The patient was a child eleven months old, and the dislocation was caused by the effort of a shoemaker to put on its shoe while it was sitting on its nurse's knee.

In two cases in which the head was split into two pieces, one of which remained in the socket attached to the ligamentum teres (Moxon, p. 403, and Birkett, Chap. III., p. 31), it is evident that the flexion, adduction, and rotation were not carried far enough to turn the head out of the socket, and the dislocation, strictly speaking, was a complication of a fracture of the head produced by violent pressure of the inner segment against the outer and upper margin of the cavity; in like manner the dislocation may be facilitated by the breaking off of a considerable portion of the acetabular ring. There is reason to think that some dislocations are produced in this manner by violence acting directly upon the upper part of the thigh, as in the passage across it of the wheel of a heavy

wagon.

It is by no means uncommon for a dorsal dislocation to be produced by the transformation of one downward and forward (obturator) during manipulations made to effect reduction, the head passing below and behind the acetabulum during flexion and adduction of the limb, and, in like manner, a dorsal may be transformed into an obturator dislocation.

Occasionally dorsal dislocation takes place gradually while the patient is confined to bed by illness, especially by acute articular rheumatism and the infectious or eruptive fevers. These "spontaneous" dislocations will be considered in Chapter XXVII.

Morris' expressed the opinion, formed after he had made a number of experiments upon the cadaver, that dorsal dislocation always took place while the thigh was abducted; but although he showed that the capsule can be more easily ruptured by exaggerated abduction than by flexion, adduction, and inward rotation, yet that fact cannot for a moment support his opinion in the face of the overwhelming testimony that proves the common occurrence in the position of adduction and flexion. Indeed, Moffat's case, just quoted, was published to controvert Morris's opinion, and it seems to have passed without a reply from him. A similar opinion appears to have been published by Fabbri many years before; but no author, so far as I have read, mentions the opinion except to express his disagreement with it.

Pathology. The condition of the capsule and of the muscles about the joint and the position of the head of the femur have been clearly shown by direct examination of a considerable number of specimens of recent dislocation, and by old ones, and by experiment upon the cadaver. Among the autopsies of fresh dislocations recently reported may be mentioned those by Moxon, above quoted, MacCormac, Adams,3 Morris (loc. cit.), Lee, and Humphrey," who describes three recent cases.

The capsule is torn always in its lower posterior part, and usually also in its under part, but the rent varies greatly in extent and shape.

1 Morris: Med.-Chir. Transactions, 1877, vol. 60, p. 161.

2 MacCormac: St. Thomas's Hosp. Reports, 1871, vol. 2, p 143.

3 Adams: Trans. Path. Soc. of London, 1870, vol. 21, p. 305.
Lee: St. George's Hosp. Reports, 1872-74, vol. 7, p. 169.
Humphrey: Lancet, 1886, ii. p. 1011.

Frequently it lies about midway between the upper and lower posterior insertions of the capsule; sometimes the capsule is torn away from the femur, and, rarely, away from the acetabulum. In Humphrey's three cases the rent had three branches radiating from a point "opposite the tuber ischii." Thus, he describes one as "a valvular rent in the under and back part of the capsule, commencing just behind the pubo-femoral ligament, midway between the acetabular and femoral attachments, as a single tear which divided and extended upward and backward to the tuber ischii, and upward and forward to the trochanter near the attachment of the obturator externus;" the rent in his second case was almost identical with that in the first; and that in the third is described as a "great vertical rent along the back of the capsule, nearer to its femoral than to its acetabular attachment, extending from the pubo-femoral ligament to the level of the fore part of the great trochanter, and there is a transverse rent under the position of the gemellus inferior running from the vertical rent to the cotyloid ligament."

FIG. 121.

In Morris's case (Fig. 121), "the capsule was ruptured on its lower and inner side, and was clearly peeled up from off the back of the neck of the femur as far as the digital fossa. The rent commenced below the pectineo-femoral band, midway between the acetabulum and the femur, and ran (1) outward and backward to the neck of the latter, which it reached just above and behind the small trochanter, and (2) inward and backward across the thin portion of the capsule toward the acetabulum which it nearly reached a little behind the ischial border of the cotyloid notch. It thus formed two sides of a large opening which was made quadrilateral in form by the detachment of the flap from the back of the femoral neck."

In Lee's case the capsule was "freely lacerated all around, a small portion remaining attached to the femur in front and behind." This was, therefore, an "irregular" dislocation, and to the extensive laceration of the capsule corresponded a variation in the symptoms which fully corroborates Prof. Bigelow's views; the report says: "Two of the main signs of dislocation were absent, namely, the advanced position of the knee with the foot resting upon the opposite one, and marked shortening." The head of the femur was below the pyriformis muscle and immediately behind the acetabulum.

The preservation of the anterior portion of the capsule, the ilio-femoral ligament, is constant, as has been said, in the cases which Bigelow terms "regular," those which are marked by the common and characteristic symptoms of the dislocation, and, as he also pointed out, the strong portion of the capsule at its upper and posterior part is also usually untorn and opposes the ascent of the head upon the ilium.

The ligamentum teres is usually torn from its attachment to the femur, but sometimes is ruptured.

