Why does a l5/s1 prolase impinge on the s1 nerve root and not the l5 nerve root?
The link below is the best picture I could find, sorry. Assume the lowest lumbar is L5 in the diagram. You will notice that the L5 nerve root exits BELOW the L5 pedicle but ABOVE the L5 intervertebral disc (remember in the lumbar spine the intervertebral disc and nerve are named for the verterba ABOVE it). Because of this, the L5 nerve root is unaffected. Now look in the spinal canal and you will see the S1 nerve root going inferiorly and anteriorly as it will exit the S1 foramen. The prolapse occurs posteriorly and will affect the S1 nerve root before it exits the spinal canal. Hope this helps.
