Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Engineering Science


Biomedical Engineering


Willing, Ryan

2nd Supervisor

Degen, Ryan



Optimal management of the hip capsule during arthroscopic surgery has not been established. The impact of incisions made to the capsule during minimally invasive procedures on joint biomechanics, and whether repair provides any benefit, continue to be debated. The effectiveness of capsular repair to restore native kinematics may be insufficient. Therefore, a better understanding of joint behavior during various capsule conditions is needed. A new robotic system was used to analyze the effect of progressive capsulotomy incision and repairs on the behavior of a normal hip within range of motion (ROM) limits with respect to the intact joint. Complete repairs increased the torque at end ROM across all tested joint positions compared to their unrepaired counterparts, though equivalent restraint to the intact joint was not always restored. Although repairs did not restore native joint kinematics, total displacement was increased with an interportal or T-capsulotomy, with and without repair.

Summary for Lay Audience

The hip joint is surrounded by a collection of ligaments that make up the capsule: the iliofemoral, ischiofemoral and pubofemoral ligaments. During minimally invasive hip surgery (arthroscopy), the capsule is invasively incised. Advances in the sophistication of surgical instrumentation and training have improved capabilities for arthroscopy, expanding the frequency with which they are performed. Despite this, optimal management of capsular tissues has not yet been established. Currently, the choice of capsular incision pattern may largely be dictated by the access and visibility required to treat a given pathology. However, the decision on whether to repair capsular incisions is primarily reliant on physician preference. This decision may affect translations of the femur (thigh bone) within the joint socket, and overall joint biomechanics. In recent literature, investigations of the role of the individual capsular ligaments and their contribution to joint laxity (flexibility) have suggested that they each provide stability in different directions. However, changes in joint behavior or the role of the capsule as a whole after arthroscopic incisions have not been sufficiently explored. In this study, a new joint motion simulator was used to observe the effect of successive capsulotomy incisions and subsequent repairs on hip joint kinematics. Compared to an intact (healthy) capsule, it was found that resistance to rotational laxity was reduced following capsulotomy, most significantly during external rotation (femur rotating from body’s midline towards the outside within the joint socket). Resistance was increased with repair but did not fully restore that of the intact joint. Varying the capsulotomy approach had less of an effect on translation of the femoral head than it did on capsule laxity. Though it was observed that the femur tended to favor a position towards the back of the joint socket compared to intact after undergoing a capsulotomy, the differences were very small. This suggests that repairing a capsulotomy is less important to ensure hip stability than previously thought.