Of the muscles, the quadratus femoris is usually completely torn across, but sometimes (Humphrey's third case) is intact; the gemelli commonly

are torn, but the obturator internus which is so closely associated with them frequently escapes or is only partly lacerated, probably because of its greater length. The pyriformis and obturator externus are sometimes torn partly or entirely across; the glutei usually escape injury entirely or are only slightly lacerated.

The head of the femur may lie close to the margin of the acetabulum, even overlapping the cavity, or it may be displaced to a variable distance backward or backward and upward. The lowest point at which its centre rests is the base of the spine of the ischium (Adams, loc. cit., and Quain') overlapping both sciatic notches; and the highest, except perhaps in exceptional cases, appears to be opposite the apex of the great sciatic notch, which, in the recumbent position, is directly below the anterior superior spine of the ilium, the line uniting the two passing about an inch above the margin of the cotyloid cavity. Forty years ago Quain demonstrated by his autopsy (Fig. 127) the error contained in the name given by Sir Astley Cooper to the lower form of dislocation "into the sciatic notch," and formally called attention to it; and a few years later Malgaigne showed that the head of the bone was much less upon the ilium in the higher form than was supposed, and further that in many, perhaps a majority, of the dislocations "upon the dorsum ilii" the femur left the socket at its lower posterior part and subsequently passed upward, so that in such cases the primary dislocation was "ischiatic," and the "iliac" was secondary. This view has been amply confirmed. In 11 specimens of old dislocations which Malgaigne examined, the head of the femur rose in 5 only to the level of a line drawn from the anterior superior spine of the ilium to the apex of the great sciatic notch, in 2 it rose half a centimetre above this line, in 2 one centimetre, in 1 one and a half centimetres, and in 1 two centimetres. There is no reason to suppose that in old dislocations the head is at a lower level than in recent ones, indeed it is probably somewhat higher.

When the head of the femur leaves the socket at its lower part it passes usually below the obturator internus and then rises behind it, so

FIG. 122.

that this muscle is interposed between. it and the acetabulum (Figs. 122 and 123). Or it may be immediately beneath the obturator internus and press it forcibly upward, as in Adams's case (Fig. 124), which remained unreduced until the patient's death on the fourteenth day, and in which the muscle was so tightly stretched over the upper part of the head that a deep groove had formed in the articular cartilage of the latter exactly corresponding in size and direction to the tendon; the head rested on the spine of the ischium, and the obturator externus and quadratus femoris were ruptured. Or the head may pass above the obturator internus, between it and the pyriformis, as in MacCormac's case (Fig. 125) in

which it rested "behind the acetabular ridge opposite the middle and upper part of the great ischiatic foramen, behind the posterior border of the gluteus medius, and only covered by the gluteus maximus and the integument." This is an example of a real primary "iliac" dislocation, and the rent in the capsule was "merely on the back part, and the neck was as it were locked over the acetabular ridge, and the strong anterior part of the capsule was tightly stretched." Figure 126, representing a specimen obtained experimentally by Bigelow shows the untorn anterior and lower portion of the capsule in this form.

The edge of the acetabulum is sometimes chipped, and in two of the cases above quoted (Quain, Morris) there was a fracture through the ilium. into the cotyloid cavity, and in the latter there was also a fracture of the ramus of the ischium. In both cases the injury was caused by great

violence.

In a case reported by Birkett, and quoted in Chapter III., the head of the femur was split vertically, the inner half remaining in the acetabulum and still attached to the ligamentum teres, and the other, continuous with the neck, being displaced backward above the obturator internus. A similar case, quoted above among compound dislocations, p. 403, was reported by Moxon; and in another reported by Riedel and also quoted in Chapter III., p. 32, the head and neck were split longitudinally, both fragments being displaced from the socket. In a case seen by Lossen1 the neck of the femur had been broken at the moment of dislocation, but doubtless after the head of the bone had left the socket. In several reported cases the neck has been broken during an attempt to reduce,

1 Lossen: Deutsche Chir., Lief. 65, p. 55.

and in a few in which fracture has been recognized it has remained. uncertain whether it occurred simultaneously with the dislocation or was caused by the surgeon. (See Chapter XXVII.)

The sciatic nerve commonly lies behind the head of the femur and at the most is only slightly pressed upon, but in Quain's case it was stretched over the neck of the femur (Fig. 127) "having passed into contact with the bone in the interval between the fragments of the quadratus femoris. Between the nerve and the bone was the torn tendon of the obturator externus." The nerve has been found in a similar position in some experiments upon the cadaver.

Symptoms.-The patient is unable to bear his weight upon or voluntarily to move his injured limb; if he stands upright it shows moderate flexion and adduction, marked inversion, and more or less shortening, the toes resting on those of the other foot. When he is placed upon his back the apparent adduction and flexion are increased, the knee resting just above. the other patella or crossing the thigh at a higher point. The contours of the outer and posterior regions of the hip are changed by loss of the normal depression behind the trochanter, elevation of the gluteal fold, and abnormal fulness due to the approximation of the insertions of the gluteal muscles. The trochanter rises to a variable distance above the line drawn from the anterior superior spine of the ilium to the tuberosity of the ischium, and its distance from the first named prominence is increased. The head of the femur can be obscurely felt through the gluteus maximus and recognized by its movement when the limb is flexed or rotated. The empty socket cannot be felt from in front, because it is covered by the anterior portion of the capsule and the psoas and iliacus, but the depressibility of the soft parts in Scarpa's space is as great as, or