Shoulder Dislocation Case File

Shoulder Dislocation Case File

Eugene C. Toy, MD, Lawrence M. Ross, MD, PhD, Han Zhang, MD, Cristo Papasakelariou, MD, FACOG

CASE 5

While playing football, a 17-year-old defensive end was attempting to tackle a fullback with an outstretched left arm. The arm was hit with substantial force, and he now complains of severe shoulder pain and his left arm is hanging down with some external rotation. The pain prevents him from moving the limb. A radiograph is negative for a fracture, but the head of the humerus is superimposed on the neck of the scapula.

⯈ What is the most likely diagnosis?

⯈ What is the most likely nerve injured?

ANSWERS TO CASE 5:

Shoulder Dislocation

Summary: A 17-year-old football player’s left arm was outstretched and hit with some force. He has shoulder pain, and his arm hangs limp down his side with external rotation. There is no fracture, and the humeral head is superimposed on the scapular neck.

• Most likely diagnosis: Glenohumeral joint dislocation (shoulder dislocation)

• Most likely nerve injured: Axillary nerve

CLINICAL CORRELATION

The shoulder is the most commonly dislocated large joint of the body and is usually dislocated in an anterior direction. Typically, the dislocation is also inferior such that the humeral head is located inferior and lateral to the coracoid process. The humeral head will often have an infraglenoid and infraclavicular position. The diagnosis may be difficult to make. The typical mechanism consists in a violent force to the humerus that is abducted and externally rotated, resulting in extension of the joint; this action displaces the humeral head inferiorly, thus tearing the weak inferior portion of the shoulder joint capsule. This is facilitated by the fulcrum effect of the acromion. The strong flexor and adductor muscles pull the humeral head anteriorly and medially to the usual subcoracoid position. Typically, the patient will not move the arm and will support the limb flexed at the elbow with the opposite hand. The arm will be slightly abducted and medially rotated. The usually rounded curve of the shoulder is lost, and there is a depression evident inferior to the acromion. The humeral head is palpable, if not visible, in the deltopectoral triangle. First priorities are assessment of the neural and vascular integrity of the upper limb by testing motor and sensory functions of the fingers and palpation of the radial pulse. Different methods to reduce the dislocation exist, including the modified Hippocratic method, in which one operator pulls on a sheet placed around the thorax of the patient, while a second operator gently applies traction on the wrist of the affected side. Other injuries that may accompany a shoulder dislocation include strain on the tendons of the subscapularis and supraspinatus muscles, tears of the glenoid labrum, fracture of the greater tubercle of the humerus, trauma to the axillary nerve (as demonstrated by loss of sensation in the shoulder patch region over the deltoid muscle), and trauma to the axillary artery or its branches, such as the posterior circumflex humeral or subscapular arteries.

APPROACH TO:

The Shoulder

OBJECTIVES

1. Be able to describe the bones and joints that make up the shoulder girdle

2. Be able to delineate the anatomy of the glenohumeral joint

3. Be able to list the extrinsic muscles of the shoulder, their action at the shoulder, and their innervation

4. Be able to describe the components of the rotator cuff and their action, innervation, and functional importance to the shoulder.

DEFINITIONS

SHOULDER: Junction between the arm and the trunk.

SHOULDER GIRDLE: The clavicle, the scapula, and the proximal humerus.

DISCUSSION

The shoulder girdle and the shoulder joint proper consist of the clavicle, the scapula, and the proximal portion of the humerus. The only bony articulation between the shoulder girdle and the trunk occurs at the sternoclavicular joint. This strong joint has two joint spaces created by a cartilage articular disk. The synovial articulation of the clavicle with the manubrium of the sternum is strengthened by a joint capsule, anterior and posterior sternoclavicular, and interclavicular and costoclavicular ligaments. The lateral end of the clavicle articulates with the acromion of the scapula to form the acromioclavicular joint. An incomplete articular disk is present within this synovial joint. A thin, loose capsule surrounds the acromioclavicular joint, which is reinforced superiorly by an acromioclavicular ligament, but its chief strength and support is derived from the trapezoid and conoid ligaments, which together form the coracoclavicular ligament.

The articulation of the glenoid cavity on the neck of the scapula with the head of the humerus forms the glenohumeral joint. This shallow ball-and-socket synovial joint forms the shoulder joint proper. The anatomy of this joint allows a wide range of motion, although stability is decreased. The diameter of the humeral head is about three times greater than the diameter of the glenoid cavity, which is increased somewhat by a rim of fibrocartilage attached to the margin of the glenoid, the glenoid labrum. The joint capsule attaches to the margin of the glenoid proximally and to the anatomical neck of the humerus distally. The capsule has openings for the tendon of the long head of the biceps muscle and for the subscapular bursa, which communicates with the joint cavity. Three glenohumeral ligaments, bandlike thickenings of the anterior capsule, are identifiable only internally (Figure 5-1). The coracohumeral ligament reinforces the capsule superiorly, and the transverse humeral ligament bridges the intertubercular groove with the tendon and synovial sheath

Figure 5-1. Anatomy of the shoulder joint. (Reproduced, with permission, from Lindner HH. Clinical

Anatomy. East Norwalk, CT: Appleton & Lange, 1989:528.)

of the long head of the biceps brachii muscle. The roof of the glenohumeral joint is formed by the inferior surface of the acromion and the coracoacromial ligament.

