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

Abstract

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 (R2 = 0.97, p < 0.001). Only good correlation was noted between the clinical pivot shift and the rotation (R2 = 0.77, p < 0.0001), maximum ATT (R2 = 0.87, p < 0.0001) and APT (R2 = 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 ofp 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.

Basic biomechanic principles of knee instability

“…Testing both ACL-deficient and healthy contralateral knees, a significant difference in the anterior translation of the lateral compartment at 0°and 20°of flexion (p = .005 and p = .002, respectively) was demonstrated [39]. In addition, the lateral plateau of ACLdeficient knees was found to translate 7.7 mm posteriorly between 20°and 40°of flexion, an important finding as this is where the pivot shift phenomenon has been documented to occur [45,46]. This study suggests that measurement of tibiofemoral kinematic during flexion using the KneeM device was useful for quantifying rotatory laxity in ACLdeficient and may provide clinicians with enhanced understanding of knee stability on review of knee imaging.…”

Posterior Cruciate Ligament and Posterolateral Corner Deficiency Results in a Reverse Pivot Shift

“…Motion of these points was analyzed throughout a given motion path regarding a tracked central point in the notch of the femur. Customized software allowed us to compare the motion path during the pivot shift with the reference motion path of extension-flexion [9,22]. We reported the maximum tibial translations and rotation during the RPS maneuver as the difference between reference motion path and RPS motion path in the medial and lateral compartments [5].…”

Software for compartmental translation analysis and virtual three-dimensional visualization of the pivot shift phenomenon

“…Three mechanized pivot shift tests were performed on each knee in both ACL-intact and ACLdeficient conditions, totaling 60 measurements [15]. The mechanized pivot shifting device reproducibly induces a positive pivot shift test in ACLdeficient knees and has been shown to provide better repeatability than a manual examination [14] ( Figure 1).…”

“…The experimental set-up for mechanized pivot shift testing. The lower limb is mounted in full extension on the mechanized pivot shifter, abducted by at least 15 at the hip joint. The foot is affixed to the base plate and is externally rotated.…”