Question

What is the most common shoulder injury in people under the age of 40?

Answer

The subscapularis muscle is the most commonly injured structure in the shoulder in individuals under the age of 40. It is attached to the undersurface of the scapula, the subscapular fossa, sandwiched between the scapula and the ribs. Its tendon is attached to the humerus on the lesser tubercle. This muscle helps you open a jar, hug someone, lift things, clap your hands, throw a ball and complete the forehand and serving actions in tennis.

In addition to being the most commonly injured muscle-tendon unit, the subscapularis is by far the strongest of the four rotator cuff muscles. If a client under age 40 has a shoulder injury, there is a 70 percent chance it is a subscapularis tendon injury. A subscapularis tendon injury is frequently missed for two reasons. Pain from a subscapularis injury is often felt at the back of the arm and not in the front of the shoulder where the tendon is attached. This is because of the phenomenon of referred pain discussed previously in this column.

The second likely reason for this confusion is that the subscapularis is such a strong muscle that, unless it is severely injured, it does not test positively (it doesn't hurt) during the most commonly used test to locate this injury.

The primary assessment test for this injury is resisted medial rotation. When performed with the arm in the neutral position, the subscapularis is very strong, tests negative and often doesn't cause any pain. The trick to getting the injury to show itself is to laterally rotate the arm with the elbow bent at 90 degrees and have the client resist from this laterally rotated position.