Osteoeconomics: Reconsidering the role of hip resurfacing in the 21st century
Despite lingering concerns, hip resurfacing is still promising for active patients younger than 60.
Concern with longevity in total hip replacement has long revolved around particle wear and resultant osteolysis. With this in mind, surgeons interest in bone-preserving hip replacement procedures has been fueled by patient demand and increasingly active lifestyles.
Until last year, limited resurfacing involving the femoral head was the only available option approved by the FDA. Now there are two available hip resurfacing systems to treat degenerative hip disease. Like many late designs in conventional total hip arthroplasty (THA), metal-on-metal hip resurfacing allows use of large diameter femoral and acetabular components. In addition, less native bone is removed (Figure 2), which is unique to hip resurfacing.
Hip resurfacing dates back several decades. Concerned about aseptic loosening, surgeons found no implant appeared to deliver a theoretic lifetime beyond 20 years. Early hip resurfacing designs used thin polyethylene that was prone to particle wear. Existing metal-on-metal designs were hampered by machine tolerancing, resulting in equatorial contact between the femoral head and acetabular articulation, leading to excessively high rates of particle debris and wear.
Metal-on-metal use then fell out of favor due to the evolution of the Charnley low-friction arthroplasty. Long-term data, however, have not supported the superiority of metal on polyethylene.
Images: Dayton MR
In a 20-year survival follow-up of both McKee-Farrar and Charnley THAs, Jacobsson et al found superior survival rates of metal-on-metal implants during this period of 77%, in contrast with survival of Charnley low-friction arthroplasty at 73%.
Advantages of metal-on-metal bearing surfaces include low wear rates, a capacity for self-polishing, and the potential for larger head and cup sizes.
Brown et al reported in 2002 survival rates between 20 and 28 years for between 74% and 84% of patients, respectively.
Renewed interest in metal-on-metal surface bearings began in the late 1980s. This resurgence stemmed from noted metal-polyethylene linear wear rates of roughly 0.1 mm per year published by Jacobsson et al.
Smith-Peterson, Judet and McKee introduced first-generation metal-on-metal articulations, and Freeman, Amstutz and Moller followed with second-generation implants. The most recent generation of hip resurfacing implants was developed in conjunction with British surgeons such as McMinn.
There are unique issues that bear consideration in hip resurfacing, including patients comfort level with a metal-on-metal bearing surface and the risk of elevated cobalt and chromium ion levels. Dramatic improvements in design have helped the theoretical survivability of hip resurfacing. Polar bearing contact now allows uniform fluid levels to coexist between the femoral head and the acetabular components, thus enhancing optimal fluid film lubrication.
A second issue concerns the technical difficulty in placing these unique implants. Osteopenic bone and formation of multiple cysts in the femoral head may predispose patients to complications such as fracture (Figure 3).
Contrasts between hip resurfacing and THA reveal that hip resurfacing is a procedure that may involve large incisions with extensive exposure. Longer intraoperative time may be necessary and additional tissue releases are required. While the femoral component is cemented, the acetabular component is not, and it promotes rapid bone ingrowth and ongrowth without taking additional acetabular bone compared to primary total hip arthroplasty.
Hip resurfacing shortcomings
Limitations in hip resurfacing do exist, including the inability to change femoral offset or leg length. Unusual morphology of the proximal femur is considered a potential contraindication (Figure 4). You should weigh additional concerns for patients who are interested solely in the cosmetic aspect of minimally invasive techniques, have pre-existing leg length inequality of greater than 1 cm, relative varus neck shaft angle, poor acetabular bone coverage or excessive cyst formation in their osseous structures.
Contraindications also exist for bone with a density T-score of less than -2.5. Females of childbearing age are not candidates due to metal ion dissemination, nor are patients who required complex techniques in primary total hip arthroplasty, such as in dysplastic hip disease.
Failure mechanisms of hip resurfacing consist mostly of femoral neck fractures. Predisposition for fracture includes notching during femoral reaming, large femoral head cysts, female gender, osteoporotic bone, and aggressive osteophyte removal from the femoral head-neck junction.
Huo and Gilbert reported fracture rates in excess of 20% in their initial experience with subsequent reduction to 1% to 2% in more recent data. Failure mechanisms may also include aseptic loosening, advanced osteonecrosis or varus positioning. Amstutz et al, and Back et al, published outcomes of up to 60 months with survivability ranging from 94% to 99% . Australian hip registry data from 2005 indicate revision rates between 2% and 4%.
A viable technique
Hip resurfacing is a viable technique where failure rates are comparable to THA, but distinct fracture risk does exist for patients who are not appropriate candidates. Designs of similar head-cup large articulations with conventional femoral stems exist in the event that contraindications prevail in otherwise appropriate candidates. Implants with significant varus placement should be avoided, as should hip resurfacing in late-stage collapse or progressive osteonecrosis following surgery. Extensive osteopenia, bone loss or cysts in the femur may also predispose to failure.
Two hip resurfacing devices have been approved by the FDA and additional designs have been submitted for approval. The success of hip resurfacing is reliant upon responsible surgeon training, prudent patient selection and education. Additional technologies which may enhance the use of hip resurfacing include computer navigation for appropriate component placement a factor likely to improve outcomes. Despite stated concerns, hip resurfacing appears to be a promising treatment for active patients younger than 60 years of age.
For more information:
- Michael R. Dayton, MD, at the University of Colorado Health Science Center, can be reached at Box 6510, Mailstop F722, Aurora, CO 80045; 720-848-2167; e-mail: Michael.Dayton@UCHSC.edu. He is a paid consultant to Smith & Nephew.
- Amstutz HC Beaule PE, Dorey FJ, LeDuff MJ, Campbell PA, Gruen TA: Metal-on-metal hybrid surface arthroplasty: two to six-year follow-up study. J Bone Joint Surg Am. 2004;86(1):28-39.
- Australian National Joint Registry Annual Report 2005.
- Back DL, Dalziel R, Young D, Shimmin A: Early results of primary Birmingham hip resurfacings: An independent prospective study of the first 230 hips. J Bone Joint Surg Br. 2005;87:324-329.
- Brown SR, Davies WA, DeHeer DH, Swanson AB: Long-term survival of McKee-Farrar total hip prostheses. Clin Orthop. 2002;(402):157-63.
- Huo MH, Gilbert NF: Whats new in hip arthroplasty. J Bone Joint Surg Am. 2005;87(9):2133-46.
- Jacobsson SA, Djerf K, Walstrom O: Twenty-year results of McKee-Farrar versus Charnley prosthesis. Clin Orthop. 1996;329(Suppl):S60-8.