Another type of diffuse kyphosis without compensatory curvature is met with in arthritis deformans, in which the kyphosis is associated with the disappearance of the intervertebral discs and ankylosis of the vertebral bodies by bridges of new bone in the position of the anterior common ligament.
Partial or localised kyphosis, on the other hand, is the result of organic changes in the bodies of the vertebræ of the segment of spine affected. It is most often met with in Pott's disease in which the extent of the curve depends on the number of bodies affected, and its degree on the amount of destruction that the bodies have undergone. With the resumption of the erect posture, and in order that the eyes should look directly forwards, a compensatory lordosis is acquired above and below the segment that is the seat of kyphosis ([Fig. 211]). A similar but less marked type of kyphosis may follow upon compression fracture of the spine—in the condition known as traumatic spondylitis; and as a result of other lesions, such as osteomalacia, or malignant disease, in which the bodies undergo softening and yield, so that the spinous processes project posteriorly.
SCOLIOSIS
Scoliosis or lateral curvature is by far the commonest and most important deviation of the spine. The student will obtain a clearer conception of the nature of this deformity if we consider in the first place those types for which an obvious explanation is available.
Static scoliosis, for example, when one leg is shorter than the other, the pelvis is tilted down on the short side, the thoracico-lumbar spine deviates laterally to the normal side, and to restore the equilibrium of the trunk the cervico-thoracic spine deviates again in the opposite direction. The causes of one leg being shorter than the other are numerous and varied; they include such conditions as unilateral congenital dislocation of the hip, fractures united with overriding of the fragments, diseases of the joints, e.g., hip disease, or of the bones, especially such as interfere with the function of ossifying junctions; and acquired deformities such as unilateral flat-foot, knock-knee, or bow-leg. Clinically, this type of scoliosis is identified by observing that when the patient sits down the deviation of the spine disappears; it is relieved or got rid of by raising the sole and the heel of the boot on the short side, and, if required, by inserting an “elevator” inside the boot.
When there is shortening of the muscles on one side of the trunk there develops a lateral curvature of the spine with its convexity to the normal side; a good example of this is afforded in cases of infantile hemiplegia ([Fig. 224]) in which the deviation affects the entire column: a localised form is seen in congenital wry-neck, in which the convexity of the cervico-dorsal curve is on the side of the normal sterno-mastoid with a compensatory deviation to the opposite side in the spine below ([Fig. 272]). Unilateral paralysis of muscles acting on the trunk may also cause a lateral deviation of the spine, as is well seen in paralysis of the trapezius, which results in a cervical scoliosis with the convexity to the non-paralysed side.
Fig. 224.—Scoliosis following upon Poliomyelitis affecting right arm and leg.
(Mr. D. M. Greig's case.)
Asymmetry of the thorax, such as may follow on empyema with defective expansion of the lung, causes a lateral deviation of the dorsal spine with the convexity towards the normal side.