Chapter 4 Structure and Function of the Shoulder

Chapter 4 Structure and Function of the Shoulder Complex Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

Sternum Located anterior thorax midpoint Manubrium Ø Body Ø Most superior portion of the sternum that articulates with the clavicle—comprising the sternoclavicular joint Middle portion; anterior attachment point for ribs 2 through 7 Xiphoid process Ø Inferior tip of the sternum, meaning “sword shaped” Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 2

Clavicle S-shaped bone linking the scapula to the sternum Acromial end (flattened lateral portion) Ø Articulates with the acromion of the scapula, forming the acromioclavicular joint Medial (sternal) end of the clavicle Ø Articulates with the manubrium of the sternum, forming the sternoclavicular joint Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 3

Scapula Highly mobile, triangular-shaped bone resting on the posterior side of the thorax Subscapular fossa Slightly concave anterior aspect of the bone Ø Allows the scapula to glide smoothly along the convex posterior rib cage Ø Glenoid fossa Ø Slightly concave, oval-shaped surface that accepts the head of the humerus, comprising the glenohumeral joint Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 4

Scapula – cont’d Superior and inferior glenoid tubercles Border superior and inferior aspects of the glenoid fossa Ø Serve as proximal attachments for the long heads of the biceps and triceps, respectively Ø Scapular spine Ø Divides scapula’s posterior aspect into the supraspinatous fossa and infraspinatous fossa Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 5

Scapula – cont’d Acromion process Wide, flattened projection of bone from the most superiorlateral aspect of the scapula Ø Forms a functional “roof” over the humeral head, protecting delicate structures Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 6

Scapula – cont’d Coracoid process Ø “Finger-like” bone projection from the anterior scapular surface; attachment site for several muscles and ligaments of the shoulder complex Medial and lateral borders Ø Meet at the inferior angle of the scapula • Inferior angle is important in tracking scapular motion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 7

Proximal-to-Mid Humerus Proximal humerus Ø Attachment point for many ligaments and muscles, linking the upper extremity to the shoulder girdle Humeral head Ø Nearly one half of a full sphere that articulates with the glenoid fossa, comprising the glenohumeral joint Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 8

Proximal-to-Mid Humerus – cont’d Lesser tubercle Ø Greater tubercle Ø Sharp, anterior projection of bone just below the humeral head Larger, more rounded lateral projection of bone Intertubercular (bicipital) groove Ø Divides the greater and lesser tubercles Ø Houses tendon of the long head of the biceps Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 9

Proximal-to-Mid Humerus – cont’d Deltoid tuberosity On the lateral aspect of the upper one third of the humerus shaft Ø Distal insertion of all three heads of the deltoid muscle Ø Radial (spiral) groove Runs obliquely across the posterior surface of the humerus Ø Houses the radial nerve Ø Helps define the distal attachment for the lateral and medial heads of the triceps Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 10

Arthrology Shoulder complex functions through interactions of four joints: Ø Ø Sternoclavicular Scapulothoracic Acromioclavicular Glenohumeral Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 11

Sternoclavicular Joint Created by the articulation of the medial aspect of the clavicle with the sternum Provides the only direct bony attachment of the upper extremity to the axial skeleton Stable while also allowing extensive mobility Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 12

Sternoclavicular Joint – cont’d Allows motion in all three cardinal planes Supported by a thick network of ligaments, an articular disc, and a joint capsule High degree of stability explains why fractures of the clavicle occur more than dislocations of the sternoclavicular joint Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 13

Sternoclavicular Joint: Supporting Structures Sternoclavicular ligament Ø Joint capsule Ø Contains anterior and posterior fibers joining the clavicle to the manubrium Surrounds the entire joint; reinforced by the anterior and posterior sternoclavicular joint ligaments Interclavicular ligament Ø Spans the jugular notch, connecting the superior medial aspects of the clavicles; limits clavicular depression Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 14

