In vivo analysis of the pivot shift phenomenon during computer navigated ACL reconstruction

ACL insufficiency can be documented clinically with the pivot shift maneuver, but the specific pathologic kinematics of the pivot shift is difficult to quantify. Navigation provides an opportunity to analyze in vivo the motions that comprise the pivot shift and the kinematic changes that are inherent after ACL reconstruction. We hypothesized that tibial rotation, anterior tibial translation (ATT), acceleration of posterior translation (APT) and the newly described angle of P, quantified during navigated pivot shift examination, correlate with clinical grading of the pivot shift phenomena. Navigation data from 12 patients who underwent navigated ACL surgery were retrospectively reviewed. A characteristic P-shaped track of motion is recorded by the navigation software during the pivot-shift examination. The "angle of P" was developed as a means characterizing this track of motion and was measured in all cases. The tibial rotation, maximum anterior tibial translation and acceleration of posterior translation during the pivot shift were also measured. The charts of these patients were reviewed to obtain information on the clinical grading of the pivot-shift before and after ACL reconstruction. Spearman correlation analysis was then used to identify significant correlations between clinical grade of the pivot shift and the angle of p measured with computer navigation. After reconstruction, the clinical grade of the pivot shift was zero in all patients. The tibial rotation, maximum ATT, APT and the angle of p also decreased. On analysis of 24 EUAs, 12 before reconstruction and 12 after, there was excellent and significant correlation between the clinical grade of pivot shift examination and the angle of P (R-2 = 0.97, p < 0.001). Only good correlation was noted between the clinical pivot shift and the rotation (R-2 = 0.77, p < 0.0001), maximum ATT (R-2 = 0.87, p < 0.0001) and APT (R-2 = 0.81,p < 0.0001). There was a stepwise increase of 6-7 mm of translation and 5-6 degrees of rotation for each increasing grade of pivot shift. There were also increases in the angle of P and APT for each increasing grade of pivot. A decrease in tibial rotation, maximum ATT, APT and angle of p is detected by computer navigation with ACL reconstruction, correlating with clinical grading. Clinical quantification of the distinct elements of the pivot shift may allow for more accurate evaluation of different ACL reconstruction constructs. There is also potential for these variables to be measured intraoperatively and guide ACL reconstruction when computer navigation is employed.