PEDIATRIC KNEE

OVERVIEW

The knee is a ginglymoid (hinge) joint consisting of three articulations: patellofemoral, tibiofemoral, and tibiofibular.

Under normal cyclic loading, the knee may experience up to five times body weight per step.

The normal range of motion is from 10 degrees of extension to 140 degrees of flexion, with 8 to 12 degrees of rotation through the flexion/extension arc.

The dynamic and static stability of the knee is conferred mainly by soft tissues (ligaments, muscles, tendons, menisci) in addition to the bony articulations.

Because ligaments in the immature skeleton are more resistant to tensile stresses than are physeal plates and metaphyseal bone, trauma leads to physeal separation and avulsions not seen in the skeletally mature patient.

There are three physeal plates with secondary ossification centers.

Appearance of ossification centers is as follows:

• Distal femur: 39th fetal week

• Proximal tibia: by 2 months

• Tibial tubercle: 9 years

Physeal closure is as follows:

• Distal femur: 16 to 19 years

• Proximal tibia: 16 to 19 years

• Tibial tubercle: 15 to 17 years

The patella is a sesamoid bone, with its own ossification center, which appears at age 3 to 5 years.

Tibial spine: This is the site of insertion of the anterior cruciate ligament (ACL).

Two-thirds of longitudinal growth of the lower extremity is provided by the distal femoral (9 mm per year) and proximal tibial (6 mm per year) physes.

DISTAL FEMORAL PHYSEAL FRACTURES

Epidemiology

This is the most commonly injured physis around the knee.

They comprise 1% to 6% of all physeal injuries and less than 1% of all fractures in children.

Most (two-thirds) are Salter–Harris type II fractures and occur in adolescents.

They comprise 12% to 18% of all femur fractures in children.

Anatomy

The distal femoral epiphysis is the largest and fastest growing physis in the body.

There is no inherent protection of the physis. Ligamentous and tendinous structures insert on the epiphysis.

The sciatic nerve divides at the level of the distal femur.

The popliteal artery gives off the superior geniculate branches to the knee just posterior to the femoral metaphysis.

Mechanism of Injury

Direct trauma to the distal femur may occur from vehicular trauma, falling onto a flexed knee, or during athletic activity, such as a lateral blow to the knee with a planted, cleated foot as in football. In infants, distal femoral fracture may be associated with child abuse.

Indirect injury: Varus/valgus or hyperextension/hyperflexion force; results in simultaneous compression to one aspect of the physis with distraction to the other. Indirect force may result in epiphyseal separation from the metaphysis. Most typically, the physeal separation begins on the tension side and exits the metaphysis on the compression side (Salter–Harris type II).

Birth injury secondary to breech presentation or arthrogryposis may cause this physeal separation injury.

Minimal trauma in conditions that cause generalized weakening of the growth plate (osteomyelitis, leukemia, myelodysplasia) may also be causative.

Clinical Evaluation

Patients are typically unable to bear weight on the injured lower extremity, although patients with a nondisplaced physeal injury from a low-energy mechanism (e.g., athletic injury) may ambulate with an antalgic gait.

Older children and adolescents may relate a history of hearing or feeling a “pop” along with associated knee effusion and soft tissue swelling; this may be confused with a ligamentous injury.

The knee is typically in flexion owing to hamstring spasm.

Gross shortening or angular deformity is variable, with potential compromise of the neurovascular structures resulting from traction injury, laceration, or compression. A complete neurovascular assessment is thus critical.

Point tenderness may be elicited over the physis; this is usually performed by palpating the distal

femur at the level of the superior pole of the patella and adductor tubercle.

Most commonly, epiphyseal displacement is in the coronal plane producing a varus or valgus deformity.

Radiographic Evaluation (Table 49.1)

Anteroposterior (AP), lateral, and oblique views should be obtained. Radiographs of the contralateral lower extremity may be obtained for comparison if the diagnosis is in doubt.

Stress views may be obtained to diagnose nondisplaced separations in which the clinical examination is highly suggestive of physeal injury (knees with effusion and point tenderness over physis in the setting of a negative AP and lateral radiograph). Adequate analgesia is necessary to relax muscular spasm and to prevent both false-negative stress radiographs and physeal injury.

The physeal line should be 3- to 5-mm thick until adolescence.

Salter–Harris type III injuries usually have vertically oriented epiphyseal fracture components that are best appreciated on an AP view.

Computed tomography may be useful to assess fracture fragment definition.

In infants, separation of the distal femoral physis may be difficult to assess unless there is gross displacement because only the center of the epiphysis is ossified at birth; this should be in line with the anatomic axis of the femur on both AP and lateral views. Magnetic resonance imaging, ultrasound, or arthrography may aid in the diagnosis of distal femoral injury in these patients.

