TEC Assessment Index

Metal-on-Metal Total Hip Resurfacing

Assessment Program
Volume 22, No. 3
June 2007

Executive Summary

Background

In patients with debilitating degenerative joint disease of the hip for whom conventional approaches (analgesics, assistive devices, weight loss) are no longer effective, a total hip replacement procedure (arthroplasty) is indicated to relieve pain and restore patient function. Total hip arthroplasty (THA) involves removal of the femoral bone head and neck, revision of the diseased acetabulum, and implantation of a prosthesis with a stemmed femoral component and press-fit acetabular cup. THA is a reliable surgical intervention, with high success rates for joint survivorship and improved function at 5–10 years follow-up using current metal-on-metal (MoM) prostheses. Complications of primary THA are predictable and relatively minor when balanced against beneficial outcomes. By contrast, revision THA is reportedly more complex than primary THA, with significantly longer lengths of stay, higher rates of perioperative complications, unexpected surgical findings, and often a poorer prognosis than the primary procedure.

With advancements in technology, there is renewed interest in total hip resurfacing (HR) using a metal alloy femoral head cap and acetabular cup as an alternative to traditional THA. HR, compared to traditional THA, retains the native femoral bone neck and head and typically removes a comparable amount of bone from the acetabulum, thereby replacing damaged cartilage and associated joint structures. Because the native femoral bone is conserved, revision of a resurfaced joint to a stemmed THA is typically easier and less complicated than revision of a primary THA. Thus, HR may be an advantageous option for younger and/or more active individuals likely to outlive the functional lifespan (10 years or more) of a traditional hip replacement device. However, questions exist about the relative health benefits and harms of HR compared to THA, in the intended population.

Objective

To evaluate available evidence on the benefits and harms of HR as an alternative to THA in comparable patients. The Assessment will consider relative symptomatic and functional improvement, and complications of HR. Key considerations are the durability of HR reflected by revision rates due to joint failure. Throughout the Assessment, unless otherwise indicated, it will be assumed "HR" and "THA" refer to the use of MoM prostheses.

Search Strategy

MEDLINE (via PubMed) search through January 2007 using search string "(resurface OR resurfacing) AND (hip OR hips OR acetabulum OR acetabular)"; additional text searching EMBASE for full-length reports of clinical trials that describe health outcomes (benefits and harms) of HR. Systematic reviews, meta-analyses, manufacturers websites, registries, and the U.S. Food and Drug Administration (FDA) website were additional sources of information.

Selection Criteria

Studies of individuals with advanced DJD of the hip who receive a HR device that report data on clinical outcomes (benefits or harms). Relevant benefits include pain relief and functional improvement; harms include perioperative complications, femoral bone neck fracture, and joint failure requiring revision to THA.

Main Results

The following Summary Table shows the body of evidence on outcomes of HR, organized by data source.

Clinical Data Summary on HR and THA in Patients Younger than 65 Years of Age

One published RCT in patients aged 49–51 years showed substantial and equivalent postsurgical functional improvement in HR and THA recipients, with no significant difference in the rates of revision and perioperative complications at 1 year of follow-up. Australian Orthopedic Association (AOA) Registry data showed a significantly higher 5-year revision rate for HR than for THA in a large number of patients, 90% of whom were younger than 65 years of age. However, the registry data do not distinguish between MoM and other types of THA prostheses, nor are patient demographics well characterized.

Results from 12 published, uncontrolled series of HR consistently demonstrated symptomatic and functional improvements from baseline using standard outcome measures at 2–3 years of follow-up. Individual study revision rates ranged from 0.3% to 5% for most studies, with an overall revision rate of 2.7%. Exceptions were the two smallest studies (60 patients each), which reported revision rates of 8% and 22%. Femoral bone neck fracture accounted for nearly 25% of HR revisions, but its risk can be reduced by patient selection criteria (e.g., adequate bone density, no obesity or prior hip surgery) and experienced surgical technique. Perioperative complications were consistent among the series.

Clinical data in a premarket approval (PMA) application to the FDA by the manufacturer of the Birmingham Hip Resurfacing System (BHR) showed substantial symptomatic and functional improvement from baseline values at 5-year follow-up in a large cohort of patients younger than 65 years of age. Five-year revision rates of 1.13% and 2.25% were reported in two separate BHR cohorts comprising 2,385 (McMinn) and 3,374 (Worldwide) cases, respectively. An overall 8.5% incidence of perioperative complications was reported for the McMinn cohort.

Author's Comments and Conclusions

A substantial body of evidence shows HR is associated with consistent and strong symptomatic and functional improvements at follow-up times up to 5 years. HR results are comparable to those obtained with current generation THA at similar time points in patients younger than 65 years of age. HR differs procedurally from THA in conserving a patient's native femoral bone neck. When HR patients subsequently require revision to THA, the operation is technically similar to primary THA and likely avoids the complications of revision of a primary THA. Thus, the benefits comprise initial HR results as good as THA and a simpler revision to THA when needed. Although longer-term (i.e., greater than 5 years) data on the relative durability of HR compared to THA are unavailable, current evidence is sufficient to conclude that HR is a safe and effective means for initial surgical treatment in younger, properly selected patients who require a total hip replacement. Primary use of HR in the indicated patient subpopulation thus defers standard THA.

