Applied Anatomy

Shoulder movements are a synthesis of motion at four articulations: sternoclavicular, acromioclavicular, glenohumeral, and scapulothoracic.


The sternoclavicular (SC) joint is a spheroidal joint between the medial end of the clavicle and both the manubrium and the first costal cartilage. An intraarticular fibrocartilaginous disk stabilizes the joint and prevents medial displacement of the clavicle. The joint capsule is reinforced by the anterior and posterior SC ligaments.


The acromioclavicular (AC) joint is a spheroidal joint between the lateral end of the clavicle and the acromion process of the scapula ( Figure 2-1 ). A small, intraarticular fibro cartilaginous disk divides the joint into two compartments. A subcutaneous, noncommunicating bursa may be present over the joint. The stability of the AC joint depends on the capsule and the superior and inferior AC ligaments. The coracoclavicular ligament (conoid and trapezoid parts) extends between the distal clavicle and the coracoid process of the scapula ( Figure 2-2 ). It suspends the scapula, stabilizes both the clavicle and the scapula, and maintains a close relation between the two bones during shoulder movements, thus limiting scapular rotation around the AC joint. The AC and SC joints augment the range of shoulder movements, particularly abduction and rotation. The joints also allow slight axial rotation of the clavicle, as well as elevation/depression and forward/backward thrusting of the shoulder.






The glenohumeral (GH) joint , the main articulation of the shoulder complex, is a multiaxial, ball-and-socket synovial articulation between the glenoid fossa of the scapula and the humeral head ( Figure 2-1 ). The lax articular capsule and the small area of contact between the shallow glenoid fossa and the spheroidal humeral head permit a wide range of motion. The stability of the joint depends on a number of static and dynamic stabilizers. Static stabilizers include negative intraarticular pressure; GH bone geometry; the capsule; the glenoid labrum; the superior, middle, and inferior GH ligaments; and the coracohumeral ligament. The capsule, which fuses in part with the tendons of the rotator cuff, has two apertures: one for the long biceps tendon (origin from the supraglenoid tubercle) and one for the subscapularis bursa. The labrum, a ring of fibrocartilage that surrounds and deepens the glenoid cavity, contributes significantly to GH joint stability. Through a bumper effect, it functions as a “chock block” to prevent translational forces.

The inferior GH ligament complex is the primary ligamentous stabilizer of the abducted GH joint and serves to prevent anteroinferior shoulder dislocation. The middle GH ligament is tensioned at 45° of abduction, and the superior GH ligament is tight in adduction.

Dynamic stabilizers play an important role in the stability of the shoulder. They include two musculotendinous layers: 1) an inner stratum, made of the rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) and the long biceps tendon (origin from supraglenoid tubercle from glenoid fossa), and 2) an outer stratum, composed of the deltoid, teres major, pectoralis major, latissimus dorsi, and trapezius muscles.

The muscles of the inner stratum stabilize and retain the humeral head in the glenoid cavity during shoulder movements (cavity-compression mechanism), while simultaneously providing abduction (supraspinatus—origin from the supraspinatus fossa of scapula and insertion into the superior part of the greater tuberosity), external rotation (infraspinatus and teres minor—origin from the infraspinatus fossa and axillary border of the scapula, respectively, and insertion into the posterior aspect of the greater tuberosity), and internal rotation (subscapularis—origin from the subscapularis fossa and insertion into the lesser tuberosity). At the initiation of shoulder abduction, both the rotator cuff and the long biceps tendon depress and stabilize the humeral head against the glenoid cavity to counteract the upward pull of the more powerful deltoid muscle. The mechanism whereby these two groups of muscles combine to produce abduction, the one (deltoid muscle) elevating and the other (rotator cuff and biceps tendons) stabilizing the humeral head, is termed force-coupling. The muscles of the outer stratum are the prime movers of the shoulder. These provide abduction, flexion, extension, adduction, and some degree of rotation.

