Читать книгу Fractures in the Horse - Группа авторов - Страница 125

Nuclear scintigraphy has been used in man to monitor healing in both monotonic and stress fractures [19, 28, 77, 114]. In the first (acute) phase, there is a diffuse area of IRU due to increased blood flow around the fracture site. This is greater than the morphological fracture and persists for two to four weeks after injury. The second (subacute) stage has the most intense well‐defined IRU which corresponds more accurately with the anatomical fracture and lasts for 8–12 weeks (Figure 5.8b). Over the coming weeks and months as callus remodels during the third (reparative) stage, there is a more localized area of IRU with greater separation between normal and abnormal tissues followed by a gradual reduction in activity. The time of scintigraphic normalization is greater than that identified clinically or radiographically due to ongoing bone remodelling. In man, monotonic fractures can take up to 24 months [77] and stress fractures between four to six months [28]. In stress fractures, severity was a major determinant of time to resolution, and patients who failed to rest and had continuing pain had persistent unresolved lesions [28].

Figure 5.10 Four‐year‐old Thoroughbred racehorse with acute severe right hindlimb lameness. (a) Caudocranial radiograph of the right tibia on the day of presentation. No abnormalities detected. (b) Lateral and caudal scintigrams of the right tibia. Linear IRU is present in the distal tibial metaphysis and diaphysis compatible with a propagating tibial fracture. (c) Radiographs taken at two, four and eight weeks post injury. Progressive osseous resorption permits identification of sharply marginated radiolucent fracture lines (black arrows). Areas of increased radiopacity are consistent with formation of trabecular and cortical callus (white arrows), which gradually bridges the fracture. Note also the distal lateral fracture line eight weeks post injury that is slow to become radiographically apparent.

It has been suggested that horses with evidence of stress fracture undergo scintigraphic review before they return to work [106]. This is not routinely practised in the UK where financial constraints and well‐accepted stress fracture management regimes have precluded longitudinal studies. Horses in training that have undergone nuclear scintigraphy in subsequent seasons have demonstrated subtle uptake at previous fracture sites. The degree and distribution of the ^99mTc‐MDP uptake is usually mild, ill‐defined and compatible with bone remodelling.

In a study of equine distal phalangeal fractures, activity was reported to persist for >25 months. This was ascribed to a fibrocartilaginous union, fracture instability, osteolysis and osteoid formation [115].

A study of dorsal cortical fractures of the third metacarpal bone reported correlation between persistence of a radiographically evident fracture line with less intense scintigraphic uptake and individuals who did not heal and required surgical intervention [58]. The supposition made was that the degree of ^99mTc‐MDP uptake was directly correlated with osteogenesis and rate of repair, thus diminished uptake in the absence of radiographic resolution indicated either a delayed or non‐union.

Sequential evaluations in the days and weeks following surgery were reported in three horses (four year old, yearling and foal) that had sustained a variety of traumatic fractures to the third metacarpal or metatarsal bones. Two cases developed photopenic regions less than six days post‐operatively, one was described as extensive and at necropsy this correlated with osteomyelitis and sequestration [116].