SHOULDER COMPLEXDr. Michael P. Gillespie

ARTICULATIONS OF THE SHOULDER

Four articulations of the shoulder exist involving the sternum, clavicle, ribs, scapula and humerus.

The series of joints of the shoulder complex allow for extensive range of motion to the upper extremity.

This extensive range of motion allows us to reach and manipulate objects.

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JOINTS OF THE SHOULDER COMPLEX

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MUSCLE INTERACTIONS

Muscles of the shoulder complex rarely act isolation, but rather work in “teams” to produce highly coordinated movements.

These movements are expressed over multiple joints.

The coordinated actions of multiple muscles allows for great versatility, control and range of motion.

Paralysis or weakness of any single muscle often disrupts the entire kinematic sequencing of the entire shoulder complex.

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OSTEOLOGY

Sternum Clavicle Scapula Proximal-to-Mid Humerus

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OSTEOLOGIC FEATURES OF THE STERNUM

Manubrium Pair of oval-shaped clavicular facets, which

articulate with the clavicles. Costal facets – attachment for first two ribs. Jugular notch – superior aspect

Body Xiphoid Process

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STERNUM: ANTERIOR VIEW

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OSTEOLOGIC FEATURES OF THE CLAVICLE

Shaft Sternal end Costal facet Costal tuberosity Acromial end Acromial facet Conoid tubercle Trapezoid line

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CLAVICLE: SUPERIOR AND INFERIOR SURFACES

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OSTEOLOGIC FEATURES OF THE SCAPULA Angles: Inferior, superior, and lateral Medial or vertebral border Lateral or axillary border Superior border Supraspinatous fossa Infraspinatous fossa Spine Root of the spine Acromion Clavicular facet Glenoid fossa Supraglenoid and infraglenoid tubercles Coracoid process Subscapular fossa

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SCAPULA: POSTERIOR & ANTERIOR VIEW

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OSTEOLOGIC FEATURES OF THE PROXIMAL-TO-MID HUMERUS

Head of the humerus Anatomic neck Lesser tubercle and crest Greater tubercle and crest Upper, middle, and lower facets on the

greater tubercle Intertubercular (bicipital) groove Deltoid tuberosity Radial (spiral) groove

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HUMERUS: ANTERIOR & SUPERIOR VIEWS

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FOUR JOINTS WITHIN THE SHOULDER COMPLEX

Sternoclavicular Acromioclavicular Scapulothoracic Glenohumeral

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ARTHROLOGY OF THE SHOULDER COMPLEX The most proximal articulation within the shoulder

complex is the sternoclavicular joint. The clavicle functions as a mechanical strut

holding the scapula at a relatively fixed distance from the trunk.

The acromioclavicular joint attaches the scapula to the clavicle.

The anterior surface of the scapula rests against the posterior-lateral surface of the thorax, forming the scapulothoracic joint. This is not a true anatomic joint. It is an interface between bones.

The scapula serves as a base of operation for the glenohumeral joint. The glenohumeral joint is the most distal and mobile link of the complex.

“Shoulder movement” describes the combined motions at the glenohumeral and scapulothoracic joints.

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PRIMARY MOVEMENTS OF THE SCAPULOTHORACIC JOINT

Elevation Depression Protraction Retraction Upward Rotation Downward Rotation

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ELEVATION & DEPRESSION OF THE SCAPULOTHORACIC JOINT

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PROTRACTION & RETRACTION OF THE SCAPULOTHORACIC JOINT

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UPWARD ROTATION & DOWNWARD ROTATION OF THE SCAPULOTHORACIC JOINT

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STERNOCLAVICULAR JOINT: GENERAL FEATURES

The SC joint functions as the basilar joint of the entire upper extremity and links the appendicular skeleton to the axial skeleton.

The joint must be firmly attached, yet allow considerable range of movement.

