CHAPTER XIX.

DISLOCATIONS OF THE ELBOW.

DISLOCATIONS OF BOTH BONES BACKWARD, FORWARD, LATERAL,

DIVERGENT.

Anatomy.-On either side of the lower end of the humerus is a prominence, the epicondyle, which can be easily felt, and is of great importance in the recognition of any change in the relations of the bones that constitute the elbow joint. The inner one, commonly called the epitrochlea, is more prominent and well-defined than the outer one, and its upper margin joins the shaft of the humerus by a sharp curve, while on the outer side of the shaft the supinator ridge connects the side of the shaft with the epicondyle by a gradual slope. Below the epitrochlea is the flattened circular side of the trochlea, projecting downward and forward about half an inch, with a sharp, well-defined margin, which is masked by the olecranon and ulna when the bones are in place. From this edge the articular surface of the trochlea passes outward like a cone, its diameter becoming rapidly smaller for about half an inch, and then enlarges again, but less abruptly, for nearly an equal distance. Above it, posteriorly, is a deep depression, the olecranon fossa, into which the tip of the olecranon is received in full extension of the joint, and above it, anteriorly, is a corresponding, smaller one, to receive the tip of the coronoid process in full flexion. On the outer side of the anterior and lower part of the trochlea, and separated from it by a shallow vertical groove, is the capitellum, or radial head, of the humerus with which the head of the radius articulates, a rounded prominence looking directly forward.

The ulna articulates with the trochlea by its greater sigmoid cavity, which is concave from above downward and has a central longitudinal ridge which fits like a wedge into the central depression of the trochlea, or like a rope into the groove of the wheel of a pulley, and thus opposes displacement to either side. The posterior end of the concavity is formed by the tip of the olecranon, the anterior end by the coronoid process.

The radius articulates with the capitellum by the slightly concave, circular upper surface of its cylindrical head, and with the lesser sigmoid cavity on the outer side of the ulna and coracoid process by the side of its head. This articular surface on the side of the head is about threeeighths of an inch long (from above downward) on the inner and posterior side of the bone, the part that is in contact with the ulna in supination, but is shorter on the outer side at the part which comes in contact with the ulna in pronation.

The long axes of the trochlear cones and the ovoid capitellum coincide with one another and represent the axis of the joint for flexion and

extension; this line crosses the lower end of the humerus from a point just below and in front of the external epicondyle to one that is just covered by the lower part of the epitrochlea, and is inclined downward and inward from the transverse axis of the lower end of the humerus, so that the long axis of the forearm does not coincide with that of the arm but deviates to the outer side as it passes downward.

When the bones are in place and the forearm fully extended the uppermost part of the olecranon, the "point of the elbow," lies on or close below a transverse line drawn behind the limb from the epitrochlea to the epicondyle; and when the elbow is flexed at a right angle the same point lies a little more than an inch directly below and nearly midway between these two prominences in the prolongation of the long axis of the shaft of the humerus. Ordinarily the

relations of these three points to one another can be readily determined, even when the region is swollen, and they are the most convenient and trustworthy aid in the recognition of the existence of a dislocation of the ulna.

The outer border of the head of the radius can be felt about three-quarters of an inch below the epicondyle in a line drawn from the latter to the wrist, and it can be felt to move when the hand is gently rotated. This is the only point where the interarticular line is distinctly accessible to palpation; at all other points it is too thickly covered by soft parts or masked by the parallelism and close contact of adjoining surfaces.

The internal lateral ligament arises above from the anterior, lower, and posterior portion of the epitrochlea and is broadly inserted below along the inner margin of the greater sigmoid cavity.

The external lateral ligament, shorter and narrower than the internal, arises above just below the epicondyle and becomes blended below with the orbicular ligament that surrounds the head of the radius, some of its posterior fibres being continued to the ulna.

The anterior and posterior ligaments are thin and loose, and close in the joint between the lateral ligaments in front and behind, respectively. The orbicular, or annular, ligament, placed like a ring about the head of the radius and the adjoining portion of its neck, occupies three-fourths of a circle of which the remaining fourth is formed by the lesser sigmoid cavity of the ulna; it is thus attached by its two ends to the ulna and encircles the head of the radius. It is reinforced externally and

posteriorly by the fibres of the external lateral ligament. The synovial sac extends beyond its lower border for a short distance along the neck of the radius, and is then reflected upward and attached to this bone.

The capsule forms a single, completely closed sac, enveloping all parts of the joint and extending above the olecranon and coracoid fossa. Some of the deepest fibres of the triceps and brachialis anticus are attached to it and draw it out of the way when it is relaxed in flexion or extension.

The ulnar nerve passes close behind the joint on the inner side between the olecranon and epitrochlea in close relations with the capsule and lateral ligament.

