Assessment of polyethylene wear in total hip replacement.

The three-dimensional technique is a method for the measurement of polyethylene wear in patients with total hip joint replacement. Application of image processing technology allows automation of point selection from digital images of radiographs scanned into the computer. Validation of image processing modifications reveals a three-fold increase in accuracy and a 40-fold increase in reproducibility compared with manual input of points from a digitizer during bench testing. A review of three-dimensional technique application to clinical patients gives information on the factors that influence polyethylene wear. Increasing age, activity level, femoral head size, decreasing polyethylene thickness, and insertion of total hip prostheses without cement all increase polyethylene wear. Restoration of femoral offset during total hip replacement seems to decreases polyethylene wear. No apparent difference in polyethylene wear rate could be found between two groups of patients, one group had a stainless steel-polyethylene articulation and the other had a ceramic-polyethylene articulation. Measurement of the serial polyethylene wear of individual patients reveals a high rate of femoral head penetration during the first 2 years after total hip replacement using metal-backed acetabular components inserted without cement. Interpretation of this femoral head penetration as true polyethylene wear may be erroneous, however, because creep of the polyethylene and acetabular liner movement within its metal shell cannot be measured.