Sunday, November 22, 2009

Anatomy of the Equine Hindleg

The Hindleg

The hindleg, together with the frontleg, forms the appendicular skeleton of the horse. Unlike the front leg, the hindleg is directly attached to the spine via the pelvis. This ideal design maximizes the hindlegs' power to move the body forward. However, this direct attachment puts the spine at risk of concussion which is why proper hindleg construction is a MUST. Any concussion that does not get absorbed by the hindleg gets directly transmitted to the spine. It is for this reason that the hindleg has many angles instead of it being straight, like the frontleg.

The Pelvis

The pelvis is a circular structure constructed by the fusion of 6 bones (3 on each side of the body). These bones are the:

1. Ilium (haunch bone) - this bone joins onto the spine at the sacrum forming the iliosacral joint.

2. Ischium (seat bone) – this bone forms the point of hip and buttock.

3. Pubis

By early adulthood these 6 bones are fused together forming one solid structure. The strong muscles of the hindquarters attach to several projections of the pelvis. The longer the pelvic bones, the longer and more powerful the muscles.

The Femur and Tibia

The femur is the longest bone in the horse's body. Together with the pelvis it forms the hip joint. It forms part the stifle joint where it joins with the tibia. The stifle joint is similar to the knee joint in the human with the patella as a kneecap. In most horses the fibula is almost completely fused onto the tibia.

The hock (Tarsus)

This structure is made up of 6 bones of which two are fused together. These bones are aligned in 3 rows. The largest tarsal bone is called the calcaneus and corresponds to the human heel. This bone gives rise to the point of hock. At the point of the hock tendons of the gastrocnemius, biceps femoris and portions of the superficial digital flexor attach.

The lower leg

Anatomy of the lower leg is the same as in the front leg. However, there are some minor differences in terms of tendons/ligaments and angles of the joints.

Tendons and Ligaments

In the hindleg there are only two extensor tendons: the long digital extensor tendon and the lateral digital extensor tendon. The suspensory ligament, superficial digital flexor tendon, deep digital flexor tendon and inferior check ligament are all found in the hindleg in the exact same locations, however, they originate from different muscles. The SDF tendon has no superior check ligament in the hindleg.

The tendon and ligament of the hindleg is not injured as often as those of the frontleg. This is because the hindlegs, usually, carry less weight than the frontlegs and are constructed to better absorb concussion.

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