Modern total hip arthroplasty (THA) designs

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1 120 Bulletin of the NYU Hospital for Joint Diseases 2009;67(2):120-7 Resurfacing Versus Conventional Total Hip Arthroplasty Review of Comparative Clinical and Basic Science Studies David R. Marker, B.S., Kyle Strimbu, B.S., Mike S. McGrath, M.D., Michael G. Zywiel, M.D., and Michael A. Mont, M.D. Abstract Objective: Although standard total hip arthroplasties have a long and successful history as the standard of care for advanced, symptomatic osteoarthritis, there is increasing patient demand and surgeon interest in femoral boneconserving resurfacing alternatives. The purpose of this study was to assess the state of the research that directly compares the outcomes of conventional total hip arthroplasty procedures with the current generation of metal-on-metal resurfacing hip arthroplasties. Methods: A comprehensive review was performed of the published literature that directly compared total hip arthroplasty and resurfacing hip arthroplasty and that considered basic science, radiographic, and clinical studies. Results: Of the basic science studies, two investigations found evidence that favored total hip arthroplasty, while three favored resurfacing hip arthroplasty. For the clinical studies, all reports showed that resurfacing hip arthroplasty had similar or better outcomes than total hip arthroplasty at short- to midterm follow-up. The gait studies suggest that resurfacing provides a more natural gait than conventional total hip arthroplasty. Conclusions: While there is still much debate and room for additional research on this topic, multiple midterm clinical results suggest that resurfacing hip arthroplasty represents a safe, effective alternative to conventional total hip arthroplasty, especially for younger, active patients. David R. Marker, B.S., Kyle Strimbu, B.S., Mike S. McGrath, M.D., Michael G. Zywiel, M.D., and Michael A. Mont, M.D., are from the Rubin Institute for Advanced Orthopedics, Center for Joint Preservation and Reconstruction, Sinai Hospital of Baltimore, Baltimore, Maryland. Correspondence: Michael A. Mont, M.D., Rubin Institute of Advanced Orthopedics, Center for Joint Preservation and Reconstruction, Sinai Hospital of Baltimore, 2401 West Belvedere Avenue, Baltimore, Maryland 21215; mmont@lifebridgehealth.org. Modern total hip arthroplasty () designs and surgical approaches have shown excellent long-term results for the treatment of late-stage symptomatic osteoarthritis, especially in older, less active patients. Some concerns exist that may provide less optimal outcomes in younger and more active patients. As such, there has long been an interest in more boneconserving replacement procedures, such as resurfacing hip arthroplasty (). Earlier generations of hip resurfacing devices frequently failed, largely due to problems with excessive wear of their bearing surface materials. Since that time, improvements in surgical technique and design, specifically the introduction of thinner shelled metal-on-metal interfaces with improved tolerances, have led to a renewed and growing interest and use of resurfacing, especially in young and active patients. Since the introduction of metal-on-metal resurfacing devices, in the 1990s, over 300,000 procedures have been performed worldwide. 1 Multiple studies of short- and midterm outcomes of resurfacing implants have reported clinical success rates upwards of 94%, 2 with several studies reporting five-year survival rates of 98%. 3,4 These outcomes are similar to those that have been reported for patients treated with conventional. Some investigators have argued that resurfacing may offer advantages over, in terms of conservation of femoral bone stock, increased range of motion (ROM), a more normal gait pattern, lower dislocation rates, and ease of revision. In order to assess these claims, a number of investigators have conducted studies directly comparing and. These studies have varied in their approach in terms of the outcome parameters used to assess and. The purpose of the present study was to provide a comprehensive meta-analysis of the current literature that has directly compared modern with conventional. Our primary question was: How do the outcomes for Marker DR, Strimbu K, McGrath MS, Zywiel MG, Mont MA. Resurfacing versus conventional total hip arthroplasty: review of comparative clinical and basic science studies. Bull NYU Hosp Jt Dis. 2009;67(2):120-7.

