Axioscapular Muscles

Axioscapular Muscles

The axioscapular muscles originate in the axial skeleton (skull, vertebrae, pelvis, sternum and ribs) with their insertion into the scapula. These muscles are responsible for positioning and stabilizing the scapula to allow for upper limb movements such as reaching, grasping, and lifting. The resting position of the scapula has received considerable attention. The medial scapular border should be approximately 3 inches from the spine and essentially parallel to the spinous processes. The location of the collarbone can provide clues as to the amount of elevation or depression of the scapula. The acromioclavicular joint should be slightly higher than the sternoclavicular joint. Sahrmann believes that most patients with shoulder pain develop the condition due to impaired movement of the scapula that disrupts the relationship between the humeral head and the glenoid fossa. The resting scapular position can also cause the axioscapular muscles to stretch or shorten which can also affect shoulder function. 

Trapezius

Concentric contraction of the superior trapezius muscle with the fixed spine creates an elevation of the scapula through its attachment to the distal clavicle and acromion. If the scapula is fixed or the ipsilateral load on the upper limb is heavy, the trapezius muscle can create ipsilateral rotation and lateral flexion of the cervical spine. The middle fibers of the trapezius muscle adduct the scapula with concentric contraction or help the rhomboid muscles to control the abduction of the scapula during eccentric contraction. The lower fibers of the trapezius muscle depress and adduct the scapula with concentric contraction. When combined with the concentric contraction of the superior trapezius and serratus anterior muscles, a pair of forces is produced that causes the scapular to rotate upward. Levator Scapula Concentric contraction of the levator scapula muscle with the fixed spine results in elevation, adduction, and downward rotation of the scapula. According to Sahrmann, this muscle is synergistic with the superior trapezius for scapula elevation and adduction, but an antagonist of scapula rotation. Shortening this muscle can elevate the medial portion of the scapula, but not the acromial end, thus causing the scapula to rotate downward. The differentiation between shortening of the levator scapula and rhomboid muscles (scapula adduction and downward rotation) versus superior muscle lengthening (scapula abduction and downward rotation) is believed to be extremely important in designing a corrective therapy intervention program.

Rhomboid Major and Minor

The rhomboid muscles work with the middle trapezius muscle during concentric contraction to retract the scapula and with the levator scapulae and pectoralis minor muscles to create downward scapular rotation. Shortening or tightness of the rhomboid muscles can position the scapula closer to the

spinous processes and may result in downward rotation of the scapula. scapular upward rotation as a result of rhomboid muscle shortness. Normally, the inferior angle of the scapula should reach the midaxillary line during full shoulder flexion. Serratus Anterior Concentric contraction of the serratus anterior muscle causes scapular abduction and protraction and upward rotation of the scapula. When the scapula is habitually abducted, this muscle may undergo shortening together with the pectoralis minor

muscle. Conversely, when the rhomboid and levator scapulae muscles are short, the serratus anterior muscle is placed in an elongated position together with the pectoralis minor muscle. If the serratus anterior is elongated, a change in the length-tension curve may result in weakness of this muscle in

its shortened position during flexion or abduction of the shoulder.

Pectoralis Minor

The pectoralis minor muscle can assist the serratus anterior muscle in protracting the scapula during a concentric contraction. In addition, it creates scapular downward rotation when concentric contraction is combined with the levator scapulae and rhomboid muscles. Tightness of this muscle can create

a forward “tipping” of the scapula, which may be noted as a prominence of the inferior angle of the scapula. Shortening of the pectoralis minor muscle may be combined with shortening of the serratus anterior muscle in an individual with an abducted scapular position at rest. Shortening of the pectoralis minor muscle may impede the upward rotation of the scapula during elevation of the arm and may limit shoulder flexion range of motion. When the patient with a short pectoralis minor is in the supine position, it is apparent that the acromion process is elevated off the table to a greater degree than normal. Sahrmann recommended that the lateral angle of the spine of the scapula should be no more than 1 inch

off the table. However, this distance changes significantly in subjects of differing body build. Pressure over the anterior shoulder in the area of the coracoid process stretches this muscle. Muraki et al  found that maximum stretch is placed on the pectoralis minor when the shoulder is first flexed to 30.

. The patient with tightness in this muscle should

describe a “pull” in the anterior chest in line with the muscle

fibers when stretched.

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