FEMORAL HEAD DIAMETER AFFECTS THE REVISION RATE IN TOTAL HIP ARTHROPLASTY: AN ANALYSIS OF 1,720 HIP REPLACEMENTS WITH 9–21 YEARS FOLLOW-UP

Abstract

Introduction. Since the early days of total hip arthroplasty (THA) the choice of the proper diameter of the femoral head has been debated with respect to its effect on wear. The most widely accepted theory explaining aseptic loosening of THA is that of polyethylene particles induced osteolysis. In a previous study concerning 1,660 ScanHip THA’s that were followed for up to 12 years the cumulative revision rate was not found to be dependent on if a 22 mm or a 32 mm head size had been used1. We have reexamined these patients to see whether a longer follow-up time (9–21 years) would disclose an effect of head size on the revision rate.

Patients and Methods. We analyzed the CRR for 1,720 Scan Hip^® Classic I THA implanted in 1,550 patients, with 22 and 32mm heads, performed at Lund University Hospital during 1983 to 1995. Patients with the 3 most common diagnoses were included in the analysis, i.e. osteoarthritis, rheumatoid arthritis and femoral neck fracture. The end-point was defined as revision of any component for aseptic loosening before the end of 2004.

Results. Using the life table method analyzed cumulative revision rate for osteoarthritis, femoral neck fracture and rheumatoid arthritis patients and found that the 32 mm head had higher cumulative revision rate (p=0.04 (Wilcoxon)). Further analysis with Cox regression adjusting for age and sex showed that the 32 mm head had 2.8 times greater risk of revision (CI 1.7–4.6), p< 0.001. For each year increase in age the risk of revision was reduced 0.96 times (CI 0.95 – 0.97), p< 0.001, males had 1.5 times (CI 1.1 – 2.1), p=0.01 greater risk of revision than females.

Discussion. The reason that we did not find any significant difference in cumulative revision rates when followed up to 12 years, depending on head size in previous study (Kesteris et al. 1998) may be the time it takes for wear particles to induce the chain of events, eventually ending up in loosening. However extended follow-up up to 21 years after THA revealed significant differences in cumulative revision rates depending on head size.