The upper limb is attached to the trunk primarily by muscles. This group of muscles, the extrinsic muscles of the shoulder, originates from the trunk and inserts onto the scapula in most instances or the humerus directly. The action of muscles attaching to the scapula produces movement of the scapula, which greatly increases the range of motion at the shoulder. The extrinsic muscles and the action and innervation of each are listed in Table 5-1.

Table 5-1 • EXTRINSIC MUSCLES OF THE SHOULDER
Muscle	Action	Innervation
Trapezius	Retracts, elevates, depresses, rotates scapula	Spinal accessory nerve
Latissimus dorsi	Extends, adducts, medially rotates arm	Thoracodorsal nerve
Levator scapulae	Elevates, rotates scapula	Dorsal scapular nerve
Rhomboid major and minor	Retracts and rotates scapula	Dorsal scapular nerve
Serratus anterior	Protracts and rotates scapula	Long thoracic nerve
Pectoralis major	Adducts and medially rotates arm	Lateral and medial pectoral nerves
Pectoralis minor	Stabilizes scapula	Medial pectoral nerve

Table 5-2 • INTRINSIC MUSCLES OF THE SHOULDER
Muscle	Action	Innervation
Deltoid	Abducts, flexes, and extends arm	Axillary nerve
Teres major	Adducts and medially rotates arm	Lower subscapular nerve
Supraspinatus*	Initiates abduction of arm	Suprascapular nerve
Infraspinatus*	Laterally rotates arm	Suprascapular nerve
Teres minor*	Laterally rotates arm	Axillary nerve
Subscapularis*	Adducts and medially rotates arm	Upper and lower subscapular nerve

*Rotator cuff muscles.

The intrinsic muscles of the shoulder originate from the scapula and insert onto the humerus. They include the deltoid, the teres major, and the rotator cuff muscles. The rotator cuff tendons surround and blend with the capsule of the glenohumeral joint and provide major strength and stability to the joint. The intrinsic muscles of the shoulder and their actions and innervations are presented in Table 5-2. The tendon of the supraspinatus muscle passes superior to the capsule, between it and the acromion and deltoid muscle to insert onto the greater tubercle. The subacromial (subdeltoid) bursa intervenes between the tendon and the undersurface of the acromion and the deltoid muscle. Nevertheless, the supraspinatus tendon is typically damaged with rotator cuff tears.

COMPREHENSION QUESTIONS

5.1 You are evaluating a radiograph of the only bony articulation between the upper limb and the trunk. Which of the following joints are you evaluating?

A. Glenohumeral

B. Acromioclavicular

C. Humeroclavicular

D. Coracoclavicular

E. Sternoclavicular

5.2 You are explaining the anatomy of the shoulder to a young athlete who has sustained an injury to one of his shoulders. You tell him that the chief stability to this joint is from which of the following?

A. Glenohumeral ligaments

B. Acromioclavicular ligament

C. Rotator cuff muscles

D. Coracoclavicular ligaments

E. Coracohumeral ligament

5.3 A college baseball pitcher has shoulder discomfort, and you suspect a rotator cuff tear. You will most likely see damage to the tendon of which of the following muscles?

A. Supraspinatus

B. Infraspinatus

C. Subscapularis

D. Teres major

E. Teres minor

ANSWERS

5.1 E. The upper limb is attached to the trunk only at the sternoclavicular joint. The primary attachment is muscular.

5.2 C. The primary stability to the glenohumeral joint is provided by the tendons of the rotator cuff.

5.3 A. The tendon of the supraspinatus is typically damaged in a rotator cuff tear due to the narrow space between the head of the humerus and the acromion.

ANATOMY PEARLS

⯈ Shoulder dislocations are common, are almost always anterior, and place the axillary nerve at risk.

⯈ The only bony articulation between the upper limb and the trunk is at the sternoclavicular joint. The primary attachment of the limb to the trunk is by musculature.

⯈ The shallow ball-and-socket glenohumeral joint permits a wide range of motion, but with decreased stability.

⯈ The tendons of the rotator cuff muscles provide primary strength and stability to the glenohumeral joint.

⯈ The supraspinatus muscle tendon blends with the superior capsule. Although it is protected from the undersurface of the acromion by the subacromial (subdeltoid) bursa, its tendon is usually injured in rotator cuff tears.

References

Gilroy AM, MacPherson BR, Ross LM. Atlas of Anatomy, 2nd ed. New York, NY: Thieme Medical Publishers; 2012:282−287. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins, 2014:704−707, 712, 796−800, 814−815. Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders, 2014: plates 405−408.

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