Dolph Houben

174 CHAPTER 9 The overarching aim of this thesis was to microsurgically transplant living allogenic bone and joint while maintaining viability without the need for life-long immunosuppression in a pre-clinical animal model. In this chapter, the main findings of the studies are summarized, discussed and suggestions for future research are given. Summary and conclusions Part I: The first part of this thesis focuses on the current clinical outcomes of autogenous vascularized bone grafts (VBG) for the reconstruction of large segmental bone defects in the lower extremity. We focus on the outcomes of VBGs used alone or in combination with a massive allograft. The eventual goal is limb-salvage and preservation of form and function, while minimizing complications and re-operations. We hypothesized that segmental bone defects are best reconstructed with a vascularized autograft combined with or without a massive cortical allograft. In Chapter 2 , we performed a review of literature on the outcomes of VBGs for the reconstruction of large segmental defects in the lower extremity. Segmental bone loss is often the result of trauma, primary malignant tumor resection, meta-static tumor resection, infection, failed primary reconstruction, or congenital pseudarthrosis. Treatment of these large bone defects is challenging. Historically, vascularized bone grafts have been used since the 19 th century. The desirability of a vascularized bone graft above a non-vascularized bone graft has been emphasized by several early researchers [1-3] . Due to the rapid development of microsurgical techniques the free fibula flap has become one of the most important VBG for the reconstruction of segmental bone defects. The first successful free vascularized fibula transfer at Mayo Clinic was performed in 1979 by Dr. M.B. Wood. The structure and shape of the fibula make it useful for diaphyseal reconstruction; a straight segment of bone between 26 and 30 cm can be harvested, and stability can be obtained with rigid internal fixation to the recipient bone. Vascularized bone flaps remain viable due to microvascular repair of the nutrient pedicle of the bone, permitting the survival of osteogenic cells [4, 5] . The viability of VBG results in faster union rates, fewer fatigue fractures, rapid remodeling and hypertrophy, and less resorption compared to non-vascularized bone transfer [6-8] . Primary union rates of 67-84% have been found in the literature, however after secondary bone grafting, the rate of union is 81-92% [9-11] . Complication rates after vascularized bone grafting for reconstruction of a bone defect in the lower extremity are strongly dependent on the location and underlying pathology of the defect. Risk factors for poor outcomes are post- operative chemotherapy, tobacco use, and a history of osteomyelitis [9, 11] . Free fibula flaps often poorly match the diameter of the defect in the lower extremity. Therefore, they are susceptible to early stress fractures in the first year due to insufficient protection from mechanical overload. Combining vascularized fibular grafts with a massive allograft shell can reduce the mechanical load. This technique has been known in literature as the Capanna technique [12] . In Chapter 3 , we performed a systematic review of literature on the outcome of this technique. We found that combining a massive allograft and an intramedullary vascularized