Purpose: Rotational instability in ACL insufficient knee addresses the symptom or the abnormal motion which can be reproduced and subjectively evaluated in the clinical exam. Clinically available quantitative measurement for this instability has not been established due to mixed testing maneuvers and complex kinematics. The purpose was to measure knee kinematics during three manually performed rotational tests and to determine the optimal method to detect the abnormality in ACL deficient knees.
Method: Thirteen unilateral ACL deficient patients were tested by internal and external pure rotational stress tests and pivot shift test under anesthesia before scheduled ACL reconstructions. Rotation and coupled motion, i.e., tibial anteroposterior translation, were measured using an electromagnetic measurement system. Additionally, the acceleration of the tibial posterior translation during pivot shift test was calculated. The differences of these parameters between ACL intact and deficient knees were tested.
Results: Knee rotation is not different between ACL intact and deficient during both pure rotational stress test and pivot shift test. The coupled anterior tibial translation during pivot shift test was significantly different between ACL intact, 13.5 ± 4.1 mm, and deficient knees, 23.1 ± 4.4 mm, (P < 0.01) as well as the acceleration of the tibial posterior translation (1.1 ± 0.4 m/sec(2) in intact knees, 3.2 ± 1.5 m/sec(2) in deficient knees; P < 0.01). The coupled motion during pure rotational stress tests was similar regardless of ACL condition.
Conclusion: The rotational instability of the ACL deficiency was reproduced only by the pivot shift test and detected only by measuring the tibial anteroposterior translation and acceleration of the tibial posterior reduction. Level of evidence Diagnostic study, Level III.