DIURNAL CHANGES IN SPINAL MECHANICS AND THEIR

DIURNAL
CHANGES
AND
THEIR
P. DOLAN,
From
Diurnal
changes
We
have
in the loads
reviewed
the
SPINAL
CLINICAL
M. A. ADAMS,
discs.
IN
acting
effects
SIGNIFICANCE
W. C. HUTTON,
the University
on the spine
of
these
MECHANICS
affect
changes
R. W. PORTER
of Bristol
the water
on
spinal
content
mechanics,
and height
and
of the intervertebral
their
possible
clinical
significance.
Cadaveric
lumbar
spines
subjected
to periods
of creep loading
show a disc height change
similar
to the
physiological
change.
As a result intervertebral
discs bulge more,
become
stiffer
in compression
and more
flexible
in bending.
Disc tissue
becomes
more elastic
as its water content
falls, and its affinity
for water
Disc prolapse
becomes more difficult.
The neural
of the compressive
and bending
sfresses
acting
increases.
proportion
that these changes
We conclude
are not fully compensated
for by modified
muscle activity.
that different
spinal
structures
are more heavily
loaded
the time of onset of symptoms
more about the pathophysiology
Therefore,
understand
and signs, and any diurnal
variation
oflow
back pain and sciatica.
During
the recumbency
of sleep,
the loading
on the
intervertebral
discs
is reduced,
and
their
relatively
unopposed
swelling
pressure
results
in them
absorbing
fluid and increasing
in volume
(Urban
and McMullin
1988). The absorbed
fluid is expelled
during
the day when
the loading
of the spine
is increased.
There
is, thus,
a
diurnal
variation
in the fluid content
and height
of the
discs
which
properties
We
these
causes
different
We then
a
variation
in
of the spine.
review
the experimental
changes,
and
spinal
suggest
then
the changes
at different
time of onset
variation
M. A. Adams,
PhD,
Research
Fellow
P. Dolan,
PhD,
Research
Fellow
Comparative
Orthopaedic
Research
Row, Bristol
BS1 SLS, England.
W. C. Hutton,
DSc, Professor
Department
of Orthopaedics,
USA.
©
should
be sent
in their
in their
CADAVERIC
times
severity,
of the
may
day.
help
us
SPINES
Periods
of creep
loading
of cadaveric
lumbar
spines
cause
a change
in disc height
similar
to the diurnal
change
seen in vivo. Certain
mechanical
properties
have
been measured
before
and after the period
of loading.
Disc height.
Constant
loading
at 1 000 N for six hours
(simulating
light
manual
labour:
Nachemson
1981)
causes
disc
height
to decrease
by 1 .53
± 0.34 mm
(Adams,
Dolan
and Hutton
1987).
The
height
loss is
rapid
at first but much
slower
by the end of the six hours
concerning
in loading
severity,
at different
of
day.
and
might
(Fig.
1). Similar
results
have
been
reported
experiments
(Adams
and Hutton
1983 ; Koeller,
and Hartmann
1984). Ifthe
applied
compressive
increased
and then
at hourly
intervals
to 3 000 N in order
in
other
Funke
force is
from
1 000 N to 2 000 N
to simulate
manual
labour
of increasing
severity,
then the height
loss shows
no sign
of slowing
down,
and the cumulative
loss after
three
hours is 2.13 ± 0.35 mm (Adams
et al 1987, see Fig. 1).
Unit,
Emory
to Dr M.
1990 British
Editorial
Society
ofBone
0301-620X/90/2027
$2.00
J Bone Joint Surg [Br]
1990 ; 72-B :266-70.
266
mechanical
times
of the
of symptoms
University
University,
R. W. Porter,
MD, FRCS,
Consultant
Orthopaedic
Doncaster
Royal
Infirmary,
Armthorpe
Road,
Yorkshire
DN2
5LT, England.
