Shoe Boil - Limb Anatomy

Limb Anatomy

Each forelimb of the horse runs from the scapula or shoulder blade to the navicular bone. In between are the humerus (arm), radius (forearm), ulna (elbow), carpal (knee), large metacarpal (cannon), small metacarpal (splint), sesamoid, first phalanx (long pastern), second phalanx (short pastern) and third phalanx (coffin or pedal) bones. Each hind limb of the horse runs from the pelvis to the navicular bone. After the pelvis come the femur (thigh), patella, tibia, fibula, tarsal (hock), large metatarsal (cannon) and small metatarsal (splint) bones. Below these, the arrangement of sesamoid and phalanx bones is the same as in the forelimbs. In the forelimbs there are also the elbow, knee, fetlock, pastern and coffin joints. The hind limbs contain the stifle and hock joints in the upper portion, and the same arrangement of fetlock, pastern and coffin joints as the lower forelimbs.

There are three main muscle groups of the forelimb. The triceps muscle straightens the elbow and foreleg, running from the elbow to the bottom of the shoulder blade. The muscles which extend the lower leg are called extensor muscles, while the flexion of the lower leg joints is achieved through movement of the flexor muscles. There are five main muscles and muscle groups in the hind legs. The vastus muscle flexes the hind leg and runs from stifle to hip, while the gluteal muscles, the large muscles in the hip, extend the femur. Forward motion and flexion of the hind legs is achieved through the movement of the quadriceps group of muscles on the front of the femur, while the muscles at the back of the hindquarters, called the hamstring group, provide forward motion of the body and rearward extension of the hind limbs. Extension of the hock is achieved by the Achilles tendon, located above the hock.

There are two apparatus in the limbs of the horse - the suspensory apparatus and the stay apparatus. The fetlock joint is supported by group of lower leg ligaments, tendons and bones known as the suspensory apparatus. This apparatus carries much of the weight, prevents overextension of the joint and absorbs shock. It also helps provide a rebound effect, which assists the foot in leaving the ground. The suspensory apparatus consists of the suspensory ligament, the check ligament, the deep digital flexor tendon, the superficial flexor tendon, the common digital extensor tendon and the sesamoid bones. Horses use a group of ligaments, tendons and muscles known as the stay apparatus to lock major joints in the limbs, allowing them to remain standing while relaxed or asleep. The lower part of the stay apparatus consists of the suspensory apparatus, which is the same in both sets of limbs, while the upper portion differs between the fore and hind limbs. The upper portion of the stay apparatus in the forelimbs includes the major attachment, extensor and flexor muscles and tendons. The same portion in the hind limbs consists of the major muscles, ligaments and tendons, as well as the reciprocal joints of the hock and stifle.