What are the nerve roots involved in sensory, motor function, and deep tendon reflexes for lumbar 4 (L4), lumbar 5 (L5), and sacral 1 (S1)?

From the Guidelines

The nerve roots L4, L5, and S1 have specific distributions for sensory, motor involvement, and deep tendon reflexes, which are crucial for localizing lesions during neurological examinations. The L4 nerve root is associated with:

• Sensory involvement: medial leg and knee
• Motor involvement: quadriceps and tibialis anterior muscles
• Deep tendon reflex: patellar (knee jerk) reflex 1 The L5 nerve root is associated with:
• Sensory involvement: lateral leg, dorsum of the foot, and first web space
• Motor involvement: extensor hallucis longus and hip abductors
• Deep tendon reflex: none specific, but can be evaluated through great toe and foot dorsiflexion strength 1 The S1 nerve root is associated with:
• Sensory involvement: lateral foot and sole
• Motor involvement: gastrocnemius and hamstrings
• Deep tendon reflex: Achilles (ankle jerk) reflex 1 These distributions are essential for identifying which nerve root is affected in cases of radiculopathies, peripheral neuropathies, and other neurological conditions affecting the lower extremities. Key points to consider during a neurological examination include:
• Evaluating knee strength and reflexes for L4 nerve root dysfunction
• Assessing great toe and foot dorsiflexion strength for L5 nerve root dysfunction
• Evaluating foot plantarflexion and ankle reflexes for S1 nerve root dysfunction 1

From the Research

Nerve Roots and Their Functions

The nerve roots for sensory, motor involvement, and deep tendon reflexes for L4, L5, and S1 are as follows:

• L4:
  • Sensory: medial aspect of the lower leg, medial malleolus, and the first and second toes 2, 3
  • Motor: hip flexion, knee extension, and ankle dorsiflexion 2, 3
  • Deep tendon reflexes: knee jerk reflex 3
• L5:
  • Sensory: lateral aspect of the lower leg, dorsum of the foot, and the third and fourth toes 2, 3
  • Motor: hip abduction, knee flexion, and ankle dorsiflexion and eversion 2, 3
  • Deep tendon reflexes: none specifically associated, but may be involved in the ankle jerk reflex 3
• S1:
  • Sensory: posterior aspect of the lower leg, lateral malleolus, and the fifth toe 2, 3
  • Motor: hip extension, knee flexion, and ankle plantarflexion 2, 3
  • Deep tendon reflexes: ankle jerk reflex 3

Clinical Relevance

Understanding the nerve root involvement is crucial for diagnosing and treating radiculopathy, as seen in studies 4, 5, 6. The distribution of pain and neurological findings can help clinicians determine the affected nerve root. However, the overlap in pain patterns and the complexity of nerve root anatomy can make diagnosis challenging 4, 5.

Nerve Root Innervation

The innervation of muscles and skin in the lower extremity is determined by the lumbosacral plexus, with each nerve root contributing to specific functions:

• L4: contributes to the femoral nerve and the obturator nerve 2, 3
• L5: contributes to the peroneal nerve and the tibial nerve 2, 3
• S1: contributes to the tibial nerve and the sural nerve 2, 3