ANALYSIS OF RETRIEVED THR CUPS OF HIGHLY CROSS-LINKED UHMWPE FROM SOUTH AFRICA

Abstract

The world’s clinical experience of highly cross-linked UHMWPE cups (HCLPE) lies in the cemented THR experience beginning in Japan (H, Oonishi), then South Africa (CJ. Grobbelaar) followed by England (M. Wroblewski). The South-African THR concept was to cross-link RCH1000 to a depth of only 300um with 10 Mrad radiation dose in a pressurized acetylene atmosphere. Subsequent sterilization was 3 Mrad in air. The modified Charnley stem had a 30 mm stainless-steel head. Between 1977 and 1983, over 1,000 cases had been implanted by surgeons Grobbelaar and Weber (Grobbelaar, SABJS-99). Analysis has been performed on 100 survivors with follow-up 14 – 21 years. In the Pretoria series, there were only two of 64 cases with revision for granulomas and in the Johannesburg series two of 39 survivors with wear-related problems. Wear was only measurable in nine of 39 cases analyzed radiographically and total linear wear varied from 0.7 to 1.5 mm.

We have had the first-time opportunity to perform the retrieval analysis on Dr Weber’s cases. We now have & #65298; cases of revised cups and one sample off the shelf. These were examined by SEM to examine the microwear phenomena of the HCLPE surfaces. On the peripheral of the load-bearing area, the machine tracks were folded and their edges became fibrillated, some nodules, ripples, fibrils and folds (with attached fibrils) were observed. Fibrils were small in size and quite rare. Multi-oriented scratches and delaminations were sometimes observed.

This study is the first time review for the retrieval analysis on Dr. Weber’s HCLPE cases. The SEM study showed that the load-bearing area had very little wear evident after 20 years. This confirms the clinical and radiographic observation of Dr. Weber. While the retrieval data to date includes only 2 HCLPE cups, these results are encouraging.