Neurological Evaluation Of The Lumbar Nerve Roots

Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

Neurological Evaluation of Lumbar Nerve Roots

Overview

Assessment of a lumbar nerve root is based on three components:

Sensory changes + Motor changes + Reflex changes

roots from L1 to S1 and correlates them with the corresponding disc level.

1. L1 Nerve Root

Disc level

T12–L1 disc herniation – L1 nerve root

Sensory

The L1 sensory area is described as:

Halfway between the inguinal ligament and mid-thigh

Motor

Hip flexion

Main muscle mentioned:

• Iliopsoas

Root contribution stated:

• L1, L2, L3

Reflex

• No specific reflex for L1

2. L2 Nerve Root

Disc level

L1–L2 disc herniation – L2 nerve root

Sensory

Mid-anterior thigh

Motor

• Hip flexion — L1, L2, L3
• Hip adduction — L2, L3, L4
• Knee extension — L2, L3, L4

Reflex

• No specific reflex for L2

3. L3 Nerve Root

Disc level

L2–L3 disc herniation – L3 nerve root

Sensory

Distal thigh, including the knee region

Motor

• Hip flexion — L1, L2, L3
• Hip adduction — L2, L3, L4
• Knee extension — L2, L3, L4

Reflex

• No specific reflex for L3

4. L4 Nerve Root

Disc level

L3–L4 disc herniation – L4 nerve root

Sensory

Medial side of the leg extending down to the medial side of the foot

Motor

The important movements emphasized are:

• Ankle dorsiflexion
  • Tibialis anterior
• Knee extension

Femoral Stretch Test

associates a positive femoral stretch test with L4 nerve-root involvement.

Positive test

Pain in the ipsilateral anterior thigh

Positive femoral stretch test – consider L3–L4 disc herniation affecting L4

Reflex

Patellar reflex — mainly L4

5. L5 Nerve Root

Disc level

L4–L5 disc herniation – L5 nerve root

emphasizes that L5 is particularly important in examinations and clinical scenarios.

Sensory

Dorsum of the foot and adjacent leg

Quick localization:

Top of the foot = L5

Motor

Great-toe extension

The major motor finding emphasized is:

Great-toe extension = L5

Therefore, weakness of great-toe extension in the appropriate clinical setting suggests:

L4–L5 disc herniation – L5 root involvement

Hip abduction

also associates L5 with:

• Gluteus medius
• Gluteus minimus

Weakness may produce:

Trendelenburg gait

Straight Leg Raise

SLR may be positive with L5 nerve-root irritation.

The test is used to identify whether low-back pain may have a component of:

Disc herniation irritating a nerve root

Reflex

No specific reflex for L5 is emphasized in the transcript.

6. S1 Nerve Root

Disc level

L5–S1 disc herniation – S1 nerve root

Sensory

Lateral and plantar aspect of the foot

Quick localization:

Lateral foot = S1

Motor

Hip extension

Muscle:

• Gluteus maximus

notes that this is not commonly used as the main clinical test.

Ankle plantar flexion

This is the clinically emphasized motor test.

Muscles:

• Gastrocnemius
• Soleus

Thus:

S1 – ankle plantar flexion

Foot eversion

Muscles mentioned:

• Peroneus longus
• Peroneus brevis

Straight Leg Raise

A positive SLR may also occur with S1 nerve-root irritation.

refers to this as a stretch test used when disc-related radiculopathy is suspected.

Reflex

Ankle reflex = S1

High-Yield Root Localization Table

Root	Disc level	Sensory area	Motor finding	Reflex
L1	T12–L1	Upper anterior thigh / between inguinal ligament and mid-thigh	Hip flexion	None
L2	L1–L2	Mid-anterior thigh	Hip flexion, hip adduction, knee extension	None
L3	L2–L3	Distal thigh / knee region	Hip flexion, hip adduction, knee extension	None
L4	L3–L4	Medial leg – medial foot	Ankle dorsiflexion, knee extension	Patellar
L5	L4–L5	Dorsum/top of foot	Great-toe extension, hip abduction	None emphasized
S1	L5–S1	Lateral + plantar foot	Plantar flexion, eversion	Ankle

Most Important Roots for Clinical Examination: L4, L5, S1

specifically highlights these three roots.

Motor

Root	Best motor finding emphasized
L4	Ankle dorsiflexion
L5	Great-toe extension / hip abduction
S1	Ankle plantar flexion

Sensory

Root	Sensory landmark
L4	Medial foot
L5	Dorsum/top of foot
S1	Lateral foot

Reflexes

Root	Reflex
L4	Patellar reflex
L5	No specific reflex emphasized
S1	Ankle reflex

Provocative Tests

Femoral Stretch Test

associates this predominantly with:

L4 nerve-root irritation

Positive when there is:

Ipsilateral anterior-thigh pain

Straight Leg Raising Test

Associated particularly with:

• L5
• S1

A positive test supports the possibility of a herniated disc causing nerve-root irritation.

Disc Level – Nerve Root

gives the following straightforward relationship:

T12–L1 – L1
L1–L2 – L2
L2–L3 – L3
L3–L4 – L4
L4–L5 – L5
L5–S1 – S1

Practical Neurological Examination

For a patient with suspected lumbar radiculopathy:

1. Sensory examination
   Determine the dermatomal area involved.
2. Motor examination
   Test the corresponding movement/muscle.
3. Reflex examination
   Especially:

• Patellar reflex – L4
• Ankle reflex – S1

4. Nerve stretch tests

• Femoral stretch – upper lumbar/L4 pattern
• SLR – L5/S1 pattern

5. Correlate with the suspected disc level

Key Take-Home Points

• Every lumbar root should be assessed using sensory + motor + reflex findings.
• L4 – medial foot + ankle dorsiflexion + patellar reflex.
• L5 – dorsum of foot + great-toe extension + hip abduction.
• S1 – lateral/plantar foot + ankle plantar flexion + ankle reflex.
• Trendelenburg gait may occur with L5-associated gluteus medius/minimus weakness in ‘s framework.
• Femoral stretch test may be positive with L4 root irritation.
• SLR may be positive with L5 or S1 nerve-root irritation.
•  considers L4, L5 and S1 the three most important roots for routine clinical examination.

Exam Pearls

L4 = medial foot + dorsiflexion + knee jerk

L5 = dorsum of foot + great-toe extension + Trendelenburg/hip abductor weakness

S1 = lateral foot + plantar flexion + ankle jerk

L4–L5 disc – L5 root

L5–S1 disc – S1 root

Femoral stretch – think L4

SLR – think L5/S1