Objectives. To quantify and compare peri-acetabular bone mineral density
(BMD) between a monoblock acetabular component using a metal-on-metal
(MoM) bearing and a modular titanium shell with a polyethylene (PE)
insert. The secondary outcome was to measure patient-reported clinical
function. Methods. A total of 50 patients (25 per group) were randomised to MoM
or metal-on-polyethlene (MoP). There were 27 women (11 MoM) and
23 men (14 MoM) with a mean age of 61.6 years (47.7 to 73.2). Measurements
of peri-prosthetic acetabular and contralateral hip (covariate)
BMD were performed at baseline and at one and two years’ follow-up.
The Western Ontario and McMaster Universities osteoarthritis index
(WOMAC), University of California, Los Angeles (UCLA) activity score,
Harris hip score, and RAND-36 were also completed at these intervals. Results. At two years, only zone 1 showed a loss in BMD (-2.5%) in MoM
group compared with a gain in the MoP group (+2.2%). Zone 2 showed
loss in both groups (-2.2% for MoM; -3.9% for MoP) and zones 3 and
4 a gain in both groups (+0.1% for MoM; +3.3% for MoP). No other
between-group differences were detected. When adjusting for BMD
of the contralateral hip, no differences in BMD were observed. The
only significant differences in functional scores at two years were
higher UCLA activity (7.3 (. sd. 1.2) vs 6.1
(. sd. 1.5); p = 0.01) and RAND-36 physical function (82.1
(. sd. 13.0) vs 64.5 (. sd. 26.4);
p = 0.02) for MoM bearings versus MoP. One revision
was performed in the MoM group, for aseptic acetabular loosening
at 11 months. Conclusions. When controlling for systemic BMD, there were no significant
differences between MoM and MoP groups in