The coracoacromial arch—made up of the coracoid process, coracoacromial ligament, and acromion—acts as a protective, secondary socket for the humeral head, under which the rotator cuff tendons and long biceps tendon glide, with the subacromial bursa lying in between. The arch prevents upward displacement of the humeral head and protects the head and rotator cuff from direct trauma. The undersurface of the acromion is commonly flat (type 1); less frequently, it is downwardly curved (type 2) or hooked (type 3), but these conditions are more commonly associated with subacromial impingement.

The synovium of the shoulder lines the inner surface of the capsule. It has two extracapsular outpouchings, the tenosynovial sheath of the long biceps tendon and the bursa beneath the subscapularis tendon ( Figure 2-2 ). A communicating infraspinatus bursa is sometimes present. The subcoracoid bursa lies between the shoulder capsule and the coracoid process, but it rarely communicates with the joint.


The so-called scapulothoracic articulation is not a true joint but functions as an integral part of the shoulder complex. The scapula, which is connected to the posterior aspect of the chest wall by the axioappendicular muscles, provides the origin for the rotator cuff muscles and deltoid, and the trapezius inserts into its superior aspect. Scapulothoracic movements that include rotation, elevation, depression, protrusion, retraction, and circumduction are important for the normal functioning of the shoulder. The scapulothoracic bursa is located between the serratus anterior and the chest wall, just medial to the inferior angle of the scapula.


The shoulder joint derives its nerve supply from three branches of the brachial plexus: suprascapular, axillary, and lateral pectoral nerves (C5/C6). The axillary nerve and the posterior circumflex humeral artery pass through the quadrilateral or quadrangular space, which lies inferoposterior to the GH joint, bounded by the teres minor superiorly, the teres major inferiorly, the long head of triceps medially, and the shaft of the humerus laterally ( Figure 2-3 ).



(From Rockwood CA, Matsen FA, Wirth MA, et al., eds.: The Shoulder, 4th ed. Philadelphia: Saunders, 2009.)


Shoulder pain is a common symptom of diverse causes ( Table 2-1 ). The pain may originate in the GH or AC joint or in periarticular structures, or it may be referred from the cervical spine, brachial plexus, thoracic outlet, or infradiaphragmatic structures. Important points in the history include age, hand dominance, occupational and sport activities involving heavy lifting or overhead repetitive movements, history of trauma, onset, location, character, duration, radiation of the shoulder pain, aggravating and relieving factors, presence of night pain, and the effect on shoulder function. Associated symptoms—shoulder stiffness, restriction of movement, grinding, clicking, instability, or weakness—may also provide useful diagnostic clues.



Articular Causes
GH and AC arthritis: OA, RA, PsA, trauma, infection, crystal-induced
Ligamentous and labral lesions
GH and AC joint instability
Osseous: fracture, osteonecrosis, neoplasm, infection
Periarticular Causes
Chronic impingement and rotator cuff tendinitis
Bicipital tendinitis
Rotator cuff and long biceps tendon tears
Subacromial bursitis
Adhesive capsulitis
Neurological Lesions About the Shoulder
Thoracic outlet syndrome
Acute brachial plexus neuritis
Quadrilateral space syndrome
Suprascapular nerve entrapment syndrome
Cervical radiculopathy
Referred and Miscellaneous Causes
Angina pectoris
Diaphragmatic and infradiaphragmatic disorders: pericarditis, pleurisy, gallbladder disease, subphrenic abscess
Axillary artery or vein thrombosis
Reflex sympathetic dystrophy syndrome and shoulder–hand syndrome
Polymyalgia rheumatica, myositis
Diffuse fibromyalgia and myofascial pain syndrome
Somatization disorder and psychogenic regional pain syndrome

AC, acromioclavicular; GH, glenohumeral; OA, osteoarthritis; PsA, psoriatic arthritis; RA, rheumatoid arthritis

It is also important to determine whether the shoulder pain is isolated or associated with other stiff, painful, or swollen joints. Shoulder pain may be a feature of a more systemic arthritis. Other joint history, and a history of systemic features, may need to be taken into consideration.

