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Polished, tapered stems are now widely used for cemented total hip replacement and many such designs have been introduced. However, a change in stem geometry may have a profound influence on stability. Stems with a wide, rectangular proximal section may be more stable than those which are narrower proximally. We examined the influence of proximal geometry on stability by comparing the two-year migration of the Exeter stem with a more recent design, the CPS-Plus, which has a wider shoulder and a more rectangular cross-section. The hypothesis was that these design features would increase rotational stability. Both stems subsided approximately 1 mm relative to the femur during the first two years after implantation. The Exeter stem was found to rotate into valgus (mean 0.2 degrees , sd 0.42 degrees ) and internally rotate (mean 1.28 degrees , sd 0.99 degrees ). The CPS-Plus showed no significant valgus rotation (mean 0.07 [correction] degrees, sd 0.29 [correction] degrees ) or internal rotation (mean -0.03 degrees , sd 0.75 degrees ). A wider, more rectangular cross-section improves rotational stability and may have a better long-term outcome.

Original publication

DOI

10.1302/0301-620x.87b7.16079

Type

Journal article

Journal

The Journal of bone and joint surgery. British volume

Publication Date

07/2005

Volume

87

Pages

921 - 927

Addresses

Oxford Orthopaedic Engineering Centre, The Botnar Research Centre, Nuffield Orthopaedic Centre, Windmill Road, Headington, Oxford OX3 7LD, UK.

Keywords

Femur, Hip Joint, Humans, Osteoarthritis, Hip, Prosthesis Failure, Treatment Outcome, Arthroplasty, Replacement, Hip, Prosthesis Design, Rotation, Aged, Aged, 80 and over, Middle Aged, Female, Male