Mechanized pivot shift test achieves greater accuracy than manual pivot shift test

Abstract

The objective of this study was to design a navigated mechanized pivot shift test setup and evaluate its repeatability in the ACL-deficient knee. It was hypothesized that translations and rotations measured with the mechanized pivot shift would be more repeatable when compared to those obtained with a manual pivot shift. Twelve fresh frozen cadaveric hip-to-toe whole lower extremities were used for this study. A manual pivot shift test was performed in the intact knee and in the ACL-deficient knee and was repeated three times. A navigation system simultaneously recorded tibial translation and rotation. The mechanized pivot shift test consists of a modified continuous passive motion (CPM) machine and a custom-made foot holder to allow for the application of internal rotation moments at the knee. Valgus moments were achieved by a 45 degrees tilt of the CPM machine with respect to the supine position and a Velcro strap secured across the proximal tibia. The mechanized pivot shift was repeated three times. Repeated measures ANOVA was used to compare manual and mechanized pivot shift testing. An intra-class correlation coefficient (ICC) was used to determine variability within each knee at each testing condition. In the ACL-deficient knee, translation with manual pivot shift testing (11.7 +/- 2.6 mm) was significantly higher than with mechanized pivot shift testing (7.4 +/- 2.5 mm; p < 0.05). Rotation with the manual pivot shift testing (18.6 +/- 5.4 degrees) was also significantly higher than with mechanized pivot shift testing (11.0 +/- 2.3 degrees; p < 0.05). The intra-class ICC for translations was 0.76 for manual pivot shift and 0.92 for the mechanized pivot shift test. The intra-class ICC for rotations was 0.89 for manual pivot shift and 0.82 for the mechanized pivot shift test. This study introduced a modified CPM for mechanized pivot shift testing. Although recorded translations and rotations with the mechanized pivot shift test were lower than with manual testing, the clinical advantage of mechanized pivot shift testing is a more repeatable measurement of ATT when compared to manual pivot shift testing. This setup may increase consistency of clinical grading of the pivot shift test.