Examination Of L4 Nerve Root

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

 

L4 Nerve Root Examination

Overview

Examination of any nerve root has three components:

Sensory examination – Motor examination – Reflex examination

For L4,  emphasizes:

• Sensation: medial side of the foot
• Motor: mainly tibialis anterior for ankle dorsiflexion; quadriceps can also reflect L4 function
• Reflex: patellar tendon reflex

1. Sensory Examination

lower-limb sensory sequence as:

• L4 – medial side of the foot
• L5 – dorsum/top of the foot
• S1 – lateral aspect of the foot

L4 Sensory Area

Medial side of the foot

Quick Recall

L4 medial – L5 dorsum – S1 lateral

2. Reflex Examination

Patellar Reflex / Knee Jerk

The patellar tendon reflex is supplied by:

L2, L3, L4

but states it is predominantly an:

L4 reflex

Therefore, an L4 lesion may produce:

• Reduced knee jerk
• Absent knee jerk in more significant involvement

Viva Pearl

L4 – patellar reflex

3. Motor Examination

Tibialis Anterior

uses tibialis anterior as the practical muscle for testing L4.

Functions mentioned:

• Ankle dorsiflexion
• Foot inversion

Therefore:

Ask the patient to dorsiflex the ankle against resistance.

Weakness suggests L4 involvement in the speaker’s framework.

Quadriceps

The quadriceps receives innervation from:

L2, L3, L4 via the femoral nerve

emphasizes that L4 is an important/predominant contribution.

Therefore quadriceps weakness may suggest:

• L4 nerve-root involvement
• Femoral nerve involvement

Functional Clue

The patient may have:

Difficulty squatting due to quadriceps weakness

4. L4 Motor Summary

Muscle	Function	Root emphasis in transcript
Tibialis anterior	Ankle dorsiflexion, inversion	L4
Quadriceps	Knee extension	L2–L4, especially L4

Practical Examination

L4 motor – test ankle dorsiflexion with tibialis anterior

5. Foot Drop

If the patient has foot drop,  notes that:

Tibialis anterior may not be functioning properly.

Because uses tibialis anterior as an L4 motor muscle, foot drop should prompt evaluation of this muscle and the relevant neurological level.

6. L3–L4 Disc Herniation

distinguishes posterolateral and foraminal/far-lateral disc herniation.

Posterolateral L3–L4 Disc Herniation

This affects the:

Traversing L4 nerve root

So:

L3–L4 posterolateral disc – L4 root

notes that this level of posterolateral disc herniation is relatively uncommon.

Foraminal L3–L4 Disc Herniation

This affects the:

Exiting L3 nerve root

Therefore:

L3–L4 foraminal disc – L3 root

7. Provocative Test

In upper lumbar nerve-root involvement around L3–L4,  says the patient may have:

Positive femoral nerve stretch test

while the:

Straight leg raise may not be positive

Exam Pearl

L3/L4 region – femoral stretch more useful than SLR

8. L4–L5 Disc Herniation

Posterolateral L4–L5 Disc

A posterolateral disc herniation at L4–L5 affects:

L5 nerve root

This may produce:

• Weakness of toe extension / great-toe extension
• Sensory change over dorsum of foot

Far-Lateral L4–L5 Disc

A far-lateral/foraminal L4–L5 disc affects the:

Exiting L4 nerve root

Therefore:

L4–L5 posterolateral – L5

L4–L5 far lateral – L4

9. Disc–Root Relationship

Disc level / location	Root affected
L3–L4 posterolateral	L4 traversing root
L3–L4 foraminal	L3 exiting root
L4–L5 posterolateral	L5 traversing root
L4–L5 far lateral	L4 exiting root

This is one of the most important concepts in .

10. Complete L4 Root Syndrome

According to the speaker, L4 nerve-root irritation may produce:

Sensory

• Decreased sensation over the medial side of the foot

Motor

• Weak ankle dorsiflexion
• Quadriceps weakness may occur

Reflex

• Reduced patellar reflex

Functional

• Difficulty squatting because of quadriceps weakness

High-Yield L4 Examination Table

Component	L4 finding
Sensory	Medial side of foot
Motor	Tibialis anterior — ankle dorsiflexion
Additional motor	Quadriceps — knee extension
Reflex	Patellar tendon reflex
Functional problem	Difficulty squatting
Provocative test	Femoral nerve stretch may be positive
Posterolateral disc causing L4	L3–L4
Far-lateral disc causing L4	L4–L5

Key Take-Home Points

• Any nerve-root examination includes sensory, motor and reflex testing.
• L4 sensation = medial foot in this transcript.
• L4 reflex = patellar tendon reflex.
• practically tests L4 using tibialis anterior and ankle dorsiflexion.
• Quadriceps is supplied by L2–L4, with L4 strongly represented in .
• Posterolateral L3–L4 disc – traversing L4 root.
• Far-lateral L4–L5 disc – exiting L4 root.
• Femoral stretch may be positive in L3/L4 root irritation.
• Quadriceps weakness may make squatting difficult.

Exam Pearls

L4 = medial foot + dorsiflexion + knee jerk

L3–L4 posterolateral disc – L4

L4–L5 far lateral disc – L4

Femoral stretch – think upper lumbar roots

Difficulty squatting – check quadriceps / L4