Purpose: The aim of this paper is to draw delegates’ attention to the published evidence that exists about these injuries and to challenge the concept that these laxities can be ignored, especially when associated with injuries to the ACL and PCL.

Background: The common impression that injuries to the PLC occur infrequently, require major force and are best treated by early repair, is true for Grade III injuries. Grade II injuries are more common, more difficult to detect clinically and may develop insidiously.

Even enhanced MR imaging cannot reliably assess grade II injuries to the PLC. This can result in patients with lack of trust in the knee, pain on kneeling, difficulty with twisting, slopes and rough ground, being reassured by their surgeon that their knee is stable, when both know that this is not the case.

Failure to detect a Grade II injury to the PLC in association with an ACL or PCL tear may result in ongoing subtle symptoms of instability, overloading and possible failure of a cruciate reconstruction.

Methods: A careful literature review was carried out with particular emphasis on the biomechanical studies which provide the scientific basis on which the common clinical tests are based.

Results:

Significant damage to the popliteus mechanism is required to produce a clinically detectable increase in ER.

Grade II lesions of the PLC may fail to reach that threshold.

Of the traditional tests, only the Dial test and electronic Goniometer test can be easily used towards extension. The former is not very sensitive, the latter is time consuming.

Increased posterior tibial translation (PTT) is a more reliable assessment of Grade II lesions and biomechanical studies support the prominent role of the posterolateral corner at 20° of knee flexion

Only two obscure clinical tests and the unpublished posterior Lachman test assess PTT below 30° of knee flexion

Conclusion: Until surgeons specifically test for increased PTT at 10–20° of knee flexion, Grade II lesions of the PLC will largely go unrecognised.

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.