1. The Rotator Cuff Surrounds the Humeral Head
The rotator cuff is made up of four tendons--the supraspinatus, infraspinatus, teres minor and subscapularis. These originate from the shoulder blade and attach to the humeral head (the top of the arm bone, which moves against the glenoid portion of the scapula). Together, they help keep the humeral head in place and also help to lift the arm. The supraspinatus tendon helps to lift the arm. The subscapularis helps to internally rotate the arm, such as when you reach behind you to scratch your back. The infraspinatus and teres minor are two distinct muscles, with two distinct nerve supplies, but their tendons tend to blend together and are usually considered one unit. Together, they externally rotate your arm, spinning it away from the body. Baseball pitchers externally rotate to cock their arms and internally rotate when they throw the ball.
2. Most Tears Involve the Supraspinatus Tendon
The tendon most commonly torn is the one going right over the humeral head--the supraspinatus tendon. You can imagine it gets trapped between the humeral head and the acromion (shelf of bone you can feel on the edge of your shoulder) above it, each time you lift your arm. The rotator cuff tendon either tears within its substance or pulls off of the humeral head.
3. Tears Can Happen with Acute Trauma
Usually, you will have a pretty good idea of when you tore your rotator cuff tendon. It may be from a fall--either directly onto the shoulder or while reaching out to protect yourself. Severe falls can result in fractures or even dislocations of the shoulder. All of these situations can cause the tendon to be pulled apart or impacted against the sharp bone pieces. Tears also can happen from lifting a heavy object. Usually, it happens when lifting above shoulder level, such as when you lift luggage into the overhead bins on a plane. Repetitive overhead activities also can precipitate rotator cuff tears. That is why you hear of so many baseball pitchers having rotator cuff issues.
4. Other Tears Happen Over Time
Tears can also happen with the normal wear and tear of life. Usually, you will experience an insidious onset of pain over the lateral part of your shoulder. Often, there is pain at night, especially if you roll onto that particular side. As we age, the tendon degenerates and weakens, ultimately tearing.
5. Rotator Cuff Tears Can Cause Significant Disability
In addition to the pain the rotator cuff tear causes, there can be weakness in lifting, such as washing your hair or reaching the top cupboard. Similarly, there can be pain with lowering the arm from a raised position. You may feel crepitus, or cracking, in the joint. It may affect your sleep and it may start causing neck pain as other muscles try to help compensate for the loss of function.
