Porth's Essentials of Pathophysiology, 4e

Disorders of the Skeletal System: Trauma, Infections, Neoplasms, and Childhood Disorders 1081

C h a p t e r 4 3

head against the glenoid. The rotator cuff muscles are separated from the overlying “coracoacromial arch” by the subdeltoid and subcoracoid bursae. Disorders of the rotator cuff, such as tendinitis, subacromial bursitis, and partial and complete tears, account for a substantial majority of shoulder prob- lems (see Fig. 43-2). Rotator cuff injuries can result from excessive use, a direct blow, or stretch injury, usu- ally involving throwing or swinging, as with baseball pitchers or tennis players. 5,8 While rotator cuff injuries sometimes occur with acute injury, most result from a combination of factors, including altered blood supply to the tendons, repeated mechanical insult as the tendon passes under the coracoacromial arch, and age-related degeneration. Repetitive overhead throwing, which produces significant stress on the glenohumeral com- plex of the rotator cuff, is a common cause of rotator cuff tendinitis. Full-thickness tears are more common in persons older than 40 years of age, although they can occur in athletes. 5,9,11 Tears generally originate in the supraspinous tendon and may progress posteriorly and anteriorly. The major clinical features of rotator cuff disorders are pain (especially at night), tenderness, and occasion- ally muscle atrophy. Pain and impingement may be noted when motions of the arm squeeze and pinch cuff tendons between the humerus and the overlying arch. With rotator cuff tears, there may be difficulty abducting and rotating the arm. Several physical examination maneuvers, including assessment of active and passive range of motion, are used to define shoulder pathology. The history and mechanism of injury are important. In addition to standard radio- graphs, an arthrogram or magnetic resonance imaging (MRI) scan may be obtained. Arthroscopic examination under anesthesia may be done for diagnostic purposes. Conservative treatment with anti-inflammatory agents, corticosteroid injections, and physical therapy often is used. A period of rest is followed by a customized exercise and rehabilitation program to improve strength, flexibil- ity, and endurance. Surgical repair may be considered for persons with an acute traumatic rotator cuff tear or those with significant symptoms and failed rehabilitation. Knee Injuries The knee is a common site of injury, particularly sports- related injuries in which the knee is subjected to abnor- mal twisting and compression forces. 8,12,13 These forces can result in injury to the ligaments and menisci, patel- lar subluxation and dislocation, and the patellofemoral pain syndrome. Many knee injuries can predispose to osteoarthritis in later life. The knee joint consists of lateral and medial femoral condyles, the lateral and medial femotibial condyles, and the patella 10 (Fig. 43-3). It is essentially a round bone (femoral condyles) sitting on a flat bone (tibial condyles) with no intrinsic bony stability and depends on its liga- ments and menisci for support. 8 The most important ligaments are the medial and lateral collateral ligaments along with their associated posterior capsular structures

Clavicle

Supraspinatus muscle

Coracoid

Rupture of supraspinatus tendon

Acromion

Subacromial bursa (distended with fluid due to inflammation)

Glenoid cavity

Scapula

Humerus

are among the most common fractures of childhood. 10 The typical mechanism of fracture is a fall on the lateral shoulder, or less commonly by a direct blow or by fall- ing on an outstretched arm. Most clavicle fractures are treated nonoperatively, with either a simple arm sling or figure-of-eight clavicle strap. 5,8 Three articulations form the shoulder joint—the acromioclavicular joint, which joins the clavicle to the acromion of the scapula; the glenohumeral joint, which connects the head of the humerus to the relatively shal- low glenoid cavity in the scapula; and the sternoclavicu- lar joint, which joins the sternum to the clavicle. 10 The stability of these joints is provided by a series of muscles and tendons. The acromioclavicular joint is a common site of sprains in athletes and physically active persons. The classic cause of an acromioclavicular joint injury is a direct blow to the acromion with the humerus in an adducted position. This force drives the acromion medially and inferiorly. Acromioclavicular joint injuries also may be caused by indirect trauma, such as falling on an outstretched arm or elbow. The glenohumeral joint is one of the most commonly dislocated joints. It is also the joint most likely to develop problems with instability. Most acute dislocations involve anterior dis- placement of the humeral head with respect to the gle- noid cavity, the result of the shoulder being abducted and forcefully extended and rotated. Other mechanisms include a fall on an outstretched arm or a blow to the posterior shoulder. Movement of the shoulder results from the coordi- nated efforts of the muscles of the rotator cuff: the supra- spinous, teres minor, infraspinatus, and subscapularis. 5,8 These muscles and their musculotendinous attachments form a cover around the head of the humerus and function to rotate the arm and stabilize the humoral FIGURE 43-2. Structures of the glenohumeral shoulder joint, showing the location of common rotator cuff injuries.The supraspinatus muscle is the most commonly injured part of the rotator cuff. (Adapted from Moore KL, Dalley AF. Clinically Oriented Anatomy. 5th ed. Philadelphia, PA: Lippincott Williams &Wilkins; 2006:763.)