MATURE OSTEOBLASTS IN HUMAN NONUNION FRACTURES EXPRESS COLLAGEN TYPE-III

Aims-High levels of collagen type III are biochemically detectable in biopsies of non-uniting fractures, and in the serum of patients suffer ing from this condition. The aim of this study was to determine whethe r the expression of collagen type III was limited to fibrous tissue in nonunions, or whether some was present in bone. Methods-Biopsies from normally healing human fractures and non-unions were examined using i n situ hybridisation and immunohistochemistry. Results-The mesenchymal cell population, which includes fibroblast and osteoblast precursors, expressed mRNA for collagen type III. However, mature osteoblasts on the surface of woven bone varied profoundly between normally healing f ractures (in which they were negative or occasionally weakly positive) and nonunions (in which they were strongly positive). Areas of woven bone that had osteoblasts positive for collagen type III mRNA also imm unostained positively for the protein. Conclusions-This study shows th at nonunion fracture callus osteoblasts on the surfaces of woven bone exhibit an unusual phenotype: they express collagen type III, a molecu le characteristic of an earlier stage of osteoblast differentiation, w hich is not expressed by osteoblasts on woven bone surfaces of bone th at develops normally. This finding may be useful in developing an earl y clinical test for impending non-union.