Extract
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.