The L5 nerve root arises from the spinal canal, it is part
of the lumbosacral plexus. It is also part of the sciatic nerve. The L5 nerve
root supplies the muscle that allows extension of the toes and dorsiflexion of
the ankle. It is also responsible for supplying sensation to the dorsum of the
foot and leg. When the L5 nerve root gets involved, you will have sciatica with
a positive straight leg raising. Straight leg raising (tension sign) occurs
from L5-S1 involvement. The tension sign
produces pain and paresthesia in the leg at 30-70 degrees of hip flexion. Injuries to the L5 nerve root include
intervertebral disc herniation, spondylolisthesis, sacral fractures and
sacroiliac joint injury. In
intervertebral disc herniation the L5 nerve root involvement can cause
Trendelenburg gait due to posterolateral disc herniation. This is because it
affects the gluteus medius and minimus. Trendelenburg gait can also occur with
L5-S1 foraminal disc herniation. Posterolateral disc herniation affects the
transversing or the descending nerve root at the level of L4-L5 (affects the L5
nerve root). Foraminal disc herniation, which is far lateral or the extra
foraminal, affects the exiting nerve root or upper nerve root (L5-S1 will
affect L5 nerve root). The lumbar disc herniation affects L 4-L5, and L5- S1
level in about 95% of the time and it will involve the L5-S1 nerve roots. In
general, the L5 nerve root involvement will cause weakness with hip abduction,
big toe extension, and ankle dorsiflexion.
If there is a sacroiliac joint injury, the lumbosacral plexus can be
injured. That will predominately affect the L5 nerve root causing the patient
to have foot drop. When doing surgery on the sacroiliac joint, and the surgeon
goes anteriorly to fix the injury and places a retractor in the anterior aspect
of the sacrum, the L4-L5 nerve roots can be injured. These nerves are about 1
cm medial to the sacroiliac joint at it inferior part. In displaced sacral
fracture, the L5 nerve root can be injured especially if it is a fracture of
the ala of the sacrum which occurs about 5% of the time. With degenerative
spondylolisthesis, the vertebra do not slip a lot. Degenerative
spondylolisthesis occurs at L4-L5, occurs more often in females and involves
the L5 nerve root. In isthmic spondylolisthesis,
if it occurs at L5-S1, it may involve the L5 nerve root and cause hamstring
tightness. Spondylolysis is a fracture
of the Pars interarticularis. With isthmic spondylolisthesis the vertebra is
slipped and it may slip a lot.
