Ultrasound of Medial by Lisa Howell

Medial Tarsal Tunnel Syndrome Medial Tarsal Tunnel Syndrome (Posterior Tibial ) is a compression neuropathy Occurs when Posterior (PTN) and / or its branches are entrapped within Tarsal Tunnel of Medial ankle Proximal syndrome compression main trunk of PTN, affects entire foot Distal syndrome compression of divisional branches of PTN Medial TTS: -More complex than in wrist -Diagnosis and treatment of TTS depends on cause, and severity - typically radiates down medial ankle to heel and/or plantar aspect of foot -Symptoms occur whilst standing, during exercise, and at night when patient is at rest [Ref: 1, 6] Anatomy Medial Ankle

Medial Tarsal Tunnel MTT Fibro-osseous tunnel of medial ankle, posterior and inferior to medial malleolus (MM) Tendons of medial ankle Tibialis posterior (PTT), Flexor digitorum longus (FDL), and Flexor hallucis longus (FHL) Ligaments of medial ankle Deltoid ligament is fan shaped, and originates at MM It is divided into a deep and superficial layers Deep layer : Anterior tibiotalar lig, and Posterior tibiotalar lig Superficial layer: Tibionavicular lig, Tibiospring lig, and Tibiocalcaneal lig Neurovascular bundle Posterior tibial nerve (PTN), Posterior tibial artery (PTA), and Posterior tibial veins (PTV) [Ref : 1,6 ]

Anatomy of PTN Posterior Tibial Nerve (PTN) branch of divides at medial ankle into three branches :

● Medial Calcaneal Nerve ● Medial Plantar Nerve

● Lateral Plantar Nerve Proximal Medial Tarsal Tunnel Flexor Retinaculum (FR) forms the roof of prox MTT Medial Calcaneal nerve (MCN) first branch of PTN MCN superficial to Abductor Hallucis muscle (AHM) Innervates posterior medial part of calcaneus, and posterior fat pad of foot Distal Medial Tarsal Tunnel Lateral Plantar nerve (LPN), and Medial Plantar nerve (MPN) are the

terminal branches of PTN [Ref: 1,6] Frank.H.Netter, MD. Atlas of Human Anatomy

Anatomy PTN branches LPN and MPN branch beneath Abductor Hallucis muscle Plantar nerves divide into digital nerves at level of metatarsal bases, then continue into web spaces Medial Plantar nerve Innervates plantar aspect of 1st, 2nd, 3rd toes, and medial plantar aspect of 4th toe Lateral plantar nerve Innervates plantar aspect of 5 th and lateral part of 4th toe Inferior calcaneal nerve (Baxter's nerve) first branch of lateral plantar nerve ICN is beneath Abductor Hallucis muscle ICN innervates abductor of 5th toe, and periosteum of large calcaneal tuberosity [Ref: 1,6 ]

Medial Ankle / PTN

Frank H Netter MD, Atlas of Human Anatomy

Anatomy Peripheral nerves Mesoneurium connective tissue that supports nerve trunk Epineurium Outer epineurium is continuous with mesoneurium, and forms outer sheath of nerves Inner epineurium connective tissue intervening b/w outer sheath and fascicles Endoneurium fascicle of nerve Nerve fascicles contain nerve tissue, with collections of axons, myelin sheaths, and schwann cells Perineurium connective sheath surrounds fascicles, and contains intraneural blood vessels [Ref 1,18] Anatomy Peripheral Nerves Vasa nervorum vascular supply of each each nerve -ensures impulse transmission and axonal transport perineural vessels course longitudinally in external epineurium intraneural vessels branch amongst fascicles in perinerium vascular plexuses connect perineural and intraneural vessels Size and number of fascicles vary in each nerve depending on: -distance from the origin -amount of pressure to which nerve is subjected -occurrence of nerve branching Also affected by BMI, Height, Gender, Age, and temperature [Ref:1,18]

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Normal U/S appearance PN Peripheral Nerves are more hypoechoic than tendons Run along borders of other structures i.e fascia, blood vessels, or subcutaneous Show sliding movement over tendons and muscles Longitudinal axis: Tubular structures PN appear as multiple hypoechoic parallel lines (fascicles), separated by hyperechoic lines (perineurium) Short axis: Honey comb appearance PN appear as a hyperechoic ovoid area, with multiple hypoechoic dots (fascicles)

