Sciatica is the pain along the sciatic nerve. The sciatic nerve starts from the nerve roots of the fourth, fifth lumbar vertebra and the first two sacrums.
It gives motion to the muscles of the lower limb and receives cutaneous sensation from the tibia and of the limb.
The slipped disc of the fourth or the fifth lumbar disk can push significantly the sciatic nerve roots and give us areas with impaired sensation in the lower limb and muscle atrophies with difficulty in walking.
The examination of the sciatic nerve, is done with the patient lying down and lifting the lower limb from the horizontal position. If there is a problem in the sciatic nerve, the elevation of the lower extremity above 20 or 30 degrees, creates pain in the back.
Many times the pain of the lower back Pain that extends into the buttock is incorrectly considered to be sciatic.
Sensory mapping of the sciatic nerve roots of lower limbs
In the picture, we see the sensory mapping of lumbar roots of the lower limbs where L1 is the first lumbar L2, the second, etc. Thus, if you have impaired sensation in the lower limb, with the indication L4, it means that the lesion is found in the fourth lumbar vertebra.
Usually, the MRI of the lumbar spine can show us multiple views of the disks, but when combined with a good clinical examination of the patient, it will show us which disk creates a problem and which does not.