46 - Entrapment Neuropathies Flashcards
Peripheral nerve anatomy
- A nerve is a very complex structure – not going to test this
Dermatomes
- L4, L5, S1 are the main dermatomes you will be seeing in the lower extremity
- Consults for peripheral neuropathy are very common in podiatry
Management of peripheral neuropathy
- Peripheral neuropathy is a manifestation of a systemic disease (idiopathic, diabetes, chemotherapy, alcoholism, etc.)
- He used to try to manage these patients, but now he will send them to family practice, neuropathy, or even back to their oncologist
Nerve entrapment
- Impingement of a peripheral nerve trunk by neighboring anatomic structures.
- Most often occurs where nerve traverses a fibro-osseous tunnel
- Tarsal tunnel – located posterior to medial malleolus, tunnel composed of medial malleolus, wall of calcaneus, retinacula – a lot of structures run through this small area
- Each structure has a small osseous-fibrous tunnel and it doesn’t take too much to impinge that nerve, typically a space-occupying lesion (engorged vein is common)
- “A region of localized injury and inflammation in a peripheral nerve caused by mechanical irritation from some impinging neighboring anatomical structure.”
Seddon’s classification of nerve entrapment
o Published in 1942 in British Medical Journal
o H.J. Seddon – Professor of Orthopaedic Surgery at University of Oxford
o Described 3 types of nerve injury based on study of 460 cases
3 types of nerve injury due to Seddon
- Neurotmesis (Nerve Division)
- Axonotmesis (Lesion in continuity)
- Neuropraxia (Transient block)
Neurotmesis
Nerve division
o Most devastating nerve injury
o Implies complete disruption of a nerve as well as associated connective tissue, typically caused by lacerations, gunshots, fractures, severe traction, etc.
o Budding neurites unable to bridge defect (neurites that do bridge often do so in malalignment resulting in poor reinnervation)
o Requires surgical intervention – resect necrotic tissue, realign fasciculi, nerve fiber regeneration occurs at approximately 1mm/day
Axonotmesis
Lesion in continuity
o Axonal disruption
o Supportive connective tissue is maintained
o Typical causes: prolonged compression, traction, ischemia, toxins
o Distally: Wallerian degeneration, distal axon degradation
o Proximally: Axon and nerve cell body convert from neurotransmitter production to axonal regeneration
o Affects myelinated and unmyelinated fibers
o In general; due to maintenance of supportive structures new axons are able to regenerate and grow down corresponding endoneural tube
o Functional recovery is dependent on proximity of lesion:
- Proximal lesions have wider distribution
- * As distance from site of lesion to end organ increases, functional recovery diminishes – This means that the further away the lesion is from the structure it is innervating, the chance of a functional recovery decreases*
Neuropraxia
Transient block
o Disruption of the myelin sheath
o Susceptible nerves: thickly myelinated, large diameter, rapidly conducting
o Physiologic conduction blockade (blunt trauma, compression)
o People do very well recovering from a neuropraxia, short lived paralysis may develop
o Repair can occur in days to months
o Patients usually fully recover as injury involves only the myelin sheath
Sunderland’s classification
o Don’t need to worry about class/degree of an injury – this is more for a historical review
o Expansion of Seddon’s classification (1951) with 5 degrees (3 classes of injury)
First Degree (Class I)
o Conduction deficit without axonal interruption, equivalent to Seddon’s Neuropraxia
Second Degree (Class II)
o Axon severed without breaching the endoneurium
o Breakdown of myelin and wallerian degeneration, EMG changes of denervation occur
o Regeneration follows pattern of axonal regrowth, equivalent to Seddon’s axonotmesis
Third Degree (Class II)
o Nerve fiber disruption – lesion in endoneurium ONLY (epi/perineurieum remain intact)
o Recovery is possible but may require surgery
o Regeneration is irregular, residual defects common, unpredictable with poor outcomes
Fourth Degree (Class II)
o Only epineurium remains intact, injury requires surgical repair
Fifth Degree (Class III)
o Complete transection of the nerve, requires surgical repair
Common sites of peripheral nerve entrapment
o Tarsal Tunnel (tibial nerve)
o Intermetatarsal spaces (common and proper digital nerves – also occurs plantar to intermetatarsal ligament)
o Adductor canal (Saphenous Nerve)
o Fibular head (Common Peroneal Nerve)
o Deep fascia proximal to ankle (Superficial Peroneal Nerve)
o Lateral Malleolus (Sural Nerve)
- **This is why anatomy is important **
o If you know your anatomy, all of this will make sense – this is what he will ask in the OR
Evaluation and treatment of nerve entrapment
- Tarsal Tunnel Syndrome
- Morton’s neuroma
Tarsal tunnel syndrome
- Entrapment neuropathy involving the Tibial nerve
- First described by Kopell & Thompson in N Engl J Med in 1960
- Involves entrapment of the Tibial (or one of its terminal branches)
- Often compared/likened to carpal tunnel syndrome – need to keep this in mind because these patients may take longer to treat, may not respond to treatment, may need to do a release
Anatomy of tarsal tunnel
- Fibro-osseous canal
- Posterior to medial malleolus
Borders:
o Anterior – Tibia
o Lateral – Talus (posterior process) & calcaneus
o Medial – Flexor retinaculum (Lacinate ligament)
Tibial nerve
- Enters proximally
Branches within tunnel into 3 terminal branches:
o Medial Plantar Nerve
o Lateral Plantar Nerve
o Medial Calcaneal Nerve
Common symptoms of entrapment neuropathies
- Patient’s present with various symptoms
- Commonly complain of diffuse plantar pain and/or medial ankle pain (Burning, Stabbing, Shooting, “Electrical,” Numbing, Tingling)
Pain aggravated by standing and relieved with rest
o Some patients report pain worse at night and better throughout the day after walking/activity.
