Tk. Cobb et al., EFFECT OF THE ELEVATED-RIM ACETABULAR LINER ON LOOSENING AFTER TOTAL HIP-ARTHROPLASTY, Journal of bone and joint surgery. American volume, 79A(9), 1997, pp. 1361-1364
Elevated-rim acetabular liners recently were shown to be associated wi
th improved stability of total hip prostheses in a large clinical seri
es. However, the effect of this design on loosening remains unknown. T
o address this question, we reviewed the results of 5167 primary and r
evision total hip arthroplasties that had been performed at our instit
ution from September 1, 1985, through December 31, 1991; 2469 of the a
cetabular components hail an elevated-rim liner (10 degrees of elevati
on), and 2698 had a standard liner. Five-year follow-up data were avai
lable for 1237 hips (174 that had an elevated-rim acetabular liner and
1063 that had a standard acetabular liner). The cumulative probabilit
y of revision because of loosening of the implant was estimated as a f
unction of time since the operation with use of the Kaplan-Meier survi
vorship method. The five-year probability of survival of the acetabula
r component was 98.8 per cent (95 per cent confidence interval, 97.9 t
o 99.6 per cent) for the prostheses that had an elevated-rim liner and
98.3 per cent (95 per cent confidence interval, 97.7 to 99.0 per cent
) for those that had a standard liner (p = 0.87). The effect of the el
evated-rim acetabular liner on the probability of revision because of
loosening of the acetabular or the femoral component was analyzed for
several subgroups: components inserted with cement, components inserte
d without cement, primary total hip arthroplasties, revision total hip
arthroplasties, male patients, and female patients. With the numbers
available, no significant differences were found in the probability of
survival of the acetabular or the femoral component in any of the sub
groups. Theoretical considerations suggest that the geometric design o
f the elevated-rim acetabular liner may have biomechanical characteris
tics that predispose the implant to early loosening. However, our init
ial review of the results of total hip arthroplasties after a mean fol
low-up period of five years (range, 0.25 to tell years) failed to demo
nstrate any difference in the cumulative probability of revision becau
se of loosening of the implant. Continued surveillance is warranted an
d ongoing.