The purpose of this study was to examine the effects of cement-free implant fixation on microperfusion in the vicinity of the bone-implant interface and to elucidate the effects of mechanical loading on interstitial fluid flow.

Experiments were conducted on both forelimbs of sheep (n=8, age: 4–7 years) using an ex vivo model. Immediately after euthanasia, forelimbs were amputated and a system of perfusion with Procion red (0,08 %) as flow indicator was established. In one group (4 animals), an prosthesis was inserted into the reamed intramedullary cavity of the metacarpus. In a second group (4 animals) no implant was inserted. For each pair, one limb (chosen randomly) was subjected to cyclic loading. Loading was applied at a rate of 1 Hz for 5 minutes. Infusion lasted 5 minutes in all limbs. After the experiment histological cross sections were taken and analysed for the amount of tracer present. Twelve regions were marked on the slide prior to examination and acquired under fluorescence mode. The average pixel intensity of each field of view, was measured using ‘Scion Image’ software.

The mean (± standard deviation) of the 12 readings (pixel intensities) for each group were as follows: Non-implanted group, loaded: 83.31 (± 13.56); Non-implanted group, unloaded 80.80 (± 9.22); Implanted group, loaded: 71.86 (± 19.28); Implanted group, unloaded 66.79 (± 15.52). Anova analysis showed the effect of loading not to be significant statistically (p = 0.082) but the effect of implant to be highly significant (p0.0001).

Implant fixation and mechanical loading affect both microperfusion and interstitial fluid flow modulated mass transport in bony tissue surrounding implants. It appears that the presence of an implant per se reduces perfusion as well as fluid flow in the vicinity of the bone-implant interface. Within subchondral bone loading does not have a significant effect on transport of small molecular weight tracers.