There is a trend to attempt to minimize the soft tissue exposure/damage in

Tag : joint bearing
With the bearing couple options availablecurrently, the resurfacing implant with its retained calcar bonestock will result in earlier impingement. It has been demonstratedthat head sizes >38 to 40 mm tend not to offer any greater rangeof motion, as they reduce implant-implant impingement but notbone-bone impingement. 2
Another claimed advantage to resurfacing implants is that theyoffer decreased wear rates. It has been well demonstrated that thelarger the bearing couple in a metal-on-metal design, the lower thewear rate, because of multiple issues including the potential toachieve fluid film lubrication. 3 However, with the implants available today, this is not anargument for a resurfacing implant, but for a large-diametermetal-on-metal bearing.
A final claimed advantage of resurfacing implants is a greateractivity level and return to sports. This is anecdotal andunproven. Patient selection and bias prevent accurate assessment ofthis issue. A blinded clinical trial would be required to addressthis question adequately. Disadvantages of Resurfacing
Metal ion exposure is a complex issue with unknown, if any,clinical consequences. Resurfacing implants, like allmetal-on-metal bearing couples, expose patients to elevated metalions. While historically the levels of these ions measured inresurfacing patients were higher than seen in typicalmetal-on-metal THA designs, more recent publications have shownmore equivalent levels. 4
Currently there is a trend to attempt to minimize the soft tissueexposure/damage in performing THA. One need not be performing anytype of minimally invasive surgery, but simply doing only theexposure necessary to perform the procedure safely. With theretention of the femoral head in a resurfacing implant, it ischallenging to perform this procedure with the same exposure asrequired for a THA, and often a larger dissection is required.
Patient selection is critical to the success of any arthroplastyprocedure. Total hip arthroplasty is widely applicable to abroad-based patient population. The same cannot be said ofresurfacing implants. We have been warned to avoid them inosteopenic patients, men older than 65 years, and potentially womenof all ages. Femoral neck fractures continue to be the primary modeof early component failure in these patient populations (Figure 1).More literature and research is required for us to properlyunderstand the indications and contraindications of this procedure,particularly when one considers the tremendous success rates ofconventional THA.
Another concern with respect to resurfacing implants relates torevision. Currently when a surgeon is faced with a revision THA,there is a modular acetabular component in place, and apolyethylene exchange is performed. However, there is no clinicaldata on the outcomes of mating a new large-diameter metal head to aresurfacing shell that has been in vivo for many years. In otherwords, in 20 years when a revision may be required for severalproposed clinical scenarios (eg, late femoral neck fracture; Figure2), and the resurfacing acetabular bearing has already seenmillions of cycles, wear will be present in that bearing. Trying toretain that component will result in a mismatch between the shelland femoral head in terms of tolerances. Perhaps this will beacceptable; however, there will be increased wear and metal ionsproduced, at least in the short term. The data is not available topredict clinical outcomes. Clinical Results
Total hip arthroplasty revolutionized the management of thearthritic hip. One of the greatest advantages of the procedure isits generalizability. While there is an effect of surgeon volume onresults, the procedure has excellent results in many surgeons’hands when applied to a variable group of patients. Can the same besaid of resurfacing? Experts in the field can and do achieveexcellent results. 5,6 However, these are high-volume surgeons with specific referralpatterns to maintain significant numbers of resurfacing procedures.To answer the question of generalizability, one needs to look toregistry data, and the Australian registry, with >9000resurfacings performed, is an excellent source of data. 7 A cursory review of the data demonstrates that early revisions forTHA are slightly below 2% and for resurfacing implants slightlyabove 2%, with the majority of resurfacings failing secondary tofemoral neck fractures. However, the patient populations areobviously different, and when the data is adjusted for age andgender, the relative risk of an early revision is 50% higher with aresurfacing compared to a total hip. Specifically at risk for theresurfacing are patients with a diagnosis other than osteoarthritisand all women and men older than 65 years. Men younger than 65years show equivalence, with resurfacing and total hipsdemonstrating similar results. Therefore, in that very select groupof patients, the early results appear to be similar.
