Characterising neovascularisation in fracture healing with laser Doppler and micro-CT scanning

Vascularity of the soft tissues around a bone fracture is critical for successful healing, particularly when the vessels in the medullary canal are ruptured. The objective of this work was to use laser Doppler and micro-computer tomography (micro-CT) scanning to characterise neovascularisation of the soft tissues surrounding the fracture during healing. Thirty-two Sprague–Dawley rats underwent mid-shaft osteotomy of the left femur, stabilised with a custom-designed external fixator. Five animals were killed at each of 2, 4 days, 1, 2, 4 and 6 weeks post-operatively. Femoral blood perfusion in the fractured and intact contralateral limbs was measured using laser Doppler scanning pre- and post-operatively and throughout the healing period. At sacrifice, the common iliac artery was cannulated and infused with silicone contrast agent. Micro-CT scans of the femur and adjacent soft tissues revealed vessel characteristics and distribution in relation to the fracture zone. Blood perfusion dropped immediately after surgery and then recovered to greater than the pre-operative level by proliferation of small vessels around the fracture zone. Multi-modal imaging allowed both longitudinal functional and detailed structural analysis of the neovascularisation process

Fracture non-union: using the blast wave to our advantage

Fracture non-union is the failure of a fracture to heal and can confer long-term problems to the affected individual. The blast and ballistic mechanisms that typically cause combat injuries mean that fracture non-union is a particular problem amongst military personnel. Furthermore, a systematic review undertaken as part of this project showed that rates of fracture non-union have not improved over a century of warfare, highlighting the enduring clinical burden that this condition confers to defence. With limited treatment option for fracture non-union, mesenchymal stem cells (MSCs) represent a promising therapeutic option. Bone marrow aspirate concentrate (BMAC), purported to contain high levels of MSCs, is already used in clinical practice to treat fracture non-union. Mechanotransduction describes the process through which a mechanical force can confer a biochemical signal within a cell, altering gene expression and stimulating cell differentiation. Blast victims present with a high incidence of heterotopic ossification, with the mechanism of action postulated as being a mechanotransducive transfer of energy from the blast wave stimulating osteoblastic transformation of MSCs. The experimental aspect of this project therefore sought to investigate whether a blast wave can induce osteoblastic transformation in MSCs, potentially offering a novel therapy to aid fracture healing. Upregulation in osteogenic gene expression and calcium mineralisation was observed in MSCs following blast wave exposure. However, these findings were not reproduced in BMAC samples with flow cytometry demonstrating a marked paucity of MSCs. Subsequent work demonstrated that growth factors likely mediate the osteogenic effect of BMAC and can be enhanced following exposure of BMAC to a single blast wave. The data presented in this thesis has shown that blast waves when used in conjunction with BMAC may provide a novel therapy for the treatment of fractures at high risk of developing a non-union, such as those sustained in combat from a blast mechanism. Development of subsequent pre-clinical and clinical studies is required to translate this work into a feasible clinical option to aid in the treatment and avoidance of fracture non-union.Open Acces