Correspondence
the
evidence
discuss
structures
that the
signs,
and any diurnal
be an aid to diagnosis.
arch and associated
ligaments
resist an increasing
on the spine. Observations
on living people
show
of Bristol,
Atlanta,
Surgeon
Doncaster,
A. Adams.
and
Joint
Surgery
Park
Georgia,
South
about
mostly
1935).
change
The average
diurnal
variation
in human
stature
is
19 mm (Tyrrell,
Reilly
and Troup
1985) which
is
attributable
to changes
in disc height
(De Puky
A 19 mm
change
in stature
corresponds
to a
ofabout
1 .5 mm in the height
ofeach
lumbar
disc
(Adams
et a! 1987),
so the loading
regimes
above
are sufficient
to simulate
physiological
reduction
in disc height.
Changes
in disc height
are caused
by fluid
and creep
deformation
of the annulus
fibrosus
THE
JOURNAL
OF BONE
AND
JOINT
discussed
diurnal
exchange
(Koeller
SURGERY
DIURNAL
et a! 1984).
probably
loading
The
relative
CHANGES
importance
IN SPINAL
of each
depends
upon
the severity
(Adams
et a! 1987) and factors
the degree
of disc
The diurnal
similar
magnitude
MECHANICS
mechanism
and duration
such as age
degeneration.
disc height
change
of
to the normal
narrowing
1.5 mm
ofthe
foramen
averages
and Goel 1983).
only
about
15 to 20 mm
THEIR
Fluid
of
and
is of a
lumbar
discs expected
with age (Koeller
et a! 1986). It could have
a significant
effect
when
there
is pathology
in the nerve
root canal
since
the total height
of the lumbar
intervertebral
Takata
AND
CLINICAL
loss
dissipation
267
SIGNIFICANCE
is accompanied
during
by a reduction
a loading/unloading
in energy
cycle
(Koeller
et
a! 1984).
This means
that the dehydrated
disc behaves
more like an elastic
solid and less like a viscous
fluid.
Disc
swelling
pressure.
Disc
swelling
pressure
can be
defined
as that
physical
pressure
which
must
be applied
to the disc in order to prevent
it from swelling
up in saline
(Urban
and
McMullin
1988).
It is a measure
of the
tissue’s
affinity
for water.
Swelling
pressure
can be measured
by adjusting
the
(Panjabi,
compressive
force
acting
on a motion
segment
until
there
Disc
water
content.
Creep
loading
reduces
the water
content
of the discs.
After
four hours
loading
at about
700 N, when disc height
is reduced
by about
1.5 mm, the
average
fluid loss is 12% from the annulus
and 5% from
the nucleus
(Adams
and Hutton
1983). Discs from people
under
the age of 35 years lose almost
twice this amount.
is no detectable
change
in disc height.
This force is then
divided
by the cross-sectional
area of the disc. Swelling
pressure
increases
rapidly
during
creep loading
as shown
in Figure
1, and its rise can be accelerated
by more
intense
loading
(unpublished
results
from our laboratory,
1988).
The clinical
significance
of swelling
pressure
is
Most
hours
that it determines
the
height
(and mechanical
of high loading.
of the fluid loss probably
occurs
of loading
because
longer-term
in the first few
creep
tests cause
only a little more
fluid loss : 24 hours
loading
at about
1 000 N reduces
the fluid content
of annulus
and nucleus
by 1 1% and
Gowin
1985).
8%
respectively
(Kraemer,
Kolditz
Compressive
stiffness.
Creep
loading
increases
the disc’s
compressive
stiffness.
The increase
is about
50% after
two to three hours ofphysiological
cyclic loading
(Koeller
et al 1984) and can rise to 100% after 28 hours (Smeathers
1984). Motion
segment
stiffness
is ofclinical
significance
because
it determines
how much the disc and surrounding
soft tissues
deform
during
physiological
dynamic
loading
and
/
2
,
Height
loss
ofthe
spine.
Disc bulging.
(mm)
100
it may
//
ofthe
disc
has been
observed
after creep
loading
(Koeller
et a! 1984).
increase
has not been measured
directly,
be inferred
from
the
This suggests
that the diurnal
1 .5 mm should
be accompanied
C
140
results
The
but
of Brinckmann
and
reduction
by an
in disc height
of
increased
radial
bulge
of about
0.5 mm.
For comparison,
the increased
radial
bulge caused
by increasing
the compressive
force
on the spine
from 300 N (lying
in bed) to 1 000 N (light
manual
work),
is only about
0.2 mm (Brinckmann
and
Horst
1985).
