2017 ISAKOS Biennial Congress ePoster #1019

 

Starting Position and Examiner-Induced Motion Decisive for Magnitude of Reduction Translation During the Pivot Shift

Jan-Hendrik Naendrup, BS, MD, Köln GERMANY
Jason P. Zlotnicki, MD, Pittsburgh, PA UNITED STATES
Toni Patterson, BS, Pittsburgh UNITED STATES
Humza Shaikh, MD, BA, Pittsburgh, PA UNITED STATES
Volker Musahl, MD, Prof., Pittsburgh, Pennsylvania UNITED STATES
Richard E Debski, PhD, Pittsburgh, PA UNITED STATES

Orthopaedic Robotics Lab, Pittsburgh, PA, UNITED STATES

FDA Status Cleared

Summary

This study emphasizes the complexity and multi-planarity of the pivot. The anterior translation of the lateral knee compartment during the pivot shift depends on the joint position and examiner-induced motions in different degrees of freedom..

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Abstract

Introduction

For the assessment of rotatory knee instability, the pivot shift constitutes one of the most important clinical tests and often determines if surgical treatment is recommended. However, due to its complexity – maintaining internal and valgus rotation during knee flexion until palpable reduction of the tibia - the pivot shift exam is dependent on the skills of the examiner, and thus subject to great variability. One way to quantify rotatory knee laxity is to measure the translation of the lateral tibial plateau generated during the exam. The magnitude of lateral compartment anterior translation and flexion angle at the beginning of tibial reduction has not been quantified using 6 degree of freedom (DOF) measurements. We hypothesized that anterior translation of the lateral compartment and flexion angle at the beginning of the tibial reduction moment are most affected by the varus/valgus and internal/external rotation axes.

Methods

Approval was obtained from University of Pittsburgh Institutional Review Board prior to the start of this study. 25 knee examiners, belonging to different levels of clinicians (5 each: medical students, residents, physical therapists, athletic trainers and sports medicine fellows), were enrolled in this study. Each participant performed a total of 20 pivot shift exams on one of two fresh-frozen, cadaveric, full lower extremity specimens (pelvis to toe) with an ACL deficiency and a lateral meniscectomy. An electromagnetic tracking system (Nest of Birds, Ascension Tech.) was used to record 6-DOF kinematics. The joint position at the beginning of the reduction translation and the induced joint motion were correlated with the magnitude of lateral compartment translation and the flexion angle at the beginning of the reduction translation using the Pearson correlation coefficient.

Results

While the position with respect to internal rotation at the point in time just before the beginning of reduction translation had a mild correlation (r = .444, p < .001) with a magnitude of lateral compartment translation, the examiner-induced amount of external rotation during the reduction translation showed a strong correlation (r = .847, p < .001). An ANOVA analysis revealed that 78.8% of the variability in the magnitude of lateral compartment translation was accounted for by the external rotation during the pivot shift reduction translation. In addition, the amount of valgus rotation (r = .564, p < .001) and proximal translation (r = .745, p < .001) just before the beginning of reduction translation significantly correlates with the flexion angle at the beginning of the reduction translation, where the pivot shift is palpable.

Discussion

Joint position and examiner-induced motion in several DOF has a great influence on the magnitude of anterior translation of the lateral knee compartment during the pivot shift and on the flexion angle at the beginning of the reduction translation. In particular, the induced motions in the internal/external rotation axis and varus/valgus rotation axis during the exam seem to have a bigger effect on the lateral compartment translation than the knee position prior to the reduction translation. The difficult learnability of the pivot shift test and its variability might be explicable by this insight, because the examiner has to induce several necessary motions in different degrees of freedom just at the right point in time. In the future, a more uniform pivot shift technique and better teaching methods need to be developed to decrease the variability of the pivot shift test.