Background: Debris from polyethylene wear causes
osteolysis. In this study, we examined the effect of acetabular
liner modularity on polyethylene wear and osteolysis.
Methods: We compared forty-one hips (thirty-nine
patients) treated with a nonmodular, porous-coated acetabular component
with a matched group of forty-one hips (forty patients) treated
with a modular acetabular component. The groups were matched by
patient gender and age, type of polyethylene material, method of
polyethylene sterilization, femoral head size and manufacturer,
and stem manufacturer. The mean follow-up period was 5.3 years (range,
3.8 to 6.8 years) for the nonmodular group and 5.5 years (range,
3.8 to 8.0 years) for the modular group. Using serial radiographs
and a computer-assisted method, we measured two-dimensional head
penetration into the polyethylene liner. Temporal head-penetration
data and linear regression analysis were used to calculate the true
Results: The nonmodular acetabular components demonstrated
a lower, but not a significantly lower, mean true wear rate than did
the modular components (0.11 compared with 0.16 mm/yr,
p = 0.22), and they were associated with a significantly lower
rate of osteolysis (2% compared with 22%, p = 0.01).
In addition, the true wear rates of the nonmodular components were
less variable than those of the modular components. The 95% confidence
interval for the wear rates of the nonmodular components (0.08 to
0.13 mm/yr) was nearly half that of the modular group (0.11
to 0.20 mm/yr).
Conclusions: The lower and more consistent true
wear rates of the nonmodular components could be attributed to the
fact that these cups were designed to have greater liner-shell conformity, greater
liner thickness, and less liner-shell micromotion than modular components.
These design factors could have favorably altered the stress distribution
throughout the liner and could have thereby decreased wear. Although
nonmodular components may present a partial solution to the problems
of wear and osteolysis, they pose a disadvantage when a failed liner
in a bone-ingrown acetabular component needs to be revised.