The Rachitie Pelvis.
Rachitis is a disease that attacks infants, usually at the age of from eighteen to twenty months—that is to say, at a time of life at which the osseous structure is developing rapidly; it is characterized by arrest of development, softening, and fragility and flexibility of the affected bones. The bones never regain their normal development after the disease has ceased to be active. The deformities occur from below upwards (tibia, femur, pelvis, etc.), especially in children who become rachitic after they have begun to walk.
Rickets is not sufficient in itself to produce deformities; by softening the bones and rendering them more flexible, it renders them liable to become deformed, but this malformation is only duo to the influence of external causes. Beside the three factors mentioned by Schroeder, the weight of the trunk, the traction of the ilia at the level of the symphysis, and the counter-pressure exercised from below upwards by the femora, we must, with Kehrer, consider muscular traction, and, with Depaul, accidental weights, independent of the body.
Let us study the effects produced upon the pelvis by these different agencies. If the child remains absolutely in the dorsal position, the in fluence of the first three factors will be nil, hence the form of the pelvis will not be changed. (Schroeder's " Liegbecken," the pelvis of the re clining posture.) The weight of the body is the only one of these forces that can act alone, and it can only act in cases of congenital fissure of the symphysis. Although the three forces are more or less concomitant, one may predominate, and thus cause characteristic deformities. If the child does not walk, the counter-pressure of the femora is absent, and the weight of the body and the traction at the symphysis result in antero posterior flattening, with lengthening of the transverse diameter. (Schroeder's of the sitting posture.") If the three forces act to gather upon a pelvis the bones of which are all softened, there results the osteomalacic form.
But, aside from these agencies, there is another that is quite as impor tant, the external pressure to which the pelvis is subjected, even in the dorsal recumbent posture, and still more when the child is carried on the arm. Being compressed between the trunk on one side and the femora on the other (acting on its antero-lateral wall), the pelvis becomes flea toned and deformed by the projection of the sacrum anteriorly, and by the flattening of the symphysis and the horizontal rami of the pubes.
Hence there results shortening of the conjugate diameter of the brim; the oblique diameters are but slightly changed, since the traction which is exerted posteriorly upon the iliac bones, is transmitted to the symphysis, and partly opposes the action of the femora. The cavity and the outlet are usually but slightly affected, indeed their dimensions may be in creased, but if the sacrum is curved inwards strongly, the depth of the pelvis is diminished. As these forces are not equal, regular, or directed toward the same point, the pelvis may present various irregularities in its shape. The sacrum may have a lateral, as well as an anterior, devia tion, or the pelvis may be more deformed on one side than on the other; Enslly, the change may affect the outlet, and sometimes deviation of the ischia, or the end of the sacrum and coccyx, may cause contraction of the inferior strait, either transversely or antero-posteriorly.
Aside from weight, we must also take into account traction, whether exercised by muscular or by fibrous tissue; the latter may cause deformity of the iliac crests, the ischio-pubic rami, and various apophyses and tuber osities, to which muscles are attached.
Finally, we must not forget that rickets is associated with arrest of de velopment, that causes that smallness and slenderness of the bones so com monly found in rachitio pelves. It is the exception to find the bones thick and massive. Rachitic females are usually of small stature, with short, slender limbs; there is often curvature of the spine, in consequence of which they have a peculiar oscillating gait. The hips are large, the but tocks prominent; the lower limbs present more or less marked curvatures, while the arms are short, slender, and occasionally curved inwards, the hands being small and short. The thorax presents projections at the chondro-sternal articulations (rachitic rosary), while the head is large, the forehead prominent, and the lower jaw projects forward. Pajot has called attention to the asymmetry of the face, and the inequality of the eyes.