Popliteus injury

Popliteus injuries or injuries of the popliteus musculotendinous complex occur within the scope of posterolateral corner injuries of the knee and include avulsions, complete and partial tendinous and myotendinous tears as well as muscle injuries.

Epidemiology

Popliteus injuries can be found in up to two-thirds of patients undergoing surgery for posterolateral instability ^1,2 with myotendinous strains being the most common subtype ³.

Associations

Popliteus injuries can occur in isolation but are most frequently associated with other ligament injuries of the knee including ^1-3,6:

• lateral collateral ligament injury
• posterior cruciate ligament injury
• anterior cruciate ligament injury
• meniscal tears
• lateral gastrocnemius injury

Diagnosis

The diagnosis is based on typical clinical features and tests indicating posterolateral instability supplemented by relevant imaging findings. Popliteal tendon avulsions and/or tendon ruptures can be confirmed on arthroscopy.

Clinical presentation

A common presentation of a popliteus injury is posterolateral instability, which can be evaluated clinically with several tests including dial test, external rotation recurvatum test, reverse pivot shift test, varus stress test and posterolateral drawer test ^4,5.

Pathology

Etiology

Injury mechanisms include the following ^2,3:

• varus force on a hyperextended knee (direct impact on the anteromedial proximal tibia)
• forced external rotation of the tibia in mild knee flexion or extension
• direct muscle trauma (contusion)

Subtypes

Popliteus injuries can be subdivided into the following ³:

• popliteus tendon avulsion
• popliteus tendon tears (partial/complete)
• myotendinous junction injury (different degrees)
• muscle contusion

Radiographic features

Plain radiograph

Standard anteroposterior (AP), lateral and skyline views might show a bony avulsion in a minority of cases and most cases will not show anything ⁴. However, they should be obtained in the setting of an acute injury to exclude fractures. 

Varus stress radiographs might show increased gapping in the lateral compartment in case of an associated lateral collateral ligament injury ^4,5.

MRI

MRI can detect, determine the extent, location and type of the injury. Besides, it can aid in grading the injury and will reveal associated injuries including lateral collateral ligament injury, anterior or posterior cruciate ligament injury and meniscal tears.

Tendon and myotendinous injuries are characterized by fluid signal intensity tracking and surrounding the tendon and muscle fibers and/or fiber discontinuity. A bony avulsion will additionally show a bony fragment.

Radiology report

The radiological include a description of the following ³:

• type and degree of the injury (avulsed bone fragment)
• extent and location of the injury (intraarticular/extraarticular)
• associated injuries:
  • posterolateral ligamentous complex
  • cruciate ligament injuries
  • meniscal tears

Treatment and prognosis

Treatment will depend on associated injuries especially posterior and anterior cruciate ligament injuries as well as the extent of injury of the other posterolateral corner structures and includes conservative measures and surgical options.

Surgical treatment is based on the nature, extent and location of the injury and includes direct repair if possible with arthroscopic, open or combined approaches or reconstruction (e.g. with semitendinosus graft) ^1,3.

Differential diagnosis

Conditions that might mimic the imaging appearance of a popliteus injury include ³:

• tibial nerve injury
• cyamella
• lateral collateral ligament injury

See also

• popliteus tendinopathy