Ten percent of fractures end in delayed or non-union. NSAIDs have been linked to an inhibitory action on fracture repair for three decades yet the mechanism of action remains to be elucidated. Cancer research has identified that NSAIDs impede cell proliferation by inhibiting angiogenesis. It is proposed that a similar mechanism occurs in the induction of NSAID induced non-union. We have investigated this hypothesis in a randomised placebo control trial of the NSAID rofecoxib using a murine femoral fracture.

All animals had an open femoral fracture treated using an external fixator. Outcomes measures included x-ray, histology and biomechanical testing, with laser Doppler used to assess blood flow across the fracture gap.

Radiology showed similar healing patterns in both groups; however, at the later stages (day 32) the NSAID group had significantly poorer healing. Histological analysis showed that controls healed quicker (days 24 and 32), with more callus (day 8) and less fibrous tissue (Day 32). Biomechanical testing showed controls were stronger at day 32. Both groups exhibited a similar pattern of blood flow; however NSAIDs exhibited a lower median flow from day 4 onwards (significant at days 4, 16 and 24).

Positive correlations were demonstrated between both histological and radiographic assessments of healing, with increasing blood flow. NSAID animals exhibited lower flows and poorer healing by all outcomes. Regression analysis demonstrates, however, that the negative effect of NSAIDs on fracture repair is independent of its inhibitory action on blood flow.

COX-2 inhibitors are marketed as having cleaner side effect profiles and are widely used in trauma patients. Following development of a novel method of analysing functional vascularity across a fracture gap, we have demonstrated that the COX-2 inhibitor rofecoxib has a significant negative effect on blood flow at the fracture gap alongside inhibiting fracture repair.

Introduction: Angiogenesis is essential during bone formation. Many studies have looked at the developing vascular network during normal and abnormal bone growth, using histological, immunohistological and contrast-radiological techniques; however all require sacrifice of animals to obtain tissue samples for examination and consequently chronological investigation of angiogenesis is not possible. We have endeavoured to produce an animal model, whereby quantitative assessment of blood flow, and callus formation across a fracture gap, can be repeatedly assessed.

Methods: The model is an adaptation of a 4-pin externally fixated murine femoral fracture previously developed in this department. Three extra conduits have been drilled onto the fixator cross-bar, such that it now links with an x-ray jig and implantable optical cable. The x-ray jig permits repeated lateral x-rays whereas the optical cable which is implanted adjacent to the fracture gap and connected to a laser, measures blood flow using the principle of the Doppler shift of light. Ten mice underwent surgery. Doppler readings and x-rays were taken on the day of surgery and subsequently at days 1, 2, 4, 8, 12, 16, 24 and 32.

Results: Fracture gap pixel density was seen to rise steadily and plateau at day 24, with significant statistical differences between the day of surgery and early time points, and then again between these early time-points (days 2, 4 and 8) and the late time-point day 24. Blood flow was noted to fall following the day of surgery and then slowly increase, with a rapid rise in flow at day 8 until day 16, when levels began to fall again to resting levels.

Conclusion: The data correlates with previous histo-morphological work performed in this department and also with early results from immunohistochemical studies. The above graph for blood flow conforms to that expected in a murine model of fracture healing, with a short initial drop in flow followed by a large rise as angiogenesis follows chondrocyte hypertrophy at the end of the first week, leading to callus formation. This in vivo model may be used to assess the effects on angiogenesis and callus formation of osteogenic compounds and investigate possible antiangiogenic mechanisms of action of medications such as NSAIDs that are known to be detrimental to fracture repair.