Brad Dowling BVSc MVetClinStud FACVSc
Registered Specialist in Equine Surgery
North Queensland Specialist Equine Service
Townsville Veterinary Clinic
The horse’s hock is made up of four joints. The upper-most joint is the flexible or hinge joint and the three lower-most joints are the non-flexible joints. The lower-most hock joints are referred to as high-load-low-motion joints and serve as the ‘shock absorbers’ of the hind legs. Bone spavin or arthritis of the lower hock joints is the most common cause of hind limb lameness in performance horses. Lameness associated with the lower hock joints has been reported to occur in approximately 70% of horses with hind limb lameness.
The causes of hock arthritis include the intensity and type of exercise and conformation of the horse. Exercise or athletic trauma leads to damage and death of the cartilage lining of the joint, which causes pain and arthritis. Horses’ with straight hocks, sickle hocks or cow hocks are more likely to develop hock arthritis. Young growing horses with hock osteochondrosis (OCD) may also develop hock arthritis. Horses’ competing in show jumping, eventing, western performance events and camp drafting are prone to hock arthritis.
Some horses develop an obvious lameness that is easily seen or felt by the rider. However, more often than not the signs are subtle and owners may notice signs of resisting during work, a change in attitude, bucking, reluctance to stop, or back up or do roll-backs. Some horses have difficulty picking up canter leads, become stiff to the leg and develop back pain. A diagnosis can be achieved through a combination of a thorough lameness examination and x-rays.
Treatment of hock arthritis depends on how advanced the condition is at the time of diagnosis. Medical treatment in the form of pain relieving drugs such as phenylbutazone (Bute), or cortisone will often provide initial relief from signs. However, as the condition worsens horses will often remain lame. As radical as it sounds fusion of the lower hock joints can and does provide relief from lameness. As mentioned before these joints are not meant to move very much.
As the condition worsens, the joint cartilage is lost and the bones move against each other causing pain. Fusing the joints prevents this movement and alleviates pain and lameness. Initial studies looked at surgical drilling to fuse these joints, however the expense and relatively high complication rates have limited the use of these techniques. More recently chemical fusion has been evaluated and found to be less invasive, more economical and allow horses to return to work faster. Chemical fusion of the lower hock joints can be performed in the standing sedated horse, and horses can generally return to work within 7 days.
Treated horses undergo a graded exercise program with most able to return to full work by 6 months. One study reported approximately 80% of horses to be sound 12 months after undergoing the procedure (Dowling BA et al Australian Veterinary Journal 2004).