Three-Dimensional Functional Impingement in Total Hip Arthroplasty: A Biomechanical Analysis

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Medical Imaging

Background:

• Component offset is a known factor influencing impingement after total hip arthroplasty (THA).
• Traditional radiographic evaluation of offset differs from assessment in functional, impingement-prone positions.
• The precise impact of acetabular and femoral component offsets on range of motion (ROM) requires further quantification.

Purpose of the Study:

• To quantify the effect of acetabular (cup/liner) and femoral (head/stem) offsets on ROM changes.
• To evaluate these effects in two functional positions prone to impingement: 90° flexion/internal rotation and 10° extension/external rotation.
• To determine which component offsets have the greatest impact on extra-prosthetic impingement.

Main Methods:

• Retrospective analysis of 16 THA patients with pre- and post-operative CT scans.
• Creation of 3D models from CT scans to mitigate metal artifact and accurately represent implant placement.
• Simulation of ±5 mm offsets for acetabular cup, liner, femoral stem, and femoral head to calculate maximum ROM to bone-bone impingement.

Main Results:

• Increased offset generally increased ROM to impingement; decreased offset reduced it.
• In 90° flexion/internal rotation, liner offset had the largest effect on ROM, followed by cup, head, and stem offsets.
• In 10° extension/external rotation, cup offset had the largest effect, followed by liner, head, and stem offsets.

Conclusions:

• Increasing component offset, regardless of the method, can reduce impingement.
• Changes in the center of rotation through acetabular cup or liner offsets exert the most significant influence on extra-prosthetic impingement.