A mechanized and standardized pivot shifter: technical description and first evaluation

The pivot shift test (PST) is a complex, multiplanar maneuver used to assess rotatory instability of the knee. The grading is subjective due to the broad range of examination techniques and lack of tibiofemoral motion quantification. The goal of this study was to develop and evaluate a mechanized device for quantitative assessment of the PST. We constructed a mechanized pivot shifter (MPS). In five cadaveric hip-to-toes specimens, the anterior cruciate ligament was resected. We used a surgical navigation system for acquisition of the tibiofemoral motion path during the PST. Two sets of measurements were obtained for the MPS and for two examiners performing the manual technique. Mean lateral compartment translation magnitudes for each MPS measurement were 13.5 mm (sigma = 6.7) and 13.6 mm (sigma = 6.7). For examiner 1, 14.9 mm (sigma = 6.5) and 15.7 mm (sigma = 6.3). For examiner 2, 16.9 mm (sigma = 6.3) and 16.1 mm (sigma = 5.2). Differences were not significant (n.s.). The MPS had narrower limits of agreement than both examiner 1 and examiner 2. The MPS demonstrated no significant differences in the tibiofemoral translation magnitudes compared to the manual technique. It resulted in better test-retest reliability and more consistent measurements of tibiofemoral translation when compared to manual PST. The high repeatability factor conferred by the MPS is a clinical advantage.