The Shoulder

Published on 16/03/2015 by admin

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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).

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.

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.

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.

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.

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).

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.

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).

TREATMENT

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.

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.

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.

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.

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.
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.

Electromyography (EMG) may be helpful to rule out the rare case of suprascapular nerve compression, which can mimic rotator cuff disease. It is especially indicated in young patients when weakness and atrophy are present.

CALCIFIC DEPOSITS IN THE ROTATOR CUFF

Calcium deposits in the rotator cuff tendon may be associated with pain and stiffness in the shoulder. Whether the calcific changes are a cause of symptoms or simply the result of degeneration is not known. Benign calcific deposits are a common incidental finding and probably result from degenerative changes in the same area where ruptures take place. They are most frequently found in the supraspinatus tendon. Most deposits remain small and deep in the tendon, and pain may be absent. Others may produce an inflammatory reaction and swelling, perhaps as the process of resorption takes place. Impingement of these swollen tissues against the overlying coracoacromial arch may then occur.

Disorders of the Biceps Tendon

TENOSYNOVITIS

Tenosynovitis of the long head of the biceps is a common cause of shoulder pain in adults older than 40 years of age. It may also occur in the young athlete from repeated strains, such as those caused by the throwing motion. The basic lesion is an inflammation in the tendon and its sheath in the bicipital groove. The disorder may be primary or secondary to disease of the overlying rotator cuff. It may be difficult to differentiate from rotator cuff disorders.