Findings
- Within the palmar aspect of the third metacarpal bone lateral condyle, a large and poorly defined region of decreased signal intensity is noted within the subchondral bone (blue outline). Centrally, within this region of low signal intensity, there is a thin, sharply marginated and linear high signal intensity lesion, measuring approximately 2 cm, noted on the PD and STIR sequences, which courses in a proximal-distal orientation (yellow arrowheads). This high signal lesion extends to the palmar and distal articular margins of the third metacarpal bone.
- On the STIR sequence, there is an ill-defined increase in signal intensity noted within the medullary cavity surrounding the low signal region within the third metacarpal bone of the lateral condyle.
Conclusions
- Incomplete right third metacarpal bone lateral condylar fracture with focal sclerosis and mild condylar bone marrow fluid (e.g. edema).
A little bit more…
- Most common in Thoroughbred racehorses but also reported in Standardbreds, Quarter Horses, and polo ponies.
- Some studies report that it represent the most common fracture type acquired during racing or race training. In California, 54 out of 263 (20.5%) TBs euthanized because of a fracture had a partial or complete fracture of the lateral condyle of MCIII.
- TBs have significantly more lateral condylar fractures and the forelimb is more often affected.
- Horses in their first year of racing may be at an increased risk of fracture on the racecourse.
- Fractures typically occur in a sagittal orientation with or without displacement of the fractured fragment.
- Proposed fracture classification based on their locations:
- Some studies report that the left forelimb may be more commonly affected by others report an equal distribution between the left and right forelimbs.
- Likely stress-related secondary to chronic concussive trauma from excessive forces on the MC/MT bones. Bone will undergo modeling in size and shape in response to excessive forces. Fatigue fractures results when damage exceeds the bone’s ability to repair itself.
Diagnosis
- The dorsodistal-palmaroproximal oblique projection (bucket shot) highlights the palmar/plantar margin of the distal MC/MT bone, where these lesions occur more frequently.
- Computed tomography and PET-CT may help detect these fractures at an earlier stage.
References
- Parkin, T. D. H., et al. “Risk factors for fatal lateral condylar fracture of the third metacarpus/metatarsus in UK racing.” Equine veterinary journal 37.3 (2005): 192-199.
- Whitton, R. Christopher, et al. “Third metacarpal condylar fatigue fractures in equine athletes occur within previously modelled subchondral bone.” Bone 47.4 (2010): 826-831.
- Radtke, Catherine L., et al. “Macroscopic changes in the distal ends of the third metacarpal and metatarsal bones of Thoroughbred racehorses with condylar fractures.” American journal of veterinary research 64.9 (2003): 1110-1116.
- Bassage, Lance H., and Dean W. Richardson. “Longitudinal fractures of the condyles of the third metacarpal and metatarsal bones in racehorses: 224 cases (1986–1995).” Journal of the American Veterinary Medical Association 212.11 (1998): 1757-1764.
- Zekas, Lisa J., et al. “Characterisation of the type and location of fractures of the third metacarpal/metatarsal condyles in 135 horses in central Kentucky (1986–1994).” Equine veterinary journal 31.4 (1999): 304-308.
- Riggs, C. M. “Aetiopathogenesis of parasagittal fractures of the distal condyles of the third metacarpal and third metatarsal bones‐review of the literature.” Equine veterinary journal 31.2 (1999): 116-120.
