates the production

of inflammatory cytokines. Which cytokine is produced at the highest level on the first day after injury?

Interleukin-6 (IL-6)
Interleukin-1 beta (IL-1β)
Chemokine ligand 22 (CCL-22)
Damage-associated molecular patterns (DAMPs)

Discussion: B

The development of arthritis after joint injury is common and can result from multiple causes, including cartilage contusion, meniscal injury, ligament tear, or intra-articular fracture. The accuracy of reduction does not necessarily prevent the development of posttraumatic arthritis. Data from animal studies of posttraumatic arthritis demonstrate the production of inflammatory cytokines that lead to chondrocyte death and matrix destruction. In the first few days after injury IL-1β (predominantly) and tumor necrosis factor alpha are the primary cytokines produced, followed by nitric oxide, matrix metalloproteinases, and aggrecanases, which degrade the chondral matrix CCL-22 increases at around 5 days after injury, however. Other factors called DAMPs, which are generated through the mechanical or enzymatic degradation of joint tissues, also stimulate an innate inflammatory response.

Question 3 of 100

What is the main function of lubricin in synovial joints?

Serves as a component of the extracellular matrix
Inhibits matrix metalloproteinase
Increases cross-linking between collagen fibers
Reduces the coefficient of friction in the joint Discussion: D

Lubricin reduces the friction between the surfaces in the joint, leading to decreased shear forces going through the hyaline cartilage. It is a glycoprotein that is produced by the chondrocytes in the superficial zone and is not a primary component of the extracellular matrix. A lack of lubricin has been associated with syndromes causing arthritic changes at an early age.

Question 4 of 100

Anti-sclerostin antibody increases bone formation by targeting

what molecular pathway?

Wnt
Bone morphogenetic protein (BMP)
Notch
Indian hedgehog

Discussion: A

All of the listed factors serve critical functions in bone formation. Only BMP-based therapies currently are FDA approved, however. Sclerostin is an extracellular antagonist of Wnt signaling and, to a lesser extent, BMP signaling. Blosozumab currently is an investigational antibody therapy designed to block sclerostin’s ability to inhibit Wnt signaling, netting a positive effect on bone formation. In a phase 2 trial involving 120 postmenopausal women, 1 year of blosozumab treatment resulted in a 17% increase in bone mineral density in the lumbar spine.

Question 5 of 100

CLINICAL SITUATION

Figures 1 through 3 display radiographs and an MRI from a 29-year-old man who has complained of left leg pain since sustaining a gunshot wound 18 months ago. He denies any fevers or chills but does have pain and drainage from his wound. His erythrocyte sedimentation rate (ESR) is 105 mm/h (reference range: 0-20 mm/h), C-reactive protein (CRP) level is 12 mg/L (reference range: 0.08-3.1 mg/L), white blood cell (WBC) count is 8,000 /µL (reference range: 4500-11000 /µL), and vitamin D level is 15 ng/mL (reference range: 20-40ng/ml).

What is the tissue indicated by the arrow in Figure 4?

An unresorb ed butterfly fragment
Nonviable, infected bone
Heterotop ic ossification
Reactive bone formation Discussion: B

This patient has chronic osteomyelitis and infected nonunion of the tibia. The bone indicated by the arrow is sequestrum, or infected, dead bone. Involucrum is new bone laid down around the infection. Treatment of this infection requires debridement and local antibiotic delivery, often accomplished with an antibiotic-impregnated cement. The elution characteristics often vary by cement type, but generally, peak concentrations are reached in 24 hours, and the concentrations can remain bactericidal for 4 months.

illustrating why following a vancomycin trough is important. Drugs that kill in a concentration-dependent way still have effect, even after a limited exposure; this fact explains why the dosing for gentamycin is recommended once per day for open fractures.

Lastly, a biofilm is characterized by bacteria entering a no-growth, or sessile, phase, which makes them even more resistant to antibiotics that depend on replication to carry out their effect. Planktonic bacteria are the free bacteria that spread and often cause sepsis and active infection.

Question 6 of 100

CLINICAL SITUATION

After thorough debridement, the surgeon wishes to place an antibiotic-coated intramedullary nail made of polymethylmethacrylate (PMMA), plus vancomycin and tobramycin coat the nail by mixing them in the PMMA cement. Although in vivo concentrations of the antibiotics often peak during the first 24 hours, up to how many months can the concentrations be expected to remain bactericidal?

Discussion: B

Vancomycin is a common antibiotic used in cement delivery. Its mechanism of action disrupts cell-wall synthesis. It also kills bacteria in a time-dependent manner, not in a concentration-dependent way like tobramycin and other aminoglycosides. This means that, for the drug to be effective, the concentration must be above the minimal inhibitory concentration between doses, illustrating why following a vancomycin trough is important. Drugs that kill in a concentration-dependent way still have effect, even after a limited exposure; this fact explains why the dosing for gentamycin is recommended once per day for open fractures.

Question 7 of 100

CLINICAL SITUATION

The mechanism of action for vancomycin and tobramycin differ, in that vancomycin is

concentration-dependent, killing by inhibiting cell wall synthesis.
concentration-dependent, killing by binding the 30S ribosomal subunit.
time-dependent, killing by inhibiting cell wall synthesis.
time-dependent, killing by binding the 30S ribosomal subunit.

Discussion: C

Question 8 of 100

CLINICAL SITUATION

A major reason for implant removal is the formation of a bacterial biofilm that is extremely difficult to eradicate. This biofilm mostly likely includes bacteria in what stage?

Planktonic
Sessile
Rapid-proliferation
Metabolic

Discussion: B

generally, peak concentrations are reached in 24 hours, and the concentrations can remain bactericidal for 4 months.

Question 9 of 100

A clinical study enrolls patients into two groups to analyze the effects of smoking on patient-reported outcomes following elective spinal diskectomy. Patients are to be blinded and enrolled consecutively. The study data are analyzed after enrolling half the number of patients estimated to be needed by the power analysis. No statistically significant differences are found. Accepting the results at this point would be an example of

selection bias.
type 1 error.
type 2 error.
intent to treat.

Discussion: C

Type 2 error occurs when a clinical trial is underpowered to detect the treatment outcome differences between two groups. Type 1 error occurs when a false positive effect is detected. Selection bias refers to failure to properly randomize to achieve a representative sampling of the population. Intent to treat is a method of analysis based on initial allocation.

Question 10 of 100

Figures 1 and 2 show the radiographs from a 10-year-old female

gymnast with a 3-month history of wrist swelling and pain. During competition, her pain worsens acutely, and she now reports reduced range of motion. What is the location of the injury?

Zone of provisional calcification
Hypertrophic zone
Proliferative zone
Germinal layer Discussion: A

Skeletally immature athletes are at risk for injuries not seen in adults because of differences in the structure of the growing bone and physis. Growth plates are susceptible to shear injury at the epiphyseal-metaphyseal junction. Epiphyseal injuries present with

persistent or severe pain, deformity, or the inability to move a joint. Typically, physeal injuries occur from repetitive loading that disrupts the metaphyseal perfusion, inhibiting ossification in the zone of provisional calcification. The hypertrophic zone widens as chondrocytes continue to transition from the germinal layer to the proliferative zone. Widening of the physis may be seen radiographically.

Question 11 of 100

Fretting corrosion is defined as

motion between two pieces of metal that are loose.
the microisolation of oxygen, leading to disruption of passivation.
an electrochemical circuit formed between two different metals.
micromotion between two pieces of metal that are not loose. Discussion: D

Modular junctions are susceptible to fretting corrosion. During fretting corrosion, surface pressure between contacting surfaces at modular articulations cause friction. Surface pressure often is initiated by micromotion at the interfaces during mechanical loading. This micromotion physically can disrupt the passivation layer, leading to the release of metal particles and the facilitation of crevice corrosion. Micromotion is not the result of a loose implant. Rather, when the joint is loaded, the various components of the modular implant flex (slip region) while remaining together (stick region).

Question 12 of 100

A 10-year-old child arrives at the emergency department with pain

in the leg and a limp. An MRI shows acute osteomyelitis of the tibia without abscess formation. Blood cultures are positive for Staphylococcus aureus. The patient is admitted and treated

with intravenous antibiotic therapy. The next day, shortness of breath develops, and CT shows multiple pulmonary emboli. What gene in S aureus is responsible for the clinical deterioration of this patient?

Gene involved in biofilm formation
Penicillinase gene
Panton-Valentine Leukocidin (PVL) gene
Alteration in penicillin binding protein gene Discussion: C

The clinical deterioration seen in this patient mainly results from septic pulmonary emboli caused by septic deep vein thrombophlebitis. Septic deep vein thrombophlebitis can be seen as a complication of osteomyelitis in children. It more often is seen with tibial osteomyelitis. Leukocidin, a product of the PVL gene in the bacteria, has been reported to be responsible for this complication. Biofilm formation causes adherence to implants. Penicillinase and penicillin binding protein genes are responsible for drug resistance.

Question 13 of 100

CLINICAL SITUATION

Figures 1 and 2 show radiographs from a 12-year-old girl with a several-year history of multiple bony protuberances. On examination, she has palpable masses about the bilateral knees, wrists, and shoulders.

What is the inheritance pattern of the patient’s most likely diagnosis?

Autosomal dominant
Autosomal recessive
X-linked recessive
X-linked dominant Discussion: A

The radiographs demonstrate multiple osteochondromas or exostoses about the distal femur and proximal tibia. The patient’s most likely diagnosis is hereditary multiple exostoses (HME). The average age at diagnosis is 3 years old, and 94% of patients have exostoses about the knee. Other common sites include the proximal humerus, scapula, wrist, and proximal femur. The vast majority of patients display an autosomal dominant inheritance pattern, although spontaneous mutations have been described.