2 Bulletin of the NYU Hospital for Joint Diseases 2009;67(2): patients compare to their counterparts who receive a? More specifically, we asked what evidence is there in the current literature to answer the following questions: 1. Do and provide similar biomechanics? 2. Are there advantages for over, based on gait studies? 3. Are the radiographic outcomes similar for and patients? 4. Are the clinical outcomes similar? and 5. Are the outcomes of patients who require revision of to similar to patients receiving a primary? Materials and Methods We conducted a comprehensive, systematic review of the published medical literature, searching for reports on studies directly comparing conventional procedures and modern metal-on-metal procedures. We used as our starting point keyword searches for the terms total hip arthroplasty and hip resurfacing, and then narrowed our review to include only articles that considered the outcomes of both procedures in either a clinical or basic science comparison study. We searched the bibliographies of all relevant studies and related review articles to find additional pertinent studies. In addition, we reviewed the most recent Proceedings of the American Academy of Orthopaedic Surgeons (February 2008) to identify any versus comparison studies from that conference. Additional inclusion criteria were: 1. Only studies published in the past 10 years that provided results for modern prostheses designs were included. For example, we excluded studies similar to those by Amstutz and colleagues 5 and Gore and coworkers 6 that were published in 1984 and 1985, respectively. 2. Similarly, we did not include studies (such as an article by Meldrum and associates 7 ) that were published recently but provided long-term results of prior generation hip resurfacing designs. 3. We included the translated abstracts from papers published in foreign languages but not any additional content from the articles. Finally, 4. Only the most recent outcomes were used for patient cohorts from a given institution. For example, if a patient cohort was initially reported in the Proceedings of the American Academy of Orthopaedic Surgeons, but later published in a journal, then only the recent journal article was included in our analysis. In order to answer the primary questions of our study, we stratified the studies into five categories. The first category consisted of the basic science papers. These investigations included any reports comparing and in cadavers, composite models, or computer simulations, as well as any combination thereof. Gait analysis studies were stratified separately from the other basic science categories. The remaining categories included: comparative studies assessing radiographic parameters and outcomes, studies of clinical outcomes, and studies comparing the conversion of failed resurfacings to primary conventional. Initially, attempts were made to aggregate the reported outcomes from the studies for each of the categories (basic science, gait analysis, radiographic evaluations, clinical outcomes, and revision outcomes). However, due to differences in the outcome measures used in the various studies, it was determined that only limited aggregation was possible, making a statistical analysis invalid. Rather than aggregating the outcome measures, we identified how many studies in each of the categories reported statistically significant differences that favored or, or showed similar outcomes. Results Basic Science Studies There were five basic science studies that compared and (Table 1). These studies focused on differences in natural joint biomechanics (such as ROM), amount of bone Table 1 Literature Review of Basic Science Studies that Compared Resurfacing and Conventional Total Hip Arthroplasty Authors Design Outcomes Conclusions Advantage Liu, Three-dimensional finite (2005) 8 element analysis Doherty, Three-dimensional CT (2007) 9 computer models Bengs, In vitro comparison of 8 (2008) 10 different or prosthetic models has less contact pressure (-53%) and increased contact area (+220%). Flexion and extension: = 109 and 13 vs = 125 and 34. Conventional allowed for statistically significantly greater range of motion than. Deuel, In vitro cadaver models Microstrain of 621 for native femurs (2008) 11 was similar to but not. Su, (2009) 12 In vitro cadaver models Femoral bone loss: = 26 g vs = 75 g (p < 0.001). Acetabular bone loss: = 26 g vs = 75 g (p = 0.60). may have less wear debris and better long-term outcomes than. has a reduced range of motion. has a reduced range of motion due to impingement. Bone strain for are more similar to the native femur than. leads to less femoral bone loss and similar acetabular bone loss compared to.

