CHAPTER VI. DISLOCATIONS OF THE SHOULDER. Surgical Anatomy. — The peculiar construction of the shoulder joint, its wide range of motion and exposed position, result in its being the most common site of dislocation in the body. The articulation is typical of the ball and socket joint. The bones entering into its formation are the head of the humerus and the glenoid cavity of the scapula. <Callout type="important" title="Important">The coraco-acromial ligament arches over the head of the humerus, filling in the space between the two processes and serves to prevent upward displacement of the humerus.</Callout> The wide range of motion possible in this joint is the result of the disproportion in the sizes of the articular surfaces of the humeral head and glenoid cavity. Extreme mobility renders the upper extremity more serviceable in many ways, but on the other hand it is evident that this type of joint construction is dependent almost entirely on ligaments and muscles for its stability. The coraco-acromial and capsular are the only ligaments of surgical importance in the shoulder joint. <Callout type="warning" title="Warning">The capsule is much too lax on all sides to keep the articular surfaces in contact, but this very laxity is necessary to allow the freedom of motion which this joint enjoys.</Callout> A portion of the capsule becomes taut only when the arm is carried to the extreme limit of motion in a given direction. (See Figs. 52 and 53.) Some portions of the capsule are more subject to strain than others, and accordingly we find such parts reinforced by muscle tendons or thickenings in the capsule itself. These thickenings have been given special names, such as the coraco-humeral in the upper part of the joint, and the ligaments of Flood 44 DISLOCATIONS OF THE SHOULDER 45 and Schlemm anteriorly. The transverse humeral ligament serves to confine the long tendon of the biceps within the bicipital groove, and the glenoid ligament forms a margin around the glenoid cavity, increasing its depth. <Callout type="tip" title="Tip">The deltoid muscle keeps the humerus well up in place against the under surface of the arch made by the coracoid, coraco-acromial ligament and acromion.</Callout> Paralysis of this muscle results in a dropping of the humerus with separation of the articular surfaces in the shoulder joint. The tendon of the long head of the biceps strengthens the upper part of the capsule, keeps the head of the humerus in proper apposition with the glenoid during the various movements of the arm and prevents the head from being pulled too closely upward under the acromion. <Callout type="risk" title="Risk">The subscapularis is the muscle most frequently penetrated by the head, causing injury to the capsule and tendons.</Callout> The action of the coraco-brachialis is similar to that of the deltoid in holding the humerus up. The tendon of the subscapularis reinforces the capsule, and in the anterior dislocations is not infrequently torn when this particular portion of the capsule is penetrated by the head. The tendons of the supraspinatus, infraspinatus and teres minor reinforce the capsule and aid in maintaining the proper relations of the articulating surfaces. The brachial plexus and axillary artery occupy a position internal to the head as they descend through the axilla, and may be injured in dislocations of the shoulder. In the forward and downward types of luxation direct pressure may be made on these structures by the humeral head; the pulsating axillary artery may often be palpated as it stretches across the head in subglenoid luxations. The injuries sustained by the structures about the joint depend on the direction taken by the head as it leaves the glenoid and the degree of violence producing the luxation. The planes of least resistance about the joint lie between the muscles rather than through them, though naturally the greater the violence producing the dislocation the greater the probability of a muscle being penetrated by the head. The subscapularis is the muscle most frequently penetrated in this manner. <Callout type="important" title="Important">The capsular ligament is practically always torn at the point where the head leaves the glenoid fossa and, since the common displacements are of the anterior variety, the rent will usually be found in the antero-inferior portion of the capsule.</Callout> A few cases of anterior luxation without injury to the capsule have been reported in which the joint was previously much relaxed and the capsule unusually roomy. Injury to the capsule is not infrequently accompanied by injury to the tendons which overlie and reinforce it and, when the violence producing the luxation is great, there may be a disruption of tendon continuity. The trauma causing the luxation may at the same time produce a fracture of the glenoid cavity or of the upper end of the humerus. The anterior rim of the glenoid may be broken off by the head of the humerus as the articular surfaces are forced past each other. The head and tuberosities may suffer a variety of fractures which are so diverse that two cases are rarely seen alike. The greater tuberosity is sometimes found parted from the shaft and displaced in the line of the pull of the muscles attached to it. This fragment may lie in the glenoid cavity where it offers obstruction to reduction. Fractures of the surgical neck, with or without dislocation of the shoulder, are more constant in type than fractures of the anatomical neck. Fracture of the anatomical neck, especially when complicated by dislocation, is sometimes represented by a comminuted, crushed condition of the upper end of the humerus, in which the lines of fracture are extremely variable. The cap of bone represented by the articular surface is usually less comminuted than either the underlying structure or the tuberosities. Fracture of the upper end of the humerus more often occurs in those cases of dislocation which have been produced by direct Fig. 55 Fig. 54. — Normal shoulder. CL, clavicle: C, coracoid process; A ess; G., glenoid cavity; H.H., humeral head; H.S., humeral shaft. Fig. 55. — Subcoracoid dislocation. acromion proc- Fig. 56. — Intracoracoid or subclavicular dislocation. Ci., clavicle; C, coracoid proc- ess; A., acromion process; B'., glenoid cavity; H.R., humeral head; H.S., humeral shaft. Fig. 57. — Intraclavicular dislocation with moderate deformity. violence, the blow having been sustained on the outer side of the shoulder just below the acromion. 