Does anterior laxity of the uninjured knee influence clinical outcomes of ACL reconstruction?

BACKGROUND: The purpose of this study was to evaluate the association between the postoperative outcomes of anterior cruciate ligament (ACL) reconstruction and the anterior laxity of the uninjured knee.

METHODS: We retrospectively reviewed 163 patients who had undergone unilateral ACL reconstruction from January 2002 to August 2009. Patients were divided into three groups according to the anterior laxity of the contralateral, normal knee in 30° of knee flexion as measured with a KT2000 arthrometer exerting a force of 134 N: <5 mm for Group 1, 5 to 7.5 mm for Group 2, and >7.5 mm for Group 3. Anterior laxity of the uninjured knee was assessed preoperatively, and anterior laxity of the reconstructed knee was assessed at twenty-four months postoperatively. Anterior stability of the knee was also assessed with use of the Lachman and pivot-shift tests. Functional outcomes were assessed with the Lysholm score and the International Knee Documentation Committee (IKDC) score.

RESULTS: The three groups differed significantly with respect to the postoperative side-to-side difference in anterior laxity (p = 0.015), Lysholm score (p < 0.001), and IKDC subjective score (p < 0.001). The mean side-to-side difference in anterior laxity of the reconstructed knee was 2.1 ± 1.3 mm in Group 1, 2.2 ± 1.3 mm in Group 2, and 2.9 ± 1.4 mm in Group 3. The postoperative Lysholm score was 91.8 ± 4.5 in Group 1, 90.3 ± 5.5 in Group 2, and 85.4 ± 6.6 in Group 3. The postoperative IKDC subjective score was 89.3 ± 6.4 in Group 1, 87.9 ± 6.0 in Group 2, and 82.6 ± 8.2 in Group 3. Post hoc testing showed that Group 3 had significantly greater anterior laxity (p ≤ 0.039) and lower functional scores (p ≤ 0.001) compared with Groups 1 and 2.

CONCLUSIONS: Greater anterior laxity of the uninjured knee was associated with poorer stability and functional outcomes after ACL reconstruction. Excessive anterior laxity of the uninjured knee thus appears to represent a risk factor for inferior outcomes.