Foot drop

View Details

Status

Done

Definition

Weakness of anterior tibialis (primarily L4 and to a lesser extent L5), often accompanied by a weak extensor digitorum longus and extensor hallucis longus (primarily L5 with some S1 contribution), all of which are innervated by the deep peroneal nerve.

Anatomy

Muscle	Function	L5	S1	Deep peroneal nerve	Superficial peroneal nerve	Tibial nerve
Posterior upper leg muscles	Hip internal rotation Hip abduction Hip extension	x	x	ㅤ	ㅤ	ㅤ
Tibialis anterior muscle	Foot dorsiflexion (inversion)	x	ㅤ	x	ㅤ	ㅤ
Tibialis posterior muscle	Plantar flexion Inversion	x	x	ㅤ	ㅤ	x
Extensor hallucis longus/brevis muscles	Hallux extension	x	ㅤ	x	ㅤ	ㅤ
Extensor digitorum longus/brevis muscles	Toe extension 2–5 Eversion	x	x	x	ㅤ	ㅤ
Peroneus muscles	Eversion	x	x	ㅤ	x	ㅤ

notion image

DDx

L4 or L5 Radiculopathy

With L4 or L5 root lesions
Weak

Posterior tibialis
Gluteus medius

Sciatic nerve palsy

The peroneal division of the sciatic nerve tends to be more vulnerable to injury than the tibial division.
Flail foot results from paralysis of dorsiflexors plus plantar flexors
Due to

During surgery for hip fracture-dislocation
injection injuries (IM injections should be given superiorly and laterally to a line drawn between the posterior superior iliac spine and the greater trochanter of the hip).

Peroneal nerve palsy (usually common peroneal nerve)

With common peroneal nerve (CPN) palsy

There is sparing of

Posterior tibialis (foot inversion, innervated by posterior tibial nerve)
Gluteus medius (internal rotation of the thigh with the hip flexed, innervated by superior gluteal nerve, primarily L5 with some L4, the take-off is shortly after the roots exit from neural foramen).
Medial hamstring (L5) reflex

Localisation of lesion

notion image

Level of lesion	Motor weakness	Nerve root tension signs	TInel’s test at fibular neck	EMG
L5 root	- Tibialis posterior (supplied by L4/L5 via tibial nerve) → Foot inversion weakness - Gluteal medius/minimus (supplied by L4/L5/S1 via superior gluteal nerve) → Hip abduction weakness	On hip flexion	Negative	Denervation: - Paraspinal muscle - Tibialis posterior - Gluteal muscles
Lumbosacral trunk	- Tibialis posterior (supplied by L4/L5 via tibial nerve) → Foot inversion weakness - Gluteal medius/minimus (supplied by L4/L5/S1 via superior gluteal nerve) → Hip abduction weakness	On hip flexion	Negative	Denervation: - Tibialis posterior - Gluteal muscles
Peroneal division of sciatic nerve	ㅤ	ㅤ	Negative	Denervation: - Short head of biceps femoris (not clinically accessible)
Common peroneal nerve	Foot eversion weakness	On ankle inversion	Positive	ㅤ

Aetiologies of foot drop

ㅤ	Mechanism	Aetiology
Central nervous system	Displacement/compression	Extra-axial brain tumors (e.g. meningioma, metastases) Tumor edema
ㅤ	Destruction	Intra-axial tumors (e.g. glioma) Hemorrhage Ischemia → Prerequisite: involving parts of the central region/pyramidal tract
ㅤ	Developmental disorder	Infantile cerebral palsy
Intraspinal nerve roots L4/L5	Compression	Disc herniation Stenosis Neurinoma Other tumors
ㅤ	Direct trauma	Nerve root avulsion (extremely rare) Iatrogenic injury
Peripheral nervous system	External compression	Positioning during surgery or prolonged bed rest Plaster splint Compression stockings Pressure on lower leg (e.g. sitting with crossed legs)
ㅤ	Internal compression	Narrowness along fibular tunnel, myositis ossificans Anterior compartment syndrome
ㅤ	Direct trauma	Fibula fractures Adduction trauma with knee dislocation Gunshot wound Iatrogenic
ㅤ	Space-occupying lesions	Intra-/extra-neural ganglion cysts Baker’s cystes Fibular bone tumors Nerve tumors (neurofibroma, schwannoma, nerve sheath tumors) Lipoma and others
Other	Neuromuscular disease	Focal myopathies Multifocal motor neuropathy

Muscular

Muscular dystrophy
Anterior compartment syndrome

Neurologic

Peripheral nerve palsies (more common).

