kinetic aspect
KINETIC ASPECT OF TOTAL SPINE
The total erect spine that has been described in its static postural state
.is capable of movement and now must be analyzed in its kinetic potentialities
The functional units are the component operational units of
the entire spinal column and, as the units individually move, so moves
.the total column
Movement is initiated by muscular action exerting its traction effect
through its muscular attachments upon the bony prominences of the
functional unit. A constant attempt is made by the antigravity forces to
maintain balance against gravity. Of these antigravity forces, muscular
action initiated by a proprioceptively stimulated righting reflex immediately
attempts to correct the "off-center" shift. During movement, the
body makes a constant effort to maintain its balance
FIGURE 31. Flexion-extension of total spine. Composite diagram depicting flexion and
extension of total spine. Flexion of the lumbar spine occurs to the extent of reversing
,slightly past the lomosis, whereas extension is moderate. In all movements of flexion
extension, or static erect position the thoracic spine does not alter its curve. (F - flexion
(.S - static spine; E - extension
percent of flexion occurs between L, and L, vertebrae. and the remaining
5 or 10 percent occurs between L, and L,. The greatest portion
.(of this last 5 to 10 percent offlexion is found between L, and L, (Fig. 32
The theory of total trunk flexion may be summarized as occurring
primarily at the lumbosacral joint. the L,-L,joint and to a lesser degree
between the remainder of the lumbar vertebrae with total lumbar
flexion limited to the extent of reversal of the static lordosis. Extension
of the total spinal column also occurs exclusively within the lumbar
segment but to a greater degree than the extent of flexion. No significant
.flexion-extension occurs in the dors'aJ spine
If a person were to bend forward in an attempt to touch his fingers to
the floor without bending at the knees. he would require more than the
degree of flexion attributed to the lumbar spine flexion. Were this
lumbar curve reversal the only flexion possible for the individual, less
than half the distance toward the floor would be reached. Additional
.bending must be possible, and this flexion occurs at the hip joints
The flexion possible at the hips is attributed to rotation of the pelvis
around the fulcrum of the two lateral hip joints. Such rotation occurs in
an anterior-posterior sagittal plane with the anterior portion or symphysis
pubis area lowering or rising, while the sacrum at the posterior
end of the rocker describes the same arc. The level of the sacrum
changes its angle in respect to the horizontal as does a balanced teeter
board.
,As the pelvis rotates forward, the sacral angle becomes more obtuse
and the lumbar spines takes off at a more forward ascent. If no flexion of
the lumbar spine had taken place when full forward rotation of the
pelvis had occurred, the person may have been able to bend forward to
a significant degree with his fingers almost touching the floor ifhis hips
were sufficiently limber to permit that degree of pelvic rotation.
Smooth symmetrical total bending, however, is the result of the
physiologic manner in which man is intended to bend. This is done
.with pelvic rotation and flexion of the spine occurring simultaneously
A smooth-graded ratio must exist between the degree of pelvic rotation
and the degree of lumbar lordotic reversal that constitutes the lumbarpelvic
rhythm. The mathematical relationship of lumbar curve, or the
lordosis, and reversal to the simultaneous degree of rotation of the
pelvis, which is the change in the sacral angle, constitutes the fundamental
kinetic concept of the spine. This rhythmic relationship of
spine-trunk-flexion to pelvic rotation is similar in body mechanics to
the scapulohumeral rhythm considered to be the physiologic kinetic
pattern of the shoulder girdle
Movement of the total spine has been previously pictured as that of
an articulated flexible rod requiring movement at each component
segment. Movement at the anterior portion of the functional unit is
permitted by the fluid shift of the nucleus pulposus within its elastic
annulus. Excessive movement is prevented by fascia and the longitudinal
ligaments which, by their resiliency, exert a cushioning effect
and thus protect the fibers of the annulus from bearing the full tearing
.effect of forceful flexion or excessive extension
The facets have been ascribed as the guiding portion of the functional
unit permitting flexion-extension in the lumbar region and rotation
lateral-flexion in the thoracic area because of the directional plane of
the facet joints. All movement contrary to this articular plane is essentially
.prevented
The extent of the permitted range of motion is thus determined by the
extensibility of the longitudinal ligaments, the elasticity of the articular
capsule, the fluidity of the disc, and the elasticity of the muscles. Since
it is known that direction of movement of the lumbar spine is the effect
of flexion and extension, it may be asked to what extent these
.movements are possible in the normal spine
Extension of the lumbar spine may be slight, but it is usually possible
to a moderate degree. Most children have the capability of arching
backwards to a large degree, and with training and persistent exercise
this function may persist through adulthood. Inherited ligamentous
laxity will enhance this more extreme hyperextension. The anterior
.longitudinal ligament plays the major restricting role in limiting hyperextension
Forward flexion of the lumbar spine is possible to a much smaller
extent than is extension. Such forward flexion of the lumbar spine is
possible only to the extent of and slightly more than the reversal of the
(static lumbar lordosis (Fig. 30
The lumbar spine, which is usually composed of five vertebrae, must
have its movement occur within the five intervertebral interspaces. In
.total flexion the degree of flexion movement varies at each interspace
Most f"rward flexion movement occurs at the last interspace which is
the intervertebral space between the last lumbar (L,) and the sacrum
(5,). An estimated three quarters (75 percent) of all lumbar flexion
occurs at this interspace, which marks the junction of the lumbar spine
to the sacral-pelvic bone and constitutes the lumbosacral joint.
