Influence of Design Parameters on Cup-Stem Orientations for Impingement Free RoM in Hip Implants

Abstract

<p>This study was conducted to study the influence of design parameters namely the head/neck ratio (R), neck-shaft angle (NSA), oscillation angle (OsA) and stem offset (5&#61553;) on cup-stem orientations namely the cup inclination (CIL cup anteversion (CA) and stem antetorsion (SA). R is often linked to influence NSA, OsA and impingement. An effort has been made to analyze range of motion (RoM) with NSA greater than 135 [degrees] and R lower than 2.3 that may produce impingement. This study attempted to answer following assumptions whether a) implants with higher H-N ratio can achieve higher oscillations and higher stem anterosion, b) stems with higher neck shaft angle can achieve higher cup anteversion with lower stem offset and stem antetorsion, c) stem with higher offsets can achieve lower cup anteversion with higher stem antetorsion, and d) lower cup anteversion can be achieved when stem antetorsion is higher. A theoretical and a simulated method were implemented to anaylze RoM until impingement between cup and neck occurred. Cup abduction and anterior opening were held constant for this study. Multivariate prediction models were developed to predict optimal cupstem orientations for the chosen design parameters of 12 hip implants. Optimal design parameters to achieve an impingement free RoM were as follows: NSA = 139.25°, R= 3.08, OsA= 199.83°, 5&#61553;&#61472;= 34.45 mm, CAPredicted = 16.26°, CI Predicted = 42.7r and SA Predicted = 30.3r, respectively. Multivariate models may be further developed for use in surgery planning to achieve optimal component placement. Finite element analysis was perform to validate impingement sites obtained through mathematical model.</p><p>This presentation occurred at the Wright State University Campus-Wide Celebration of Research, Scholarship and Creative Activities on April 8, 2011</p>