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TISSUES THAT STABILIZE THE STERNOCLAVICULAR JOINT

Anterior and posterior sternoclavicular ligaments

Interclavicular ligament Costoclavicular ligament Articular disc Sternocleidomastoid, sternothyroid,

sternohyoid, and subclavius muscles

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KINEMATICS OF THE STERNOCLAVICULAR JOINT

Osteokinematics of the SC joint involve rotation in all three degrees of freedom.

Elevation & Depression Protraction & Retraction Axial (Longitudinal) Rotation of the Clavicle

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OSTEOKINEMATICS OF THE STERNOCLAVICULAR JOINT

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ACROMIOCLAVICULAR JOINT: GENERAL FEATURES

The AC joint is the articulation between the lateral end of the clavicle and the acromion of the scapula.

An articular disc is present in most AC joints. The joint has an articular capsule and

significant ligament support.

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TISSUES THAT STABILIZE THE ACROMIOCLAVICULAR JOINT

Superior and inferior acromioclavicular joint ligaments

Costoclavicular ligament Articular disc (when present) Deltoid and upper trapezius muscles

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KINEMATICS OF THE ACROMIOCLAVICULAR JOINT

The motions of the AC joint are described by the movement of the scapula relative to the lateral end of the clavicle.

Upward & Downward Rotation Horizontal & Sagittal Plane “Rotational

Adjustments” at the AC joint

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OSTEOKINEMATICS OF THE ACROMIOCLAVICULAR JOINT

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OSTEOKINEMATICS OF THE ACROMIOCLAVICULAR JOINT

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ACROMIOCLAVICULAR JOINT DISLOCATION

The AC joint is inherently susceptible to dislocation due to the sloped nature of the articulation and the high probability of receiving large shearing forces.

Falling and striking the tip of the shoulder abruptly against the ground would produce such a shearing force.

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SCAPULOTHORACIC JOINT

The scapulothroacic Joint is not a true joint, but rather a point of contact between the anterior surface of the scapula and the posterior-lateral wall of the thorax.

The two surfaces do not make direct contact. They are separated by muscles such as the subscapularis, serratus anterior, and erector spinae.

An audible click during scapular movements may indicate abnormal contact within the articulation.

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KINEMATICS OF THE SCAPULOTHORACIC JOINT

The movements at the scapulothoracic joint are a result of cooperation between the SC and the AC joints.

Elevation & Depression Protraction & Retraction Upward & Downward Rotation

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SCAPULOTHORACIC ELEVATION

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SCAPULOTHORACIC PROTRACTION

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SCAPULOTHORACIC UPWARD ROTATION

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FUNCTIONAL IMPORTANCE OF UPWARD ROTATION Many functional activities require us to raise the

arm fully overhead. The upward rotation of the scapula accounts for

nearly 1/3 of the 180 degrees of shoulder abduction or flexion.

Functions The upwardly rotated scapula projects the glenoid fossa

upward and anterior-laterally, providing a structural base to maximize upward and lateral reach.

The upwardly rotated scapula preserves the optimal length-tension relationship of the abductor muscles of the glenohumeral joint (middle deltoid & supraspinatous).

The upwardly rotated scapula helps maintain the volume within the subacromial space. A reduced subacromial space can lead to painful and damaging impingement of the supraspinatus tendon and subacromial bursa).

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GLENOHUMERAL JOINT: GENERAL FEATURES

The GH joint is the articulation formed between the large convex head of the humerus and the shallow concavity of the glenoid fossa.

It operates in conjunction with the moving scapula to produce an extensive range of motion of the shoulder.

In anatomic position, the articular surface of the glenoid fossa is directed anterior-laterally in the scapular plane.

In anatomic position, the humeral head is directed medially and superiorly, as well as posteriorly.

This orientation places the head of the humerus directly against the face of the glenoid fossa. 36

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GLENOHUMERAL JOINT: ANTERIOR VIEW

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“LOOSE FIT” OF THE GLENOHUMERAL JOINT & INSTABILITY Several features of the glenohumeral joint contribute to

a design that favors mobility at the expense of stability. The articular surface of the glenoid fossa covers only about

1/3 of the articular surface of the humeral head. The longitudinal diameter of the humeral head is about 1.9

times larger than the longitudinal diamter of the glenoid fossa.