Common Disorders of the Shoulder


The spectrum of rotator cuff pathology ranges from mild rotator cuff tendinopathy to partial and complete rotator cuff tears. If the tear increases in size, a massive rotator cuff tear (< 5 cm) may develop. This can lead to the proximal migration of the humeral head and secondary GH osteoarthritis (cuff tear arthropathy).

Causative factors include repetitive low-grade trauma or unaccustomed activities, excessive overhead use in sport or work, lack of conditioning, aging, and compromise of the rotator cuff space by osteophytes on the undersurface of the AC joint, type 2 or 3 acromion, or an os acromiale (unfused acromial epiphysis). Abnormal tensile stresses that exceed the elastic limits of tendons can lead to cumulative microfailure of the molecular links between tendon fibrils, called fibrillar creep. With aging, tendons become less flexible and less elastic, making them more susceptible to injury and tears. A short-ended musculotendinous unit, from lack of regular stretching exercises, is also prone to injury.

In young persons, rotator cuff tendinopathy is often caused by a sport-related injury; for example, from use of the arm in an overhead position in baseball, racquetball, tennis, or swimming. In older individuals, an antecedent history of repetitive movements above the shoulder level or of strenuous or unaccustomed arm activity is common. Symptoms include aching pain in the shoulder, lateral aspect of the upper arm, and deltoid insertion; pain with movement, particularly abduction and internal rotation; night pain when rolling onto the affected side; restriction of shoulder movements; and sometimes weakness caused by a rotator cuff tear. The patient typically experiences shoulder pain on active abduction, especially between 60° and 120°, and difficulty with overhead work, lifting, or reaching behind the back when dressing. Clinical findings include a painful arc between 60° to 120° of abduction, limitation of active movement by pain, and tenderness localized to the rotator cuff and greater tuberosity. The supraspinatus test, Neer impingement test, Neer impingement sign, and Hawkins impingement sign (see Special Tests of Shoulder, p. 13) are often positive.

Rotator cuff tears can be partial or complete, acute or chronic, small or massive. In young adults, acute tears often result from direct trauma or a sport-related injury. In older patients, minor trauma, superimposed on cuff tendon that is already frayed from chronic impingement and age-related attritional changes, can lead to tears.

Clinical features include shoulder pain on abduction, night pain, varying degrees of weakness of abduction and external rotation, local tenderness, wasting of the supraspinatus and/or infraspinatus muscles, and loss of range of motion with difficulty elevating the arm to greater than 90° without shrugging the shoulder (positive shrug sign). The supraspinatus test, Neer impingement sign, and Hawkins impingement sign are usually positive. Rupture of the long biceps tendon may also be present. In complete tears, the drop-arm sign is positive. The diagnosis of rotator cuff tears can be confirmed by ultrasonography, magnetic resonance imaging (MRI), or arthroscopy.


Bicipital tendinitis often results from chronic subacromial impingement occurring in association with rotator cuff tendinitis and rotator cuff tears. Primary isolated bicipital tendinitis is rare and develops as an overuse injury resulting from repetitive stresses applied to the tendon in certain sports, such as weight lifting and ball throwing. Anterior shoulder pain that is increased by overhead activities, shoulder extension, and elbow flexion is the main symptom. There is localized tenderness over the tendon in the bicipital groove, the Yergeson sign (see Tests for Biceps Tendon, p. 16) is present, and the speed test is often positive. Passive extension of the shoulder or resisted flexion of the elbow may also reproduce the pain. Signs of chronic impingement and GH instability are often present. Rupture of the long biceps tendon is associated with a positive Popeye sign.

