There is a narrow space between bones in the shoulder joint (the roof of the shoulder blade and head of the upper arm bone) that the rotator cuff tendons pass through.
Shoulder impingement syndrome occurs when tendons in this space become compressed due to lack of space. A bursa may also be compressed.
Causes of Shoulder Impingement
Rotator cuff tendonitis (inflammation of the rotator cuff tendons) often leads to shoulder impingement syndrome. There is a small space between the head of the upper arm bone and the acromion (a bony projection from the top of the shoulder blade) that the rotator cuff passes through. If the rotator cuff becomes inflamed (tendonitis), it may not have enough room and may get squeezed. This is called impingement syndrome. This further irritates the tendon.
Shoulder impingement may occur first and cause rotator cuff tendonitis. Raising the arm overhead causes the head of the upper arm bone to slightly rise on the shoulder socket and narrows the space between the head of the upper arm and acromion causing contact between the rotator cuff tendons and the roof of the shoulder blade. Activities (such as swimming, tennis) that involve repetitive overhead arm movement cause repeated contact and friction between the rotator cuff tendon and the undersurface of the acromion, and may cause irritation and inflammation of the tendon.
A strong rotator cuff helps keep the head of the upper arm bone from riding up excessively but some contact between the rotator cuff and bones in the joint still occurs with overhead activity.
The shape of some people’s shoulder bones make the space the rotator cuff passes through more narrow and increases the risk of impingement syndrome. A large calcium deposit in the rotator cuff tendon may also narrow the space and may cause impingement.
The bursa that lies under the acromion (roof of the shoulder blade) may also be compressed and become inflamed (bursitis).
Whether impingement or tendonitis occurs first, one aggravates the other. Impingement causes more irritation and inflammation of the rotator cuff, which increases the amount of impingement. Eventually the pain becomes more severe and constant.
Symptoms of Shoulder Impingement
Symptoms usually start gradually, in the top-outer portion of the shoulder. There may be mild pain all the time, with sudden pain when reaching overhead and pain when lowering the arm from an overhead position. There may be weakness of the shoulder. If not treated, the condition may worsen.
Treatment of Shoulder Impingement
Strengthening the rotator cuff (especially the supraspinatus) helps prevent the humerus from rising excessively with overhead movement of the arm. Exercises to strengthen the muscles that support the shoulder blade are also often prescribed. Keep the shoulders down and back. Slouching narrows the subacromial space.
Surgery may be done to smooth out the undersurface of the acromion and/or remove damaged tissue from the tendon for impingement, if conservative treatment fails to bring relief.
Bursitis (inflammation of a bursa) often occurs along with tendonitis and/or impingement syndrome. A bursa is a sac (containing a small amount of fluid) located between tendon and bone that helps the moving parts of a joint glide smoothly. There is a bursa between the supraspinatus (a rotator cuff tendon) and acromion (roof of shoulder blade). Repeated overhead movements squeeze both the rotator cuff and bursa and may lead to irritation of either. A torn or inflamed tendon or a bone spur on the acromion may also irritate the bursa and cause bursitis. Click here for more on shoulder bursitis.