The transverse diameter of the humeral head is about 2.3 times larger than the opposing transverse diameter of the glenoid fossa.

The surrounding muscles and ligaments maintain the mechanical integrity of the joint.

A condition of excessive laxity or “joint play” associated with large translations of the proximal humerus relative to the glenoid is often referred to as shoulder instability. Subluxation – incomplete separation of articular surfaces

often followed by spontaneous realignment Dislocation – complete separation of articular surfaces

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“LOOSE FIT” IN GLENOHUMERAL JOINT

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GLENOHUMERAL JOINT STABILITY

A combination of passive and active mechanisms achieve GH joint stability.

Active mechanisms Forces produced by muscle Embracing nature of the rotator cuff

Passive mechanisms Forces other than activated muscle

1. restraint provided by capsule, ligaments, glenoid labrum, and tendons

2. mechanical support predicated on scapulothoracic posture

3. negative intracapsular pressure40

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ROTATOR CUFF MUSCLES & LONG HEAD OF BICEPS BRACHII The glenohumeral joint receives significant

structural reinforcement from the four rotator cuff muscles.

The subscapularis is the thickest of these muscles and lies just anterior to the scapula.

The supraspinatus, infraspinatus, and teres minor lie superior and posterior to the capsule.

These four muscles form a cuff that protects and actively stabilizes the GH joint, especially during dynamic activities.

The belly of these muscles lies close to the joint. The tendons of these muscle blend into the capsule. The tendon of the long head of the biceps

reinforces the rotator interval (between supraspinatus and subscapularis).

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ROTATOR CUFF MUSCLE SUPPORT

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TISSUES THAT REINFORCE OR DEEPEN THE GLENOHUMERAL JOINT

Joint capsule and associated capsular ligaments

Coracohumeral ligament Rotator cuff muscles (subscapularis,

supraspinatus, infraspinatus, and teres minor)

Long head of biceps brachii Glenoid labrum

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KINEMATICS OF THE GLENOHUMERAL JOINT

Movement occurs in all three degrees of freedom.

Abduction & Adduction Flexion & Extension Internal & External Rotation

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OSTEOKINEMATICS OF THE GLENOHUMERAL JOINT

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GLENOID LABRUM: VULNERABLE TO INJURY The rim of the glenoid fossa is encircled by a

fibrocartilage ring, or lip, known as the glenoid labrum.

It deepens the concavity of the fossa and increases the contact area with the humeral head to help stabilize the joint.

The superior part of the glenoid labrum is only loosely attached.

50% of the fibers of the tendon of the long head of the biceps are direct extensions of the superior glenoid labrum.

Large or repetitive forces within the biceps tendon can detach the superior labrum (near its 12 o’clock position). 46

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GLENOHUMERAL JOINT: ACTIVE ABDUCTION

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GLENOHUMERAL JOINT: FLEXION

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KINEMATIC RELATIONSHIPS OF THE GLENOHUMERAL JOINT

Osteokinematics Plane of Motion /Axis of Rotation

Arthrokinematics

Abduction & adduction

Near frontal plane / near anterior-posterior axis of rotation

Roll and slide along joint’s longitudinal diameter

Internal & external rotation

Horizontal plane / vertical axis of rotation

Roll and slide along joint’s transverse diameter

Flexion & Extension, internal & external rotation (in 90 degrees of abduction)

Near sagittal plane / near medial-lateral axis of rotation

Primarily a spin between humeral head and glenoid fossa

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SCAPULOHUMERAL RHYTHM

“Scapulohumeral rhythm” describes the kinematic relationship between glenohumeral abduction and scapulothoracic upward rotation.

After about 30 degrees of abduction, the rhythm is remarkably constant.