48 FRACTURES AND DISLOCATIONS Separation of the lesser tuberosity has been noted as a complication of dislocation of the shoulder, though it is much rarer than fracture of the necks or greater tuberosity. The most important structures which may be injured by the Fig. 58. Fig. 59. Fig. 58. — Subglenoid dislocation. CI., clavicle; C, coracoid process; A., acromion process; G., glenoid cavity; H.H., humeral head; H.S., humeral shaft. Fig. 59. — Luxatio erecta. A variation of the subglenoid type. Fig. 60. Fig. 61. Humeral head; H.S., humeral shaft; A., acromion process; S.S., spine of scapula. Fig. 62. — Outlined X-ray of a low subcoracoid dislocation of shoulder. DISLOCATIONS OF THE SHOULDER 49 displaced head are the brachial plexus and axillary artery which lie just internal to it in the axilla. When the artery is torn hemorrhage into the axilla will follow, while simple pressure on the vessel will only temporarily interfere with the pulse in the arm below. Pressure on the brachial plexus may result in partial or complete paralysis of the parts supplied by it. The exact mechanism of injury to the brachial plexus is not thoroughly understood; some writers consider it a result of direct pressure on the nerves by the head or neck of the bone, while others are of the opinion that the stretching sustained by the plexus is the usual method of injury. In any case this complication is fortunately rare, and the resulting paralysis usually transient. There is little doubt that the plexus may be injured in attempts at reduction, especially when the older method of using a fulcrum in the axilla is resorted to. Permanent injury to the artery is seldom seen ; as a rule we may look for nothing more than a temporary suspension of circulation below the point of pressure, during the time the head is out. When the dislocation is allowed to remain unreduced for a few weeks fibrous tissue is formed about the head, which will ultimately make a new socket, and in many instances we see remarkable restoration of function. The usefulness of the joint, however, can never be expected to approach the normal under such circumstances. The head of the humerus may pass from the glenoid in almost any direction, and this fact has given rise to a variety of classifications which in many instances have but served to confuse rather than help us to a clearer understanding of the subject. The simplest classification will be used here : • Subcoracoid /Subclavicular (or intracoracoid) Downward Backward /Subglenoid ^Subglenoid erect (Luxatio erecta) r Subacromial I Subspinous Upward (very rare) By far the most frequent dislocation of the shoulder is forward, and of the two sub varieties the subcoracoid is much more common. The subglenoid is next in order of frequency, while the erect type is more uncommon than either of the posterior varieties. 50 FRACTURES AND DISLOCATIONS In the subcoracoid type the head lies below the coracoid process, having escaped through the antero-inferior portion of the capsule. The line to be drawn between this luxation and the subclavicular variety is purely artificial and arbitrary. If more than three-fourths of the transverse diameter of the humeral head lie internal to the coracoid the luxation is known as subclavicular. More or less inward rotation of the humerus is present. The tendon of Fig. 62. — Outlined X-ray of a low subcoracoid dislocation of shoulder. the subscapularis is not infrequently torn, and in rare instances injury may be sustained by the supraspinatus, infraspinatus or teres muscles. Tearing of the coraco-humeral ligaments practically never occurs in this type of luxation. The head of the bone often lies on the anterior edge of the glenoid cavity. In the subclavicular type the head continues inward, clears the coracoid process and rises to a slightly higher level. The tearing of the capsular ligament is usually more severe than in the subcoracoid form and rupture of the tendons inserted into the upper end of the humerus is more common. The coraco-humeral ligament is often extensively torn and accordingly Kocher's method of reduction will fail. Subglenoid luxations. — In the typical subglenoid dislocation the head of the bone lies below the glenoid cavity. There is no hard and fast line to be drawn between the subcoracoid and subglenoid varieties, since in practice we find the head may occupy a position anywhere along the anterior rim of the glenoid cavity. In the erect type of subglenoid luxation (luxatio erecta) the head lies below the glenoid but the arm is in a position of extreme abduction. In the subacromial type the head of the bone lies behind the glenoid cavity just under cover of the acromion. The rent is in the posterior portion of the capsule. The biceps tendon may be torn out of its groove and the bellies or tendons of the muscles inserted into the greater tuberosity (especially the infraspinatus) may be extensively torn. Complicating fracture of the greater tuberosity is more common in this type of luxation than in the subcoracoid