Vascularity of the Arthritic Femoral Head and Hip Resurfacing

With the application of metal-on-metal bearings, hip resurfacing arthroplasty is being performed in a growing number of young adults worldwide. It is anticipated that the problems faced by the first generation of metal-on-polyethylene surface arthroplasties, primarily related to polyethylene wear debris-induced osteolysis1,2, have been overcome by the current generation of low-wearing metal-on-metal surface replacements3,4 (Fig. 1). Short-term clinical followup reports have been encouraging, with a 97% to 99% survival rate at four to five years5-8; however, femoral neck fractures and femoral loosening still pose a challenge5-8. In terms of surgical technique, femoral positioning in a valgus orientation9 and the avoidance of neck notching10 have been advocated. Currently, controversy surrounds the role of femoral head vascularity with regard to implant durability; some surgeons are concerned that the posterior surgical approach sacrifices the important extraosseous blood supply to the femoral head11-13 (Fig. 2), whereas others maintain that an adequate blood supply will be provided intraosseously14. Although femoral head viability may be maintained in part or in whole by an intraosseous blood supply, it is important to critically look at what level of evidence exists to support an intraosseous femoral head blood supply. Some of the evidence comes from retrieval analysis of failed metal-on-polyethylene resurfacing implants15-19 that were associated with a variable prevalence of ischemic failure (see Appendix). This varying prevalence of osteonecrosis-related failures could have been due to the different definitions or varying surgical approaches used as well as the orientation of the specimens during analysis in terms of the differentiation between generalized osteonecrosis and localized necrosis due to cement heat generation20,21. Another reason why these lesions could have been easily missed is that the bone adjacent to the cement interface had been resorbed by the granulation tissue resulting from the polyethylene wear debris1,2 and the micromotion resulting from implant loosening22. With the reduction of wear-related failures, the current generation of metal-on-metal hip resurfacings may bring to light other mechanisms of failure the same way that the elimination of “cement disease” led to the identification of polyethylene wear debris23,24. The purpose of the present report is to review some of the variables that may affect femoral head vascularity after hip resurfacing.