3 122 Bulletin of the NYU Hospital for Joint Diseases 2009;67(2):120-7 preservation, and bone strain-sheer. Two of these studies favored, while three favored. Comparing a Durom metal-on-metal resurfacing prosthesis to a conventional Metasul metal-on-metal THR prosthesis via finite element models of the two designs, Liu and colleagues reported findings that favor THR. 8 They reported that that the maximum contact pressures were 22 MPa for a Durom, compared to 47 MPa for a Metasul. These correlated to a contact area of 237 mm 2 versus 74 mm 2 for the and, respectively. With respect to ROM, two studies [a three-dimensional computer model study that assessed composites of computed tomography (CT) scans by Doherty and coworkers 9 and an in-vitro study by Bengs and associates 10 ] reported that leads to a decreased ROM, compared to when utilizing a bone-only model. In the other two basic science studies, Deuel and colleagues 11 used microstrains in a cadaver model to demonstrate that preserves femoral bone stock, and Su and coworkers 12 reported that not only preserves substantially more femoral bone, but also can be implanted with an acetabular bone loss similar to that of. Radiographic Studies There were seven studies that compared radiographic parameters for and (Table 2). Some of the outcome measures for these studies included leg length, femoral offset, size of components to estimate bone loss, and incidence of heterotopic ossification. The majority of these studies (n = 4) suggested that provided better outcomes compared to. Of the remaining studies, one indicated there was no significant difference between these two surgical approaches, and two studies suggested provided better outcomes. There were three studies that assessed changes in leg length and femoral offset following hip arthroplasty, with conflicting outcomes. Two studies reported that negative horizontal femoral offset and greater leg-length changes made less biomechanically accurate. 13,14 In contrast, in the cohort for Girard and associates, leg-length inequality was restored in 60% of versus 86% for. 15 Two studies focused on acetabular bone loss as a measure of biomechanical restoration success. Loughead and associates reported that while femoral bone can be saved with procedures, statistically significantly more acetabular Table 2 Literature Review of Studies Comparing Radiographic Data for Resurfacing and Conventional Total Hip Arthroplasty Study Procedure Hips Outcomes Conclusions Advantage Silva, (2004) Leg length change: -1.1 mm Horizontal femoral offset change: = +5.2 mm 50 Leg length change: = -2.2 mm. Horizontal femoral offset change: -8.4 mm Loughead, 28 Hip length increase: 3.6 mm may allow better biomechanical reconstruction for patients with leg-length inequalities 10 mm or low femoral offset. (2005) 13 that more accurately resemble a 26 Hip length increase: 0.3 mm results in biomechanics normal hip. Girard, (2006) Leg length inequality restored in 60% of hips 49 Leg length inequality restored in 86% of hips Loughead, 33 Mean acetabulum size: 52 mm (2006) 29 (Acetabular size difference was greater than the femoral head size difference) 35 Mean acetabulum size: 56.4 mm Hip biomechanical reconstruction is more precisely achieved through. Patients requiring larger femoral heads will have statistically significantly more acetabular bone loss for compared to. Vendittoli, 103 Acetabulum size: mm conserves femoral bone (2006) Acetabulum size: mm Girard, (2008) Horizontal femoral offset change: +4.2 mm 69 Horizontal femoral offset change: -2.8 mm Rama, (2008) Brooker grades 3 and 4 HO: 2.1% Brooker grade 4 HO: 0% 105 Booker grades 3 and 4 HO: 12.6% Booker grade 4 HO: 4.9% stock and can maintain similar acetabular bone stock compared to with proper surgical technique. had decline in horizontal femoral offset but this did not affect clinical function. may require HO prophylaxis and surgeons should use meticulous surgical technique. Similar

