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the coracoid process of the scapula to the underside of the clavicle near the acromioclavicular joint. The two portions, the medial fan-shaped conoid ligament and the lateral quadrilateral-shaped trapezoid ligament, provide horizontal stability and limit scapular rotation. They maintain vertical tension on the lateral portion of the clavicle, preventing it from rising superiorly at the acromioclavicular joint. The acromioclavicular ligament directly joins the acromion and lateral clavicle, preventing horizontal separation between the two. It also helps limit axial rotation of the clavicle during elevation of the upper extremity, an essential component of normal shoulder mechanics. The sternoclavicular ligament also limits clavicular motion, but at the medial portion rather than lateral. Finally, the coracoacromial ligament lies between the acromion and coracoid processes, forming a fibrous sling that helps stabilize the humeral head during overhead motions. MECHANICS The primary movements of the scapulothoracic joint—elevation, depression, protraction, retraction, upward rotation, and downward rotation—are the result of a combination of movement at the acromioclavicular and sternoclavicular joints. The scapula moves freely, gliding across the posterior thorax with the acromioclavicular joint, serving as the primary point of suspension of the upper extremity from the trunk. Several large, powerful prime-mover muscles attach to the clavicle and affect the function of the acromioclavicular joint. These include the pectoralis major anteriorly and inferiorly, the trapezius posteriorly and superiorly, the sternocleidomastoid medially, and the deltoid laterally. Additionally, the subclavius and pectoralis minor both strongly impact positioning of the acromioclavicular joint and the overall function of the scapulothoracic joint (see images above). Dynamic positioning of the clavicle throughout the range of movement of the glenohumeral joint significantly increases the range and movement combinations possible at the upper extremity. Upward and downward rotation of the clavicle dramatically enhances the amount of shoulder flexion and extension possible. Anterior and posterior gliding of both the acromioclavicular and sternoclavicular joints, with resultant scapular protraction and retraction, broadens shoulder horizontal adduction and abduction. Superior and inferior gliding provides scapular upward rotation and downward rotation, offering greater range of motion in both shoulder abduction and adduction. PATHOLOGY AND PURPOSE OF SOFT-TISSUE INTERVENTION Improper acromioclavicular mobility is a common cause of shoulder pain and dysfunction. Excessive mobility due to congenital joint laxity, chronic conditions, or specific injury may lead to joint instability, osteoarthritis, chronic Ta k e 5 a n d t r y A B M P F i v e - M i n u t e M u s c l e s a t w w w. a b m p . c o m / f i v e - m i n u t e - m u s c l e s . 43 subluxation or dislocation, impingement syndrome, or neurovascular compromise conditions such as thoracic outlet syndrome. Conversely, limited mobility due to muscular imbalance, hypertonicity, excessive myofascial density or adhesions, scar tissue from previous injury, chronic dysfunctional posture, or repetitive stress is equally problematic. This is more readily addressed through soft-tissue manipulation and should include assessment and restoration of mobility at both the sternoclavicular and acromioclavicular joints, as well as associated glenohumeral joint motions. Christy Cael is a licensed massage therapist and certified strength and conditioning specialist. Her private practice focuses on injury treatment, biomechanical analysis, craniosacral therapy, and massage for clients with neurological issues. She is the author of Functional Anatomy: Musculoskeletal Anatomy, Kinesiology, and Palpation for Manual Therapists (Lippincott Williams & Wilkins, 2009). Contact her at Trapezius Pectoralis major Pectoralis minor Biceps brachii Biceps brachii Clavicle Clavicle Subclavius Coracoid process Deltoid Acromion process

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