In most patients, the underlying genetic abnormality involves the EXT1 or EXT2 gene, located on chromosomes 8 and 11, respectively. These genes encode glycosyltransferases involved in the synthesis of heparan sulfate. Heparan sulfate plays an important role in physeal signaling, and chondrocyte disorganization leads to exostosis development. Chondroitin sulfate, dermatan sulfate, and keratan sulfate are other proteoglycans, but they are not involved in the pathogenesis of HME.

The lifetime risk of malignant transformation to chondrosarcoma in patients with HME has been reported to range between 1% and 25%; however, more recent studies have placed the risk between

between 3% and 7%. The most recent study demonstrated a 3% risk of malignant transformation at an average age of 29 years. Malignant transformation can occur in an exostosis in any location; however, pelvic exostoses have been shown to have a higher rate of malignant transformation.

The risk of malignant transformation has been noted to be higher in disorders involving multiple enchondromas, including Mafucci syndrome and Ollier disease. Some studies have demonstrated a nearly 100% risk of malignant transformation in Mafucci syndrome.

Question 14 of 100

CLINICAL SITUATION

Histologic analysis of this patient’s physis would reveal a reduction of what proteoglycan?

Chondroitin sulfate
Dermatan sulfate
Keratan sulfate
Heparan sulfate Discussion: D

The lifetime risk of malignant transformation to chondrosarcoma in patients with HME has been reported to range between 1% and 25%; however, more recent studies have placed the risk between between 3% and 7%. The most recent study demonstrated a 3% risk of malignant transformation at an average age of 29 years. Malignant transformation can occur in an exostosis in any location; however, pelvic exostoses have been shown to have a higher rate of malignant transformation.

Question 15 of 100

The immunomodulating medications infliximab and etanercept are

used to treat rheumatoid arthritis (RA) by targeting

Receptor activator of nuclear factor kappa-B ligand (RANKL).
Interleukin-1 (IL-1).
Beta cells.
Tumor necrosis factor alpha (TNF-α).

Discussion: D

Infliximab and etanercept are recombinant drugs designed to inhibit TNF-α, which is a macrophage-derived cytokine that mediates the destructive inflammatory response of RA. Anakinra is a biologic agent that targets IL-1. These agents are used in the treatment of RA. Denosumab is a monoclonal antibody that targets RANKL and is used in the treatment of osteoporosis.

Question 16 of 100

A short statured man standing 4 feet 6 inches with rhizomelic limb

shortening has a father and daughter with a similar short-statured appearance but has a normal-height mother. In what gene is the mutation most likely to have occurred?

SLC26A2
COL1A1
ACVR1
FGFR3

Discussion:D

The most common form of inherited rhizomelic dwarfism is achondroplasia, caused by a mutation in the FGFR3 gene. The inheritance pattern is autosomal dominant and is consistent with the previously described scenarios. COL1A1 mutations are causative for osteogenesis imperfecta; they are autosomal dominant and recessive, and affected people can be short statured but not rhizomelic. ACVR1 mutation is associated with fibrodysplasia ossificans progressive which can be inherited in an

autosomal dominant pattern, but is characterized by severe heterotopic ossification rather than rhizomelic malformity. Diastrophic dysplasia caused by mutation in SLC26A2 and is transmitted in autosomal recessive pattern, but is not typically rhizomelic.

Question 17 of 100

What is the most likely mechanism that causes the

thiazolidinedione group of antihyperglycemic medications to increase the risk of fractures? These medications

decrease the activity of receptor activator of nuclear factor kappa-B ligand (RANKL).
increase tumor necrosis factor alpha (TNF-α).
suppress osteoblastic transcription factors.
decrease osteoprotegerin. Discussion: C

Question 18 of 100

A surgeon has decided to implement a new draping technique for

the open reduction and internal fixation of ankle fractures that she believes will reduce waste. All materials have received clearance from the Food and Drug Administration. She has completed 20 such cases, and now wishes to retrospectively review this case series to perform a cost-savings analysis, the results of which will be presented at the Hospital Quality Control Committee Meeting. She has no plans to publish her data in peer reviewed journals. This type of investigation can be described as

exempt human subjects research
expedited human subjects research
human subjects research requiring full board
process improvement Discussion: D

The primary purpose of the institutional review board (IRB) is to ensure the privacy and safety of human research subjects. The IRB offers three different levels of review depending on the risk level of the study, and the full board is reserved for investigations involving the highest risk. Studies involving deidentified data and those that present no more than minimal risk can be considered exempt from review. In this case, however, the surgeon simply wishes to perform a retrospective review of her own cases for quality improvement. Therefore, this type of review is not research and is considered process improvement.

Question 19 of 100

Figure 1 shows an MRI from a 54-year-old man who has

experienced a substantial increase in axial back pain that intermittently responds to oral NSAIDs. He works for a moving company, and his lumbar range of motion has been limited, especially with flexion. The pathologic change seen on MRI can be attributed to an increase in

Type II collagen.
proteoglycan.
chondrocytic apoptosis.
water. Discussion: C

Dark disk findings on T2-weighted MRI reveal a reduction in the content of extracellular water and proteoglycan. Chondrocytes produce and maintain the normal extracellular matrix. As cells within the disk die, the extracellular matrix declines.

Question 20 of 100

When applying an external fixator, the surgeon always must

consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

The weakest point of a fixation pin

Pin diameter
Hydroxyapatite coating
Increased bone-to-rod distance
Thread-shank junction
Increased pin spread
Excessive motion of muscle and/or skin around the pin
Pin-clamp junction Discussion: D

possible and another pin as far away as possible in the same bone. Stability can be enhanced by increasing the pin diameter, the number of pins used, the pin spread, the number of planes of fixation, the diameter of the rods, and the number of rods and by decreasing the bone-to-rod distance. A fixation pin’s weakest point is the thread-shank junction. Burying the shank into the proximal cortex can double the pin’s stiffness. Hydroxyapatite-coated pins have been shown to improve the pin-bone interface and require greater extraction torque. It is thought that excessive motion of muscle and skin around the pin results in local inflammation, leading to pin tract infections. This risk can be reduced by using a gentle compressive dressing around the pin that serves as a bolster between the skin and the clamp.

Question 21 of 100

When applying an external fixator, the surgeon always must

consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

Pin site infection

Pin diameter
Hydroxyapatite coating
Increased bone-to-rod distance
Thread-shank junction
Increased pin spread
Excessive motion of muscle and/or skin around the pin
Pin-clamp junction Discussion: F

The application of external fixation always involves a risk-benefit evaluation that includes the key considerations of stability, soft-

tissue protection, and the potential for future surgery. An external fixation device may be constructed in many ways, but certain principles are to be considered. The ideal construct for stability generally consists of one pin as close to the fracture site as possible and another pin as far away as possible in the same bone. Stability can be enhanced by increasing the pin diameter, the number of pins used, the pin spread, the number of planes of fixation, the diameter of the rods, and the number of rods and by decreasing the bone-to-rod distance. A fixation pin’s weakest point is the thread-shank junction. Burying the shank into the proximal cortex can double the pin’s stiffness. Hydroxyapatite-coated pins have been shown to improve the pin-bone interface and require greater extraction torque. It is thought that excessive motion of muscle and skin around the pin results in local inflammation, leading to pin tract infections. This risk can be reduced by using a gentle compressive dressing around the pin that serves as a bolster between the skin and the clamp.

Question 22 of 100

When applying an external fixator, the surgeon always must

consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

Provides greater extraction torque of fixation pins

Pin diameter
Hydroxyapatite coating
Increased bone-to-rod distance
Thread-shank junction
Increased pin spread
Excessive motion of muscle and/or skin around the pin
Pin-clamp junction

Discussion: B

The application of external fixation always involves a risk-benefit evaluation that includes the key considerations of stability, soft-tissue protection, and the potential forfuture surgery. An external fixation device may be constructed in many ways, but certain principles are to be considered. The ideal construct for stability generally consists of one pin as close to the fracture site as possible and another pin as far away as possible in the same bone. Stability can be enhanced by increasing the pin diameter, the number of pins used, the pin spread, the number of planes of fixation, the diameter of the rods, and the number of rods and by decreasing the bone-to-rod distance. A fixation pin’s weakest point is the thread-shank junction. Burying the shank into the proximal cortex can double the pin’s stiffness. Hydroxyapatite-coated pins have been shown to improve the pin-bone interface and require greater extraction torque. It is thought that excessive motion of muscle and skin around the pin results in local inflammation, leading to pin tract infections. This risk can be reduced by using a gentle compressive dressing around the pin that serves as a bolster between the skin and the clamp.

Question 23 of 100

When applying an external fixator, the surgeon always must

consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

Increases construct stability

Pin diameter
Hydroxyapatite coating
Increased bone-to-rod distance
Thread-shank junction
Increased pin spread
Excessive motion of muscle and/or skin around the pin
Pin-clamp junction

Discussion: 5

The application of external fixation always involves a risk-benefit evaluation that includes the key considerations of stability, soft-tissue protection, and the potential for future surgery. An external fixation device may be constructed in many ways, but certain principles are to be considered. The ideal construct for stability generally consists of one pin as close to the fracture site as possible and another pin as far away as possible in the same bone. Stability can be enhanced by increasing the pin diameter, the number of pins used, the pin spread, the number of planes of fixation, the diameter of the rods, and the number of rods and by decreasing the bone-to-rod distance. A fixation pin’s weakest point is the thread-shank junction. Burying the shank into the proximal cortex can double the pin’s stiffness. Hydroxyapatite-coated pins have been shown to improve the pin-bone interface and require greater extraction torque. It is thought that excessive motion of muscle and skin around the pin results in local inflammation, leading to pin tract infections. This risk can be reduced by using a gentle compressive dressing around the pin that serves as a bolster between the skin and the clamp.

