Background: Polyethylene wear contributes substantially to both
periprosthetic osteolysis and aseptic loosening after total hip arthroplasty.
Acetabular component orientation has been shown to affect the range of motion
of the hip as well as contact stresses. A series of studies was designed to
test the hypothesis that acetabular component orientation can affect the
magnitude and direction of polyethylene wear.
Methods: A finite-element model was used to compute contact stresses
during a normal gait cycle. Wear at the end of each gait cycle was calculated
with use of the sliding-distance-coupled finite-element formulation. The wear
that was calculated with use of finite-element analysis was validated by
comparison with the findings of hip wear simulator studies with the acetabular
liner oriented to simulate 45° and 55° of abduction. In a clinical
study, fifty-six patients who underwent sixty hip arthroplasties with use of a
single prosthetic design were followed for as long as five years. Radiographs
were analyzed to measure the abduction angle of the acetabular component and
Results: The finite-element analysis predicted increased peak
contact stresses with an increased abduction angle and reduced peak contact
stresses with an increased anteversion angle. Linear wear rates ranging from
0.036 to 0.045 mm/million cycles were also predicted, and increased acetabular
abduction angles were predicted to be associated with higher linear wear
rates. In the hip wear simulator studies, significantly different wear rates
were found between the cups with acetabular abduction angles of 45° and
55° (mean, 17.2 compared with 21.7 mg/million cycles; p < 0.01). In the
clinical study, radiographic analysis revealed significant correlation between
the acetabular abduction angle and the linear polyethylene wear rate. A 40%
increase in mean linear polyethylene wear was seen in cups with an abduction
angle of =45°. The direction of wear was more medial (by 9.4°) in
cups with an abduction angle of <45°.
Conclusion: All three studies presented here underlined the
importance of optimizing the position of the acetabular component. Careful
attention to acetabular position may help to minimize wear.