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.2–5 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.6–9 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.10,11 The purpose of this study was to compare THA and HRA with regard to acetabular bone resection and restoration of leg length and offset.
Materials and Methods
The authors analyzed the radiographs of 267 consecutive primary THA procedures and 94 consecutive HRA procedures performed by a single surgeon (C.D.V.) between January 2005 and February 2009. Institutional review board approval was obtained. Patients were excluded from analysis for the following reasons: unavailable or inadequate electronic preoperative anteroposterior pelvic radiographs (87 THA, 8 HRA), history of hip surgery (7 THA, 0 HRA), radiographs in which a best-fit circle could not be adequately matched to the femoral head (0 THA, 2 HRA), and patients in which preoperative radiographic findings (disease severity or deformity) precluded consideration for HRA (20 THA, 0 HRA). Therefore, the final study comprised 154 THAs and 84 HRAs.
The surgical approach for the THAs included 97 posterior, 55 two-incision, and 2 anterolateral approaches. All HRAs were performed via a posterior approach, and a larger incision was used along with the routine release of the gluteus maximus tendon. All HRAs used Birmingham Hip Resurfacing (Smith & Nephew, Memphis, Tennessee). For the conventional THA, the bearing surface was metal-on-highly cross-linked polyethylene (HXLPE) in 145 hips and metal-on-metal in 8 hips. The femoral head size for THAs was 28 mm in 50 hips, 32 mm in 49 hips, 36 mm in 43 hips, 40 mm in 4 hips, 42 mm in 1 hip, 44 mm in 1 hip, 46 mm in 4 hips, and 52 mm in 1 hip. Acetabular components used included 140 Trilogy (Zimmer, Warsaw, Indiana), 5 Reflection (Smith & Nephew), 4 Durom (Zimmer), 3 Birmingham Hip Resurfacing, and 1 Trabecular Metal (Zimmer). Femoral components used included 84 Versys Epoch (Zimmer), 32 Versys Beaded Fullcoat (Zimmer), 23 Versys Fiber Metal Taper (Zimmer), 6 Synergy (Smith & Nephew), 3 Versys Advocate Cemented (Zimmer), 2 Echelon (Smith & Nephew), 1 Versys Fiber Metal Midcoat (Zimmer), 1 TM stem (Zimmer), 1 ML Taper (Zimmer), and 1 Spectrum EF (Smith & Nephew).
Demographic data for the THA and HRA cohorts are listed in Table 1. A significant difference was found in the mean age (63.8 vs 49.1 years, respectively; P<.0001) and in sex (55.8% vs 16.7% women, respectively; P<.0001) between the 2 groups. No significant difference was found in primary diagnosis of osteoarthritis (87% vs 91.7%, respectively; P=.3925).
Table 1: Summary of Demographic Data
The amount of acetabular bone that was resected for the THA and HRA cohorts was determined radiographically using the ratio of the acetabular component size to the native femoral head size. That is, for a given native femoral head size, the authors sought to determine whether the mean size of the acetabular component was greater in the THA or HRA group. The ratio of acetabular size to the native femoral head was used as a surrogate for the relative amount of acetabular bone stock that was removed for each group.
Using the 6-week postoperative radiograph, the native femoral head size was determined by placing a best-fit acrylic overlay circle over the native femoral head on the contralateral side and measuring the diameter of the circle. The contralateral femoral head was used because the postoperative radiograph that had an acetabular component of known dimensions allowed for accurate calibration for measurement of the native femoral head on the digital radiograph (Figure). The preoperative radiographs for each patient were evaluated to ensure that the femoral heads were equal in size bilaterally (to ensure that surrogate measurement of the contralateral head was valid). In 33 hips, the ipsilateral femoral head was directly measured on the preoperative radiographs if the patient had a previous arthroplasty on the contralateral hip because the known implant size allowed for accurate calibration and measurement of the native ipsilateral femoral head.
Figure: Anterposterior radiograph showing the calibration of measurements based on known implant size (A). Anterposterior radiograph showing the measurement of the native femoral head size based on the diameter of a best-fit circle (B).
The pre- and postoperative leg-length discrepancy was calculated using the anteroposterior pelvis radiograph. A reference line was drawn tangential to the inferior aspect of the inferior pubic rami. Next, the distance between the inferior aspect of the lesser trochanter and the reference line was measured for each side. The leg-length discrepancy was the difference in distances between each lesser trochanter and the reference. Postoperative radiographic measurement was calibrated digitally using the known acetabular component size, and preoperative radiographic measurement was calibrated using the native femoral head size that was determined on the postoperative radiograph.
