PATELLA AND EXTENSOR

MECHANISM INJURIES

PATELLAR FRACTURES

Epidemiology

Represent 1% of all skeletal injuries

Male-to-female ratio 2:1

Most common age group 20 to 50 years old

Bilateral injuries uncommon

Anatomy

The patella is the largest sesamoid bone in the body.

The quadriceps tendon inserts on the superior pole and the patellar ligament originates from the inferior pole of the patella.

There are seven articular facets; the lateral facet is the largest (50% of the articular surface).

The articular cartilage may be up to 1-cm thick.

The medial and lateral extensor retinacula are strong longitudinal expansions of the quadriceps and insert directly onto the tibia. If these remain intact in the presence of a patella fracture, then active extension will be preserved (Fig. 35.1).

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.

The blood supply arises from the geniculate arteries, which form an anastomosis circumferentially around the patella.

Mechanism of Injury

Direct: Trauma to the patella may produce incomplete, simple, stellate, or comminuted fracture patterns. Displacement is typically minimal owing to preservation of the medial and lateral retinacular expansions. Abrasions over the area or open injuries are common. Active knee extension may be preserved.

Indirect (most common): This is secondary to forcible eccentric quadriceps contraction while the knee is in a semiflexed position (e.g., in a “stumble” or “fall”). The intrinsic strength of the patella is exceeded by the pull of the musculotendinous and ligamentous structures. A transverse fracture pattern is most commonly seen with this mechanism, with variable inferior pole comminution. The degree of displacement of the fragments suggests the degree of retinacular disruption. Active knee extension is usually lost.

Combined direct/indirect mechanisms: These may be caused by trauma in which the patient experiences direct and indirect trauma to the knee, such as in a fall from a height.

Clinical Evaluation

Patients typically present with limited or no ambulatory capacity with pain, swelling, and tenderness of the involved knee. A defect at the patella may be palpable.

It is important to rule out an open fracture because these constitute a surgical urgency; this may require instillation of more than 100 mL of saline into the knee to determine communication with overlying lacerations.

Active knee extension should be evaluated to determine injury to the retinacular expansions. This may be aided by decompression of hemarthrosis or intra-articular lidocaine injection.

Associated lower extremity injuries may be present in the setting of high-energy trauma. The physician must carefully evaluate the ipsilateral hip, femur, tibia, and ankle, with appropriate

radiographic evaluation, if indicated.

Radiographic Evaluation

Anteroposterior (AP) and lateral views of the knee should be obtained.

• AP view: A bipartite patella (8% of the population) may be mistaken for a fracture; it usually occurs in the superolateral position and has smooth margins; it is bilateral in 50% of individuals.

• Lateral view: Displaced fractures usually are obvious.

• Axial view (sunrise): This may help identify osteochondral or vertical marginal fractures. This view may be difficult to obtain in the acute setting, however.

Computed tomography scanning may be used to better delineate fracture patterns, marginal

fractures, or free osteochondral fragments.

CLASSIFICATION

Descriptive

Open versus closed

Nondisplaced versus displaced

Pattern: stellate, comminuted, transverse, vertical (marginal), polar osteochondral (Fig. 35.2)

Orthopaedic Trauma Association Classification of Pate lar Fractures See Fracture and Dislocation Classification Compendium at http://www.ota.org/compendium/compendium.html.

Treatment

Nonoperative

Indications include nondisplaced or minimally displaced (2 to 3 mm) fractures with minimal

articular disruption (1 to 2 mm). This requires an intact extensor mechanism.

A cylinder cast or knee immobilizer is used for 4 to 6 weeks. Early weight bearing in extension is encouraged, advancing to full weight bearing with crutches as tolerated by the patient. Early straight leg raising and isometric quadriceps strengthening exercises should be started within a few days. After radiographic evidence of healing, progressive active flexion and extension strengthening exercises are begun with a hinged knee brace initially locked in extension for ambulation.