Question 24 of 100

When applying an external fixator, the surgeon always must consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

Decreases construct stability

Pin diameter
Hydroxyapatite coating
Increased bone-to-rod distance
Thread-shank junction
Increased pin spread
Excessive motion of muscle and/or skin around the pin
Pin-clamp junction

Discussion: C

The application of external fixation always involves a risk-benefit evaluation that includes the key considerations of stability, soft-tissue protection, and the potential for future surgery. An external fixation device may be constructed in many ways, but certain principles are to be considered. The ideal construct for stability generally consists of one pin as close to the fracture site as possible and another pin as far away as possible in the same bone. Stability can be enhanced by increasing the pin diameter, the number of pins used, the pin spread, the number of planes of fixation, the diameter of the rods, and the number of rods and by decreasing the bone-to-rod distance. A fixation pin’s weakest point is the thread-shank junction. Burying the shank into the proximal cortex can double the pin’s stiffness. Hydroxyapatite-coated pins have been shown to improve the pin-bone interface and require greater extraction torque. It is thought that excessive motion of muscle and skin around the pin results in local inflammation, leading to pin tract infections. This risk can be reduced by using a gentle compressive dressing around the pin that serves as a bolster between the skin and the clamp

Question 25 of 100

When applying an external fixator, the surgeon always must

consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

Contributes to stress riser formation

Pin diameter
Hydroxyapatite coating
Increased bone-to-rod distance
Thread-shank junction
Increased pin spread
Excessive motion of muscle and/or skin around the pin
Pin-clamp junction Discussion: A

The application of external fixation always involves a risk-benefit evaluation that includes the key considerations of stability, soft-tissue protection, and the potential for future surgery. An external fixation device may be constructed in many ways, but certain principles are to be considered. The ideal construct for stability generally consists of one pin as close to the fracture site as possible and another pin as far away as possible in the same bone. Stability can be enhanced by increasing the pin diameter, the number of pins used, the pin spread, the number of planes of fixation, the diameter of the rods, and the number of rods and by decreasing the bone-to-rod distance. A fixation pin’s weakest point is the thread-shank junction. Burying the shank into the proximal cortex can double the pin’s stiffness. Hydroxyapatite-coated pins have been shown to improve the pin-bone interface and require greater extraction torque. It is thought that excessive motion of

muscle and skin around the pin results in local inflammation, leading to pin tract infections. This risk can be reduced by using a gentle compressive dressing around the pin that serves as a bolster between the skin and the clamp.

Question 26 of 100

CLINICAL SITUATION

Figures 1 and 2 display the radiographs from a 16-year-old boy with Lesch-Nyhan syndrome. The boy has severe mental retardation, displays self-mutilating behavior, and is wheelchair bound. He has progressive scoliosis. The caregiver reports a great deal of difficulty positioning him in the wheelchair as well as difficulty with hygiene.

This condition is caused by a deficiency of which protein?

N-acetylgalactosamine-6-sulfate sulfatase
Alpha-L-iduronidase
Hypoxanthine-guanine phosphoribosyltransferase (HRPT)
Beta-glucocerebrosidase Discussions: C

Lesch-Nyhan syndrome is a rare X-linked recessive disorder found almost exclusively in males. It is characterized most notably by self-mutilation and aggressive behavior. Additionally, patients typically have severe mental retardation and may exhibit choreoathetosis. The underlying etiology is an absence of HPRT. This enzyme is involved in purine metabolism, and affected individuals have considerably elevated uric acid. Self-mutilation frequently involves biting of the lips and fingers; dental extractions frequently are needed. Hip dysplasia, including subluxation and dislocation, is very common in patients with Lesch-Nyhan syndrome, occurring in 66% of individuals in one study. Clinical manifestations of gout also are seen frequently. Scoliosis and other spinal problems as well as infections related to self-mutilation also may be seen.

A deficiency of N-acetylgalactosamine-6-sulfate sulfatase is seen in Morquio syndrome. A deficiency of alpha-L-iduronidase is observed in Hurler syndrome. A deficiency of beta-glucocerebrosidase in seen in Gaucher disease. Congenital radial head dislocation may present in isolation or may be seen with Nail-patella syndrome or Cornelia de Lange syndrome. Congenital pseudarthrosis of the tibia (CPT) frequently is associated with neurofibromatosis (NF) type 1, and approximately 50% of those with CPT have NF. Equinovarus foot deformity can be observed in multiple neuromuscular syndromes, including cerebral palsy and myelomeningocele, but is seen less commonly in patients with Lesch-Nyhan syndrome.

Question 27 of 100

CLINICAL SITUATION

deal of difficulty positioning him in the wheelchair as well as difficulty with hygiene.

This syndrome displays which inheritance pattern?

Autosomal dominant
Autosomal recessive
X-linked dominant
X-linked recessive Discussion: D

Question 28 of 100

CLINICAL SITUATION

Laboratory studies reveal elevated serum

creatine kinase.
uric acid.
alkaline phosphatase.
beta-hexosaminidase. Discussion: B

Question 29 of 100

A patient has a dorsal hand abscess. Irrigation and debridement

are performed, and cultures are obtained. Then, 48 hours later, the cultures grow methicillin-resistant Staphylococcus aureus (MRSA) that are resistant to erythromycin. Because of inducible resistance, a D-Zone test should be requested before ordering which antibiotic?

Vancomycin
Clindamycin
Trimethoprim-sulfamethoxazole
Daptomycin Discussion: B

Antibiotic resistance is an important issue with MRSA. Although all the above choices treat MRSA, each choice has advantages and disadvantages. Isolates of MRSA that are resistant to erythromycin have been shown to become resistant to clindamycin, a process called inducible resistance, which is conferred by a plasmid that alters the 50S ribosome binding site for both clindamycin and erythromycin.

Question 30 of 100

Recombinant bone morphogenetic protein-2 (BMP-2) plays a role

in what stage of fracture healing?

Traumatic
Inflammatory
Reparative
Remodeling Discussion: B

Following traumatic injury to bone, BMPs and other proinflammatory cytokines signal the initiation of fracture healing. BMP-2 does so by recruiting mesenchymal stem cells to the site of injury.

Question 31 of 100

Three hours after sustaining a tibial shaft fracture in a motorcycle

accident, a 19-year-old man has increasing pain despite receiving increased narcotic pain medications. The pain is exacerbated with passive stretching. Paresthesias develop along the tibial and peroneal nerve distributions. The progression of his conditions results from the compromise of

venous outflow relative to arterial inflow.
venous outflow independent of arterial inflow.
arterial inflow independent of venous outflow.
venous outflow and arterial inflow in an independent fashion. Discussions: A

Patients with high-energy tibia fractures are at high risk for compartment syndromes. This patient’s condition displays several key clinical indicators, including increased pain medication requirements, pain with passive stretching, and paresthesias. The progression of compartment syndrome results from a compromise of venous outflow relative to arterial inflow. As this imbalance increases, venous congestion further raises already elevated compartment pressures and, if the imbalance is untreated, eventually results in arterial collapse.

Question 32 of 100

The overexpression of which factor is responsible for dilatation of

the aorta in patients with mutations in the fibrillin gene?

Bone morphogenetic protein-2
Indian hedgehog (IHH)
Transforming growth factor beta (TGF-β)
Osteocalcin Discussion: C

Fibrillin gene mutation is seen in patients with Marfan syndrome, which prevents TGF-β binding, resulting in the increase of TGF-β levels in tissue. This increase has been associated with aortic dilatation. IHH is responsible for modulation of the growth and proliferation of chondrocytes in the growth plate. Osteocalcin is a protein produced by osteoblasts.

Question 33 of 100

Current strategies for treating the aberrant bone remodeling that

occurs in osteoporosis involve using agents that prevent bone resorption or stimulate bone formation. Agents that stimulate bone formation include

bisphosphonates.
denosumab.
calcitonin.
parathyroid hormone. Discussions: D

Parathyroid hormone binds to receptors on osteoblasts and preosteoblasts and thereby stimulates bone formation when dosed intermittently. Bisphosphonates, denosumab, and calcitonin are all bone antiresorptive agents. They primarily have inhibitory effects on osteoclasts, each by different molecular mechanisms.

Figures 1 through 4 show the AP radiograph, axial CT, coronal T2-weighted MRI, and biopsy specimen from a 73-year-old man with severe left hip pain. In this patient’s disease, osteoblastic bone formation is suppressed by

tumor ne crosis factor.
receptor activator of nuclear factor kappa-B ligand (RANKL).
interleukin-6.
Bence-Jones proteins. Discussion: A

The AP radiograph and axial CT of the pelvis reveal a lucent lesion in the supra-acetabular region. The T2-weighted coronal MRI reveals the intramedullary extent of the disease. The biopsy specimen shows scattered plasma cells consistent with the diagnosis of multiple myeloma. Major mediators of osteoclastogenesis in multiple myeloma include RANKL, interleukin-6, and macrophage inflammatory protein-1 alpha. Osteoblastic bone formation is suppressed by tumor necrosis factor and Dickkopf-1 (DKK-1). Investigations are underway to find agents that improve osteoblast differentiation by modulating inhibitors such as DKK-1 to enhance the structural integrity of involved bones.

Question 35 of 100

A 45-year-old man sustains a closed midshaft transverse tibial

fracture following a skiing injury. What is the biggest risk factor for nonunion following surgical treatment of the injury?

NSAID use
Smoking
Body mass index (BMI)
Age Discussion: B

In several studies and a large meta-analysis, smoking has been proven to increase the odds of nonunion, having an increased odds ratio of 2.16, and overall delay in healing in tibial fractures. NSAID use also can lead to nonunion or delayed union, but smoking is more likely to do so. Age and BMI can affect healing, but smoking consistently demonstrates a negative effect.

Question 36 of 100

CLINICAL SITUATION

A study evaluating hip arthroscopy for labral tears enrolls more than 200 participants, who are randomized into two groups: surgical and nonsurgical care which included physical therapy and NSAIDs. The primary endpoint was a composite consisting of: 1) the patient reporting change between preintervention pain as reported on the 10-point visual analog scale and the postintervention score at 2 years, and 2) absence of major adverse events, including death, return to the operating room, and major neurologic injury.