Offset was measured using the anteroposterior radiograph of the pelvis. A reference line was drawn parallel to the femur through the center of the medullary canal. A line was then drawn perpendicular to the reference line to the center of the femoral head. This perpendicular line was the measured offset. Postoperative radiographic measurement was calibrated digitally using the known acetabular component size, and preoperative radiographic measurement was calibrated using the native femoral head size that was determined on the postoperative radiograph.
Student’s t test was used to compare continuous variables (ie, age, acetabular bone loss, leg-length discrepancy, and change in offset), and chi-square analysis was used to evaluate categorical variables (ie, sex, primary diagnosis, and heterotopic ossification). A P value less than .05 was considered statistically significant. Statistics were calculated using Graphpad Instat software (La Jolla, California).
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.
Table 2: Summary of Biomechanical Data
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).
Mean offset was increased to a greater extent following THA than HRA (3.8 vs 0.9 mm, respectively; P=.0007). Mean offset following THA increased from 36.8 to 40.6 mm compared with 38.2 to 39 mm following HRA.
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.
This study has several limitations. First, the analysis was retrospective, and a prospective design may have led to less patients being excluded from the analysis for issues such as inadequate radiographs or radiographs that could not be found. Second, an indirect method was used for measuring acetabular bone loss. However, the methodology the authors used is reproducible, mathematically sound, and allows for an objective comparison between the 2 procedures. Finally, this analysis was not randomized and no patient matching was used; age and demographic differences did exist between the 2 groups (the patients who underwent HRA were younger and more commonly male), which may have affected the analysis.
Reports conflict regarding the relative amount of acetabular bone that is removed in THA and HRA. A cadaveric study performed by Su et al12 compared the amount of bone removed when a THA was performed on 1 side and an HRA on the other and found that 3 times less bone was removed with an HRA. In contrast, Naal et al10 retrospectively examined 2134 hip arthroplasties and, after controlling for demographic differences, found that, on average, HRA required a larger acetabular component size than THA.10 Similarly, Loughead et al11 demonstrated that the size of the acetabular component increases more for HRA than for THA as native femoral head size increases. However, a study by Vendittoli et al13 showed no difference in acetabular component size after randomizing 210 patients to THA and HRA groups.
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.10,11
As with acetabular bone loss, reports conflict with regard to the change in leg length and offset when comparing the 2 procedures. Loughead et al14 compared the radiographs of 28 THA and 26 HRA procedures and found that THA more accurately restored hip biomechanics. However, controversy exists regarding the results of this study because the acetabular component was not placed similarly in both groups.14 Silva et al15 compared 22 THAs and 19 HRAs performed by 1 surgeon. The authors did not specifically comment on restoration of leg length and offset, but they empirically noted that leg length was on average decreased more for HRA and offset was reduced in HRA but increased for THA. The authors commented that THA was more suitable for patients with a large leg-length discrepancy (more than 10 mm) or low femoral offset.15 Both of these studies suggest THA results in a more biomechanically normal hip. In contrast, Girard et al6 radiographically evaluated 55 THAs and 49 HRAs that were demographically matched and found that a higher percentage of HRAs appropriately restored leg length (86% vs 60%) and femoral offset (57% vs 28%). The current findings are in agreement with the Girard et al6 study because the current study found that HRA led to smaller changes in leg length and offset. Because leg-length discrepancy is a common concern for patients and surgeons, this would seem to be an advantage with HRA. Lecerf et al16 performed a study of 76 THAs and 80 HRA that showed an average offset increase in THA and decrease in HRA, which is in agreement with the current findings. Interestingly, the groups had equal clinical outcomes based on postoperative clinical scores, suggesting that this biomechanical measurement may be more of a theoretical concern, although trochanteric pain is not an infrequent complaint following THA that may be related to increases in offset.17
- HPCUnet. Healthcare cost and utilization project. Agency for Healthcare Research and Quality. http://hcupnet.ahrq.gov. Accessed December 20, 2012.
- Treacy RB, McBryde CW, Pynsent PB. Birmingham hip resurfacing arthroplasty. A minimum follow-up of five years. J Bone Joint Surg Br. 2005; 87:167–170 doi:10.1302/0301-620X.87B2.15030 [CrossRef] .
- Hing CB, Back DL, Bailey M, Young DA, Dalziel RE, Shimmin AJ. The results of primary Birmingham hip resurfacings at a mean of five years. An independent prospective review of the first 230 hips. J Bone Joint Surg Br. 2007; 89:1431–1438 doi:10.1302/0301-620X.89B11.19336 [CrossRef] .
