The horse’s hip is its powerhouse. As one of the largest joints, surrounded by some of the most powerful muscles, the hip is essential to movement. Lameness caused by injury or damage to the hip is rare, especially considering that 95 percent of lameness originates in the hoof. But when it occurs, hip disease can be career ending for a performance horse and possibly require euthanasia.
The most important cause of hip problems is traumatic injury causing broken bones. These can in-clude falls, smashing the hip into an object at high speed (running through a narrow gate) or slipping on ice.
Less frequently, long-term wear and tear injury from abnormal movement or structural imbalances progress to hip joint arthritis and ligament damage.
Broken bones, whether the pelvis or femur, have more dramatic clinical signs that make diagnosis straightforward. In association with a traumatic event, the horse will be lame but usually able to bear weight.
The hip muscles may be swollen or atrophied, making them asymmetrical with the normal side when viewed from behind. Finally, there should be pain and crunching/gas when the hip is touched.
Foals seem to be affected by hip fractures more often than adults, likely because the multiple hip and femur growth plates are weaker than mature bone.
Diagnosing chronic hip joint disease is more challenging. Unlike senior people with arthritic hips, horses can’t tell us where it hurts. And in a horse that is chronically lame, the most likely cause is in the hoof, so a lameness ‘work up’ is in order.
If horses were dogs, this would all be much easier. We would lay them on their side, rotate, bend and flex the leg, all the while feeling the hip joint for instability and crunching under the comparatively tiny muscles. If a hip problem is suspected, x-rays are a snap and with lower muscle mass, the bones and hip joints are sharp and clear, making diagnosis relatively straightforward.
But with horses, we have to work step by step. Typical lameness exams involve watching the horse walk and trot in a straight line and on a circle to identify the affected leg. Next the leg is examined for swelling, muscle atrophy, pain and heat. If hip injury is suspected it is especially difficult to feel the bones of the upper leg and pelvis due to the massive muscles covering these areas.
Various joints are flexed and the horse trotted off to see if this worsens the limping. Next comes a series of nerve blocks.
Starting with the toe and working up the leg, sections are frozen much like your dentist does before drilling. If the part of the leg that hurts is temporarily frozen, the horse no longer limps. When a horse continues to limp after lower leg blocks, then disease of the hip is a possibility.
To confirm that the hip is the cause of the lameness, medical imaging is necessary. Ultrasound can visualize the joint and surrounding ligaments.
X-rays are useful but are hard to get. Since there is so much muscle over the hip joint, high-powered machines are needed and the best view is taken when the horse is lying on its back.
To do this safely, the horse is given a general anesthesia, often the same one used to lay down stud colts for castration. General anesthesia always comes with risk but it is even more so if there is a fracture since the broken bones can move when the horse stands.
Another technique involves an intravenous injection of radioactive material. These particles hone in on places with high blood flow, including areas of tissue inflammation. The horse is scanned with a horse-sized gamma camera producing a fuzzy black and white image with ‘hot-spots’ where the radioactive material accumulated. If the hip is the problem, it should light up like a Christmas tree.
Once hip disease is diagnosed, treatment can also be challenging and depend on the nature of the problem. Fractures require strict stall rest and pain management for months. Arthritis and ligament injury may require rest, anti-inflammatory injections and a re-habilitation program to strengthen weakened muscles.
Dr. Jamie Rothenburger is a veterinarian who practices pathology and a PhD student at the Ontario Veterinary College. Twitter: @DrJamieR_Vet