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Today's VeTerinary PracTice | september/october 2015 | tvpjournal.com a PracTiTioner's Guide To FracTure ManaGeMenT Peer reviewed 26 radiographic views, typically confrms radiographic healing of the fracture. The callus should span the fracture gap on 3 of the possible 4 cortices: medial, lateral, cranial, and caudal. Ancillary Fixation External coaptation can be used as ancillary fxation to provide additional support in patients with radius/ulna fractures that, for example, have already undergone bone plating. As mentioned earlier, distal radius/ulna fractures, especially those in small and toy breed dogs, addressed with external coaptation alone commonly result in malalignment or nonunion. IDENTIFICATION OF BONE HEALING While a complete description of the physiology of bone healing is beyond the scope of this article, in general, bone healing of a stable fracture occurs through direct bone healing as opposed to indirect bone healing, which is seen with unstable fractures or certain fractures addressed with external coaptation as a primary means of fxation. Direct (Primary) Bone Healing Direct bone healing tends to take one of 2 forms: 1. Contact healing 2. Gap healing. Contact healing occurs when the defect between the bone ends is less than 0.01 mm. With contact healing, cutting cones—an osteoclastic tunneling process—develop, resulting in direct formation of lamellar bone oriented in the normal axial direction of the bone. Gap healing occurs when the bone ends are less than 0.8 mm to 1 mm apart. With gap healing, the initial fracture site undergoes intramembranous bone formation, with lamellar bone oriented perpendicular to the axial direction of bone. Due to the perpendicular direction of bone formation, the fracture site remains relatively weak. Haversian remodeling begins 3 to 8 weeks after fracture fxation, allowing bone to develop in a more longitudinal fashion. In a more general sense, bone union and remodeling occur simultaneously with contact healing; with gap healing, they are instead sequential steps. 5 Indirect (Secondary) Bone Healing Indirect bone healing occurs in unstable fractures or fractures treated with external coaptation as a primary means of fxation. The most characteristic feature of indirect bone healing is formation of an intermediate callus prior to bone formation. As the bone heals, the tissues pass through different stages of increasing stiffness and strength. In general, the amount of callus is related to the amount of instability present at the fracture site; the greater the instability, the greater the amount of callus. Much like wound healing, indirect bone healing has 3 overlapping phases: 1. Infammation: This phase traditionally lasts 3 to 4 days or longer, and is characterized by a fbrin-rich clot at the fracture site. This clot releases growth factors to simulate bone healing and potentially acts as a scaffold for migration of infammatory and reparative cells. 2. Repair: During this phase, the clot is slowly replaced by granulation tissue, which adds slight mechanical strength. As collagen fbers become more abundant, granulation tissue is replaced by connective tissue and, after formation of connective tissue at the fracture site, resident mesenchymal cells differentiate into chondrocytes to form cartilage. With the help of growth factors, such as bone morphogenic proteins, the cartilage begins mineralizing to form woven bone. 3. Remodeling: This phase is characterized by a slow adaption of the bone to regain its original function and strength. It is a very slow process (up to 6–9 years in humans) that represents 70% of the fracture's total healing time. The action of osteoclastic resorption and osteoblastic deposition is guided by Wolff 's law. 5 Radiographic Evidence Radiographic evidence of bone healing is noted by the general disappearance of the fracture line. Radiographic Signs of Normal Indirect Bone Healing Following is a typical timeline for radiographic signs of normal indirect bone healing: ` 5 to 7 days after trauma: Widening of the fracture gap and "smudging" of the fracture edges ` 10 to 12 days: Appearance of a bony callus ` Within 30 days: Disappearance of the fracture line ` 90 days after repair: Complete remodeling of the callus Adapted from Johnson A, Houlton J, Vannini R. AO Principles of Fracture Management . New York: Thieme Medical Publishers, 2005. Schroeder- Thomas splints are never recommended for fracture stabilization. schroeder-thomas splints are traction devices constructed of wire frame and soft bandage material. since the splint does not adequately immobilize the shoulder or hip joint, it is considered contraindicated in humeral and femoral fractures.