CHAPTER SEVENTEEN: TENDON & LIGAMENT DISORDERS
Introduction
Connective tissue is one of the major types of body tissue. Ligaments, tendons, bones, cartilage and fat are all examples of specialized types of connective tissue. Connective tissue makes up a significant portion of the musculoskeletal system. . Tendons also act to transmit the force of muscle contraction to the bone to produce movement. The area where a muscle meets a tendon is called the junction. At the Tendons are the tough bands of fibrous connective tissue that connect to musculotendinous junction the collagen fibres from the epimysium, the perimysium and the endomysiumwhich continue past the end of the muscle cells to form the tendon. This connection between muscle and tendon is made firm by the interdigitation of the collagen fibres with the plasma membranes of the myocytes. The area of attachment between the tendon and the bone is called the osseotendinous junction. This attachment is made firm through the insertion of specialized collagen fibres, called fibres, into the structure of the periosteum and bone. The body of a tendon is made of tightly packed fibres of collagen that are arranged parallel to the lines of stress. Like bone, tendons are dynamic structures that respond to stress by realigning the collagen fibres. About every six months all the collagen fibres in a tendon are replaced and realigned along stress lines to form a crimped line that is parallel to the direction of force. Most of the collagen in a tendon is type I collagen but type III and type IV collagen fibres are also present. Adjacent collagen fibres are held together by proteoglycans such as decorin and aggrecan, and new collagen is secreted by tenocytes. Tenocytes arrange collagen fibres into bundles which are called . Each fasicle is covered by a connective tissue sheath called the endotendon. Fasicles are then arranged into bundles that are covered by another layer of connective tissue called the peritendon. An entire tendon is covered by another connective tissue sheath called the epitendon. The blood supply to a tendon is found within the endotendon while nerve fibres are found within the peritendon and the epitendon. Some tendons are covered by a at points of friction. Like a joint capsule the tendon sheath has an outer fibrous layer and an inner synovial layer that secretes synovial fluid. Tendons are held in place over joints by thick, fibrous bands called retinaculae or ligaments. Ligaments attach bone to bone. They span across a to increase the stability and strength of the joint, facilitate the proper alignment of the articulating surfaces, limit freedom of movement and allow the most efficient transfer of force from the muscles. Ligaments are similar in composition and organization to tendons, although ligaments are less organized than tendons. Ligaments have less collagen but more extracellular matrix than that of a tendon. Most of the collagen in a ligament is type I collagen but other types of collagen fibres are also present as well
154
Made with FlippingBook Publishing Software