Which party in the study could be blinded to reduce some potential bias?

Surgeon
Patients
Data and Safety Monitoring Board
Data analyst Discussion: D

The goal of this series of questions is to test the knowledge of study design. Poolman and associates have described four parties who can be subject to blinding, and it is important to clearly state in the study methodology who is blinded because of the various types of bias. In this case, because of the nature of the study design, only the data analysts are able to be blinded practically.

Allocation concealment is an aspect of study design that can be applied to any clinical trial. It is important to prevent the treating physician from being able to guess the group to which the next subject will be randomized. Otherwise, an inherent risk of selection bias is present. All the methods are predictable except randomization with opaque envelopes.

Physician-driven outcomes are a concern in research. In such instances, the physician conducting the study also determines when the variables he or she is measuring are met. This practice leads to obvious clinical bias. One way of helping to reduce such bias is to set strict, a priori definitions of treatment success and failure, leaving less room for subjectivity.

Currently, the handling of conflicts of interest is a challenging problem. Although some groups support stricter options, the existing standard is for the physician to openly disclose any real or potential conflicts of interest.

Question 37 of 100

CLINICAL SITUATION

What method of allocation would best limit selection bias?

Fixed block randomization with block sizes of two
Randomization of patients according to the day of the week
Simple randomization with assignments placed in an opaque envelope
Strict alternation of subject assignments between groups

Discussion: C

Question 38 of 100

CLINICAL SITUATION

What would be the most reasonable study design option to limit the potential bias inherent in the subjectivity of choosing when to return to the operating room?

Requiring a second opinion by an independent surgeon before returning to the operating room
Recording the factors that led treating surgeons to decide to return to the operating room
Stipulating that a committee of treating surgeons must adjudicate all cases possibly needing a return to the operating room
Setting strict a priori definitions for the need to return to the operating room

Discussion: D

Question 39 of 100

CLINICAL SITUATION

What is currently considered the standard method of managing author conflicts of interest?

Rejection of all industry investments, consultation fees, and funding
Acceptance of funds used only for research purposes
Disclosure of relevant potential conflicts of interest
Review of results by the sponsors before publicatio

Discussion: C

Physician-driven outcomes are a concern in research. In such instances, the physician conducting the study also determines

when the variables he or she is measuring are met. This practice leads to obvious clinical bias. One way of helping to reduce such bias is to set strict, a priori definitions of treatment success and failure, leaving less room for subjectivity.

Question 40 of 100

Your colleagues have identified an immunologic syndrome that

creates an overabundance of CD8+ T lymphocytes. It appears to have a partial penetrance, autosomal dominant inheritance pattern. Further analysis has shown that these cells may be impairing fracture healing. Your colleagues want to meet with you to discuss enrolling patients in a clinical study to identify genetic “hot spots” that may represent loci with allelic variants that distinguish good fracture healers from poor healers. The study design most likely to identify the hot spots is

whole-exome sequencing.
genome-wide association.
prospective cohort database generation.
DNA microarray. Discussion: B

A case-matched control study (for more rare events) and prospective databases (for more common events) may help identify factors associated with good healing and poor healing. Used alone, they do not help identify genetic information related to the phenotype, however. Although whole-exome sequencing may identify variations or mutations in the coding regions of DNA, it will not find them outside of those regions. Therefore, when the nature

of the mutation or gene variation is unknown, a genome-wide association is most likely to find hot spots associated with the phenotype. DNA microarray is useful for quantifying specific genes of interest.

Question 41 of 100

In what zone of the articular cartilage are the chondrocytes

arranged in columns and the collagen fibers oriented vertical to the articular surface?

Calcified zone
Middle zone
Superficial zone
Deep zone

Discussion: D

Four zones are identified in the articular cartilage. In the superficial zone, the chondrocytes are elongated, and the collagen fibers are oriented parallel to the articular surface. In the middle zone or transitional zone, chondrocytes and collagen fibers are oriented randomly. In the deep aone, the chondrocytes are arranged in columns, and the collagen fibers are oriented vertical to the articular cartilage. The calcified zone is the transitional zone between the cartilage and the subchondral bone.

Question 42 of 100

Tendon injury classically occurs during what type of muscle

contraction?

Concentric
Isometric
Eccentric
Passive stretch

Discussion: C

Tendons demonstrate both elastic and viscoelastic properties. These biomechanical properties can be affected by pathologic processes manifesting as tendinosis, weakening the tendon and predisposing it to rupture. In such circumstances, eccentric muscle contractions can place maximal stress across the myotendinous junction, resulting in forced lengthening and rupture.

Question 43 of 100

Nonsurgical treatment has failed in a 64-year-old woman with a

history of low back pain and bilateral lower extremity pain. She has been indicated for posterolateral lumbar decompression and fusion. Imaging studies reveal dynamic instability of an L4-5 grade

1 degenerative spondylolisthesis with severe spinal stenosis. During routine medical clearance evaluation, the patient’s history reveals a screening bone mineral density of 65% of the young adult mean. Administration of which adjunct treatment has been shown to enhance the rate of fusion in such patients?

Calcitonin
Teriparatide
Denosumab
Alendronate Discussion: B

Osteoporotic patients undergoing spinal fusion procedures are at greater risk for procedurally associated complications, including pseudarthrosis, instrumentation failure, or even fracture. Recombinant parathyroid hormone has anabolic properties for the stimulation of bone growth, which has been shown to be beneficial in postmenopausal women undergoing spinal fusion. Although the other agents are used for the treatment of osteoporosis,

perioperative administration has not been shown to enhance spinal fusion rates.

Question 44 of 100

Intervertebral disk degeneration results in what changes to the

collagen content and nonenzymatic cross-linking?

Increase in collagen II, increase in nonenzymatic cross-linking of the collagen
Decrease in collagen II, decrease in nonenzymatic cross-linking of the collagen
Increase in collagen I, increase in nonenzymatic cross-linking of the collagen
Decrease in collagen I, decrease in nonenzymatic cross-linking of the collagen

Discussion: C

In degeneration of the intervertebral disk, collagen I and nonenzymatic cross-linking of the collagen increase. Collagen II decreases with degeneration. Nonenzymatic cross-linking of the collagen leads to formation of advanced glycation end products. Proteolytic cleavage of the collagen fibers also occurs in degeneration of the intervertebral disk.

Question 45 of 100

Match the stain or immunoprobe with the method of

investigation for identifying the process.

Examination of cartilage in early callus formation

Hematoxylin and eosin
Parathyroid–hormone-related protein immunostain
Safranin-0
Cathepsin-K immunostain Discussion: C

The hematoxylin and eosin stain is used very broadly in standard histology, such as to evaluate for the presence of polymorphonuclear cells in infection or osteomyelitis. Hematoxylin makes nuclei blue and therefore easier to identify. Cartilage and proteoglycan are evaluated well with safranin-O and alcian blue histology stains. The differentiation of osteoclasts, as when attempting to evaluate how briskly remodeling of bone is occurring, could employ tartrate-resistant acidic phosphatase histology staining or cathepsin-K immunostaining. Cell signaling, between parathyroid–hormone-related protein (PTHrP) and indian hedgehog protein in the growth plate has been evaluated by Immunostain for PTHrP.

Question 46 of 100

Match the stain or immunoprobe with the method of

investigation for identifying the process.

Determining osteoclast activity in bone remodeling

Hematoxylin and eosin
Parathyroid–hormone-related protein immunostain
Safranin-O
Cathepsin-K immunostain Discussion: D

proteoglycan are evaluated well with safranin-O and alcian blue histology stains. The differentiation of osteoclasts, as when attempting to evaluate how briskly remodeling of bone is occurring, could employ tartrate-resistant acidic phosphatase histology staining or cathepsin-K immunostaining. Cell signaling, between parathyroid–hormone-related protein (PTHrP) and indian hedgehog protein in the growth plate has been evaluated by Immunostain for PTHrP.

Question 47 of 100

Match the stain or immunoprobe with the method of

investigation for identifying the process.

Growth plate signaling evaluation
Parathyroid–hormone-related protein immunostain
Safranin-O
Cathepsin-K immunostain Discussion: B

Question 48 of 100

Match the stain or immunoprobe with the method of

investigation for identifying the process.

Osteomyelitis evaluation

Hematoxylin and eosin
Parathyroid–hormone-related protein immunostain
Safranin-O
Cathepsin-K immunostain Discussion: A

Question 49 of 100

After the repair of an intrasynovial flexor tendon laceration,

increasing the mechanical load during rehabilitation has what type of effect on tendon healing and repair site gapping?

Promotes tendon healing, increases the risk of repair site gapping
Promotes tendon healing, reduces the risk of repair site gapping
Inhibits tendon healing, increases the risk of repair site gapping
Inhibits tendon healing, reduces the risk of repair site gapping Discussion: A

Studies have shown that tendon fibroblasts respond positively to mechanical load, and some amount of mechanical loading is incorporated into many tendon repair rehabilitation programs. Increased loads run the risk of increasing the repair gap or even disrupting the repair altogether, however.

Question 50 of 100

A 2-year-old girl is seen in the emergency department. Her main

symptom is swelling of the right knee and refusal to bear weight. On examination, the child is febrile to 39.0°C, her right knee is mildly swollen, and she resists attempts at passive motion. The patient’s white blood cell count is 10,500 cells per milliliter, her C-reactive protein level is normal, and her erythrocyte sedimentation rate is mildly elevated at 45 mm per hour. An MRI reveals a moderate effusion but no evidence of osteomyelitis. A knee aspirate reveals a white blood cell count of 60,000 cells per milliliter. To increase the likelihood of isolating the causative bacteria, what culture medium should be utilized?

