Coronal plane knee laxity measurement: Is computer-assisted navigation useful?

Introduction: The goal of this observational study is to measure the physiological laxity of a knee, supposedly normal in the coronal plane, at 0 and 90 degrees of flexion with a navigation system that can be used during total knee replacement. Hypothesis: The physiological laxity measured by this navigation system is different from the results already published using other measurement devices. Materials and methods: Twenty patients consecutively operated on for an isolated anterior cruciate ligament injury were selected. Medial and lateral laxities at 0 and 90 degrees of knee flexion were measured by the navigation system during cruciate replacement. Results: The mean medial laxity in extension was 3.6 +/- 1.2 degrees. The mean lateral laxity in extension was 4.1 +/- 1.9 degrees. The mean medial laxity at 90 degrees of flexion was 2.1 +/- 1.2 degrees. The mean lateral laxity at 90 degrees. of flexion was 3.7 +/- 1.2 degrees. The medial and lateral laxities in extension were not asymmetric. The medial and lateral laxities at 90 degrees of flexion were asymmetric. Medial laxities in extension and at 90 degrees of flexion were asymmetric. Lateral laxities in extension and at 90 degrees of flexion were not asymmetric. Discussion: The data collected in our study suggest, during total knee replacement, the following tolerable ligamentous balance: medial and lateral laxities in extension about 3 degrees, medial laxity at 90 degrees of flexion about 2 degrees, and lateral laxity at 90 degrees of flexion about 4 degrees. Level of evidence: Level IV. Prospective study. (C) 2010 Elsevier Masson SAS. All rights reserved.