460 The Study of the Mechanics of the Spine 
processes were a factor in causing rotation in side bending and also 
whether Meyer’s theory of rotation was true. 
In the spine of an adult cadaver from the dissecting room the column 
of vertebral bodies was separated from the laminae and arches by cutting 
through the pedicles and the column of bodies was observed by itself. 
1. When fixed at the lower end and bent forward and to the left, the 
column of bodies turned with its front to the right, twisting to the right 
as did the intact spine and apparently to the same extent. In all other 
motions it behaved in the same way as did the intact spine. 
2. When fixed at the lower end and twisted with its front to the left, 
a lateral curve to the right of the same character and extent as in the in- 
tact spine occurred. In all other manipulations, also, it behaved as did 
the intact spine. Even the absence of torsion movement in the lumbar 
region in the intact spine, supposed to be due to the close interlocking of 
the articular processes, was present to the same extent in the column of 
vertebral bodies alone. The column of arches on the other hand did not 
behave as did the intact spine in its relation of twisting and side bending 
as demonstrated in a former paper. The whole experiment was repeated 
with similar results on a second cadaver. It would therefore seem reas- 
onable to conclude: 
(1) That the articular processes do not cause the torsion of the spine 
in side bending. 
(2) That torsion of the spine in lateral bending is not caused by the 
fact that the spinal column is made up of two components, the 
column of bodies and the column of arches. 
(3) That the column of vertebral bodies is the determining factor in 
this association of movements. 
(4) That the column of vertebral bodies alone and the intact spine 
behave alike and behave as would any flexible rod of the same 
shape, size, and elasticity. 
The bearing of this is obvious in its practical aspect. There is no 
such thing, as is generally taught in anatomies, as a pure side bending of 
the spine. Every side bending of the whole spine and every side yielding 
of any part of the spine is also a torsion, and carries with it from the first 
an element of torsion. Every twisting of the spine carries with it a side 
bending of the spine and there exists no such movement as a pure twist 
or torsion of the spine. 
There are, therefore, apparently only three types of spinal movement: 
1. Forward bending (flexion). 
2. Backward bending (extension). 
3 Side bending fe compound movement of the two elements which 
* ( Torsion can not be disassociated. 