Arteriography of the lower extremity should be pursued if vascular injury is suspected.

Knee dislocations are uncommon in the skeletally immature, whereas physeal separation of the distal femoral physis may be associated with vascular injury.

Classification

Salter–Harris (Fig. 49.1)

Type I: Seen in newborns and adolescents; diagnosis easily missed; physeal widening may be apparent on comparison films and instability may be demonstrated on stress radiographs

Type II: Most common injury of the distal femoral physis; displacement usually medial or lateral, with metaphyseal fragment on compression side

Type III: Intra-articular fracture exiting the epiphysis (typically medial condyle from valgus stress

Type IV: Intra-articular fracture exiting the metaphysis; high incidence of growth inhibition with bar formation; rare injury

Type V: Physeal crush injury; difficult diagnosis, made retrospectively after growth arrest; narrowing of physis possible

Displacement

Anterior: Results from hyperextension injury; high incidence of neurovascular injury from proximal metaphyseal spike driven posteriorly

Posterior: Rare injury caused by knee hyperflexion

Medial: Valgus force most common, usually Salter–Harris type II

Lateral: Varus force

Treatment

Nonoperative

This is indicated for nondisplaced fractures.

A tense knee joint effusion may be relieved by sterile aspiration for symptomatic relief.

Closed reduction using general anesthesia may be performed for displaced fractures in which a stable result can be obtained (Fig. 49.2).

Sufficient traction should be applied during manipulation to minimize grinding of physeal cartilage (90% traction, 10% leverage). The position of immobilization varies with direction of displacement.

• Medial/lateral: Immobilize in 15 to 20 degrees of knee flexion. Cast in valgus mold for medial metaphyseal fragment and varus mold for lateral metaphyseal fragment to tension intact periosteum.

• Anterior: Immobilize initially at 90 degrees of knee flexion, then decrease flexion with time.

• Posterior: Immobilize in extension.

A residual varus/valgus deformity after reduction tends not to remodel.

Crutch ambulation with toe-touch weight bearing may be instituted at 3 weeks after injury.

The cast may be discontinued at 4 to 8 weeks, depending on the patient’s age and healing status. A

removable posterior splint and active range-of-motion exercises are instituted at this time.

Athletic activities should be restricted until knee range of motion has returned, symptoms have resolved, and sufficient quadriceps strength has been regained.

Operative

Indications for open reduction and internal fixation include:

• Irreducible Salter–Harris type II fracture with interposed soft tissue: Cannulated 4.0- or 6.5-mm screw fixation may be used to secure the metaphyseal spike (Fig. 49.3).

• Unstable reduction is an indication.

• Salter–Harris types III and IV: Joint congruity must be restored.

   

   

   

To minimize residual deformity and growth disturbance, specific principles should be observed for internal fixation.

• Avoid crossing the physis if possible.

• If the physis must be crossed, use smooth pins as perpendicular as possible to the physis.

• Remove fixation that crosses the physis as soon as possible.

Postoperatively, the patient is maintained in a long leg cast in 10 degrees of knee flexion. The patient may be ambulatory with crutches in 1 to 2 days with non–weight bearing on the injured extremity. At 1 week, the patient may begin straight leg raises.

If at 4 weeks evidence of osseous healing is demonstrated radiographically, the cast may be discontinued with a posterior splint in place for protection. The patient may be advanced to partial weight bearing with active range-of-motion exercises.

The patient typically resumes a normal, active lifestyle at 4 to 6 months after injury.

Complications

Acute

Popliteal artery injury (<2%): Associated with hyperextension or anterior epiphyseal displacement injuries in which a traction injury may be sustained or by direct laceration from the sharp metaphyseal spike.

• A cool, pulseless foot that persists despite reduction should be worked up with angiography to rule out laceration.

• Vascular embarrassment that resolves following reduction should be observed for 48 to 72

  hours to rule out an intimal tear and subsequent thrombosis.

Peroneal nerve palsy (3%): Caused by traction injury during fracture or reduction or secondary to initially anterior/medial displaced epiphysis. Persistent peroneal palsy over 3 to 6 months should be evaluated by electromyography and by exploration as may be indicated.

Recurrent displacement: Fractures of questionable stability following closed reduction should receive operative fixation (either percutaneous pins or internal fixation) to prevent late or recurrent displacement. Anterior and posterior displacements are particularly unstable.

Late

Knee instability (up to 37% of patients): Knee instability may be present, indicating concomitant ligamentous compromise that was not appreciated at the time of index presentation. The patient may be treated with rehabilitation for lower extremity strengthening or may require operative treatment. Collateral ligaments may be acutely repaired if instability exists after fracture fixation.

