What causes pinching pain in the shoulder?

Physiotherapy in Victoria, Westshore, Langford, for Shoulder

Q: I just found out my shoulder pain is caused by something getting pinched in there. We're not sure just what's getting pinched but the MRIs should help clear up the anatomy of the problem. What's the cause of this condition? You know -- what brings it on?

A: The shoulder is a very complex piece of machinery. Its elegant design gives the shoulder joint great range of motion, but not much stability. As long as all the parts are in good working order, the shoulder can move freely and painlessly.

Many people refer to any pain in the shoulder as bursitis. The term bursitis really only means that the part of the shoulder called the bursa is inflamed. The bursa is a round or oval sac filled with fluid. It's located between two bones or between a bone and a tendon. It's job is to reduce the friction between those two tissues during movement.

Tendonitis is when a tendon gets inflamed. This can be another source of pain in the shoulder. Many different problems can cause inflammation of the bursa or tendons. Impingement syndrome is one of those problems. Impingement syndrome occurs when the rotator cuff tendons rub against the roof of the shoulder, the acromion.

Usually, there is enough room between the acromion and the rotator cuff so that the tendons slide easily underneath the acromion as the arm is raised. But each time you raise your arm, there is a bit of rubbing or pinching on the tendons and the bursa. This rubbing or pinching action is what is referred to as impingement.

Impingement occurs to some degree in everyone's shoulder. Day-to-day activities that involve using the arm above shoulder level cause some impingement. Usually it doesn't lead to any prolonged pain. But continuously working with the arms raised overhead, repeated throwing activities, or other repetitive actions of the shoulder can cause impingement to become a problem. Impingement becomes a problem when it causes irritation or damage to the rotator cuff tendons.

Raising the arm tends to force the humerus against the edge of the acromion. With overuse, this can cause irritation and swelling of the bursa. If any other condition decreases the amount of space between the acromion and the rotator cuff tendons, the impingement may get worse.

Bone spurs can reduce the space available for the bursa and tendons to move under the acromion. Bone spurs are bony points. They are commonly caused by wear and tear of the joint between the collarbone and the scapula, called the acromioclavicular (AC) joint. The AC joint is directly above the bursa and rotator cuff tendons.

In some people, the space is too small because the acromion is oddly sized. In these people, the acromion tilts too far down, reducing the space between it and the rotator cuff. The eventual result is impingement once again. Imaging studies can be very helpful in identifying anatomical reasons for impingement. That information guides management of this condition.

Reference: Andrea Santamato, MD, et al. Short-term Effects of High-Intensity Laser Therapy Versus Ultrasound Therapy in People with Subacromial Impingement Syndrome: A Randomized Clinical Trial. In Physiotherapy. July 2009. Vol. 89. No. 7. Pp. 643-652.