Operative

Open Reduction and Internal Fixation

Indications for open reduction and internal fixation include loss of active extension, an extensor lag, >2-mm articular incongruity, >3-mm fragment displacement, or open fracture.

There are multiple methods of operative fixation, including tension banding (using parallel longitudinal Kirschner wires or cannulated screws) (Figs. 35.3A,B) as well as circumferential cerclage wiring. Retinacular disruption should be repaired at the time of surgery. Comminuted fractures may require multiple small fragment or mini-fragment screws or wires.

Postoperatively, the patient should be placed in a splint for 3 to 6 days until skin healing, with early institution of knee motion. The patient should perform active assisted range-of-motion exercises; full weight bearing is allowed in extension but may be protected at the discretion of the surgeon.

Severely comminuted or marginally repaired fractures, particularly in older individuals, may necessitate immobilization for 3 to 6 weeks.

Hinged bracing is not indicated in extensor mechanism injuries.

Patellectomy

Partial patellectomy

• Indications for partial patellectomy are limited but include the presence of a large, salvageable fragment in the presence of smaller, comminuted polar fragments in which it is believed impossible to restore the articular surface or to achieve stable fixation. Excision of distal fragments will lead to patella baja.

• The patellar tendon may be reattached with nonabsorbable sutures placed longitudinally through drill holes along the long axis.

Total patellectomy

• Total patellectomy is reserved for extensive and severely comminuted fractures and is rarely indicated.

• Peak torque of the quadriceps is reduced by 50%.

• Repair of medial and lateral retinacular injuries at the time of patellectomy is essential.

Following partial or total patellectomy, the knee should be immobilized in a long leg cast at 10 degrees of flexion for 3 to 6 weeks.

Complications

Postoperative infection: This is uncommon and is related to open injuries that may necessitate serial debridements. Relentless infection may require excision of nonviable fragments and repair of the extensor mechanism.

Fixation failure: Incidence is increased in osteoporotic bone or after failure to achieve compression at the fracture site.

Refracture (1% to 5%): This is secondary to decreased inherent strength at the fracture site.

Nonunion (2%): Most patients retain good function, although one may consider partial patellectomy for painful nonunion. Consider revision osteosynthesis in active, younger individuals.

Osteonecrosis (proximal fragment): Associated with greater degrees of initial fracture displacement. Treatment consists of observation only, with spontaneous revascularization occurring by 2 years.

Posttraumatic osteoarthritis: This is present in more than 50% of patients in long-term studies. Intractable patellofemoral pain may require Maquet tibial tubercle advancement.

Loss of knee motion: This is secondary to prolonged immobilization or postoperative scarring.

Painful retained hardware: This is due to the subcutaneous nature of the fixation. This may necessitate removal for adequate pain relief.

Loss of extensor strength and extensor lag: Most patients will experience a loss of knee extension of approximately 5 degrees, although this is rarely clinically significant.

Patellar instability is a complication.

PATELLA DISLOCATION

Epidemiology

Patellar dislocation is more common in women, owing to physiologic laxity, as well as 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, with a second line from the center of the patella to the tibial tubercle (Fig. 35.3). 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: Forced internal rotation of the femur on an externally rotated and planted tibia with knee in flexion is the usual cause. 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 may occur following knee trauma in adolescent male patients. The patella is avulsed from quadriceps tendon and is rotated around the horizontal axis, with the proximal pole lodged in the intercondylar notch.

Superior dislocation: This occurs in elderly individuals from forced hyperextension injuries to the knee with the patella locked on an anterior femoral osteophyte.

Clinical Evaluation

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

Lateral dislocations may also cause 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 patella 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. 35.4):

• 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 lateral radiograph with the 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. A ratio of 1.2 indicates patella alta, whereas 0.8 indicates patella baja (Fig. 35.5).

   

   

   

Magnetic resonance imaging (MRI) is indicated if a large osteochondral fragment is suspected.

