Introduction and Aims: Wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups is a well-known cause of osteolysis and loosening of the components. Improvement of the wear resistance of UHMWPE could extend the clinical life of total hip arthroplasty (THA). Chemical cross-linking in acetylene with gamma radiation is a cheap and effective way of increasing wear resistance of UHMWPE.

Method: This study is a report on 132 patients operated between 1977 and 1984, using the Pretoria monobloc stainless steel hip with 30mm metal head. Acetabular cups were machined from RAM extruded rectangular bars (RCH 1000). Final cups were gamma irradiated in stainless steel containers filled with acetylene gas. Three hundred microns surface cross-linking was achieved at 100kG. At that time, 1059 hip replacements were performed by the two first authors. The retrospective study consisted of measurement of the radiological wear. The criteria was to compare and measure the wear from early post-op radiograph and longest follow-up radiograph. Linear wear was measured according to the Livermore methods. Exclusion criteria included follow-up less than 10 years, sepsis, dislocation and other non wear-related causes of failure. The rarely retrieved cross-linked ace-tabular cups were analysed individually using spectrum electron microsope (SEM).

Conclusion: The South African contribution to the method of cross-linking is important. This is a cheap and effective way to improve the quality of the polyethylene. Results of this long-term group of patients with cross-linked UHMWPE show a significant decrease in the wear rate, significantly increasing the longevity of the THR.

Wear of ultra-high molecular weight polyethylene (UHMWP) acetabular cups is a well-known cause of osteolysis and loosening of the components. Improvement of the wear resistance of UHMWP could extend the clinical life of total hip arthroplasty (THA). Chemical cross-linking in acetylene with gamma radiation is a cheap and effective way of increasing wear resistance of UHMWP.

This study is a report on 263 patients (123 males and 140 females) on whom Dr Weber performed THA between 1977 and 1984, using the Pretoria (Grobbelaar) monobloc stainless steel hip with 30-mm metal head. There were 96 patients (107 prostheses) available for follow-up at a mean of 18.3 years, with 89 surviving prosthesis in 79 patients (83.2%).

We collected complete sets of radiographs of 54 patients (mean age 71.4 years) for a radiological survey in 1999. In 41 patients (76%) we found no wear. The mean age of these patients was 72 years. Wear was noted in the other 13 patients (24%), whose mean age was 75 years. The mean follow-up time was 16 years (8 to 23). The mean magnification in the radiological study was 18%. Mean wear for the total group was 1.29 mm and mean annual wear 0.17 mm.

A similar analysis performed on a group of 64 of Dr Grobbelaar’s patients at 15.5 year mean follow-up shows remarkable similarity, with mean wear of 0.172 mm for a group of 64 patients and annual wear 0.11 mm. Dr Oonishi of Japan, who has conducted the only other long-term follow-up, found similarly promising results.