Collateral ligament (CL) injuries of the distal interphalangeal joint (coffin joint) are a fairly common injury among certain classes of athletic horses. The CL acts to connect bone to bone and stabilize the joint as it flexes and extends through its range of motion.

It is when the coffin joint slides or twists to one side or another relative to the pastern that the risk of CL tears is increased. Athletic events involving sharp turns with the joint fully loaded (thus tensing the ligament) predispose the horse to injury of this structure. Thus, jumpers and event horses tend to injure these ligaments more frequently than cutting horses or flat racers.

CL injuries are suspected when a horse is seen with a mild or imperceptible lameness in a straight line that is markedly worse when observed working in a circle in either direction. These horses are typically more noticeably lame when they are circled on hard ground than soft. They also tend to be worse in the direction where the ligament is placed under tension.

The lameness is less obvious when the horse is circled in the direction that places the ligament under a compressive load. Thus, an injury to the medial collateral ligament of the right foreleg will usually be most obvious when the horse is circled on hard ground to the right. An injury to the lateral ligament may not show this distinction as clearly, but it will still be worse in a circle than straight ahead.

X-ray findings are usually negative because any bony changes are usually too subtle to be observed. Only more severe injuries will have effusion (filling) in the coffin joint. Nerve or joint blocks are not that helpful either, because the response is too variable to be relied upon.

To learn more about CL injuries to the coffin joint, and how to properly treat such injuries, read Randy Luikart and Noel Muller’s article “Teaming Up Against Coffin Joint Ligament Injuries” featured in the May/June 2026 issue of American Farriers Journal.