Epineurium is the hyperechoic rim [Ref: 11,13] Case 1 Normal CSA PTN MM/CL

Case 1 PTN Long

3cm above MM

Abnormal U/S appearance PN ● Nerve / fascicle enlargement

● Nerve compression within Tunnel, with proximal swelling of nerve ● Loss of normal fascicular architecture of nerve

● Loss of normal nerve sliding movement

● Nerve appears hyperechoic in relation to tendons

● Vas nervorum hyperaemia Additional abnormal U/S PN findings:

● Focal or diffuse thickening of nerve

● Fusiform swelling of the nerve

● Lesion dissecting the fascicles within the nerve

● Dislocation of nerve

● Partial or complete severance of nerve [Ref:1,7,11,13]

Peripheral nerve injuries

PN injuries classification (Seddon): Sudderland used by surgeons ● Neurapraxia (Grade 1) Mildest injury Endoneurium, perineurium, and epineurium intact eg Nerve contusion, dislocation, or swelling due to pressure *low grade injuries better outcome recovery ● Axonotmesis (Grade 2) Moderate injury disruption of axons and myelin Epineurium, and perineurium intact Motor and sensory function present eg Traction and crush injuries ● Neurotmesis (Grade 3) Severe injury Complete disruption of nerve, partial or complete severance *High grade injuries require surgical intervention [Ref: 1, 11,13]

PN Tumours PN Tumours neoplasms derived from schwann cells have entering and exiting nerve often homogenous, and hypoechoic ● Schwannoma defined nerve / tumour transistion, eccentric or central nerve entry, smaller size than neurofibromas Smooth contour, cystic portions, hyperaemia, may have calcifications *Surgery to nerve with preservation of nerve continuity ● Neurofibroma central nerve location, single tumour, fusiform, or lobulated shape *Excision usually comprises affected nerve ● diffuse form, multiple neurofibromas, affects skin and subcutaneous tissues. Also Plexiform type ● Traumatic Neuroma post catherization, post surgical, or amputation

● Neurofibrolipoma [ Ref: 1, 19,20 ] MTTS

● Flexor Retinaculum restricts size of Tunnel

● Increased pressure caused by intrinsic and extrinsic forces within Tunnel causes compression of nerve and / or its branches

● Alterations blood nerve-barrier, oedema and swelling increase

● Slowing of axonal transport

● Thickening of nerve connective tissue

● Vascular compromise causes venous congestion, as pressure increases on nerves

● Nerve more susceptible to compression Initial symptoms: patient has pain, burning, tingling, and numbness Chronic symptoms: Sensory loss of sensations of pain, pressure and temperature Motor muscular weakness,and atrophy

Autonomic altered microvascular circulation [Ref: 1,3,4,13]

Disease or degenerative state of peripheral nerves in which motor, sensory, or vasomotor nerve fibres are affected Symptoms may affect entire nerve, multiple sites of nerve, or multiple nerves within a limb “Peripheral neuropathy contibutes significantly to the neurological burden of disease worldwide” “Prevalence of peripheral neuropathy is increasing.. the growing population affected by Diabetes, and the rising incidence of drug induced neuropathy associated with chemotherapy and antiviral drugs” HRUS provides superior spatial resolution than MRN that has enabled detailed visualisation of even the smallest peripheral nerves” “HRUS allows accurate assessment of different morphological characteristics of the nerve independent of CSA..fascicle diameter, fascicle to connective tissue ratio, epineurial demarcation, and nerve blood flow” E.Gallardo et al 2017 [Ref:13 ] Case 2 MTTS Idiopathic

