Metal-on-metal hip resurfacing shows excellent clinical outcomes
By Jennie McKee
Concerns of component loosening and biological incompatibility of the alloy constituents led to the phasing-out of first generation metal-on-metal bearings after their introduction in the 1960s. Improved metal-on-metal prosthesis technology has led to the reemergence of resurfacing as a viable option for total hip arthroplasty. This new generation of metal-on-metal designs is showing excellent mid-term clinical outcomes across various patient populations, according to poster exhibit P034.
A limited number of studies evaluate the results of current metal-on-metal designs. As part of a comprehensive evaluation under an investigational device exemption granted by the U.S. Food and Drug Administration, this study provides the clinical and radiographic outcomes of a metal-on-metal resurfacing at mid-term follow-up.
85 percent successful outcome
Of 1,020 metal-on-metal hip resurfacings (909 patients) performed by 10 orthopaedic surgeons between August 2000 and August 2003, 85 percent (867 hips) were considered to have a successful clinical outcome at final follow-up (mean: 51 months; range: 33 months to 69 months) based on a Harris Hip Score greater than or equal to 80 points.
The mean Harris Hip Score improved from 47 points (range: 3 to 92) preoperatively to 87 points (range: 3 to 96) postoperatively, p < 0.001. The mean final follow-up SF-12 mental component score was 55 points (range: 19 to 67) and the physical component score was 50 points (range: 17 to 64).
Indications for surgery
The most common indications for surgery were primary osteoarthritis (77 percent), osteonecrosis (11 percent), hip dysplasia (7 percent) and trauma (4 percent). The mean patient age was 50 years (range: 15 years to 81 years). The mean body mass index (BMI) was 27.5 (range: 16.3 to 48.2). Researchers evaluated all patients using Harris Hip Scores and SF-12 Health surveys. Patient radiographs were reviewed for alignment, loosening and lucencies.
In response to an investigator meeting in October 2002, the device manufacturer made thinner acetabular shells available for use.
In addition, the indications for inclusion were modified (patients with a BMI greater than 35 and those with osteopenia were excluded) and the technique was changed (only cementing, no notching, was allowed).
Complications and revisions
Forty-five hips (4 percent) required revision surgery, with the most common indications being fractures (19 hips) and component loosening (12 hips). One patient experienced protrusio acetabuli which required surgical revision. Postoperative dislocations occurred in 18 hips (1.8 percent). Radiolucencies were documented in 157 hips (15 percent), although none were progressive.
After changes were made in the prosthetic design, indications and technique, the overall complication rate was reduced. The revision rate dropped from 4.7 percent to 2.8 percent, and the rate of femoral neck fractures was reduced from 2.8 percent to 0.7 percent.
The lead researcher is Michael A. Mont, MD, of Baltimore; additional researchers include Harlan C. Amstutz, MD, and Thomas P. Schmalzried, MD, both of Los Angeles; Harold S. Boyd, MD, of Salem, Ore.; Thomas P. Vail, MD, of Durham N.C.; Edward A. Sparling, MD, of Vancourver, Wash.; William R. Kennedy, MD, of Sarasota, Fla.; Victor M. Goldberg, MD, of Cleveland, and Thorston M. Seyler, MD, of Baltimore. Dr. Mont received research support from Wright Medical Technology; all the researchers, except for Dr. Seyler, serve as consultants to Wright Medical Technologies. Dr. Seyler reports no conflicts of interest.