Ultrasound and sMRI Imaging of the Equine Foot Compared
A recent study in Belgium compared the use of ultrasound and standing magnetic resonance imaging (sMRI) to identify issues within the equine podotrochlear apparatus (the atomical features involved in what’s commonly known as navicular syndrome or disease). The researchers found the two modalities complemented each other, with ultrasound detecting more deep digital flexor tendon (DDFT) lesions and sMRI showing more palmar navicular abnormalities.
Laurence Evrard, DMV, Dipl. ECVDI, MRCVS, in the Medical Imagery Department of the Faculty of Veterinary Medicine at the University of Liège, in Belgium, led the study. She and her fellow researchers investigated the causes of foot pain in 30 horses referred to the equine hospital between 2016 and 2019 for forelimb lameness localized to the foot, as shown by nerve block. X rays of the feet had not provided any clear findings in these horses. Two board-certified equine radiologists independently ran sMRI from multiple angles on the affected feet and ultrasound through the heel bulbs and the frog of the sedated horses, using strict protocols designed for optimal ultrasound examination of the equine foot.
“Based on the results of this study, we know that agreement between ultrasound and sMRI is moderate for suprasesamoidean DDFT lesions and navicular bursitis,” she told The Horse. “Vets could therefore screen the DDFT and bursa with ultrasound in horses with foot pain, provided the technique is mastered.”
The radiologists each analyzed either the sMRI images or the ultrasound images for all the horses without knowing what the images from the other technique revealed. The researchers then compared their observations.
They found that ultrasound revealed slightly more DDFT abnormalities but fewer palmar navicular abnormalities than MRI did, she said.
This doesn’t mean the ultrasound is a better tool for finding DDFT lesions, however, said Evrard. Because the horses’ feet were not subsequently dissected (as these were client-owned horses), determining which of the two techniques was most accurate is impossible.
“It’s true that ultrasound detected more DDFT lesions than sMRI in the suprasesamoidean region, but we don’t know whether ultrasound detected false positive cases or sMRI missed (false negative) cases,” she said.
More importantly, ultrasound can miss critical details about lower regions of the foot and even about the lesions it does reveal, said Evrard.
“Whereas ultrasound appears able to detect suprasesamoidean DDFT lesions, it does not allow us to achieve a complete and accurate evaluation of lesion morphology or extent, so it is limited in its ability to provide accurate management and prognosis compared to sMRI,” she explained. “It is also limited in the identification of more distal lesions (at the level of the navicular bone down to the phalanx).
“Therefore, ultrasonography would be a useful screening tool in horses when sMRI is not an option, since it definitely adds valuable information to the routine radiographic examination,” Evrard continued.
“Detecting DDFT lesions and/or navicular bursitis with ultrasound may help the treating veterinarian to decide to treat the navicular bursa and/or to use a corrective shoeing, for example,” she said. “But sMRI should be considered to define the most appropriate management and consequently to increase the probability that the horse returns to its previous level of activity.”
The study, “Comparison Between Ultrasonographic and Standing Magnetic Resonance Imaging Findings in the Podotrochlear Apparatus of Horses With Foot Pain,” appeared July 5, 2021, in Frontiers in Veterinary Imaging.
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