To a rickety child, who rarely begins to walk till after the usual age, by far the most frequent positions are thP tvvo which we have just considered, and the mechanism of these positions, in my own estimation, is quite suf ficient to account for the first impression of the most frequent deformity of the rickety pelvis, the ovate, as well as for the not un common angular infantile distortion.
In standing and walking the supporting pres sure on the pelvic structures is sustained, either divided or alternately undivided, be tween the cotyloid cavities and the sacrum. From the peculiar disposition of the cotyloid articulation, the pressure of the head of the femur is exerted in two directions, 1st, upward and backwards along the cotylo-sacral rib, which is the principal line of pressure, and, 2nd, inwards on the lateral pelvic arch. In the up right position the softened cotylo-sacral rib yields in the direction of its C curve, which becomes more acute as the sacrum sinks. An increased obliquity of the pelvic inclination, such as has been stated to be generally conse quent upon the advance of the sacral promon tory and increased lumbar curve in the ellipti cal deformity, will bring the line of gravity, both of the trunk and v‘hole body, in front of the acetabular supports, which will cause them to increase the backward curve when pressure is exerted upon them (see fig. 122. u, a b.), But that such a condition is produced by a greater obliquity of the normal infant pelvis than that of the adult, or that this alone is sufficient to account for the elliptical defor mity taking place usually in the infant pelvis, by causing divergence of the acetabula under pressure during the upright posture, as asserted by Dr. Murphy, is a conclusion which the re sults of the observations given in a former section, as well as those of Weber, therein stated, will not at all admit of ;—for, as WhS there seen, the obliquity' of the normal infant pelvis is not at all :greater, if as great, as that of the adult.
But if the acetabula are already separated by the elliptical deformity, or if the leg bones yield inwards, so that the pressure on the aceta bular articular surface at its upper vaulted part is directed upwards and outwal ds, as seen in the accompanying diagram (fig. 122. B, a,b), then the pressure inwards of the heads of the fe murs upon the lateral pelvic arches is taken off, there is traction instead of pressure on the pubic tie, the acetabula become still more widely separated, and the elliptical deformity increased. ln such specimens of ovate pel vic defortnity as have the leg bones attached, I have found the tibim and fibulw bent much inwards, or the leg bones so disposed by an inward knee-bend as to take off' the inward pressure at the acetabula, and even sometimes by extreme adduction of the femurs, so as to exercise a strain upon the round ligaments of the hip joint and rotator muscles, and thus pro duce a direct outward traction. In this posi
tion of the bones, the action of the adult muscles which support the erect posture--viz., the great glutei and psom, will be such as to increase the deformity (seefig. 122. E, c d), as Bell as those before mentioned which sustain the spine erect.
If the angular deformity have been already impressed upon the infant pelvis by the bending of the cartilaginous junction, while the bones of the legs, and in some degree those °f the pelvis, retain a sufficient degree of hard ness to resist the bendin, then the inward pressure of the heads of the femurs remains in its full force, associated with the upward and backward pressure, and the deformity is increased by the upright position (Ag. 122. c, a b, a c). The same result is also produced in an increased degree, if the leg /tones yield outwards, so as to direct the pressure of the heads of the thigh bones more towards the median line. This will be better understood by referring to the diagram (fig. 122. D, a b, a c).
Naegele observes, that when the lower extre mities are curved and distorted the pelvis will generally be deformed ; and that such a con dition more especially, or where one hip is higher than the other, with an unsteady gait, a projecting abdomen and lower jaw, and re traction of the arnos and thorax, diminutive stature, &c., should lead the accoucheur to suspect deformed pelvis.* The adult pelvis, softened by malacos teon, appears to undergo greater distortion than is proportionate to that of the leg bones. In that upon which the experiments before mentioned, to ascertain the proportions of the osseous constituents, were performed, the bones of the lower extremities were almost entirely symmetrical and well formed, and the proportion of earthy matter contained in the femurs much greater than in the pelvic bones, especially in the pubes (at one point of which it was entirely deficient) and the sacrum. The pubes, as they are also the thinnest pieces of the innominate bones and sustain a great amount of the inward pressure, which exists, in these sases, to its full extent, seem to be the first to give way in the more complete and rapid softening of " mollifies ossium adultorum." The consequence is, the approximation of the acetabular extremities, and increased curve of the cotylo-sacral arch, so as almost to touch the sunken sacral key-stone ; and the starting forward and upwards of the crown of the pu bic counter-arch, so as to produce the rostrated symphysis.