Shoulder Impingement the Most Common Cause of Shoulder Pain
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Shoulder Impingement the Most Common Cause of Shoulder Pain 

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By: Chris Feng, DPT

It has been reported that approximately 50% of individuals will experience some type of shoulder pain once a year. Working or playing sports in a stressful overhead position may predispose the shoulder to various types of injury. Some sports that are especially demanding include baseball, tennis, volleyball, and swimming. The rotator cuff muscles are the most direct and efficient means of dynamic shoulder stability. In other words, proper firing of these muscles helps to maintain optimal position of the humeral head against the glenoid cavity when the arm is elevated upward. The rotator cuff tendons, which are responsible for stabilizing the shoulder may be subject to overuse and result in a tendonitis, a common cause of shoulder pain. If these muscles are weak and deconditioned, injury becomes more likely.

The diagnosis of shoulder impingement generally refers to the head of the humerus pinching down the soft tissue structures as the arm is lifted up. Some of these structures (not pictured) are the supraspinatus & infraspinatus tendon, long head of the biceps tendon, or subacromial bursa. These structures are located in the subacromial space, which has been reported to be only approximately 9-10 mm wide. This space is between the acromion and head of the humerus.

One characteristic symptom of impingement is that the shoulder is normally painless at rest but aggravated when elevated to its end range. The bony roof of the shoulder is called the acromion which is the lateral process of the scapula (shoulder blade).

Shoulder impingement can be divided into two main types, primary and secondary.

Primary impingement is usually noted in the age group of 40+ and results from degenerative changes to the rotator cuff tendon, local inflammation to the tendons, or bony abnormalities with the acromion process. One such abnormality detected by X-ray is when the acromion may be slightly hooked compromising this space, resulting in impingement. This normally presents with a referred pain pattern along the outside shaft of the humerus into the middle deltoid muscle. These patients will not experience the pain in the shoulder joint by the acromion, where the pain is actually coming from, but the deltoid muscle and lateral humerus.

Secondary impingement can result from postural changes or excessive mobility in the shoulder, known as hypermobility. The most common postural deviation associated with shoulder impingement is the forward head, upper spine kyphosis posture resulting in a protracted scapula This slouched position may seem comfortable to some as they watch TV, or sit at their computer workstation, but it may also increase the compression in the subacromial space as described above. A chronic position of the scapula in this position may result in muscle imbalances and impingement. A comprehensive physical therapy rehabilitation program will always include scapular stabilization strengthening exercises, and postural re-education.

The extremely mobile shoulder can be described as a golf ball on a tee surrounded by ligaments, rather than a deep ball and socket joint like the hip joint.

This extra freedom of movement in the shoulder may lead to hypermobility, or instability. This extra mobility may lead to an anterior translation (or forward movement) of the humeral head which is associated with pain and dysfunction. This dysfunction would be classified under secondary impingement. This is why it is so essential to have strong surrounding rotator cuff musculature to prevent the “excess-shoulder translation”. The surrounding scapular muscles also need to be coordinated and strong because this provides a solid foundation for pain free shoulder function.

Sometimes, patients will also manifest muscle imbalances such as tight muscles posteriorly, which can also place the scapula in a less optimal position.

Seeing a licensed physical therapist can help identify and prioritize the impairments of the shoulder and lead to a successful recovery!

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