Abstract
Introduction and Aims: The enduring success of the low friction arthroplasty advanced by Sir John Charnley may be appreciated by the fact that almost 700,000 primary and revision hip and knee arthroplasties were performed in 2003 in the US. Despite this success, the advent of wear debris generation leading to osteolysis and fixation failure are of growing concern, particularly with the increased graying and activity levels of our society. This paper addresses these concerns.
Method: Enhanced polyethylenes have been cleared by the FDA, but in the absence of clinical data supporting their safety and effectiveness. Only recently have short-term clinical experiences begun to emerge. Their proclaimed advantage lies in the reduction of wear debris generation through enhanced cross-linking of the polymer chains coincident with elimination of oxidation through the manufacturing process. These processes, however, vary in the amount and type of radiation used, the extent of polymer remelting and endpoint sterilisation methodology.
Results: Changes in the mechanical properties of these materials, particularly in their reduced resistance to fatigue crack propagation raises concerns about their long-term suitability in both hip and knee components where locking mechanisms offer foci for stress risers. Although it is claimed that the propensity for crack initiation is reduced, recent case reports suggest rapid fatigue failure once a crack has occurred. Material integrity, in this regard, is seen to be influenced by locking attachments, component positioning and highly cross-linked polyethylene choice.
Conclusion: It is concerning that 62% of acetabular polyethylene liners are manufactured from one of the highly cross-linked polyethylenes currently available. The clinical sequel to this is not manifest by the small number of short-term reports citing their efficacy. Cost as well as patient selection and the unknown clinical realities of long-term series reporting are concerns with these materials that only in vivo time will elucidate.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
None of the authors is receiving any financial benefit or support from any source.
