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When is the Right Time to Resurface?

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Abstract

With the recent approval of 2 metal-on-metal hip resurfacing devices in the United States, hip resurfacing is being performed more commonly. As with most orthopedic procedures, appropriate indications are the key to successful outcomes and avoiding complications such as femoral neck fracture. A review of the literature suggests that optimal results, and the lowest risk of early failure, are obtained in men with osteoarthritis who are younger than age 55 years. This article reviews general considerations for choosing appropriate candidates for metal-on-metal hip resurfacing, including relative and suggested contraindications to the procedure.

With the recent FDA approval of 2 metal-on-metal hip resurfacing devices (Birmingham Hip Resurfacing, Smith & Nephew, Memphis, Tenn, and Coromet 2000, Stryker, Mahwah, NJ), hip resurfacing is now a widely available option for surgeons in the United States. Previously, the use of these devices had been limited to surgeons performing hip resurfacing as part of investigational device exemption studies or on a so-called “off-label” basis and thus not routinely performed as part of general orthopedic practice. As is true with most orthopedic procedures, appropriate indications are the key to successful results. The goal of this article is to outline appropriate indications for metal-on-metal hip resurfacing to assist the orthopedic surgeon in appropriate patient selection in an effort to optimize outcomes and reduce the risk of complications. A structured review on patient selection for hip resurfacing that includes additional information on the use of patient risk indices, radiographic bone assessment, bone mineral density, femoroacetabular impingement, and a more thorough discussion of the use of hip resurfacing in patients with a history of childhood hip disorders has been performed by Nunley et al.¹

General Considerations

The most basic indications for hip resurfacing are the same as those for total hip arthroplasty (THA); end-stage arthritis of the hip that has been recalcitrant to nonoperative treatment. The patient should have corroborative physical examination findings and radiographic changes and be willing both to undergo the procedure and of adequate general medical health to tolerate a major elective operative procedure. The primary decisions to be made involve differentiating the appropriate candidate for hip resurfacing from patients who are better served with conventional THA.

Given the outstanding results achieved with conventional THA,^2-5 surgeons indicating a patient for a metal-on-metal hip resurfacing must carefully weight the risks and benefits of the 2 procedures before recommending 1 treatment option over the other. Patients who typically do most poorly with conventional THA are young, active patients. These patients been shown to have a higher risk of reoperation and failure secondary to wear of the bearing surface, osteolysis, and fixation failure of the prosthetic components themselves.³ In this population, an alternative to conventional THA seems most logical. Men may also have vocational requirements (such as heavy manual labor) that are incompatible with longevity of a conventional THA. Younger patients may also have a desire to return to running and contact sports, activities that are not recommended by most US surgeons after conventional THA.⁶

Among the purported benefits of hip resurfacing is preservation of proximal femoral bone stock, should future revision be required. As in general, the results of THA have been shown to be time limited. This may be particularly beneficial in the younger patient with a longer life expectancy. Conversion of a failed resurfacing secondary to a femoral-sided failure to a conventional THA has been reported to be straightforward because the monoblock acetabular component can usually be retained, with outcomes that are equivalent to that of a primary THA.⁷ Other potential advantages of hip resurfacing include a lower risk of dislocation (secondary to the use of a more physiologically sized femoral head), improved range of motion, and the use of a more wear-resistant bearing surface. These advantages, however, all can be obtained from conventional THA with a metal-on-metal bearing surface, particularly if a large femoral head is used.

The last potential benefit of hip resurfacing is the return to unlimited activities that include both running and heavy manual labor. Several recent studies suggest that metal-on-metal hip resurfacing is compatible with the return of patients to high-level impact and running sports and heavy manual labor.^8-10 In the 1 study that compared return to sporting activity between metal-on-metal hip resurfacing and conventional THA, patients who had undergone hip resurfacing had higher levels of activity and a lower risk of failure.⁹ The results of this study must be considered carefully, however, because the femoral component was cemented (most US surgeons prefer cementless femoral components for their active patients) and the bearing surface for the THAs was not a metal-on-metal articulation. Other studies have suggested similar results with equivalent scores on most outcome scales; however, patients who had undergone resurfacing had higher activity levels.¹¹

The majority of early revisions after hip resurfacing are related to femoral neck fractures. Although retention of the femoral neck is associated with many of benefits of hip resurfacing, it is also responsible for the majority of early failures. The surgeon must carefully weigh a given patient’s risk for femoral neck fracture (which seems to be related to the bone quality of the proximal femur)¹² when deciding between hip resurfacing and conventional THA. Although technical issues (including femoral neck notching, varus component placement, and incomplete seating of the femoral component) have been associated with femoral neck fractures, patient selection factors are also clearly important in avoiding this complication.^12-15 The final general consideration is a given patient’s ability to handle the metal ions generating from wear of the bearing surface.

