Introduction:

Shoulder disorders are a common cause of persistent musculoskeletal morbidity.  Pain and compromised shoulder function have a substantial impact on tasks essential to daily living and can lead to considerable disability, reduced health related quality of life, absenteeism from work, and use of healthcare resources.

Anatomy:

The shoulder joint, among many things, is arguably the most complicated joint in the body, obtaining the majority of its stability not by way of bone-to-bone proximity, but by muscular control and ligamentous and cartilaginous integrity.  The joint itself consists of the head of the humerus, the shallow depression on the scapula (shoulder blade) known as the glenoid cavity, and the most lateral edge of the clavicle (collar bone).  The first line of stability for the joint is made up of several ligaments, ranging in size and degrees of stiffness, which maintain close proximity of adjacent bone edges.  Another structure that provides stability is an oval shaped piece of cartilage known as the glenoid labrum.  This structure helps to stabilize the articulation between the head of the humerus and the glenoid cavity by providing additional contact surface area between the two articulating bones.

While ligament and cartilage structures help to stabilize the shoulder joint proper, the vast majority of joint integrity is produced by contraction of the many muscles that stabilize and move what is known as the shoulder girdle.  These muscles include the serratus anterior, rhomboids, levator scapulae, trapezius, deltoids, latissimus dorsi, pectoral muscles, teres major, and the muscles that comprise the rotator cuff including the supraspinatus, infraspinatus, teres minor, and the subscapularis.  Although these muscles are involved in producing different vectors of force and motion, they all play a significant role in maintaining the function and stability of the shoulder girdle.

Discussion:

As previously mentioned, the shoulder is a very complicated joint for many reasons.  Unlike several other major joint structures in the body, bone-to-bone contact does not comprise the majority of joint stability.  Muscles, ligaments, and cartilage play a much larger role in maintaining proper joint stability, movement, and overall health.  That being said, the shoulder is subject to a myriad of painful and dysfunctional injuries, movement patterns, and syndromes.  These morbidities are found in patients of all walks of life including athletes and non-athletes alike.

Some of the more common injuries present in today’s population include rotator cuff syndrome (impingement), rotator cuff tears (partial and full thickness), glenoid labrum defects and tears, adhesive capsulitis (frozen shoulder), subacromial bursitis, as well as many other catchall terms that describe shoulder pain.  Although the structures that sustain injury in these conditions may differ, the root cause is often of similar etiology.  A few things that most people who complain of shoulder pain often have in common regardless of the specific injury type, are dysfunction of the muscles responsible for shoulder stability, poor movement of the thoracic spine (mid and upper back), and overdominance of muscles responsible for arm and elbow flexion (both vertically and horizontally).