Posteromedial corner injury of the knee is a readily identifiable but frequently underappreciated injury on imaging. Importantly, it can result in increased stress on the cruciate ligaments and can result in anteromedial rotatory instability (AMRI) of the knee.
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 drawer test with the tibia held in external rotation is used to evaluate for anteromedial rotatory instability.
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.
May show non-specific findings, such as a lipohemarthrosis. A fracture of the medial tibial corner may be seen. Weight-bearing views can reveal a valgus deformity.
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 edema may be seen with rupture
- maybe an avulsion fracture at the posteromedial tibial plateau at its insertion
oblique popliteal ligament
- best seen on the 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.
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