Curvature Forward - Lordosis - is met with in greatest extent and frequency in the lumbar region: it scarcely ever occurs as a primary curve in that situation, but is almost always consecutive upon some previous one, compensating, as such, the obliquities of the pelvis produced by rickets, congenital lameness, or coxalgia on both sides. It is sometimes not limited to the lumbar region; but occurs, as a consequence of considerable angular curvature, in other parts also. Lastly, it sometimes comes on in the course of diseases of the spinal cord and of palsy, and extends the whole length of the vertebral column. Sometimes, when it is consecutive upon deformities of one side of the pelvis, arising from rickets or coxalgia, a certain amount of lateral curvature is combined with it.

Every primary curvature is compensated by a second curve in the opposite direction, which generally occupies the part of the column immediately adjoining the first; not unfrequently the second is succeeded by a third, and that even by a fourth. Upon this fact depend the various consecutive deformities which the pelvis presents in regard to its form, symmetry, and position. In cases of lateral curvature, not only is the primary deviation in the dorsal region followed by a lumbar curve in the opposite direction, or vice versd, a primary lumbar by a dorsal curve, but the primary curvature reaches along the column in extended sequence, in such a manner, that the second curve is compensated by a third, and this again not unfrequently by a fourth. The following condition is quite common: a primary curvature to the right in the thoracic portion of the spine, is followed by another to the left in the lumbar region, and the rotation of the vertebrae corresponds with the amount of the dorsal curve. But the sacrum exhibits a deviation, which commences, perhaps, at the lowest lumbar vertebra, and takes an opposite direction to that of the lumbar curve; that is to say, the sacrum appears lower than natural on the left side, and higher on the right, and betrays the rotation of its component vertebrae towards the side opposite to the lumbar curve, by projecting into the pelvis on the left side deeper than on the right. Lastly, in many cases the coccyx projects in an opposite direction to the curvature of the sacrum, and forms a fourth deviation of the column.

In another case, a primary deviation of the sacrum of a rickety pelvis to one side and backward (inclination of the pelvis on one side to an unnatural degree), may be counterbalanced by a curvature of the lumbar vertebrae to the opposite side and forward (lordosis scoliotica), and this, again, may be equalized by a dorsal curve in the contrary direction.

The amount of the compensating curvature generally equals that of the primary curve: but to this there are frequent exceptions; and the second curve may at one time be quite subordinate to the primary, at another may considerably exceed it.