Abstract
Bone morphogenic proteins (BMPs) are members of the transforming growth factor beta (TGF-beta) family and play a central role in bone formation. These morpho-gens are known to be present in bone matrix however the characteristics of their release during the grafting process has not previously been defined. The aim of this study was to determine the release BMP-7 (osteogenic protein; OP-1) from cancellous allograft that occurs during impaction grafting for revision hip arthroplasty.
Forty, 10mm cubes of cancellous bone were accurately cut from the central region of 7 fresh frozen femoral heads. The cubes were centrifuged and washed to remove the marrow contents. The cubes were then individually washed and the fluid assayed for BMP-7 activity using a commercially available enzyme linked immuno-sorbent assay kit (Raybiotech Inc.). The cubes were then divided into 4 groups with samples from each femoral head in each group. Each group was subjected to strain of either 20%, 40%, 60% or 80% using a material testing machine. The cubes were then individually washed again and the wash fluid analysed for BMP-7 activity.
BMP-7 activity was found to be present in all groups. Release of BMP-7 was found to increase with increasing strain. At 80% strain the mean concentration of BMP-7 released (830 pg/g) was 58% greater than that released at 60% strain (527 pg/g), 150% greater than the concentration at 40% strain (333 pg/g) and 476% greater than at 20% strain (144 pg/g). The differences between release at 80% and 40% strain and between 80% and 20% strain were statistically significant (p=0.036, p=0.002).
Activity of BMP-7 in fresh frozen cancellous allograft bone has not previously been demonstrated. This study shows that the freezing and storage of femoral heads allows some maintenance of biological activity. Furthermore we have shown that BMP-7 may be released in proportion to the strain applied to the bone. This confirms that the process of impaction of bone morsels during revision hip arthroplasty may release BMPs that could aid in the incorporation and remodelling of the allograft.
Correspondence should be addressed to Mr Carlos Wigderowitz, Senior Lecturer, University Department of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Dundee DD1 9SY.
