The horse leg combines form and function, balancing strength and beauty with purpose and movement. Anatomy is key to understanding how these muscles work together and why horses can move as they do. In this blog post we take a look at the anatomy of the lower horse leg and what makes up the structure that is so vital to our equine friend’s movement and performance.
The lower horse leg begins with the coffin bone and navicular bone which are situated in the outer hoof capsule (see below). The coffin bone is shaped to provide attachment points for tendons and ligaments as well as a supply of blood vessels. This helps to create a hard outer shell of the hoof capsule that provides strength and structure.
From the coffin bone, lateral cartilages protrude in a medial and lateral direction from the inner and outer sides of the distal phalanx of the lower leg. These cartilages are ossified in adulthood and give the hoof its shape. The navicular bone sits between the second and third phalanges of the lower leg and is attached to the lateral cartilages by the deep digital flexor tendon. The navicular bone is also one of the primary shock absorbers of the lower leg, helping to reduce the impact of the ground on the feet of the horse during movement.
Just above the navicular bone is a small articulating joint with a synovial fluid cavity, which is the knee of the lower leg. This joint allows the horse to flex and extend its knee as it moves forwards and backwards. Muscles are used to flex and extend the knee joint in the same way that they are utilised for the bending and twisting of the hock.
As we go further down the lower leg, we come to the five petals of the long pastern bone which merge at a point like a claw called the median phalanx. This is the most specialised area of the lower leg and is shaped to allow a large amount of weight to be placed on it without creating too much strain.
Tendons connect muscle to bone and are what enables the horse’s lower leg to move as they contract and relax. The flexor tendons of the lower leg, which include the superficial digital flexor tendon and the deep digital flexor tendon, are responsible for allowing the joints to open. The extensor tendons of the lower leg, including the common digital extensor tendon and the lateral digital extensor tendon, help to close the joints and bring the foot forward as the horse moves.
The lower leg is supported by a network of ligaments which are grouped into three main categories, check, annular and suspensory ligaments. These ligaments help to prevent excessive stress on the tendons, support the tendons and attach bones to each other.
The muscles of the lower leg are classified as postural muscles and those closer to the joint as articulator muscles. Postural muscles are responsible for supporting and stabilising the joints, whilst articulator muscles provide power and gymnastic movements.