Abstract
Introduction: Long-term, aseptic loosening is the central problem for total hip replacements (THR)1. Several studies have suggested the possibility of predicting long-term loosening of femoral components (after about 7 years) by assessment of the short-term migration pattern (1 – 2 years) using radiostereometric analysis (RSA)2. During the past 2 years, we have been conducting an RSA study of the Elite Plus (DePuy) femoral component migration in 25 (8M, 17F) primary THR patients (mean age 61 years).
Results: The Table below shows the mean and SD of the stem centroid migrations after 12 months. The mean subsidence rate of 0.71 mm/year (15 patients) during the first month reduced to 0.16 mm/year, (22 patients) during the following two months. By the latter half of the first postoperative year, the mean rate had reduced to 0.13 mm/year.
| Subsidence | 0.20 ± 0.12 mm (15) |
| Internal Rotation | 0.89 ± 0.52 deg (14) |
| Lateral | 0.13 ± 0.09 mm (8) |
| External Rotation | 0.16 deg (1) |
| Medial | 0.11 ± 0.09 mm (7) |
| Valgus Rotation | 0.09 ± 0.06 deg (5) |
| Posterior | 0.17 ± 0.12 mm (11) |
| Varus Rotation | 0.23 ± 0.14 deg (10) |
| Anterior | 0.08 ± 0.08 mm (4) |
| Flexion | 0.28 ± 0.15 deg (7) |
| Extension | 0.15 ± 0.09 deg (8) |
Discussion: A study by the Oxford group (Alfaro-Adrian et al.3 ) compared the migration of 19 Elite Plus stems with 32 Exeter (Howmedica) stems over a two year period. After 1 year, there is a remarkable similarity in the subsidence, lateral migration and internal rotation between the two groups. However, combining the posterior and anterior migrations in the present study, the mean posterior migration was 0.15 mm. This is about half of that measured by the Oxford group (0.28 mm). Furthermore, the present study shows that varus rotation is predominant – compared to valgus rotation in the Oxford group’s study.
These abstracts were prepared by Mr Peter Kay. Correspondence should be addressed to him at The Hip Centre, Wrightington Hospital, Appley Bridge, Wigan, Lancashire WN6 9EP.
References:
1 Goldring. S.R., Clark. C.R. and Wright. T.M. J Bone Joint Surg.1993. 75A:799–801. Google Scholar
2 Karrholm. J.et al. J. Bone Joint Surg.1994. 76B:912–917. Google Scholar
3 Alfaro-Adrian. J., Gill. H.S., and Murray. D.W. J. Arthroplasty. 2001, 16, 598–606. Google Scholar
