Causes

 

The scapula has been found to play an important role in shoulder impingement syndrome. It is a wide, flat bone lying on the thoracic wall that provides an attachment for three different groups of muscles. The intrinsic muscles of the scapula include the muscles of the rotator cuff- the subscapularis, teres minor, supraspinatus, and infraspinatus. These muscles attach to the surface of the scapula and are responsible for the internal and external rotation of the glenohumeral joint, along with humeral abduction. The extrinsic muscles include the biceps, triceps, and deltoid muscles and attach to the coracoid process and supraglenoid tubercle of the scapula, infraglenoid tubercle of the scapula, and spine of the scapula. These muscles are responsible for several actions of the glenohumeral joint. The third group, which is mainly responsible for stabilization and rotation of the scapula, consists of the trapezius, serratus anterior, levator scapulae, and rhomboid muscles and attach to the medial, superior, and inferior borders of the scapula. Each of these muscles has their own role in proper shoulder function and must be in balance with each other in order to avoid shoulder pathology. Abnormal scapular function is called scapular dyskinesis. One action the scapula performs during a throwing or serving motion is elevation of the acromion process in order to avoid impingement of the rotator cuff tendons. If the scapula fails to properly elevate the acromion, impingement may occur during the cocking and acceleration phase of an overhead activity. The two muscles most commonly inhibited during this first part of an overhead motion are the serratus anterior and the lower trapezius. These two muscles act as a force couple within the glenohumeral joint to properly elevate the acromion process, and if a muscle imbalance exists, shoulder impingement may develop.

 

Signs and symptoms

 

The most common symptoms in impingement syndrome are pain, weakness and a loss of movement at the affected shoulder. The pain is often worsened by shoulder overhead movement and may occur at night, especially if the patient is lying on the affected shoulder. The onset of the pain may be acute if it is due to an injury or may be insidious if it is due to a gradual process such as an osteoarthritic spur. Other symptoms can include a grinding or popping sensation during movement of the shoulder.

The range of motion at the shoulder may be limited by pain. A painful arc of movement may be present during forward elevation of the arm from 60° to 120°.Passive movement at the shoulder will appear painful when a downwards force is applied at the acromion but the pain will ease once the downwards force is removed.[1]

 

Diagnosis

 

 

MRI showing subacromial impingement with partial rupture of the supraspinatus tendon. However, no retraction or fatty degeneration of the supraspinatus muscle.

Impingement syndrome can usually be diagnosed by history and physical exam. On physical exam, the physician may twist or elevate the patient's arm to test for reproducible pain (Neer's sign and Hawkin's sign). These tests help localize the pathology to the rotator cuff, however they are not specific for impingement. Neer's sign may also be seen with subacromial bursitis.

The physician may inject lidocain (usually combined with a steroid) into the joint, and if there is an improved range of motion and decrease in pain, this is considered a positive "Impingement Test". It not only supports the diagnosis for impingement syndrome, but it is also therapeutic.

Plain x-rays of the shoulder can be used to detect some joint pathology and variations in the bones, including acromioclavicular arthritis, variations in the acromion, and calcification. However, x-rays do not allow visualization of soft tissue, thus hold a low diagnostic value.