All about the fetlock

Laura Fitzharris MRCVS and Evita Busschers MRCVS delve into the details of this complex joint and the injuries that can happen in this area

- Laura Fitzharris and Evita Busschers

THE fetlock is a high-motion joint with a similar structure in both the forelimbs and the hindlimbs. The fetlock joint is the articulation between the cannon bone (third metacarpal and metatarsal bone in the forelimb and hindlimb respectively) and the long pastern bone (first phalanx), with two sesamoid bones located at the back of the joint.

There are several soft tissue structures associated with the fetlock; the joint is stabilised by collateral ligaments, located on the inside and the outside of the joint. The suspensory ligament originates at the back of the cannon bone, passing down the back of the leg before dividing into two branches which attach to the sesamoid bones.

The sesamoidean ligaments are located lower down at the back of the fetlock and pastern and consist of five separate ligaments that attach the sesamoid bones to each other as well as to the cannon and long pastern bone.

This crucial combination of the suspensory ligament, the sesamoid bones and the sesamoidean ligaments is called the suspensory apparatus, and this structure supports the majority of the high load on the fetlock joint during the stance phase (when the leg or foot is on the ground during the weight-bearing part of the stride).

The flexor tendons are located at the back of the limb and they provide some additional support to the fetlock joint.

The fetlock is a hinge joint, meaning that the movement is predominantly in one direction – either flexion, during the swing phase of the stride when the leg is in the air, or extension, during the stance phase of the stride when the horse is weight-bearing. There is minimal twisting or side-to-side motion of the fetlock.