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Examination of L2 to S1 Nerve Roots

Muscle Strength Tests The L2 nerve root is best tested by assessing the iliopsoas muscle. Ask the patient to flex the hip, place one hand over the knee, and ask the patient to maintain hip flexion as you press downward. Note the strength of hip flexion and compare it with the opposite side.

The L3 nerve root is best tested by examining the quadriceps. Ask the patient to extend the knee, place one hand under the knee for support, and ask the patient to maintain knee extension as you press downward at the ankle. Note the strength of knee extension and compare it with the opposite side.

The L4 nerve root is best examined by testing the tibialis anterior muscle. Ask the patient to dorsiflex both ankles, place your hands on the top of the feet, and ask the patient to maintain ankle dorsiflexion as you press downward. Compare the strength of dorsiflexion on each side.

The L5 nerve root is best examined by testing the extensor hallucis longus muscle. Ask the patient to extend both great toes, place your thumbs over each distal phalanx, and ask the patient to maintain toe extension as you press downward. Compare the strength of extension on each side.

The S1 nerve root is best examined by testing the gastrocnemius and soleus muscles. Ask the patient to plantarflex both ankles, hold the feet, and ask the patient to maintain ankle plantar flexion as you pull upward. Compare the strength of plantar flexion on each side.

Sensory Tests There are key sensory areas in the lower extremities that are indicative of specific nerve roots. The sensory test is performed on each side simultaneously to assist with the comparison.
With the patient's eyes closed, touch each of the key sensory areas and ask the patient to report if they can feel the touch and whether they experience the same sensation on both sides. The key sensory areas are: For L2, over the middle part of the anteromedial thigh; for L3, over the medial femoral condyle above the knee, for L4, over the medial malleolus, for L5, over the third metatarsophalangeal joint on the dorsum of the foot,  and for S1, over the lateral heel.

S2 to S5 "Saddle Area" In patients presenting with back pain, it is essential to check for "saddle" anesthesia by touching the buttocks on both sides of the superior gluteal cleft. Sensory loss in this region is suggestive of cauda equina damage and is considered a medical emergency, requiring referral for immediate specialist assessment.

Muscle Stretch Reflexes Muscle stretch reflexes are used to assess the L4 and S1 nerve roots. Each reflex is compared with the opposite side. If the reflex is difficult to obtain, the test can be repeated with the patient clenching their teeth and clasping their hands together while attempting to pull them apart.

To assess the L4 nerve root, test the patellar reflex.
To assess the S1 nerve root, test the Achilles reflex.