Image-matching technique can detect rotational and AP instabilities in chronic ACL-deficient knees.

Purpose: The purpose of this study was to quantify rotational and antero-posterior instabilities using biplanar image-matching technique. Methods: Biplanar radiographs of both chronic ACL-deficient knees and contralateral uninjured knees were taken in the pivot shift test and in the 'giving way position' and lateral radiographs in stress arthrometer at 30° and 90°. Three-dimensional knee models were constructed using computed tomography. Using biplanar image-matching technique, the external rotational angle and the translation of the center of the both condyles of the femur were analyzed. Results: The external rotation angle of geometric center axis in the pivot shift test was 16.9° ± 5.6° and 10.9° ± 7.3° ( P = 0.004), and in the 'giving way position' was 16.1° ± 5.7° and 10.7° ± 6.6° ( P = 0.004) in ACL-deficient knees and intact knees, respectively. In the pivot shift test, the medial and the lateral femoral condylar centers of ACL-deficient knees were translated 1.2 ± 5.1 mm anteriorly and 3.9 ± 3.4 mm posteriorly, respectively, and in the 'giving way position,' 2.0 ± 3.7 mm anteriorly and 2.9 ± 2.6 mm posteriorly, respectively. In stress arthrometer at 30°, the medial and the lateral femoral condylar center translated 7.1 ± 6.0 and 6.6 ± 4.8 mm posteriorly (n.s.), respectively, and at 90° translated 2.7 ± 3.4 and 2.6 ± 3.5 mm posteriorly (n.s.), respectively. Conclusion: Rotational instability was evaluable in the pivot shift test and in the 'giving way position.' Translation of both condylar centers was similar in stress arthrometry. The image-matching technique is able to quantify dynamic rotational and antero-posterior instabilities with static parameters in ACL-deficient knees. Level of evidence: III. [ABSTRACT FROM AUTHOR]