Abstract

Clinical studies indicate that range of motion until prosthetic impingement is important in understanding unexplained failures of hip resurfacings, yet the underlying biomechanical principles have received little attention. This study investigates the mathematical relationships between component design, position, patient bone geometry and range of motion in hip resurfaced prostheses. Variations in range of motion and impingement-free safe-zones for cup position were calculated using an established method of vector analysis that facilitated parametric analysis in a time efficient manner. The alpha angle, defined as the angle between the centreline of the femoral neck and the waist of the femoral head/neck junction, was used to represent the natural femoral neck. Range of motion and impingement-free safe-zones were inversely proportional to the alpha angle and cup inclusion angle. The size of the safe-zone was most sensitive to the alpha angle with a 6 degrees reduction, decreasing the range of cup positions without impingement by 80-100%. Lowering the upper limit of cup inclination from 55 degrees to 45 degrees reduced the range of cup positions that allow impingement-free motion by 47-94%. No common safe-zone was observed for the range of component sizes and positions investigated. This offers an explanation to why clinic studies have failed to associate outcome with standardised positioning criteria.

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Authors

Ellison P

Institution

Department of Surgical Sciences, University of Bergen, Norway. Peter.ellison@kir.uib.no

Source

Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine 226:3 2012 Mar pg 246-55

MeSH

Computer Simulation
Equipment Failure Analysis
Femur Head
Hip Joint
Hip Prosthesis
Humans
Models, Biological
Prosthesis Design
Range of Motion, Articular

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

22558839