Perhaps the most sobering data to date was presented at the 2007Closed Hip Society meeting 8 discussing the American learning curve in performing hipresurfacings. This paper discussed a safety survey of the first 540Birmingham hip resurfacings performed in the Unites States. Allsurgeons were trained in the technique through industry-sponsoredcadaver workshops, and they had a technical specialist attend theirinitial 10 cases. It is only self-reported data, and thereforeclearly not an overestimation of complications. At 12-monthfollow-up of 83% of the cases, there were 9 nerve injuries, 8dislocations, and 14 early revisions (10 for femoral neckfractures, 2 for dislocations, and 2 for acetabular componentloosening). The authors believe that this complication raterepresents a minimum rate and could possibly increase when theyhave all patients reported on at 1-year follow-up. 8 Conclusion
Hip resurfacing is an attractive concept for both patient andsurgeon. Patients are drawn to preservation of their host bonestock with the idea that this procedure is perhaps less invasiveand will lead to a quicker recovery and higher functional results.Surgeons inherently understand that a hip resurfacing implant withits large metal-on-metal bearing should provide excellent wear overmany years, as well as good stability and range of motionclinically.
The challenge with the introduction of any procedure or implant forthe management of hip arthrosis is that it must be compared to theunparalleled results seen with THA. This is the case when there areno proven additional benefits to the new procedure or implant.
With the exception of the United States, hip resurfacing has beenavailable worldwide for many years. There are many published seriesin the orthopedic literature. Equivalence to THA results has beenseen for only a select group of patients. The Australian registry, 7 reporting on 104,234 primary THAs and 8945 resurfacing implants,has demonstrated a cumulative 5-year revision rate of 2.8% and3.8%, respectively. Revision rates are higher in women of all agesand in men older than 65 years when resurfacing implants areperformed compared with THA. Even more so than in THA, correctpatient selection is critical to resurfacing implant results.
A learning curve is associated with performing resurfacingimplants, as there is with other new orthopedic procedures anddevices. One must balance carefully the predictability ofconventional total hip results with the as-yet unproven benefits ofresurfacing implants when selecting any given individual patientfor this procedure. Additionally, there is a clear need for blindedprospective randomized clinical trials to demonstrate if indeed aresurfacing implant offers any clinical benefit over a THA. References Vendittoli PA, Lavigne M, Girard J, Roy AG. A randomised studycomparing resection of acetabular bone at resurfacing and total hipreplacement. J Bone Joint Surg Br . 2006; 88(8):997-1002. Burroughs BR, Hallstrom B, Golladay GJ, Hoeffel D, Harris WH. Rangeof motion and stability in total hip arthroplasty with 28-, 32-,38-, and 44-mm femoral head sizes. J Arthroplasty . 2005; 20(1):11-19. Dowson D, Hardaker C, Flett M, Isaac GH. A hip joint simulatorstudy of the performance of metal-on-metal joints: Part II: design. J Arthroplasty . 2004; 19(8 suppl 3):124-130. Vendittoli PA, Mottard S, Roy AG, Dupont C, Lavigne M. Chromium andcobalt ion release following the Durom high carbon content, forgedmetal-on-metal surface replacement of the hip. J Bone Joint Surg Br . 2007; 89(4):441-448. Amstutz HC, Beaulé PE, Dorey FJ, Le Duff MJ, Campbell PA,Gruen TA. Metal-on-metal hybrid surface arthroplasty: two tosix-year follow-up study. J Bone Joint Surg Am . 2004; 86-A(1):28-39. Daniel J, Pynsent PB, McMinn DJ. Metal-on-metal resurfacing of thehip in patients under the age of 55 years with osteoarthritis. J Bone Joint Surg Br . 2004; 86(2):177-184. Australian Orthopaedic Association National Joint ReplacementRegistry. Annual Report. http://www.aoa.org.au/docs/njarep07.pdf . Published October 2007. Accessed March 5, 2008. Della Valle CJ, Nunley RM, Raterman SJ, Barrack RL. The Americanlearning curve for total hip resurfacing. Clin Orthop Relat Res . In press. Authors
Dr MacDonald is from London Health Sciences Centre, London,Ontario, Canada.
Dr MacDonald is a consultant for DePuy.
Correspondence should be addressed to: Steven J. MacDonald, MD,FRCSC, London Health Sciences Centre, University Campus, 339Windermere Rd, London, ON, Canada N6A 5A5.