To describe clinical, imaging, gross, and histopathological abnormalities associated with osteochondral necrosis of the femoral condyles in foals and identify features suggestive of a common pathogenesis.
8 Thoroughbred foals euthanized with a presumptive diagnosis of necrosis of the femoral condyles.
Postmortem CT was performed on all distal femoral epiphyseal samples. The articular epiphyseal cartilage complex (AECC) of affected distal femurs was examined grossly and histologically, focusing on lesions of interest identified on CT images.
7 foals were between 9 and 23 days old at the time of euthanasia; 1 foal was 85 days old. Concurrent illness (neonatal maladjustment syndrome, neonatal isoerythrolysis, or infection such as enteritis and omphalitis) was diagnosed in 7 foals. The characteristic antemortem radiographic and postmortem CT finding was a crescent-shaped osteochondral flap displaced from the affected medial femoral condyle. Synovial fluid cytology from affected joints was either within normal limits or consistent with mild inflammation. Histologically, all lesions were characterized by osteochondral necrosis and detachment of the AECC. In 6 foals, polymorphonuclear cells were found within growth cartilage canals, representing septic cartilage canals.
Osteochondral necrosis was interpreted to be secondary to bacterial colonization of the distal femoral AECC, evidenced by septic cartilage canals identified in 6 of 8 foals. This uncommon condition was previously thought to arise from an ischemic event, but the disease process was not well understood. An improved understanding of the pathogenesis of osteochondral necrosis is the first step in formulating more successful preventative and treatment strategies.
To assess the repeatability of equine 18F–sodium fluoride (18F-NaF) positron emission tomography (PET) findings, and to evaluate the ability of PET to monitor the progression of areas of increased radiopharmaceutical uptake (IRU) in the fetlocks of Thoroughbred racehorses.
25 racehorses with clinical signs related to fetlock injuries.
This study is a prospective, longitudinal clinical study. Twenty-five racehorses (54 fetlocks) underwent three 18F-NaF PET scans 6 weeks apart. The first 18F-NaF PET scan was performed at the start of a 12-week period of rest from racing (lay-up). Areas of IRU in the fetlock joints were quantified using maximal standardized uptake values (SUVmax) and were graded by 2 experienced observers. Statistical comparisons were made between scans to detect changes in IRU grade and SUVmax over time.
Standing PET findings were repeatable, with 131/149 (88%) areas of IRU identified on the initial scans seen again at the 6-week follow-up scan. The palmar/plantar condyles were the sites most commonly presenting with IRU, followed by the proximal sesamoid bones. Overall, 65% of fetlocks demonstrated improvement in IRU grade during the 12-week period of rest from racing. Areas of higher IRU grade took longer to resolve than the lower graded areas.
Standing PET findings in the racehorse fetlock were repeatable. The SUV-based grading system may be helpful when determining appropriate lay-up duration for Thoroughbred racehorses. PET may be used to monitor areas of the fetlock involved in catastrophic breakdown injuries in Thoroughbred racehorses.