The Shoulder

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Chapter 5 The Shoulder

The shoulder is a complex series of joints that provide an extraordinary range of motion. This extreme mobility is accomplished, however, at the expense of some stability. This lack of stability, combined with its relatively exposed position, makes the shoulder vulnerable to injury and degenerative processes. Pain may develop not only from primary disease of the shoulder but also by referral from disorders of thoracic and abdominal origin, and these sources should be kept in mind, especially when more obvious causes are not apparent.

Anatomy

The shoulder is composed of three bones: the scapula, the clavicle, and the humerus. The scapula is a thin bone that articulates widely and closely with the posterior chest wall. It also articulates with the humerus by way of a small, shallow glenoid cavity and with the clavicle at the acromion process. The clavicle and scapula are suspended from the cervical and thoracic vertebrae by the trapezium, levator scapulae, and rhomboid muscles.

Four articulations constitute the shoulder joint: the glenohumeral, scapulothoracic, acromioclavicular (AC), and sternoclavicular joints. The stability of these joints is provided by a series of ligaments and muscles (Fig. 5-1).

FIG. 5-1 Bones and ligaments of the shoulder. R, Rotator cuff; B, long head of the biceps; AC, acromioclavicular joint capsule; CC, coracoclavicular ligaments; A, acromion; C, coracoid process; CA, coracoacromial ligaments.

Motion of the arm results from the coordinated efforts of several muscles. With the initiation of shoulder motion, the scapula is first stabilized. The muscles of the rotator (musculotendinous) cuff, especially the supraspinatus, then steady the humeral head in the glenoid cavity and cause it to descend (Fig. 5-2). This prevents the rotator cuff from impinging against the acromion. Elevation of the arm results from a combination of scapulothoracic and glenohumeral joint movements. One third of total shoulder abduction is provided by forward and lateral movement of the scapula. The remaining two thirds occurs at the glenohumeral joint through progressively increasing activity of the deltoid and supraspinatus muscles. Thus, even in the complete absence of glenohumeral motion, scapulothoracic movement can still abduct the arm approximately 60 to 70 degrees.

FIG. 5-2 Abduction of the shoulder. By stabilizing the humeral head in the glenoid (arrow), the superior portion of the rotator cuff (the supraspinatus muscle) prevents it from being forced into the acromion by the deltoid muscle. Rupture of this portion of the tendon may allow upward movement of the humeral head.

The coracoid, coracoacromial ligament, and underneath surfaces of the acromion and AC joint form a structure sometimes called the “coracoacromial arch.” The muscles of the rotator cuff (supraspinatus, teres minor, infraspinatus, and subscapularis) are separated from this overlying arch by the subacromial space. Bursal tissues occupy some of this space and may be affected by lesions of the musculotendinous cuff, AC joint, and adjacent structures (Fig. 5-3). They are frequently referred to as the subacromial bursa. Primary diseases of this bursa are rare, although secondary involvement is quite common. If bony abnormalities encroach on the subacromial space from above, the rotator cuff could be compressed as abduction occurs. When injections are given for rotator cuff disorders, it is the subacromial space that is injected.

FIG. 5-3 The subacromial space or “bursa” (B) is shown between the deltoid (D) and supraspinatus (S) muscles. Deep to the rotator cuff is the glenohumeral joint cavity (J).

Examination

The examination is performed with both shoulders widely exposed (Fig. 5-4). The general contour of the shoulder is noted, as well as any atrophy or swelling. The shoulder is thoroughly palpated, and any areas of tenderness are determined. These are frequently located over the AC joint and the rotator cuff.

FIG. 5-4 Superficial landmarks of the shoulder. The spine of the scapula lies at the level of the third dorsal vertebra. The inferior angle lies at the level of the seventh rib and eighth dorsal vertebra. The rotator cuff is palpated just distal to the acromion process.

Active and passive ranges of motion are tested and compared with those of the opposite arm. The examiner should determine whether the scapula and humerus move together or independently. Any crepitus during the examination is also noted. Active motion is measured in abduction, forward flexion, and extension. External and internal rotation can be measured by instructing the patient to reach behind the head and then backward behind the shoulder blades. Limited internal rotation is often seen in conjunction with rotator cuff disorders. Involvement of the AC joint is tested by directing the patient to adduct the arm across the front of the chest and touch the opposite shoulder (Fig. 5-5). Pain with this test suggests AC or sternoclavicular disease. The strength of the shoulder, especially at 90 degrees of forward flexion and then at 90 degrees of abduction, is tested and compared with the opposite arm.

