[Radiographic assessment of polyethylene wear in machined versus molded polyethylene in total hip prosthesis].
OBJECTIVE
Wear of polyethylene acetabular components is an important issue in total hip arthroplasty. This study was designed to evaluate differences in polyethylene wear rates between machined and direct compression molded acetabular cups.


METHODS
Two hundred thirty-nine prostheses underwent radiographic evaluation using the technique of Chevrot-Kerboull. One hundred thirty-one were all-polyethylene cups machined from extruded bar stock, and one hundred eight were all-polyethylene cups direct compression molded. Both groups, all operated on in 1988, were similar in the acetabular and femoral components, were all cemented, and the acetabular components were all-polyethylene, non metal backed. The femoral components were all Charnley-Kerboull MK III type. Patient weight, average weight, the post-operative PMA score and the duration of the follow-up were similar for the two groups (mean 7.4 years).


RESULTS
Results showed a mean linear wear rate of 0.06 mm per year for compression-molded polyethylene and 0.08 mm per year for machined polyethylene. Results were not significantly different. The number of acetabular radiolucencies in zone I (5.5 versus 5.3 p. 100) and the amount of lysis of the proximal part of the femur did not differ between the two groups. The number of excessive wears did not differ either.


CONCLUSIONS
Although polyethylene wear was lower with compression molded acetabular cups than with ram-extruded acetabular cups, results of this study suggest a non significant difference between the two types of components. A more controlled experiment would have to be performed to attribute a difference between two different types of UHMPE processing.
Courpied
J
J
Service d'Orthopédie, Hôpital Cochin, AP-HP Paris, 27, rue du Faubourg Saint-Jacques, 75014 Paris.
Delhoume
J
J
Kerboull
L
L
Kerboull
M
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D020959:Polyethylene; D011475:Prosthesis Failure; D011859:Radiography; D012189:Retrospective Studies
D020959:Polyethylene