Angular deformity (19%): This results from the initial physeal injury (Salter–Harris types I and II), asymmetric physeal closure (bar formation, Salter–Harris types III and IV), or unrecognized physeal injury (Salter–Harris type V).

• Observation, physeal bar excision (<30% of physis, >2 years of remaining growth), hemiepiphysiodesis, epiphyseolysis, or wedge osteotomy may be indicated.

Physeal closure is usually the rule for distal femoral physeal fractures. A resultant leg length

discrepancy (24%) depends on the amount of remaining growth: This is usually clinically insignificant if <2 years of growth remain; otherwise, the discrepancy tends to progress at the rate of 1 cm per year.

• Discrepancy <2.0 cm at skeletal maturity is usually of no functional or cosmetic significance.

• Discrepancy of 2.5 to 5 cm may be treated with contralateral epiphysiodesis (femoral or tibial, or both) or femoral shortening depending on the projected length discrepancy.

• Discrepancy >5 cm may be an indication for femoral lengthening combined with epiphysiodesis

  of the contralateral distal femur or proximal tibia.

Knee stiffness (16%): Results from adhesions or capsular or muscular contracture following surgery. It is usually related to the duration of immobilization; therefore, early discontinuation of

the cast with active range of motion is desirable.

PROXIMAL TIBIAL FRACTURES

Epidemiology

These comprise 0.6% to 0.8% of all physeal injuries.

The average age is 14 years.

Most occur in adolescent males.

ANATOMY

The popliteal artery traverses the posterior aspect of the knee and is tethered to the knee capsule by connective tissue septa posterior to the proximal tibia. The vascular supply is derived from the anastomosis of the inferior geniculate arteries.

The physis is well protected by osseous and soft tissue structures, which may account for the low incidence of injuries to this structure.

• Lateral: Fibula

• Anterior: Patellar tendon/ligament

• Medial: Medial collateral ligament (MCL; inserts into metaphysis)

• Posteromedial: Semimembranosus insertion

   

  Mechanism of Injury

Direct: Trauma to the proximal tibia (motor vehicle bumper, lawnmower accident)

Indirect: More common and involves hyperextension, abduction, or hyperflexion from athletic injury, motor vehicle accident, fall, or landing from a jump with a concurrent MCL tear

Birth injury: Results from hyperextension during breech delivery or arthrogryposis

Pathologic condition: Osteomyelitis of the proximal tibia and myelomeningocele are causes.

Clinical Evaluation

Patients typically present with an inability to bear weight on the injured extremity. The knee may be tense with hemarthrosis, and extension is limited by hamstring spasm.

Tenderness is present 1 to 1.5 cm distal to the joint line, and variable gross deformity may be present.

Neurovascular status should be carefully assessed for popliteal artery or peroneal nerve compromise. The anterior, lateral, superficial posterior, and deep posterior compartments should be palpated for pain or turgor. Patients suspected of having elevated compartment pressures should receive serial neurovascular examinations with measurement of compartment pressures as indicated.

Associated ligamentous injuries should be suspected, although it may be difficult to appreciate these injuries secondary to the dramatic presentation of the fracture.

Radiographic Evaluation

AP, lateral, and oblique views of the affected knee should be obtained. Radiographs of the contralateral knee may be obtained for comparison.

Stress radiographs in coronal and sagittal planes may be obtained, but hyperextension of the knee should be avoided because of potential injury to popliteal structures.

Most patients with proximal tibial physeal injuries are adolescents in whom the secondary ossicle of the tibial tubercle has appeared. A smooth, horizontal radiolucency at the base of the tibial tubercle should not be confused with an epiphyseal fracture.

Magnetic resonance imaging may aid in identification of soft tissue interposition when reduction is difficult or impossible.

Computed tomography may aid in fracture definition, especially with Salter–Harris type III or IV fractures.

Arteriography may be indicated in patients in whom vascular compromise (popliteal artery) is suspected.

Classification (Table 49.2)

Salter–Harris

Type I: Transphyseal injury; diagnosis often missed; may require stress or comparison views; 50% initially nondisplaced

Type II: Most common; transphyseal injury exiting the metaphysis; one-third nondisplaced; those that displace usually do so medially into valgus

Type III: Intra-articular fracture of the lateral plateau; MCL often torn

Type IV: Intra-articular fracture of the medial or lateral plateau; fracture line exiting the metaphysis

Type V: Crush injury; retrospective diagnosis common after growth arrest

Treatment

Nonoperative

Nondisplaced fractures may be treated with a long leg cast with the knee flexed to 30 degrees. The

patient should be followed closely with serial radiographs to detect displacement.

Displaced fractures may be addressed with gentle closed reduction, with limited varus and hyperextension stress to minimize traction to the peroneal nerve and popliteal vasculature, respectively. The patient is placed in a long leg cast in flexion (typically 30 to 60 degrees, depending on the position of stability).