4 Bulletin of the NYU Hospital for Joint Diseases 2009;67(2): Table 3 Literature Review of Studies Comparing Clinical Data for Resurfacing and Conventional Total Hip Arthroplasty Complication Study Procedure No.of patients (hips) Followup (months) Mean clinical scores in points (range) and Reoperation rates Conclusions Advantage Pollard, 54 (54) 80 OHS: 18.5 (12-41) 8% Similar Oxford Hip (2006) 2 : 54 (54) 61 UCLA: 6.8 (3-10) OHS: 15.9 (12-42) 6% Scores and failure rates. Resurfacing associated UCLA: 8.4 (4-10) with higher activity levels. Vail, (2006) (93) 36 HHS: 93 Activity score: 12.7 Reoperation: 4.3% Complication: Girard, (2008) 30 Haddad, (2008) 22 Lavigne, (2008) (57) 36 HHS: 98 Activity subscore: P-M: 17 ± 0.4 WOMAC: 11.7 ± P-M: 17 ± 0.35 WOMAC: 9.2 ± (40) 24 Hop test: 0.03 meters 3 step-ups in 15 seconds Lateral step score: 2.5 (3 = poor) 40 (40) 24 Hop test: 0.32 meters 7 step-ups in 15 seconds Lateral step score: 0.7 (3 = poor) Hospital length of stay: 6.1 days Hospital length of stay: 5.0 days 14% Reoperation: 3.5% Complication: 5.3% associated with significantly higher HHS, ROM subscore, activity subscore, and function subscore. Similar clinical scores. Similar Resurfacing associated with higher levels of function at all follow-up times. Isolated dislocations in 3 hips. 1 revision for recurrent dislocation. 2 revisions for head collapse Similar clinical scores, satisfaction rates, and complication rates. was associated with higher dislocation rates. Similar bone is lost. However, similar to the basic science study by Su and colleagues, 12 Vendittoli and coworkers reported that with careful technique and appropriately-sized implant options, acetabular implants need be no larger in patients than in patients, while also conserving femoral bone stock. 16 Rama and associates used radiographic analysis to identify asymptomatic heterotopic ossification (HO) formation in postoperative and patients. 17 They found that patients had a significantly higher rate of severe (Booker grades 3 and 4) HO formation than patients (12.6% compared to 2.1%), with Booker grade 4 HO found only in patients. Clinical Studies Nine reports compared the short- and midterm clinical results of the two procedures (Table 3). The majority of the investigations demonstrated that the two prostheses had similar clinical hip scores and revision rates. However, five studies also found that patients who underwent had higher postoperative activity levels than patients who underwent. Additional findings included lower dislocation rates associated with resurfacing and conflicting results regarding ROM. Vail and colleagues compared 52 patients (57 hips) who underwent to 84 patients (93 hips) who underwent conventional. 18 At a mean follow-up of three years (range, 2 to 4 years), the resurfacing cohort had significantly higher Harris hip scores than the conventional arthroplasty cohort. The activity, function, and ROM subscores of the resurfacing cohort were all significantly greater as well. The complication rate of the conventional arthroplasty cohort was 14%, compared with a 5.3% complication rate in the resurfacing cohort. Complications in the cohort included fracture

5 124 Bulletin of the NYU Hospital for Joint Diseases 2009;67(2):120-7 Table 3 Continued Study Lavigne (2008) 20 Lavigne (2008) 32 Stulberg (2008) 21 Mont (2009) 19 Procedure No.of patients (hips) Followup (months) Mean clinical scores in points (range) 71 (71) 12 Overall activity: 12.7 points WOMAC: 9.8 ±10.9 points UCLA: 6.75 ± 1.71 points 81 (81) 12 Overall activity: 17.9 points WOMAC: 8.1 ± 13.1 points UCLA: 7.17 ± 2.8 points (min) Total arc of motion: 196 Arc of rotation: 44.3 Flexion-extension arc:120 Abduction-adduction arc: (min) Total arc of motion: 204 Arc of rotation: 48 Flexion-extension arc:118 Abduction-adduction arc: (266) 337 (337) Complication and Reoperation rates Conclusions Advantage Pre-operative activity scores of the two groups were similar. associated with more frequent and more intense sports activities postoperatively. No statistically significant Similar range-of-motion differences were found between and patients : greater pain score (and lower HHS) at 6 weeks. HHS statistically similar at 6, 12, and 24 months. 54 (54) 39 HHS: 91 (62-100) Satisfaction: 8.8 (0-10) Activity: 7 (0-20) 54 (54) 39 HHS: 90 (50-100) Satisfaction: 9.2 (2-10) Activity: 11.7 (0-32) Two revisions Two revisions Midterm clinical outcomes and satisfaction scores similar. Resurfacing patients had higher activity scores, but also had higher preop activity scores. Abbreviations:, total hip arthroplasty;, resurfacing hip arthroplasty; OHS, Oxford hip score; UCLA, University of California at Los Angeles Activity Score; HHS, Harris Hip Score, ROM, range of motion; P-M, Postel-Merle-d Aubigne score; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index. Similar Similar (two patients), deep venous thrombosis (three patients), dislocation (four patients), aseptic loosening (one patient), and intraoperative calcar fracture (three patients). Complications in the resurfacing cohort consisted of fracture (one patient), deep venous thrombosis (one patient), and joint infection (one patient). Pollard and coworkers compared a group of 53 patients (54 hips) who received conventional with another group of 51 patients (54 hips) who had undergone. 