Approach to Foot Drop (focused on unilateral foot drop) Flashcards
Schematic drawing of the lower limb nerves
Sacral plexus
Pathways:
1. Roots (origin): S1, S2, S3, S4 and contributions from L4, L5 via lumbosacral trunk
- Passes through greater sciatic foramen and branches to supply:
Motor
- Superior gluteal nerve (L5): gluteus minimus, medius, tensor fascia latae muscles
- Inferior gluteal nerve (L5, S1): gluteus maximus
Sensation
- Perforating cutaneous nerve (S2, S3): inferomedial buttock
- Posterior cutaneous nerve of thigh (S2): posterior thigh, upper calf
- Continues as sciatic nerve
Sciatic nerve
From continuation of sacral plexus
- Motor supply (hamstring) for knee flexion
- Medially: semimembranosus, semitendinosus
- Laterally: biceps femoris
(Hamstring origins attached to ischial tuberosity - thus also assist in hip extension) - At popliteal fossa apex, formally divides into:
- Common peroneal nerve
- Tibial nerve
Common peroneal nerve
Course
1. Descends along medial border of biceps femoris and giving branch to lateral sural cutaneous nerve
2. Winds around fibular neck and leaves popliteal fossa
3. Divides into superficial and deep peroneal nerve
Sensory innervation
1. Lateral sural cutaneous nerve: lateral knee, upper calf
Tibial nerve
Motor innervation
1. Plantar flexors (S1): gastrocnemius, soleus
2. Ankle invertors (L4, L5): tibialis posterior
3. Toe flexors
Sensory innervations
1. Direct: soles
2. Medial plantar nerve: medial 3 and 1/2 of toes
3. Lateral plantar nerve: lateral 1 and 1/2 of toes
Superficial peroneal nerve
Branches from common peroneal nerve
Motor innervation: ankle eversion (S1)
1. Peroneus longus
2. Peroneus brevis
Sensory innervation
1. Lateral lower calf
2. Dorsum of foot (except 1st webspace)
Deep peroneal nerve
Branches from common peroneal nerve
Motor innervation
1. Ankle dorsiflexors/extensors (L4, L5)
- Tibialis anterior (main)
- Extensor hallucis longus
- Extensor digitorum longus
- Pronator teres
2. Toe extensors (L5)
- Extensor hallucis longus and brevis
- Extensor digitorum longus and brevis
Sensory innervation
1. 1st webspace over dorsum of foot
Foot drop algorithm
Bilateral foot drop
Bilateral UMN foot drop: spinal cord lesion (see spastic paraparesis)
Bilateral LMN foot drop:
1. Cauda equina syndrome
2. Peripheral neuropathy
3. Distal myopathy (myotonic dystrophy, FSHD)
Unilateral UMN foot drop
Innervating nerves to the anterior tibialis muscle (bottom to top)
- Offer distal myopathy, NMJ disease as cause
- Deep peroneal nerve
- Branch of common peroneal nerve
- Sciatic nerve
- Lumbar roots and sacral plexus
- Cortical foot drop
Confirmation of unilateral foot drop
“All foot drops lead to tibialis anterior muscle”
Deep peroneal nerve or higher defect
- Weakened tibialis anterior muscle causing ankle dorsiflexion weakness
- 1st dorsal webspace numbness
- Also look at extensor digitorum brevis muscle bulk (also innervated by deep peroneal nerve)
What gait in foot drop differentiates UMNL vs LMNL?