Patient Related Factors

Age

Patient age has been clearly shown to be related to the risk of complications after hip resurfacing and is among the most important factors to consider. The Australian Hip Registry has shown that the risk of early revision approximates 2.0% for conventional THA, whereas it is 2.8% for hip resurfacing.¹⁶ However, patients who are younger than age 55 at the time of the index procedure have a risk of early revision that is equivalent to that of conventional THA. In comparison, patients in the 55- to 64-year-old group have a revision risk of 3.0%, which climbs to 4.0% for patients in the 65- to 75-year-old range and to 8.5% in patients older than age 75 years. Age is probably an indicator of bone quality, and thus surgeons should carefully consider offering resurfacing to patients older than age 65 years, with the lowest expected complication rates in those younger than age 55.

Sex

Female sex has similarly been associated with an increased risk of complications after hip resurfacing and logically relates to the strength of the remaining proximal femur.¹² As with patient age, patient sex has a strong influence on the risk of early revision after hip resurfacing compared with conventional THA, according to the Australian Hip Registry. Women have an early revision rate at 3 years, which is more than twice that of their male counterparts (4.2% compared with 2.0%).¹⁶ Similarly, Shimmin and Back in their review of 50 femoral neck fractures from the Australian Registry between 1999 and 2004 estimated the risk of femoral neck fracture was nearly twice as high among women compared with men.¹⁵ Marker et al also suggested that female sex was a risk factor for femoral neck fracture and failure.¹³

Body Mass Index (BMI)

Obesity (BMI > 30) has been considered a relative contraindication to hip resurfacing. However, recent work has suggested that excellent outcomes in this patient population can be achieved, with a reported 5-year survivorship of 98.6%.¹⁷ The investigators of this work suggest that higher BMI leads to increased bone density. Other groups, however, have found that obesity is a risk factor for both femoral neck fracture and early failure.¹³ Although higher BMI may increase bone density, obesity may compromise the surgical exposure, leading to increased difficulty with femoral head preparation and/or acetabular exposure. Thus careful consideration should be given to performing hip resurfacing in this patient population.

Diagnosis

Figure 1: Preoperative radiograph of a large femoral head cyst.

The majority of reports describe the outcomes of hip resurfacing in patients with osteoarthritis, and it is in this population that results seem to be optimal.⁸ Patients with osteonecrosis of the femoral head would seem to be ideal for an alternative to conventional THA because they are often young and active, having been shown to have higher rates of failure secondary to component loosening and wear-related complications.^18,19 Osteonecrosis has been considered a relative contraindication to hip resurfacing secondary to concerns of poor bony support beneath the resurfacing femoral head and progression of the osteonecrotic process secondary to the presence of continued risk factors or the resurfacing procedure itself. Even when performed by experienced surgeons, the results of hip resurfacing seem to be inferior when performed for osteonecrosis as opposed to osteoarthritis, with a reported survivorship of 93.2% at 6.1 years.²⁰ Successful outcomes logically relate to the amount of osteonecrotic head involvement, and cases should be judged on an individual basis, with consideration given to conventional THA when larger amounts of the femoral head are involved in the disease process or if intraoperatively, the quality of the remaining head is poor. Patients with osteonecrosis should be advised that their risk of failure may be higher than those with osteoarthritis.

Anatomic Considerations

Femoral Head Cysts

Figure 2: Intraoperative photograph showing a large femoral head cyst. The procedure was converted to a standard THA.

Femoral head cysts >1 cm in diameter have been shown to be correlated with a higher risk of femoral neck fracture,^13,20,21 and if these are identified preoperatively (Figure 1) or intraoperatively (Figure 2), conventional stemmed THA should be performed.