The cast may be discontinued at 4 to 6 weeks after injury. If the patient is symptomatically improved and radiographic evidence of healing is documented, active range-of-motion and quadriceps strengthening exercises are initiated.

Operative

Displaced Salter type I or II fractures in which stable reduction cannot be maintained may be treated with percutaneous smooth pins across the physis in type I or parallel to the physis (metaphysis) in type II.

Open reduction and internal fixation are indicated for displaced Salter–Harris types III and IV fractures to restore articular congruity. This may be achieved with pin or screw fixation parallel to the physis; articular congruity is the goal.

Postoperatively, the patient is immobilized in a long leg cast with the knee flexed to 30 degrees. This is continued for 6 to 8 weeks, at which time the cast may be removed with initiation of active range-of-motion exercises.

Complications

Acute

Recurrent displacement: This may occur if closed reduction and casting without operative fixation is performed on an unstable injury. It is likely secondary to unrecognized soft tissue injury.

Popliteal artery injury (10%): This occurs especially in hyperextension injuries; it is related to tethering of the popliteal artery to the knee capsule posterior to the proximal tibia (Fig. 49.4). Arteriography may be indicated when distal pulses do not return following prompt reduction of the injury.

Peroneal nerve palsy: This traction injury results from displacement, either at the time of injury or during attempted closed reduction, especially with a varus moment applied to the injury site.

Late

Angular deformity: This results from the physeal injury (Salter–Harris types I and II), resulting in asymmetric physeal closure (bar formation, Salter–Harris types III and IV), or an unrecognized physeal injury (Salter–Harris type V).

• Observation, physeal bar excision (<30% of physis, >2 years of remaining growth), hemiepiphysiodesis, epiphyseolysis, or wedge osteotomy may be indicated.

Leg length discrepancy: This is usually clinically insignificant if <2 years of growth remain;

otherwise, discrepancy tends to progress at the rate of 1 cm per year. Treatment for leg length discrepancy remains similar to that for distal femur physeal injuries.

TIBIAL TUBERCLE FRACTURES

Epidemiology

These represent 0.4% to 2.7% of all physeal injuries.

They are seen most commonly in athletic males 14 to 16 years old.

It is important to differentiate these fractures from Osgood–Schlatter disease.

Anatomy (Fig. 49.5)

The tibial tubercle physis, which is continuous with the tibial plateau, is most vulnerable between the ages of 13 and 16 years, when it closes from posterior to anterior.

The insertion of the medial retinaculum extends beyond the proximal tibial physis into the metaphysic; therefore, after tibial tubercle fracture, limited active extension of the knee is still possible, although patella alta and extensor lag are present.

The tubercle is located one to two fingerbreadths below the joint line. It is in line with the medial patella in flexion and the lateral patella in extension.

Mechanism of Injury

The mechanism of injury is typically indirect, usually resulting from a sudden accelerating or decelerating force involving the quadriceps mechanism.

Predisposing factors include:

• Patella baja

• Tight hamstrings (increase flexion torque)

• Preexisting Osgood–Schlatter disease (uncertain whether mechanical vulnerability or overdevelopment of quadriceps mechanism)

• Disorders with physeal anomalies

   

  Clinical Evaluation

Patients typically present with a limited ability to extend the knee as well as an extensor lag. The leg is held in 20 to 40 degrees of flexion by spastic hamstrings.

Swelling and tenderness over the tibial tubercle are typically present, often with a palpable defect.

Hemarthrosis is variable.

Patella alta may be observed if displacement is severe. The transverse retinaculum may be torn. Meniscal and cruciate ligaments may be found in severe injuries.

Radiographic Evaluation

AP and lateral views of the knee are sufficient for the diagnosis, although a slight internal rotation view best delineates the injury because the tibial tubercle lies just lateral to the tibial axis.

Patella alta may be noted.

Classification

Watson–Jones

Type I: Small fragment avulsed and displaced proximally; fracture through secondary ossification center

Type II: Secondary ossification center already coalesced with proximal tibial epiphysis; fracture at level of horizontal portion of tibial physis

Type III: Fracture line passing proximally through tibial epiphysis and into joint; possibly confused with Salter–Harris type III tibial physeal injury

Ogden

This modification of the Watson–Jones classification (see earlier discussion) subdivides each type into A and B categories to account for the degree of displacement and comminution (Fig. 49.6).

Treatment

Nonoperative

This is indicated for Type IA fractures with intact extensor mechanism.

It consists of manual reduction and immobilization in a long leg cast with the knee extended, with patellar molding.