Subluxation of the bicipital tendon is caused by traumatic rupture of the intertubercular (transverse humeral) ligament. It is associated with anterior shoulder pain, a clicking sensation of the shoulder as it “goes out and pops back in,” tenderness in the bicipital groove, and a positive transverse humeral ligament test.


Adhesive capsulitis, also known as frozen shoulder, is characterized by progressive global restriction of shoulder movements and is associated with pain and functional disability. A period of immobility of the shoulder is the most common predisposing factor. The capsulitis may be secondary to shoulder trauma, rotator cuff tendinitis or tears, bicipital tendinitis, or GH arthritis, or it may coexist with diabetes mellitus, hypothyroidism, or cerebrovascular events. An initial synovitis phase is followed by fibrous thickening and contracture of the capsular folds, axillary recess, rotator cuff interval, and coracohumeral ligament. The shortening of the coracohumeral ligament and rotator cuff interval acts as a tight checkrein, limiting external rotation. Capsular adhesions are rare.

The clinical course can be divided into four overlapping stages. In stage I, there is painful limitation of active and passive shoulder movements with diffuse synovitis on both arthroscopy and biopsy. Stage II is a painful “freezing” phase; shoulder pain, tenderness, and progressive, painful, global restriction of movements are present, as well as characteristic limitation of external rotation in the absence of GH arthritis. Synovial inflammation and a tight, thickened capsule are observed on both arthroscopy and biopsy. In stage III, an adhesive or “frozen” phase, there is minimal pain; movements are markedly restricted, and the patient is unable to elevate the arm to 90° without shrugging the shoulder (positive shrug sign). Disuse atrophy of the deltoid and scapular muscles is common. A thickened, contracted capsule and fibrotic synovitis are observed on both arthroscopy and biopsy. In stage IV, a resolution or “thawing” phase, pain is minimal with an increasing range of motion.

Criteria for diagnosis of adhesive capsulitis include an insidious onset, true shoulder pain lasting longer than 3 months, night pain, painful restriction of all active and passive movements with external rotation reduced to less than 50% of normal, and a normal radiologic appearance. Although 90% of patients recover some use of the extremity within 12 to 18 months, about 40% develop more prolonged pain, restriction of movement, and functional disability.


Acute Instability

Acute shoulder instability usually results from a traumatic event such as a fall, sports injury, or motor vehicle collision. More than 90% of all acute shoulder instability is anterior. Typically the patient will present with a “squared-off ” shoulder on inspection and significant pain with any shoulder motion. A detailed neurovascular exam of the affected limb is essential. Following confirmatory x-rays, a closed reduction of the shoulder is performed.

Acute posterior dislocations are rare but should be considered when there is a history of seizure or electrocution. The arm is usually held in internal rotation, and loss of external rotation is a typical physical exam finding. Closed reduction of this injury is usually successful if the diagnosis is made promptly.

Recurrent Instability

Most cases of recurrent shoulder instability develop following an initial traumatic shoulder dislocation. A Bankart lesion, a traumatic avulsion of the anterior inferior glenoid labrum, is the essential lesion in this disorder. Patients with recurrent anterior shoulder instability complain of “not trusting” their shoulder when their arm is away from the body. On exam they have a positive anterior apprehension sign and a positive relocation sign. These patents do well with surgical stabilization of the shoulder.

Multidirectional shoulder instability tends to be atraumatic and often bilateral. The history will usually lack a single traumatic episode. Physical exam often shows generalized ligamentous laxity. A sulcus sign is commonly seen. Surgery is not as successful in these patients, and rehabilitation is the mainstay of treatment in recurrent multidirectional shoulder instability.


Trauma to the AC joint can lead to disruption of the capsule, ligaments, and fibrocartilaginous disk. Local pain, tenderness, swelling, and a painful arc from 90° of abduction upward are the main findings. Pain at the AC joint can be reproduced by passive adduction of the extended shoulder behind the back (adduction stress test) and by abducting the shoulder 90° and then adducting it across the chest at shoulder height, compressing the AC joint (cross-arm AC-loading adduction test).


