What does EHL (Extensor Hallucis Longus) stand for during a motor assessment of muscle power in the lower leg?

What Does EHL Stand For in Motor Assessment?

EHL stands for Extensor Hallucis Longus, the muscle responsible for extending (lifting) the big toe, and its assessment is a critical component of lower extremity neurological examination, particularly for detecting L5 nerve root pathology.

Clinical Anatomy and Function

• The EHL is a muscle in the anterior compartment of the leg that extends from the fibula and interosseous membrane to insert on the dorsal base of the distal phalanx of the great toe 1, 2.

• Its primary function is dorsiflexion (extension) of the great toe at both the metatarsophalangeal (MTP) and interphalangeal (IP) joints 2, 3.

Why EHL Assessment Matters

EHL weakness serves as a primary predictor of L5 nerve root radiculopathy, which commonly occurs with thoracolumbar fractures and disc herniation 1, 2. This makes it an essential part of the neurological examination when evaluating:

• Lumbar radiculopathy (especially L5 nerve root compression) 1, 2
• Deep peroneal nerve palsy 2
• Thoracolumbar spine trauma, where it contributes to ASIA (American Spinal Injury Association) classification 1

Proper Testing Technique

Test EHL strength at the MTP joint rather than the IP joint for maximum reliability and accuracy 2. The evidence strongly supports this approach:

• Testing at the MTP joint achieves 96.3% correct detection with perfect inter-observer reliability (κ = 1.00) 2
• Testing at the IP joint is significantly less reliable, with correct detection rates of only 32.5-61.5% and poor inter-observer agreement (κ = 0.28-0.69) 2

Testing Protocol:

• Position the patient's great toe with the MTP joint in neutral position 2
• Ask the patient to extend (lift) the big toe against resistance 2
• Grade strength using standard manual muscle testing (0-5 scale) 2
• Compare bilaterally for asymmetry 1

Clinical Significance in Neurological Recovery

• Serial EHL assessment helps monitor neurological recovery in thoracolumbar injuries, as lumbar or conus injuries demonstrate the greatest potential for neurologic improvement 1
• EHL function correlates with overall neurological status and bladder function recovery in spinal trauma patients 1
• No single test provides complete neurological assessment—EHL testing should be integrated with other motor, sensory, and reflex examinations 1

Common Anatomical Variants to Consider

Be aware that EHL has frequent anatomical variations that may affect clinical interpretation 3:

• Most EHL muscles possess one or more accessory tendinous slips inserting into neighboring structures 3
• These variants can complicate tendon transfer surgeries and may contribute to hallux deformities 3
• Rare double-origin variants from both tibia and fibula have been reported 4