- Learmonth ID, Young C, Rorabeck C. The operation of the century: total hip replacement. Lancet. 2007; 370:1508–1519 doi:10.1016/S0140-6736(07)60457-7 [CrossRef] .
- McMinn DJ, Daniel J, Ziaee H, Pradhan C. Indications and results of hip resurfacing. Int Orthop. 2011; 35:231–237 doi:10.1007/s00264-010-1148-8 [CrossRef] .
- Girard J, Lavigne M, Vendittoli PA, Roy AG. Biomechanical reconstruction of the hip: a randomised study comparing total hip resurfacing and total hip arthroplasty. J Bone Joint Surg Br. 2006; 88:721–726 doi:10.1302/0301-620X.88B6.17447 [CrossRef] .
- Mont MA, Seyler TM, Ragland PS, Starr R, Erhart J, Bhave A. Gait analysis of patients with resurfacing hip arthroplasty compared with hip osteoarthritis and standard total hip arthroplasty. J Arthroplasty. 2007; 22:100–108 doi:10.1016/j.arth.2006.03.010 [CrossRef] .
- Mont MA, Ragland PS, Etienne G, Seyler TM, Schmalzried TP. Hip resurfacing arthroplasty. J Am Acad Orthop Surg. 2006; 14:454–463.
- Shimmin A, Beaule PE, Campbell P. Metal-on-metal hip resurfacing arthroplasty. J Bone Joint Surg Am. 2008; 90:637–654 doi:10.2106/JBJS.G.01012 [CrossRef] .
- Naal FD, Kain MS, Hersche O, Munzinger U, Leunig M. Does hip resurfacing require larger acetabular cups than conventional THA?Clin Orthop Relat Res. 2009; (467):923–928 doi:10.1007/s11999-008-0689-2 [CrossRef] .
- Loughead JM, Starks I, Chesney D, Matthews JN, McCaskie AW, Holland JP. Removal of acetabular bone in resurfacing arthroplasty of the hip: a comparison with hybrid total hip arthroplasty. J Bone Joint Surg Br. 2006; 88:31–34 doi:10.1302/0301-620X.88B1.16764 [CrossRef] .
- Su EP, Sheehan M, Su SL. Comparison of bone removed during total hip arthroplasty with a resurfacing or conventional femoral component: a cadaveric study. J Arthroplasty. 2010; 25:325–329 doi:10.1016/j.arth.2008.10.004 [CrossRef] .
- Vendittoli PA, Lavigne M, Girard J, Roy AG. A randomised study comparing resection of acetabular bone at resurfacing and total hip replacement. J Bone Joint Surg Br. 2006; 88:997–1002.
- Loughead JM, Chesney D, Holland JP, McCaskie AW. Comparison of offset in Birmingham hip resurfacing and hybrid total hip arthroplasty. J Bone Joint Surg Br. 2005; 87:163–166.
- Silva M, Lee KH, Heisel C, Dela Rosa MA, Schmalzried TP. The biomechanical results of total hip resurfacing arthroplasty. J Bone Joint Surg Am. 2004; 86:40–46.
- Lecerf G, Fessy MH, Philippot R, et al. Femoral offset: anatomical concept, definition, assessment, implications for preoperative templating and hip arthroplasty. Orthop Traumatol Surg Res. 2009; 95:210–219 doi:10.1016/j.otsr.2009.03.010 [CrossRef] .
- Bourne RB, Rorabeck CH. Soft tissue balancing: the hip. J Arthroplasty. 2002; 17:17–22 doi:10.1054/arth.2002.33263 [CrossRef] .
Summary of Demographic Data
|Variable||THA Group, No. (%)||HRA Group, No. (%)||P|
|Mean age, y||63.8||49.1||<.0001|
| Male||68 (44.2)||70 (83.3)|
| Female||85 (55.8)||14 (16.7)|
| Osteoarthritis||133 (87)||77 (91.7)|
| Other||20 (13)||7 (8.3)|
Summary of Biomechanical Data
|Variable||THA Group||HRA Group||P|
|Acetabular bone, mm|
| Mean cup size||55.3||56.3||.0178|
| Mean native head size||46.8||49||.001|
| Mean cup/head ratio||1.19||1.16||.0051|
|Leg length, mean|
| Preoperative discrepancy||−3.2||−2.3||.204|
| Postoperative discrepancy||3.7||1||.0013|
| Preoperative discrepancy||36.8||38.2||.21|
| Postoperative discrepancy||40.6||39||.0795|