Subacromial impingement can produce shoulder pain, weakness, and referred pain or paresthesias into the region of the deltoid insertion and upper lateral arm. When subacromial impingement is suspected it is important to differentiate between the possible types of rotator cuff pathology. Rotator cuff impingement, regardless of the type, alters muscular function of the cuff and results in diminished dynamic control of the glenohumeral joint. Until optimal strength and neuromuscular control are established, continued use of the arm at or above the level of the shoulder will produce further impingement of the rotator cuff. If cuff impingement is not recognized and corrected early the problem can progress to degradation of tissue and resultant tears in the rotator cuff.

Rotator cuff tears are among the most common conditions affecting the shoulder. The rotator cuff has three well-recognized functions: rotation of the humeral head, stabilization of the humeral head in the glenoid socket by compressing the round head into the shallow socket, and the ability to provide “muscular balance,” stabilizing the glenohumeral joint when other larger muscles crossing the shoulder contract. Partial-thickness tears (PTT) can be bursal-sided or articular-sided tears. Over the course of time, PTT enlarge and propagate into full-thickness tears and develop distinct chronic pathological changes due to muscle retraction, fatty infiltration and muscle atrophy.

Suprascapular neuropathy is a relatively uncommon but significant cause of shoulder pain and dysfunction. It is is a condition which is due to irritation and damage to the suprascapular nerve. This condition can result in pain, weakness, or both depending on the cause.There are several potential causes of nerve entrapment along its path, including bony and ligamentous constraints as well as glenohumeral joint–related ganglion cysts or soft-tissue masses.

Glenohumeral instability is a relatively common problem, encompassing a wide spectrum of pathologic mobility at the shoulder joint ranging from symptomatic laxity to frank dislocation. The glenohumeral joint allows greater mobility than any other joint in the human body; however, this comes at the expense of stability. Perhaps more so than other joints, shoulder stability is predicated on adequate soft tissue (muscular and ligamentous) function and integrity, rather than bony congruity and alignment. Instability of the joint can easily result from impairments or imbalances in muscle function, ligamentous laxity, and/ or bony abnormalities.

The stability and movement of the shoulder is controlled by the rotator cuff muscles, as well as the shoulder ligaments, the capsule of the shoulder and the glenoid labrum. The labrum is a fibrocartilagenous ring which attaches to the bony rim of the glenoid fossa. A SLAP tear or SLAP lesion is an injury to the glenoid labrum. The most common complaint in patients that present with SLAP lesions is pain. Pain is typically intermittent and often associated with overhead movements.

Biceps tendinitis is an inflammation or irritation of the upper biceps tendon, that is a strong, cord-like structure that connects the biceps muscle to the bones in the shoulder. Biceps tendinitis may also refer to tendinosis, which is a syndrome of overuse and degeneration. Patients with biceps tendinitis or tendinosis usually complain of a deep, throbbing ache in the anterior shoulder. Repetitive overhead motion of the arm initiates or exacerbates the symptoms.

The clavicle acts as a strut for the shoulder complex, connecting the scapula to the central portion of the body. This allows two trans- lations to occur: upward/downward translation on the thoracic wall and retraction/protraction around the rounded thorax. The AC joint can become painful for different reasons, including trauma, osteoarthritis, repetitive strain and bone injuries of the clavicle.

The glenohumeral joint normally functions through a wide range of motions. When the articular surfaces of the humeral head or the glenoid are damaged, that motion is compromised, and arthritis commonly is the result. Osteoarthritis is a condition that destroys the smooth outer covering (articular cartilage) of bone. As the cartilage wears away, it becomes frayed and rough, and the protective space between the bones decreases. During movement, the bones of the joint rub against each other, causing pain.

Normal scapulohumeral rhythm, the coordinated movement of the scapula and humerus to achieve shoulder motion, is the key to efficient shoulder function. Scapular position and motion are closely integrated with arm motion to accomplish most shoulder functions. Because of the important but minimal bony stabilization of the scapula by the clavicle, dynamic muscle function is the major method by which the scapula is stabilized and purposefully moved to accomplish its roles. Alterations in scapular motion and position are termed “scapular dyskinesis” and are present in 67% to 100% of shoulder injuries. This dyskinesis can alter the roles of the scapula in the scapula-humeral rhythm. It can result from alterations in the bony stabilizers, alterations in muscle activation patterns, or strength in the dynamic muscle stabilizers.