CHAPTER XXIII.

DISLOCATIONS OF THE THUMB AND FINGERS.

THE tables in Chapter I. show that dislocations of the thumb and fingers in combined hospital and polyclinic services amount to nearly ten per cent. of all dislocations, and that only about half of them are treated in hospital. Of these the dislocations of the thumb, or even of its proximal phalanx alone, are much the most numerous, but the details of the statistics are not sufficient exactly to determine the relative numbers. Polaillon' gives the largest statistics of which I have knowledge, 206 cases, divided as follows:

Dislocation of the 1st (proximal) phalanx of the thumb.
1st phalanx of other fingers.

2d (middle) phalanx

3d (terminal)

84

27

26

69

206

He does not state whence these statistics are derived, but it is probable he made them up, as he did those of other joints, from cases reported in text-books and journals, and, therefore, they have not quite the same value in determining the relative frequency of the different varieties, as if they had been made up from the integral statistics of hospitals, dispensaries, or individual surgeons. For the same reason the mortality, 10 cases of the 206, or 4.85 per cent., cannot be accepted as that of the injury in general, since exceptional cases are more frequently reported than the commonplace ones. A special cause of danger, one that may make the rate of mortality higher than that of other dislocations, is found in the fact that compound dislocations are comparatively numerous, and are exceptionally liable to be followed by tetanus.

Dislocations of the proximal phalanx of the thumb.

These dislocations are not only the most frequent of those involving the phalanges, but they also derive a special interest from the frequency with which the reduction has been found to be very difficult or has entirely failed. The cause of this difficulty has been the subject of much study and experiment upon the cadaver during the last hundred years, which may be said to have culminated in an elaborate paper read by Farabeuf before the Société de Chirurgie of Paris in 1875, in which the anatomy of the joint was described with much detail. This description and his explanation of the cause of the difficulty have been generally copied and accepted by writers in Germany and France.

1 Polaillon: Dict. Encyclopédique des Sciences Méd., article Doigt, p. 166. 2 Farabeuf: Bull. de la Société de Chirurgie, 1876, p. 21.

Anatomy. The head of the metacarpal bone presents no expansion on the dorsum, and but little, if any, on the sides, but on its palmar aspect it projects in the form of a well-rounded tubercle or condyle covered with cartilage for articulation with the two sesamoid bones, which are developed in the combined anterior ligament and the tendons of the short muscles that are attached to the base of the phalanx. Of these two sesamoid bones the outer is the larger, and both are firmly and closely united to the phalanx by ligaments which are continuous with each other across the front of the joint, and together form the "glenoid ligament" which separates the tendon of the long flexor of the thumb from the joint, and is continued backward and upward to the palmar surface and sides of the metacarpal bone. These ligaments hold the sesamoid bones close to the phalanx and, allowing them to turn freely in the direction of flexion, prevent their movement in the opposite direction beyond a line parallel to the long axis of the phalanx, so that if the latter is separated from the metacarpal bone the sesamoid bones cannot be turned up against the articular surface of the phalanx. The arrangement has been aptly compared to that of the hinged side of a table, which can be let down but cannot be raised above the level of the top of the table. The connection

The metacarpo-phalangeal joint of the left thumb. (FARABEUF.) A. The external lateral ligament. B. The internal lateral ligament. C. Palmar aspect.

of the sesamoid bones is much stronger with the phalanx than with the metacarpal bone. In addition, there are the lateral ligaments uniting the phalanx and metacarpal bone. The head of the metacarpal bone is more prominent anteriorly on the outer than on the inner side, and the tendon of the flexor longus pollicis lies nearer the inner than the outer side. This tendon is lodged at its lower end in a firm sheath, which extends upward to, and is connected with, the sesamoid bones.

The muscles which are attached to the first phalanx are the abductor, adductor, and flexor brevis; the latter has two insertions, one upon the outer the other upon the inner side of the base of the phalanx, and the two sesamoids are developed within its tendons of insertion where they are continuous with the anterior ligament; the outer insertion spreads to each side of its sesamoid bone, and is attached also to the palmar surface of the base of the phalanx and to the external lateral ligament, covering in a large part of the palmar and external faces of the joint. The abductor is attached to the external sesamoid by deep tendinous fibres, and also to the intersesamoid ligament, and by expanded fibres to the

outer side of the phalanx and the extensor tendons, after the manner of insertion of the interosseous muscles in general. The adductor is in like manner attached to the internal sesamoid bone and the inner side of the phalanx and the extensor tendon. These attachments and muscles are made tense by abducting the thumb, and are relaxed by pressing the metacarpal bone into the palm of the hand. The long flexor and the extensors are relaxed by inclination of the hand toward the radial side. Consequently, to relax as much as possible the various muscles attached to the thumb, the hand should be held in straight extension and slight abduction, and the thumb should be pressed into the palm, adduction.

