Equine Tendons and Ligaments
Ligament: is a tough band of fibrous tissue that joins two bones. They have less stretch than tendons and stabilize and protect every joint in the body, including those in the spine, pelvis, hip, stifle and lower limbs.
Tendon: is a tough fibrous cord that attaches a muscle to a bone. The are energy saving in nature as they have the ability to stretch and recoil.
The major tendons in the leg are the flexors. These are behind the cannon bone, and carry the horses weight when standing. They bend the limb joints when the leg is in the air.
The suspensory ligament acts as a large elastic support for the fetlock, reducing the load of the flexor muscles need to carry.
The superficial flexor (the tendon nearest to the skin) supports the fetlock and pastern joints, whilst the deep flexor supports the pedal bone. Without these tendons the distal leg would simply collapse, and the horse would walk on the bottom of his fetlocks.
The extensor tendons are in front of the cannon bone, and straighten the limb when it is in the air, preparatory to the limb taking weight. They do not have to carry the weight of the horse and are therefore much smaller than the flexors.
As there are no muscles below the knee, both tendons and ligaments are long and susceptible to damage.
Stay Apparatus
The horse has evolved a system, known as the stay apparatus, to allow it to stand whilst using no muscular effort. The superficial and deep flexor tendons will only extend to a certain point, and then the check ligaments (radial and sub-carpal) take the load off the muscles. The suspensory ligament also takes weight without involving muscular effort. In this was the front leg, the tendons of the lower limb and the fibrous structures in the front of the upper limb stop the limb collapsing.
In the hind limb the peroneus tertius and flexor tendons ensure the distal limbs cannot flex unless the stifle does. The medial patellar ligament can be hooked over end of the femur, and in doing this, the load flexing the stifle is held mechanically, and thus the whole leg is locked straight.
In some horses the mechanism to unhook the patella malfunctions, and the leg may become fixed straight (a locking stifle), or jerk on release ( a slow-releasing patella).
