Conditions of the Hock
Dr. Patricia J. Provost
The hock is a complicated structure made up of 11 bones, numerous ligaments, several bursa, and 4 distinct joints: The tarsometatarsal joint
The distal intertarsal joint
The proximal intertarsal joint
The tarsocrural (tibiotarasal) joint
In addition, a number of tendons insert around or pass over the hock. With so many structures the hock is prone to both cosmetic blemishes and various acute and chronic conditions of lameness. The hock is a common source of chronic lameness due to arthritis, most often of the distal joints.
Arthritis of the hock can occur in any aged horse, including horses less than 1 year of age (juvenile arthritis) and affects all breeds. Arthritis can result secondary to trauma, poor conformation or as in most cases, simply as a wear and tear phenomenon of everyday work. Horses with heavy workloads and poor conformation would be expected to develop arthritis at an earlier age than those horses with perfect conformation participating in limited work.
Tarsometatarsal joint and distal intertarsal joint. Arthritis of the two distal joints of the hock is also known as degenerative joint disease, tarsitis, or in layman's terms as "bone spavin."
Proximal intertarsal joint and the tarsocrural joint. Arthritis can also affect these proximal joints, although less commonly.
Tarsocrural (tibiotarasal) joint. Inflammation in the tarsocrural joint results in an increase of joint fluid within the joint producing a visible swelling of the joint and sometimes behind the joint. This joint swelling is referred to in laymen's terms as a "bog spavin."
More common to the tarsocrural (tibiotarasal) joint is the condition osteochondrosis dissecans or OCD. OCD of the tarsocrural joint is a developmental condition, which means that the horse has had the problem since it was a neonate. The development of OCD is still not completely understood but it is thought to be influenced by genetics and nutrition. Horses' with OCD of the tarsocrural joint may or may not be lame and may or may not have joint swelling.
What to Watch For
Arthritis usually involves both hocks and is insidious in onset. Initial gait changes include stiffness at the onset of exercise with gradual improvement as the horse warms up.
Other signs include:
A narrow based gait,
Shortened anterior stride
Stabbing the toe into the dirt
Swinging the hindlimb beneath the body rather than flexing the hock
Your veterinarian will give your horse a physical examination, which will include the following:
Observation of the horse's conformation and gait at the walk, trot, and canter in a straight line and in a circle.
Palpation and passive range of flexion of the hock.
Performance of hind limb flexion tests.
Performance of intra-articular anesthesia to localize the lameness to a specific area of the leg or joint.
Radiograph the area of interest and examine for signs of arthritis or OCD.
Early stages of arthritis, which are manifested by mild stiffness at the start of exercise, can be managed with the judicious use of non-steroidal anti-inflammatory drugs, such as phenylbutazone and flunixin meglumine. Many of the non-steroidal drugs are available in oral as well as injectable forms. These drugs may lead to gastric ulceration or kidney problems if used in excess.
Horses with persistent or progressive signs of arthritis will often benefit from intra-articular therapy with either corticosteroid or hyaluronan or a combination of the two. Intra-articular injection of the joint may be necessary several to multiple times a year.
Horses with arthritis may also be treated intravenously with hyaluronan or intramuscularly with polysulfated glycosaminoglycan.
Horses which have severe arthritis not responsive to the above medications can be treated chemically or surgically to fuse the arthritic joints. Success rates vary from 60 to 80 percent.
There are numerous over-the-counter oral joint supplements currently available that are being marketed for treating arthritis. Anecdotally it appears that some of these products may be beneficial, however, there is limited scientific data to support this. Before selecting a particular product, discuss the potential benefits with your veterinarian.
Horses that have lameness secondary to the presence of OCD often benefit from surgical removal of the OCD lesions followed by 1 –3 months of rest.
Caring for a horse with degenerative joint disease of the hock is not difficult but does require common sense.
Horses that become stiff when they are stalled over night or for extended periods of time during the day often are more comfortable if they are housed in a larger stall or one that has a run-out paddock attached to it.
Horses should be allowed sufficient time to "warm-up" and become less stiff before being asked to engage in exercises that require them to flex their hocks and propel from the hind limb. This warm-up time will vary with each horse but should be between 20 to 40 minutes of walking and slow trotting.
Horses that fail to warm-up out of their stiffness should not be worked further, as doing so may injure the back and other joints, as well as result in the horse developing a very sour attitude. These horses definitely require a veterinarian's attention.
Horses recovering from surgery either to fuse an arthritic hock or to remove an OCD lesion will require several weeks to several months of stall rest. During the initial 2 – 3 weeks the hock will be protected with a sterile bandage. The bandage will need to be changed every day to every few days.
Following intra-articular medication with corticosteriods and/or hyaluronan, the horse is usually rested for 24 –48 hours then gradually returned to his regular exercise program. An increase in lameness following injection of these drugs should be brought to the immediate attention of your veterinarian.
Administration of hyaluronan, polysulfated glycosaminoglycans, phenylbutazone, flunixin meglumine and ketoprofen should be done so under the care of a veterinarian.
Consult your horse's veterinarian prior to the purchase and use of over-the-counter oral joint supplements.
There is no known method of care or treatment to eliminate or prevent arthritis of the hock. Attention should be paid to having the horse's feet properly shod or trimmed to minimize abnormal distribution of forces across the joint surfaces. Riders and trainers should also have reasonable expectations of what each horse is capable of and tailor their exercise programs accordingly.