Based on the available direct and indirect evidence, the Blue Cross and Blue Shield Association Medical Advisory Panel made the following judgments about whether HR meets the Blue Cross and Blue Shield Association Technology Evaluation Center (TEC) criteria.

1. The technology must have final approval from the appropriate governmental regulatory bodies.

The Birmingham Hip Resurfacing (BHR) System was approved for marketing by FDA on May 9, 2006. It is a single-use device, intended for hybrid fixation, using a cemented femoral head component and cementless acetabular component, intended for use in patients who require primary HR arthroplasty due to:

• non-inflammatory arthritis (DJD) such as osteoarthritis, traumatic arthritis, avascular necrosis, or dysplasia; or
• inflammatory arthritis such as rheumatoid arthritis.

The BHR System is intended for patients who, due to their relatively younger age or increased activity level, may not be suitable for traditional THA due to increased possibility of requiring future ipsilateral hip joint revision.

Two other Class B, non-experimental MoM hip resurfacing devices have received investigational device exemptions. The Cormet Hip Resurfacing System (Corin Medical) was deemed approvable with conditions by an FDA Advisory Panel February 22, 2007; a final FDA decision was not available at the time of this writing*. The Conserve® Plus Total Resurfacing Implant (Wright Medical Technology) may be considered for approval sometime in 2007.

2. The scientific evidence must permit conclusions concerning the effect of the technology on health outcomes.

Evidence for the safety and efficacy of HR is available from more than 14,000 cases with mean follow-up times up to 5 years. Published series of THA using current-generation MoM prostheses (n=526) provide indirect evidence to compare HR and THA in patients younger than 65 years of age. Older series with longer follow-up of first-generation MoM THA (n=1,646) provide guidance on the potential durability of MoM prostheses. However, as the older series include prostheses that are outdated and no longer in clinical use, complications and revision rates may be overestimated and any comparisons must be viewed cautiously. Nonetheless, taken together, sufficient direct and indirect scientific evidence exists to permit conclusions about symptomatic and functional benefits of HR in properly selected patients for whom hip replacement is indicated.

3. The technology must improve the net health outcome

4. The technology must be as beneficial as any established alternatives.

Key Assessment Question: Does HR improve health outcomes, such as pain, joint function, and activities of daily living, among patients with DJD who require hip replacement and are likely to outlive a traditional prosthesis, compared with THA?

A single RCT with 1 year of follow-up provides good direct comparative evidence that HR improves the net health outcome and is as beneficial as THA in comparable patient samples. Additional data from uncontrolled series, the BHR FDA submission, and the AOA Registry, with indirect comparisons to THA, support these conclusions.

Thus, the total body of evidence outlined in this Assessment is sufficient in magnitude of change and consistency of direction to conclude that HR improves the net health outcome and is as beneficial as THA in properly selected individuals who require a total hip replacement and, because of younger age and/or higher activity levels, are likely to outlive the 10 years or more functional lifespan of a traditional prosthetic device. Because HR leaves the femoral bone head and neck largely intact, subsequent revision to THA is typically less complicated than a procedure to replace a primary THA. Therefore, based on published clinical experience with improved current generation MoM THA, and similar 5-year survivorship rates, HR represents a safe and effective means to defer a first THA in properly selected patients who require a total hip replacement and are subsequently likely to require replacement of the ipsilateral hip due to normal wear processes.

5. The improvement must be attainable outside the investigational settings.

Evidence for the safety and effectiveness of HR comes from a range of settings including the device designers and individual practitioners worldwide. An ongoing clinical training program for U.S. orthopedic surgeons is available from the manufacturer of the FDA-approved BHR System and its establishment was a condition of FDA marketing approval. Given this, it may be concluded that clinical benefits of HR will be attainable outside the investigational settings.

Based on the above, use of an FDA-approved metal-on-metal total hip resurfacing device as an alternative to THA in patients who are likely to outlive the 10 years or more functional lifespan of a traditional MoM prosthesis meets the TEC criteria.

* The premarket approval application (PMA) for the Cormet Hip Resurfacing System was approved by the FDA on July 3, 2007.

TEC Assessment Index

KEYWORDS: Orthopedics/PainManagement(category); Surgery/Surgical Alternatives/Interventional Radiology(category; acetabular; acetabulum; AOA; BHR; Birmingham; bone; broken; cemented; cohort; complications; conserve; Conserve; conventional; Cormet; defer; degenerative joint disease; DJD; femoral head; first generation; fracture; functional; hip replacement; hip resurfacing; HR; hybrid fixation; ipsilateral; life span; lifespan; longer-term; McMinn; metal on metal; MoM; OA; orthopaedic; orthopedics; osteoarthritis; postpone; primary; prostheses; prosthetic; registry; revision; second generation; secondary; short-term; stave off; subpopulation; THA; total hip arthroplasty; total hip replacement; wear;