The Shoulder Workbook Anatomy and Physiology Review

The Shoulder Workbook 1

Shoulder 3 Sternoclavicular joint 4 Muscles 4 Rotator cuff 8

Glenohumeral joint 8 Movements 8 Capsule 10 Ligaments 10

Rotator cuff 11 Muscles composing rotator cuff 11 Function 11

Shoulder References 13 Glenohumeral joint References 14 Rotator cuff References 14

Shoulder The shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons.

The articulations between the bones of the shoulder make up the shoulder joints. "Shoulder joint" typically refers to the glenohumeral joint, which is the major joint of the "shoulder," but can more broadly include the acromioclavicular joint. In human anatomy, the shoulder joint comprises the part of the body where the humerus attaches to the scapula, the head sitting in the glenoid fossa.[1] The shoulder is the group of structures in the region of the joint.[2]

There are two kinds of cartilage in the joint. The first type is the white cartilage on the ends of the bones (called articular cartilage) which allows the bones to glide and move on each other. When this type of cartilage starts to wear out (a process called arthritis), the joint becomes painful and stiff. The labrum is a second kind of cartilage in the shoulder which is distinctly different from the articular cartilage. This cartilage is more fibrous or rigid than the cartilage on the ends of the ball and socket. Also, this cartilage is also found only around the socket where it is attached.[3]

The shoulder must be mobile enough for the wide range actions of the arms and hands, but also stable enough to allow for actions such as lifting, pushing and pulling. The compromise between mobility and stability results in a large number of shoulder problems not faced by other joints such as the hip.

Joints

There are three joints of the shoulder: The glenohumeral, acromioclavicular, and the sternoclavicular joints.

Glenohumeral joint

The glenohumeral joint is the main joint of the shoulder and the generic term "shoulder joint" usually refers to it. It is a ball and socket joint that allows the arm to rotate in a circular fashion or to hinge out and up away from the body. It is formed by the articulation between the head of the humerus and the lateral scapula (specifically­the glenoid fossa of the scapula). The "ball" of the joint is the rounded, medial anterior surface of the humerus and the "socket" is formed by the glenoid fossa, the dish­shaped portion of the lateral scapula. The shallowness of the fossa and relatively loose connections between the shoulder and the rest of the body allows the arm to have tremendous mobility, at the expense of being much easier todislocate than most other joints in the body. Approximately its 4 to 1 disproportion between the large head of the humerus and the shallow glenoid cavity.

The capsule is a soft tissue envelope that encircles the glenohumeral joint and attaches to the scapula, humerus, and head of the biceps. It is lined by a thin, smooth synovial membrane. This capsule is strengthened by the coracohumeral ligament which attaches the coracoid process of the scapula to the greater tubercle of the humerus. There are also three other ligaments attaching the lesser tubercle of the humerus to lateral scapula and are collectively called the glenohumeral ligaments.

There is also a ligament called semicirculare humeri which is a transversal band between the posterior sides of the tuberculum minus and majus of the humerus. This band is one of the most important strengthening ligaments of the joint capsule.

Sternoclavicular joint

The sternoclavicular occurs at the medial end of the clavicle with the manubrium or top most portion of the sternum. The clavicle is triangular and rounded and the manubrium is convex; the two bones articulate. The joint consists of a tight capsule and complete intra­articular disc which ensures stability of the joint. The costoclavicular ligament is the main limitation to movement, therefore, the main stabilizer of the joint. A fibrocartilaginous disc present at the joint increases the range of movement. Sternoclavicular dislocation is rare,[4] but may result from direct trauma to the clavicle or indirect forces applied to the shoulder.[5] Posterior dislocations deserve special attention, as they have the potential to be life­threatening because of the risk of damage to vital structures in the mediastinum.[6]

Muscles

The muscles that are responsible for movement in the shoulder attach to the scapula, humerus, and clavicle. The muscles that surround the shoulder form the shoulder cap and underarm.

Name Attachment Function

serratus anterior

Originates on the surface of the upper eight ribs at the side of the chest and inserts along the entire anterior length of the medial border of the scapula.

It fixes the scapula into the thoracic wall and aids in rotation and abduction of the shoulders.

subclavius Located inferior to the clavicle, originating on the first rib and inserting (penetrating) on the subclavian groove of the clavicle.

It depresses the lateral clavicle and also acts to stabilize the clavicle.

pectoralis minor

Arises from the third, fourth, and fifth ribs, near their cartilage and inserts into the medial border and upper surface of the coracoid process of the scapula.

