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A COMPARISON OF TOTAL HIP ARTHROPLASTY ACETABULAR COMPONENT DESIGNS: ARE ALL ‘CHARNLEY’ CUPS THE SAME?



Abstract

The Charnley total hip replacement has had favourable long-term survival results. On the strength of these results orthopaedic companies have introduced “Charnley Copies” incorporating identical design parameters.

The objective of the study was to determine whether the acetabular cups provided as DePuy Charnley copies by different manufacturers are identical with regards to their geometry. To analyze how any differences present may affect the motion characteristics of the arthroplasty.

A jig was designed which allowed the measurements of: i) range of movement free from impingement, ii) the arc of movement during which the femoral neck is impinging on the cup, iii) point of subluxation and dislocation of the femoral head from the cup. The cups obtained for analysis where the Standard and Long Posterior Wall models of the DePuy Charnley, Aesculap ALFA, Corin Cenator and Avatar LFA. The Aesculap Plasma Symmetrical and Asymmetrical were analyzed for comparison.

The Alfa has a greater free range of movement compared to the Charnley cup and the other copies. The Charnley cup, the Cenator and the LFA differed in their pattern of impingement. The Alfa had the earliest point of dislocation. Long Posterior Wall: The Avatar had the greatest free ROM. The Charnley and the Alfa dislocated in an anterior direction latest. The Avatar and Cenator dislocated latest in the posterior direction. Plasma Cup: Compared to the Charnley and its copies its free range of movement was greater, it had only one point of impingement and impinged through the smallest arc before dislocating. It did, however, dislocate easiest.

Charnley copies are not identical. Differences in geometry exist and these alter important motion characteristics. Long term outcome may be affected. Surgeons should be aware of these differences when choosing implants.

The abstracts were prepared by Mr Simon Donell. Correspondence should be addressed to him at the Department of Orthopaedics, Norfolk & Norwich Hospital, Level 4, Centre Block, Colney Lane, Norwich NR4 7UY, United Kingdom.