Medial and lateral laxity in knees with advanced medial osteoarthritis.

OBJECTIVE: An increase in coronal laxity is recognized as a risk factor for progression of knee osteoarthritis (OA). The purpose of this study was to evaluate coronal laxity, which was defined as the angular motion from the neutral, unloaded (baseline) position to the loaded position, in patients with advanced medial knee OA.

METHOD: Preoperative coronal laxity was assessed using radiographs in patients with medial knee OA undergoing total knee arthroplasty by applying a force of 150 N with an arthrometer. A consecutive series of 211 knees with OA and 40 normal control knees were examined. A knee with OA was defined as clinically "balanced" when the difference between medial and lateral laxity was 3° or less. Values are expressed as median [25th , 75th percentile].

RESULTS: The laxity was 4° [3, 5] from the baseline on the medial side and 3° [2, 4] on the lateral side. The distribution of medial and lateral laxity indicated that 90% (189/211) of patients fell within 3°. The equivalence test showed that the medial and lateral laxity was similar, with an equivalence margin of 3° (P < 0.001). In the control knees, the laxity was 3° [2, 4] from the baseline on the medial side and 2° [2, 4] on the lateral side. The differences between the knees with advanced OA and the controls were significant (P = 0.005, medial; P = 0.006, lateral).

CONCLUSION: This study showed that a clinically balanced knee was maintained even in patients with advanced medial knee OA.