Robotically Simulated Pivot Shift That Represents the Clinical Exam

A thorough understanding of anterior cruciate ligament (ACL) function and the effects of surgical interventions on knee biomechanics requires robust technologies and simulation paradigms that align with clinical insight. In vitro orthopedic biomechanical testing for the elucidation of ACL integrity doesn't have an established testing paradigm to simulate the clinical pivot shift exam on cadaveric specimens. The study aim was to develop a robotically simulated pivot shift that represents the clinical exam. An orthopedic surgeon performed a pivot shift on an instrumented ACL-deficient cadaver leg to capture 6 degree-of-freedom motion/loads. The same knee was mounted to the robot and the sensitivity of the motion/loading profiles quantified. Three loading profile candidates that generated positive pivot shifts on the instrumented knee were selected and applied to 7 ACL-intact/deficient specimens and resulted in the identification of a profile that was able to induce a positive pivot shift in all ACL-deficient specimens ( p < 0.001). The simulated shifts began at 22 ± 8° and ended at 33 ± 6° of flexion with the average magnitude of the shifts being 12.8 ± 3.2 mm in anterior tibial translation and 17.6 ± 4.3° in external tibial rotation. The establishment and replication of a robotically simulated clinical pivot shift across multiple specimens show the robustness of the loading profile to accommodate anatomical and experimental variability. Further evaluation and refinement should be undertaken to create a useful tool in evaluating ACL function and reconstruction techniques. Statement of clinical significance: Creation and successful demonstration of the simulated clinical pivot shift validates a profile for robotic musculoskeletal simulators to analyze ACL related clinical questions. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2601-2608, 2019.