Eosin methylene blue agar
Granada agar
Blood agar
Mannitol salt agar Discussion: C

Kingella kingae is increasingly recognized as an important cause of osteoarticular infections, especially in patients between the ages of 6 months and 4 years. K kingae is a fastidious gram-negative coccobacillus and is part of the normal oral pharangeal flora in young children. Infections due to K kingae frequently present in a

delayed fashion with subacute symptoms. In one study, the mean length of symptoms prior to presentation was 9 days. Additionally, only 15% of patients were febrile on admission. The true incidence of infections associated with K kingae may be considerably higher than previously thought, given the difficulty of growing K kingae on standard culture media. In one study, only 10% of confirmed cases of osteoarticular infections associated with K kingae displayed growth on standard solid culture media. Blood agar is recommended for patients suspected of K kingae infection. Additionally, polymerase chain reaction has shown promise as an accurate and quick diagnostic tool; however, it is not widely available. Eosin methylene blue agar is toxic to gram-positive bacteria but is used to isolate coliforms. Granada agar is used to isolate group B Streptococcus species. Mannitol salt agar is specific for gram-positive bacteria, especially mannitol fermenters.

Question 51 of 100

CLINICAL SITUATION

A 23-year-old man sustained a moderately comminuted femoral shaft fracture and simple oblique humeral shaft fracture in a motor vehicle collision. The humerus underwent open reduction and internal fixation with compression plating, whereas the femur was treated with an intramedullary device.

What type of healing is expected after this type of fixation in the femur?

Intramembranous ossification
Secondary bone healing with Haversian remodeling
Secondary bone healing with callus formation
Primary bone healing with Haversian remodeling Discussion: C

Bone remodeling includes primary and secondary healing. Primary healing occurs with absolute fixation, minimal or no comminution, and decreased fracture motion; it is accomplished through Haversian remodeling. This process proceeds through osteoclast resorption, osteoblastic layering, lamellar layering, and finally, cement line creation. The Wolff law is defined as bone remodeling in response to mechanical stress. Increased fracture comminution or motion and relative fixation are associated with secondary healing and callus formation.

Question 52 of 100

CLINICAL SITUATION

One determinant of primary versus secondary bone healing is that the response of bone remodeling is based on the stress applied to it. Which principle governs this process?

Hueter-Volkmann law
Piezoelectric changes
Regeneration potential
Wolff law

Discussion: D

cement line creation. The Wolff law is defined as bone remodeling in response to mechanical stress. Increased fracture comminution or motion and relative fixation are associated with secondary healing and callus formation.

Question 53 of 100

CLINICAL SITUATION

What factor is most associated with an increased likelihood of primary bone healing?

Increased fracture comminution
Relative fixation
Decreased fracture motion
Bridging construct fixation

Discussion: C

Figures 1 through 3 show radiographs from a 32-year-old man who sustained a closed both-bone forearm fracture. Figures 2 and 3 were taken 6 weeks postoperatively. A histological sample of the fracture site at this point would most likely show

mesenchymal cells laying fibrous tissue and inflammatory cells.
chondrocytes and cartilage undergoing endochondral ossification.
osteoclasts and osteoblasts remodeling lamellar bone.
osteoblastic formation of woven bone. Discussion: C

The radiographs reveal a fracture that is going through primary fracture healing with rigid stability and compression. No callus formation is present. All the answer choices describe events occurring in secondary fracture healing, except the osteoclast and osteoblast remodeling. In this process, cutting cones are formed. Osteoclasts form the head of the cone, and osteoblasts lay down new bone behind.

Question 55 of 100

Polylactic acid and polyglycolic acid are used to make resorbable

orthopaedic implants. How do the resorption time and stiffness of polylactic acid compare with those of polyglycolic acid?

Polylactic acid has higher stiffness and takes longer to resorb
Polyglycolic acid has higher stiffness and takes longer to resorb
Polylactic acid has higher stiffness but resorbs faster
Polyglycolic acid has higher stiffness but resorbs faster Discussion: D

Polylactic and polyglycolic acids are degraded in the body by hydrolysis. Polyglycolic acid has a modulus of elasticity of 7 GPa and degrades within 6 to 12 months, whereas polylactic acid has a modulus of elasticity of 2.7 GPa and requires more than 24 months to resorb fully.

Question 56 of 100

Compared with intrinsic tendon repair mechanisms for

intrasubstance intrasynovial flexion tendon tears, extrinsic tendon repair mechanisms have what effects on the speed of healing and adhesion formation?

Faster healing increased adhesion formation
Faster healing decreased adhesion formation
Slower healing increased adhesion formation
Slower healing decreased adhesion formation Discussion: C

Intrasynovial tendons are those enclosed within a synovial sheath. Intrinsic repair mechanisms describe the healing processes that rely on the proliferation and migration of cells within the injured

tendon itself to help bridge the injury. In extrinsic healing mechanisms, cells from the surrounding tissue outside the tendon invade the damaged area. Extrinsic healing can represent a substantial part of the overall healing response and is faster than intrinsic healing for intrasynovial flexor tendons. Extrinsic healing results in adhesion formation between the tendon and the surrounding tissue, however.

Question 57 of 100

A 13-year-old girl with progressive adolescent onset idiopathic

scoliosis undergoes corrective surgery with posterior fusion and instrumentation from T2-12. During the procedure, several maneuvers are performed to correct a single main thoracic curve. Which maneuver is responsible for improving apical translation?

Direct vertebral rotation
Concave distraction
Convex compression
90° rod rotation Discussion: D

Scoliosis is a three-dimensional deformity of the spine that is multifactorial in etiology. Halting progression by achieving fusion is the primary aim of surgical intervention, but safe correction with instrumentation maneuvers aims to improve each of the planes of deformity. Rod rotation at the apex assists in coronal translation. Distraction and compression affect both the coronal and sagittal planes. Direct vertebral rotation maneuvers address vertebral rotation.

Question 58 of 100

A 45-year-old woman is being seen for an evaluation of metabolic

bone disease because of a history of multiple fractures in the past

2 years. Laboratory data show calcium: 9 mg/dL (reference range: 8.2-10.2 mg/dL), phosphorus: 1.5 mg/dL (reference range: 2.3-4.7 mg/dL), parathyroid hormone: 30 pg/mL (reference range: 10-65 pg/mL), l,25 hydroxy vitamin D: 18 ng/ml (reference range: 25-45 ng/mL). She recently was diagnosed with osteoblastoma in the thoracic spine. What factor is responsible for the laboratory abnormalities seen in this patient?

FGFR3 gene mutation
Fibroblast growth factor 23 (FGF23) excess
Transforming growth factor beta (TGF-β) excess
Activation of receptor activator of nuclear factor kappa-B ligand (RANKL)

Discussion: B

This patient has oncogenic osteomalacia. Laboratory data show hypophosphatemia and low 1,25 hydroxy vitamin D levels. Oncogenic osteomalacia is seen in association with mesenchymal tumors, especially osteoblastoma, fibrous dysplasia, and fibromas. Osteomalacia is caused by the overactivity of FGF23, which decreases phosphate reabsorption in the kidneys, causing hypophosphatemia. It also inhibits the activity of 1 alpha hydroxylase (responsible for converting 25 hydroxy vitamin D to 1,25 hydroxy vitamin D), causing decreased levels of 1,25 hydroxy vitamin D. FGFR 3 activating mutation causes achondroplasia. TGF-β excess is seen in patients with Marfan syndrome.

Question 59 of 100

You are serving as the principal investigator (PI) of a site that is

taking part in a multicenter randomized clinical trial. Your site will enroll 10 patients within the study that includes more than 1,000 patients. So far you have enrolled eight patients, four in each of two treatment groups, but you have noticed that two in one group

stayed in the hospital much longer than the others. What entity should investigate whether this occurrence is a concern in the study overall?

You, as the site PI
The research coordinator at the primary investigative site
Your institutional review board (IRB)
The Data and Safety Monitoring Board (DSMB) Discussion: D

The DSMB is a group that serves as part of the oversight process of a clinical trial to independently monitor and assess the conduction of a study. Its duties include the monitoring of events that may be considered adverse outcomes and the review of safety issues for the study. It is the duty of the PI to report adverse events and to act on them when needed, but neither the PI at the site, the site’s IRB, nor the research coordinator have access to all of the data and all lack the independence needed to investigate overall trends.

Question 60 of 100

CLINICAL SITUATION

A 35-year-old man sustains a lower extremity injury during a motor vehicle collision. He is transported to a local trauma center, where he is diagnosed with an intra-articular fracture. Concerned about his prognosis and the risk of developing arthritis, he asks the treating surgeon what type of recovery he may expect after his injury.

The reparative response following osteochondral fracture, compared with that of chondral fractures, includes

restoration of the normal organization of collagen fibrils.
a paucity of inflammatory cells in the fracture gap.
hyperproliferation of synovial tissue.
formation of a fibrin clot and an inflammatory response. Discussion: D

Posttraumatic arthritis is common, and its prevalence likely is underestimated following joint injury. Cartilage injuries can include surface defects, chondral fractures, or intra-articular fractures, which involve the cartilage surface and subchondral bone. Intra-articular fractures place patients at risk for posttraumatic arthritis because of the magnitude of the energy imparted to the joint surface and the extent of damage to the joint. Compared with other joints, the ankle joint is most prone to developing posttraumatic arthritis. The condition is debilitating and is similar in impact on the quality of life to end-stage kidney disease and congestive heart failure. Intra-articular fracture severity is predictive of eventual arthritis development. Following fracture reduction, joint incongruities increase the contact stress to the remaining joint, contributing to further joint degeneration. Distraction arthroplasty is an option that does not sacrifice the patient’s native joint, but it has not been shown to be superior to ankle fusion for end-stage arthritis of the ankle. Weight bearing or articulated distraction frames offer the advantage of fluctuating the intra-articular hydrostatic pressure of the synovial fluid, which is favorable biologically for the repairing cartilage.