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 as tolerated.

Surgical intervention for acute dislocations may be indicated depending on activity level and involves repair of the medial patellofemoral ligament. Surgery is also indicated in conjunction

with a displaced osteochondral fracture.

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

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

Operative

This is primarily used with recurrent dislocations.

No single procedure corrects all patellar 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 the 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 patella.

• Proximal patella 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 patellar dislocations that have not responded to nonoperative therapy and acute dislocations in young, athletic patients, especially with medial patellar avulsion fractures or radiographic lateral subluxation/tilt after closed reduction.

• Distal patella realignment: Reorientation of the patellar ligament and 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 and normal Q angles. It is designed to advance and medialize tibial tubercle, thus correcting patella alta and normalizing the Q angle.

  Complications

Redislocation: The risk is higher in patients younger than 20 years at the time of the first episode. Recurrent dislocation is an indication for surgical intervention.

Loss of knee motion: This may result from prolonged immobilization. Surgical intervention may lead to scarring with resultant arthrofibrosis. This emphasizes the need for aggressive physical therapy to increase quadriceps tone to maintain patella alignment and to maintain knee motion.

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

QUADRICEPS TENDON RUPTURE

This typically occurs in patients >40 years old and is due to an eccentric quadriceps contraction.

It usually ruptures within 2 cm proximal to the superior pole of the patella.

Rupture level is often associated with the patient’s age.

• Rupture occurs at the bone-tendon junction in most patients >40 years old.

• Rupture occurs at the midsubstance in most patients <40 years old.

Risk factors for quadriceps rupture:

• Tendinitis

• Anabolic steroid use

• Local steroid injection

• Diabetes mellitus

• Inflammatory arthropathy

• Chronic renal failure

History

• Sensation of a sudden “pop” while stressing the extensor mechanism

• Pain at the site of injury

• Inability/difficulty weight bearing

Physical examination

• Knee joint effusion

• Tenderness at the upper pole of patella

• Loss of active knee extension

  • With partial tears, intact active extension

• Palpable defect proximal to the superior pole of the patella

  • If defect present but patient able to extend the knee, then intact extensor retinaculum

  • If no active extension, then both tendon and retinaculum completely torn

Radiographic examination

• AP and lateral, of the knee

• Distal displacement of the patella

• Patellofemoral relationship

  • This is based on a lateral x-ray with the knee in 30 degrees of flexion.

  • The lower pole of the patella should be at the level of the line projected anteriorly from the intercondylar notch (Blumensaat line).

  • Patella alta possible with patellar tendon rupture and patella baja possible with quadriceps

    tendon rupture.

• MRI or ultrasound

  • Useful for unclear diagnosis

Treatment

• Nonoperative

  • This is reserved for incomplete tears in which active, full knee extension is preserved.

  • The leg is immobilized in extension for approximately 4 to 6 weeks.

  • Progressive physical therapy may be required to regain strength and motion.

Operative

• This is indicated for complete ruptures.

• Reapproximation of tendon to bone is done using nonabsorbable sutures passed through bone tunnels.

• Repair the tendon close to the articular surface to avoid patellar tilting.

• Midsubstance tears may undergo end-to-end repair after edges are freshened and slightly overlapped (Fig. 35.6).

• The patient may benefit from reinforcement from a distally based partial-thickness quadriceps

  tendon turned down across the repair site (Scuderi technique).

• Chronic tears may require a V–Y advancement of a retracted quadriceps tendon (Codivilla V–Y-plasty technique).

   

   

   

Postoperative management

• A knee immobilizer or cylinder cast is used for 5 to 6 weeks.

• Immediate weight bearing in extension as tolerated is allowed.

• Hinged knee bracing is not indicated in extensor mechanism injuries of the knee.

