Horse Leg Anatomy – Tendons in Upper Horse Leg

horse leg anatomy tendons in upper

The horse’s limbs contain many muscles with a complex network of tendons and ligaments. When a muscle contracts, it pulls on the bones of the limb and hoof. This action bends or straightens the joints of the leg and lifts or lowers the hoof.

The lower limbs are the primary propulsive limbs of the horse (Mertens, 1994). When a horse walks or trots, 60 percent of the vertical impulses that support the centre of mass (COM) are directed through the hoof-foot interface and the proximal metatarsal bones of the front limbs. The rest of the force is distributed between the lateral and medial gastrocnemius, soleus and triceps surae.

In order to generate the necessary forces, thoracic and pelvic limb muscles must be capable of contracting with high velocity. This functional specialisation is evident across a wide range of animals and is characterised by the development of proximal muscle groups that are specialised for producing large forces (e.g. long head of the triceps) and distal limb muscles that are specialised for economically generating small forces (e.g. latissimus dorsi and pectoralis profundus).

Muscle architecture in equine limbs is highly adapted to the demands of quadrupedal locomotion. The proximal limb muscles are characterised by the presence of short fascicles with very little internal tendon, while the distal limb muscles have long fascicles with thicker internal tendon. This muscular structure enables limbs to be flexed and straightened quickly during stance phase and to be held mechanically stable during swing and the first half of stance.

This is facilitated by a set of powerful muscles, the peroneus longus and the superficial digital flexor tendon (DDFT). In contrast to the extensor tendon in the forelimb, the DDFT has very long fascicles interwoven with numerous strands of internal tendon, and is capable of generating four times the force of the forelimb DDF. The DDFT apparatus also includes the medial patellar ligament, which can be hooked over the end of the femur to help lock the stifle during swing and constrain extension during the early phases of stance. When this mechanism malfunctions, the stifle may remain locked straight or flex when loaded (a locking stifle).

The hind limb has similar architecture to the forelimb, with the peroneus tertius and flexor tendons ensuring that the distal limbs cannot flex until the stifle is flexed. However, these muscles do not have the same capacity for power as the thoracic limb muscles.

The fetlock joint is a hinge joint that moves the pasterns and hoof backwards and forwards but not from side to side. This complex joint requires a high level of coordination and is very vulnerable to injury. The fetlock is supported by a complex array of tendons and ligaments including the sesamoid bones, which are particularly susceptible to fracture. The lateral and ulnar collateral ligaments are also important in preventing rotation of the fetlock and are often damaged in cases of fetlock lameness.