Both inflammatory arthritis, such as rheumatoid arthritis, and degenerative arthritis, such as osteoarthritis, can affect the shoulder joints. Inflammatory arthritis may involve the AC, GH, or SC joint, and the patient may experience swelling and tenderness of the affected joints. The shoulder is painful with range of motion in all directions, and range may be limited. Other synovial joints in the body are often affected, and treatment is generally directed toward the systemic condition.

Primary osteoarthritis is common in the AC joint and less common in the GH joint. In some cases it may occur at the GH joint secondary to an inflammatory process. In osteoarthritis the shoulder is generally painful with activity and may get progressively worse over time. It is painful throughout the range of motion, which is often limited. Crepitus is classically felt over the affected joint.


Thoracic outlet syndrome is often caused by compression of the lower brachial plexus and subclavian artery between the scalene muscles or by a cervical rib. It is associated with shoulder pain, which often radiates distally along the ulnar border of the forearm and hand. Pallor, coldness, and numbness, commonly of the ring and little fingers, may occur. The Adson maneuver is often positive: the ipsilateral radial pulse disappears when the patient abducts, extends, and externally rotates the shoulder while taking a deep breath with the head rotated maximally toward the affected side. Neurologic findings are subtle and affect both interosseous and hypothenar muscles, as well as cutaneous sensation of the little and ring fingers and the ulnar aspect of the forearm. Compression of the subclavian artery can be demonstrated by MRI-angiography.

Acute brachial plexus neuritis (acute brachial plexitis or brachial neuralgic amyotrophy) is an uncommon disorder characterized by a rapid onset of burning pain in the shoulder and upper arm, followed a few days later by profound upper-arm weakness affecting multiple muscles supplied by the upper brachial plexus: supraspinatus, infraspinatus, deltoid, and sometimes biceps. Diagnostic studies include electromyography (EMG) and MRI. The course of the neuritis is usually one of gradual recovery in 3 to 4 months.

Quadrilateral space syndrome is a rare disorder that results from compression of the axillary nerve and posterior circumflex humeral artery in the quadrilateral space. It is caused by athletic activities, GH dislocation, or shoulder surgery. Nondermatomal pain and paresthesia of the shoulder and upper posterior arm, exacerbated by abduction and external rotation, are the main symptoms. Tenderness over the quadrilateral space, aggravation of symptoms by external rotation, variable atrophy and weakness of the deltoid and teres minor muscles, and sometimes sensory loss over the anterolateral aspect of the shoulder and upper arm are the principal findings. The diagnosis can be confirmed by EMG, MRI, or MRI-angiography.

Suprascapular nerve entrapment syndrome is characterized by deep aching pain in the upper posterior aspect of the scapula, made worse by shoulder adduction, and by weakness of abduction and external rotation. It is caused by compression of the suprascapular nerve in the suprascapular notch, beneath the suprascapular or transverse scapular ligament, or by a ganglion or lipoma. It can also result from repetitive trauma due to excessive overhead movements. Local tenderness over the suprascapular notch and variable weakness and wasting of the supraspinatus and infraspinatus muscles are the main findings.

Cervical radiculopathy, caused by a cervical disk lesion, is associated with pain in the shoulder, radicular sensory symptoms, motor weakness, and reflex changes. Radicular pain and/or paresthesia may be reproduced by one of two tests. The Spurling test involves a combination of cervical spine extension and tilt toward the affected extremity with pressure applied downward on the patient’s head. In the upper extremity root extension test, the patient’s arm is extended, abducted, and externally rotated with the elbow and wrist extended, and the head is tilted to the opposite side. Diagnostic studies include cervical spine radiography, MRI, and nerve conduction studies.

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Mar 11, 2019 | Posted by in RHEUMATOLOGY | Comments Off on THE SHOULDER
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