Compressive
stiffness
(%)
1 fl(l
Diurnal
disc bulging
will have clinical
implications
when
the central
or root canal
is stenotic.
The width
of
the intervertebral
foramen
is normally
about
8 to 10 mm
(Panjabi
et a! 1983) but it can be much
less in the root
100
Resistance
to flexion
(%)
2
L.J
3
Hours
Fig.
of creep
No. 2, MARCH
1990
4
5
6
loading
I
The effect ofcompressive
creep loading
on
of lumbar
motion
segments.
The
solid
compressive
force of 1 000 N applied
for
refer to a compressive
force of 1 000 N in
second,
and 3 000 N in the third.
Resistance
the physiological
limit determined
before
pressure’
of an intervertebral
disc is defined
72-B,
bulging
Horst
(1985).
They altered
the volume
of the disc, either
by injecting
fluid into it or by fracturing
the vertebral
body
end-plate,
and found
that
the change
in radial
bulging
was about
one-third
of the change
in disc height.
/
/
(N/cm2)
VOL.
Radial
to increase
size of this
C
Swelling
pressure
rate at which
a disc recovers
lost
properties)
at the end of a period
some mechanical
properties
lines
refer
to a constant
six hours.
The broken
lines
the first hour,
2 000 N in the
to flexion
was measured
at
creep
loading.
The ‘swelling
in the text.
canal and the lateral
recess.
Loading
of the apophysial
joints.
The
on the apophysia!joints
segments
were loaded
measured
a typical
(lumbar
posture
spine
(spine
slightly
in slight
apophysialjoints
either
there
simulated
has been
to simulate
resist
posture
is little
(Adams
resistance
standing
flexed)
and
extension).
little,
if any,
compressive
when
sitting
an erect
standing
Before
creep,
the
compressive
force
and Hutton
1980).
After
in the flexed
spine,
but
posture
the
force
motion
posture
apophysial
joints
in
creep,
in the
resist
268
M. A. ADAMS,
an average
some
cases,
more
result
of 16% of the
the proportion
extended
in high
of the
Hutton
Forward
applied
can
compressive
be as high
postures,
compressive
stress concentrations
apophysial
1984) and
bending
force.
as 70%.
In
In
performed
stresses
Adams
1984).
increases
separately,
and
a
and
in the early
morning
in the osteoligamentous
generate
lumbar
performed
proportion
much
higher
spine
than
do
later in the day.
ofthese
increased
45%
Backward
bending properties.
Creep
loading
reduces
the
disc’s
resistance
to backward
bending
by about
40%
(Adams,
Dolan
and Hutton
1988).
This is balanced
by
increased
resistance
from
the apophysial
joints
and
spinous
processes,
so that
the resistance
to backward
bending
of the
movement,
Prolapsed
be induced
combined
whole
motion
are unaltered
intervertebral
to prolapse
bending,
shear
segment,
and
Table
I. Diurnal
the lumbar
spine
variation
Intervertebral
disc
Posterior
longitudinal
ligament
Vertebral
body end-plate
Segmental
nerve root
Apophysial joint
Articular
surface
Capsule
and ligaments
Supra/interspinous
of maximal
stress
Period
Comment
AM
AM
AM
AM
PM
Especially
Especially
in bending
in flexion
Increased
Increased
tension
compression
PM
AM
PM
AM
PM
ligaments
on
the
Flexion
Extension
Increased
Increased
extension
various
diurnal
changes
structures
in
in spinal
mechanics
segments
prolapse
repeated
cadavers
reduce
content
lowered
fluid
content
is artificially
(by injecting
can
probably
of the
nucleus
raised
(by
chymopapain)
(see
Table
I).
loaded
in this way, 26 failed
by posterior
(Adams
and Hutton
1982). The experiment
on a further
group
of 19 motion
segments
of a similar
age range
after they had been
loaded
(Adams
prolapsed,
and
et
they
a! 1987).
were both
Only
from
two of
the same
disc
was
from
creep
these
spine.
