Low back pain is a very common presentation
that physicians are encountered with.
When you have low back pain, on your
differential is usually herniated disc.
So, in the lumbar spine,
herniated disc is a very common occurence.
It's actually one of the more frequent occurences
other than in the cervical spine at C5, C6.
So, our intervertebral disc consist of the
annulus fibrosus and the nuclues pulposus.
The annulus is a fibrous ring and it's
consist of interlocking crosshatch fibers.
And what happens is when you
rotate right and left,
those fibers will actually
compress and get tighter.
It's also attached to the anterior
and posterior longitudinal ligament.
The anterior ligament is really wide and broad
and covers the anterior portion of the disc.
Whereas the posterior longitudinal ligament
tends to be a little bit more narrow and thin.
This increases the risk of a posterior and lateral
herniation which is the most common type of herniation.
The annulus fibrosus is
also concave posteriorly.
Your nucleus pulposus is in the center.
This is made from the notochord.
It's surrounded by the annulus and it
has reciprocal motion characteristics.
There's high water content there.
It's compressible and it relies on this
pressure that you have when you move
and compress and decompress throughout
the day for nutrient and waste exchange.
So that reciprocal motion at the nucleus
pulposus is that when I flex forward,
that pulposus is actually
And when I extend, that nucleus
pulposus is driven anteriorly.
So the most common cause of
a herniated disc
is flexing forward with your back and
adding a stress or load to the spine.
So lifting something heavy and lifting up or
actually lifting something heavy and twisting
is really the worst motion and
adds the most pressure to the back
causing a potential herniated disc.
The lumbar spine has the nerve roots
L1 to L5 passing through it.
This is important because it innervates most of the
back and the lower extremities and the visceral organs,
and a herniated disc could
potentially compress on those nerves
When you think of a disc herniation,
it's important to know
what level that disc herniation is occuring
and what nerve is being compressed.
So when you're evaluating a patient,
you're looking for key signs and symptoms
and aspects of your physical exam which helps you
to localize which nerve root is being compressed.
So if I have a disc herniation
between two segments,
it would usually herniate and entrap
the nerve root of the segment below.
So in this case, in the image you could see
how if I have a disc bulge between L4 and L5,
it will compress the L5 nerve root
because the L4 nerve root
has already exited the spinal column
away from the disc above it.
So, in order to assess if there
is a neurologic deficit,
there's many different types of testing
that we could do.
The most common things that we check to
make sure that the nerve root is intact
or that the nerve is working well
is to perform 3 main steps.
The first step is to check sensation.
So, these nerves innervate our skin
and specific areas of the body will
correlate with specific nerve roots.
So, in checking sensation, we could look
to see if there's a loss of sensation
to tell us if there's a compression or irritation
that's compromising the nerve activity.
Reflexes could also be tested.
Certain reflexes will correlate
with specific nerve roots.
The patellar reflex checking to see if your patella
tendon reacts to a stretch is a testing for L4.
Your achilles reflex is testing S1.
Different nerve roots innervate muscles
and so you could see
associated muscle weakness when a
certain nerve root is weakened.
A lot of our muscles actually have
a mixed innervation, multi-levels.
So certain muscles could be a little bit more
specific for key nerve roots but sometimes
you may have a mixed pattern, so you may
not see, necessarily note a lot of strength,
lack of strength or weakness unless
it's a very severe compression.
Straight leg raising is a test
that you see in the image here.
Straight leg raising is a special test where
we are applying a stretch on those nerves
to see if that stretch will cause an irritation,
so it is applied with the patient lying supine
and you slowly bring the leg straight up
in flexion to about 70 degrees.
If the patient could do that without pain,
that's usually a negatve test.
If they're unable to tolerate that
straight leg raise before they reach 70 degrees
and they're having pain that shoots down the leg,
not just tightness or pain behind the knee
because of hamstring tightness,
then that is a positive test.
So a positive test is shooting pain
really going down the leg
or like a numbness and tingling sensation.
If you are not sure if someone
or pretending to have back pain
due to secondary gain,
what you could do is you could also perform
this test with the patient seated.
So as they're seated, slowly straighten out their
leg and this is actually going to give you
the same amount of leg flexion as you
extend the knee so the leg is straight.
And if they have the pain
when they're lying supine,
they should also have the pain
when they're seated.
If they're malingering, then they might
know the test to do the straight leg
but not show the same reaction of pain
when you straighten out their leg
when they're in a seated position.
Here is the dermatomes.
As you could see, the dermatomes
are overlapping at certain points.
So in order to be the most specific, you wanna
test key areas especially for the lumbar spine.
So the lower lumbar segments tend to be the
ones that are compressed the most often.
So typically, we're trying to
differentiate between L4, L5 and S1.
So looking at the foot,
if we are testing for L4, L5 and S1,
you could look at the foot and check
the medial foot for L4, the top of the
foot for L5 and the lateral foot for S1.