Ernest Eckford Tucker
Proper and Secondary Movements
Proper motion of a joint is the motion defined by
the articular surfaces within average limits of motion. The limitation
to this proper motion is given by ligaments, or by cartilage as in the
case of the intervertebral disc, or by bony contact; and this imitation
then transforms the proper or primary motion into secondary motion.
For illustration, a vertebra rotates to one side, the plane of motion being
the base of the body of the vertebra. But the intervertebral disc
or the ligaments in front of it check this motion almost immediately, and
act as the ropes of a swing, transforming the horizontal motion into motion
around the attachment of those ligaments as an axis. The latter is
a secondary motion.
These secondary motions are of vast importance.
Beyond the limit of normal motion lies danger of lesion; and lesions almost
invariably occur through exaggeration of secondary motions. They
are also important in the correction of lesions; for it is necessary to
carry a joint to the limit of its normal motion to get any tension upon
it. The character of the tension produced depends on this secondary
Extensive laboratory work needs to be done on this
subject. A beginning of work of this character was made by the classes
of the A. S. O., to be described later.
In the spine as a whole, extension and flexion* occurs
in the lumbar region, rotation in the dorsal, both in the cervical, except
in the axis, in which rotation only occurs.
| *NOTE: Extension and flexion are loosely defined.
Accurate definition is needed for this work. As here used, flexion
means bending toward the umbilicus, or toward lines drawn vertically and
horizontally through it; extension means ;moving away from the umbilicus
or vertical and horizontal lines drawn through it. Thus, flexion
of the spine involves opening out or extension of individual vertebral
joints; but to avoid confusion, such motion will be referred to as flexion
of the individual joint, the umbilicus being regarded as the basis of comparison.
The ribs are extended in inspiration, flexed in expiration.
Side-bending occurs in all vertebrae except the
The work of the students in the classes of January
and June, 1917, of the A. S. O., referred to, was on the subject of axes
of rotation. That of Messrs. (now Doctors) Fish and Lawrence was
published in the A. S. O. Journal in 1916. The same discovery was
made by each of these gentlemen working independently of the other, and
both of them deserve credit for the discovery. The work of one student,
Mr. (now Dr.) Louis E. Browne, alone, was on the subject of axes of flexion
and extension, and the credit for the verification of those axes belongs
to him alone.
Mr. Browne’s work showed that the axes of flexion
and extension in the dorsal region coincided closely with the position
of the head of the ribs as they articulate with the facets on the bodies
of the vertebrae; the axes in the lumbar vertebrae and the lower two or
three dorsal vertebrae were in the same relative position, coinciding with
the position of the semi-solid core of the intervertebral discs in those
regions. This theory had been advanced in class; but “he who proves
discovers,” and Mr. Browne’s was the first work aiming to prove this point.
The work of the other two students (Fish and Lawrence)
came, however, as a complete surprise. Their work dealt with the
axes of rotation; and proved that the axes of rotation of lumbar vertebrae
lay at varying distances behind the articular surfaces, in some even behind
the tips of the spines of the vertebrae. When a profile drawing of
the spine was made and these centers were placed at the proper distances
behind, a further discovery was made; that a line drawn through all of
these centers formed a continuous curve. The center of rotation of
the fifth lumbar was about three inches behind the tip of th spine; and
the line beginning there swept forward to opposite the second and third
vertebrae, then backward again until opposite the eleventh dorsal it was
practically at infinity; in other words there was no rotation in the eleventh
dorsal spine—the surfaces lay in the same plane; there was slight rotation
in the twelfth (inferior articular surface of the twelfth with the superior
articular surface of the first lumbar); most and sharpest rotation
between the second and third lumbar, less again as we approach the sacrum.
Doubtless these facts conform to some natural law oaf mechanics.
We find also that the spine of the second lumbar is the largest, usually,
corresponding with this fact of greater rotation and also being the point
where the lines of tensions from iliac crests to ribs cross each other.
The centers of rotation of dorsal vertebrae, on the
other hand, were shown by these drawings to be in front.
The center of rotation of the eleventh dorsal was
neither in front nor behind; those of the tenth dorsal and of all other
dorsal vertebrae were, however, in front of the articular surfaces.
Here again when these centers were placed on a profile drawing of the spine,
and a line was drawn joining them, it described a continuous curve, farthest
away in the lower dorsals, nearest in the mid dorsals, farther away again
in the upper dorsals, until with the first dorsal or seventh cervical
it again reached infinity.
At this point the centers of rotation again jumped
across to the rear of the spinal column and again described a continuous
curve, convex toward the spine as before.
This work was subsequently verified by the other
students in the classes, though there was much variation in the results.
For instance it was found that the centers of rotation for the upper dorsals,
determined with the most careful work, were very irregular in many spines.
This means merely that the amount of motion there is so slight that nature
did not develop the articular surfaces in accurate conformation with the
dynamic or mechanic law, whatever it is, which led to the fairly accurate
relations of surfaces in other parts of the spine. It also implies
the opposite, namely, that articular surfaces are developed normally in
automatic adjustment to the mechanical laws applying to their motion.
Variations were found also in the lumbar region.
In some the articular surfaces of even the fifth lumbar vertebra faced
each other so sharply as to throw the center of rotation near to or in
the tip of the spine of that vertebra (which means that gross lesion might
exist here with no evidence thereof in the relation of the spines); in
some they were not curves at all, with no point of rotation, but lay at
an angle—almost at right angle—with each other, indicating that there was
no rotation here, that the only motion possible in these joints was that
of bilateral or unilateral flexion and extension (the latter meaning side-bending).