- Circumduction gait - UMNL weakness
- Symptomatic side circumduct due to spasticity and pyramidal pattern weakness (hip and knee weakness causes difficulty clearing foot off ground)
1A. Strumpell’s tibialis phenomenon
- Knee flexion triggers involuntary ankle dorsiflexion/inversion which worsens foot clearnce
- Adopts compensatory circumduction gait
- High steppage gait - LMNL weakness
- Hip flexion elevates symptomatic foot off the ground
Three milestones of high level foot drop
Hip extension - sacral plexus (very high)
Knee flexion - sciatic nerve
Hip abduction - L4/L5 level
Very high level foot drop
- Sacral plexopathy
- Hip extension weakness - gluteus maximus
- Innervated by inferior gluteal nerve (from L5, S1, S2) - Hip abduction weakness - gluteus medius and minimus
- Innervated by superior gluteal nerve (from L4/L5) - Variable sensory deficit, commonly L4/L5 (myotomal pattern)
Hip extension weakness
Muscle: gluteus maximus
Nerve: inferior gluteal nerve
Myotome: L5, S1, S2
Possible localisation:
1. Sacral plexus
2. Sciatic nerve
3. Sacral roots (radiculopathy) co-exist with L4/L5 radiculopathy - DDD
Hip abduction and internal rotation weakness
Muscle: gluteus medius, gluteus minimus
Nerve: superior gluteal nerve
Myotome: L5
Possible localisation:
1. Sacral plexus
2. L4/L5 lumbar roots (radiculopathy)
L4 to L5 (or localising L4 or L5) radiculopathy
Difficult discerning L4 from L5 radiculopathy
Suggest to comment as L4 to L5 radiculopathy
Relative weakness between:
- L4 - deep peroneal nerve (ankle dorsiflexion)
- L5 - deep peroneal nerve (hallux extension)
- Ankle dorsiflexion and hallux extension equally weak = deep peroneal neuropathy
- Hallux extension weaker than ankle dorsiflexion = L5 radiculopathy (and vice versa)
However patient’s muscle weakness may not often be congruent to level
High level foot drop
- Sciatic nerve
- Tibial nerve
- Knee flexion weakness - hamstrings
- Innervated by sciatic nerve - Plantar flexion and inversion weakness - gastrocnemius, soleus, tibialis posterior
- Innervated by tibial nerve
- Inversion by L4/L5 and plantarflexion by S1
(Tibialis anterior inverts ankle too, thus plantarflexion determines tibial nerve involvement) - Sensory deficit over common peroneal and tibial nerve
Knee flexion weakness
Muscle: hamstrings (biceps femoris, semitendinosus, semimembranosus)
Nerve: sciatic nerve
Myotome: L5 or S1
Possible localisation:
1. Sciatic nerve
Ankle plantarflexion/inversion weakness
Muscle: gastrocnemius, soleus, tibialis posterior
Nerve: tibial nerve
Myotome: L4, L5 (inversion), S1 (plantarflex)
Possible localisation:
1. Tibial nerve
Causes of high level foot drop
- Compressive / traumatic - prolapsed disc, trauma, tumour
- Vasculitis
- Radiation inflammatory neuropathy
- Metabolic - diabetic amyotrophy
Common peroneal foot dropl
Common peroneal nerve branches to superficial peroneal nerve
- Ankle eversion weakness - peroneus longus and brevis (supplied by superficial peroneal nerve)
- Sensory deficit over lateral aspect of calf and dorsum of foot
- This is on top of branching to deep peroneal nerve causing weak dorsiflexion
Causes of common peroneal nerve lesion:
1. Compressive neuropathy of fibular head (prolonged bed rest, trauma)
2. Trauma/surgery to fibula head
3. Mononeuropathy (DM)
4. Mononeuritis multiplex (DM, vasculitis)
Ankle eversion weakness
Muscle: peroneus longus, brevis
Nerve: superficial peroneal nerve (branch of common peroneal nerve)
Possible localisation:
1. Superficial to common peroneal nerve
Cortical foot drop and gait
(brain and brainstem lesion)
- Cortical foot drop: UMN pattern
- Features of hypertonic, clonus, hyperreflexia, upgoing plantars - Significant gait difference
- UMN - circumduction gait (spasticity, pyramidal pattern of weakness over hip and knee flexors - difficult clearing foot off the ground)
(Strumpell’s tibialis phenomenon)
(in comparison LMN - high stepping gait and flexing hip to elevate dropped foot off the ground)
