A Secondary Injury of the Anterolateral Structure Plays a Minor Role in Anterior and Anterolateral Instability of ACL-deficient Knees in the Case of Functional Iliotibial Band.

PURPOSE To analyze the contribution of a secondary anterolateral structure (ALS) deficiency to knee instability based on anterior cruciate ligament (ACL) deficiency, in the condition of a functional iliotibial band (ITB). METHODS Nine freshly-frozen cadaveric knees were sectioned sequentially to create ACL-deficiency and ACL-ALS deficiency, using intact knees before sectioning as controls. When ITB was tensioned with 30N, four separate aspects of knee instability were tested as follows: anterior translation in 90N anterior load, isolated internal rotation in 5N·m internal rotational torque from 0° to 90° in 15° increments, and anterolateral translation and internal rotation during a simulated pivot-shift test at 0°, 15°, 30° and 45°. The contribution of ACL deficiency alone and an additional ALS deficiency to knee instability were evaluated. RESULTS The addition of an ALS lesion produced no significant exacerbation of either anterior translational or pivot shift instability in ACL-deficient knees. Additional ALS deficiency in an ACL deficient knee resulted in a significant increase in isolated internal rotation from 45° to 90°(P=.001 at 45° and P＜.001 in other cases). After sequentially sectioning, the contribution to instability of additional ALS deficiency to the entire instability in ACL-ALS deficient knees were significantly smaller than that of ACL deficiency alone during anterior load and pivot-shift test (P＜.001 in all cases), but significantly contributed more to isolated internal rotational instability at 60° (P=.011) and 90° (P=.015) CONCLUSIONS: When ITB was tensioned, ALS played a minor role in controlling both anterior or pivot shift stability in ACL-deficient knees while did the major role in restraining isolated internal rotation from 45° to 90°.