This muscle aids in respiration, medially rotates the scapula, protracts the scapula, and also draws the scapula inferiorly.

sternocleidomastoid Attaches to the sternum (sterno­), the clavicle (cleido­), and the mastoid process of thetemporal bone of the skull.

Most of its actions flex and rotate the head. In regards to the shoulder, however, it also aids in respiration by elevating the sternoclavicular joint when the head is fixed.

levator scapulae Arises from the transverse processes of the first four cervical vertebrae and inserts into the medial border of the scapula.

It is capable of rotating the scapula downward and elevating the scapula.

rhomboid majorand rhomboid minor (work together)

They arise from the spinous processes of the thoracic vertebrae T1 to T5 as well as from the spinous processes of the seventh cervical. They insert on the medial border of the scapula, from about the level of the scapular spine to the scapula's inferior angle.

They are responsible for downward rotation of the scapula with the levator scapulae, as well as adduction of the scapula.

trapezius

Arises from the occipital bone, the ligamentum nuchae, the spinous process of the seventh cervical, and the spinous processes of all the thoracic vertebrae, and from the corresponding portion of the supraspinal ligament. It inserts on the lateral clavicle, theacromion process, and into the spine of the scapula.

Different portions of the fibers perform different actions on the scapula: depression, upward rotation, elevation, and adductions.

deltoid, anterior fibers Arises from the anterior border and upper surface of the lateral third of the clavicle.

The anterior fibres are involved in shoulder abduction when the shoulder is externally rotated. The anterior deltoid is weak in strict transverse flexion but assists the pectoralis major during shoulder transverse flexion / shoulder flexion (elbow slightly inferior to shoulders).

deltoid, middle fibers Arises from the lateral margin and upper surface of the acromion.

The middle fibres are involved in shoulder abduction when the shoulder is internally rotated, are involved in shoulder flexion when the shoulder is internally rotated, and are involved in shoulder transverse abduction (shoulder externally rotated) ­­ but are not utilized significantly during strict transverse extension (shoulder internally rotated).

deltoid, posterior fibers

Arises from the lower lip of the posterior border of the spine of the scapula, as far back as the triangular surface at its medial end.

The posterior fibres are strongly involved in transverse extension particularly since the latissimus dorsi muscle is very weak in strict transverse extension. The posterior deltoid is also the primary shoulder hyperextensor.

Movements

The muscles and joints of the shoulder allow it to move through a remarkable range of motion, making it one of the most mobile joints in the human body. The shoulder can abduct, adduct, rotate, be raised in front of and behind the torso and move through a full 360° in the sagittal plane. This tremendous range of motion also makes the shoulder extremely unstable, far more prone to dislocation and injury than other joints [7]

The following describes the terms used for different movements of the shoulder:[8]

Name Description Muscles

Scapularretraction [9] (aka scapular adduction)

The scapula is moved posteriorly and medially along the back, moving the arm and shoulder joint posteriorly. Retracting both scapulae gives a sensation of "squeezing the shoulder blades together."

rhomboideus major, minor, and trapezius

Scapularprotraction[9](aka scapular abduction)

The opposite motion of scapular retraction. The scapula is moved anteriorly and laterally along the back, moving the arm and shoulder joint anteriorly. If both scapulae are protracted, the scapulae are separated and thepectoralis major muscles are squeezed together.

serratus anterior (prime mover), pectoralis minor and major

Scapularelevation [10] The scapula is raised in a shrugging motion.

levator scapulae, the upper fibers of the trapezius

Scapulardepression [10] The scapula is lowered from elevation. The scapulae may be depressed so that the angle formed by the neck and

pectoralis minor, lower fibers of the trapezius, subclavius, latissimus dorsi

shoulders is obtuse, giving the appearance of "slumped" shoulders.

Arm abduction[11]

Arm abduction occurs when the arms are held at the sides, parallel to the length of the torso, and are then raised in the plane of the torso. This movement may be broken down into two parts: True abduction of the arm, which takes the humerus from parallel to the spine to perpendicular; and upward rotation of the scapula, which raises the humerus above the shoulders until it points straight upwards.

True abduction: supraspinatus (first 15 degrees), deltoid; Upward rotation: trapezius, serratus anterior

Arm adduction[12]

Arm adduction is the opposite motion of arm abduction. It can be broken down into two parts: downward rotation of the scapula and true adduction of the arm.

Downward rotation: pectoralis minor, pectoralis major, subclavius, latissimus dorsi (same as scapular depression, with pec major replacing lower fibers of trapezius); True Adduction: same as downward rotation with addition of teres major and the lowest fibers of the deltoid

Arm flexion [13] The humerus is rotated out of the plane of the torso so that it points forward (anteriorly).

pectoralis major, coracobrachialis, biceps brachii, anterior fibers of deltoid.

