Structure and Function of the Shoulder Complex In this episode of eOrthopodTV, orthopaedic surgeon Randale C. Sechrest, MD narrates an animated tutorial on the basic anatomy of the shoulder. Injury to 1 or more of these components through overuse or acute trauma disrupts this complex interrelationship and places the shoulder at increased risk. Shoulder internal rotation often occurs naturally with pronation, whereas shoulder external rotation naturally occurs with supination. "The Shoulder Complex." 7–1). For organizational purposes, this text divides these muscles into two categories: (1) Muscles of the shoulder girdle, and (2) muscles of the GH joint. References. The labrum performs this important function in two ways. Muscles of the shoulder. These muscles surround the humeral head and actively hold the humeral head against the glenoid fossa. In essence, this joint links the motion of the scapula (and attached humerus) to the lateral end of the clavicle. Bankart lesions, on the other hand, involve tears to the anterior-inferior portion of the glenoid labrum. The scapular spine divides the posterior aspect of the scapula into the supraspinatous fossa (above) and the infraspinatous fossa (below). (From Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation, ed 2, St Louis, 2010, Mosby, Figures 5-7, (From Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation, ed 2, St Louis, 2010, Mosby, Figure 5-11. The shoulder relies heavily on coordinated muscle activity for normal function owing to its limited osseous constraint. Only gold members can continue reading. The muscles of the shoulder complex, therefore, must work in a highly coordinated fashion. 1998;26(2):325-337. The primary stabilizing force of this joint is garnered from the surrounding musculature, particularly the rotator cuff muscles. The cooperative nature of the shoulder musculature increases the versatility, control, and range of active movements available to the upper extremity. The axes of rotation are color coded with the associated planes of motion. Proximal-to-Mid Humerus However, previous studies have failed to examine the sophisticated interrelationship between all muscles. Dyskinesis can be caused by inflexibility, weakness, or muscle imbalances. Shoulder joint kinesthesia can be adversely affected as a result of athletic trauma and lead to a variety of clinical entities that are commonly The shoulder complex plays an integral role in performing an athletic skill involving the upper extremity. Upward rotation occurs as the glenoid fossa of the scapula rotates upwardly, as a natural component of raising the arm overhead (Figure 4-9, C). The shoulder has several other important structures: The rotator cuff is a collection of muscles and tendons that surround the shoulder, giving it support and allowing a wide range of … What tendons, joints, muscles, and bones make up the human shoulder? Figure 4-2 An anterior view of the sternum with the left clavicle and ribs removed. Analysis of shoulder complex function after posterior spinal fusion in adolescents with idiopathic scoliosis. Components of shoulder complex Clavicle, humerus and scapula are linked with 3 interdependent linkages: SC joint, AC joint & GH joint. Muscles of the Shoulder Girdle Elevation and depression of the SC joint is a near-frontal plane movement about a near–anterior-posterior axis of rotation, allowing roughly 45 degrees of clavicular elevation and 10 degrees of depression. Symptoms of SLAP lesions often involve pain with overhead activities and “clicking” or “popping” of the shoulder. Rather, muscles work in teams to produce highly coordinated movements that are expressed over multiple joints. • Coracoacromial Ligament: Attaches the coracoid process to the acromion process; one of the few ligaments of the body that attaches proximally and distally to the same bone. Box 4-1 summarizes the interactions among the joints during common shoulder motions. Unit X – The Neck and Shoulder Complex Objectives: At the completion of Unit 10 the student will be able to: 1. INTEGRATED FUNCTION OF THE SHOULDER COMPLEX. As illustrated in Figure 4-17, B, when the scapula becomes downwardly rotated, as commonly occurs after a stroke involving weakness or paralysis of the trapezius muscles, the static locking mechanism becomes ineffective. muscles of the shoulder; human muscle system. Equally important, these motions allow the scapula to maintain firm contact with the posterior thorax. Sternoclavicular, scapulothoracic, acromioclavicular, and glenohumeral. all 3 of these muscles can extend the shoulder. This chapter provides an overview of the kinesiology of the four joints of the shoulder complex and the important muscular synergies that support proper function of the shoulder (, (From Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation, ed 2, St Louis, 2010, Mosby, Figure 5-1. Second, the labrum creates a “suction cup effect” between the head of the humerus and the glenoid fossa. • Clavicular elevation and posterior rotation, Two Ways to Help Prevent Shoulder Impingement. The muscles in the shoulder aid in a wide range of movement and help protect and maintain the main shoulder joint, known as the glenohumeral joint. The muscles of the shoulder complex, therefore, must work in a highly coordinated fashion. To illustrate this, first try to perform frontal plane abduction with your arm in full internal rotation (thumb pointing down), then in a neutral position (palm facing down), and finally in full external rotation (thumb pointing up). The acromioclavicular (AC) joint is considered a gliding or plane joint, created by the articulation between the lateral aspect of the clavicle and the acromion process of the scapula (Figure 4-10). Scapula Putting It All Together In essence, this joint links the motion of the. The AC joint allows motion in all three planes: Upward and downward rotation, rotation in the horizontal plane (internal and external rotation), and rotation in the sagittal plane (anterior and posterior tilting) (Figure 4-11). Arthrology For example, if the shoulder is abducted to 90 degrees, only about 60 degrees of that motion occurs from GH abduction; the additional 30 degrees or so is achieved through upward rotation of the scapula. Shoulder abduction in the scapular plane, often referred to as scaption, positions the greater tuberosity of the humerus under the highest point of the acromion and helps to prevent bony impingement, regardless of the amount of rotation of the glenohumeral joint. Figure 4-4 Posterior (A) and anterior (B) surfaces of the right scapula. The labrum serves to deepen the socket of the GH joint, nearly doubling the functional depth of the glenoid fossa. Depression occurs when the scapula slides inferiorly on the thorax (Figure 4-9, A; e.g., returning shrugged shoulders to a resting position; depressing the entire shoulder, as occurs when pushing up from a