o Many patients will report pain radiating proximal into the calf
When evaluating for entrapment neuropathies, look for other systemic disease
Diabetes, rheumatologic, obesity, radiculopathy
More common causes of entrapment neuropathies
o Space occupying lesion(s): ganglion, lipoma, varicosities, neurilemoma
o Exostosis or fracture fragments
o Hindfoot varus or valgus
o Talo-calcaneal coalition
o Accessory muscle within canal: accessory soleus, accessory FDL
When evaluating for entrapment neuropathy, carefully review and identify patient’s activities
o High performance athletes - sprinters, jumpers, martial arts
o Anything that puts a heavy load on the ankle
When evaluating for entrapment neuropathy, carefully examine patient in NWB and WB
o Varus or Valgus alignment
o Decreases volume within tarsal tunnel – increase pressure on tibial nerve
When evaluating for entrapment neuropathy, test stability of the hindfoot
o Instability of plantar fascia
o Instability of PTT
o Instability of supportive structures leads to increased traction on Tibial nerve
When evaluating for entrapment neuropathy, palpate entire course of the nerve
o Space occupying lesions
o Palpable osseous ridges/fragments
When evaluating for entrapment neuropathy, percuss over the tarsal tunnel
o Percussion over area of entrapment may elicit radiating pain along course of the nerve
o Tinel sign – Pain radiating distal: most common, patients will feel shooting pain along the course of the MPN and LPN
o Villeix sign – Pain radiating proximal
o TD = touch down, Tarsal tunnel is distal
o VP = vice president, Vileix sign is proximal
Diagnostic studies for entrapment neuropathy
- X-ray
- MRI
- Ultrasound
- Electrodiagnostic
X-ray
o Fractures
o Degenerative Joint Disease
MRI
o Space-occupying lesion
o 1993 – Frey & Kerr: MRI studies revealed pathology in 88% of patients with Tarsal Tunnel Syndrome, confirmed intra-operatively in 90% of patients
o MRI is a pretty reliable – ALWAYS get a pre-op MRI to prepare/plan for surgery
Ultrasound
o Technician dependent – He does not use it for anything, except PT
Electrodiagnostic studies
o Nerve conduction velocity (NCV) o Electromyography (EMG)
Diagnostic criteria
KNOW THIS ***
Three criteria
o History of neuritic symptoms
o Positive Tinel sign
o Supporting NCV studies
Diagnosis guidelines
o If none of above criteria is met then diagnosis should be excluded **
o If one of above criteria is met then other diagnosis should be considered *
o If all 3 criteria are met, symptoms are reproducible, then diagnosis is considered
Non-surgical treatment (if you know there is no space occupying lesion)
o NSAIDs o Oral vitamin B6 o Gabapentin o Lyrica o Immobilization o Corticosteroid injections o Stabilization of hindfoot with orthotics
Indications for surgical treatment
- Space occupying lesions
- Failed conservative treatment
Tarsal tunnel syndrome surgery
- Does not repair the retinaculum because they will scar, just throws 1-2 stitches
- Then implements immobilization
Morton’s neuroma history
- 1845 – Neuritic pain between the 3rd and 4th metatarsals was first described
- 1876 – Neuroma/hypertrophy of the common plantar digital nerve was hypothesized by Morton as etiology of intermetatarsal pain
Morton’s neuroma definition
- Entrapment of the common plantar digital nerve occupying the 3rd inner space
Morton’s neuroma causative factors
Many causative factors presumed – He thinks it is a COMBINATION of all of them ***
Transverse metatarsal ligament
o Narrower inner space between 3rd and 4th metatarsals
o Increased mobility between 3rd and 4th rays
o Tethering of nerve beneath metatarsal heads during dorsiflexion when ambulating
ALL VERY PLAUSABLE THEORIES
Physical exam for Morton’s neuroma
- Medial-Lateral squeeze and focal tenderness to deep palpation
- Positive Mulder’s click (not usually audible, but can feel it on larger neuromas)
- Complaints of anesthesia to neighboring toes
Non-surgical treatment of Morton’s neuroma
- Padding, orthoses
- Corticosteroid injections
- NSAIDs, ultrasound, icing
- Alcohol sclerosis injections (need to do 6 weeks of injections 1x/week)
Surgical treatment of Morton’s neuroma
- External neurolysis
- Excision of involved nerve
Plantar and dorsal approaches described – he goes in dorsally
o Assistant pushes up on the interspace, cut intermetatarsal ligament
o If it is big enough neuroma, he cuts it out by taking out the entire digital nerves then resect the common back as far as he can
o If it isn’t that big, he just resects it
