Читать книгу Fractures in the Horse - Группа авторов - Страница 152

In the horse, internal fixation, whether through open reduction or minimally invasive techniques, is the most commonly used method for repairing fractures. In simple, usually articular fractures, one or more lag screws can be used to re‐appose the joint surface and provide compression to promote primary fracture healing. In these cases, the severity of articular deficits and/or articular cartilage damage usually dictates prognosis as the fractures are usually stable. In equine athletes, this commonly occurs through pathologic bone as seen in the carpus (Chapter 24) or in the metacarpo/metatarsophalangeal joints (Chapters 19–21) [14]. In these locations fractures usually heal, but the pathologic bone commonly influences the articular surface and consequently reduces the prognosis for an athlete.

The stability and process of fracture healing following plate fixation, whether by open reduction or minimally invasive approaches, is highly dependent upon anatomic location and the quality of reduction and stabilization at the site. Even with meticulous reconstruction of a long bone fracture, perfect anatomic reduction usually does not occur, and some areas undergo gap healing. It is generally accepted that the proportion of load that can be borne by bone has a direct bearing on outcome. The role of gap healing on cyclic fatigue of implants is unknown but is a potential factor in determining the risk of repair failure.

Intra‐osseous nails are used in anatomically appropriate situations to convert highly unstable fractures to ones with sufficient stability to permit secondary bone healing. Strict anatomic reduction does not occur. They maintain bone length, i.e. prevent diaphyseal overriding and reduce bending and torsional forces. Rush pins have similar goals, but in horses rarely are able to be of benefit.

In limb fractures, wires are sometimes used to help maintain reduction, especially in long oblique fracture repairs. However, small screws and/or countersunk lag screws are often most appropriate. Wire can also be used to create a tension band, usually as a supplement to other fixation techniques in order to optimize the biomechanics of repairs. In fractures of the mandible and maxilla, wires are used to close fracture gaps and increase stability in order to improve the environment for secondary bone healing (Chapter 36).