b, by foetal hydrarthrosis (Parise, 1842) or other joint affection, such as fungous synovitis with effusion (Verneuil and Broca), or caries and destruction of the capsule (Morel Lavallée, Albers, Von Ammon).

3. Congenital dislocation (of the hip) is due to the peculiar position of the lower limbs of the fœtus in utero.

a, it is possible that in the strongly flexed position of the hip the pressure of the head of the femur upon the posterior or lower portions of the capsule may, when the latter is abnormally weak, cause dislocation (Dupuytren, 1826).

b, congenital dislocation of the hip is due to abnormal adduction of the thigh in utero, to a compressed position of the foetus due to deficiency in the amount of the amniotic liquid (Roser, 1864). 4. Congenital dislocation of the hip, like most congenital deformities of the joints, such as club-foot, wry neck, and spinal curvature, is the result of primary muscular contraction, which is itself to be regarded as the result of an affection of the central nervous system (J. Guérin, 1840, and, following him, Chaussier, Melicher, Mercer-Adam, Carnochan, Erichsen, and others).

5. Congenital dislocation of the hip is often only the last stage of a paralysis and consequent atrophy of the pelvi trochanteric muscles. This foetal paralysis leads gradually to relaxation of the ligaments, and this, often only after the lapse of time, and especially after the children have begun to walk, and by the action of the weight of the body, to dislocation (Verneuil, 1866). This theory has recently (1878) been brought forward again by some of Verneuil's pupils (Reclus, Dalby), and extended to congenital dislocations of the humerus (Kirmisson).

(Krönlein in this fails accurately to define the position of the supporters of this theory. Their contention is not so much that congenital dislocations are thus produced, but rather that some so-called congenital dislocations originate after birth in a paralysis, and are mistakenly thought to have been congenital. Reclus' formulates his conclusions as follows:

1. From the group of so-called congenital dislocations paralytic dislocations must henceforth be withdrawn.

2. These dislocations follow "amyotrophies," and may appear at any age, although they have rarely been seen except in infancy.

3. For their production two conditions are necessary-atrophy of a muscular group; integrity of its antagonists.

4. At the hip the iliac dislocation is the most common. It is due to the contraction of the adductors, which is unopposed because of the atrophy of the gluteal and pelvi-trochanteric muscles.)

6. Congenital dislocation of the hip is due in most cases—and these should be regarded as typical-to a defect of formation or development, which prevents the joint from assuming the normal shape. This very generally held theory was presented by Palletta, and then taken up and specially developed by Schreger, Dupuytren, Breschet, Von Ammon,

and others.

Schreger emphasizes the fact that so-called congenital defects are not

1 Revue Mensuelle Méd. et Chir., 1878, p. 88.

produced by an abnormal change in preëxisting, normally formed parts, but are due to defective formation or arrest of development, and that is especially true of congenital dislocations of the hip. Dupuytren and Breschet suggest a delayed development of the three pelvic bones forming the acetabulum. Since the vascular and nutritive supply of the pelvic organs and walls is independent of that of the lower limbs, it may happen, according to Breschet, that the growth of the pelvis is delayed, and fails to keep pace with that of the femora. The latter are then drawn back to the lowest point on the outer surface of the former, and rest in the external iliac fossa. Von Ammon,' in his remarkable work, expresses himself very clearly concerning congenital dislocations, which he terms dysarthroses congenita. "Even "Even if their external appearance,' he says, "corresponds somewhat with that of dislocations acquired after birth, yet in their method of formation they differ essentially from them, and they also have only the slightest resemblance to those secondary dislocations that follow joint disease. . In many cases there is in part the greatest certainty, and in part the greatest probability, that the affection depends upon an arrest of the constituent parts of the joint at an earlier fœtal stage of development." And further (loc. cit., p. 3): "If the term luxatio' is in general understood to mean the slipping of a movable bone out of its natural joint connections, it is applicable only with the greatest restrictions to the congenital dislocations in question.

There are cases of so-called congenital dislocation in which the head of the bone has never left its corresponding joint surface-that is, has never been dislocated, but rather, on the contrary, has never been in normal and proper relations with it." According to Von Ammon, then, a congenital dislocation is an arrest of development. The acetabulum does not develop into the usual, symmetrically rounded, deep socket, but retains its earlier saucer-shape; while the head of the femur, continuing to grow, becomes too large for the small acetabulum, and no longer suitable to lodge in it. (Krönlein, loc. cit., p. 84.)

Von Ammon recognized not only this typical form of congenital dislocation but also the other varieties that had been described by other authors, and quoted cases and reproduced drawings in illustration of them. So far as the typical form is concerned, but little less has been added since his time to our knowledge of its pathogeny, and that little is contained in a paper published by Grawitz in 1878, who, by microscopical examination of twelve specimens of congenital dislocation in seven newborn children, showed that the arrest of development consisted in a failure of the Y cartilage of the acetabulum to carry on the growth of one or all of the three segments of the os innominatum. He found, in his first case, for example, the acetabulum only as large as that of a foetus of about the fifth month, and the Y cartilage broader than usual because of diminished ossification of the three adjoining bones, the pubis, ischium, and ilium (Fig. 9). The cartilage was hyaline and vascularized, and with normal, elongated cells containing one, two, or three nuclei.

Von Ammon: Die angeborenen chirurgischen Krankheiten des Menschen, 1842, p. ix. 'Grawitz: Virchow's Arch., 1878, vol. 74, p. 1.

