Bones of the Shoulder with a Direct Relationship with the Rib Cage

Bones of the Shoulder with a Direct Relationship with the Rib Cage

Clavicle

The clavicle is attached to the rib cage by a fascia, the sternoclavicular joint capsule, and associated ligaments. The sternoclavicular joint is sellar and contains a fibrocartilaginous disc. Ligamentous attachments of the clavicle to the sternum and first rib include: the anterior and posterior sternoclavicular ligaments; the interclavicular ligament, which is continuous with the deep cervical fascia; and the costoclavicular ligament, which joins the first rib and its costal cartilage.

Scapula

The scapulothoracic articulation, although not a true joint, has been described as a functional joint because of its close interaction with the rib cage.  The main components between the scapula and the ribs (ribs two to seven in the resting position) are the scapulothoracic bursa, the serratus anterior muscle, and the subscapularis muscle.  The scapula does, however, have direct fascial and ligamentous connections to the rib cage: the costocoracoid membrane and the costocoracoid ligament.

BIOMECHANICAL RELATIONSHIP

The shoulder is designed to be extremely mobile. One of its main functions is to allow the use of the hands to the maximum. All shoulder movements involve direct or indirect involvement of the spine and the cervical, thoracic and lumbar ribs. Most of the movement of the shoulder occurs between the head of the humerus and the glenoid fossa, with notable and important contributions from the sternoclavicular, acromioclavicular and scapulothoracic joints. What is often less appreciated is the movement that must take place along the spine and rib cage to allow the shoulder and upper limb to reach the maximum possible range. Physicians should realize that the spine (cervical to lumbar) and ribs do not remain completely rigid during active flexion or abduction of the arm. Although it is well known that distal mobility (shoulder and upper extremity) requires proximal stability (spine and rib cage), proximal stability does not preclude carefully controlled movement of the spine and ribs. Raising the arm from the side of the body and above the head, abduction (normal range, 180), involves all of the shoulder joints. The main muscles involved are the trapezius, the levator scapulae, the serratus anterior, the deltoid and the rotator cuff muscles. The major and minor rhomboid muscles simulate the activity of the middle trapezius and are most active in abduction as synergistic stabilizers by eccentric contraction during upward rotation of the scapula. A pair of forces is formed using the superior trapezius and superior anterior serratus muscles to produce upward rotation and elevation of the scapula. These two muscle segments, along with the levator scapula muscle, also support the shoulder against downward gravity. A second pair of forces, active in the same task, uses the inferior trapezius and inferior anterior serratus muscles. In addition to the activity of the muscles originating in the spinal column, there is direct involvement of the spinal joints with the abduction of the final range (generally greater than 150). When the shoulder and arm are abducted beyond approximately 150, a component movement of flexion of the contralateral side (usually in combination with rotation in the opposite direction) and extension of the thoracic spine is observed. When both arms are abducted, a necessary increase in lumbar lordosis occurs through activity of the erector muscles of the lumbar spine. Lumbar lordosis can also increase due to muscle tension in the great dorsal spine. Full shoulder flexion is generally achieved in conjunction with thoracic and lumbar spine extension and with some elevation and expansion of the ribs towards the end of range of motion (ROM). People with adhesive capsulitis or other chronic conditions that limit shoulder mobility necessarily put more pressure on the regions of the spine (cervical, thoracic, and lumbar) and ribs to reach the ROM they need for a particular task. When a particular task is repeated over and over in this way, hypermobility or overuse injuries to the spine or ribs can occur. The thoracolumbar junction, especially during repeated airborne activities, is particularly vulnerable to stress from overuse in this way. During functional activities of daily living (ADL), mobility of the spine and ribs is as important as shoulder mobility for a particular task or activity to be successful. If normal mobility is not present in the spine and ribs, more stress can be placed on the shoulder to complete the activity. Again, if a particular task is repeated over and over in this way, hypermobility, impingement, or overuse injury (biceps or rotator cuff tendinosis) can occur in the shoulder. To ensure full functional recovery of the shoulder and prevent future overload or strain injuries, the physician must treat all relevant spinal and rib dysfunctions that could cause stress and overexertion on the shoulder tissues. Measurement of macroscopic osteocinematic motion of the shoulder is not sufficient. You also need to know how the shoulder reaches its final ROM. The doctor also needs to know what is happening arthrokinetically in the affected joints of the spine and ribs. Although the patient appears to have normal active ROM (AROM) in the shoulder, he may have thoracic and costal hypomobility which has led to the development of glenohumeral hypermobility or, conversely, hypomobility in the glenohumeral joint with compensatory thoracolumbar hypermobility. A simple assessment of the patient's ability to achieve full goniometric AROM in a static posture is not sufficient. The ability to achieve fully functional ROM during repeat ADL, work, sports, and hobbies should also be of great concern.

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