Arm extension[13] The humerus is rotated out of the plane of the torso so that it points backwards (posteriorly)

latissimus dorsi and teres major, long head of triceps, posterior fibers of the deltoid

Medial rotationof the arm [14]

Medial rotation of the arm is most easily observed when the elbow is held at a 90­degree angle and the fingers are extended so they are parallel to the ground. Medial rotation occurs when the arm is rotated at the shoulder so that the fingers change from pointing straight forward to pointing across the body.

subscapularis, latissimus dorsi, teres major, pectoralis major, anterior fibers of deltoid

Lateral rotationof the arm[14]

The opposite of medial rotation of the arm.

infraspinatus and teres minor, posterior fibers of deltoid

Armcircumduction[15]

Movement of the shoulder in a circular motion so that if the elbow and fingers are fully extended the subject draws a circle in the air lateral to the body. In circumduction, the arm is not lifted above parallel to the ground so that "circle" that is drawn is flattened on top.

pectoralis major, subscapularis, coracobrachialis, biceps brachii, supraspinatus, deltoid, latissimus dorsi, teres major and minor, infraspinatus, long head of triceps

Rotator cuff

The rotator cuff is an anatomical term given to the group of muscles and their tendons that act to stabilize the shoulder. It is composed of the tendons and muscles (supraspinatus, infraspinatus, teres minor andsubscapularis) that hold the head of the humerus (ball) in the glenoid fossa (socket).

Two filmy sac­like structures called bursae permit smooth gliding between bone, muscle, and tendon. They cushion and protect the rotator cuff from the bony arch of the acromion.

Glenohumeral joint The glenohumeral joint, (from ancient Greek glene, eyeball, puppet, doll + ­oid, 'form of', + Latinhumerus, shoulder) or shoulder joint, is a multiaxial synovial ball and socket joint and involves articulation between the glenoid fossa of the scapula (shoulder blade) and the head of the humerus(upper arm bone). Due to the very limited interface of the humerus and scapula, it is the most mobile joint of the human body.

Movements The glenoid fossa is shallow and contains the glenoid labrum which deepens it and aids in stability. With 120 degrees of unassisted flexion, the glenohumeral joint is the most mobile joint in the body. Scapulohumeral rhythm helps to achieve further range of movement. The Scapulohumeral rhythm is the movement of the scapula across the thoracic cage in relation to the humerus. This movement can be compromised by anything that changes the position of the scapula. This could be an imbalance in the muscles that hold the scapula in place which are the upper and lower trapezius. This imbalance could cause a forward head carriage which in turn can affect the range of movements of the shoulder. The rotator cuff muscles of the shoulder produce a high tensile force, and help to pull the head of the humerus into the glenoid fossa.

Movements of the shoulder joint. Movement Muscles Origin Insertion Flexion (150°–170°)

Anterior fibers of deltoid Clavicle Middle of lateral surface of shaft of humerus

Clavicular part of pectoralis major

Clavicle Lateral lip of bicipital groove of humerus

Long head of biceps brachii Supraglenoid tubercle of scapula

Tuberosity of radius, Deep fascia of forearm

Short head of biceps brachii

Coracoid process of scapula

Coracobrachialis Coracoid process Medial aspect of shaft of humerus

Extension (40°)

Posterior fibers of deltoid Spine of scapula Middle of lateral surface of shaft of humerus

Latissimus dorsi Iliac crest, lumbar fascia, spines of lower six thoracic vertebrae, lower 3–4 ribs, inferior angle of scapula

Floor of bicipital groove of humerus

Teres major Lateral border of scapula Medial lip of bicipital groove of humerus

Abduction (160°–180°)

Middle fibers of deltoid Acromion process of scapula

Middle of lateral surface of shaft of humerus

Supraspinatus Supraspinous fossa of scapula

Greater tuberosity of humerus

Adduction (30°–40°)

Sternal part of pectoralis major

Sternum, upper six costal cartilages

Lateral lip of bicipital groove of humerus

Latissimus dorsi Iliac crest, lumbar fascia, spines of lower six thoracic vertebrae, lower 3­4 ribs, inferior angle of scapula

Floor of bicipital groove of humerus

Teres major Lower third of lateral border of scapula

Medial lip of bicipital groove of humerus

Teres minor Upper two thirds of lateral border of scapula

Greater tuberosity of humerus

Lateral rotation (in abduction: 95°; in adduction: 70°)