The cast is worn for 4 to 6 weeks, at which time the patient may be placed in a posterior splint for

an additional 2 weeks. Gentle active range-of-motion exercises and quadriceps strengthening exercises are instituted and advanced as symptoms abate.

Operative

Indicated for types IB, II, III fractures or irreducible type IA fractures (periosteum may be interposed).

A vertical midline approach is used; the fracture can be stabilized using smooth pins (>3 years from skeletal maturity), screws, threaded Steinmann pins, or a tension band.

Postoperatively, the extremity is placed in a long leg cast in extension with patella molding for 4 to 6 weeks, at which time the patient may be placed in a posterior splint for an additional 2 weeks. Gentle active range-of-motion exercises and quadriceps strengthening exercises are instituted and advanced as symptoms abate.

Complications

Genu recurvatum: This occurs secondary to premature closure of anterior physis; it is rare because injury occurs typically in adolescent patients near skeletal maturity.

Loss of knee motion: Loss of flexion may be related to scarring or postoperative immobilization. Loss of extension may be related to nonanatomic reduction and emphasizes the need for operative fixation of types IB, II, and III fractures.

Patella alta: This may occur if reduction is insufficient.

Osteonecrosis of fracture fragment: This is rare because of soft tissue attachments.

Compartment syndrome: This is rare, but it may occur with concomitant tearing of the anterior tibial recurrent vessels that retract to the anterior compartment when torn.

TIBIAL SPINE (INTERCONDYLAR EMINENCE) FRACTURES

Epidemiology

Relatively rare injury, occurring in 3 per 100,000 children per year

Most commonly caused by a fall from a bicycle (50%)

Anatomy

There are two tibial spines: anterior and posterior. The ACL spans the medial aspect of the lateral femoral condyle to the anterior tibial spine.

In the immature skeleton, ligaments are more resistant to tensile stresses than are physeal cartilage or cancellous bone; therefore, forces that would lead to an ACL tear in an adult cause avulsion of the incompletely ossified tibial spine in a child.

Mechanism of Injury

Indirect trauma: The mechanism includes rotatory, hyperextension, and valgus forces.

Direct trauma: This is extremely rare, secondary to multiple trauma with significant knee injury.

Clinical Evaluation

Patients are typically reluctant to bear weight on the affected extremity.

Hemarthrosis is usually present, with painful range of motion and a variable bony block to full extension.

The MCL and lateral collateral ligament (LCL) should be stressed with varus/valgus pressure to rule out associated injury.

Radiographic Evaluation

AP and lateral views should be obtained. The AP view should be scrutinized for osseous fragments within the tibiofemoral articulation; these may be difficult to appreciate because only a thin, ossified sleeve may be avulsed.

Obtaining an AP radiograph to account for the 5 degrees of posterior slope of the proximal tibia may aid in visualization of an avulsed fragment.

Stress views may be useful in identification of associated ligamentous or physeal disruptions.

Classification

Meyers and McKeever (Fig. 49.7)

Type I: Minimal or no displacement of fragment

Type II: Angular elevation of anterior portion with intact posterior hinge

Type III: Complete displacement with or without rotation (15%)

Type IV: Comminuted (5%)

Types I and II account for 80% of tibial spine fractures.

Treatment

Nonoperative

This is indicated for types I and II fractures of the tibial spine.

The knee should be immobilized in extension; the fat pad may contact the spine in extension and thus help with reduction.

After 4 to 6 weeks, the cast is removed with initiation of active range-of-motion and quadriceps and hamstrings strengthening.

Operative

This is indicated for types III and IV fractures of the tibial spine owing to historically uniformly poor results with nonoperative management. (Recent 2009 evidence may contradict this thinking.)

Debridement of fracture site is recommended with fixation using sutures, pins, or screws.

The fracture may be repaired arthroscopically with an ACL guide, or by arthrotomy.

Postoperatively, the patient is placed in a long leg cast with the knee in slight (10 to 20 degree) flexion. In 4 to 6 weeks, the cast is removed with initiation of active range-of-motion and quadriceps and hamstrings strengthening.

Complications

Loss of extension: This is present in up to 60% of cases. Extension loss is typically clinically insignificant and may represent a bony block to extension caused by malunion of a type III fracture.

Knee instability: This may persist with type III or IV fractures accompanied by collateral ligament injuries and/or physeal fractures.

PATELLA FRACTURES

Epidemiology

It is very rare in children; only 1% of all patella fractures are seen in patients less than 16 years of age.

Anatomy

The patella is the largest sesamoid in the body.

The function of the patella is to increase the mechanical advantage and leverage of the quadriceps tendon, aid in nourishment of the femoral articular surface, and protect the femoral condyles from direct trauma.

Forces generated by the quadriceps in children are not as high as in adults owing to a smaller muscle mass and shorter moment arm.