The dislocation may be forward or backward, complete or incomplete. Backward dislocations.-This is the most frequent form, and the one in which reduction of the dislocation is often difficult.

The common cause is exaggerated dorsal flexion of the first phalanx. When the normal limit of the movement is reached the anterior ligament is put upon the stretch and, the movement being continued, yields at its attachment to the metacarpal bone, so that the sesamoid bones accompany the phalanx in its movement.

a. Incomplete form.-If this movement is not carried further than to the position shown in Fig. 104 the articular end of the phalanx rests

FIG. 104.

FIG. 105.

Incomplete dislocation of the thumb.

Incomplete dislocation. (FARABEUF.)

against the posterior margin of the head of the metacarpal bone, and is maintained in this position by the tension of the portions of the adductor and abductor muscles which are attached directly to the phalanx, for their line of traction is now posterior to and above the new centre of motion. The attitude of the member is represented in Fig. 105.

This incomplete form is the one which many people, especially the young, can voluntarily produce by contracting the extensor muscles. The anterior ligament and the sesamoid bones rest like an apron against the antero-inferior articular surface of the metacarpal bone, and the dislocation can be readily reduced by moderate traction upon the phalanx and flexion.

b. Complete form.-If, however, the movement is carried further, the phalanx entirely leaves the articular surface of the metacarpal bone, and

FIG. 106.

moves upward on its dorsum, being followed by the anterior ligament and the sesamoid bones (Figs. 106, 107, 108). The external lateral ligament is torn, and usually the internal one also; the tendon of the flexor longus pollicis may remain in position, and be tightly stretched across the articular face of the metacarpal bone, as has been seen in some compound dislocations (e. g., Esmarch'), or, and more commonly, it accompanies the inner sesamoid bone to the inner side of the metacarpal; occasionally it passes to the outer side of the metacarpal bone, accompanying the external sesamoid, but probably it does so only when, in the production of the dislocation, the thumb is bent to the outer side as well as backward. The head of the metacarpal bone projects through the rent in the capsule, and the tendons of the adductor, abductor, and the two portions of the flexor brevis rest against its sides. The phalanx stands.

FIG. 107.

Simple complete dislocation of the thumb. (FARABEUF.)

f

Simple complete dislocation; outer side. (FARABEUF.)

erect upon the dorsum of the metacarpal bone, being held there by the tension of the abductor and adductor. The dislocation is sometimes made compound by the rupture of the soft parts on the palmar aspect of the joint.

The appearance of the member is characteristic (Fig. 109). The phalanx is thrown back vertically upon the metacarpal bone, and the latter is adducted, the thenar eminence being consequently increased in thickness and diminished in breadth. The head of the metacarpal bone proects in front as a round, smooth prominence close under the skin, over

1 Esmarch: Berlin. klin. Wochenschrift, 1876, p. 629, first case.

which the tendon of the long flexor may perhaps be felt. The phalanx is quite movable from side to side, and can be rotated; it can also be

Simple complete dislocation; right thumb. The long flexor tendon is

displaced to the inner side (FARA

BEUF.)

Simple complete dislocation. (FARABEUF.)

turned down so as to be parallel with the metacarpal bone, but this movement should not be made, lest it should increase the difficulty of reduction by effecting a change into the "complex" form. c. Complex form.-Under this title Farabeuf places those cases in which, usually because of injudicious attempts to reduce, the phalanx has

FIG. 110.

f

Complex dislocation. (FARABEUF.)

been lowered until it is nearly or quite parallel to the long axis of the metacarpal bone, and in which, in consequence, the sesamoid bones have

FIG. 111.

Complex dislocation of the thumb; outer side. The hook raises the periosteal continuation of the lateral ligament, exposing the reflected sesamoid bone. (FARABEUF.)

been turned upward, and lie on the dorsum of the metacarpal bone above the base of the phalanx (Figs. 110, 111). The attached muscles are correspondingly displaced along the sides of the metacarpal bone, and