Creep-loaded
discs,
in vivo,
may
also
susceptible
to prolapse,
perhaps
because
of the
fluid content
of the nucleus
pulposus
and the
flexion
stresses
in the posterior
annulus.
discs
be less
reduced
reduced
tension
in flexion
compression
in
CLINICAL
posture
the muscles
effects
of
2
Spinal
These
range
PM
Fig.
showing
the
by creep loading.
disc. Some cadaveric
discs can
posteriorly
by loading
them
in
and compression.
Of61 motion
AM
Diagrams
Also, the
stresses
in the morning.
before
creep
to bending
is
for the disc
is 85%
R. W. PORTER
similar
movements
discs resist a higher
by 2#{176}
or 3#{176}
(Adams
et
to about
12.5#{176}extra
lumbar
spine.
At the
physiological
limit of flexion
(as determined
loading)
the motion
segment’s
resistance
reduced
by about
70% (Fig. 1). The reduction
measured
W. C. HUTFON,
creep
loading
can
on the lower margins
joint
surfaces
(Dunlop,
capsule
(Yang
and King
properties.
Creep
loading
motion
segment’s
range
of flexion
al 1987)
which
is equivalent
movement
for the whole
of the
and ligaments,
respectively.
P. DOLAN,
be
attributed
pulposus.
injecting
then
to
the
posture
If the
fluid
saline)
there
or
is a
changes
results
corresponding
increase
or decrease
in the disc’s resistance
to bending
(Andersson
and Schultz
1979 ; Dolan,
Adams
and Hutton 1987).
These results
indicate
that, inlife,
flexion
movements
DIURNAL
and
of the
in order
mobifity.
back
VARIATION
It is possible
and
abdomen
to compensate
in the underlying
from our laboratory
for
spine.
show
may
some
that,
modify
of the
in vivo,
spinal
diurnal
However,
unpublished
that the lumbar
lordosis
increases
by about
3#{176}
during
the day. This would
increase
the loading
of the apophysial
joints
and compound
the
effects
due to loss of disc height.
It could be thought
that the higher
bending
stiffness
ofthe
osteoligamentous
spine in the early morning
would
THE JOURNAL
OF BONE
AND
JOINT
SURGERY
DIURNAL
be offset
bending,
CHANGES
IN SPINAL
MECHANICS
by the trunk
muscles
restricting
the range
of
so that the bending
stresses
on the spine remain
AND
THEIR
We
anics
CLINICAL
suggest
SIGNIFICANCE
that
are ofclinical
diurnal
269
variations
significance.
in spinal
Since
different
mech-
structures
the same.
However,
the experimental
evidence
suggests
that this does not happen
to any significant
extent.
In
vivo, the range
of lumbar
flexion
is reduced
by only 5#{176}
in
are more heavily
loaded
at different
times of the day, the
time of onset
of a patient’s
symptoms,
and any diurnal
changes
in their
degree
of severity,
might
help
us to
the early morning
(Adams
et a! 1987) whereas
the range
of flexion
of the underlying
spine
is reduced
by about
12.5#{176}before
creep
loading
(see
above).
Calculations
comparing
the in vivo and in vitro evidence
suggest
that,
in life, bending
stresses
on the lumbar
discs and ligaments
understand
can be increased
the early morning
The
movement
by about
(Adams
slight
diurnal
in vivo may
‘warm-up’
(Baxter
observed
in
hip
300% and 80%
et a! 1987).
variation
be partly
1987).
movements
though
there
is unlikely
mechanical
properties
of
normnal
articular
like the disc.
cartilage
has
(Adams
et a!
1987)
to be any
variation
the underlying
joints,
swell
up
been
even
in
the
since
overnight
spinal
injury
little
published
information
symptoms
and signs,
nor in
pain. Varma
(1987) recorded
of back pain occurred
in the
day. This
who
found
more
agrees
with
that
mine
commonly
pathophysiology
of different
back
pain
I lists some
of the structures
thought
to be
for low back pain and sciatica,
and indicates
are most heavily
loaded.
The disc resists
all of
the compressive
force on the spine
in the morning,
and
in addition,
is much
more
highly
stressed
during
flexion
and extension
movements.
A herniated
disc,
however,
may behave
The posterior
the morning
a study
workers
differently
from one with an intact
annulus.
longitudinal
ligament
is stretched
more in
because
of the increased
height
of the disc,
although
reduced
radial bulging
ofthe
disc will counteract
this effect
to some extent.
