Examination Of L5 Nerve Root

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

 

L5 Nerve Root Examination

Overview

Examination of any nerve root has three components:

Sensory examination – Motor examination – Reflex examination

For L5, :

• Sensory: dorsum/top of the foot
• Motor: great-toe extension, toe extension, hip abduction, medial hamstrings
• Reflex: no commonly used specific reflex

1. Sensory Examination

gives an easy sensory sequence:

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

L5 sensory area

Dorsum of the foot

Quick recall

L4 medial – L5 dorsum – S1 lateral

2. Reflex Examination

states:

There is no specific routinely used reflex for L5.

For comparison:

• L4 – patellar reflex
• S1 – Achilles reflex

So in L5 radiculopathy, diagnosis depends more heavily on:

• Sensory examination
• Motor examination
• Provocative tests

3. Motor Examination

lists several muscles with important L5 contribution.

Distal muscles

• Extensor hallucis longus
• Extensor digitorum longus
• Extensor digitorum brevis

The most useful practical test is:

Great-toe extension

Extensor Hallucis Longus

Function:

Extension of the great toe

Test by asking the patient to extend the great toe against resistance.

Viva Pearl

L5 – EHL – great-toe extension

Extensor Digitorum Longus

Function:

Extension of the lesser toes

Therefore weakness of toe extension may accompany L5 radiculopathy.

4. Proximal L5 Muscles:

• Gluteus medius
• Medial hamstrings:
  • Semimembranosus
  • Semitendinosus

Therefore, L5 radiculopathy may produce:

• Weak hip abduction
• Weak knee flexion
• Weak great-toe extension

5. Hip Abduction

The main muscles discussed are:

• Gluteus medius
• Gluteus minimus

They are supplied through the:

Superior gluteal nerve

L5 involvement may weaken hip abduction.

This can produce a:

Trendelenburg gait

6. Trendelenburg Gait

explains:

When the patient stands on the affected limb:

• The pelvis drops on the opposite side
• The trunk leans toward the affected side

The trunk lean acts as a compensatory mechanism.

Quick Recall

Stand on weak side – opposite pelvis drops – trunk leans toward weak side

7. Hamstring Examination

describes testing the medial hamstrings by allowing the lower limbs to hang freely and asking the patient to:

Flex the knee

Then palpate medially for contraction of:

• Semimembranosus
• Semitendinosus

These are discussed as having important L5 contribution.

contrasts this with the lateral hamstring:

Biceps femoris, which associates more with S1.

8. Ankle Dorsiflexion

states that L5 may also contribute to:

Ankle dorsiflexion

However, in framework, dorsiflexion is considered more predominantly an L4 action.

Therefore:

• L4 – tibialis anterior / ankle dorsiflexion
• L5 – especially great-toe extension

This distinction is useful clinically.

9. Clinical Features of L5 Radiculopathy

An L5 lesion may cause:

Sensory

• Decreased sensation over the dorsum of foot

Motor

• Weak great-toe extension
• Weak toe extension
• Weak hip abduction
• Weak knee flexion
• Possible ankle dorsiflexion weakness
• Possible foot drop

Gait

• Trendelenburg gait due to hip-abductor weakness
• Foot-drop gait if dorsiflexion weakness is significant

Reflex

• No specific routinely used L5 reflex

10. EMG Findings

states that L5 radiculopathy may show fibrillation/sharp-wave activity in L5-supplied muscles from proximal to distal, including:

• Gluteus medius
• Medial hamstrings
• Extensor hallucis longus
• Extensor digitorum longus
• Extensor digitorum brevis

This pattern can support localization to the L5 root.

11. L4–L5 Disc Herniation

Posterolateral L4–L5 Disc

states:

Posterolateral L4–L5 disc herniation ? traversing L5 root

This is the classic disc-root relationship emphasized in the lecture.

Expected findings

• Dorsal-foot sensory disturbance
• Weak great-toe extension
• Possible weakness of hip abduction
• Positive SLR

Foraminal L4–L5 Disc

contrasts this with:

Foraminal L4–L5 disc herniation ? exiting L4 root

Therefore:

Disc pattern	Root affected
L4–L5 posterolateral	L5
L4–L5 foraminal/far lateral	L4

12. L5–S1 Isthmic Spondylolisthesis

L5–S1 isthmic spondylolisthesis may cause L5 radiculopathy.

13. Straight Leg Raise

When L5 is irritated by disc herniation, the patient may have:

• Sciatica
• Positive straight-leg raise

associates the SLR tension sign with:

L5 and S1 nerve-root irritation

Positive SLR

describes reproduction of:

• Leg pain
• Paresthesia

at approximately:

30–70° of hip flexion

Exam Pearl

SLR – lower lumbar/sacral radiculopathy, especially L5/S1

14. Femoral Stretch Test

contrasts SLR with the:

Femoral nerve stretch test

which is used more for the upper lumbar roots, particularly around L3/L4 in this lecture series.

Therefore:

• SLR – L5/S1
• Femoral stretch – upper lumbar roots

High-Yield L5 Table

Component	L5
Sensory	Dorsum of foot
Main motor test	Great-toe extension
Muscle	EHL
Other motor	EDL, EDB
Proximal motor	Gluteus medius, medial hamstrings
Hip movement	Abduction
Knee movement	Flexion contribution
Reflex	No specific routinely used reflex
Gait abnormality	Trendelenburg gait
Possible additional deficit	Foot drop
Provocative test	Straight-leg raise
Common posterolateral disc	L4–L5

L4 vs L5 vs S1 Quick Comparison

Feature	L4	L5	S1
Sensation	Medial foot	Dorsum of foot	Lateral/plantar foot
Key motor	Ankle dorsiflexion	Great-toe extension	Plantar flexion
Proximal motor	Quadriceps	Hip abductors / medial hamstrings	—
Reflex	Patellar	None specific	Achilles
Provocative test	Femoral stretch	SLR	SLR

Practical Examination Sequence

SENSORY

Check dorsum of foot

MOTOR — DISTAL

Great-toe extension – EHL
Toe extension – EDL

MOTOR — PROXIMAL

Hip abduction – gluteus medius
Knee flexion – medial hamstrings

REFLEX

No specific L5 reflex

GAIT

Look for Trendelenburg gait and foot drop

PROVOCATIVE

Straight-leg raise

LOCALIZE DISC

Posterolateral L4–L5 – L5

Key Take-Home Points

• L5 root examination consists of sensory + motor + reflex assessment.
• L5 sensory territory = dorsum of the foot.
• There is no commonly used specific L5 reflex.
• The best practical distal motor test is great-toe extension using EHL.
• Other L5 muscles include EDL, EDB, gluteus medius and medial hamstrings.
• L5 weakness can produce Trendelenburg gait through hip-abductor weakness.
• L5 involvement can also contribute to foot drop.
• Posterolateral L4–L5 disc – traversing L5 root.
• Foraminal L4–L5 disc affects the exiting L4 root.
• SLR is useful for L5/S1 root irritation.

Exam Pearls

L5 = dorsum of foot + EHL + no reflex

L5 motor = great-toe extension

L5 proximal clue = hip abduction weakness

Trendelenburg gait can occur in L5 radiculopathy

L4–L5 posterolateral disc – L5

SLR – L5/S1