An isolated Posterolateral corner injury with rotational instability and hypermobile lateral meniscus: a novel entity

Although complete tear of the knee posterolateral corner (PLC) commonly occurs in combination with other knee ligamentous injuries, the incidence of isolated PLC injury was reported only 28% and overlooked in many cases. Nevertheless, an isolated PLC injury does not only provoke posterolateral instability, but also may be associated to hypermobile lateral meniscus. This study aims at showing the characteristics of isolated PLC injuries and to alert potential overlooked cases by describing their arthroscopic findings and clinical characteristics.

Seventy-one patients with a clinically proven isolated PLC injury who underwent knee arthroscopy were included in this study. Pre-operative symptoms and clinical signs at examination were recorded: Pain at the posterolateral aspect, feelings of instability, catching, locking; and for clinical signs: McMurray test, varus stress test in extension and at 30° of flexion, posterolateral drawer test at 30° and 80°, dial test at 30° and 80° of flexion. In terms of arthroscopic findings, systematic meniscal stability was performed to evaluate the presence of hypermobile lateral meniscus, "lateral drive through test" was also recorded in all cases.

Positive Lateral Drive through test was found in 69 patients (95.8%). Hypermobile lateral meniscus was seen in all patients.

Hyper mobile lateral meniscus was concomitant with all isolated PLC injuries in our case series. As the typical arthroscopic characteristic, lateral drive through test positive were seen in 95.8%. In order to prevent overlooking this concomitant pathology, meticulous arthroscopic observation is crucial.

Level IV.