Читать книгу Fractures in the Horse - Группа авторов - Страница 129

In anatomically accessible areas, CT has the potential to provide additional and useful information for the identification and characterization of all fractures, whether they are managed conservatively or with surgical intervention. The benefits must be weighed against the potential risks associated with acquisition such as general anaesthesia and moving the horse to or through the scanner.

CT is considered the gold standard for fracture diagnosis and evaluation of three‐dimensional configuration. Complex, comminuted, articular fractures, small, minimally displaced fractures of long bones or simple fractures in complicated anatomic regions are best evaluated with cross‐sectional CT imaging with or without 3D or surface rendering. In humans and horses, CT has been shown to be more sensitive than radiographs for identifying fractures and recognizing comminution [117–121].

The three‐dimensional nature of CT has proved integral to presurgical planning and has been reported for the central tarsal bone [122], distal phalanx [123, 124], navicular bone [124] and proximal phalanx [125]. This is also the case in the authors experience for third carpal bone fractures (Figure 5.11); further applications are documented throughout the book. It has been repeatedly shown to give better spatial information and thus recognition of fracture configuration and complexity and the structure of affected bones and fragments [126]. In addition, areas with complex anatomy or shape, such as the distal phalanx, where dimensions vary according to orientation, and cases with multifocal pathology are only adequately assessed by CT [123, 126, 127].

Osseous trauma of the skull is better evaluated with CT than plain radiographs with respect to identification [128], classification and surgical planning [129], although small fractures maybe missed if inappropriate window parameters are chosen [130] (Chapter 36). The basics of acquisition, i.e. thin slice thickness, and appropriate reading, i.e. bone algorithms, are essential [131]. CT can also differentiate between structures that radiographically mimic fractures such as suture lines or overlapping sinuses.

Figure 5.11 Evaluation and surgical planning of two‐third carpal bone fractures. (a) Dorsal 35° proximal–dorsodistal oblique radiograph demonstrating a parasagittal plane fracture of the radial facet and corresponding dorsal plane reformatted CT image revealing the fracture line to extend from the middle carpal joint to the distal subchondral bone plate. A lag screw was therefore placed in a central position in the bone. (b) Flexed dorsal 35° proximal–dorsodistal oblique radiograph demonstrating a dorsal plane fracture of the radial facet and corresponding sagittal plane reformatted CT image demonstrating the fracture to be located in the proximal third of the bone. The surgical implant was therefore placed proximally in the bone at the mid‐point of the fracture.

Small, portable CT machines can be used during surgical procedures. CT‐assisted surgery of navicular bone and distal phalangeal fractures has increased surgical accuracy and reduced surgery time. Barium paste as markers for orientation applied to the hoof wall [124], and surgical skin staples [122] have been used as surface locators.