Saturday, March 13, 2004
From January 1995 to April 1998, 136 primary hip replacements were performed on 126 patients utilizing HylamerTM polyethylene cups. Thirty-six males and 90 females were involved in the study of three types of HylamerTM cups: gamma-irradiated in air (GIA), gamma-irradiated in barrier packaging (GIB) and gas-plasma (GP). Annual follow-up included Harris hip scores and radiographic review; follow-up is now five to seven-years (mean 72 months). Thirteen patients were lost to follow-up. The gamma-air sterilization data were compared to our clinical results with HylamerTM GIB and GP cups.
According to the researchers, early results had demonstrated significant clinical improvement in their elderly patients. The Harris hip scores went from 39 points to 97 points and the function score improved from 42 to 84. With GIA Hyalmer cups, radiographic evaluation demonstrated gross cup loosening in eight patients and 12 additional cases demonstrated significant acetabular osteolysis.
On the femoral side, 30 patients had significant osteolysis in the proximal Gruen zones (7a, 1a). Twelve patients showed considerable osteolysis in Gruen zone 7. Sixteen revisions were performed for severe osteolysis and pain. An additional ten patients will require revision for severe osteolysis, despite any clinical symptoms. Overall this represents a 19 percent failure with short-term follow-up.
The extent of HylamerTM wear was first assessed on routine radiographs and then confirmed by dimensional measurement on GIA cups revised from this group of elderly patients. As expected, the highest wear rates (0.45 mm/year) were demonstrated in the GIA group with the most severe osteolysis and highest revision rates (Table 1: Figs. 1, 2). In our study the long shelf-life (4.3 years average) had a significant effect on wear for these GIA cups (Table 1). In contrast the GIB sterilization method of HylamerTM demonstrated an 81% wear reduction over GIA. The GIB method had 35% wear reduction compared to the GP cups. The shelf life of the GIB and GP cups was no more than a year and hence had no impact.
The researchers found their study to be consistent with other reports describing aggressive wear rates with gamma-irradiated HylamerTM cups. This study is unique because of the age of the patients. Some of the worst osteolysis cases were in patients over 80 years of age.
With this realization, all the patients who received HylamerTM cups were contacted and asked to come back for clinical and radiographic review to determine the presence and/or extent of their osteolysis. CT scans were used in selected patients to better define the margins of acetabular lesions that may not always be appreciated on clinical radiographs.
The clinically silent progress of these aggressive osteolytic lesions demonstrates the need for continued clinical follow-up. The Joint Registry team at Loma Linda University is committed to a regular follow-up schedule to minimize risk of late failure in such patients.
Thomas Kent Donaldson, MD, of Loma Linda, Calif., led the research team; other researchers included Laurie Andrusak; Ian C. Clarke, PhD; Mark Sutton, MD; and Paul Williams, also of Loma Linda, Calif.
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