Posterolateral corner injury of the knee can occur in isolation or with other internal derangements of the knee, particularly cruciate ligament injuries. The importance of injuries to the posterolateral ligamentous complex lies in the possible long-term joint instability and cruciate graft failure if these are not identified and treated.
Posterolateral corner (PLC) injury is thought to account for approximately 16% of acute injuries of the knee 4,5. It is often seen in sports-related injuries and mostly related to direct anteromedial tibial impact trauma, but is also caused by hyperextension and external rotation injuries, non-contact varus stress injuries, and anterior or posterior dislocations of the knee. An unstable posterolateral corner injury is present in up to 60% of patients with posterior cruciate ligament rupture.
Trauma to the anteromedial tibia while in extension is a frequent cause of this type of injury by producing varus stress. Patients often present with symptoms due to associated cruciate ligament injury or peroneal nerve damage. Diagnosis is made by varus stress, dial, or reverse pivot shift tests.
There is no consensus between authors and textbooks in what constitutes the posterolateral ligamentous complex. The three main structures based on biomechanical studies are:
- lateral (fibular) collateral ligament
- popliteus muscle and popliteofibular ligament complex
- popliteofibular ligament
Other structures stated to be in the posterolateral ligamentous complex include the short and long heads tendons of the biceps femoris muscle, arcuate ligament, meniscopopliteal fascicles, and fabellofibular ligament.
Presence of the following findings should raise the suspicion for underlying posterolateral corner injuries which usually occur with concomitant cruciate, meniscal, and posteromedial corner injuries:
- Segond fracture
- arcuate sign
- avulsion fracture of iliotibial band
- fractures of anteromedial tibia plateau and anteromedial femoral condyle
In hyperextension and direct anteromedial blow mechanism of injuries to the posterolateral ligamentous complex, bone contusion may be expected at the anteromedial femoral condyle and anteromedial tibial plateau. Components of the posterolateral corner that with some variability may be identified on MRI are:
- popliteofibular ligament: usually injured from fibular styloid attachment- mermaid sign
- fibular collateral ligament
- popliteus tendon: most commonly injured at its musculotendinous junction
- biceps femoris tendon
- fabellofibular ligament
- arcuate ligament
Treatment and prognosis
Type and timing of treatment of posterolateral corner injury depend on concomitant injuries, in particular, cruciate and meniscal injuries, the grade of injury and individual level of physical activity 6:
- grade 1 and 2: usually respond well to conservative non-surgical treatments, which normally involves a hinged knee brace and physiotherapy
- when in isolation or with cruciate tears, and in those symptomatic patients for which conservative management has failed, surgical treatment is advocated
- where ACL and PCL ruptures are present it is recommended all three injuries are treated in conjunction to achieve the best outcome
In cases of early surgical management (within 2 weeks) repair can be considered, however, this is less favored as there is a high risk of failure and the need for a formal reconstruction. Anatomical reconstruction of the PLC using hamstring autograft is common in Australia, the allograft is considered when repairing multiple ligament injuries. Repair and isometric-focused treatments have shown a less favourable outcome.
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