Comparison of the PIVOT App and Pivot Shift Test for Assessing Knee Laxity after ACL Injury: Validity and Impact of Thigh Muscle Coactivity

The pivot shift is an important and widely used orthopaedic test for assessing anterior cruciate ligament (ACL)-deficient (ACL-D) knees. A continuous measure of the pivot shift test may allow for a more objective assessment of ACL laxity.

To assess the efficacy of a novel iPad application (PIVOT App) that uses video image analysis to evaluate ACL deficiency. The main objectives were to (1) assess the PIVOT App's ability to distinguish between categorically assigned pivot shift test grades; (2) assess the PIVOT App's ability to differentiate between normal and abnormal knees, and (3) quantify the effects of thigh muscle coactivity on pivot shift grades using electromyography (EMG) analysis.

Cohort Study (Diagnosis); Level of evidence, 3.

ACL-deficient (ACL-D) participants recruited via convenience sampling underwent the pivot shift test on their injured and contralateral knees. Some patients were evaluated in the clinic (n = 33), and others were evaluated under anesthesia (n = 20). Control participants (n = 7) with no history of knee injury also had the pivot shift test conducted on both knees while awake in the clinic. Tests were graded categorically by the examiner and simultaneously videotaped and analyzed by the PIVOT App, while EMG activity was recorded from the rectus femoris and semitendinosus muscles.

Pivot shift grades 1, 2, and 3 classified knees showed a consistent, incremental increase in tibial reduction. Grade 0 knees showed lower tibial reduction than grade 2 and 3 knees (P < .05). The PIVOT App's classification accuracy of normal versus abnormal knees was 73%. There were no effects of RF or ST EMG activity on the pivot shift test.

The PIVOT App is a promising, noninvasive measuring device that can provide an objective, continuous assessment of the pivot shift test, addressing multiple limitations of the current reference standard.