The Horse

MAR 2018

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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YOUR GUIDE TO THE 2017 AAEP CONVENTION SPONSORED BY A18 TheHorse.com/AAEP2017 AAEP Wrap-Up THE HORSE March 2018 Grade 1 to 3 lame (out of 5) on one leg. All horses had MRI evidence of a sagittal groove injury, Gold said, but the characteristics varied: ■ Three had osseous cystlike lesions (a bone defect or abnormality); ■ Eight had subchondral (the layer below the joint cartilage) bone loss; ■ Four had incomplete midsagittal frac- tures ("cracks"), near the center of the bone; and ■ Four had high fluid signal intensity (lighter color on MRI) of the groove's subchondral and trabecular bone (indi- cating fluid in the bone). Vets took radiographs in 13 horses to compare results to the MRI, she said. They found apparent abnormalities in just six horses' radiographs. Gold said 15 horses had fetlock joint osteoarthritis. Practitioners had treated 18 horses con- servatively and sent one horse to surgery. At follow-up—on average, 29 months after diagnosis—Gold said six horses (31.5%) had returned to their prior use and 13 (68.5%) remained unsound. All un- sound horses blocked to the fetlock joint. Two horses with incomplete fractures had healed and their lameness resolved. Two of the lame horses' fractures had not healed or they developed an osseous cystlike lesion in the groove, and three persistently lame horses had subchondral bone osseous cystlike lesions. In eight horses diagnosed initially with abnormal pastern signal, lesions were smaller, but only two of these animals were sound at follow-up. In horses with ill-defined subchondral bone loss at the sagittal groove, lesions were smaller in five horses, unchanged in two, and more extensive in one. Concurrent fetlock joint osteoarthritis was worse in three horses and remained unchanged in 12. Researchers on previous studies saw better outcomes for sagittal groove injuries in racehorses, she said, but this could indicate these horses experience a different pathologic (disease or damage) process than sport horses. Horses in this study might have experienced chronic joint trauma and a delayed diagnosis or might have had arthritis prior to the sagittal groove trauma, Gold said. Both could have complicated healing. "Based on this sample, the prog- nosis for performance soundness in COURTESY DR. SARAH GOLD In Dr. Sarah Gold's study, some osteochondral cystlike lesions in the subchondral bone of the sagit- tal groove were less visible on radiographs (left, center) than on MRI (right). Which PSD Horses Are Good Hind- Limb Neurectomy Candidates? Proximal suspensory desmitis (PSD) can sideline horses for months. Hind-limb cases can be especially challenging to manage—conservative treatment has a poor prognosis, and while surgery generally produces better results, not all horses are candi- dates. The good news? Vets can carefully select surgical cases to improve outcomes. Ashlee Watts, DVM, PhD, Dipl. ACVS, an assistant professor of large animal surgery at the Texas A&M; University College of Vet- erinary Medicine & Biomedical Sciences, in College Station, said vets have a better understanding of the disease and diagnostic blocks than they had historically, along with access to improved imaging (ultrasound and MRI). Even when equipped with these advances, selecting the right patients for surgery doesn't come without challenges. Watts reviewed which horses should and shouldn't go under the knife. Proximal suspensory desmitis is inflammation and tissue dam- age in the upper part of the sus- pensory ligament that connects to the top back of the cannon bone and the proximal sesamoid bones at the back of the fetlock. Traditional treatment involves stall or pasture rest with or without medical therapies. Surgeries include neurectomy of the deep branch of the lateral plantar nerve (cutting the nerve) and fasciotomy (ligament splitting). Watts shared these tips for selecting surgical candidates: ■ Ensure an accurate diagnosis. ■ Be sure the suspensory injury is chronic. Performing surgery on acute cases leaves horses at risk for developing very severe, chronic PSD afterward. ■ Do not send horses with hyperextended hind-limb and hock conformation to surgery. "This conformation is known to significantly increase the risk of catastrophic failure of the suspensory apparatus following fasciotomy and neurectomy," Watts said. Vets should conduct a recheck ultrasound two months after surgery to look for iatrogenic (inadvertently caused by the clinician) lesions—which can occur but don't appear to affect prognosis—and/or new injury. This exam also affords an opportunity to get "new" baseline images. "When cases are selected appropriately, the complication rate is very low and the prognosis for a full return to work is very good, with approximately 80% of horses returning to the previous level of work for at least one year," Watts said. "It has been our experience and that of others that when the horse responds favorably to fasciotomy and neu- rectomy, the long-term outcome beyond one year is excellent." —Erica Larson A B C

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