The blood supply to the patella derives from the anastomotic ring from the superior and inferior geniculate arteries. An additional supply through the distal pole is from the fat pad.

The ossification center appears between 3 and 5 years. Ossification then proceeds peripherally and is complete by 10 to 13 years.

Patella fracture must be differentiated from a bipartite patella (present in up to 8% of patients), which is commonly located superolaterally. One should obtain contralateral films because bilateral bipartite patella is present in up to 50% of cases.

Mechanism of Injury

Direct: This is the most common and involves trauma to the patella secondary to a fall or motor vehicle accident. Cartilage anlage acts as a cushion to a direct blow.

Indirect: This is a sudden accelerating or decelerating force on the quadriceps.

Marginal fracture: This is usually medial owing to patellar subluxation or dislocation laterally.

Predisposing factors include:

• Trauma to the knee extensor mechanism

• Contracture of the extensor mechanism

   

  Clinical Evaluation

Patients typically present with refusal to bear weight on the affected extremity.

Swelling, tenderness, and hemarthrosis are usually present, often with limited or absent active extension of the knee.

Patella alta may be present with avulsion or sleeve fractures, and a palpable osseous defect may be appreciated.

An apprehension test may be positive and may indicate the presence of a spontaneously reduced patellar dislocation that resulted in a marginal fracture.

Radiographic Evaluation

AP, lateral, and patellar (sunrise) views of the knee should be obtained.

Transverse fracture patterns are most often appreciated on lateral view of the knee. The extent of displacement may be better appreciated on a stress view with the knee flexed to 30 degrees (greater flexion may not be tolerated by the patient).

Longitudinally oriented and marginal fractures may be best appreciated on AP or sunrise views. It is important to distinguish this from osteochondral fracture, which may involve a large amount of articular surface.

Stellate fractures and bipartite patella are best appreciated on AP radiographs. Comparison views of the opposite patella may aid in delineating a bipartite patella.

Classification

Based on Pattern (Fig. 49.8)

Transverse: Complete versus incomplete

Marginal fractures: Generally resulting from lateral subluxation or dislocation of the patella; may be either medial (avulsion) or lateral (direct trauma from condyle)

Sleeve fracture: Unique to immature skeleton; consisting of an extensive sleeve of cartilage pulled from the osseous patella with or without an osseous fragment from the pole

Stellate: Generally from direct trauma in the older child

Treatment

Nonoperative

This is indicated for nondisplaced and minimally displaced (<3 mm) fractures with an intact extensor mechanism.

This consists of a well-molded cylinder cast with the knee in extension.

Progressive weight bearing is permitted as tolerated. The cast is generally discontinued at 4 to 6 weeks.

Operative

Displaced fractures (>3-mm diastasis or >3-mm articular step-off): Stabilization involves use of cerclage wire, tension band technique, sutures, or screws; the retinaculum must also be repaired.

Sleeve fracture: Careful reduction of the involved pole and cartilaginous sleeve is performed with fixation and retinacular repair; if this is missed, the result is an elongated patella with extensor lag and quadriceps weakness.

Postoperatively, the leg is maintained in a well-molded cylinder cast for 4 to 6 weeks. Quadriceps strengthening and active range-of-motion exercises are instituted as soon as possible.

Partial patellectomy should be reserved for severe comminution.

Complications

Quadriceps weakness: Compromised quadriceps function occurs secondary to missed diagnosis or inadequate treatment with functional elongation of the extensor mechanism and loss of mechanical advantage.

Patella alta: This results from functional elongation of the extensor mechanism and is associated with quadriceps atrophy and weakness.

Posttraumatic osteoarthritis: Degenerative changes occur secondary to chondral damage at the time of injury.

OSTEOCHONDRAL FRACTURES

Epidemiology

These typically involve the medial or lateral femoral condyles or the patella.

These often occur in association with patellar dislocation.

Anatomy

As the knee flexes, the patella engages the condylar groove. At 90 to 135 degrees, the patella rides within the notch.

Mechanism of Injury

Exogenous: A direct blow or a shearing force (patellar dislocation). This is the most common pathologic process.

Endogenous: A flexion/rotation injury of the knee. Contact between the tibia and the femoral condyle results in osteochondral fracture of the condyle.

Clinical Evaluation

The patient presents with knee effusion and tenderness over the site of fracture.

The knee is held in a position of comfort, usually in 15 to 20 degrees of flexion.

Radiographic Evaluation

Standard knee AP and lateral x-rays often establish the diagnosis.

Schuss and Tunnel views may be helpful to localize the fragment near the notch.

Treatment

Operative excision versus fixation of fragment depends on the size and location of the defect as well as on the timing of surgery.

Small fragments or injuries to non–weight-bearing regions may be excised either open or arthroscopically.

