The influence of avascularity on the mechanical properties of human bone-patellar-tendon-bone grafts

Our aim was to analyse the effect of avascularity on the morphology and mec hanical properties (tensile strength, viscoelasticity) of human bone-patell ar-tendon-bone (BPTB) grafts in vitro. These were harvested at postmortem a nd stored submerged in denaturated human plasma at a constant pH, pO(2), pC O(2), temperature and humidity under sterile conditions. Mechanical testing was performed two and four weeks after removal of the graft. The mean ulti mate strength was 1085.7 +/- 255.8 N (control), 1009.0 +/- 314.9 N (two wee ks cultured) and 1076.8 +/- 414.8 N (four weeks cultured), There was no sig nificant difference in linear stiffness or deformation to failure between t he groups. There was a difference in viscoelasticity between the control gr oup and the avascular grafts and the latter had significant lower peak load -to-load ratios after 15 minutes compared with the control group, After two and four weeks the graft contained viable fibroblasts. There was regular c ellularity in the superficial layers and decreased cellularity in the midpo rtion, The structure of the collagen including the crimp pattern appeared t o be normal in polarised light. We conclude that avascularity does not significantly affect ultimate failur e loads or stiffness of BPTB grafts. Slight changes in viscoelasticity were induced, but the significance of the increased stress relaxation is not fu lly understood.