The shoulder contains four joints, one of which is the glenohumeral joint, which is most often involved in the shoulder impingement/tendinitis syndromes. The GH joint is composed of the head of the humerus (upper arm bone) that sits in a shallow concave capsule. Attaching to the front of the shoulder is the biceps tendon, which also attaches the biceps muscle. The biceps muscle bends the elbow and helps raise the arm in front of the body. The rotator cuff consists of four muscles, (supraspinatus, infraspinatus, Teres minor, and subscapularis) that not only help to move the arm, but also holds and supports the arm in the shoulder joint. The supraspinatus tendon is the main tendon involved in impingement disorders. It lies under the subdeltoid bursa and acromion and lies above the humeral head.
Subdeltoid bursitis - the bursa is a pillow of fluid that cushions the tendon from impingement against the bone and surrounding tendons. It can irritate and inflame with ensuing midrange pain during shoulder elevation forward (flexion), or lateral lifting (abduction). Symptoms can be light and dull or severe causing a limited range of movement. Palpation in the front of the shoulder can yield intense symptoms.
Shoulder impingement - occurs when there is excessive use of the arm over the head. (i.e. lifting boxes, weights above shoulder level, over hand throwing or falling on an outstretched arm). The supraspinatus, infraspinatus, teres minor muscles, and the subdeltoid bursa are primarily involved in the shoulder impingement syndrome. The subdeltoids bursa's function is to help cushion the tendon during arm elevation. The bursa is prone to irritation and inflammation, especially with overhead arm usage. When the bursa or the tendons become inflamed with shoulder elevation the supraspinatus tendon will become compressed between the acromion in the humeral head. The resulting symptoms may include sharp pain with side arm movements (abduction) from the mid range to the end range of movement; pain radiating to the back of the shoulder; into the deltoid muscle and down the arm into the lateral elbow and into the back of the hand.
Bicipital tendinitis - an irritation that occurs to the biceps tendon usually as it slides through the bicipital groove in the anterior part of the shoulder. A constant dull ache is felt in the front of the shoulder running into the biceps muscle. When the arm is lifted forward, an increasing level of pressure is felt in the anterior shoulder. Symptoms can be sharp, and a pinching sensation can be felt at end of range movements. The primary cause of bicipital tendinitis is repetitive overhead arm movement, (i.e. overhead nailing).