Sternoclavicular Joint: Supporting Structures – cont’d Costoclavicular ligament Attaches the clavicle to the costal cartilage of the first rib Ø Limits extremes of clavicular motion except depression Ø Articular disc Absorbs shock between the clavicle and the sternum Ø Helps improve joint congruency Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 15

Sternoclavicular Joint: Kinematics Saddle joint with concave and convex surfaces on each of the joint’s articular surfaces Allows clavicle movement in all three planes Motions include: Elevation and depression Ø Protraction and retraction Ø Rotation Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 16

Sternoclavicular Joint: Kinematics – cont’d Elevation and depression Ø Near-frontal plane movement, allowing roughly 45 degrees of clavicular elevation and 10 degrees of depression Protraction and retraction Ø Occurs in the horizontal plane about a vertical axis of rotation, allowing about 15 to 30 degrees of clavicular motion in either direction Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 17

Sternoclavicular Joint: Kinematics – cont’d Rotation Clavicle rotates posteriorly about its longitudinal axis Ø As the shoulder abducts, the coracoclavicular ligament becomes taut and spins the clavicle posteriorly Ø Clavicle rotates anteriorly, back to its rest position, as the shoulder is extended or adducted Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 18

Scapulothoracic Joint Not a “true” joint in the traditional sense Refers to the junction created by the anterior aspect of the scapula on the posterior thorax Typically describes the motion of the scapula relative to the posterior rib cage Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 19

Scapulothoracic Joint – cont’d Motions at the scapulothoracic joint include: Elevation and depression Ø Retraction and protraction Ø Upward and downward rotation Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 20

Scapulothoracic Joint: Elevation and Depression Scapular elevation Ø Involves the scapula sliding superiorly on the thorax • e. g. , shrugging the shoulders Depression Ø When the scapula slides inferiorly on the thorax • e. g. , returning shrugged shoulders to a resting position Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 21

Scapulothoracic Joint: Kinematics Protraction Ø Retraction Ø Movement of the scapulae toward the midline Upward rotation Ø Motion of the scapulae sliding laterally on the thorax Occurs as the scapular glenoid fossa rotates upward Downward rotation Ø Occurs as the scapula returns from an upwardly rotated position to its resting position Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 22

Acromioclavicular Joint Considered a gliding or plane joint Created by the articulation between the lateral aspect of the clavicle and the acromion process of the scapula Links the motion of the scapula (and attached humerus) to the lateral end of the clavicle Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 23

Acromioclavicular Joint: Supporting Structures Acromioclavicular ligament Joins the clavicle to the acromion Ø Helps prevent dislocations of the scapula Ø Links motion of scapula to clavicle—or vice versa Ø Coracoclavicular ligament Composed of the conoid and trapezoid ligaments Ø Helps suspend the scapula from the clavicle and prevents inferior acromial dislocation Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 24

Acromioclavicular Joint: Supporting Structures – cont’d Articular disc Improves joint congruency Ø Helps to absorb the compressive forces Ø Coracoacromial ligament Attaches the coracoid process to the acromion process Ø Part of the coracoacromial arch—a functional “roof” that protects the head of the humerus Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 25

Acromioclavicular Joint: Kinematics Allows motion in all three planes Upward and downward rotation Ø Rotation in the horizontal plane Ø Rotation in the sagittal plane Ø Motions “fine-tune” the kinematic relationship between the scapula and humerus These motions allow the scapula to maintain firm contact with the posterior thorax Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 26

Glenohumeral Joint Created by the articulation of the humeral head with the glenoid fossa of the scapula Allows abundant motion in all three planes but does not promote a high degree of stability Rotator cuff muscles provide the primary stabilizing force of this joint Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 27

Glenohumeral Joint: Supporting Structures Rotator cuff Ø Surrounds the humeral head and actively “holds” the humeral head against the glenoid fossa Muscles include: Ø Ø Supraspinatus Infraspinatus Subscapularis Teres minor Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 28

