Rotator Cuff Tendon
Let’s start with a simpler question – what is a rotator cuff tendon? Quite simply a tendon is a tough band of tissue that connects muscle to bone. It is a strong, sinuous material that is capable of withstanding tension.
A tendon works together with a muscle and can only exert a pulling force. Often it is over use of the rotator cuff tendon that leads to a rotator cuff injury.
The unique anatomy of the rotator cuff means that it includes eight distinct tendons. There are four muscles each attached to bones at each end.
It is on the Humeral Head of the upper arm that four of the tendons attach to form the “cuff”. More often than not rotator cuff injury symptoms are focussed upon this area.
Tendons are very similar to ligaments and fascia. The difference being that ligaments connect bone to bone and fascia connect one muscle to another. They are all made up of over 80% collagen. It is the properties of collagen that is the key to tendon injury and treatment.
Rotator cuff tendon structure
A cuff tendon is made up of parallel collagen fibres. In fact collagen makes up approximately 86% of the dry weight of a tendon. The remainder is composed of elastin 2%, proteoglycans 2% and a mix of various other inorganic compounds. In a rotator cuff tendon the collagen is made up of approximately 97-98% type 1 collagen.
A collagen molecule is approximately 300 nm long and 1-2 nm wide. The collagen molecules are then grouped together to form fibrils. In tendons, the fibrils then group together to form fascicles, which are about 10 mm in length with a diameter of 50-300 μm.
Finally the fascicles group together into a tendon fibre with a diameter of 100-500 μm. Groups of fascicles are surrounded by the epitendon and peritendon to form the actual tendon itself.
Collagen is not one substance; it is a group of naturally occurring proteins. In nature, it is found exclusively in animals. It is most commonly found in the flesh and connective tissues of mammals. Collagen is the major building block of connective tissue. Collagen is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content.
Collagen occurs in many places throughout the body. Collagen is mostly found in fibrous tissues such as tendon, ligament and skin, and is also abundant in cornea, cartilage, bone, blood vessels, the gut, and intervertebral disc.
So far a total of 29 distinct types of collagen have been identified. Over 90% of the collagen in the human body, however, is of either type I, II, III, or IV.
Rotator cuff tendon – further key points
Rotator cuff tendons are believed to contain no nerve fibres. Nerve endings associated with the tendons are located in the surrounding epi and peritendon.
Rotator cuff tendons are known to have a very poor blood supply. This in turn means that nutrient and oxygen supply is poor. The result is that rotator cuff torn tendons can take a long time to heal.
The length of any tendon varies from person to person. Tendon length is the most important physical attribute in discerning muscle size.
For example if you have a short tendons and a long bicep muscle you will have the potential to grow that bicep more than a similar person with longer tendon and shorter bicep muscle. Bodybuilders will generally have shorter tendons and athletes generally longer tendons.
Tendon length is purely genetic. Tendon length can not be increased, or decreased, in response to external stimulus.
Healing a rotator cuff tendon
It was previously believed that tendons were not capable of repair. However, it has been shown more recently that tendons are capable of healing and recovering from injuries However, the healed tendons never regain the same mechanical properties as before the injury.
The three main stages of tendon healing are inflammation, repair or proliferation, and remodeling, which can be further divided into consolidation and maturation. These stages can overlap with each other.
It has been consistently shown that exercises for torn cuff tendons will promote the growth of healthy new tendon. It is known that exercise and stretching can badly affect healing during the initial inflammatory phase. Great care should, therefore, be taken within the first week or so of a rotator cuff injury. After this initial phase however rotator cuff tendon exercise is the key to a successful recovery.
It has been clearly demonstrated that exercise and stretching of the tendons following an acute injury can help to promote the formation of new collagen molecules. This in turn leads to increased strength and diameter of the healed tendons. This represents a significant improvement from the past when injured tendons were often immobilised for too long.
The unique nature of the cuff tendon anatomy and the molecular properties of tendons in general can cause real problems. Rotator cuff injury symptoms and causes vary greatly but what is now clear is that exercises for torn rotator cuff tendons have a huge role to play in recovery.
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