In vivo laxity of stable versus anterior cruciate ligament-injured knees using a navigation system: a comparative study.

We compared antero-posterior translation and internal-external rotation of the tibia in stable knees without anterior cruciate ligament (ACL) injury with those of ACL injured knees using a navigation system and suggest an objective data. Forty-four patients treated for a meniscal tear without ACL injury were allocated to stable group, and 41 patients were allocated to ACL injury group. Antero-posterior displacement and rotation of knees were measured in 0, 30, 60 and 90 degrees of flexion using navigation. Mean anterior displacements were 3.6 +/- 2.0, 6.7 +/- 2.7, 6.0 +/- 2.4 and 4.7 +/- 1.8 mm at 0, 30, 60 and 90 degrees of flexion, respectively, in stable group, and 6.8 +/- 3.6, 14.7 +/- 3.5, 11.9 +/- 4.6 and 8.5 +/- 4.0 mm in ACL injury group. Mean total rotation values were 18.8 +/- 4.5 degrees, 31.4 +/- 4.2 degrees, 30.1 +/- 5.1 degrees and 29.2 +/- 5.9 degrees in stable group and 22.7 +/- 6.9 degrees , 37.6 +/- 5.8 degrees, 34.0 +/- 9.4 degrees and 31.8 +/- 8.8 degrees in ACL injury group. Quantitative values of antero-posterior translations and rotations of stable and ACL injured knees were obtained using a navigation system. The laxity data may be useful to establish the diagnosis of an ACL injury and evaluation of post-operative results.