Today's Veterinary Practice

JUL-AUG 2015

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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Today's VeTerinary PracTice | July/august 2015 | tvpjournal.com a PracTiTioner's Guide To FracTure ManaGeMenT Peer reviewed 18 Fractures occur commonly in both dogs and cats. While typically fractures occur after a traumatic incident, such as being hit by a car or falling from a height, some fractures occur following a pathologic weakening of the bone, which is seen with certain neoplastic conditions, such as osteosarcoma. Since fractures are frequently seen in general practice, it is important for veterinarians to understand fracture biomechanics as well as how to: • Classify and diagnose fractures • Choose the correct fixation to ensure proper bone healing • Identify bone healing • Address complications, if they occur. In Part 1 of this 2-part series, fracture biomechanics, fracture classifcation and diagnosis, and factors to consider when selecting a fxation technique are discussed. In Part 2, selection of fxation technique and specifc techniques, identifcation of bone healing, and potential complications will be addressed. FRACTURE BIOMECHANICS Bone is an amazing tissue with complex properties that allow it to adapt to its environment but typically conserve its general structure and shape. By following Wolff 's law, bone adapts and changes in areas of high stress, while minimizing changes in areas of low stress. Basically, bone is shaped for the greatest strength while, at the same time, minimizing bone mass that would contribute to increased weight of the animal. Qualities of Bone Bone is considered both viscoelastic and anisotropic: • The viscoelastic property of bone states that the strength of bone depends on the rate upon which it is loaded. For example, bone is stronger when it is loaded rapidly versus slowly (ie, the more rapidly bone is loaded, the more inflexible it becomes). This property is advantageous because most injuries are inflicted by impact with high loading rate forces. Therefore, fewer fractures actually occur because the more rapidly bone is stressed, the stiffer it becomes. However, once any bone reaches a failure point of loading, it will fracture. 1 • The anisotropic nature of bone suggests that bone strength is dependent on the direction in which it is loaded. For example, bone is stronger when loaded longitudinally versus transversely, which explains why bone is more likely to fracture with sudden high impact placed transversely upon the bone. Fracture Forces Bone is subject to many forces; a fracture occurs when the sum of these forces exceeds the ultimate strength of the bone. Therefore, understanding the forces placed upon bone is crucial to counteracting these forces when stabilizing a fracture. Part 1: Diagnosing Fractures & choosing a Fixation technique A Practitioner's Guide to Fracture Management Meredith Kapler, DVM North Carolina State University David Dycus, DVM, MS, Diplomate ACVS (Small Animal) Veterinary Orthopedic & Sports Medicine Group, Annapolis Junction, Maryland Table 1. Five Main Forces That Act on Bone The most common forces acting on bone, and those that MUST be counteracted with bone fxation are: 1. Bending 2. Compression 3. Shearing 4. Tension 5. Torsion Wolff's law —a theory developed by german anatomist and surgeon Julius Wolff—states that bone in a healthy person or animal will adapt to the loads under which it is placed or, more simply, bone adapts to pressure, or a lack of it.

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