Peroneal nerve injury:

Branches that may be involved:

Deep peroneal nerve:

Isolated foot drop
minimal sensory loss

(except possibly in great toe web space)

Superficial peroneal nerve:

Weakness of peroneus longus and brevis (foot eversion) with no foot drop.

These two muscles causes plantar flexion and eversion

Sensory loss: lateral aspect of lower half of leg and foot

Common peroneal nerve:

Combination of above (i.e., foot drop + weak foot eversion, with sparing of tibialis posterior (foot inversion).
Sensory loss: lateral aspect of lower half of leg and foot)

notion image

L5 radiculopathy: (or, less commonly, L4):

Foot drop: severe or complete paralysis of ankle dorsiflexion occurs in 5–10% of HLD

Due to

Disc disease at L4–5: most common
Lumbar spinal stenosis at L4–5
Sacral ala fracture

Results in

pain and/or sensory changes in L5 (or L4) dermatome
weakness with radiculopathy tends to be more pronounced in distal muscles (e.g. anterior tibialis) than in proximal (e.g. gluteus maximus)

Painless foot drop is unlikely to be due to radiculopathy;

Consider peroneal neuropathy, diabetic neuropathy, lesion anywhere along pyramidal tract, motor neuron disease

Management

50% of cases recover with or without treatment.
Postacchini 2002 Prospective n116 Recovery of motor deficits after microdiscectomy for lumbar disc herniation 6.4 years f/u mean

muscle which most frequently had severe or very severe weakness was (in order)

extensor hallucis longus,

triceps surae,

extensor digitorum communis,

tibialis anterior

76% of patients had complete recovery of strength.

Persistent weakness was found in

16% of patients who had had a mild preoperative deficit
39% of those with severe or very severe weakness.
very severe preoperative deficit showed no recovery

Petr 2019 Retrospective n330 microsurgical discectomy

Early surgery <48 hrs

Significantly faster recovery of moderate/severe paresis (MRC 0-3)

no significant differences in recovery for mild paresis (MRC 4).

Sensory deficits also recovered faster

Predictors of motor recovery

BMI
preoperative MRC-grade
duration of motor deficits

Lumbar plexus injury
Lumbosacral plexus neuropathy
Injury to lateral trunk of sciatic nerve
Peripheral neuropathy:

Weakness tends to be greater distally, producing wrist or foot drop.
Due to

Charcot-Marie-Tooth

Demyelination → progressive motor weakness
findings tend to be rather dramatic in spite of the fact that it often doesn’t seem to bother the patient very much

Diabetic

Early in the course of motor neuron disease (ALS)
Heavy metal poisoning

lead toxicity: in children may cause foot drop with no sensory loss

Central nervous system causes: (foot drop here is usually painless)

Cortical lesion (UMN):

Parasagittal lesions in region of motor strip

Sensation will be spared if the lesion does not extend posteriorly to the sensory cortex

There may be a Babinski sign or hyperactive Achilles reflex (so-called “spastic foot drop”).
Usually painless

Spinal cord injury:

including cervical spinal myelopathy

Anatomic.

non-neurogenic causes

Clinical features

Loss of dorsiflexion causes foot slap with the front of the foot when the heel strikes the ground while walking.

Increasing falls

Tripping on own foot

Patients may develop high step gait

Destabilize ankle: Associated weakness of tibialis posterior, when present (e.g. with L5 radiculopathy) → destabilizes the ankle → permitting eversion → predisposes to falls and to ankle fractures

Chronic foot drop may produce Achilles tendon contracture with talipes equinus.

Wasting of the extensor digitorum brevis may be seen

Evaluation

EMG:

Can help differentiate L5 radiculopathy from peroneal nerve palsy, plexus lesion, or motor neuron disease (for details).
EMG is not reliable until symptoms have been present at least ≈ 3 weeks

MRI

For disc disease

Management

notion image

Outcome

Fozia 2021

Favourable outcome

Earlier surgery (<6 week) rather than late surgery

notion image

Milder weakness (MRC >2-3) rather than MRC 0

notion image

References

Carolus 2019

Made with Bullet