Arthroscopic evaluation of knee lateral compartment widening after lateral ligamentous injury.

PURPOSE: To evaluate whether diagnostic arthroscopy of the lateral tibiofemoral compartment can determine the presence of a lateral ligamentous knee injury. METHODS: Nine cadaveric knee specimens were used with varus stresses of 12 Nm and the force at which no further lateral opening occurred. Arthroscopic measurements were taken of the lateral compartments with knees at 30°, 45° and 90°. Measurements were recorded in the intact knees and with sequential sectioning of LCL, popliteus, popliteofibular, ACL and PCL. Measurements and opening differences between each ligament state were recorded. RESULTS: No significant difference existed between the two forces compared (p < 0.05). There was a significant difference in opening distance measured at all knee angles with sequential sectioning (p < 0.001). Sequential opening difference between each ligament state was significantly different (p < 0.001) and also when compared across each knee angle (p < 0.001). At 30° for an isolated LCL injury, the average lateral opening was 10.1 mm. For a combined LCL and PLC (popliteus tendon and popliteofibular ligament) injury, the average lateral opening was 12.9 mm. For LCL-, PLC- and ACL-deficient knees, there was average lateral opening of 16.5 mm. CONCLUSIONS: LCL and combined lateral ligamentous injuries can be differentiated during arthroscopy with varus stress. This may be useful when deciding if there is a need for operative repair of any injured lateral ligamentous structures.