2 The hips were matched by gender and age at surgery, body mass index (BMI), and preoperative activity level. At a mean follow-up of 80 months (range, 42 to 120 months) for the cohort and 61 months (range, 52 to 71 months) for the resurfacing cohort, the mean Oxford hip scores were similar. However, the patients who underwent resurfacing had significantly higher UCLA activity scores and EuroQol (quality of life) scores than their counterparts who underwent conventional. Mont and associates compared two matched groups of 54 patients, who had undergone either conventional or metal-on-metal. 19 The patients were matched by age, gender, diagnosis, BMI, preoperative Harris hip score, and length of follow-up. At a mean follow-up of 40 months (range, 24 to 60 months), the Harris hip, pain, and satisfaction scores were similar, but the patients who underwent resurfacing had higher activity scores. The investigators concluded that the higher postoperative activity scores may have been a result of selection bias, as the resurfacing cohort also had a significantly higher mean preoperative activity score, and patients who engaged in high activity levels preoperatively were more likely to request resurfacing. Lavigne and colleagues conducted a randomized controlled study that compared 81 patients who underwent resurfacing with 71 patients who underwent conventional. 20 The functional results, satisfaction ratings, ROM scores, and complication rates were similar at the 1 year follow-up. However, the mean overall activity score of the resurfacing cohort was substantially higher than that of the group (p < 0.001), and a substantially higher number of patients who underwent resurfacing returned to moderate

6 Bulletin of the NYU Hospital for Joint Diseases 2009;67(2): or high activity levels (77%), compared with patients who underwent conventional (39%). The preoperative activity levels of the two groups were similar, so the investigators concluded that the large head of the resurfacing prostheses might confer greater joint stability; this might be a factor that led to increased activity levels. In separate presentations, the same investigators reported that the patients who underwent resurfacing had significantly shorter hospital durations (6 vs 5 days), significantly lower rates of dislocation at the 24-month follow-up (0 vs 4 dislocations), and similar ranges of motion, compared with the patients who underwent conventional arthroplasty. Stulberg and coworkers compared a group of 337 patients who underwent resurfacing with 266 patients who received conventional, and found that the patients who underwent resurfacing experienced pain for a longer postoperative period, but increased their functional status sooner than the patients who underwent conventional arthroplasties. 21 At 6 weeks following the procedure, the patients who underwent resurfacing reported a greater prevalence of pain, and so the Harris hip scores were significantly lower. However, the mean Harris hip function subscore was higher for the resurfacing group at the 6- and 12-month follow-up assessments, although the Harris hip scores of the two groups were not significantly different. By 24 months postoperatively, the two groups had similar functional scores, and the Harris hip scores were comparable. Haddad and associates examined a series of tests of high-level hip function, including an unsupported single leg stance for one minute, unsupported step-ups onto 40-cm blocks, lateral step-ups, and a hop test. 22 The comparison of 40 patients who underwent resurfacing with 40 patients who received conventional revealed that the two groups had similar preoperative scores on all tests, but that the resurfacing cohort had dramatically higher scores on the hop test and both step-up tests at 6 weeks, as well as 2 years after the procedure. Gait Studies There were three gait studies and one study that assessed the postural balance in and patients. All these studies showed similar or better outcomes for compared to their counterparts. In a retrospective, gender-matched study, Mont and colleagues compared the walking velocity as well as extensor and abductor moments of 15 patients who underwent procedures to those of 15 patients who received procedures and 10 patients with osteoarthritis who were not treated surgically. 