For every 3 degrees of shoulder abduction, 2 degrees occur by GH joint abduction and 1 degree occurs by scapulothoracic upward rotation.

A full arc of 180 degrees of abduction is the result of a simultaneous 120 degrees of GH joint abduction and 60 degrees of scapulothoracic upward rotation.

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SCAPULOHUMERAL RHYTHM

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SHOULDER ABDUCTION IN THE FRONTAL PLANE VERSUS THE SCAPULAR PLANE

Shoulder abduction in the frontal plane is often used as a representative motion to evaluate overall shoulder function; however, this motion is not very natural.

Abducting the shoulder in the scapular plane (about 35 degrees anterior to the frontal plane) is a more natural movement and generally allows greater elevation of the humerus than in the frontal plane.

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ABDUCTION: FRONTAL VS. SCAPULAR

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INNERVATION OF MUSCLES & JOINTS OF THE SHOULDER COMPLEX

Brachial Plexus Innervation of Muscle Innervation to the Joints

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BRACHIAL PLEXUS

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NERVES THAT FLOW FROM THE BRACHIAL PLEXUS AND INNERVATE THE SHOULDER

Nerve Primary Nerve Root(s)

Muscles Supplied

Axillary C5, C6 Deltoid, teres mino

Thoracodorsal (middle subscapular)

C6, C7, C8 Latissimus dorsi

Upper subscapular C5, C6 Subscapularis (upper fibers)

Lower subscapular C5, C6 Subscapularis (lower fibers), teres major

Lateral pectoral C5, C6, C7 Pectoralis major and occasionally pectoralis minor

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NERVES THAT FLOW FROM THE BRACHIAL PLEXUS AND INNERVATE THE SHOULDER

Nerve Primary Nerve Root(s)

Muscles Supplied

Medial pectoral C8, T1 Pectoralis major (sternocostal head), pectoralis minor

Suprascapular C5, C6 Supraspinatus, infraspinatus

Subclavian C5, C6 subclavius

Dorsal scapular C5 Rhomboid major & minor, levator scapula*

Long thoracic C5, C6, C7 Serratus anterior

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* Also innervated by C3 & C4 nerve roots from cervical plexus

PRIMARY MUSCLES ACTING AT THE SCAPULOTHORACIC JOINT

Elevators Upper trapezius Levator scapulae Rhomboids

Depressors Lower trapezius Latissimus dorsi Pectoralis major Subclavius

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PRIMARY MUSCLES ACTING AT THE SCAPULOTHORACIC JOINT

Protractors Serratus anterior

Retractors Middle trapezius Rhomboids Lower trapezius

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PRIMARY MUSCLES ACTING AT THE SCAPULOTHORACIC JOINT

Upward Rotators Serratus anterior Upper and lower trapezius

Downward Rotators Rhomboids Pectoralis minor

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ELEVATORS OF THE SCAPULOTHORACIC JOINT

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DEPRESSORS OF THE SCAPULOTHORACIC JOINT

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PROTRACTION OF THE SCAPULOTHORACIC JOINT

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RETRACTION OF THE SCAPULOTHORACIC JOINT

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MUSCLES PRIMARILY RESPONSIBLE FOR ELEVATION OF THE ARM The term “elevation” of the arm describes the

active movement of bringing the arm overhead without specifying the exact plane of motion.

