Patient-Specific Guides for Acetabular Prosthesis result in Better Hip ROMs: a 3D Regeneration Research

Abstract

Objective: Orientation of the acetabular prosthesis is extremely relevant for total hip arthroplasty (THA) stability, which is usually predicted by hip range of motion (ROM). The desired acetabular cup orientation includes inclination of 40° and anteversion of 15°. The classical method uses mechanical alignment as a guide, which could be unstable and unreliable. Two anatomical structures, transverse acetabular ligament (TAL) and ischiadic-pubis line (IPL) have been suggested as patient-specific guide for orientations. The purpose of this study was to provide a basis for selection of an optimal guide for orientation in THA practice, by comparing these methods in THA simulation model. Materials and Methods: CT angiography of lower extremities from 47 participants (94 hips) treated at Union Hospital were imported to Mimics to regenerate pelvis and bilateral femurs. The desired orientation was inclination of 40° and anteversion of 15°. Bilateral acetabular prosthesis for each participant was guided by TAL and IPL, respectively. Inclinations and anteversions of the TAL and IPL guided prosthesis were measured and compared with the goal. Hip joints were rotated outward, inward, backward and forward to evaluate four parameters of hip ROMs, i.e. abduction, adduction, extension and flexion. Hip joints were manipulated to perform circumduction and to draw boundary map. Result. The mean inclinations generated by TAL and IPL guides were 36.35° and 36.90° respectively, which was significantly smaller compared to goal inclination (p=2.2×10-16 and p=2.2×10-16 respectively). The mean anteversions generated TAL and IPL guides were 23.09° and 20.93°, which was significantly larger compared goal anteversion (p=2.2×10-16 and 2.2×10-16 respectively). The analysis of ROMs showed compared with hip ROMs by goal orientations, both TAL and IPL guides led to increased abduction (38.25°±8.30° and 38.47°±8.00° respectively, p<2×10-16 and p<2×10-16, respectively) and flexion (98.47°±9.71° and 100.50°±10.44°, p<2.2×10-16 and p<2.159×10-16, respectively); while decreased abduction (38.25°±8.30° and 38.47°±8.00°, p<2×10-16 and p<2×10-16, respectively) and extension (27.66°±10.18° and 25.93°±9.29°, p<2×10-16 and p<2×10-16, respectively). Conclusion. Compared with the goal orientations, the use of TAL and IPL guides led to greater motion in flexion and adduction, and lower motions in abduction and extension, thus suggesting these guides might be more suitable for post lateral THA.