Nicholas M. Brown, MD; Jared R. H. Foran, MD; Craig J. Della Valle, MD
The purpose of this study was to compare total hip arthroplasty (THA) and hip resurfacing arthroplasty (HRA) with regard to the amount of acetabular bone stock removed and the ability to restore leg length and offset. Anteroposterior pelvis radiographs of 153 consecutive THAs and 84 consecutive HRAs were compared. Excluded patients were those with prior hip surgery, those in which a best-fit circle could not be adequately matched to the femoral head, and those with preoperative radiographic findings that precluded consideration for HRA (ie, disease severity, deformity, leg-length discrepancy).
A significant difference was found between THA and HRA with regards to age and sex but not primary diagnosis. Relative differences in acetabular bone removal were compared using a ratio of acetabular implant diameter to preoperative ipsilateral femoral head diameter measured with a best-fit circle. The ratio of acetabular cup diameter to preoperative ipsilateral femoral head diameter was significantly greater following THA than following HRA, indicating relatively more acetabular bone removal in THA procedures. Mean leg-length discrepancy was significantly greater following THA than following HRA. Offset was increased to a greater extent following THA than following HRA. Overall, HRA was associated with relatively less acetabular bone stock removal and less alteration in leg length and offset than was THA……Conventional total hip arthroplasty (THA) is a common and successful treatment option for end-stage degenerative hip disease, with more than 300,000 procedures performed annually in the United States.1 In the past decade, metal-on-metal hip resurfacing arthroplasty (HRA) has had a resurgence in popularity, especially among younger, more active patients. More than 300,000 HRAs have been performed worldwide, with reports of survival as high as 96% at 13-year follow-up. The advantages and disadvantages of each procedure have been debated in the literature, with inconsistent conclusions. Proponents of HRA cite preservation of femoral bone stock and restoration of biomechanics as key advantages of this procedure. Opponents argue that although HRA preserves femoral bone, it may sacrifice acetabular bone stock, which may ultimately be of greater concern in the setting of revision arthroplasty. The purpose of this study was to compare THA and HRA with regard to acetabular bone resection and restoration of leg length and offset.
The ratio of acetabular component diameter to native femoral head diameter was significantly greater following THA than HRA (1.19 vs 1.16; P=.005), indicating relatively more acetabular bone removal in THA. Mean acetabular component size used was larger for the HRA group than the THA group (56.3 vs 55.3 mm, respectively; P=.0178). This was likely due to significant sex differences between the group, with a preponderance of men in the HRA group. However, on average, patients in the HRA group also had larger native femoral heads (49.0 vs 46.8 mm; P=.0006), which was directly proportional to native acetabular size (Table 2). For this reason the mean ratio of native femoral head to acetabular component size was used for the analysis.
No significant difference was found in mean preoperative leg-length discrepancy between the HRA and THA groups (−2.3 vs −3.2 mm, respectively; P=.204). However, HRA was associated with significantly less postoperative leg-length discrepancy (1 vs 3.7 mm, respectively; P=.0013). Also, HRA was associated with a significantly smaller average absolute change in leg length (3.2 vs 6.7 mm, respectively; P<.0001). The choice between conventional THA and HRA for appropriately selected patients is controversial. Among the proposed benefits of HRA is bone stock preservation, although this has been questioned secondary to concerns over the use of larger acetabular components in some series.10�12 Other proposed benefits include a more anatomic reconstruction with smaller changes in leg length and offset.6 The current authors attempted to address these controversies with a comprehensive radiographic analysis... ...The current results suggest that in this surgeon�s practice, HRA was associated with significantly less acetabular bone stock removal. Although this difference was statistically significant, the difference was small and likely not clinically significant. The finding of more acetabular bone removal in the THA group may be related to the surgeon�s desire to maximize femoral head size when performing conventional THA and, in cases where it was safe to do so, a larger acetabular component size may have been inserted in an attempt to accommodate a larger femoral head size. Furthermore, the surgeon routinely started preparing the femoral head for HRA prior to acetabular component placement, and greater certainty regarding the femoral head size may have allowed for the placement of smaller acetabular components. Nonetheless, the current study suggests that HRA is not necessarily associated with more acetabular bone stock removal, as was suggested by the first studies on this topic.