When a horse fractures the point of his shoulder—the supraglenoid tubercle, located in the lower scapula—it’s usually career-ending. In fact, in many cases, it’s career-preventing; this type of fracture is most common in young horses that haven’t yet started training and often occurs as a result of direct trauma to the shoulder or avulsion fractures caused by tension of the biceps tendon. And even when surgeons repair the fracture successfully, complications such as fixation failure, arthritis, nerve damage, and muscular atrophy can cause chronic lameness.
Researchers in Switzerland recently took a look at a potential new solution for this problem: a locking plate designed for human geriatric patients. The team found that the distal femoral locking plate (DFLP), used to repair femur fractures in elderly patients with porous bones, showed promise in healing broken equine scapulas. The plate allows surgeons to place multiple screws into the fracture fragment for better fixation. The trick, however, is not to damage the highly sensitive suprascapular nerve in the process.
“The suprascapular nerve innervates the muscles in the shoulder area that provide lateral support to the shoulder, and if it’s damaged, those muscles are going to atrophy,” said Andrea Bischofberger, DrMedVet, Dipl. ACVS, ECVS, an equine surgeon at the University of Zürich Vetsuisse-Faculty Equine Hospital.
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Placing a 16- to 20-centimeter-long plate along the flat scapula bone risks damaging, even crushing, that suprascapular nerve that lies across the surface of the bone, she said. Given the stability benefits of the plates compared to fixation using only screws, the researchers sought to find a solution for protecting the nerve.
“Screw fixation in the past has often led to incomplete fracture repair in these horses because they just don’t hold the broken bone parts together nearly as well as a plate can,” Bischofberger said. “Most of them end up pasture-sound but can’t be ridden anymore. We knew that if we could protect that nerve while using the plate, we had a chance of getting these horses back to athletic soundness.”
Bischofberger and her fellow researchers tested different DFLP placement techniques in three horses presented to their equine hospital with supraglenoid tubercle fractures.
In the first, a yearling colt, the surgeons lay the plate on the back part of the scapula, where the suprascapular nerve had already branched off. The colt’s fracture healed well, but he showed muscle atrophy in the shoulder that caused a shortened step, shoulder instability, and lameness. Two years later, surgeons removed the plate.
“After this he had slight lameness and muscle atrophy, but he was making good progress and the owner was satisfied,” Bischofberger said.
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In the second case, a 10-year-old gelding, the surgeons tried lifting the suprascapular nerve and placing the plate under it. While this resulted in good healing, the horse showed much more muscle atrophy than the first horse did, even though he was being ridden at the walk and the trot just eight months after surgery.
The surgeons chose to remove his plate as well, and they found that the nerve had been “visibly damaged by the plate.” Two years later, though, he had recovered well, with no more shoulder muscle atrophy. He was sound in walk, trot, and canter and was being ridden for pleasure, his owner reported.
For the third case, the surgeons decided to try yet another technique: looping over the suprascapular nerve. They repaired a yearling filly’s fracture with a plate that they bent into a looplike shape to go over the nerve without touching it, said Bischofberger.
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Case 3 had the best outcome of the three, despite a slight post-operative, superficial surgical site infection. The filly healed very well. Two years after surgery, she had started training under saddle with no lameness or atrophy. She was working in all three gaits and had been started over fences.
“It’s a challenge to find stable fixation methods that don’t interfere with other structures or impinge on critical nerves, but the results in these three cases are encouraging,” Bischofberger said.
The study, “Fixation of supraglenoid tubercle fractures using distal femoral locking plates in three Warmblood horses,” was published in Veterinary and Comparative Orthopaedics and Traumatology.