Magnetic Resonance Imaging, Computed Tomographic and Radiographic Findings in the Metacarpophalangeal Joints of 31 Warmblood Showjumpers in Full Work and Competing Regularly

Simple Summary Magnetic resonance imaging (MRI) and computed tomography are increasingly used in the diagnosis of fetlock region pain in sports horses and racehorses. To establish an accurate diagnosis, it is paramount to be familiar with abnormalities that can be seen in horses in full work and without relevant lameness. The aim of this study was to describe MRI, computed tomographic (CT) and radiographic findings in the front fetlocks of showjumpers who were in full training and competing regularly. Thirty-one horses without previous fetlock disease or current lameness were included. The most common finding was densification (bone hardening) in the region just under the joint surface in the cannon bone and long pastern bone. These changes likely reflect an adaptive response to exercise. Small indentations and focal decrease or loss of bone density were seen in multiple locations and might reflect early stages of disease or might be incidental. In conclusion, MRI and CT abnormalities previously associated with lameness were seen in the front fetlocks of showjumpers in full work and without relevant lameness. This should be considered when interpreting imaging studies of lame horses.Abstract There is a limited description of magnetic resonance imaging (MRI) and no information on computed tomographic (CT) findings in the fetlock of non-lame, non-racing sports horses. This study aimed to document comparative CT, MRI and radiographic findings in the metacarpophalangeal joints of showjumpers in full work. Clinical and gait assessments, low-field MRI, fan-beam CT and radiographic examinations of both metacarpophalangeal joints were performed on 31 showjumpers. Images were analysed descriptively. In most limbs (53/62, 85.5%), there were CT and MRI changes consistent with densification in the sagittal ridge and/or condyles of the third metacarpal bone (McIII). Hypoattenuation (subchondral bone resorption) was seen in CT reconstructions in the metacarpal condyle dorsoproximally (n = 2) and dorsodistally (n = 1), in the sagittal groove (n = 2) and medial fovea (n = 1) of the proximal phalanx. The McIII resorptive lesions were detected on MR images but not the proximal phalanx lesions. None were identified on radiographs. In conclusion, MRI and CT abnormalities previously associated with lameness were seen in the front fetlocks of showjumpers without relevant lameness. Densification in the sagittal ridge and the metacarpal condyles likely reflects an adaptive change to exercise. Subchondral bone resorption may indicate an early stage of disease; follow-up information is needed to establish its clinical significance.