Rotator cuff tendon, like any tendon, is a sturdy band of tissue that connects muscle to bone. It is a strong, sinuous material that is able to withstand tension. A tendon works with its muscle to exert a pulling force. It is over use of the tendon that often leads to a rotator cuff injury. Within
the cuff there are eight distinct tendons. There are four muscles and each is connected at both ends by tendons. It is where each of the tendons attach to the Humeral Head of the upper arm that they form the "cuff". More often than not rotator cuff injury symptoms are focused upon this area.
Tendons are made up of in excess of 80% collagen. It is the properties of collagen that provides an explanation of tendon injury and treatment. A tendon is composed of parallel collagen fibres. In fact collagen makes up approximately 86% of the dry weight of a tendon.
In a rotator cuff tendon the collagen is made up of approximately 97-98% type 1 collagen. So far 29 different types of collagen have been identified within the human body.
Collagen is not one substance; it is a group of naturally occurring proteins. In nature, it is found exclusively in animals, particularly in the flesh and connective tissues of mammals. Collagen is the most commonly occurring protein in mammals. It makes up approximately 25% to 35% of the bodies protein content.
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.
Further tendon key facts
1. The length of any tendon changes from one person to the next. Tendon length is the most significant factor in discerning muscle size.
2. Tendon length is purely genetic. It can not be increased, or decreased, in response to external stimulus.
3. The tendons are believed to contain no nerve fibres. Nerve endings related to the tendons are to be found in the surrounding epi and peri tendon.
4. The tendons are known to have a very poor blood supply. This means that oxygen and nutrient provision is poor. The consequence is that rotator cuff torn tendons take an extended period to heal.
Healing a tendon
It has been established that exercises for torn rotator cuff tendons will promote the growth of healthy new tendon. Exercise and stretching during the initial inflammatory phase can adversely affect healing. Care should, therefore, be taken within the first few days of an injury.
After this initial phase exercise is the answer to a successful recovery. Exercise and stretching following an acute injury promotes the formation of new, healthy collagen molecules. This leads to increased diameter and strength of the healed tendons.