Large fragments may be fixed with subchondral or headless lag screws.

If surgery is delayed more than 10 days after the injury, the piece should be excised because the cartilage is not typically viable.

Postoperatively, in patients with internal fixation, a long leg cast with 30 degrees of flexion is applied. The patient is typically non–weight bearing for 6 weeks.

If excision is performed, the patient may bear weight as tolerated and range the knee after soft tissues heal.

PATELLA DISLOCATION

Epidemiology

Patella dislocation is more common in females. Dislocation is also associated with physiologic laxity, and in patients with hypermobility and connective tissue disorders (e.g., Ehlers–Danlos or Marfan syndrome).

Anatomy

The “Q angle” is defined as the angle subtended by a line drawn from the anterior superior iliac spine through the center of the patella and a second line from the center of the patella to the tibial

tubercle (Fig. 49.9). The Q angle ensures that the resultant vector of pull with quadriceps action is laterally directed; this lateral moment is normally counterbalanced by patellofemoral, patellotibial, and retinacular structures as well as patellar engagement within the trochlear groove. An increased Q angle predisposes to patella dislocation.

Dislocations are associated with patella alta, congenital abnormalities of the patella and trochlea, hypoplasia of the vastus medialis, and hypertrophic lateral retinaculum.

Mechanism of Injury

Lateral dislocation: The mechanism is forced internal rotation of the femur on an externally rotated and planted tibia with the knee in flexion. It is associated with a 5% risk of osteochondral fractures.

Medial instability is rare and usually iatrogenic, congenital, traumatic, or associated with atrophy of the quadriceps musculature.

Intra-articular dislocation: This is uncommon, but it may occur following knee trauma in adolescent boys. The patella is avulsed from the quadriceps tendon and is rotated around the horizontal axis, with the proximal pole lodged in the intercondylar notch.

Clinical Evaluation

Patients with an unreduced patella dislocation will present with hemarthrosis, an inability to flex the knee, and a displaced patella on palpation.

Patients with a lateral dislocation may also present with medial retinacular pain.

Patients with reduced or chronic patella dislocation may demonstrate a positive “apprehension test,” in which a laterally directed force applied to the patella with the knee in extension

reproduces the sensation of impending dislocation, causing pain and quadriceps contraction to limit patellar mobility.

Radiographic Evaluation

AP and lateral views of the knee should be obtained. In addition, an axial (sunrise) view of both patellae should be obtained. Various axial views have been described by several authors (Fig. 49.10).

• Hughston 55 degrees of knee flexion: sulcus angle, patellar index

• Merchant 45 degrees of knee flexion: sulcus angle, congruence angle

   

   

   

Laurin 20 degrees of knee flexion: patellofemoral index, lateral patellofemoral angle

Assessment of patella alta or baja is based on the lateral radiograph of the knee.

• Blumensaat line: The lower pole of the patella should lie on a line projected anteriorly from the intercondylar notch on the lateral radiograph with the patient’s knee flexed to 30 degrees.

• Insall–Salvati ratio: The ratio of the length of the patellar ligament (LL; from the inferior pole

  of the patella to the tibial tubercle) to the patellar length (LP; the greatest diagonal length of the patella) should be 1.0. (This ratio is appropriate for the adolescent; children have other measures for assessment of the patella). A ratio of 1.2 indicates patella alta, whereas 0.8 indicates patella baja (Fig. 49.11).

   

   

   

  Classification

  Reduced versus unreduced Congenital versus acquired

  Acute (traumatic) versus chronic (recurrent) Lateral, medial, intra-articular, superior

  Treatment

  Nonoperative

Reduction and casting or bracing in knee extension may be undertaken with or without arthrocentesis for comfort.

The patient may ambulate in locked extension for 3 weeks, at which time progressive flexion can be instituted with physical therapy for quadriceps strengthening. After a total of 6 to 8 weeks, the patient may be weaned from the brace.

Surgical intervention for acute dislocations is rarely indicated except for displaced intra-articular fractures.

Intra-articular dislocations may require reduction with patient under anesthesia.

Functional taping with moderate success has been described in the physical therapy literature.

Operative

This is primarily used in cases of recurrent dislocations.

No single procedure corrects all patella malalignment problems—the patient’s age, diagnosis, level of activity, and condition of the patellofemoral articulation must be taken into consideration.

Patellofemoral instability should be addressed by correction of all malalignment factors.

Degenerative articular changes influence the selection of realignment procedure.

Surgical interventions include:

• Lateral release: Indicated for patellofemoral pain with lateral tilt, lateral retinacular pain with lateral patellar position, and lateral patellar compression syndrome. It may be performed arthroscopically or as an open procedure.

• Medial plication: This may be performed at the time of lateral release to centralize the patella.