FIG. 5-5 The crossover maneuver. Testing for acromioclavicular pain by having the patient touch behind the opposite shoulder (arrow). Local AC tenderness may also be present.

Roentgenographic Anatomy

The shoulder is routinely examined by anteroposterior views with the arm rotated externally and internally (Fig. 5-6). A lateral view of the shoulder joint should always be taken. This may be obtained by utilizing a transaxillary or lateral scapular Y exposure. The scapular Y view is helpful in evaluating the shape of the acromion as well as assessing any bony abnormalities that could narrow the subacromial space. It is also valuable in determining if the humeral head is dislocated or not.

FIG. 5-6 Roentgenographic anatomy of the shoulder. A, The AP view. S, surgical neck of the humerus; A, anatomic neck of the humerus; T, greater tuberosity; C, coracoid process; AC, acromion process; G, glenoid fossa. B, The scapular Y view. The humeral head should be centered at the intersection of the coracoid, spine, and body. This view also can visualize any bony abnormalities of the underneath surface of the acromion which could cause impingement.

Disorders of the Rotator Cuff

The tendons of the rotator cuff muscles fuse together near their insertions into the tuberosities of the humerus to form a musculotendinous cuff. Conditions affecting these tendons comprise the majority of all problems causing shoulder pain. Concepts regarding the etiology of rotator cuff disorders continue to evolve, but degeneration related to aging plays a major role. This degeneration is probably the result of many factors. Repetitive microtrauma, impairment in cuff vascularity because of advancing age, and shoulder instability with secondary overload of the cuff all may play a role. External abnormalities that narrow the subacromial space (subacromial osteophytes or an abnormal downward-shaped acromion) can also threaten the rotator cuff and predispose to impingement.

Degeneration is most severe near the tendon insertion. The supraspinatus is affected most often, and weakness of this tendon may allow the humeral head to migrate upward and lead to impingement against the acromion. Secondary changes in the form of thickening and chronic inflammation frequently develop in the overlying bursa, and with abduction, the tendon and bursa may be compressed against the coracoacromial arch. The throwing motion or “overhead” work are often factors in the development of these conditions. (Overhead work is work performed above shoulder height.)

A wide spectrum of disorders may affect the rotator cuff, and some difficulty may be encountered in separating them. Tendinitis, complete and incomplete rotator cuff ruptures, and calcific deposits are all capable of producing similar signs and symptoms. A variety of terms have developed to describe these diseases: supraspinatus syndrome, chronic impingement syndrome, painful arc syndrome, and internal derangement of the subacromial joint. The treatment for all of these lesions tends to be similar, except for that of complete rupture of the capsular rotator muscles, which may cause loss of motor function. Surgical repair is sometimes necessary for this lesion.

TENDINITIS

A painful rotator cuff can develop at any age, although it is rare in children. It is sometimes related to chronic overuse. The term tendinitis has typically been used for this diagnosis, but the terminology is changing to reflect knowledge regarding the underlying pathology. Because the cellular changes associated with inflammation are often absent in these cases, the terms tendinopathy or tendinosis have been proposed. Small degenerative separations or “tears” of the rotator cuff may even develop over time. Scarring and thickening of the involved area of tendon and bursa occur, decreasing the distance between the cuff and the overlying coracoacromial arch. Bony abnormalities of the acromion may also be a factor in compromising this space. Pain and crepitus (“impingement”) may be noted when motions of the arm, especially abduction, squeeze and pinch these tissues between the humerus and the overlying arch. Even with an intact cuff, impingement may develop if the supraspinatus does not function effectively, allowing the humeral head to be pulled upward with deltoid contraction.

CLINICAL FEATURES

The major clinical manifestations are pain (especially at night for unknown reasons), tenderness, and occasionally atrophy. The patient is often unable to lie on the affected shoulder and may feel a locking or catching sensation with certain motions, especially abduction. The pain is often referred down the deltoid muscle. When abducting the shoulder, the patient may automatically turn the palm up, thereby externally rotating the shoulder, a maneuver that gives the rotator cuff more room beneath the coracoacromial arch. Active, palm-down abduction is frequently painful. Forced passive elevation of the arm may cause the supraspinatus to impinge against the acromion, causing pain. Pain may also be reproduced by internal rotation and forward flexion (Fig. 5-7).

FIG. 5-7 The impingement test. Forced internal rotation of the abducted, slightly flexed arm may impinge the supraspinatus tendon against the coracoacromial ligament.