In many the two articular surfaces on either side of the same vertebra
did not have the same centre of rotation, but that of each was centered
around a point lying in or directly posterior to the opposite surface—each
surface determined the center of rotation of the opposite surface.
This fact probably indicates that rotation was not a proper function in
those vertebrae, but was accomplished by a primary side-bending and secondary
In some spines the centers for the lower three or
four were found to lie behind, those of the upper three or four to lie
in front; but again at such relative distances as to form continuous curves,
as in the dorsal and lumbar regions.
In the work done by Mr. Fish, for instance, it was
found that in the spine he examined the centers of rotation for the facets
in the lumbar region did not coincide on the two sides, being farthest
apart in the fifth lumbar (where the articular processes are farthest apart)
and approaching each other evenly until they coincided opposite the tenth
or eleventh dorsal. These were centers for rotation; but it was the
side-bending involved in rotation that gave these different centers, as
will be shown later.
The centers for side-bending or tilting to right
or left were not determined. The center probably varies with each
instant of motion, being first the center of the body of the vertebra,
then its inferior surface, then moving to the point of greatest resistance,
which appears to be usually the articulation of the convex side.
Side-bending occurs as said to a slight degree in all vertebrae, abut apparently
chiefly in the lumbar region.
In other words, in the lumbar region the lateral
motion is usually probably primarily side-bending, secondarily rotation;
whereas in the dorsal region it is probably primarily rotation, secondarily
side-bending. The distinction is merely theoretical, for they both
occur together, and one hardly occurs without the other. The intervertebral
disc in the dorsal region is, however, not thick enough to allow much side-bending.
The angle of motion in the dorsal region, in its various parts, may be
quickly learned by taking each vertebra in turn and sighting with the eye
so that the articular surfaces of the interior costal facet and of the
inferior articular process will both lie in the same plane.
In the dorsal region and the ribs the smallness of
the articular surfaces indicates that the amount of actual motion is very
slight. Articular surfaces in the spine never move over the full
range of their surfaces; they probably rarely even approach each other’s
limits, or even move so that half of either surface is uncovered.
One articular surface is always larger than the other; and the actual range
of normal motion is probably comprised within the larger of the two—limited
to the distance that the smaller can slide around without leaving the surface
of the larger. This for the reason that articular surface forms automatically
when bone slides on bone, and if the range of motion were exceeded more
articular surface would tend to form. The lightness of the motion
in the dorsal region is still further indicated in the smallness of the
costal facets on the vertebral bodies, and in the flatness of the superior
and inferior surfaces of the vertebral bodies with the thinness of the
intervertebral discs. A mere cartilaginous yielding distributed through
the whole spine amounts to a very large total of motion.
The proper motion of the ribs is practically limited
to that as seen ;In respiration, which, variously adjusted and combined,
can allow all of the actual motion that is observed. Examining the
facets on the transverse processes we find that they are in many if not
most spines not facts at all, but deep grooves, covering in some cases
the half of a circle. The only proper motion possible here is a turning
motion—a sliding in and out being prevented by the articulation of the
head of the bone with the bodies of the vertebrae. The head of the
bone is carried with one or the other of the two vertebrae that it touches
(the one body in the case of the twelfth and eleventh ribs) and slides
on the facet of the other; but this motion is so slight at the facet on
the transverse process as to cause little more than an elastic yielding.
“Bucket-bail” motions of ribs do not seem to be possible, judging by the
anatomical conformation of the facets.
Some work done by Mr. (now Dr.) Schoonmaker in the
A. S. O. shows that the facets on the transverse processes of vertebrae
also vary in continuous and graded series. In the vertical plane
they face toward a point in front of the lower part of the chest; in the
transverse plane they face directly forward in the first dorsal and turn
gradually to face forty-five degrees out in the tenth dorsal. The
axis of turning (flexion and extension) is of course the center of each
rib itself. These facets represent the direction in which normal
pressure is brought to bear on the articulations, from muscular action
and from atmospheric pressure without, and from blowing, etc., within the
chest; for of course articular surfaces must be directly perpendicular
to the pressure that bears against them, or they would slide to the limit
of their motion and stay there.
The proper motions of cervical vertebrae are direct
extension and flexion in the median line, and unilateral extension and
flexion. Experiments made on each other by students in the A. S.
O. classes referred to showed that here also one side moved at a time.
In the first stages of this unilateral extension, the concave side is fully
extended or approximated before the opposite side begins to move, but the
limit of approximation is soon reached, and then the opposite side begins
to open out, or flex, while the approximated side remains stationary with
only the slight turning on its own axis that is necessary. Each side
becomes the center of rotation for the other side. This fact is not
expressed in the articular surfaces for the reason that they must be smooth
to allow the other motions, that require gliding in other directions.
The proper motion of the atlas on the axis is a pure
rotation around the odontoid process.
The proper motion of the occiput on the atlas is extension-flexion,
or nodding; with slight side-bending and slighter rotation. The atlanto-axial
is almost a ball-and-socket joint with very slight ranges of motion.
LIMITATIONS TO MOTION
None of these proper motions remain proper for long—they
are proper motions in only the first stages of motion. Ligaments and bony
interferences quickly change the character of the motion and develop secondary
and even tertiary motions. The more it departs from the proper motion,
the more it enters the phase of secondary motion, the greater the danger of
lesion; and when it has passed the normal limits to secondary motion, it may
be said that momentary lesion is always and necessarily produced—but in a vast
majority of cases such lesions correct themselves. In the hundredth case,
however, it does not correct itself but remains in the abnormal position until
corrected. The frequency with which that hundredth case arises is a matter
for Principles of Osteopathy, not for technic.