Neurological Evaluation of the Lumbar Nerve Roots

 

To study the involvement of any nerve root we look for sensory change, motor changes, reflex changes. A herniated disc at T12-L1 affects the L1 nerve root. The sensory of the L1 nerve root is half the distance between the inguinal ligament and mid-thigh. Motor involvement is hip flexion. There are no reflexes of L1. A herniated disc at L1-L2 affects the L2 nerve root. The sensory of the L2 nerve root is mid-anterior thigh. Motor involvement is hip flexion, hip adduction, and knee extension. There are no reflexes of L2. A herniated disc at L2-L3 affects L3 nerve root. The sensory of the L3 nerve root is distal part of the thigh including the knee area. Motor involvement is hip flexion and knee extension. A herniated disc at L3-L4 affects the L4 nerve root. The sensory of the L4 nerve root is medial side of the leg down to the medial side of the foot. Motor involvement is L4 ankle dorsiflexion (tibialis anterior) and knee extension. L4 reflex changes will be a positive femoral stretch test. The test is positive if pain is felt in the ipsilateral anterior thigh. If the test is positive, it means that there is probably a disc herniation between L3-L4, affecting the L4 nerve root. The patellar reflex is mainly L4. A herniated disc at L4-L5 affects the L5 nerve root. The sensory of the L5 nerve root is dorsum of the foot and leg. Motor involvement is hip abduction (gluteus medius) and extension of the big toe. L5 nerve root is very popular in the exam. If you see a big toe extension, this involves the L5 nerve root (L4, L5 disc herniation). The patient may have Trendelenburg gait due to injury to the L5 nerve root (disc herniation between L4, L5 affecting the L5 nerve root). Both the gluteus medius and minimus muscles are innervated by the L5 nerve root. Straight leg raise can be positive with L5 nerve root irritation. This test is used to determine if the patient with low back pain has an underlying herniated disc irritating the nerves. A herniated disc at L5-S1 affects the S1 nerve root. The sensory of S1 nerve root is lateral and plantar aspects of the foot. Motor involvement is S1 hip extension (gluteus maximus), S1 ankle plantar flexion (gastro-soleus), and S1 foot eversion (peroneus longus and peroneus brevis). Positive straight leg raise examination to determine whether patient with low back pain has an underlying component of a herniated disc or not (stretch test). Reflexes are S1 ankle reflex.