Question 61 of 100

CLINICAL SITUATION

treating surgeon what type of recovery he may expect after his injury.

Following intra-articular fracture, the risk of posttraumatic arthritis is correlated strongly with what risk factor?

Patient sex
Duration of patient tobacco use
Intra-articular fracture severity
Axial versus torsional mechanisms Discussion: C

Question 62 of 100

CLINICAL SITUATION

Following open reduction and internal fixation, residual incongruity contributes to joint degeneration through

aberrant contact stresses across the joint.
collagen formation in the residual fracture gap.
a longer required time of prohibited weight bearing.
ongoing inflammation generated from the synovium. Discussion: A

an option that does not sacrifice the patient’s native joint, but it has not been shown to be superior to ankle fusion for end-stage arthritis of the ankle. Weight bearing or articulated distraction frames offer the advantage of fluctuating the intra-articular hydrostatic pressure of the synovial fluid, which is favorable biologically for the repairing cartilage.

Question 63 of 100

CLINICAL SITUATION

Early posttraumatic arthritis develops. To attempt to salvage his native joint, he is indicated for distraction arthroplasty. A distraction frame that allows partial weight bearing improves cartilage repair through

fluctuations in the intra-articular hydrostatic synovial pressure.
maintenance of cartilage stiffness during joint loading.
earlier return to a normal postsurgical range of motion.
improved maintenance of limb strength, facilitating rehabilitation. Discussion: A

surface and the extent of damage to the joint. Compared with other joints, the ankle joint is most prone to developing posttraumatic arthritis. The condition is debilitating and is similar in impact on the quality of life to end-stage kidney disease and congestive heart failure. Intra-articular fracture severity is predictive of eventual arthritis development. Following fracture reduction, joint incongruities increase the contact stress to the remaining joint, contributing to further joint degeneration. Distraction arthroplasty is an option that does not sacrifice the patient’s native joint, but it has not been shown to be superior to ankle fusion for end-stage arthritis of the ankle. Weight bearing or articulated distraction frames offer the advantage of fluctuating the intra-articular hydrostatic pressure of the synovial fluid, which is favorable biologically for the repairing cartilage.

Question 64 of 100

The basement membrane and the interstitial stroma are the

foremost obstacles to cancer cell invasion. What enzymes have been shown to be vital for tumor invasion?

Matrix metalloproteinases (MMPs)
Alkaline phosphatases
Tartrate resistant acid phosphatases
Cathepsins Discussion: A

Proteolytic enzymes (proteinases) are divided into two major groups: metalloproteinases (collagenase, gelatinase, and stromelysin) and cathepsins B and D. The family of enzymes that has been shown to be vital for matrix destruction during tumor invasion is the MMP family. The MMPs comprise a family of zinc-binding enzymes that degrade components of the extracellular matrix. MMPs can be secreted directly by tumor cells or by normal

host cells that are stimulated by tumor-secreted cytokines. The secretion of MMPs has been correlated with tumor invasiveness, and metalloproteinase inhibitors have been shown to inhibit the invasiveness of normal and malignant cells.

Question 65 of 100

The anulus fibrosus of the intervertebral disk develops directly from

which embryonic structure?

Neural tube
Primitive streak
Sclerotomal cells
Unsegmented notocord Discussion: C

Following resegmentation of the sclerotomes, cells from the sclerotomes themselves are differentiated into anulus fibrosus components.

Question 66 of 100

Following Achilles tendon repair, a 33-year-old man is lost to follow-

up and becomes immobilized for 6 months. Concerns about weakness in his tendon from a lack of motion primarily reflect what fundamental deficiency in this patient’s tendon?

Collagen organization
Collagen production
Paratenon proliferation
Paratenon regeneration Discussions: A

Some of the fundamental changes associated with the healing of collagen-based tissues are the organization, reorganization, and

remodeling of the collagen fibers. These processes can be induced and influenced by the application of forces such as directional tension through motion. Motion may also have some influence on collagen production, but the most important effect of motion is organization of the collagen along lines of tension. Also, the paratenon can be a source of support for the healing tendon, but its proliferation and regeneration are not functions of motion as it relates to tendon healing.

Question 67 of 100

How does the proteoglycan content of the nucleus pulposus

intervertebral disk change from the newborn period into adolescence?

Chondroitin sulfate and keratan sulfate increase in concentration with age.
Chondroitin sulfate and keratan sulfate decrease in concentration with age.
Chondroitin sulfate increases and keratan sulfate decreases with age.
Chondroitin sulfate decreases and keratan sulfate increases with age.

Discussion: D

The intervertebral disk is made up of a nucleus pulposus and an anulus fibrosus. The dry weight of the nucleus pulposus of the intervertebral disk consists mostly of collagen and proteoglycans. After birth, the side chains of the aggrecans are made mostly of chondroitin sulfate, which gradually is replaced by keratan sulfate with age.

Question 68 of 100

Increased cross-linking of ultrahigh-molecular-weight polyethylene

(UHMWPE) results in

decreased wear and increased toughness.
decreased wear and decreased toughness.
increased wear and decreased toughness.
increased wear and increased toughness. Discussion: B

Studies have shown statistically significantly decreased wear rates in joint arthroplasty when highly cross-linked UHMWPE is used in place of conventional polyethylene. These results have been impressive, but the decreased toughness of highly cross-linked UHMWPE has been associated with such complications as rim fractures found in retrieved acetabular components.

Question 69 of 100

Figures 1 and 2 show radiographs from a 12-year-old girl in the

emergency department. She reports a 3-week history of left groin pain. The girl denies any antecedent trauma or constitutional symptoms. She has been able to bear weight and denies any history of endocrine or renal disorders. On examination, she is moderately obese and has limited passive motion of the hip secondary to pain. Displacement has occurred primarily through which zone of the physis?

Resting
Proliferative
Hypertrophic
Primary spongiosa Discussion: C

The radiographs reveal a left slipped capital femoral epiphysis (SCFE). SCFE leads to displacement of the metaphysis relative to the epiphysis, with the metaphysis moving anterior and rotating externally. It is the most common disorder affecting the adolescent hip. Risk factors include obesity, endocrine disorders, renal osteodystrophy, and male sex. Displacement occurs primarily through the hypertrophic zone, although some displacement may occur through the zone of provisional calcification. The resting zone is usually normal but may account for a smaller percentage of the overall physis thickness given the relative increase in the thickness of the proliferative and hypertrophic zones.

Question 70 of 100

What are the effects of remelting and annealing on crystal

formation in ultrahigh-molecular-weight polyethylene (UHMWPE)?

Annealing increases and remelting decreases crystal formation
Both increase crystal formation
Annealing decreases and remelting increases crystal formation
Both decrease crystal formation Discussion: A

Annealing and remelting are performed after gamma radiation of the UHMWPE to reduce free radicals. In annealing, the material is heated below the melting point, whereas in remelting, the material is heated above the melting point. Annealing increases the crystal formation of the UHMWPE, and remelting decreases crystal

formation. Both processes reduce but do not eradicate free radicals completely.

Question 71 of 100

A pharmaceutical company is evaluating the efficacy of a biologic

agent to enhance fusion rates in lumbar arthrodesis procedures. For statistical analysis, a large number of patients are separated into two cohorts depending on fusion status. To determine a statistical numerical difference between the two groups, which test should be employed?

Chi-square
Fisher exact
Mann-Whitney
Unpaired t Discussion: A

Patients in the study are separated into fusion and nonfusion groups by a categorical variable. The Fischer exact test compares categorical data in smaller distinct numbers. T-tests compare continuous data, unpaired for different individuals and paired for matched samples. The chi-square test compares categorical data in larger formats.

Question 72 of 100

Figure 1 shows a histology slide from a patient’s bone biopsy. This

patient is most likely to have what genetic abnormality?

Figure 1 used with permission from Frassica FJ. Metabolic bone and inflammatory joint disease. In: Lieberman JR, ed. AAOS Comprehensive Orthopaedic Review. Vol 1. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2009:491-502, Figure 2B.

11;22 chromosomal translocation
5q35-qter (ubiquitin-binding protein sequestosome-1) mutation
Fibroblast growth factor receptor 3 (FGFR3) mutation
STY-SSX1 or STY-SSX2 fusion Discussion: B

This hematoxylin and eosin stain shows the disorganized bone and multiple cement lines typical of Paget disease. Paget disease has been linked to mutations in a sequestosome gene, which has multiple cellular activities. The mechanism by which mutation results in the Paget phenotype is not completely understood. FGFR3 mutation is associated with achondroplasia, which would display a normal appearing bone histology. 11;22 translocation is associated with Ewing sarcoma, and a related biopsy would display multiple small round blue cells. The X;18 translocation causing fusion of the STY and SSX genes is associated with synovial sarcoma, which would appear on biopsy as bone with hypercellular soft tissue.

Question 73 of 100

Select the appropriate material property for the definition

listed.

Changes in a material’s shape because of load; it is reversible when the load is remov

Brittle
Hysteresis
Viscoelastic
Yield point
Elastic deformation
Plastic deformation

Discussion: 5

Materials exhibit a different stress-strain curve during loading based on their inherent properties. As a load is applied, the curve can be linear (brittle material), can undergo plastic deformation (ductile material), or can vary based on the rate of the load applied (viscoelastic material). As the material relaxes, it may or may not return to its original shape. Hysteresis describes a material whose relaxation curve does not match the loading curve. A material that is able to return to its original shape is said to have elastic deformation, whereas plastic deformation is permanent. The transition from elastic to plastic deformation is the yield point at which the material will no longer return to its original shape.

Question 74 of 100

Select the appropriate material property for the definition

listed.

