Читать книгу Fractures in the Horse - Группа авторов - Страница 160

Bone grafts can provide both mechanical support and enhanced osteoregeneration. Different graft types work in differing ways. The three principal properties are osteoconduction, osteoinduction and osteogenesis. Osteoconduction refers to the ability to support attachment of osteoprogenitor cells and allow migration and growth within the three‐dimensional architecture of the graft. Osteoinduction occurs when the graft itself can induce progenitor cells to develop into bone forming cells. Osteogenesis is defined as osteodifferentiation and new bone formation by donor cells derived from the host or the graft [76].

Autogenous bone grafts are most commonly used in all species. In humans, it is second only to blood transfusions as the most common tissue transfer, although there is a search for non‐autogenous bone regenerative products because of the limited supply and morbidity caused by acquisition. Horses tend to have a large supply of suitable autogenous bone, and morbidity at the retrieval site is usually minimal. Autogenous bone is the gold standard by which all other graft products are compared, and it is still the most effective for inducing bone healing. Autogenous bone grafts provide all three methods of function (osteoconduction, osteoinduction and osteogenesis). They can be either cortical, cancellous or vascularized. Autogenous cancellous bone graft is most commonly used. In horses, it is typically acquired from the tuber coxae and packed into the fracture gaps at the time of surgery. Alternative sites include the proximal tibia, humerus and sternebrae. Site is dictated by patient recumbency and surgeon preference. Autogenous cancellous bone graft contains mesenchymal stem cells, matrix proteins and a large surface area which stimulates vascularity and host integration. The graft helps form the haematoma, initial inflammation and granulation tissue bed. Neovascularization is stimulated, and osteoid forms around some of the tissue. Autogenous vascularized cortical grafts provide vascular integrity so that the grafted bone can remodel and heal. They are rarely, if ever used in horses. Autogenous cortical bone grafts are rarely used in horses and can only be incorporated through creeping substitution via osteoclastic function and long‐term osseous integration. Osteochondral grafts are commonly used in humans and occasionally in horses [77].

Allogenic grafts are acquired from a different animal of the same species with the benefit that they can be acquired, stored and used off the shelf. Allogenic bone grafts can be in the form of cancellous chips, cortical bone segments (which are used in humans to provide mechanical stability), osteochondral grafts or decalcified bone matrix. However, allogenic grafting triggers an immune response, and the consequential increased inflammatory phase may impede healing. They are rarely used in horses.

Decalcified bone matrix has been used for decades in the human field but showed no positive effect on healing in an experimental equine study [78]. Decalcified bone matrix is prepared by eliminating potential allogenic substances through a decalcification procedure that maintains the non‐calcified bone matrix including potential growth factors and allows for osteoconduction. Decalcified bone matrix is rarely used in equine fracture repair but may have a place in fractures with large residual defects [76].