Acetabular Dysplasia

Hip resurfacing can be considered for patients with mild to moderate acetabular dysplasia (Crowe I or II); however, in patients with more severe degrees of dysplasia, inadequate support may exist for initial acetabular component stability. Although some resurfacing acetabular components offer the potential for adjunctive screw fixation, most do not, and rely on initial press-fit fixation only until bone ingrowth occurs. Further, in patients with leg length discrepancies >1 cm or high-riding hip dysplasia, conventional THA is both more flexible (allowing for femoral shortening if required) and has a greater ability to equalize leg lengths (Figure 3). As discussed below, acetabular dysplasia is often associated with femoral head abnormalities, and a higher risk of femoral component loosening has been identified in this patient population.²¹

Femoral Head Shape

The easiest femoral heads to prepare for a resurfacing are those with a relatively round femoral head and a large head:neck ratio (Figure 4). There are a number of childhood hip diseases (such as Legg-Calve-Perthes) that lead to malformation of the femoral head and can similarly lead to difficulties with femoral head preparation (Figure 3).

Femoral Canal Size and Shape

Figure 5: Patient with high femoral offset that will be difficult to restore using a conventional stemmed THA.

Patients with either a very small femoral canal, which would require substantial femoral canal reaming to fit even a tapered conventional stemmed femoral implant, or those with a very large canal, which would require a very large conventional hip stem (particularly if cementless fixation is desired), are also potentially good candidates for hip resurfacing to avoid these potential problems. Similarly, in patients with extremely high native offset, it may be easier for the surgeon to restore appropriate hip biomechanics with hip resurfacing (Figure 5). Patients with proximal femoral deformity, retained hardware, or obliteration of the femoral canal may also be good candidates for hip resurfacing to avoid the potential complexities associated with a traditional stemmed femoral component in these situations.

Contraindications and Relative Contraindications

The most universally agreed-on contraindication to hip resurfacing is impaired renal function secondary to an inability to process the metallic ions generated by wear of the bearing surface. Similarly, patients with a known metal hypersensitivity should be treated with an alternate bearing surface and not a metal-on-metal hip resurfacing. A final contraindication includes elderly patients with a limited life span and poor proximal femoral bone stock, in whom conventional THA should reasonably last the patient their lifetime and in whom the risk of femoral neck fracture would be unreasonable. As described previously, patients with a leg-length discrepancy >1 cm are similarly better managed with conventional THA, which has improved flexibility to restore appropriate leg lengths.

Women of Childbearing Age

The primary concern regarding hip resurfacing in younger women is how the increased levels of cobalt and chromium normally associated with a metal-on-metal bearing could effect fetal development. Recent work suggests that although cobalt and chromium do cross the placenta, it exhibits a “modulatory” effect, decreasing their concentration.²² Although this study and others²¹ have reported normal childbirth in patients who have undergone metal-on-metal hip resurfacing, caution should be exercised in this patient population until more data are available.

Conclusions

In the final analysis, the decision to choose metal-on-metal hip resurfacing over conventional THA is complex and must be considered carefully given the outstanding results with conventional stemmed femoral components. The results of hip resurfacing are best (and the complication rate lowest) in men younger than age 55 with osteoarthritis. Given that these same patients are widely considered to be at high risk for complications and failure with conventional THA, they are most appropriate for the procedure. Surgeons are encouraged to educate their patients regarding the risks and benefits of both procedures so that they can participate in the decision-making process. Careful patient selection for hip resurfacing will lead to optimal patient outcomes and a low risk of complications.

References

1. Nunley RA, Della Valle CJ, Barrack RL. Is patient selection important for hip resurfacing? Clin Orthop Relat Res. 2009;467(1).
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Authors

Dr Della Valle is from the Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, Illinois; and Drs Nunley and Barrack are from the Department of Orthopaedic Surgery, Washington University, St Louis, Missouri.

Dr Della Valle is a consultant for Zimmer and has received paid travel from Smith & Nephew and Stryker Orthopaedics. Dr Barrack receives royalties from Smith & Nephew. Drs Nunley and Barrack have received institutional research support from Smith and Nephew, and Dr Della received institutional research support from Zimmer.

Correspondence should be addressed to Craig J. Della Valle, MD, Rush University Medical Center, 1725 West Harrison, Suite 1063, Chicago, IL 60612.