STRAIN INDUCED RELEASE OF BMP-7 FROM FRESH FROZEN FEMORAL HEAD ALLOGRAFT.

Abstract

Introduction: The success of impaction-grafting depends on mechanical stability and adequate bony incorporation of the graft. Full incorporation of this type of graft has been demonstrated histologically and depends on many factors including the biological activity of the graft. Bone morphogenic proteins (BMPs) are known to play a central role in bone formation and their presence reflects the biological activity of a graft material. The aim of this study was to determine the activity of fresh frozen femoral head (FFH) grafts by analysing BMP-7 release after milling and during strain imposed by the impaction process.

Methods: 10mm cancellous bone cubes were cut from 5 samples of FFH. The cubes were washed, centrifuged and washed again to remove the marrow contents. Specimens from each femoral head were allocated to five groups and subjected to strains of 0%, 20%, 40%, 60% and 80% with a material testing machine. The cubes were washed again and the wash fluid analysed for bmp-7 activity using a commercially available elisa kit. Additionally, samples of bone were taken after standard milling of FFH, washed and the fluid analysed for bmp-7 activity.

Results: bmp-7 activity was found to be present in all groups. Release of bmp-7 was found to increase with increasing strain in a linear relationship. At 80% strain the mean concentration of bmp-7 released (2.2 ng/g bone) was approximately double that released at 20% strain.

Discussion: activity of bmp-7 in FFH has not previously been demonstrated. This study shows that the freezing and storage of femoral heads allows some maintainance of biological activity. Furthermore we have shown that bmp-7 may be released from FFH cancellous bone in proportion to the strain applied to the bone. This may go some way to explaining the full bony incorporation often seen after impaction-grafting.