Your doctor has told you that you have a rotator cuff tear. What does this mean?
A rotator cuff tear involves one or more of the four muscles that starts on your shoulder blade, the scapula, and inserts on your upper arm, or humerus. These 4 muscles work together to lift and rotate your arm and keep the ball of the shoulder joint (proximal humerus) centered on the socket (glenoid). Although there are 4 separate muscles they share a common tendon – tendons attach muscles to bone. This group of tendons is called the rotator cuff.
How it happens
The muscle that is most commonly torn in a rotator cuff tear is the supraspinatus. This muscle lifts your arm up over your head. It has a poor blood supply where its tendon inserts on your shoulder and this alone makes it very likely to degenerate and tear as we get older – or less young, as I like to say. To make matters worse, if you have a bone spur it can press on this tendon and interfere with its blood supply even more or scratch the tendon until it tears.
The largest muscle of the rotator cuff, the subscapularis, starts on the front of the shoulder blade and its tendon inserts on the front the shoulder. This muscle rotates your hand to your stomach when your elbow is at your side, called internal rotation. It is very important in keeping the ball centered in the socket, so when it completely tears it should be repaired. It is also important because the area where it inserts on your shoulder forms a wall behind which glides the tendon of your biceps. Tears here can cause the biceps tendon to jump out of its groove. If the biceps tendon continues to do this it can cut through the subscapularis tendon.
On the back of your shoulder blade are the infraspinatus and teres minor muscles. Together these muscles do the opposite of your subscapularis and externally rotate your arm, like when you rotate your hand away from your stomach with your elbow at your side. This makes them important for getting your hand to your mouth or the back of your head.
Why do I have a rotator cuff tear?
Rotator cuff tears occur for a variety of reasons. Most commonly the rotator cuff tears after an accident or injury. You may have a fall or you were lifting something and felt a pull or tear. The tendon may have been weakened from age related wear and tear. Some people have a spur on the edge of the point of the shoulder, called the acromion, that rubs on the tendon and weakens it over time. The end result will be pain down the front and outer part of the arm, often worse with activity or at night when we are trying to sleep. You may feel weakness when you try to reach your hand up or behind your back. It is best to have your shoulder evaluated by an orthopaedic surgeon in these cases.