Lumbar Puncture – Topographic Back Anatomy

00:00 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.

00:28 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 space. And so, as we see here, we see the needle.

01:14 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.

01:29 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.