Resident Veterinary Medical Teaching Hospital, Large Animal Clinic Woodland, California
Metacarpal condylar fractures in Thoroughbred racehorses result from cumulative microdamage and maladaptive stress remodeling. Positron Emission Tomography (PET) is available for imaging standing horses and is very sensitive for detection of bone stress remodeling. We hypothesized condylar fractures will be associated with increased 18F-NaF uptake that will decrease as the fracture heals, other pathology within the fetlock joint will be present, and the contralateral limb will display an abnormal pattern, representing early stages of condylar fracture development. Fourteen Thoroughbred racehorses having sustained a condylar fracture were imaged using 18F-NaF PET within 48 hours of fracture repair with follow-up scans 3 and 5 months later. Uptake at the fracture site and in additional structures was present in all 14 horses. Eight fractures originated from the parasagittal groove (PSG) (six lateral and two medial) and six occurred through the palmar/plantar condyle (all lateral). Fractures outside of the PSG were often associated with uptake consistent with palmar osteochondral disease. Seven of the 8 horses with fractures through the PSG did not demonstrate condylar uptake consistent with palmar osteochondral disease. In nine horses with follow up scans, six had no activity at the previous fracture site by 90 days. Three horses developed periarticular uptake consistent with degenerative changes by 90 days, with two having persistent uptake at the fracture site. Limitations include small sample size and absence of structural imaging. The recognition of specific pattern of 18F-NaF uptake could help prevent condylar fractures. 18F-NaF PET is also a pertinent tool for post-operative management.
