Following the reintroduction of metal-on-metal articulating surfaces for
total hip arthroplasty in Europe in 1988, we developed a surface arthroplasty
prosthetic system using a metal-on-metal articulation. The present study
describes the clinical and radiographic results of the first 400 hips treated
with metal-on-metal hybrid surface arthroplasties at an average follow-up of
three and a half years.
Between November 1996 and November 2000, 400 metal-on-metal hybrid surface
arthroplasties were performed in 355 patients. All femoral head components
were cemented, but only fifty-nine of the short metaphyseal stems were
cemented. The patients had an average age of forty-eight years, 73% were men,
and 66% had a diagnosis of osteoarthritis. Clinical and radiographic follow-up
was performed at three months postoperatively and yearly thereafter.
The majority of the patients returned to a high level of activity,
including sports, and 54% had activity scores of >7 on the University of
California at Los Angeles activity assessment system. Kaplan-Meier
survivorship curves demonstrated that the rate of survival of the components
at four years was 94.4%. For patients with a surface arthroplasty risk index
score of >3, the rate of survival of the components at four years was 89%
compared with a rate of 97% for those with a score of =3. The patients with
a higher risk index were 4.2 times more likely to undergo revision to a total
hip replacement at four years. Twelve hips (3%) had a revision to a total hip
replacement. Seven of the twelve hips were revised because of loosening of the
femoral component, and three were revised because of a femoral neck fracture.
Substantial radiolucencies were seen around sixteen uncemented metaphyseal
femoral stems. No femoral radiolucencies were observed among the hips in which
the metaphyseal stem was cemented. The most important risk factors for femoral
component loosening and substantial stem radiolucencies were large femoral
head cysts (p = 0.029), patient height (p = 0.032), female gender (p = 0.005),
and smaller component size in male patients (p = 0.005).
The preliminary experience with this hybrid metal-on-metal bearing is
encouraging. Optimal femoral bone preparation and component fixation are
critical to improving durability. The metal-on-metal hybrid surface
arthroplasty is easily revised to a standard femoral component if