Changes in a material’s shape that is irreversible after the load is removed

Brittle
Hysteresis
Viscoelastic
Yield point
Elastic deformation
Plastic deformatio

Discussion: 6

Question 75 of 100

Select the appropriate material property for the definition

listed.

When a loading curve does not match the relaxation curve

Brittle
Hysteresis
Viscoelastic
Yield point
Elastic deformation
Plastic deformation Discussion: B

relaxation curve does not match the loading curve. A material that is able to return to its original shape is said to have elastic deformation, whereas plastic deformation is permanent. The transition from elastic to plastic deformation is the yield point at which the material will no longer return to its original shape.

Question 76 of 100

Select the appropriate material property for the definition

listed.

The amount of strain required to transition from elastic to plastic deformation

Brittle
Hysteresis
Viscoelastic
Yield point
Elastic deformation
Plastic deformation Discussion: D

Question 77 of 100

Select the appropriate material property for the definition

listed.

Description of a material that undergoes a linear stress-strain relationship until failure

Brittle
Hysteresis
Viscoelastic
Yield point
Elastic deformation
Plastic deformation Discussion: A

Question 78 of 100

Select the appropriate material property for the definition

listed.

Description of a material in which the stress-strain curve depends on the rate and duration of load application

Brittle
Hysteresis
Viscoelastic
Yield point
Elastic deformation
Plastic deformation Discussion: C

Question 79 of 100

The surface wear that occurs between two implant surfaces

designed to be in contact with one another is known as

fatigue wear.
corrosion wear.
third-body wear.
adhesion wear.

Discussion: D

Adhesion wear occurs between implant surfaces that are designed to be in contact. Corrosion often occurs when contact occurs between different metals, as in a cobalt-chrome alloy metal head on a titanium taper. Third-body wear is a type of abrasive wear that occurs when particulates that are usually extra-articular become entrapped in an articulation and cause wear at the articulating surfaces. Fatigue wear develops from progressive mechanical use and is the result of repetitive cyclic loads.

Question 80 of 100

Necrotizing fasciitis that occurs following varicella infection in

children most often is caused by what bacteria?

Group A streptococcus
Group B streptococcus
Staphylococcus aureus
Clostridium perfringens Discussion: A

Varicella zoster virus infection leads to one of two clinically distinct forms of disease: varicella (chickenpox) and herpes zoster (shingles). Before a vaccine was introduced in 1995, an estimated four million cases occurred per year in the United States, along with nearly 11,000 hospital admissions and 100 deaths annually. In children, chickenpox is generally a mild disease and presents with fever, malaise, pharyngitis, and loss of appetite, followed by the development of a pruritic vesicular rash. Complications, including invasive skin and soft-tissue infections, pneumonia, and encephalitis, occur in around 2% of patients, with skin and soft-tissue infections being most common. Necrotizing fasciitis is an uncommon but devastating complication and is associated with a

high mortality rate. Early identification, followed by aggressive surgical debridement and appropriate antibiotic selection is critical. Group A β-hemolytic Streptococcus, most commonly Streptococcus pyogenes, is the most common causative organism, occurring in up to 80% of patients in some series. In fact, between 15% and 30% of invasive group A streptococcal infections are associated with varicella. Group B Streptococcus is a potential cause of infection in neonates and young infants, especially those having poor prenatal care. Staphylococcus aureus is the most common cause of musculoskeletal infections in the general population. Clostridium perfringens is the most common cause of traumatic clostridial myonecrosis or “gas gangrene” but is not common following varicella infection.

Question 81 of 100

A 44-year-old man arrives at the trauma bay intubated and sedated

following a motorcycle collision. He has sustained multiple injuries and remains hemodynamically unstable. His neurologic status is unknown. The trauma team would like to remove the patient’s cervical orthosis. CT reveals multilevel spondylosis, however, that is inconclusive for the extent of injury. Which MRI sequence would best show acute traumatic injury?

T2-weighted
Gradient echo
Short-tau inversion-recovery (STIR)
Fluid-attenuated inversion-recovery Discussion: C

Determining the extent of injury to the cervical spine in an obtunded polytrauma patient can be extremely difficult. Complications are encountered, including missed diagnosis or unnecessarily

prolonged cervical collar treatment. STIR sequences reveal early-phase fluid such as that resulting from contusion and acute trauma. T2-weighted images and T2 fat suppression images are less sensitive to acute-phase fluids because of a lack of fat and marrow edema suppression.

Question 82 of 100

Which protein overexpression resulting from a translocation in a

subpopulation of cells within the synovium is associated with pigmented villonodular synovitis (PVNS) or giant cell tumor of the tendon sheath (GCTTS)?

Colony stimulating factor 1 (CSF 1)
Receptor activator of nuclear factor kappa B ligand (RANKL)
Tumor necrosis factor alpha (TNF-α)
Interleukin-2 (IL-2) Discussion: A

Several studies have found a subpopulation of cells within PVNS and GCTTS and some other types of chronic synovial inflammatory conditions that show an increased expression of CSF 1. This overexpression is thought to result from a translocation within this cell subpopulation. RANKL is a protein that is released by osteoblasts, which bind to RANK on osteoclasts, leading to activation of the osteoclasts. This interaction is involved in the bone resorption frequently seen in PVNS, but the tumor cells themselves are not known to express RANKL directly, and RANKL is not known to be associated with a translocation. TNF-α and IL-2 are proinflammatory proteins released by the white blood cells at the sites of inflammation. Although likely important to the inflammatory process present in PVNS and GCTTS, TNF-α and IL-2 are not associated with a subpopulation of cells within the tumor.

Question 83 of 100

Regarding the modulus of elasticity and wear rates, how does

cobalt chrome compare with titanium? Cobalt chrome has a

lower modulus of elasticity and increased wear rates.
lower modulus of elasticity and reduced wear rates.
higher modulus of elasticity and reduced wear rates.
higher module of elasticity and increased wear rates. Discussion: C

Titanium and cobalt chrome are used commonly in orthopaedic implants. Cobalt chrome has a higher modulus of elasticity and reduced wear rates compared with titanium. Because of the higher modulus of elasticity, cobalt chrome causes more stress shielding. Titanium has better biocompatibility, but its wear properties are inferior to those of cobalt chrome. For this reason, titanium is used mostly in the nonarticular part of orthopaedic implants.

Question 84 of 100

Match each soft-tissue fixation method with its most common

mode of failure.

Tendon slippage

Interference screw
Staple
Suture anchor
Suture post
Transfixion pins
Cortical button Discussion: A

The surgical fixation of soft tissue to bone is a common orthopaedic procedure. Numerous factors influence the strength of the soft–tissue-to-bone fixation construct, including tissue quality, implant strength, contact area, tensioning, and the biology of the location. Each fixation technique differs with respect to stability and failure mechanism. Interference screws can achieve excellent fixation but have the potential for graft pullout or laceration. Staples have less stiffness than interference screws and can irritate the overlying tissues. Transfixion pins fail secondary to pin breakage or partial tearing of the graft. Primary failure of cortical buttons includes pulling through cortical bone or migration.

Question 85 of 100

Match each soft-tissue fixation method with its most common

mode of failure.

Device pullout

Interference screw
Staple
Suture anchor
Suture post
Transfixion pins
Cortical button Discussion: B

stiffness than interference screws and can irritate the overlying tissues. Transfixion pins fail secondary to pin breakage or partial tearing of the graft. Primary failure of cortical buttons includes pulling through cortical bone or migration.

Question 86 of 100

Match each soft-tissue fixation method with its most common

mode of failure.

Device breakage

Interference screw
Staple
Suture anchor
Suture post
Transfixion pins
Cortical button

Discussion: 5

Question 87 of 100

Match each soft-tissue fixation method with its most common

mode of failure.

Pulling through bone

Interference screw
Staple
Suture anchor
Suture post
Transfixion pins
Cortical button

Discussion: 6

Question 88 of 100

Match each soft-tissue fixation method with its most common

mode of failure.

Tendon laceration

Interference screw
Staple
Suture anchor
Suture post
Transfixion pins
Cortical button Discussion: A

Question 89 of 100

Commonly used to produce orthopaedic implants, 316L stainless

steel is an alloy of what elements?

Cobalt, chromium, molybdenum
Iron, carbon, chromium, nickel, molybdenum, manganese
Iron, carbon, titanium, nickel, molybdenum, manganese
Titanium, aluminum, vanadium, iron, oxygen

Discussion: B

316L stainless steel is an alloy of iron, carbon, chromium, nickel, molybdenum, and manganese, as well as smaller amounts of phosphorus, sulfur, silicon, and nitrogen. Iron makes up the bulk of stainless steel, and carbon is limited to less than 0.03% to limit intragranular corrosion. Chromium increases hardness and

corrosion resistance. Likewise, nickel and molybdenum help prevent corrosion.

Cobalt chrome alloy, commonly used in spinal implants, is composed of cobalt, chromium, and molybdenum. Ti6Al4V titanium alloy is one of the most commonly used titanium alloys and is composed of titanium, aluminum, vanadium, iron, and oxygen.

Question 90 of 100

CLINICAL SITUATION

A surgeon devises an experiment to test the axial loading and rotational stability of bridge plate fixation. Figure 1 shows a locking compression plate fixed to a forearm simulation bone with a 2-mm gap between the fragments to simulate comminution.

Assuming that screws were placed in all holes, which screw would be expected to experience the highest stress during axial loading?

Screw 1
Screw 2
Screw 4
Screw 5 Discussion: A

The model shown in Figure 1 demonstrates a bridge plate concept that attempts to achieve secondary healing. Strain theory predicts that flexibility of the plate is important to stimulate healing; however, this flexibility must be balanced with appropriate stability. Multiple studies have investigated the stress, strain, and flexibility of plate fixation. The screws nearest the fracture absorb the highest stress in bridge plating, unlike the application of rigid fixation with direct

compression of the bone ends, in which the stress is maximal at the screws farthest from the fracture.