Owing to the absence of flexion in the thoracic spine and with the
postulation that 75 percent of lumbar flexion occurs at the lumbosacral
joint, it may be argued then that 75 percent of all spine flexion occurs at
.,the lumbosacral joint and at L,-L
The remaining percentage of forward flexion is proportioned between
the remainder of the lumbar-vertebral interspaces. Fifteen to 20
FIGURE 31. Flexion-extension of total spine. Composite diagram depicting flexion and
extension of total spine. Flexion of the lumbar spine occurs to the extent of reversing
,slightly past the lomosis, whereas extension is moderate. In all movements of flexion
extension, or static erect position the thoracic spine does not alter its curve. (F - flexion
(.S - static spine; E - extension
FIGURE 32. Segmental site and degree of lumbar spine flexion. The degree of flexion
noted in the lumbar spine as a percentage of total spine flexion is indicated. The major
portion of flexion (75 percent) occurs at the lumbosacral joint; 15 to 20 percent of flexion
occurs at the L.-L$ interspace; and the remaining 5 to 10 percent is distributed between
Lj and L.. The forward-flexed diagram indicates the mere reversal past lordosis or total
flexion of the lumbar curvepercent of flexion occurs between L, and L, vertebrae. and the remaining
5 or 10 percent occurs between L, and L,. The greatest portion
.(of this last 5 to 10 percent offlexion is found between L, and L, (Fig. 32
The theory of total trunk flexion may be summarized as occurring
primarily at the lumbosacral joint. the L,-L,joint and to a lesser degree
between the remainder of the lumbar vertebrae with total lumbar
flexion limited to the extent of reversal of the static lordosis. Extension
of the total spinal column also occurs exclusively within the lumbar
segment but to a greater degree than the extent of flexion. No significant
.flexion-extension occurs in the dors'aJ spine
If a person were to bend forward in an attempt to touch his fingers to
the floor without bending at the knees. he would require more than the
degree of flexion attributed to the lumbar spine flexion. Were this
lumbar curve reversal the only flexion possible for the individual, less
than half the distance toward the floor would be reached. Additional
.bending must be possible, and this flexion occurs at the hip joints
The flexion possible at the hips is attributed to rotation of the pelvis
around the fulcrum of the two lateral hip joints. Such rotation occurs in
an anterior-posterior sagittal plane with the anterior portion or symphysis
pubis area lowering or rising, while the sacrum at the posterior
end of the rocker describes the same arc. The level of the sacrum
changes its angle in respect to the horizontal as does a balanced teeter
board.
,As the pelvis rotates forward, the sacral angle becomes more obtuse
and the lumbar spines takes off at a more forward ascent. If no flexion of
the lumbar spine had taken place when full forward rotation of the
pelvis had occurred, the person may have been able to bend forward to
a significant degree with his fingers almost touching the floor ifhis hips
were sufficiently limber to permit that degree of pelvic rotation.
Smooth symmetrical total bending, however, is the result of the
physiologic manner in which man is intended to bend. This is done
.with pelvic rotation and flexion of the spine occurring simultaneously
A smooth-graded ratio must exist between the degree of pelvic rotation
and the degree of lumbar lordotic reversal that constitutes the lumbarpelvic
rhythm. The mathematical relationship of lumbar curve, or the
lordosis, and reversal to the simultaneous degree of rotation of the
pelvis, which is the change in the sacral angle, constitutes the fundamental
kinetic concept of the spine. This rhythmic relationship of
spine-trunk-flexion to pelvic rotation is similar in body mechanics to
the scapulohumeral rhythm considered to be the physiologic kinetic
pattern of the shoulder girdle
