Posteromedial corner injury of the knee

Posteromedial corner injury of the knee is a readily identifiable but frequently underappreciated on imaging. Importantly, it can result in increased stress on the cruciate ligaments and can result in anteromedial rotatory instability of (AMRI) of the knee.

Clinical presentation

These injuries are frequently seen in athletes and are usually sustained with the knee in valgus. Physical examination may reveal tenderness along the medial joint line. The anterior draw test with the tibia held in external rotation is used to evaluate for anteromedial rotatory instability. 

Pathology

The structures that comprise the posteromedial corner (PMC) are located between posterior margin of the tibial collateral ligament and medial border of the posterior cruciate ligament:

• posterior oblique ligament:
  • injury in virtually all cases with associated instability
  • made of three parts
    • superficial arm
    • tibial arm
    • capsular arm
• oblique popliteal ligament
• meniscotibial ligament
• semimembranosus tendon
• medial meniscus: posterior third

Up to 88% of injuries can be associated with a cruciate ligament injury, overwhelmingly the ACL ¹.

Radiographic features

Plain radiographs

May show non-specific findings, such as a lipohaemarthrosis. A fracture of the medial tibial corner may be seen. Weight-bearing views can reveal a valgus deformity.

MRI

MRI is the investigation of choice, as it can readily demonstrate all components of the PMC. 

• posterior oblique ligament
  • can be thickened with adjacent fluid if sprained
  • marrow oedema may be seen with rupture
• meniscocapsular
  • easiest seen on coronal plane
  • reverse Segond fracture if meniscotibial ligament insertion is pulled off
• semimembranosus tendon
  • maybe an avulsion fracture at the posteromedial tibial plateau at its insertion
• oblique popliteal ligament
  • best seen on axial plane
• medial meniscus

Treatment and prognosis

Whether or not surgical intervention is offered depends on the presence of knee instability and concurrent cruciate or other ligamentous injuries. Surgical approaches vary with either surgical repair or reconstruction.