The rigidity of a construct can be manipulated by changing the working length of the plate. Creating a longer working length by leaving the screw holes closer to the fracture site empty reduces the rigidity of the construct. In the second item, two screws close to the fracture and then one screw far away on either side creates the most rigid construct, much like an external fixator. Remembering that strain is (change in length)/length, the surgeon could reduce the strain seen in the implant by increasing the working length of the plate or by placing screws farther away from the fracture.

Torsional stability is different from bending or axial compression stability. Torsional stability depends more on the number of screws on either side of the fracture than on the location of the screws. Biomechanical studies have shown that adding more than four screws will not improve torsional stability statistically, provided good purchase is achieved within the bone.

Lastly, as described previously, the working length of the plate is the distance between the innermost screws spanning the fracture site.

Question 91 of 100

CLINICAL SITUATION

Placing screws into which holes would provide maximum rigidity to this construct in axial compression?

1, 2 ,3
1, 2, 5
1, 4, 5
2, 4, 5

Discussion: B

screws will not improve torsional stability statistically, provided good purchase is achieved within the bone.

Lastly, as described previously, the working length of the plate is the distance between the innermost screws spanning the fracture site.

Question 92 of 100

CLINICAL SITUATION

Screws have been placed into holes 2, 3, and 5 on either side of the osteotomy, but the surgeon wants to make sure that the construct achieves maximal torsional stability, while avoiding the placement of unnecessary screws. How can the surgeon adjust the fixation to meet these goals?

Move the innermost screw to hole 1 on both sides of the osteotomy.
Keep the construct as it is, because it meets these goals.
Place an additional screw into hole 1 on both sides of the plate.
Place two additional screws into holes 1 and 4 on both sides of the plate.

Discussion: C

this flexibility must be balanced with appropriate stability. Multiple studies have investigated the stress, strain, and flexibility of plate fixation. The screws nearest the fracture absorb the highest stress in bridge plating, unlike the application of rigid fixation with direct compression of the bone ends, in which the stress is maximal at the screws farthest from the fracture.

Lastly, as described previously, the working length of the plate is the distance between the innermost screws spanning the fracture site.

Question 93 of 100

CLINICAL SITUATION

Assuming that screws have been placed into holes 2, 3, and 5, what is considered to be the working length of the plate?

The distance between the screw holes labeled “2”
The distance between the screw holes labeled “5”
The distance from the center of the fracture (or plate) to the screw hole labeled “2”
The distance from the center of the fracture (or plate) to the screw hole labeled “5”

Discussion: A

Lastly, as described previously, the working length of the plate is the distance between the innermost screws spanning the fracture site.

Question 94 of 100

A recent nonrandomized prospective study was completed

evaluating the efficacy of bracing in patients with adolescent idiopathic scoliosis. The outcome measurements were progression and need for posterior instrumentation and fusion. In the highly compliant group (brace wear of more than 10 hours per day), two of 31 patients (6%) required surgery. In the noncompliant group, 12 of 27 patients (44%) required surgery. Of patients who were considered to be highly compliant, how many needed to be treated with bracing to avoid one surgery?

Discussion: B

The statistic number needed to treat (NNT) is the number of patients who must be treated with a particular intervention, in this case bracing, in order to achieve one additional favorable outcome, in this case avoidance of surgery. It is defined as 1/absolute risk reduction (ARR). In this question, the risk of needing surgery is 6%

in the highly compliant group and 44% in the noncompliant group. Thus, the ARR is 38% or .38, and the NNT is 2.6, which is rounded up, yielding an NNT of 3.

Question 95 of 100

A 57-year-old man with chronic kidney disease who recently began

undergoing dialysis treatment five times per week comes to your office for a 3-month follow-up appointment after a right total knee replacement. The patient is at risk of renal osteodystrophy because of the failure of vitamin D conversion to which of the following active metabolites?

Ergocalciferol (vitamin D2)
Cholecalciferol (vitamin D3)
24, 25-dihydroxycholecalciferol
Calcitriol (1,25-dihydroxycholecalciferol) Discussion: D

Calcitriol is the active metabolite of vitamin D that is formed by 1 alpha-hydroxylase from calcidiol. Secondary hyperparathyroidism is a condition commonly seen in patients with chronic kidney disease characterized by hyerphosphatemia, hypocalcemia, high parathyroid hormone levels, and a reduced amount of calcitriol from damage to the kidney.

Question 96 of 100

Crevice corrosion is defined as

motion between two pieces of metal that are loose.
the microisolation of oxygen, leading to disruption of passivation.
an electrochemical circuit formed between two different metals.
micromotion between two pieces of metal that are not loose.

Discussion: B

All modular junctions are susceptible to crevice corrosion. At modular junctions machined with tight tolerances such as the head-neck junction, the space between the two surfaces is shielded partially from the aqueous chemical environment of the body fluid. This microisolation of the tiny gaps (or crevices) between the two surfaces of the implant is the source of crevice corrosion. The imbalance of oxygen between the cathode (the surface of the implant outside the crevice) and the anode inside the crevice) creates a current, even if each part of the modular junction is made from the same metal. At the anode, oxygen is low, whereas the concentrations of metal, hydrogen, and chloride ions are high. In this oxygen-poor environment, the surface of the implant cannot repassivate. If the metal ion released is chromium, it reacts with phosphate to form a black or green, tarry or glassy precipitate (ie, chromium (III) phosphate and/or other metal oxides) near the crevice and on the surface of the implant. Hence, the serum chromium level remains normal or only slightly elevated in patients with corrosion at modular junctions, whereas the serum cobalt level rises because of its increased solubility. This fact can be used to distinguish a failed metal-on-metal articulation—which in general has an equivalent rise in serum cobalt and chromium levels—from a failed modular junction—which in general has a differential elevation of the serum cobalt level severalfold above that of the serum chromium level.

Question 97 of 100

When applying the technique shown in Figures 1 and 2, when

would the surgeon expect concentrations of bone morphogenetic protein-2 (BMP-2) or bone promoting proteins to peak, and when should he or she expect the concentrations to return to baseline?

2 weeks, 3 months
2 weeks, 6 months
4 weeks, 3 months
4 weeks, 6 months Discussion: D

The surgeons in Figure 2 are attempting to use the induced–membrane technique described by Masquelet. After the placement of a cement spacer, a well-vascularied membrane forms around the spacer that harbors proteins such as BMP-2 and vascular endothelial growth factor that can promote bony healing. Basic science studies and animal models indicate that peak concentrations of these proteins occur at 4 weeks and return to baseline by around 6 months.

Question 98 of 100

What study is used to statistically combine multiple similar studies

and derive a pooled estimate closest to the truth of a particular research question?

Meta-analysis
Systematic review
Cohort study
Case-control study

Discussion: A

A systematic review evaluates a clearly formulated question and uses systematic and explicit methods to identify, select, and critically appraise relevant research and to collect and analyze data from the studies that are included in the review. Statistical methods (meta-analysis) may or may not be used to analyze and summarize the results of the included studies. Meta-analysis refers to the use of statistical techniques in a systematic review to integrate the results of included studies. A cohort study is best used to evaluate the effects of risk factors on the outcome of a disease process or treatment. A case-control study evaluates the outcome of a disease process or treatment and compares a group of patients that have the disease process with a group that does not have it.

Question 99 of 100

What is the most abundant matrix protein produced by

osteoblasts?

Type I collagen
Receptor activator of nuclear factor kappa-B (RANK)
Aggrecan
Interleukin-1 (IL-1)

Discussion: A

Type I collagen is the major matrix protein produced by osteoblasts and is an essential component of bone. RANK is a cell receptor that is important in the regulation of osteoclasts. Aggrecan is an important proteoglycan component of cartilage. IL-1 is an inflammatory factor.

Question 100 of 100

Increasing the mineral-to-matrix ratio of bone beyond normal would

have what effect on the modulus of elasticity and the duration of the plastic phase?

Increase the modulus of elasticity, shorten the plastic phase
Increase the modulus of elasticity, lengthen the plastic phase
Decrease the modulus of elasticity, shorten the plastic phase
Decrease the modulus of elasticity, lengthen the plastic phase

Discussion: A

Increasing the mineral content of bone will increase the stiffness and modulus of elasticity of bone, because an applied fore creates less deformation, and stress creates less strain. As the increased mineral content increases the stiffness and decreases compliance, the plastic phase will shorten, leading to a quick transition from the elastic through the plastic phases and catastrophic failure.

Orthopedic MCQS online Basic 018

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Orthopedic MCQS online Basic 018

Orthopedic MCQS online Basic 018

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

When applying an external fixator, the surgeon always must

consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

When applying an external fixator, the surgeon always must

consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

When applying an external fixator, the surgeon always must

consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

When applying an external fixator, the surgeon always must

consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

When applying an external fixator, the surgeon always must consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

When applying an external fixator, the surgeon always must

consider the risk-benefit ratio between stability and potential complications. For the following external fixation principle, match the most likely contributing factor listed.

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

Match the stain or immunoprobe with the method of

investigation for identifying the process.

Match the stain or immunoprobe with the method of

investigation for identifying the process.

Match the stain or immunoprobe with the method of

investigation for identifying the process.

Match the stain or immunoprobe with the method of

investigation for identifying the process.

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

Select the appropriate material property for the definition

listed.

Select the appropriate material property for the definition

listed.

Select the appropriate material property for the definition

listed.

Select the appropriate material property for the definition

listed.

Select the appropriate material property for the definition

listed.

Select the appropriate material property for the definition

listed.

Match each soft-tissue fixation method with its most common

mode of failure.

Match each soft-tissue fixation method with its most common

mode of failure.

Match each soft-tissue fixation method with its most common

mode of failure.

Match each soft-tissue fixation method with its most common

mode of failure.

Match each soft-tissue fixation method with its most common

mode of failure.

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION

CLINICAL SITUATION