In Vivo Biological Response to Vitamin E and Vitamin-E-Doped Polyethylene

Abstract

Cross-linking has decreased the wear of ultra-high molecular weight polyethylene, a cause of osteolysis leading to total joint replacement failure. Compared with melting or annealing, doping cross-linked ultra-high molecular weight polyethylene with vitamin E stabilizes free radicals from irradiation while maintaining mechanical properties and wear resistance. This study was done to determine the local tissue effects of free vitamin E and vitamin E eluted from ultra-high molecular weight polyethylene implants in the joint space. Three studies were performed. First, pure vitamin E and solubilized vitamin E were injected into rabbit knees to simulate vitamin-E elution from radiation cross-linked ultra-high molecular weight polyethylene; second, vitamin-E-doped, irradiated ultra-high molecular weight polyethylene plugs were implanted into dorsal subcutaneous pouches of rabbits to determine the local effects of vitamin-E elution from radiation cross-linked ultra-high molecular weight polyethylene; and, third, two groups of vitamin-E-doped, irradiated acetabular liners (high surface and uniform vitamin-E concentration profiles) were compared with undoped, control ultra-high molecular weight polyethylene liners in a canine model of total hip replacement to determine the effect of possible vitamin-E elution on bone ingrowth and the local tissue response to it in a load-bearing environment. Injection of solubilized vitamin E resulted in histologically normal surrounding soft tissue at both two and twelve-week follow-up intervals, while injection of pure vitamin E resulted in acute and chronic inflammation at the time of the two-week follow-up. Both control and vitamin-E-doped subcutaneous plugs showed inflammation associated with surgery at two weeks of follow-up, but showed stable fibrous encapsulation without inflammation at twelve weeks of follow-up. In the canine total hip replacement model, there was no qualitative difference in local tissue appearance and no significant difference in the percent bone ingrowth and the percent bone density between the control and vitamin-E groups. These investigations showed that vitamin-E-doped ultra-high molecular weight polyethylene plugs and total hip replacement components are well tolerated in both a small and a large-animal model with no observed adverse effects on the surrounding tissues at twelve weeks of follow-up.