The skeletal anatomy of a horse’s front and hind limbs is comparable to the anatomy of the human hands and feet. The horse’s cannon bone, or metacarpal, is the same as a bone in the palm of a hand. The human phalanges, or finger bones, are comparable to the bones making up a horse’s hoof and pastern. Fortunately, most humans and horses are born with normal limbs. However, both children and foals can be afflicted with contracted limb abnormalities.

When a child is born with tightly clenched fists and club feet, it might have one of several muscle contracture syndromes collectively known as Distal Arthrogryposis (DA). The child might or might not have other congenital abnormalities, such as spinal curvature (scoliosis), facial muscle contractures, or a small mouth.

DA is caused by mutations in one or more genes that control skeletal muscle contraction. These gene mutations cause abnormal muscle protein production that disrupts normal muscle function. The skeletal muscles contract but are unable to relax, causing limb contractures during fetal development. Most of the mutations are inherited, but the mode of inheritance can vary. Symptoms can vary markedly within and between families. Mutations can arise spontaneously as new (de novo) mutations. Some children with DA respond to surgery and physical therapy; others do not