THE BONY PELVIS. 



495 



DEVIATIONS OF THE SPINE ABOVE THE SACRUM. 



When, as in lateral curvature or scoliosis, there is a pathological curve developed, 

 the centre of gravity is shifted from the midline to one side and it falls nearer the foot 

 of the side toward which the trunk is inclined (see Fig. 496, A). This makes the 

 equilibrium unstable so that to restore stability the hips are inclined to the oppo- 

 site side and the centre of gravity is brought once more midway between the ankles 

 (Fig. 496, B}. This condition is produced when there is a single incomplete curve or 

 deviation to one side; if, however, the curve is complete and again reaches the median 

 line, as is often the case in scoliosis, then the centre of gravity is not disturbed and 

 there is no lateral shifting of the pelvis (see Fig. 496, C). If the primary curve is 

 accompanied by a secondary curve, both being complete and crossing the median 

 line, then also there is no shifting of the pelvis (Fig. 496, D). If, however, the 

 curves are so irregular as to shift more of the weight to one side than the other, 

 then the pelvis shifts (Fig. 496, E}. This causes the hip on the side opposite to the 



A. 



C. D. 



FIG. 496. Deviation of the spine above the sacrum. 



E, 



Fig. A. If the trunk is inclined to one side, a vertical line a-b through the centre of gravity is shifted to c-f, 

 and therefore falls outside of the base of support d-e and unstable equilibrium results. 



Fig. B. The inclining of the trunk to the right has been compensated by shifting the pelvis to the left, and 

 the vertical a-b through the centre of gravity c falls within the base of support d-e and stable equilibrium has again 

 been restored. 



Fig. C. If the deviation of the lower part of the trunk to the left is counterbalanced by a deviation of the 

 upper part to the right then the vertical a-b through the centre of gravity c falls within the base of support d-e 

 and the body remains in stable equilibrium. 



Fig. D. If a complete curve in the lumbar region is compensated by a complete curve in the dorsal and 

 cervical regions above, then the centre of gravity c is not shifted and a vertical line through it still falls within 

 the base of support d-e, and the body remains in stable equilibrium. 



Fig. E. If the curves are irregular, shifting more of the weight of the upper part of the body to the right, 

 the pelvis is shifted to the left until the centre of gravity c is again brought within the base of support d-e and 

 stable equilibrium is again restored. 



inclination to appear higher than the other, but it is not really so and the pelvis still 

 remains level. It is therefore evident that it is unnecessary and unwise to attempt 

 to correct the deformity by raising the apparently low hip by a high shoe. All 

 these conditions occur in the lateral curvatures or scolioses of childhood and adoles- 

 cence as well as the deviations which occur from empyema, sciatica, Pott's disease, 

 and other affections. A knowledge of the principles involved is essential to com- 

 prehending their production and to directing the exercises and applying the appa- 

 ratus used in their correction. 