Glenohumeral Joint: Supporting Structures – cont’d Glenohumeral joint capsule Thin fibrous capsule including the superior, middle, and inferior glenohumeral ligaments Ø Attaches between glenoid fossa rim and humerus neck Ø Coracohumeral ligament Attaches between the coracoid process and the anterior side of the greater tubercle Ø Limits external rotation, flexion, extension, and inferior displacement of the humeral head Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 29

Glenohumeral Joint: Supporting Structures – cont’d Glenoid labrum Fibrocartilaginous ring encircling glenoid fossa rim Ø Nearly doubles functional depth of the glenoid fossa Ø Stabilizes by maintaining a suction effect between the humerus and glenoid fossa Ø Long head of the biceps Ø Proximal portion attaches to the superior glenoid tubercle; provides anterior stability Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 30

Glenohumeral Joint: Kinematics Ball-in-socket joint that allows 3 degrees of freedom Primary motions include: Flexion and extension Ø Abduction and adduction Ø Internal and external rotation Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 31

Glenohumeral Joint: Abduction and Adduction Occurs in the frontal plane about an anterior-posterior axis of rotation The glenohumeral joint normally allows about 120 degrees of abduction Full 180 degrees of shoulder abduction is obtained by combining 60 degrees of scapular upward rotation Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 32

Glenohumeral Joint: Abduction and Adduction Abduction involves the convex head of the humerus rolling superiorly while simultaneously sliding inferiorly (adduction is the same, reverse direction) Impingement Ø Without an inferior slide, upward humerus roll results in the humeral head “jamming” into the acromion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 33

Glenohumeral Joint: Flexion and Extension Occur in the sagittal plane Humeral head spins about a relatively fixed axis About 120 degrees of flexion and 45 degrees of extension are available 180 degrees of shoulder flexion is obtained using about 60 degrees of scapular upward rotation Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 34

Glenohumeral Joint: Internal and External Rotation Occurs in the horizontal plane about a vertical axis of rotation Internal rotation—anterior surface of the humerus rotates medially; external rotation—anterior surface of the humerus rotates laterally Convex humeral head rolls and slides in opposite directions on the concave glenoid fossa Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 35

Glenohumeral Joint: Horizontal Adduction and Abduction Horizontal adduction Ø Movement of the humerus toward the midline in the horizontal plane with shoulder in roughly 90 degrees of abduction Horizontal abduction Ø Movement away from the midline in the horizontal plane Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 36

Interaction among Shoulder Complex Joints Movement of entire shoulder is result of movement in each of its four joints All four joints must properly interact for normal shoulder motion to occur Excellent example is the scapulohumeral rhythm Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 37

Scapulohumeral Rhythm During normal shoulder abduction (or flexion), a natural 2: 1 ratio exists between the glenohumeral and scapulothoracic joint For every 2 degrees of glenohumeral abduction, the scapula must simultaneously upwardly rotate roughly 1 degree Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 38

Innervation of the Shoulder Complex Brachial plexus innervates entire upper extremity Majority of shoulder complex muscles are innervated from two brachial plexus regions Nerves that branch from the posterior cord Ø Nerves branching from the more proximal segments of the plexus Ø Exception trapezius muscle, innervated primarily by cranial nerve XI Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 39

Scapulothoracic Joint Elevators Upper trapezius, levator scapulae, and rhomboids are responsible for elevating the scapula Good scapulothoracic posture is a slightly retracted and elevated position of the scapula, resulting in the glenoid fossa facing slightly upward Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 40

Functional Consideration: Weakness of the Upper Trapezius Weakness or paralysis of the upper trapezius, over time, will likely lead to a depressed, or downwardly rotated, scapula A chronically depressed clavicle may eventually lead to a superior dislocation of the sternoclavicular joint Perhaps more commonly, weakness of the upper trapezius will lead to subluxation of the glenohumeral joint Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 41

Depressors of the Scapulothoracic Joint Scapulothoracic depression is performed by the lower trapezius, latissimus dorsi, pectoralis minor, and the subclavius These muscles work together to depress the shoulder girdle and humerus, resulting in shoulder depression Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 42

