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

J Bone Joint Surg Br

Publication Date

07/2005

Volume

87

Pages

921 - 927

Keywords

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