Working Diagnosis:
Right posterolateral corner jury with tears of the LCL and popliteus.

Treatment:
Right knee arthroscopy and open repair of ligamentous tears was performed approximately one week following the injury. Patient was then placed in a Total Range of Motion brace locked at 30 deg. Physical therapy was performed to maintain range of motion and to increase quadricep strengthening.

Outcome:
Approximately three weeks post-operatively the patient was instructed to weight bear as tolerated with the brace locked in full extension. Physical therapy and range of motion exercises were continued for strength and range of motion augmentation. Patient will be reevaluated two months post-operatively. Full return to play is anticipated at six months post-op.

Author's Comments:
Posterolateral corner (PLC) injuries are uncommon and even less common as an isolated injury, making up < 2% of all ligamentous knee injuries (Ranawat et al.,2008). Other studies note that the PCL and/or ACL are involved in approximately 70% of cases. Repair of the PLC injury with a robust reconstruction of PLC with concurrent repair of cruciate ligament injuries is vital with a fail rate of 9% and a 38% failure rate with staged cruciate ligament reconstruction (Geeslin et al.,2016). Grade 1 and 2 PLC injuries lack chronic instability and are therefore managed non-operatively, whereas Grade 3 injuries display persistent instability and requires operative management (Kennedy et al.,2019).

Editor's Comments:
Posterolateral corner (PLC) injuries are traumatic knee injuries that are associated with lateral knee instability and usually present with a concomitant cruciate ligament injury (PCL > ACL). Diagnosis can be suspected with a knee effusion and a positive dial test, but MRI studies are required for confirmation. Treatment is generally operative reconstruction of the PLC complex and the associated ligamentous injuries when present. Missed PLC injury diagnosis is a common cause for ACL reconstruction failure. Common associated injuries are common peroneal nerve and vascular injuries. Mechanism of injury for PLC are blow to anteromedial knee, varus blow to flexed knee, contact and noncontact hyperextension injuries, external rotation twisting injury, and/or knee dislocation.

References:
Posterior Corner Injury of the Knee: Evaluation and Management. Ranawat et al. J Am Acad Orthop Surg. 2008 Sep;16(9):506-18.

A Systematic Review of the Outcomes of Posterolateral Corner Knee Injuries, Part 1. Geeslin et al. Am J Sports Med. 2016 May;44(5):1336-42.

Fibular Collateral Ligament/ Posterolateral Corner Injury: When to Repair, Reconstruct, or Both. Kennedy et al. Clin Sports Med. 2019 Apr;38(2):261-274.

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