Muscles work with their tendons and ligaments to produce movement. Problems with tendons and ligaments are also relatively common reasons for lameness and other issues in 'working horses'. They are structurally similar but tendons are usually more flexible.
Tendons attach Muscle to bone and are continuous with the periosteum of the bone. A tendon will concentrate the pull of its parent muscle onto a small area. In the lower leg of a horse the tendon also helps to support the joints. They are able to sustain enormous loads .
Structure of a Tendon
Tendons are mostly made up of collagen arranged in helical strands (sort of twisted). These are then arranged into bundles of fibres. Then, much like with muscles, the bundles are arranged into bigger bundles and so on. These fibres run lengthways through the tendons like strands in a rope. The way the fibres are arranged provides the strength to the tendon.
When the tendon is resting the fibres are 'crimped' but when they are stretched the 'crimp' disappears. There is a great deal of heat created within the tendon when it is under exertion - this needs to be taken away by the Circulatory System. As the horse evolved and the cannon bones became longer the arteries and veins did not expand adequately to meet the needs of the tendon tissue. This can be the cause of problems.
This is usually due to overstretching as a result of a weak or tired parent muscle. The limb will lose its effectiveness and this can be permanent . The parent muscle will also demonstrate weakness.
Tendon damage is caused by:
- an insuffucient number of fibroblasts due to a restricted blood supply
- an excessive rate of collagen breakdown
To correctly repair tendons the tensile strength, elasticity and ability to glide have to be restored. When new collagen is laid it is usually set down in a random pattern - not in parallel as originally. However, with the correct exercise and treatment the collagen fibres can be reorganised into a parallel pattern.
A healthy tendon has some elasticity which is why fitness work is so important. An increase in work puts stress on the tendons, this results in a higher turnover of fibres which in turn means there are more young fibres which then provides more elasticity.
Ligaments connect bone to bone - the exception being the check ligament which attaches tendon to bone. Ligaments hold bones together and stabilise joints, they also restrict their movement to the required movement eg: hinge joint which also helps the joint efficiency.
Ligaments are also made up of collagen but in ligaments the collagen is arranged randomly. The collagen fibres are again arranged into bundles and protected by a sheath.
Ligaments gradually stretch when under tension and will usually return to their original shape when the tension stops. If a ligament is stretched past a certain point or for a long period of time it will be unable to return to its original shape (torn ligaments). Overstretched ligaments will lead to a loss in stability of the joint so if the suspensory ligament is torn the fetlock joint will lose its stability. They are slow to recover when torn.
What is collagen?
Collagen is a tough protein and it is found in skin, tendons, bone and cartilage. Also found in other connective tissue it allows the tendons to stretch and then contract and gives them their toughness.
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