Laxity of the Hip Capsule in Natural and Posteriorly Implanted Specimens

The hip capsule consists of ligament tissue that surrounds the hip joint, providing stability to ensure proper alignment, prevent dislocation, and facilitate proper joint function. The objective of this study was to characterize the torque-rotation response of the natural and posteriorly implanted hip capsule in healthy cadaveric specimens in multiple degrees-of-freedom (DOF) and under combined loading scenarios using the AMTI VIVO, a robotic joint simulator. The anterior portion of the hip capsule was stained with Methylene Blue and virtual extensometers were calculated by Digital Image Correlation (DIC) software for Finite Element Analysis (FEA) model validation. The range of motion (ROM) was evaluated at up to 3 Nm of torque applied in both internal/external rotation and abduction/adduction and varied throughout the range of flexion. The 4-dimensional (combined IE, AD/AB and Flex/Ext resistive torque) total resistive torque rotation space exhibits an \u27active zone\u27 whereby the resistive torque attempts to restore it back to the \u27neutral zone\u27 where the resistive torque is minimized. Large differences in capsular laxity between natural and implanted specimens were observed, particularly with an increased adduction torque resistance and a reduced internal rotation torque resistance in implanted specimens. Broad variability was observed across specimens highlighting the need for development of patient-specific computational models. These findings assist in characterization of capsular function, informing surgical strategies for hip arthroplasty and long term with a goal of improving patient outcomes