Cause of Shoulder Impingement
As discussed in our post last week, the shoulder is a complex joint. It has a wide range of motion which is great for function but often stability can be difficult to maintain. There are two main causes of shoulder discomfort which include over-use and trauma. The mechanism of injury can point toward what is causing discomfort. Other causes of shoulder pain or discomfort include referred pain from the cervical spine, visceral sources (such as gallbladder, diaphragm, etc), or trigger points. Lastly, arthritis, tumor, or infections may cause discomfort but are rare.
Trauma can happen to the shoulder in a variety of ways including falling on an outstretched hand, direct impact from sports, car accidents, or any high forces to the shoulder itself. To determine the type of injury caused by a traumatic event, a full history, and exam must be taken. Often the most common injuries that occur and should be ruled out are fractures, tendon tears, labrum damage, or dislocation.
The most difficult position for the shoulder to maintain stability is during shoulder elevation or extreme abduction. During high levels of elevation and shoulder abduction, the muscles, ligaments, and capsule of the shoulder are stressed. Therefore, sports with many repetitions of those movements have higher rates of shoulder overuse injuries. Specific examples include work that involves placing things overhead or reaching for objects. Other examples include weight lifting, swimming, gymnastics, and throwing sports such as baseball, softball, or football.
What is shoulder impingement syndrome?
There are two types of shoulder impingement including primary and secondary impingement. Both types involve irritation of tendons as they move and rub against the outer edge of the shoulder blade, otherwise known as the acromion. Primary impingement is the least common type and is due to a narrowing of the space where shoulder tendons exit the shoulder girdle. Secondary impingement is caused by shoulder girdle instability and repetitive use of the shoulder which causes irritation of the tendons as they exit the subacromial space. The most common tendon involved in impingement syndrome is the supraspinatus.
A very common condition caused by overuse is shoulder impingement syndrome. This condition is most common in ages 18-35-year-old athletes. Risk factors for impingement syndrome include calcification, shoulder instability, AC joint degeneration, muscular imbalances, labral tears, or acromial abnormalities. The pain is commonly described as “achy” and is felt on the lateral side of the shoulder. The pain is also decreased when activity is reduced.
Conservative care is recommended for shoulder impingement if no structural causes are contributing to pain. Common muscular imbalances will be evaluated including the strength or tightness of the pectoralis muscles, lats, internal rotators, and trapezius muscles. Along with evaluating the weakness or tightness of the shoulder external rotators, serratus anterior, elevator scapula, and middle/lower traps.
During initial treatment, the patient may be asked to reduce the number of repetitions of shoulder abduction/elevation past 90 degrees. Muscles and joint motion will be evaluated to reduce the amount of stress on the irritated tendons. In later stages of treatment, targeted stretching and strengthening will be beneficial along with increasing proprioceptive exercises.
Aside from chiropractic and physical therapy, other options for treatment include acupuncture, steroid injections, and surgery. Acupuncture has been shown to be effective in the treatment of shoulder impingement syndrome. Whereas, steroid injections have mixed results for both short and long-term recovery and have been shown to be no more effective than NSAIDs or therapeutic exercises.