TGF-beta1 as a marker of delayed fracture healing

Mitogens of the TGF-beta superfamily have been shown to be crucial local and systemic regulatory molecules involved in fracture healing. However, there exists only little information about systemic regulation of bone regeneration by growth factors and no reports comparing serum levels of bone growth factors between normal and failed fracture healing have been published so far. We hypothesized that quality of fracture healing might be reflected by systemic alterations of key regulatory growth factors involved in bone formation and remodeling. Therefore, the aim of this study was to evaluate possible differences in serum levels of BMP-2, BMP-4, and TGF-beta1 in patients with normal and delayed fracture healing. 103 patients with diaphyseal fractures of long bones were recruited prospectively. Peripheral blood samples were collected over a period of 6 months following a standardized time schedule. At the end of the individual investigation period, growth factor serum levels were measured using commercially available enzyme immunoassays. For the elimination of disturbing influences, patients in both groups were matched by gender, age, fracture type, and localization as well as applied technique of osteosynthesis. During a study period of 1 year, 10 patients with an atrophic type of delayed union could be retrieved and matched to 10 patients with normal fracture healing. The diagnosis of delayed union was assumed in case of failed consolidation 4 months after trauma. We found an increase of TGF-beta1 serum levels up to 2 weeks after fracture in both groups with a following return to the reference value within 6 weeks after trauma. However, decline of serum concentration occurred earlier in patients with delayed fracture healing. At 4 weeks after trauma, serum levels of TGF-beta1 were significantly lower in patients of the delayed union group. Serum levels of BMP-2 and BMP-4 were below detection level in all patients, respectively. These findings support the critical role of TGF-beta1 in fracture healing. Events during the consolidation phase seem to be dependent on sufficient availability of TGF-beta1.