There are two quite distinct forms of anteroposterior curvature, the curve in the one form being rounded^ and mainly an exaggeration of the natural curvature, and in the other sharp or angular.

(A) Angular Curvature. Pott's Disease Of The Spine

This depends on disease or injury to the bodies of the vertebrae. For the most part it is a Local tuberculosis of one or more of the bodies with the caseous necrosis and caries described above (see Fig. 281). The softened bodies of the vertebrae give way under the superincumbent weight, and the spine is bent at a sharp angle, the spinous processes becoming unduly prominent behind. The affection of the bodies may be un-symmetrical, and if collapse be more at one side than the other the angular curvature will not be exactly anteroposterior.

This form of curvature is more rarely due' to traumatic causes, as crushing of the bodies by heavy weights falling on the head or back, or by a fall from a height. This condition is shown in Fig. 285, where a vertebra is seen crushed and with part ot it displaced against the cord. This may lead immediately to an angular curvature.

It is worthy of special notice that angular curvature is much more obvious in the dorsal region than elsewhere, as it here increases the natural posterior curvature. In the cervical and lumbar regions, where the natural convexity is forwards, there may be a rounded posterior curvature produced, or, even with extensive disease, there may be very little posterior curvature visible externally.

The spinal cord is not necessarily injured by angular curvature, but in many cases it is crushed and interrupted. It may be so even during the process of healing, the sclerosis or condensation of the vertebrae sometimes causing further shrinking and increase of the curvature.

Fig. 285. - Vertebra crushed and part of it displaced backwards so as to injure the cord. There was acute curvature and paralysis. (The curvature is not shown in figure as the parts have been replaced so as to display the lesion).

(B) Kyphosis Or Posterior Curvature

In angular curvature the convexity is backwards, and the name kyphosis is sometimes applied. The term is more commonly employed to indicate a more gradual rounded curvature. This is mainly an exaggeration of the normal curvature with the convexity backwards in the dorsal region, and is due chiefly to muscular weakness or a habit of stooping. It is most frequent in children and old people, leading in its most exaggerated form to hump-back (a condition, however, which is more frequently the result of rotatory curvature), and in a lesser degree to round shoulders.

(C) Lordosis Or Anterior Curvature

In this condition the convexity of the curve is forwards, and the tendency of it is to throw the head backwards. It is most common in the lumbar region, and in the majority of cases is due to rickets. Rickets when it affects the pelvis causes the sacrum to assume a more horizontal position than normal, and in order to retain the erect position the lumbar anterior curve is exaggerated. It may also be produced by congenital dislocation of the hip-joint (stated by Adams to be of considerable frequency), and anchylosis of the hip. There may be also, but rarely, a direct lordosis in the lumbar region from rickets, the natural curvature being increased by reason of the softness of the bones. In the dorsal and cervical regions lordosis is very uncommon.