The movements of the joint are flexion and extension, which, strictly speaking, are provided for by the humero-ulnar articulation, and rotation of the forearm, which belongs to the radio-ulnar joints. The relations of the head of the radius to the humerus give greater breadth to the joint and thus secure it more effectually against angular lateral motion. Flexion is arrested by the interposition of the soft parts between the bones in front or, if pushed to the extreme, by the contact of the tip of the coracoid process with the humerus. Extension is arrested by the tension of the ligaments and muscles on the front of the joint and by the contact of the tip of the olecranon with the back of the humerus. Lateral angular motion is prevented by the lateral ligaments.

Frequency. In order of frequency the dislocations of the elbow come next after those of the shoulder. The Tables in Chapter I. in which both hospital and polyclinic cases are included show percentages varying from 27 (Krönlein, 109 in a total of 400) to 16 (Prahl, 69 in a total of 420). Table III., in which several statistics are combined, gives 315 cases in a total of 1432, or 22 per cent., for combined hospital and polyclinic service, while 964 hospital cases give only 97, or 10 per cent. Krönlein's 109 cases arranged according to age, sex, and variety are as follows:

This shows the same preponderance in males over females, 4 to 1, that is shown by dislocations in general, and that the great majority, 80 out of 109, occur during the first twenty-four years of life. Attention was called in Chapter XVI. to the difference in respect of age between dislocations of the elbow and those of the shoulder, the latter being rare at the age when the former are common, and most frequent in middle life; and Krönlein's opinion was there quoted that fractures of the clavicle are in childhood the equivalent injury-that is, are produced by the same cause of dislocations of the shoulder by direct violence in middle life,

and that dislocations of the elbow are the equivalent injury of dislocations of the shoulder by indirect violence.

Classification. The different forms of dislocation of the elbow are numerous, for the two bones of the forearm may be displaced together in any one of the four principal directions, or each may take a different direction, or either may be dislocated while the other remains in place. The number of named forms has been still further increased by making in some a distinction between "complete" and "incomplete" which not only is not justified by any corresponding important pathological or clinical difference, but which also does not even correspond with the definition of "incomplete" given by those who make most use of the term. The following table prepared by Denucé1 in 1869, and reprinted by Pingaud' in 1878, gives in a convenient form most of the varieties thus far observed; it is reproduced here because of the prominence given to it by its publication in these two important works, and because of the frequent references to it in current literature, but it must be regarded rather as a working schedule or table of contents prepared for convenience of reference than as a complete classification or even as an accurate one within its own limits. While some of its subdivisions are created on the authority of single, and more or less doubtful cases, others are made to include cases that differ quite as much from one another as do those that are separately classified.

CLASSIFICATION OF DISLOCATIONS AT THE ELBOW. (DENUCÉ.)

C. Of the radius by elongation, or the incomplete dislocation of children.

Denucé: Dict. de Méd. et Chir. pratiques, art. Coude.

2 Pingaud: Dict. encyclopédique des Sci. Méd., art. Co de.

4. Simultaneous dislocations of the two bones,

A. Dislocation of the ulna backward and of the radius forward.

B. Dislocation of the ulna backward and of the radius outward.

Many of these varieties are closely allied to one another, and produced by causes that differ very slightly. Thus, if the joint is hyper-extended, the ligaments torn, and a backward dislocation of both bones begun, the final position taken will vary with the direction in which the force continues to act, and with the addition to it of lateral flexion of the joint or rotation of the forearm, so that forms as widely different in appearance as direct backward dislocation, lateral dislocation, and divergent dislocation may be produced. It will be proper, therefore, as well as convenient, to describe under the more common type, backward dislocation of both bones, much that concerns many of the other forms, and to limit the descriptions of the latter mainly to the points of difference.

The classification which will be here followed is the same in its principal features as the above and as those adopted by most recent writers. The differences are in the grouping and recognition of the varieties.

Dislocations of the forearm on the arm,

Dislocations of the ulna alone,

Dislocations of the radius alone,

Congenital and pathological dislocations.

2. Complete, or 2d degree.

1, 2. Backward and upward, {1. Incomplete, or 1st degree. 3. Backward and outward, behind radius.

This variety rests upon a single reported case (Cooper: Disloc. and Fracts., Am. ed., 1844, p. 384), a compound dislocation quoted by Cooper as a dislocation backward. It does not appear from the account that the radius and ulna were separated from each other, and consequently this classification is misleading. It should not be confounded with Malgaigne's "dislocation of the ulna backward and to the outside of the radius," which is bracketed by him with the above variety A, class 4, to form a class entitled "Double dislocation of the ulna upon the humerus and radius," but which is more properly placed by Denucé in class 2, dislocations of the ulna alone, 4th variety, backward and outward, the mechanism of which is torsion (pronation) of the forearm about the radius, by which the ulna is carried backward and outward.