is less accurate in defining these vertebral
relationships. Why may this be important clinically?
Well, if you want to perform a lumbar puncture,
you want to make sure that the needle that’s
utilized in this procedure is well below the
termination of the spinal cord. The needle
is typically introduced between L3 and L4
or just inferior to that at the level of L4, L5.
So, if we take a look at the next slide, we
see an illustration of a lumbar puncture and
the clinically applied anatomy. So, what will
happen is the patient will be on their side
and they will be in the foetal position thereby
flexing their back. This then will allow for
separation of the posterior vertebral arch
components and will more readily receive the
needle that is being advanced between the
vertebral components to enter the subarachnoid
And so, as we see here, we see the needle.
It’s a little bit perhaps off from the midline.
But, here is your supraspinous ligament. It’s
a little bit to the right here. So, the needle
has advanced through the interspinous ligament.
It then went between the narrow gap between
the ligamentum flavum on this side and the
one on the opposite side. But, it could go
through the ligamentum flavum if you’re
a little bit deviated to the right or left
of the midline. It then enters the vertebral
canal and then punctures the dura mater and
the arachnoid mater. And now, the needle is
in the subarachnoid space well below the termination
of the spinal cord. And so, you simply see
the nerve roots that constitute the horse’s
tail known as the cauda equina. Pull back
on the syringe plunger and cerebral spinal
fluid could then be readily obtained.