Acetabular polyethylene wear and acetabular inclination and femoral offset

Abstract

Restoration of femoral offset and acetabular inclination may have an effect on polyethylene (PE) wear in THA. We therefore assessed the effect of femoral offset and acetabular inclination (angle) on acetabular conventional (not highly cross-linked) PE wear in uncemented THA. We prospectively followed 43 uncemented THAs for a minimum of 49 months (mean, 64 months; range, 49-88 months). Radiographs were assessed for femoral offset, acetabular inclination, and conventional PE wear. The mean (+/- standard deviation) linear wear rate in all THAs was 0.14 mm/year (+/- 0.01 mm/year) and the mean volumetric wear rate was 53.1 mm(3)/year (+/- 5.5 mm(3)/year). In THAs with an acetabular angle less than 45 degrees , the mean wear was 0.12 mm/year (+/- 0.01 mm/year) compared with 0.18 mm/year (+/- 0.02 mm/year) in those with a reconstructed acetabular angle greater than 45 degrees . Reproduction of a reconstructed femoral offset to within 5 mm of the native femoral offset was associated with a reduction in conventional PE wear (0.12 mm/year versus 0.16 mm/year). Careful placement of the acetabular component to ensure an acetabular angle less than 45 degrees in the reconstructed hip allows for reduced conventional PE wear.

Level of evidence: Level II, prospective study. See Guidelines for Authors for a complete description of levels of evidence.

Figures

Fig. 1

A flowchart shows the acetabular and femoral offset groups.

Fig. 2

An image of a Mallory-Head® femoral prosthesis and RingLoc® acetabular component show measurement of native and reconstructed femoral offset and acetabular inclination. Reconstructed femoral offset (a) was measured as the distance from the center of rotation of the femoral head (b) to the long axis of the femoral shaft (c). We repeated measurements on the disease-free contralateral hip (d). Acetabular inclination (abduction) was measured by drawing a horizontal line joining the inferior border of the inferior pubic rami (e). The acetabular inclination angle (g) was subtended by a second line drawn parallel to the opening plane of the acetabular component (f) and the horizontal reference line.

Fig. 3

A bar chart shows increased wear with an acetabular inclination greater than 45º.

Fig. 4

A bar chart shows increased wear with restoration of the femoral offset within greater than 5 mm of the native femoral offset.