sitting position). This position not only improves the contact of the articulation but allows the surrounding soft tissues to help support this joint. These muscles are discussed at length in a subsequent section. Glenohumeral Joint This motion involves the typical scapulohumeral rhythm: a 2 : 1 ratio of glenohumeral flexion and scapulothoracic upward rotation. • Identify the bones and primary bony features relevant to the shoulder complex. All motions are functionally linked to the motions that occur at the other three joints of the shoulder complex; these functional relationships are discussed in depth later. Motions include elevation and depression, protraction and retraction, and axial rotation (Figure 4-8). • Cite the proximal and distal attachments, actions, and innervation of the muscles of the shoulder complex. The cooperative nature of the shoulder musculature increases the versatility, control, and range of active movements available to the upper extremity. The acromion process is a wide, flattened projection of bone from the most superior-lateral aspect of the scapula. This position not only improves the contact of the articulation but allows the surrounding soft tissues to help support this joint. Additionally a functional joint called scapulothoracic joint ( ST joint) is considered as a part oh shoulder complex. 3. Patients with Bankart lesions typically complain of significant shoulder instability, or feel as if the shoulder could “pop out” during various activities. This important concept is discussed further in a subsequent section. The muscles of the shoulder complex provide stability and movement. The greater and lesser tubercles are divided by the intertubercular groove, often called the. Symptoms of SLAP lesions often involve pain with overhead activities and “clicking” or “popping” of the shoulder. However, the shoulder complex relies on more than just the scapula for safe and efficient function. 1. ), (From Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation, ed 2, St Louis, 2010, Mosby, Figure 5-39. It helps limit the extremes of external rotation, flexion, and extension, as well as inferior displacement of the humeral head (see Figure 4-12). To illustrate this, first try to perform frontal plane abduction with your arm in full internal rotation (thumb pointing down), then in a neutral position (palm facing down), and finally in full external rotation (thumb pointing up). Anterior view of the right acromioclavicular joint, including many of the surrounding ligaments. Because strong forces are frequently transferred across the AC joint, several important stabilizing structures are required to maintain its structural integrity. Figure 4-10 Anterior view of the right acromioclavicular joint, including many of the surrounding ligaments. Protraction and Retraction Identify the bones and primary bony features relevant to the shoulder complex. The proximal attachments of surrounding muscles are shown in red. • Capsular Ligaments: A thin fibrous capsule that includes the superior, middle, and inferior glenohumeral ligaments. Normal movement and posture of the scapulothoracic joint are essential to the normal function of the shoulder. A, The rope indicates a muscular force that holds the glenoid fossa slightly upward. Proximal attachments of muscles are shown in red, distal attachments in gray. The body or middle portion of the sternum serves as the anterior attachment for ribs 2 through 7. The divisions then reorganize into lateral, medial, and posterior cords, named by their position relative to the axillary artery. The articular structures of the shoulder complex, in particular the GH Joint, are designed primarily for mobility, allowing us to move and position the hand through a wide range of space, allowing the greatest range of motion of any joint in the body. The primary motions of this joint are abduction and adduction, flexion and extension, and internal and external rotation (Figure 4-13). Up to this point, we have discussed the arthrology and kinematics of each joint of the shoulder complex. Furthermore, motion at the scapulothoracic joint is dependent on the combined movements of the AC and SC joints. Abduction and adduction of the GH joint occur in the frontal plane about an anterior-posterior axis of rotation, which courses through the humeral head. The limited range of motion experienced in a neutral or internally rotated position is caused by the greater tuberosity impinging against the acromion process. The medial or sternal end of the clavicle articulates with the manubrium of the sternum, forming the sternoclavicular joint. To achieve full range of motion during abduction, the prominent greater tuberosity must be positioned to clear the undersurface of the acromion; this can be accomplished by externally rotating the shoulder or performing abduction in the scapular plane. The superior capsular ligaments provide an upward force vector to counteract the downward force of gravity. 2. Related The cooperative nature of the shoulder musculature increases the versatility, control, and range of active movements available to the upper extremity. The manubrium is the most superior portion of the sternum that articulates with the clavicle—forming the sternoclavicular joint. Acromioclavicular and Sternoclavicular Joint Interaction Within the Scapulohumeral Rhythm, Elevation and posterior rotation of the clavicle, Downward rotation and retraction of the scapula, Depression and retraction of the clavicle, Clavicular elevation and posterior rotation, Even with the humerus in full external rotation, complete abduction of the shoulder may result in impingement if performed in the true frontal plane (, A side view of the right glenohumeral joint comparing abduction of the humerus in the, Ideal posture of the scapula positions the glenoid fossa so that it is tilted about 5 degrees upward (. More distally, on the lateral aspect of the upper one third of the shaft of the humerus is the deltoid tuberosity—the distal insertion of all three heads of the deltoid muscle. = 60 degrees of scapulothoracic joint upward rotation When these forces are combined, the resultant vector is a compressive force directed through the middle of the glenoid fossa, enhancing the static stability of the GH joint. First, the superior portion of the labrum is only loosely attached to the adjacent glenoid rim. This joint provides the only direct bony attachment of the upper extremity to the axial skeleton—accordingly, the joint must be stable while also allowing extensive mobility. • Coracoacromial Ligament: Attaches the coracoid process to the acromion process; one of the few ligaments of the body that attaches proximally and distally to the same bone. The manubrium is the most superior portion of the sternum that articulates with the clavicle—forming the sternoclavicular joint. 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