23 The study found that at a mean 13-month follow-up, patients in the group walked faster and with more normal gaits by these measures than patients in either the group or the control group. Two more recent studies evaluated the gait patterns of and patients using slightly different parameters. Lavigne and coworkers examined the distribution of energy generation and absorption in three groups of patients:, with large-diameter heads, and with small-diameter heads. 24 They found that patients who received and large-diameter head returned to more normal gait patterns than patients who had small-diameter femoral heads. Shimmin and associates compared and patients who had Harris hip scores of 100 to age-matched asymptomatic control patients. 25 They reported that there was no significant difference in gait, at either fast walking or jogging paces, among any of the groups. The postural balance study by Nantel and colleagues reported that s had greater medial to lateral centers of pressure and mass displacement during dual stance when compared to (p < 0.05). 26 They suggested that these differences may be attributed to the larger bearing component for and the better anatomical preservation when compared to. Conversions of Failed Resurfacings There were two studies that compared the outcomes of failed procedures, then converted to conventional s, to patients who had primary conventional. These two studies, by Ball and coworkers 27 and McGrath and associates, 28 assessed the concept that revisions of resurfacings are comparable to primary s. Ball and colleagues compared the revisions of 21 resurfacings (in 20 patients) to a group of 58 hips (in 64 patients) who had undergone primary, all by the same surgeon. 27 They found no significant difference between the two groups in terms of operative blood loss, operative time, or complication rates. At mean follow-up times of 46 months for the conversion group and 57 months for the primary group, there were also no significant differences between the groups in terms of Harris hip scores; UCLA pain, walking, or activity subscores; or the SF-12 scores. Ball and coworkers concluded that claims of the ease, safety, and efficacy of surgical revision of resurfaced hips were justified. McGrath and associates 28 compared the perioperative factors, complications, and clinical as well as radiographic outcomes of 39 patients whose resurfacings were converted to to a group of primary patients matched by gender, age, BMI, and preoperative Harris hip score, all performed by the same surgeon. They found mean operative time for the conversions were longer by 19 minutes, but all other perioperative measures were similar. At a mean followup of 45 months, the Harris hip scores of the two groups were similar (92 for the conversion group; 94 for the primary group). They also concluded that the conversion of failed resurfacings can be considered comparable procedures with similar outcomes to primary s. Discussion There are limitations to the present analysis that include the level of evidence of the studies reviewed, as there were few randomized, prospective trials. Another limitation is the

7 126 Bulletin of the NYU Hospital for Joint Diseases 2009;67(2):120-7 length of follow-up for the studies. Conventional procedures have long-term data stretching past the 20-year mark. In contrast, the most recent generation of resurfacing devices has not yet been in use long enough to provide comparable long-term follow-up data. Despite these limitations, the early findings in these comparative studies appear promising and suggest that provides similar and in some cases potentially improved outcomes compared to. As research on the comparative efficacy of the two procedures continues, attention should be paid, in particular, to the types of measures used to evaluate the outcomes. As some investigators have begun to hypothesize, including Haddad and colleagues, 22 the measures traditionally used to evaluate outcomes might not be as effective at distinguishing between the outcomes of the two procedures. If, as some surgeons suggest, resurfacing returns patients earlier to higher activity levels, more challenging clinical tests of function might be necessary to see the true comparative benefits and limitations of each procedure. In summary, there is renewed and growing interest in the current generation of