Glenohumeral Joint Muscles Anterior and middle deltoid Supraspinatous Coracobrachialis Biceps (long head)

Scapulothoracic Joint Muscles Serratus anterior Trapezius

Rotator Cuff Muscles Supraspinatus Infraspinatus Teres minor Subscapularis

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FUNCTION OF THE ROTATOR CUFF MUSCLES IN ABDUCTION AT THE GLENOHUMERAL JOINT

Supraspinatus Drives the superior roll of the humeral head Compress the humeral head firmly against the

glenoid fossa Creates a semirigid spacer above the humeral

head, restricting excessive superior translation of the humerus

Infraspinatus, Teres Minor, and Subscapularis Exert a depression force on the humeral head

Infraspinatus and Teres Minor Externally rotate the humerus

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SHOULDER ADDUCTION & EXTENSION

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SCAPULOTHORACIC DOWNWARD ROTATION & GLENOHUMERAL ADDUCTION

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INTERNAL ROTATION OF THE SHOULDER

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SHOULDER INSTABILITY

Posttraumatic Instability Atraumatic Instability Acquired Shoulder Instability

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POSTTRAUMATIC INSTABILITY Posttraumatic instability is attributed to a specific

event involving a traumatic dislocation of the glenohumeral joint.

The vast majority of traumatic dislocations occur in the anterior direction, typically related to a fall or forceful collision.

The pathomechanics of an anterior dislocation often involve the motion or position of extreme external rotation in an abducted position.

The force then drives the humeral head off the anterior aspect of the glenoid fossa.

This dislocation often injures the rotator cuff muscles, middle and inferior GH ligaments, and anterior-inferior rim of the glenoid labrum (Bankart lesions).

Posttraumatic dislocations frequently lead to future recurrences.

Posttraumatic instability does NOT respond well to conservative care and often requires surgery.

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ATRAUMATIC INSTABILITY

These individuals tend to display generalized and excessive ligamentous laxity throughout the body, often described as being congenital.

This type of instability is usually not associated with a traumatic event.

The instability can be unidirectional or multidirectional, and bilateral.

Atraumatic instability tends to respond favorably to conservative therapy involving strengthening and coordination exercises.

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ACQUIRED SHOULDER INSTABILITY The pathogenics of acquired shoulder instability

are related to overstretching and subsequent microtrauma of the capsular ligaments within the GH joint.

This condition is associated with repetitive, high-velocity shoulder motions that involve extreme external rotation and abduction.

These motions are common in throwing sports, swimming, tennis, and volleyball.

The anterior bands of the inferior GH ligament and to a lesser extent the middle GH ligament are vulnerable to plastic deformation.

This tissue deformation leads to increased laxity. This can contribute to other conditions such as

rotator cuff syndrome and internal impingement syndrome.

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SUPRASPINATUS VULNERABILITY

The supraspinatus is one of the most used muscles of the entire shoulder complex.

It assists the deltoid during abduction. It provides dynamic and static stability to the GH

joint. It is subjected to large internal forces even during

routine activities. The muscle exhibits a 1:20 mechanical advantage

over a load in the hand, implying that the muscle must exert a force 20 times greater than the weight of the load.

This can lead to tears of the muscle as it inserts into the capsule and greater tubercle of the humerus.

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SHOULDER IMPINGEMENT SYNDROME

Subacromial shoulder impingement syndrome is among the most common painful disorders of the shoulder.

It is caused by repeated an unnatural compression of the tissues within the subacromial space.

The tissues affected are the supraspinatus tendon, the tendon of the long head of the biceps brachii, the superior capsule, and the subacromial bursa.

These tissues become compressed between the humeral head and the coracoacromial arch.

This impingement can be a very important factor in rotator cuff syndrome.

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DIRECT OR INDIRECT CAUSES OF SHOULDER IMPINGEMENT SYNDROME Abnormal kinematics at the glenohumeral and

scapulothoracic joints. “Slouched” posture that affects the alignment of the

scapulothoracic joint. Fatigue, weakness, poor control, or tightness of the

muscles that govern motions at the GH or scapulothoracic joints.

Inflammation and swelling of tissues within and around the subacromial space.

Excessive wear and subsequent degenration of the tendons of the rotator cuff muscles.

Instability of the GH joint. Adhesions within the inferior GH joint capsule. Excessive tightness in the posterior capsule of the GH

joint (and associated anterior migration of the humeral head towards the lower margin of the coracoacromial arch).

Abnormal shape of the acromion or coracoacromial arch.76

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