Assessment of polyethylene wear in total hip replacement

The three-dimensional technique is a method for the measurement of polyethy lene wear in patients with total hip joint replacement. Application of,imag e processing technology allows automation of point selection from digital i mages of radiographs scanned into the computer. Validation of image process ing modifications reveals a three-fold increase in accuracy and a 40-fold i ncrease in reproducibility compared with manual input of points from a digi tizer during bench testing. A review of three-dimensional technique applica tion to clinical patients gives information on the factors that influence p olyethylene wear. Increasing age, activity level, femoral head size, decrea sing 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 di fference in polyethylene wear rate could be found between two groups of pat ients, one group had a stainless steel-polyethylene articulation and the ot her had a ceramic-polyethylene articulation. Measurement of the serial poly ethylene wear of individual patients reveals a high rate of femoral head pe netration during the first 2 years after total hip replacement using metal- backed acetabular components inserted without cement. Interpretation of thi s femoral head penetration as true polyethylene wear may be erroneous, howe ver, because creep of the polyethylene and acetabular liner movement within its metal shell cannot be measured.