Use of metal-on-metal total hip resurfacing for the treatment of osteonecrosis of the femoral head

Is patient selection important for hip resurfacing?

The optimal implant option for hip arthroplasty in the young, active patient remains controversial. There has been renewed interest for metal-on-metal hip resurfacing due to improved design and manufacturing of implants, better materials, enhanced implant fixation, theoretical advantages over conventional total hip arthroplasty, and recent Food and Drug Administration approval of two devices. Recent studies indicate satisfactory short- and midterm clinical results (1- to 10-year followup) with low complication rates, but there is a learning curve associated with this procedure, a more extensive surgical approach is necessary, and long-term results have yet to be determined. Proper patient selection may help avoid complications and improve patient outcomes. Patient selection criteria in the literature appear based predominantly on theoretical considerations without any consensus on stratifying patient risk. The most commonly reported complications encountered with hip resurfacing include femoral neck fracture, acetabular component loosening, metal hypersensitivity, dislocation, and nerve injury. At the time of clinical evaluation, patient age; gender; diagnosis; bone density, quality, and morphology; activity level; leg lengths; renal function; and metal hypersensitivity are important factors when considering a patient for hip resurfacing. Based on our review, we believe the best candidates for hip resurfacing are men under age 65 with osteoarthritis and relatively normal bony morphology.

LEVEL OF EVIDENCE

Level V, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Metal-on-metal hip resurfacing arthroplasty: a review of periprosthetic biological reactions

Metal-on-metal hip resurfacing arthroplasty has undergone a recent resurgence as an alternative treatment option for young and active patients with significant osteoarthritis. The claimed advantages of metal-on-metal hip resurfacing arthroplasty include lower wear rate, preservation of bone stock for subsequent revision procedures, restoration of anatomic hip mechanics, and enhanced stability due to the larger diameter of articulation. A disadvantage, however, is that the metal-on-metal resurfacing releases large amounts of very small wear particles and metal ions. The long-term biological consequences of the exposure to these Co-Cr particles and ions remain largely unknown. The purpose of this review is to provide an overview of the current literature on the adverse periprosthetic biological reactions associated with metal-on-metal hip resurfacing arthroplasty.

[Hip resurfacing: current state of knowledge]

SUMMARY

The tribologic quality of metal-on-metal bearings has enabled a second generation of hip resurfacing techniques. Compared with a conventional hip prosthesis, this type of arthroplasty has many advantages: sparing femoral (and acetabular) bone stock, preservation of hip joint biomechanics (femoral offset, leg length), better recovery for high-level sports activities, easier revision, less risk of dislocation, less risk of extension to the shaft in the event of osteolysis. Hip resurfacing can thus be considered as true "minimally invasive bone surgery". There are however specific complications of resurfacing, including femoral neck fracture and collapse of the femoral head. All of the conventional approaches can be used for hip resurfacing procedures, but a precise operative technique is mandatory. The key to success is a proper position of the femoral piece. Certain biomechanical rules for implantation are required in order to limit the cam effect, spare femoral bone, and maintain harmonious loading. Hip resurfacing can be indicated for young and/or active subjects for whom restoration of hip biomechanics offers a real advantage over conventional hip arthroplasty. The mid-term results have been encouraging, both clinically and radiographically.

Femoral neck fractures after metal-on-metal total hip resurfacing: a prospective cohort study

There has been a renewed interest in metal-on-metal resurfacing total hip arthroplasty. Recent studies have reported high success rates at short to midterm follow-up. Despite these excellent early outcomes, femoral neck fractures have been reported as a major complication after this procedure. The purpose of this study was to identify the incidence of this complication in a prospective cohort of patients. In addition, various demographic and radiographic factors such as surgeon experience, age, sex, body mass index, femoral neck notching, and cysts were assessed as potential risk factors. Between November 2000 and August 2006, 550 metal-on-metal total hip resurfacings were performed by a single surgeon. The absolute risk for femoral neck fracture in this cohort was 2.5%. Of the 14 fractures, 12 occurred in the first 69 resurfacings performed. After this time, the incidence of fracture was 0.4%. Women and obese patients were shown to have higher cumulative incidences of fractures. These findings suggest the need for careful patient selection and surgical technique, especially for surgeons during the early learning curve for this technically difficult surgery.