Functional Consideration: “Reverse Action” of the Shoulder Depressors Reverse action of the shoulder depressors can be extremely useful clinically because thorax elevation is useful for activities Ø e. g. , crutch walking, ambulation with a walker These muscles can be useful sources of muscular substitution for persons with weakened or paralyzed lower extremities Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 43

Upward Rotators of the Scapula Upward rotation is an important component of upper extremity elevation Upward rotation of the scapula is created by a forcecouple generated by the serratus anterior, upper trapezius, and lower trapezius These muscles have much different lines of pull, but all rotate the scapula in the same direction Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 44

Sole Scapular Protractor: Serratus Anterior Scapulothoracic protraction: Serratus anterior generates force that moves the scapula away from the body’s midline Ø Force produced by serratus anterior is transferred through the scapula to the humerus and used forward reaching and pushing activities Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 45

Functional Consideration: Winging of the Scapula “Winging” refers to the medial border of the scapula lifting away from the rib cage and is a sign of serratus anterior weakness Rehabilitation programs designed to strengthen the serratus anterior often incorporate a “push-up-plus” This exercise exaggerates the final phase of a pushup, which involves additional protraction of the scapulae at the end phase of the push-up Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 46

Downward Rotators of the Scapula Primary muscles involved with this action are the rhomboids, pectoralis minor, and latissimus dorsi Latissimus dorsi and the rhomboids have significantly different lines of pull but produce scapular motion in the same rotary direction Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 47

Downward Retractors of the Scapula Scapular retraction is often referred to as “pinching your shoulder blades together” Linked to upper extremity movements such as rowing or pulling Primary scapular retractors are the rhomboids and the middle trapezius but can include all three of the trapezius muscles Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 48

Functional Consideration: Controlling Scapular Motion Resisted shoulder adduction requires optimal interaction between the glenohumeral adductors and the scapular downward rotators The shoulder adductor and extensor muscles can be no stronger than the scapulothoracic retractor and downward rotator muscles Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 49

Glenohumeral Joint Muscles: Abductors and Flexors Abductors Ø Supraspinatus and the anterior and middle deltoid Flexors Ø Anterior deltoid, clavicular head of the pectoralis major, coracobrachialis, and biceps brachii Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 50

Functional Consideration: Scapulohumeral Rhythm Revisited Upward rotation of the scapula is an essential component of abduction or flexion of the shoulder Motion augments the total range of motion of the shoulder Upward scapula rotation helps maintain favorable length-tension relationship of and flexors throughout extensive ranges of motion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 51

Glenohumeral Joint Muscles: Adductors and Extensors Adductors Ø Teres major, latissimus dorsi, and pectoralis major Extensors Ø Latissimus dorsi, teres major, pectoralis major, posterior deltoid, and long head of the triceps Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 52

Rotator Cuff Supraspinatus, infraspinatus, teres minor, and subscapularis Surround the humeral head anteriorly, superiorly, and posteriorly Stabilizes humeral head on glenoid fossa Function as dynamic stabilizers for the glenohumeral joint Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 53

Glenohumeral Joint Muscles: Internal and External Rotators Internal rotators Ø Teres major, pectoralis major, subscapularis, latissimus dorsi, and the anterior deltoid External rotators Ø Glenohumeral joints are the teres minor, infraspinatus, and posterior deltoid Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 54

Functional Consideration: Activation of the Rotators during a Throwing Motion Typically, this motion occurs with shoulder abducted greater than 90 degrees Quick, concentric contraction of external rotators “cocks” shoulder, followed by concentric contraction of internal rotators that generates huge amounts of internal rotation torque Large torques and high velocities produced during a vigorous throwing motion are good examples of how the elastic nature of muscle can be used for functional advantage Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 55

Summary Shoulder complex is one of most complex musculoskeletal systems in body Proper motion of shoulder requires coordinated action of many muscles across multiple joints; dysfunction is common Same factors making dysfunction likely also make shoulder complex highly adaptable Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 56