Maximum tenderness is usually noted over the supraspinatus insertion at the acromiohumeral sulcus because this is the most common area of involvement, although palpable tenderness may be difficult to elicit in obese or muscular individuals. Internal rotation is often decreased because of contracture of the posterior capsule (Fig. 5-8). There is usually little actual loss of muscle power. The pain and crepitus are most severe in the arc of motion between 60 and 120 degrees of abduction. This is where the traumatized soft tissues are maximally compressed between the tuberosity and the overlying arch.

FIG. 5-8 Internal rotation of the shoulder. Note how high the thumb can reach and compare with the opposite side.

The roentgenogram is usually normal, but some sclerosis may be present in the tuberosity secondary to long-standing local irritation. Osteophytes or abnormalities in the shape of the acromion may be noted (Fig. 5-9).

FIG. 5-9 Outlet or Y view of the shoulder revealing a downward angled acromion (arrows) with osteophyte formation at its tip projecting into the subacromial space. Normally, the acromion is flat on this view.

TREATMENT

1 Relief of pain and restoration of function are the therapeutic goals. An important part of the treatment program is rest. This allows the inflammatory process to subside, relieves pain, and restores function. Simply avoiding excessive use of the arm may constitute sufficient rest, but occasionally a sling is needed for a short time. The patient should avoid all “overhead” work until pain free.

2 Antiinflammatory medication is usually helpful.

3 Moist heat or other counterirritants are used several times each day.

4 Local steroid injections often dramatically relieve pain and swelling but should be used with caution, especially in the young patient: 1 to 2 mL of steroid mixed with 2 to 3 mL of lidocaine is injected, under sterile conditions, into the subacromial space (Fig. 5-10). The injection may be repeated two to three times every 3 weeks.

5 Function is restored by a careful, gentle exercise program directed at preserving muscle tone and preventing stiffness. Range-of-motion exercises are important, especially those that stretch the posterior capsule and correct any internal rotation contracture (Fig. 5-11). Stretching the posterior capsule is particularly important because a tight posterior capsule can aggravate the symptoms of rotator cuff tendinitis. Exercises are begun early but are performed only within the limits of pain. Work habits, especially overhead activities, that cause impingement should be avoided. If needed, a sling may be worn initially between the exercises to rest the shoulder, but it is gradually discontinued as the exercises are increased. Gentle strengthening exercises for the rotator cuff, especially the supraspinatus, may be helpful. A good program can result in better humeral head depression, thereby increasing the subacromial space, offsetting the powerful deltoid and preventing impingement. These exercises may be performed with simple elastic tubing or bungee cord obtainable at any hardware store. These exercises need to be performed carefully and may not be possible if there is too much pain. They are also not indicated in the presence of a known rotator cuff rupture since they may worsen the problem.

FIG. 5-10 Injection of the subacromial space. A slightly posterior approach is often best because there is more room. The needle is angled slightly upward and placed in the sulcus between the head of the humerus and the acromion (marked). It should be able to be inserted completely, and, if the needle tip is properly positioned, the fluid should flow easily without resistance. If not, the needle should be repositioned.

FIG. 5-11 Exercises for rotator cuff tendinitis. A, Elastic band exercises for strengthening. In addition to external rotation with abduction (shown), flexion, extension, and internal rotation are performed by attaching the strap to a door or wall. Always keep the arms below shoulder level. B and C, Internal rotation stretching exercises to correct any contracture of the posterior capsule.

Improvement is usually seen within 3 to 5 weeks (Fig. 5-12). If it is not, a more serious cuff lesion, such as a rupture, should be suspected. At this point, the patient should be referred for orthopedic evaluation and possible magnetic resonance imaging (MRI). Surgery is reserved for those cases that fail to respond to conservative treatment and patients who have reparable underlying pathology.

FIG. 5-12 Algorithm for rotator cuff inflammation.

RUPTURES OF THE ROTATOR CUFF

Ruptures of the rotator cuff are almost always chronic in nature and result from continued deterioration and degeneration (Fig. 5-13). The separation may be partial or complete. Ruptures are uncommon before the age of 40 years, although they may occur in young athletes. Acute tears are rare. Many ruptures are completely asymptomatic.

FIG. 5-13 Rupture of the rotator cuff (arrow). Full-thickness rupture allows joint fluid to escape from the glenohumeral joint into the subacromial region. This is often an MRI clue to a full-thickness tear.

