The Collateral Ligaments and Posterolateral Corner: What Radiologists Should Know

Abstract

Ligamentous and tendinous structures of the posterolateral corner of the knee provide important static and dynamic stability to the knee joint and act in conjunction with anterior and posterior cruciate ligaments. Injuries of these structures are not uncommon. Failure to treat posterolateral corner injuries leads to posterolateral instability of the knee and subsequently poor outcome of cruciate ligament reconstructions. Currently, MRI is the diagnostic modality of choice in the evaluation of posterolateral corner injuries of the knee. We review normal MR imaging anatomy of the complex anatomical structures of the posterolateral corner of the knee, their biomechanical function, injuries, and current treatment options.

Demystifying the “Dark Side of the Knee”: An Update on Imaging of the Posterolateral Corner

“…[1][2][3][4] PLC structures are pivotal to providing static and dynamic stability to the knee and resisting varus angulation and external tibial rotation. 1,2,[4][5][6][7] Several structures have been described in the PLC, but key components include the lateral (fibular) collateral ligament (LCL), the popliteofibular ligament (PFL), and the popliteus tendon (PT)/ popliteus myotendinous complex (PMTC). 1,2,[4][5][6][7][8] LCL is the major stabilizer against varus stress.…”

“…1,2,[4][5][6][7] Several structures have been described in the PLC, but key components include the lateral (fibular) collateral ligament (LCL), the popliteofibular ligament (PFL), and the popliteus tendon (PT)/ popliteus myotendinous complex (PMTC). 1,2,[4][5][6][7][8] LCL is the major stabilizer against varus stress. The PFL and the PT stabilize against external rotation; if the LCL is torn and fails, they will act as secondary stabilizers against varus stress.…”

“…PLC injuries, previously believed to be rarer, 8,10 account for up to 16% of all knee ligamentous injuries, with only 28% occurring in isolation. 1,3,6,7,10,11 They are commonly associated with posterior cruciate ligament (PCL) and ACL injuries. In the acute setting, up to 62% (27-62%) of patients have concomitant tears of the PCL, and up to 10% have concomitant tears of the ACL.…”

“…In the acute setting, up to 62% (27-62%) of patients have concomitant tears of the PCL, and up to 10% have concomitant tears of the ACL. 1,6 Furthermore, in acute trauma, it is crucial to assess the popliteal neurovascular bundle and the common peroneal nerve, at risk during knee injuries leading to PLC damage. 7 Peroneal nerve lesions have been reported to occur in up to a third of patients with PLC damage.…”

“…10 As detailed later, menisci, medial ligamentous structures, and adjacent bone injuries are also often associated. 1,2,[4][5][6][7][8]12 Acute PLC injuries are commonly underdiagnosed clinically. 8 Recognizing these injuries on imaging, particularly on magnetic resonance imaging (MRI), is often crucial for proper diagnosis and effective treatment to prevent long-term complications, such as chronic posterolateral instability, cruciate ligament graft failure, and, ultimately, to prevent secondary osteoarthritis.…”