Vertebral
body end-plates
can
be ruptured
by increasing
the fluid content
of the nucleus
pulposus
of the working
et a! (1980)
sustained
effect
not
in
of spinal
to muscle
similar
does
Low back
pain. There
is
about
diurnal
variations
in
the time ofonset
oflow
back
that 47% of ‘first episodes’
early part
by Evans
A
Table
responsible
when they
respectively
in the range
attributable
the
syndromes.
(Jayson,
Herbert
The
morning
segmental
because
they are compressed
bulging
of the
intervertebral
in the morning.
and
Barks
1973)
that
the end-plates
are more
highly
morning
when the discs are swollen
with
so it is likely
stressed
fluid.
nerve roots are stretched
the spine
is about
19 mm
more
disc,
in the afternoon
the
reduced
by
foramen,
and
by
more
in the
longer;
but
by extra radial
height
of the
the
buckling
this timejoint
the capsular
variation
nous ligaments
will all be most stretched
during
forward
bending
movements
performed
in the early
morning
because
the increased
disc height
allows
them less slack.
injuries.
DISCUSSION
The
experimental
evidence
can
be
summarised
as
follows
: with creep
loading,
the intervertebral
discs lose
height,
bulge
more,
become
stiffer
in compression
and
more
flexible
in bending.
Disc
tissue
becomes
more
elastic
as its water
content
is reduced,
and its affinity
for
water
increases.
Disc prolapse
becomes
less likely.
The
neural
arch
proportion
acting
Figure
and associated
ligaments
resist an increasing
of the compressive
and
bending
stresses
on the spine.
These
results
are summarised
2.
In life, these
changes
will occur
mostly
in the
few hours
of the
ofthe
changes
day,
will
but the time
depend
upon
scale
the
and
throughout
the
spinal
mechanics
changes.
VOL. 72-B.
No. 2, MARCH
1990
day
spinal
in
at
pain may be expected
to increase.
However,
ligaments
and the supraspinous
and interspi-
we
attempt
clinical
symptoms
to understand
studies
into the
and
signs
could
more
diurnal
about
spinal
changes
of
be rewarding.
REFERENCES
first
Adams
minor
diurnal
MA,
Hutton
apophysial
Bone
of loading
probably
cause
similar
to the
are
especially
bending,
and
This work
was supported
by the Arthritis
and Rheumatism
Council,
Action
Research
for the Crippled
Child
and the Back Pain Association.
No benefits
in any form
have
been
received
or will be received
from a commercial
party
related
directly
or indirectly
to the subject
of
this article.
the magnitude
severity
in the afternoon,
during
backward
surfaces
in
on the spine : heavy
labour
will have a greater
effect,
and
in less time, than sedentary
activity.
The swelling
pressure
results
suggest
that the effects
of intense
loading
will be
reversed
more
rapidly
than
the effects
of less intense
activity
of longer
duration.
Alternating
periods
of rest
and activity
changes
in
As
pathology,
joint
the
trends
due to changes
in spinal
mechanics
and they must
be taken
into consideration
in any surveys
of diurnal
closer
together
postures
and
apophysial
of
ligamentum
pressed
lordotic
The
the
Accidents
in general
tend to become
more frequent
towards
the end of a working
shift, when people
are tired
and
inattentive.
These
effects
will tend
to mask
any
in spinal
flavum.
in
joints
Joint
Surg
WC.
in
[Br]
The
resisting
1980;
effect
of posture
on the
intervertebral
compressive
62-B :358-62.
Adams
MA, Hutton
WC. Prolapsed
injury. Spine 1982; 7:184-91.
Adams
MA,
lumbar
Hutton
WC.
intervertebral
Adams
MA, Dolan
thelumbarspine.
Adams
MA,
Dolan
bending. Spine
Andersson
The
effect
discs.
P, Hutton
Spine
intervertebral
WC.
1987;
Spine
GB, Schultz
AB.
properties
of intervertebral
of the
forces.
J
: a hyperfiexion
of posture on the fluid content
1983; 8:665-71.
Diurnal
12:130-7.
P, Hutton
WC.
1988; 13:1019-26.
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