A NOVEL INTRAPELVIC TOTAL HIP ARTHROPLASTY TECHNIQUE ACCURATELY POSITIONS COMPONENTS AND MAINTAINS TISSUE TENSION

INTRODUCTION Capsular soft tissue is believed to be crucial to avoid instability events preceding impingement, a common reason for failure. Assessment of capsular contribution to stability after THA is limited by the inherent need of capsule dissection. Our goal was to develop a capsule-sparring cadaveric THA implantation model for experimental testing using off-the-shelf implants. METHODS Four bilateral cadaveric specimens underwent THA: intrapelvic THR on one side and DAA on the other. Pre- and postoperative CT scans were used to determine the final position of DAA THA components. All hips later underwent testing on a six degree-of-freedom robotic manipulator. Anterior and posterior capsules were tested by rotating the femur to impingement at clinically relevant at-risk positions. RESULTS Intrapelvic implantation of the components achieved high accuracy with acetabular cup inclination and anteversion as well as femoral stem varus/valgus and combined anteversion. Anterior hip capsule torque was greater in intrapelvic specimen than in DAA specimen as to be expected considering the anterior capsule is inherently compromised during a DAA THA. Similar torque at impingement was observed in the posterior region of the capsule between both groups. DISCUSSION These results suggest that component positioning can controlled, and soft tissue structures and tension can be maintained during the intrapelvic procedure. This technique enables future investigation of ligament contributions without the inherent limitations of a compromised capsule seen in previous biomechanical hip studies.