An image analysis method to quantify the lateral pivot shift test

Purpose Although various kinematic measurements with advanced technology have been used for quantitative evaluation of the pivot shift test, there is no clinically available quantification method of the pivot shift test. The purpose was to describe a novel image analysis technique for quantitative assessment of the pivot shift test using universally available and affordable devices. Methods Five ACL deficient knees were tested during examination under anesthesia. Three skin markers were attached to bony landmarks on the lateral side of the knee joint, (1) Gerdy's tubercle, (2) fibular head, and (3) lateral epicondyle. A standard digital video camera captured motion of the lateral aspect of the knee during the pivot shift test. The image was processed into a 2-dimensional (2-D) coordinate system with Image J software (National Institute of Health, USA) to trace the three landmarks. The anteroposterior (AP) position of the femur was calculated on consecutive still images extracted from the video recording. AP translation over time was reported. Results The reduction phase of the pivot shift could be tracked consistently by a sudden anterior translation of the distal femur. The sudden anterior translation of the lateral epicondyle was on average 3.7 +/- 2.1 mm and occurred within 0.2 +/- 0.1 s from the start of this anterior translation till the end. Conclusion The sudden shift of the lateral compartment of the knee joint was successfully detected by this newly developed image analysis measurement method. This image analysis technique facilitates a simple and affordable method to evaluate the lateral pivot shift test.