Axiohumeral Muscles

Axiohumeral Muscles

The axio-humeral muscles originate in the axial skeleton and have their insertion in the humerus. These muscles have a direct effect on the glenohumeral joint and an indirect effect on the scapular position due to their proximal attachments to the humerus. Pectoralis major The pectoralis major muscle is a powerful medial rotator and adductor of the arm. Shortening this muscle can bring the humerus into an internally rotated position and the scapula into an abducted position. Also, shortening this muscle limits the extent of horizontal shoulder abduction. To evaluate the length of the sternocostal head of this muscle, the subject must be supine with the arm at 155 ° of abduction and in lateral rotation. In this position, the subject's arm should be able to make contact with the table surface. Careful observation of the anterior chest wall can also detect elevation of the ipsilateral side of the chest as the upper extremity reaches its final elevation range. This tension is commonly found in people with abducted (prolonged) scapula and medially rotated humerus.

Latissimus Dorsi

The latissimus dorsi muscle is capable of performing adduction, medial rotation, and extension of the humerus. To assess the length of this muscle, the subject is positioned supine with the hips and knees flexed to flatten the lumbar spine. The subject then raises the arm into shoulder flexion and maintains lateral rotation of the humerus while the therapist observes restricted passive elevation and possible compensatory movement in the lower spine . In a subject with shortening of the latissimus dorsi muscle, shoulder flexion is limited, the rib cage will moves anteriorly, and the lumbar spine may elevate off the table as the muscle becomes taut. This muscle is capable of indirectly influencing scapular position because of its attachment to the humerus.

Scapulohumeral Muscles

The scapulohumeral muscles have their origin on the scapula and insertion on the humerus. They consist of the supraspinatus, infraspinatus, teres minor, subscapularis, and teres major muscles. The supraspinatus, infraspinatus, teres minor, and subscapularis comprise the rotator cuff muscles of the

shoulder. The rotator cuff muscles center the humeral head in the glenoid fossa and provide the “fine tuning” or “steering” necessary for performing various upper limb tasks.

Subscapularis

When contracting concentrically, the subscapularis muscle is a medial rotator of the humerus. This muscle also functions to center the humeral head in the glenoid fossa and acts as a humeral head depressor with the other rotator cuff muscles during overhead activities. To assess the length of the subscapularis muscle, the subject is positioned supine with the elbow held against the trunk while the humerus is rotated into lateral rotation. Performing this motion bilaterally permits the examiner to compare the two extremities quickly. In addition, tightness of the subscapularis muscle prevents dissociation of the humerus from the scapula during the final 40 of elevation. The lack of dissociation of the humerus from the scapula causes abduction of the scapula or protrusion of the inferior angle beyond the lateral wall of

the trunk.

Post a Comment

0 Comments