A significant burden of disease exists with respect to critical sized bone defects; outcomes are unpredictable and often poor. There is no absolute agreement on what constitutes a “critically-sized” bone defect however it is widely considered as one that would not heal spontaneously despite surgical stabilisation, thus requiring re-operation. The aetiology of such defects is varied. High-energy trauma with soft tissue loss and periosteal stripping, bone infection and tumour resection all require extensive debridement and the critical-sized defects generated require careful consideration and strategic management. Current management practice of these defects lacks consensus. Existing literature tells us that tibial defects 25mm or great have a poor natural history; however, there is no universally agreed management strategy and there remains a significant evidence gap. Drawing its origins from musculoskeletal oncology, the Capanna technique describes a hybrid mode of reconstruction. Mass allograft is combined with a vascularised fibula autograft, allowing the patient to benefit from the favourable characteristics of two popular reconstruction techniques. Allograft confers initial mechanical stability with autograft contributing osteogenic, inductive and conductive capacity to encourage union. Secondarily its inherent vascularity affords the construct the ability to withstand deleterious effects of stressors such as infection that may threaten union. The strengths of this hybrid construct we believe can be used within the context of critical-sized bone defects within tibial trauma to the same success as seen within tumour reconstruction. Utilising the Capanna technique in trauma requires modification to the original procedure. In tumour surgery pre-operative cross-sectional imaging is a pre-requisite. This allows surgeons to assess margins, plan resections and order allograft to match the defect. In trauma this is not possible. We therefore propose a two-stage approach to address critical-sized tibial defects in open fractures. After initial debridement, external fixation and soft tissue management via a combined orthoplastics approach, CT imaging is performed to assess the defect geometry, with a polymethylmethacrylate (PMMA) spacer placed at index procedure to maintain soft tissue tension, alignment and deliver local antibiotics. Once comfortable that no further debridement is required and the risk of infection is appropriate then 3D printing technology can be used to mill custom jigs. Appropriate tibial allograft is ordered based on CT measurements. A pedicled fibula graft is raised through a lateral approach. The peroneal vessels are mobilised to the tibioperoneal trunk and passed medially into the bone void. The cadaveric bone is prepared using the custom jig on the back table and posterolateral troughs made to allow insertion of the fibula, permitting some hypertrophic expansion. A separate medial incision allows attachment of the custom jig to host tibia allowing for reciprocal cuts to match the allograft. The fibula is implanted into the allograft, ensuring nil tension on the pedicle and, after docking the graft, the hybrid construct is secured with multi-planar locking plates to provide rotational stability. The medial window allows plate placement safely away from the vascular pedicle.Introduction
Methodology
