Robert W. Lovett - 461 
This is the case because from a mechanical point of view the spine is a 
flexible rod permanently curved by the physiological curves in the antero 
posterior plane. Side bending necessitates movement in another plane 
and consequently a twist, and twisting for a similar reason causes side 
bending. 
In lateral curvature the problem is simplified by a recognition of these 
facts. Any lateral yielding of the spine at any part must be accompanied 
by a twist of the spine and the transverse axis of the shoulder girdle will 
no longer be parallel to that of the pelvis. As the lateral curve increases, 
the twist will tend to increase. But in addition to being a flexible rod 
the human spine must be regarded as a flexible rod endowed with a sense 
of equilibrium and adjustment. In a general way in the upright posi- 
tion the head must be kept over the base of support and the head pointing 
approximately straight ahead. This is a matter of continual and in- 
stinctive muscular effort on the part of the patient. If now a lateral 
curve has been acquired, the shoulders will be twisted in their relation to 
the pelvis and as the curve increases, the twist would naturally increase. 
That a twist exists in each case of lateral curve is easily seen in any case 
of postural lateral curvature looked down on from above in the standing 
position, when the shoulders can be seen to be no longer parallel to the 
pelvis. But the twist cannot increase beyond a certain point because of 
the patient’s instinctive effort to keep the shoulders parallel to the pelvis. 
The lateral curve is a present and probably increasing factor, and to 
bring the shoulders again parallel to the pelvis, a compensating twist 
must be added to the one already existing which results in the phenome- 
non known as rotation and enables the shoulders to be again brought into 
approximate parallelism with the pelvis. To this resultant combination 
of two twists which results in the prominence of the ribs on one side of the 
spine, or of the transverse processes of the lumbar vertebrae on one side of 
the spine, or to both together, the name “ rotation” has been applied in 
the nomenclature of lateral curvature. 
REFERENCES. 
1. Lorenz.—Path. und Ther. der Seitl. Ruckgrats-Verkrummungen, p. 28, 
Wien, 15386. 
2. KENLENBURG.—Die Seitl. Ruckgrats-Verkrummungen, Berlin, 1876, p. 116. 
3. HuGues.—Archiv fiir Anat., 1892, 265. 
4. Bibliography in 
RiEDINGER.—Morph. und Mech. der Skol., Wiesbaden, 1901. 
WULLSTEIN.- -Die Skoliose, Stuttgart, 1902. 