CLINICAL FEATURES

Obtaining a history sometimes reveals a fall on the outstretched hand or an attempt to lift a heavy object, but usually there is no obvious injury. Pain and weakness may become progressively worse, and the patient notes an inability to abduct or flex the shoulder, depending on the area of the rupture. The pain is often referred down the deltoid muscle. Occasionally, the patient may have had a previous history of chronic impingement pain, and the diagnosis of rupture is often considered only when the patient fails to respond to the usual treatment for tendinitis.

If the rupture is partial, the clinical findings are similar to those seen in chronic tendinitis, and even with complete rupture, the shoulder may have a full range of motion because of continued function of the other rotator muscles and deltoid. Usually, however, with both partial and complete ruptures, there is at least some weakness in abduction or flexion. The weakness is usually most severe in abduction, because the muscle most commonly torn is the supraspinatus. (Supraspinatus rupture or weakness causes loss of the depressor effect, allowing the head to ride up, which increases the sense of grinding.) If the rupture is more anterior into the subscapularis, forward flexion may also be weak. Weakness against external rotation suggests rupture of the infraspinatus. It may be impossible to actively abduct the arm more than 45 to 50 degrees, after which further abduction is obtained by scapulothoracic motion. Tenderness at the site of the tear is a common finding, and with complete ruptures a defect in the cuff may be palpated through the deltoid muscle. Passive range of motion is frequently normal in the pain-free shoulder, although there is usually a positive impingement sign. Sometimes in complete massive tears, the patient can only “shrug” the shoulder and may have to use the opposite hand to raise the arm any further.

Atrophy of the cuff muscles is frequently present, and the “drop-arm” test may be positive if the tear is significant (Fig. 5-14). In this test, the arm is passively abducted to 90 degrees with the thumb pointing down, and then released. If the shoulder can maintain abduction, slight downward pressure is applied to the forearm, and the strength of the affected shoulder is compared with the normal shoulder. If pain is severe during the examination, lidocaine infiltration of the tender area can relieve the pain. The strength is then measured again. Inability to maintain shoulder abduction with this test is suggestive of a significant rotator cuff tear. Atrophy in the young is rare and should suggest nerve injury.

FIG. 5-14 The drop-arm test. The patient is asked to lower the arm from full elevation to 90 degrees and hold it. With large tears, the arm may drop, or the patient cannot hold the arm against resistence. It may also be difficult to slowly lower the arm to the side. Compare with the opposite side.

On rare occasions, the majority of the cuff may gradually become ruptured, along with all of the adjacent capsular structures. This completely destabilizes the joint, thus allowing the head of the humerus to sublux in and out of the joint when the arm is moved around. The patient will complain of the abnormal movement, which can be easily reproduced on clinical examination.

Acute hemarthrosis and prominent ecchymosis down the arm may occasionally accompany long-standing rotator cuff tears, especially those with cuff-tear arthropathy (a term used to describe end-stage rotator cuff disease caused by a large defect with additional humeral head roughening and glenohumeral joint changes). This is probably the result of further rupture with bleeding of remaining rotator cuff musculature.

Chronic subdeltoid swelling usually means that a large amount of synovial fluid has escaped from the glenohumeral joint to the subacromial space and indicates an extensive rotator cuff rupture. The entire deltoid may appear grossly enlarged.

SPECIAL STUDIES

In patients who have shoulder pain that clearly originates in the shoulder, it may be difficult to differentiate tendinitis from partial or complete rotator cuff tears on a clinical basis. Roentgenographic evaluation as described below may be of assistance.

1 Plain films should be obtained within the first few weeks of symptoms although they may not be necessary on the first visit. They are often indicated simply because of the nonspecific nature of rotator cuff symptoms and to rule out other obvious causes of shoulder pain. In long-standing cases, the examination may reveal calcific deposits or chronic changes in the tuberosity of the humerus (Fig. 5-15). Degenerative arthritis may also be present in the AC or glenohumeral joint.

2 Arthrography of the shoulder may help distinguish between complete and incomplete tears (Fig. 5-16). Its primary drawback is its invasive nature. It is often combined with MRI or computed tomographic (CT) scan. It should probably only be performed if there has been serious discussion regarding surgery.

3 Ultrasonography has some popularity in the evaluation of the rotator cuff. It is safe and noninvasive and is most accurate in large and moderately large tears. Its value is largely dependent on the interest and experience of the radiologist.

4 MRI now plays a major role in diagnosing rotator cuff disease. It can diagnose if a tear is present and may help determine if the tear is reparable or not by elucidating the amount of separation and atrophy (Fig. 5-17). Because of the expense and discomfort involved, it should not be used as a “screening test.” In addition, it is probably not indicated unless surgery is a consideration and only after the appropriate medical treatment.