Smaller femoral component size has been implicated as underlying the risk factor that explains the higher failure rate in women who have a hip resurfacing arthroplasty (HRA). We suspect that the diagnosis of dysplasia may be a more important causative risk factor than either small component size or female gender.
From January 2002 to July 2008, a total of 1,216 HRA cases, 1,082 with the primary diagnosis of osteoarthritis and 134 with dysplasia, were included in this study. Of them, 867 cases were performed in men and 349 performed in women. The average femoral component size was 51 ± 4 mm. Cox proportional hazard regression models were used to evaluate the significance of each variable and determine the causative risk factors for failure.
The average follow-up was 5 ± 2 years. Thirty-nine cases failed (20 in men vs. 19 in women). The failure rate for the whole group was 3.2% (2.3% in men vs. 5.4% in women; P = 0.01). Dysplasia (P = 0.05) was identified as the only significant risk factor in our multi-variable analysis; small femoral component size (P = 0.09) and gender (P = 0.76) were not significant risk factors. Women with the primary diagnosis of dysplasia had a survivorship rate of only 75% compared to 93% for the entire group at eight-year follow-up post-operatively.
In our study, we found that the high incidence of dysplasia in young women undergoing HRA was the reason that women had a higher failure rate after HRA. In dysplasia, 70% of failures were due to acetabular problems, of which 50% were due to failure of fixation and 20% due to adverse wear.