Hock Joints Horse Care
by HEATHER SMITH THOMAS The horse’s hock is one of the most complex and hardest percent of the motion of the hock, for flexion and extension. worked joints in the body, so it needs to be strong and Communicating directly with that joint, but responsible for sturdy to avoid injury. David McCarroll, DVM, at Inter- only a very small range of motion, is the proximal intertarsal state Equine Services in Goldsby, Oklahoma, works with joint (PIT joint). There is an opening in the joint capsule many equine athletes, treating various injuries. He says between these two joints, that allows the fluids between good conformation is essential to good hock health. those joints to interchange,” he explains. Evaluating Hock Strength: A Look At Conformation “Immediately below the PIT joint is a separate joint “Because of the horse’s anatomy, the hock is always under that normally does not communicate with the others. a certain degree of flexion—enabling it to be a shock This is the distal intertarsal joint (DIT joint). The joint absorber to reduce effects of that connects the hock to the concussion,” he explains. A cannon bone is the tarhorse with a fairly large angle in sometatarsal (TMT) joint,” he the hock (as opposed to an acute says. angle in an over-bent limb, or a The top joint (TCJ) is a too-wide angle in the overhigh motion, low concussion straight, post-legged limb) can joint, and the three lower withstand concussion the best. joints are low motion, high “The average hock angle of concussion joints. These lower a good athletic horse will be joints are the ones most comsomewhere between 154 to monly affected when the hock 159 degrees.” This is a fairly is overworked. open hock joint rather than The conformation of the an acutely angled joint. “A hock—normal versus abnorsmall-angled hock would be a mal—will make a difference in weak, sickle hock,” he says. the horse’s risks for injury and “Conformation of the rear soundness issues. A normal limb is not determined by the hock, when viewed from the hock alone. For an athlete, side, is directly under the point you want a fairly flat croup, of the buttocks. If you drop a An injured, enlarged hock joint forward sloping femur (the straight line from the rearmost bone between the pelvis and stifle), normal to straight part of the hip (buttocks) it would come down to the point appearance of the stifle, normal to straight appearance of of the hock, to the fetlock, to the ground. the hock, and a slope to the pastern,” says McCarroll. “A post-legged horse has too little angulation of hock Horses with excessive slope in the hock tend to have a and stifle,” he says. A line dropped from the point of the steeper pastern and more soundness problem. You want a buttocks will fall in back of the hock and lower leg and pastern with some angle to it. An upright pastern and a miss it completely. narrow-angled hock tend to go together. This combina“There should be some angle, with a forward sloping tion puts more stress on the fulcrum (the hock). femur, and a fairly open stifle and hock. The angulation of “The hock consists of six bones, four extensor tendons, hock and stifle are usually similar,” he explains. a set of four collateral ligaments on each side of the hock, A common fault is standing under behind; horse’s feet and two flexor tendons which pass through the hock. It are too far forward, in front of the line coming straight also has a large Achilles tendon that comes from the mus- down behind the horse. Sickle hocks is when the hock cles of the gaskin—from behind the stifle—to the point of may be directly under the point of the buttocks, but the the hock. The hock joint is analogous to the human horse’s feet are too far forward, with angled cannon bones. ankle, with the major difference being that the horse’s “There’s no straightness to the hock. There’s more narrowing of the angle in the hock,” he explains. hock is up off the ground,” he says. “Another abnormal hock conformation would be the The hock consists of several small joints within the larger structure. “The four separate joints include the tarsocrural Continued on next page joint (TCJ)—the top joint—responsible for more than 80
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