Stiff shoulder? Limited range of motion? Let's not forget pain! More than 9 million people each year visit their doctor for shoulder problems. Why is this so common?
First of all let's understand the shoulder a little more. The "shoulder bone" is composed of 3 separate bones: the humerus, clavicle, and scapula.
Most people understand that the humerus is the upper arm. At the top of the humerus is the humeral head, which has a couple pointy parts on one side and a round smooth aspect on the other. The rounded part fits into the other bone, the scapula, at the glenoid fossa forming the glenohumeral joint (a.k.a. the shoulder joint). The clavicle is a long slender bone above the shoulder that acts as a strut for movement, as well as a spot for multiple muscles to attach to. The clavicle also protects nerves and blood vessels that lie directly behind it.
Four muscles start from the scapula and wrap around the head of the humerus to form the rotator cuff. These are the supraspinatus, infraspinatus, subscapularis, and teres minor. They give the humerus the strength to move around in whatever direction we please. Rotator cuff tears account for more than half of all the visits to the doctor for injuries regarding the shoulder. They are, by far, the most common shoulder injury we see in Radiology.
Virtually all patients with rotator cuff injuries present with pain during movement of the arm or shoulder. This is because the upper arm moves by way of the 4 muscles of the rotator cuff. Their function is to contract and pull the arm in the desired direction.
When one of these muscles are damaged the patient usually has pain that is specific to the directional function of the specific muscle. For example, the supraspinatus muscle is the major muscle responsible for lifting the arm up and directly away from the body. When this muscle is torn the patient presents with pain when raising the arm. This is actually the most commonly torn muscle in the rotator cuff.
Rotator cuff tears can present in different grades but can be lumped into 2 different categories: partial tear and full thickness tear. A partial tear is the most common type. The muscle tendon is torn (injured) but still attached to the humeral head. These types of injuries can be seen with trauma to the shoulder or from repetitive motions that wear on the cuff. Partial tears typically respond well to conservative treatment like physical therapy and steroid injections. The only time surgery is needed is if the patient is not responding well to treatment or if the pain is intolerable.
A full thickness tear, as the name implies, is a type of injury in which the tendon is completely torn off the bone or from itself. These types of rotator cuff tears require surgery 100% of the time for a full recovery. Without surgical intervention the muscle will retract and the patient will never recover 100% of their strength and function in that shoulder. Although partial tears can eventually turn into full tears, full thickness tears are normally the result of trauma to the shoulder.
Figure 1A is an example of a fully intact supraspinatus muscle tendon. 1B shows a partial tear and 1C shows a full thickness tear. In an MRI, edema (fluid), indicating damage, shows up as bright signal (In T2 imaging). Notice the fully intact supraspinatus tendon has little to no signal. The partial tear demonstrates moderate signal within the muscle and tendon. The fully torn supraspinatus demonstrates significant edema within the muscle and tendon extending into other portions of the shoulder girdle.