form. The tendon of the subscapularis may be torn from its insertion into the lesser tuberosity. The subspinous form is an exaggeration of the subacromial, in which the head continues in its backward course till it lies in the infraspinous fossa just below the spine of the scapula. The violence producing this form is great and it is usually only a short time following the accident until the surrounding tissues and skin covering the head are filled with ecchymotic blood. Injury to surrounding muscles and ligaments is usually more extensive than in the subacromial type. The upward variety is only possible when the acromion has been fractured, and is so extremely rare that it might better be considered a surgical curiosity. There is no hard and fast line to be drawn between the subcoracoid and subglenoid varieties since in practice we find the humeral head may occupy positions at different levels anywhere along the anterior rim of the glenoid cavity. This fact is demonstrated by the accompanying photographs and Rontgenograms. In like manner the subcoracoid luxation merges into the subclavicular type. Etiology. — This is the most common dislocation in the entire body. It occurs most frequently in adult life and results from various types of trauma applied to the shoulder. The most common form of luxation is usually produced by violence applied to the shoulder when the arm is in extreme abduction. Symptoms.— Immediately following the accident the patient suffers severe, acute, nauseating pain which is increased by motion of the affected shoulder. Loss of function is produced by the inhibitory effect of pain, by the reflex spasm of the muscles and by the mechanical disturbance in the joint. If the luxation is allowed to go uncorrected the first two conditions grow gradually less while the last named persists and results in permanent disability. The nature of the deformity will depend on the type of luxation. In the subcoracoid variety there is a flattening of the shoulder which when palpated, as shown in Fig. 65, allows the examining fingers to pass inward under the acromion process. The upper end of the humerus is displaced inward and the axis of the arm DISLOCATIONS OF THE SHOULDER 53 Fig. 64. — Simple subcoracoid dislocation of left shoulder presenting the usual symptoms : flattening of the shoulder, change in axis of arm and lowering of the axillary fold. Fig. 65. — Examining depression below the shoulder. Note how, with moderate pressure, the fingers sink in below the acromion. Photograph taken just after the accident and immediately prior to reduction by Kocher's method. 54 FRACTURES AND DISLOCATIONS is altered. This change in the axis of the humerus may be recognized at a glance. The humeral head rests beneath the tip of the coracoid process and occupies a slightly lower position than normal. Lowering of the humerus as a whole lowers the attachment of the pectoralis major and accordingly the anterior axillary fold will be lower on the injured side. An abnormal prominence will be noted below the coracoid where the head has found its new resting place. The elbow seldom lies in contact with the side of the chest Fig. 61. Figs. 66 and 67. — Lateral and anterior views of a subcoracoid luxation of right shoulder. This shoulder has been dislocated eight times, the first luxation being about ten years ago. The manner in which the fibres of the deltoid pass in straight lines from the acromion to their insertion indicates the absence of the head of the humerus from the glenoid cavity. Reduction accomplished by Kocher's method with the patient in the sitting position.
Key Takeaways
- The shoulder joint is a ball and socket type, highly mobile but dependent on ligaments and muscles for stability.
- Capsular laxity allows for freedom of motion but can lead to dislocation if overstrained.
- Common types of shoulder dislocations include subcoracoid, subglenoid, and subacromial.
Practical Tips
- Always immobilize the affected arm in a sling when transporting a patient with a suspected shoulder dislocation to prevent further injury.
- Perform a thorough examination for associated fractures or nerve injuries before attempting reduction.
- Use gentle traction and counter-traction techniques during reduction, avoiding excessive force that could exacerbate damage.
Warnings & Risks
- Avoid using a fulcrum in the axilla when reducing a shoulder dislocation to prevent injury to the brachial plexus or axillary artery.
- Be cautious of complications such as nerve compression or vascular injury during reduction and follow-up care.
Modern Application
While the surgical techniques described here are historical, understanding the anatomy and common types of shoulder dislocations remains crucial for modern survival preparedness. Knowing how to identify these injuries quickly can be lifesaving in emergency situations where immediate medical attention may not be available.
Frequently Asked Questions
Q: What is the most common type of shoulder dislocation mentioned in this chapter?
The subcoracoid type is described as the most frequent, with more than three-fourths of the humeral head lying internal to the coracoid process.
Q: How can one identify a subcoracoid dislocation during an examination?
During palpation, the examining fingers may pass inward under the acromion process. The humeral head is displaced inward and the axis of the arm changes, with the humerus resting beneath the coracoid process.
Q: What are some common injuries that can occur during shoulder dislocation besides the dislocation itself?
Injuries to the brachial plexus or axillary artery may occur due to their proximity to the head of the humerus. These injuries can result in paralysis or temporary suspension of circulation, respectively.