Complications

• Rerupture

• Persistent quadriceps atrophy/weakness

• Loss of knee motion

• Infection

   

  PATELLA TENDON RUPTURE

Less common than quadriceps tendon rupture

Most common in patients <40 years old

Associated with degenerative changes of the tendon (calcification may be seen radiographically)

Rupture common at the inferior pole of the patella

Risk factors

• Rheumatoid arthritis

• Systemic lupus erythematosus

• Diabetes

• Chronic renal failure

• Systemic corticosteroid therapy

• Local steroid injection

• Chronic patella tendinitis

Anatomy of patellar tendon

• Averages 4-mm thick but widens to 5 to 6 mm at the tibial tubercle

• Merges with the medial and lateral retinaculum

• Composition: 90% type I collagen

Blood supply

• Fat pad vessels supply the posterior aspect of the tendon via the inferior medial and lateral geniculate arteries.

• Retinacular vessels supply the anterior portion of the tendon via the inferior medial geniculate

  and recurrent tibial arteries.

• Proximal and distal insertion areas are relatively avascular and subsequently are a common site of rupture.

Biomechanics

• The greatest forces are at 60 degrees of knee flexion.

• Forces through the patellar tendon are 3.2 times body weight while climbing stairs.

History

• Often, a report of forceful quadriceps contraction against a flexed knee

• Possible audible “pop”

• Inability to bear weight or extend the knee against gravity

Physical examination

Palpable defect

Hemarthrosis

Painful passive knee flexion

Partial or complete loss of active extension

Quadriceps atrophy with chronic injury

Radiographic examination

• AP and lateral x-rays

• Patella alta visible on lateral view

  • Patella superior to Blumensaat line

  • Ultrasonography is an effective means to determine continuity of the tendon

  • However, operator and reader dependent

• MRI

  • Effective means to assess patella tendon, especially if other intra-articular or soft tissue injuries suspected

Classification

• No widely accepted means of classification

• Can be categorized by the location of tear

Proximal insertion most common

• Timing between injury and surgery

  • Most important factor for prognosis

  • Acute: within 2 weeks

Treatment

• Surgical treatment is required for restoration of the extensor mechanism.

• Repairs are categorized as early or delayed.

Nonoperative

• Nonoperative treatment is reserved for partial tears in which the patient is able to extend the knee fully.

• Treatment is immobilization in full knee extension for 3 to 6 weeks.

Early repair

• The overall outcome is better than for a delayed repair.

• Primary repair of the tendon is performed.

• Surgical approach is through a midline incision.

• Patellar tendon rupture and retinacular tears are exposed.

• Frayed edges and hematoma are debrided.

• Nonabsorbable sutures are used to repair the tendon to the patella.

• Sutures are passed through parallel, longitudinal bone tunnels and are tied proximally.

• Retinacular tears should be repaired.

• One can reinforce the repair with a cerclage wire, cable, or tape.

• One should assess the repair intraoperatively with knee flexion.

Postoperative management

• Knee immobilizer or casting is in extension.

• Immediate isometric quadriceps exercises are prescribed.

• Active flexion with passive extension may occur at 2 weeks; if allowed, start with 0 to 45 degrees and advance 30 degrees each week.

• Active extension occurs at 6 weeks.

• Initial full weight bearing is in extension for 6 weeks.

• All restrictions are lifted after full range of motion and 90% of the contralateral quadriceps strength are obtained, usually at 4 to 6 months.

Delayed repair

• This occurs >6 weeks from the initial injury.

• It often results in a poorer outcome.

• Quadriceps contraction and patellar migration are commonly encountered.

• Adhesions between the patella and femur may be present.

• Options include hamstring and fascia lata autograft augmentation of primary repair or Achilles tendon allograft.

• Postoperative management

  • It is more conservative than with early repair.

  • A bivalved cylinder cast is worn for 6 weeks.

  • Active range of motion is started at 6 weeks.

Complications

• Knee stiffness

• Persistent quadriceps weakness

• Rerupture

• Infection

• Patella baja