Rotator Cuff, Part 1 – Tendinopathy
Rotator cuff tendinopathy is a common cause of shoulder pain and weakness. The shoulder is a ball and socket joint and it is relatively unstable as the socket is shallow compared to the ball. This anatomy allows for the very large range of motion that we have in our shoulders. But, it also means that the movement in the shoulder needs to be controlled by a coordinated action of several muscles around the shoulder joint and the shoulder blade. Since the socket of the shoulder is part of the shoulder blade, the muscles around the shoulder blade control the position of the socket. The muscles of the rotator cuff help to stabilize the ball in the socket during movement and are susceptible to injury.
Theoretical factors that contribute to rotator cuff tendinopathy:
The rotator cuff tendons attach to the front of the ball of the shoulder joint and have to course under a bony arch (coracoacromial arch). They may be irritated if the tendons come in contact with the bony arch (impingement). The size of the space under the arch is individually determined by your bony anatomy but it can also be influenced by posture.
Once there is irritation of the rotator cuff tendon, it may become enlarged or swollen, taking up more space under the bony arch leading to increased chance of further impingement.
Weakness or muscle imbalance or poorly coordinated muscle action leads to less control of the ball in the socket and impingement
Repetitive overhead activities – people that engage in repetitive overhead activities are at higher risk for developing rotator cuff problems. Fatigue can lead to less coordinated control by the muscles and higher chance of impingement. As well the overuse on the rotator cuff can lead to cumulative microtrauma
Instability – people that have excessive range of motion in the shoulder joint sometimes have less control and the ball of the shoulder slides around too much in the socket leading to impingement.
The article Rotator Cuff Part 2 will focus on degenerative rotator cuff tears.