Treating Intraosseous Pressure in Horses

Treating Intraosseous Pressure in Horses

Today, close to three years since the initial injury, Mashatu is sound, in full work, and is still one of the top horses in the stable, van der Merwe said.

Photo: Leanne van der Merwe

It started with a simple wound—a gash on the leg foreleg during an African safari trail ride. With time, bandages, antibiotics, and phenylbutazone, the then 9-year-old gelding's wound healed well and caused no signs of lameness. So why did Mashatu become markedly lame a week later? And why, five weeks after the injury, did he end up non-weight-bearing lame on the affected limb?

According to his treating veterinarians at the Onderstpoort Veterinary Academic Hospital in the Republic of South Africa, intraosseous pressure—pressure inside the bone itself; specifically, inside the radius' medullary cavity—was to blame for Mashatu’s pain.

The solution? According to the authors of a recently published study, a 3.2-mm drill bit.

In Mashatu's case, veterinarians couldn't find any visible injuries on the affected leg, and X rays only revealed some irregular new bone formation from the wound healing process. But on a nuclear scintigraphy exam, or a bone scan, veterinarians found significant radiopharmaceutical build-up, or a "hot spot," inside the left radius bone behind the five-week-old scar, said Mashatu's treating veterinarian, Luis M. Rubio-Martinez, DVM, DVSc, PhD, Dipl. ACVS, ECVS. Rubio-Martinez was an associate professor in equine surgery at the University of Pretoria at that time and treating veterinarian for Mashatu at Onderstpoort. 

Veterinarians suspected increased intramedullary pressure, Rubio-Martinez said, and administered a nerve block around the hot spot, which improved the horse's lameness.

Then, veterinarians decided to perform a unique equine surgery only reported once before, in 1999. They drilled two 3.2-mm (1.26-inch) holes, 6 cm (2.36 inches) apart, into the bone's medullar cavity. Pressure readings from the holes revealed very high levels of pressure, and the surgeons aspirated out the fluid build-up—consisting primarily of blood—from inside the bone. Their pioneering effort was a success.

“The horse was on his feet after recovery from anesthesia, he was able to walk, putting full weight on the affected limb without the need of much pain medication,” Rubio-Martinez said.

The horse still had a slight limp at the walk, Rubio-Martinez added, but this improved gradually over time. Full recovery took a year and a half, including several months of stall rest and then paddock rest as the bone healed.

Today, close to three years since the initial injury, the horse is “perfectly sound and in full work,” Rubio-Martinez said.

So how do veterinarians believe intraosseous pressure develops?

Intramedullary pressure is usually “secondary to a decrease of outflow of blood from inside the bone towards the outside,” said Rubio-Martinez. “Our hypothesis is that the inflammation and new bone around the radius that probably developed after the trauma impaired the normal outflow vessels of the bone, and this caused an accumulation of blood inside the bone. Also, inflammation in that area could have led to chronic inflammation and fibrosis, which could have been impairing the normal drainage of the bone.”

He said he considered the release process with drill bits to be a one-time intervention. “Once we create the holes, the pressure inside the bone is released, and then we expect that the bone will remodel in a way that will allow a normal drainage again,” Rubio-Martinez said. “Intraosseous pressure should be considered as a cause for lameness in horses,” he concluded.

Pressure-free and pain-free, Mashatu now gallops as a spunky 12-year-old gelding should, said Leanne van der Merwe, equine manager of Ant’s Nest Lodge safari riding tour company at the time of the injury.

“Mashatu was and still is one of the top horses in the stables,” she said. “He is kind, beautiful, and enjoys what he does. He gives his best to everyone who rides him, right to the end. I believe that this is what made Mashatu persevere through this trauma, and made him pull through with flying colors.”

Mashatu was initially treated by Paul Huber, DVM, of Kranskop Dierekliniek in Nylstroon before Huber referred the horse to Rubio-Martinez, who is currently an equine surgeon and senior lecturer in Equine Orthopaedics & Surgery at the School of Veterinary Science of the University of Liverpool, the UK. Ann Carstens, BVSc, MS, MMedVet, DECVID, DTE, PhD, is an associate professor in diagnostic imaging at the University of Pretoria and provided assistance with Mashatu's scintigraphic evaluation.

The study, "Medullary decompression of the radius as treatment for lameness in a horse," was published in Veterinary Comparative Orthopaedics and Traumatology

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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