Help
Add this page to your collection
Show collection (0 pages)
Suggest pagesOrthopaedic Surgery/Disorders of The Rotator Cuff
This page may need to be | Disorders of The Rotator Cuff | ||
| <<Shoulder | Impingement Syndrome>> |
With age the normal elasticity of tendons is diminished. Signal change on MRI correlates with this age related change which is considered pathological when it occurs in the extreme or prematurely. Mechanically, the altered tissue is stiffer. Injury is most likely to occur where the muscle is functioning in an eccentric mode, lengthening of the muscle tendon unit, while the muscle contracts as in the late follow through phase of throwing in which the cuff contributes to the coordinated deceleration of the arm. The greater stiffness of the elastin depleted tendon leads to failure. The elastin normally functions like a snubber on a mooring line which dampens the sudden jolt as the stucture of the rope reaches the limit of it's abliity to stretch. The location of the failure varies with rate of load. Episodic near failure at the tuberosity may result in remodeling changes at the tendon bone interface as an adaptive response to shore up the tendon insertion.
Whether through failure of through periodic contractile inhibition secondary to pain, the rotator cuff becomes functionally insufficient even before failure of its substance leads to a loss to the normal head centering function with glenohumeral abduction. Eventually there is cephalad migration under the influence of the deltoid. The acromion and AC ligament receive compressive loads and adaptive changes occur leading to thickening of the anterior inferior acromion and ossification of the AC ligament. This abnormal boney structure then creates a secondary mode of injury by abrading the dorsal surface of the tendon acting like a wood plane. Osteophytes at the inferior surface of the A-C joint have a similar effect contributing to the process of outlet impingement.
Rotator cuff injury in the throwing athelete has a different mechanism. The throwing athelete may develop excessive external rotion and a restricted internal rotation as a consequence of mechanical stresses on the shoulder capsule which occur with the throwing motion. The anterior capsule stretches in late cocking phase and the posterior capsule strethces in follow.
The loss of elasticity of tendons happens by an unknown mechanism. An abnormal pattern of remodeling with the rotator cuff tendon appears to be the net effect of an altered gene expression triggered by the extreme mechanical demands. Abnormally high levels of metalloproteinases implying altered collagen processing are noted in assays of torn rotator cuffs.