• Proximal patellar realignment: Medialization of the proximal pull of the patella is indicated when a lateral release/medial plication fails to centralize the patella. The release of tight proximal lateral structures and reinforcement of the pull of medial supporting structures, especially the vastus medialis obliquus, are performed in an effort to decrease lateral patellar tracking and improve congruence of the patellofemoral articulation. Indications include recurrent patella dislocations after failed nonoperative therapy and acute dislocations in young, athletic patients, especially with medial patella avulsion fractures or radiographic lateral subluxation/tilt after closed reduction.

• Distal patella realignment: Reorientation of the patella ligament and the tibial tubercle is indicated when an adult patient experiences recurrent dislocations and patellofemoral pain with malalignment of the extensor mechanism. This is contraindicated in patients with open physes (in children, the gracilis tendon may be transferred into the patella) and normal Q angles. It is designed to advance and medialize the tibial tubercle, thus correcting patella alta and normalizing the Q angle.

  Complications

Redislocation: A younger age at initial dislocation increases the risk of recurrent dislocation. Recurrent dislocation is an indication for surgical intervention.

Loss of knee motion: This may result from prolonged immobilization.

Patellofemoral pain: This may result from retinacular disruption at the time of dislocation or from chondral injury.

KNEE DISLOCATION

Epidemiology

This is infrequent in skeletally immature individuals, because physeal injuries to the distal femur or proximal tibia are more likely to result.

Anatomy

This typically occurs with major ligamentous disruptions (both cruciates or equivalent spine injuries with disruption of either MCL or/and LCL) about the knee.

It is associated with major disruption of soft tissue and damage to neurovascular structures; vascular repair must take place within the first 6 to 8 hours to avoid permanent damage.

It is associated with other knee injuries, including tibial spine fractures, osteochondral injuries, and meniscal tears.

Mechanism of Injury

Most dislocations occur as a result of multiple trauma from motor vehicle accidents or falls from a height.

Clinical Evaluation

Patients almost always present with gross knee distortion. Immediate reduction should be undertaken without waiting for radiographs in the displaced position. Of paramount importance is the arterial supply, with secondary consideration given to neurologic status.

The extent of ligamentous injury is related to the degree of displacement, with injury occurring with displacement greater than 10% to 25% of the resting length of the ligament. Gross instability may be appreciated after reduction.

A careful neurovascular examination is critical both before and after reduction. The popliteal artery is at risk during traumatic dislocation of the knee owing to the bowstring effect across the popliteal fossa secondary to proximal and distal tethering. Peroneal nerve injuries are also common, mostly in the form of traction neurapraxias.

Radiographic Evaluation

Gross dislocation should be reduced first and not delayed for films.

AP and lateral views are sufficient to establish the diagnosis; the most common direction is anterior.

Radiographs should be scrutinized for associated injuries to the tibial spine, distal femoral physis, or proximal tibial physis. Stress views may be obtained to detect collateral ligament injury.

It remains controversial whether all patients should have an arteriogram. Some authors state that if pulses are present both before and after reduction, arteriography is not indicated. The patient must be monitored for 48 to 72 hours after reduction because late thrombus may develop as a result of intimal damage.

Classification

Descriptive

Classification is based on displacement of the proximal tibia in relation to the distal femur. It also should include open versus closed and reducible versus irreducible. The injury may be classified as occult, indicating a knee dislocation with spontaneous reduction.

Anterior: Forceful knee hyperextension beyond 30 degrees; most common; associated with PCL with or without ACL tear, with increasing incidence of popliteal artery disruption with increasing degree of hyperextension

Posterior: Posteriorly directed force against proximal tibia of flexed knee; “dashboard” injury; accompanied by ACL/PCL disruption as well as popliteal artery compromise with increasing proximal tibial displacement

Lateral: Valgus force; medial supporting structures disrupted, often with tears of both cruciate

ligaments

Medial: Varus force; lateral and posterolateral structures disrupted

Rotational: Varus/valgus with rotatory component; usually result in buttonholing of femoral condyle through capsule

Treatment

Treatment is based on prompt recognition and reduction of the knee dislocation, with recognition of vascular injury and operative intervention if necessary.

No large series have been reported, but early ligamentous repair is indicated for young patients.

Complications

Vascular compromise: Unrecognized and untreated vascular compromise to the leg, usually in the form of an unrecognized intimal injury with late thrombosis and ischemia, represents the most serious and potentially devastating complication from a knee dislocation. Careful, serial evaluation of neurovascular status is essential, up to 48 to 72 hours after injury, with aggressive use of arteriography as indicated.

Peroneal nerve injury: This usually represents a traction neurapraxia that will resolve. Electromyography may be indicated if resolution does not occur within 3 to 6 months.