Nonseptic osteitis of the distal phalanx and its palmar processes

Comparison of distal extremity magnetic resonance imaging findings in Australian racing Standardbreds and Thoroughbreds

INTRODUCTION

Foot-related lameness is common in Standardbred and Thoroughbred racehorses. Magnetic resonance imaging (MRI) provides information on both the soft tissue and osseous structures of the distal extremity. The aim of this study was to determine whether abnormalities identified on distal limb MRI differed between these two racehorse populations.

MATERIALS AND METHODS

The records of Standardbred and Thoroughbred racehorse distal extremity MRI examinations conducted at Camden Equine Centre and Ballarat Veterinary Practice between 2013 and 2023 were retrieved. Horses were included if pain causing lameness had been localised to the foot using perineural or intra-articular analgesia. MRI abnormalities of the structures within the distal extremity were recorded and comparisons made between the two groups.

RESULTS

There was a significant difference in the rate of occurrence of certain MRI abnormalities between the Thoroughbred and Standardbred racehorse populations, including distal phalangeal fractures, proximal phalangeal short tau inversion recovery (STIR) hyperintensity (distal aspect), the presence and severity of ungular cartilage ossification, abnormalities of the navicular bone distal border synovial invaginations/vascular channels and navicular bone distal border fragments. The presence of distal extremity STIR hyperintensity and fractures was significantly higher in Standardbred compared to Thoroughbred racehorses when these findings were grouped and considered in combination.

CONCLUSION

There were many similarities in the distal extremity MRI abnormalities identified in lame Australian Standardbred and Thoroughbred racehorses. However, distal phalangeal fractures, ungular cartilage ossification and distal extremity STIR hyperintensity were identified in significantly more in Standardbred than Thoroughbred racehorses.

Evaluation of the diagnostic accuracy of skeletal scintigraphy for the causes of front foot pain determined by magnetic resonance imaging

There is good correlation between increased radiopharmaceutical uptake anywhere in the feet of sports or leisure horses and the presence of foot pain. However, low sensitivity of scintigraphy for identifying lesions contributing to foot pain as determined by magnetic resonance imaging (MRI) has been reported. The aim of this retrospective, cross-sectional, analytical study was to assess the accuracy of scintigraphy for identifying the cause(s) of foot pain, using MRI as the reference standard. Sports and leisure horses that underwent both skeletal scintigraphy and MRI of the front feet between March 2008 and December 2014 and for which a definitive diagnosis of the cause(s) of front foot pain was reached were included (121 feet of 70 horses). Imaging studies were evaluated retrospectively, blindly. Agreements between scintigraphic localization of increased radiopharmaceutical uptake and subjective categorization of lesions with MRI diagnosis were assessed using Kappa statistics (κ). Measures of diagnostic accuracy were calculated. Sensitivity of increased radiopharmaceutical uptake varied among regions (31.8-76.2%) but specificity was at least high for all (84.6-100%). Agreements between both scintigraphy measures and MRI diagnosis were substantial for the distal phalanx (palmar processes and body) (κ = 0.77 and κ = 0.74, respectively), and ungular cartilages and chondral ligaments (κ = 0.62, for both). When all regions were combined, agreements of increased radiopharmaceutical uptake (κ = 0.49) and relevance categorization (κ = 0.45) with MRI diagnosis were moderate. In conclusion, skeletal scintigraphy does not meet the minimum reliability level for a diagnostic test, but is reliable for identification of osseous trauma to the distal phalanx and ungular cartilages.