On comparison with sections of a normal pelvis of the same size, a striking difference appeared at the junction of the bone and cartilage. The formative zone in all three epiphyses was very imperfect, its cells scanty and widely separated, and the zone of cells arranged above one another

Section through the Y cartilage of the acetabulum into the obturator foramen. 4, normal pelvis ; B, pelvis of child with congenital dislocation of the hip. (GRAWITZ.)

in rows adjoining the line of ossification was not one-third as wide as it normally is, and the arrangement of its cells was irregular and broken. In two cases (Cases IV. and V.) the difference was even greater than in the first, for the zone of calcification was entirely lacking, and the cartilage cells contained no nuclei but only fat granules. In some of the cases the Y cartilage was centrally interrupted by an interposed wedge of embryonal adipose tissue. On the other hand, the appearances in the femur were those of normal growth, except in one case. In no case was there premature ossification of the Y cartilage, such as had been alleged shortly before by Dollinger' in explanation of the same affection.

The conclusion, I think, cannot be avoided that while in a limited number of cases dislocations existing at birth, especially in joints other than the hip, may have been caused by traumatism, abnormal position of the limb, or paralysis in the manner alleged by various writers, yet in the great majority of congenital dislocations of the hip the cause is to be found exclusively in arrest of development of the acetabulum by deficient action or vitality of the cells of the Y cartilage. And to the testimony in support of this opinion furnished by anatomical examination of specimens may be added that drawn from clinical observation, such as the coexistence of other deformities due to arrest of development, the frequency of double and multiple dislocations, the inherited tendency to the affection, and its great predominance in females.

Many of the congenital dislocations of other joints than the hip must also be regarded as due to defective formation of the corresponding bones, but the defect is rather a malformation apparently, than the result of an arrest of the development of one of the bones constituting the joint. At the elbow, however, in dislocation of the head of the radius, this bone is sometimes found relatively, and even actually, longer than the ulna, so that the dislocation may be in part the result of an arrest of the growth of the ulna. In a specimen taken from an adult, pictured by Humphrey'

1 Dollinger: Arch. für klin. chirurgie, 1877, vol. 20, p. 622.

2 Humphrey Med. Chirurg. Trans., vol. 45, p. 296.

(Fig. 10), of dislocation of the head of the radius forward and upward, there was ankylosis of the joint between the ulna and humerus, and the lower third of the ulna of the other arm was lacking.

FIG. 10.

Congenital dislocation of the head of the radius upward and forward, with exaggerated growth in length.

In some dislocations of the knee characterized by hyperextension of the leg upon the thigh the cause appears to have been muscular contrac

tion.

Of the other etiological varieties that have been asserted to exist, one at least seems to have been proved by direct examination to exist, that in which the dislocation follows distention of the capsule and ligaments by dropsy of the joint during intrauterine life.

Pathology.-The opportunities for studying the pathology of congenital dislocations other than those of the hip have been so very rare, and the study of those that exist has been made so uncertain by the doubtfulness of the diagnosis in some and the difficulty in distinguishing between primary and later changes in others, that but little can be positively said concerning them. In studying specimens of dislocation of the hip it is necessary, as Gurlt pointed out, to distinguish between those obtained from very young children who have never walked, those from older children whose growth was not completed, and those from adults.

Hip. The common form is dislocation upon the dorsum of the ilium; the only exceptions, and they are extremely rare, are upon the pubis and into the obturator foramen.

In the newborn child with a dislocation the acetabulum is smaller and flatter than normal, and is continuous by its flattened posterior border with another articular surface or new acetabulum lying above and behind the original one. Usually, too, the head of the femur is smaller than normal, although still too large for the acetabulum, and the neck short or almost absent (Fig. 12); sometimes the head and neck together have a conical, pointed form. The ligamentum teres is long and flattened, the capsule is complete and embraces both the old and the new acetabulum (Fig. 11). The microscopical changes have been described above.

The mechanism of the alteration seems plain; as the femur and its socket are originally developed out of one continuous strip of tissue they are at first in normal relations to each other, but as the development of the acetabulum goes on more slowly and imperfectly than that of the head of the femur the latter becomes relatively too large, and being no longer firmly held in place it is gradually drawn backward and upward by the continuous action of the attached muscles, the corresponding edge of the capsule is pressed away from the cotyloid border, and a new articular surface is

formed at the point where the head of the femur comes to rest. Meanwhile, the defective development of the original acetabulum persists, and its variation from the normal is probably still further increased by the absence from it of the femur. The remaining bones and the muscles not being put to sufficient use to feel the effect of the changed relations in the joint suffer no change unless involved in some associated defect of development.

But as soon as the child begins to walk, this change in the relations of the bones and muscles to each other makes itself felt, and as the local developmental weakness persists, two factors are now at work to remove the condition of the parts still further from the normal. The acetabulum, by its continued failure to share equally in the growth of the pelvis, becomes relatively smaller and more deformed, the head of the femur is removed still further from it, and becomes deformed in consequence of its irregular bearings upon the surface of the ilium; the ligamentum teres becomes longer, flatter, and thinner, and the capsule thick and strong, and its cavity commonly larger than usual. As the individual advances in life, and after puberty has been reached, the ascent of the femur is finally arrested, partly by the formation of a socket, and partly by the resistance of the capsule and the muscles. The elements of support then resemble in a measure those sometimes found with ununited fracture of the neck of the femur, and the pelvis, instead of resting directly upon the femur, is suspended from it by the capsule, ligaments, some of the pelvi-trochanteric muscles, and even by the psoas-iliacus, the