Читать книгу Fractures in the Horse - Группа авторов - Страница 113

Osteoblasts have been seen forming callus in experimental fractures within hours of injury [76], and in man scintigraphic uptake has been observed at fracture sites between 6 and 72 hours following the onset of pain [77–79]. A human study concluded that the minimum time for a bone scan to become abnormal following monotonic fracture was influenced by age with younger patients having a quicker detection time [77]. This likely reflects a confounding effect of metabolic bone disease in older patients and should have limited impact on the majority of equine patients. It is likely that most stress fractures will be identifiable scintigraphically when lameness is evident and this has been documented in human and equine patients [27, 28, 31,36–39, 62,79–90]. However, there are two scenarios that may contribute to false negatives. It is possible that very early stress reactions characterized only by cortical tunnelling in the absence of new bone formation may appear as unremarkable cold spots [91]. Secondly, in the equine patient when pelvic fractures are presented in prodromal or per acute phases, a combination of location with muscle and distance attenuation can conceal IRU. This can result in a negative scan with retrospective diagnosis following osseous displacement [92] or in the case of a stress reaction, progression to fracture when the horse returns to training. To avoid false negatives, a delay is recommended between the onset of lameness or trauma and nuclear scintigraphy. Five to seven days have been proposed as a minimum [93]; however, a 10–14 day delay would make the possibility of obtaining a false negative unlikely. Alternatively, if the initial evaluation is negative and a pelvic fracture is still suspected, an additional scintigraphic examination could be performed at a second time point after not less than 10–14 days (Figure 5.8) [91, 92]. The financial and ionizing radiation implications would, in most circumstances, support an initial delay.