Radicle is a medical term for a spinal nerve root as it comes out of the spinal dural sac and goes through its exit canal between two vertebrae. Pathology is an abnormality of body structure. So radiculopathy indicates an abnormality in a nerve root. How do you tell it’s the nerve root and not the nerve? Close to where they exit the spine, nerve roots join up, then mix and mingle with other nerve roots in a plexus before the individual nerves come off, each nerve having components of various nerve roots.

However, each nerve root has an autonomous zone that only it supplies. The L4 root activates the quadriceps muscle, receives pain sensation from an area just below the front of the knee and the knee-jerk reflex is carried to and from the spinal cord via the L4 root. The L5 root activates muscles that raise the front of the foot and toes and/or turn the foot inward, carries pain from the big toe, and carries the reflex on the inside of the ankle (the posterior tibial reflex). The S1 root activates the calf muscles (raises the heel), carries pain from the little toe and the ankle-jerk reflex.

These specific changes are often not apparent to a person with back and leg pain due to a herniated disc except in cases of severe weakness such as a foot drop. It takes careful examination with a safety pin to detect decreased pin-prick sensation over only one autonomous zone. Likewise with muscle strength and reflex testing. Finding just one of these changes in only one autonomous zone greatly increases the likelihood of a diagnosis of HNP. I will show the evidence for that in the next post.

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