The choice to proceed with a resurfacing over a conventional hip replacement must take into account one’s training. Shimmin reported from the Australian Registry failure rates of 5.8% at 4 years if one’s hospital performed fewer than 50 hip resurfacings per year, 4.7% if it performed between 50 and 100, and only 2.7% if it performed more than 100 (17). He reported that it would take a surgeon 50 resurfacings to reach a level of experience commensurate with a low failure rate, and 13 cases to get halfway there. Similarly, Mont reported 11 failures in his first 50, as compared to one failure in his next 50, and then two failures in all cases beyond his first 100. One can argue, though, that these same effects are seen in hip replacement as well, with the learning curve occurring during residency rather than in independent practice. Further, Katz et al. (37) have demonstrated similar volume-related findings to those in the Australian Registry, regarding hip replacements. Both procedures are technically demanding and show superior results when performed by surgeons and hospitals with more experience.

A surgeon well trained in resurfacing of the hip can confidently choose this procedure for male patients under 65, as survival has been comparable so far to conventional hip replacement, and may be better in the long term. With the information available,
it is difficult to prove a substantial difference in functional outcome when hip resurfacings are compared to large diameter head hip replacements. Hip resurfacings do have better ion levels when compared to this group. When resurfacings are compared to smaller head hip replacements, though, randomized trials do tend to show better function in resurfacing but not exceptionally so. Hip replacements likely have a higher risk of dislocation when traditional head diameters are used, and fear of dislocation in these circumstances may prevent greater activity with hip replacement. With the information available, hip resurfacings better replicate leg lengths and offset. Femoral neck fracture, which will be discussed below, is a complication unique to hip resurfacing, but is rare when the procedure is performed in younger males and by experienced surgeons.

Much of the registry data confirms that young men with good bone stock and large femoral heads are ideal candidates for hip resurfacing. Data from the British National Joint Registry have demonstrated that men younger than 60 experience a greater than two times less revision risk than the rest of the population (23). Further results from the Australian Registry confirm these sentiments. At 7 years, men below the age of 65 demonstrated better survival than any other group receiving resurfacing, and better longevity than men in this age group receiving total hip replacement—4.2% versus 4.6% revised at 7 years for those less than 55 (38). This group in particular has a low risk of femoral neck fracture and has high activity levels that could accelerate wear of softer articulations typical in standard hip arthroplasty.

When considering only gender, men have shown better survival than women with hip resurfacing at 7 years in the Australian Registry, with revision of 4.5% versus 10.1% (Fig. 67.4). Older men, however, do worse than younger men, with a revision rate of 6.5% for those 65 and older, and 4.2% and 4.3% for the younger age groups (39). In terms of complications related to gender and age differences, Glyn-Jones et al. (40) found a pseudotumor rate of 0.5% in males younger than 40, 6% in women over 40, and 13.1% in women less than 40.

As mentioned, in the Australian Registry, men over 65 with resurfacings are revised at a rate of 6.5% at 7 years. Total hip replacements do significantly better in this age group with rates of 4.4% and 4.6% at 7 years, for those between 65 and 75 and those over 75, respectively. Hip resurfacings in younger age groups do better than in the elderly. The age groups of <55 and those between 55 and 65 have had similar results, with revision rates at 7 years of 4.2% and 4.3%, respectively. This difference is almost statistically significant, versus elderly patients.

Resurfacing is generally not performed in elderly women, as the femoral neck fracture rate is elevated in this potentially osteoporotic group with smaller femoral necks. Shimmin and Back (41) found a rate of 0.98% of femoral neck fractures in men in the Australian Registry in 2005, and a doubling of the rate to 1.91% in women. Interestingly the average age of the women was only 56 years, while that of the men was 62 years.

Complications were also found to be higher among the more elderly patients in the initial American experience with hip resurfacing (19). McGrath et al. (42) acknowledged the less-optimal results among elderly patients in registries, but found that in matching their patients over 60 with those under 60, there was no significant difference in revision rate, radiographic failures, or functional score outcome. From the Australian Registry, it appears that once the initial increased failure rate is surpassed, the subsequent yearly failure rate
is similar between males older than 65 and those younger (Fig. 67.5).

The issue of head size is more important when considering females for hip resurfacing. It is less important with male patients as a great majority have sizes of femoral head adequate to avoid bearing surface complications (40). Seventy percent of the females in Glyn-Jones’ study had femoral heads 48 mm in size or smaller, as compared to 9% of the males (Fig. 67.6). They could find no definitive cut-off value of head size, but found that those with femoral heads below the average size for their gender had a fivefold increase in risk for adverse local tissue reactions.

The report of Pandit et al. raised the issue as to whether female gender was responsible for the soft tissue masses seen in their patients, as all patients developing these masses were women. A gender specific immune difference or a differential exposure to jewelry could possibly explain this phenomenon. Two factors, however, are more likely confounding variables. As above, women receiving hip resurfacing generally have smaller head sizes than men, and more women have the diagnosis of dysplasia. The smaller head size may prevent fluid film formation, which would increase wear and the propensity for lymphocyte-mediated reactions. Dysplasia, which is more common in women, could cause placement of both components in more anteversion and the acetabulum in more abduction, creating a tendency to edge load the bearing surface, thus increasing wear and the risk for wear-related problems. Implants associated with soft tissue masses have indeed shown wear patches consistent with edge loading (43). Further, dysplastic patients tend to have smaller head sizes.

In reviewing only female patients with hip resurfacing, the Australian Registry has found head size much more than female gender to be the predetermining factor when it comes to survivorship. Both men and women with head sizes less than 50 mm did poorly, the men being revised at a rate of 9.3% at 7 years, and women with heads less than 50 mm with a rate of 11.2%. Similarly, the curve for women with larger heads (50 mm or greater) corresponds closely to the curve for men with larger heads up to 7 years, with revision rates of only 3.5% and 3.7%, respectively (Fig. 67.7 and Table 67.1). Only 13.7% of the women, however, received a head 50 mm or larger, whereas 83.8% of men did so. It appears from this data that in the unusual circumstance of a female femoral head being large enough to accommodate a 50 mm or greater head, there is no contraindication to hip resurfacing.