Scientific Articles   |    
Polyethylene Wear and Acetabular Component Orientation
Shantanu Patil, MD; Arnie Bergula, BS; Peter C. Chen, PhD; Clifford W. ColwellJr., MD; Darryl D. D'Lima, MD
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The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. One or more commercial entities paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2003 Nov 01;85(suppl 4):56-63
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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 polyethylene wear.

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.

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