[Analytical computational model for the determination of the influence of design and surgical factors on the range of motion of total hip replacements].

Impingement and dislocations rank among the frequent failure causes of hip endoprotheses. The further optimization of endoprotheses requires a comprehensive mathematical description of the kinematics with consideration of surgical and design parameters. For the investigation of dislocation behavior, spatial movements up to impingement with associated load scenarios should be generated. We present fundamentals for the determination of the range of motion of total hip replacements with consideration of multidirectional, superimposed movements. Therefore, the remaining angle, e.g., of abduction/adduction or internal/external rotation depending on flexion/extension can be calculated. Thereby, the substantial design parameters such as head and neck diameter, CCD angle and head coverage are considered. Moreover, the position of the acetabular cup in terms of inclination and anteversion angle as well as neck anteversion is considered. Using this approach, especially designed for superimposed movements, residual range of motion for given movements, e.g., abduction or internal rotation for given angles of flexion/extension can be calculated. Thus, the critical dislocation-initiating joint positions for primary or revision total hip arthroplasty can be determined for arbitrary superimposed movements; subsequently, the operating surgeon can evaluate the maximum range of motion for a given implant position. Additionally, the calculations are of help for further geometrical optimization of implants. The calculation algorithms can be used to create ROM maps (graphical illustration of the range of motion depending on implant position) which support the operating surgeon in placement of the implant components. Moreover, our results are utilized for experimental test setups to analyze impingement and subluxation.