ISOLATED LAXITY OF THE POSTERO-LATERAL CORNER (PLC) OF THE KNEE

Abstract

Aim To describe the presentation, clinical signs and arthroscopic features of isolated laxity of the PLC

Methods The records of 50 patients who had a reconstruction for isolated laxity of the PLC were reviewed. Any patient with injuries to the anterior cruciate, posterior crucicate or lateral collateral ligaments were excluded.

Results History: • 21 patients could not remember an injury. • 12 patients had twisting/squatting injuries. • 17 patients had sporting injuries

Presenting Symptoms The commonest presenting symptoms were associated with overloading the anterior structures of the knee. These presenting symptoms tended to overshadow symptoms of instability which were quite subtle and usually only emerged on direct questioning or after painful lesions had been dealt with arthroscopically.

Clinical Signs All patients had increased posterior translation of the tibia compared to the other side when the knee was examined in 20° of flexion using a modified Lachman test.

Arthroscopic Features The lateral compartment opened easily in 38 (76%) and the posterior half of the lateral meniscus subluxed as far as the equator of the lateral femoral condyle in 32 (64%).

Discussion When the knee is held in 20° of flexion, posterior translation of the tibia is prevented by the structures in the posterolateral corner. A modification of the Lachman test is described which easily demonstrates laxity of the PLC to both clinician and patient.

Conclusion Laxity of the PLC is a common clinical finding, easily detected by a modification of the Lachman test. Patients may present without a history of injury, complaining of pain at the front of the knee and with subtle symptoms of instability. Laxity of the PLC should be considered in patients with recurrent or persistent symptoms following arthroscopy.