Infraspinatus Infraspinous fossa of scapula

Greater tuberosity of humerus

Teres minor Upper two thirds of lateral border of scapula

Greater tuberosity of humerus

Posterior fibers of deltoid Spine of scapula Middle of lateral surface of shaft of humerus

Medial rotation (in abduction: 40°–50°; in adduction: 70°)

Subscapularis Subscapular fossa Lesser tuberosity of humerus

Latissimus dorsi Iliac crest, lumbar fascia, spines of lower 3­4 ribs, inferior angle of scapula

Floor of bicipital groove of humerus

Teres major Lower third of lateral border of scapula

Medial lip of bicipital groove of humerus

Anterior fibers of deltoid Clavicle Middle of lateral surface of shaft of humerus

Capsule The shoulder joint has a loose capsule that is lax inferiorly and therefore is at risk of dislocationinferiorly. The long head of the biceps brachii muscle travels inside the capsule to attach to thesupraglenoid tubercle of the scapula.

Because the tendon is inside the capsule, it requires a synovial tendon sheath to minimize friction.

A number of bursae in the capsule aid mobility. Namely, they are the subdeltoid bursa (between the joint capsule and deltoid muscle), subcoracoid bursa (between joint capsule and coracoid process ofscapula), coracobrachial bursa (between subscapularis muscle and tendon of coracobrachialis muscle), subacromial bursa (between joint capsule and acromion of scapula) and the subscapular bursa (between joint capsule and tendon of subscapularis muscle, also known as subtendinous bursa of subscapularis muscle). The bursa are formed by the synovial membrane of the joint capsule. An inferior pouching of the joint capsule between teres minor and subscapularis is known as the axillary recess.

The shoulder joint is a muscle dependent joint as it lacks strong ligaments

.

Ligaments Superior, middle and inferior glenohumeral ligaments Coracohumeral ligament Transverse humeral ligament Coraco­acromial ligament [1]

Rotator cuff Muscles composing rotator cuff

Muscle Origin on scapula

Attachment on humerus Function Innervation

Supraspinatus muscle

supraspinous fossa

superior and middle facet of the greater tuberosity

abducts the arm Suprascapular nerve (C5)

Infraspinatus muscle

infraspinous fossa

posterior facet of the greater tuberosity

externally rotates the arm

Suprascapular nerve (C5­C6)

Teres minor muscle

middle half of lateral border

inferior facet of the greater tuberosity

externally rotates the arm

Axillary nerve (C5)

Subscapularis muscle

subscapular fossa

lesser tuberosity (60%) or humeral neck(40%)

internally rotates thehumerus

Upper and Lower subscapular nerve (C5­C6)

The supraspinatus muscle fans out in a horizontal band to insert on the superior and middle facets of the greater tubercle. The greater tubercle projects as the most lateral structure of the humeral head. Medial to this, in turn, is the lesser tuberosity of the humeral head. The subscapularis muscle origin is divided from the remainder of the rotator cuff origins as it is deep to the scapula

Function

The rotator cuff muscles are important in shoulder movements and in maintaining glenohumeral joint (shoulder joint) stability.[2] These muscles arise from thescapula and connect to the head of the humerus, forming a cuff at the shoulder joint. They hold the head of the humerus in the small and shallow glenoid fossaof the scapula. The glenohumeral joint has been analogously described as a golf ball (head of the humerus) sitting on a golf tee (glenoid fossa).[3]

During abduction of the arm, moving it outward and away from the trunk, the rotator cuff compresses the glenohumeral joint, a term known as concavity compression, in order to allow the large deltoid muscle to further elevate the arm. In other words, without the rotator cuff, the humeral head would ride up partially out of the glenoid fossa, lessening the efficiency of the deltoid muscle. The anterior and posterior directions of the glenoid fossa are more susceptible to shear force perturbations as the glenoid fossa is not as deep relative to the superior and inferior directions. The rotator cuff's contributions to concavity compression and

stability vary according to their stiffness and the direction of the force they apply upon the joint.

Despite stabilizing the glenohumeral joint and controlling humeral head translation, the rotator cuff muscles also perform multiple functions, including abduction, internal rotation, and external rotation of the shoulder. The infraspinatus and subscapularis have significant roles in scapular plane shoulder abduction (scaption), generating forces that are two to three times greater than the force produced by the supraspinatus muscle.[4] However, the supraspinatus is more effective for general shoulder abduction because of its moment arm.[5] The anterior portion of the supraspinatus tendon is submitted to significantly greater load and stress, and performs its mainfunctional role.[6]

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2014

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Hartman and Mike Robertson: The rotator cuff, of course. (Or for those of you from Indiana, that would be your "rotary cup").

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