on the part of both surgeons and patients. Based on this interest, there have been a number of studies in the last decade that have been conducted to directly compare the outcomes of this procedure to. Our review of this literature suggests that basic science, radiographic, clinical, and gait outcomes are similar between the two procedures. Disclosure Statement Michael A. Mont, M.D., is a consultant for Stryker Orthopedics and Wright Medical Technology. The other authors certify that they have no commercial associations (e.g., consultancies, stock ownership, equity interest, patent and licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. Each author certifies that his or her institution has approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research. References 1. Learmonth ID, Young C, Rorabeck C. The operation of the century: total hip replacement. Lancet. 2007;370: Pollard TC, Baker RP, Eastaugh-Waring SJ, Bannister GC. Treatment of the young active patient with osteoarthritis of the hip. A five- to seven-year comparison of hybrid total hip arthroplasty and metal-on-metal resurfacing. J Bone Joint Surg Br. 2006;88: Treacy RB, McBryde CW, Pynsent PB. Birmingham hip resurfacing arthroplasty. A minimum follow-up of five years. J Bone Joint Surg Br. 2005;87: Hing CB, Back DL, Bailey M, 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: Amstutz HC, Thomas BJ, Jinnah R, Treatment of primary osteoarthritis of the hip. A comparison of total joint and surface replacement arthroplasty. J Bone Joint Surg Am. 1984;66: Gore DR, Murray MP, Gardner GM, Sepic SB. Hip function after total vs. surface replacement. Acta Orthop Scand. 1985;56: Meldrum RD, Maiers GP 2nd, Feinberg JR, Long-term outcome of surface replacement with comparison to an ageand time-matched primary total hip arthroplasty cohort. J Arthroplasty. 2008;23: Liu F, Udofia IJ, Jin ZM, Comparison of contact mechanics between a total hip replacement and a hip resurfacing with a metal-on-metal articulation. Proceedings of the Institution of Mechanical Engineers, Part C. 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8 Bulletin of the NYU Hospital for Joint Diseases 2009;67(2): Haddad FS, Bull J. Hip resurfacing has superior sustained functional outcomes when compared to total hip arthroplasty. Proceedings of the 75th Annual American Academy of Orthopaedic Surgeons Meeting; March 5-9, 2008; San Francisco, California, p Mont MA, Seyler TM, Ragland PS, Gait analysis of patients with resurfacing hip arthroplasty compared with hip osteoarthritis and standard total hip arthroplasty. J Arthroplasty. 2007;22: Lavigne M, Vendittoli PA, Nantel J, Prince F. Gait analysis in three types of hip replacement. Proceedings of the 75th Annual American Academy of Orthopaedic Surgeons Meeting; March 5-9, 2008; San Francisco, California, p Shimmin AJ, Bennell K, Wriglet T, Gait analysis comparison of the functional outcome of hip resurfacing and total hip replacement. Proceedings of the 75th Annual American Academy of Orthopaedic Surgeons Meeting; March 5-9, 2008; San Francisco, California, p Nantel J, Termoz N, Centomo H, Postural balance during quiet standing in patients with total hip arthroplasty and surface replacement arthroplasty. Clin Biomech (Bristol, Avon). 2008;23: Ball ST, Le Duff MJ, Amstutz HC. Early results of conversion of a failed femoral component in hip resurfacing arthroplasty. J Bone Joint Surg Am. 2007;89: McGrath MS, Marker DR, Seyler TM, Surface replacement is comparable to primary total hip arthroplasty. Clin Orthop Relat Res. 2009;(467): Loughead JM, Starks I, Chesney D, Removal of acetabular bone in resurfacing arthroplasty of the hip: a comparison with hybrid total hip arthroplasty. J Bone Joint Surg Br. 2006;88: Girard J, Vendittoli PA, Roy AG, Lavigne M. [Femoral offset restoration and clinical function after total hip arthroplasty and surface replacement of the hip: a randomized study]. Rev Chir Orthop Reparatrice Appar Mot. 2008;94: [French] 31. Lavigne M, Vendittoli P, Roy A, Lusignan D. A randomized study comparing surface replacement arthroplasty to total hip arthroplasty. Proceedings of the 75th Annual American Academy of Orthopaedic Surgeons Meeting; March 5-9, 2008; San Francisco, California, p Lavigne M, Mottard S, Girard J, Vendittoli PA. Range of motion after hip resurfacing and : a single-blind randomized clinical study. Proceedings of the 75th Annual American Academy of Orthopaedic Surgeons Meeting; March 5-9, 2008; San Francisco, California, p