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The occurrence of pseudotumours (soft tissue masses relating to the hip joint) following metal-on-metal hip resurfacing arthroplasty has been associated with higher than normal bearing wear and high serum metal ion levels although both these findings do not necessarily coexist. The purpose of this study was to examine patient activity patterns and their influence on acetabular component edge loading in a group of subjects with known serum metal ion levels. Fifteen subjects with metal-on-metal hip resurfacing arthroplasty (eight males and seven females) were recruited for motion analysis followed by computed tomography scans. They were divided into three groups based on their serum metal ion levels and the orientation of their acetabular component: well-positioned acetabular component with low metal ions, mal-positioned acetabular component with low metal ions and mal-positioned acetabular component with high ions. A combination of motion analysis, subject-specific modelling (AnyBody Modeling System, Aalborg, Denmark) and computed tomography measurements was used to calculate dynamically the contact patch-to-rim distance for each subject during gait and sit-to-stand. The contact-pitch-to-rim distance for the high ion group was significantly lower (p<0.001) than for the two low ion groups (well-positioned and mal-positioned) during the stance phase of gait (0%-60%) and loading phase of sit-to-stand (20%-80%). The results of this study, in particular, the significant difference between the two mal-positioned groups, suggest that wear of metal-on-metal hip resurfacing arthroplasty is not only affected by acetabular cup orientation but also influenced by individual patient activity patterns.

Original publication

DOI

10.1177/0954411913483639

Type

Journal article

Journal

Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine

Publication Date

07/2013

Volume

227

Pages

799 - 810

Addresses

Nuffield Orthopaedic Centre, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK. stephen.mellon@ndorms.ox.ac.uk

Keywords

Humans, Tomography, X-Ray Computed, Gait, Arthroplasty, Replacement, Hip, Hip Prosthesis, Movement, Models, Biological, Adult, Middle Aged, Female, Male, Biomechanical Phenomena