Symptomatic FR MM/CL

Case 2 Symptomatic MTTS MM/CL

Case 2 Symptomatic MTTS

Trifurcation PTN

Symptomatic MTTS 3cm prox

Case 3 MTTS Pes Planus /Tenosynovitis

Case 3 MTTS CSA /FR positive Tinel's sign

Case 3 MTTS PTN prox long

Case 3 MTTS PTN compression

Case 4 Guillain-Barre Syndrome Sural Nerve

Case 4 GBS Traumatic Neuroma post biopsy

Case 4 GBS Sural nerve post biopsy

Ultrasound Technique

● High frequency Transducer 10-15MHz Linear or Hockey stick L8- 18iMHz ● Optimize settings focal zone, B mode, depth, etc ● Patients clinical indications and clinical history ● Patient positioned lying on bed with affected leg in external rotation, knee bent, and a small towel beneath lateral aspect of ankle ● Anatomical landmarks ● Examine Medial ankle tendons, ligaments, and nerves ● U/S CSA measurements inside epineurium as per criteria -level MM/CL, and 3cm, and 10cm prox to MM/CL for MTTS -level MM/CL, and 3cm prox to MM for severity of DPN, & MTNF ● Document pathology ● Static and dynamic study plantar and dorsiflexion, standing view for talus coalition, or dilatation of veins [Ref: 4,5,7,15,17,21,22]

Ultrasound Technique

● Short axis and longitudinal (Elevator technique) Image PTN, and its division into its branches ● Comparison to non symptomatic side

● Discrepant size b/w Medial and Lateral Plantar branches

● Minimal pressure with Transducer held perpendicular to nerve

● Laceration measure distance b/w nerve stumps

● Surgical planning relationship of lesion to adjacent neurovascular structures, and tendons or landmarks

● Colour doppler identify neurovascular bundle, and intraneural hyperaemia *Morton's Neuroma or may present similar symptoms, if study negative, scan PTN *Positive Tinel's sign patient experiences a sharp pain when you Tap over nerve [Ref:6]

Technique

Causes of MTTS

● Work / sporting activities causing repetitive injury to ankle joints eg gymnastics or marathon runner ● Inflammatory conditions OA, Tenosynovitis ● Autoimmune conditions RA, Psoriatic ● Masses Ganglion, Lipoma ● Tumours Schwannoma, Neurofibroma ● Trauma bone fracture ● Soft tissue injury haematoma or oedema. Ankle injuries 14% sports related injuries ● Laceration partial or full thickness tears ● Compression of L4, L5, and S1 Sciatic nerve (increase risk of Double crush Syndrome) [Ref: 1, 6,7]

Causes of MTTS/ PN

● Nutritional deficiences B12, Vitamin D, Dopamine

● Alcoholism / smoking

● Toxins Insecticides, poisons arsenic

● Surgical intervention Haematoma, scarring, infection, incomplete dissection of FR

● Bone deformity Valgus flat foot, medial process of Talus compresses PTN, and its plantar branches in standing position

● Accessory muscle or tendon Flexor Digitorium accessorius longus

● Dilatation of plantar veins distal tarsal tunnel Standing view Plantar vein dilatation diameter >5mm distal Tarsal Tunnel [Ref:1,4,6,7,11]

Peripheral Neuropathy

● Infectious conditions Leprosy, Lyme disease, HIV, Herpes virus ● Hereditary Charcot-Marie-Tooth disease, Amyloidosis ● Immune mediated CIPD, Guillain- Barre Syndrome, MMN ● Uraemic 90% Dialysis patients ● Hypothyroidism induced ● Drug induced Chemotherapy or Antiviral induced ● Hormonal Oophorectomy, OCP, and menopause , Pregnancy and post partum Obesity, BMI>30kgs, higher parity (2 or more live births) Hormonal levels, biochemical changes, and altered biomechanic Relaxin effect ligament laxity of spring ligament and Posterior Tibialis tendon 1cm lowering talar head flattening longitudinal arch more susceptible to MTTS [Ref: 1,4,5,7,11,16, 23]

Measurement MTT DPN

“Large study of Diabetic patients demonstrated the CSA of the PTN as measured by ultrasound is a valid and reliable tool to detect the presence, and predict the severity of DSP CSA PTN measured 3cm prox to MM for DSP *19mmsq Sensitivity 69% and Specificity 77% S.Riazi et al 2012 [Ref:5 ] CSA PTN (MM/CL) significantly larger *DPN 8.4mm +/– 3.9mmsq Healthy control 6.4mm+/ 1.3mmsq Flexor Retinaculum significantly thicker DPN 1.07mm Healthy control 0.84mm T/W ratio significantly increased DPN patients 0.64 Healthy control 0.5 J. Macare van Maurik et al 2014 [Ref: 4]

MTTS measurement “The CSA and MTNF of the PTN is larger in Diabetic patients with or without peripheral neuropathy than in healthy controls, and ultrasonography can be used as good screening tool in these patients” CSA PTN 3cm cranial to MM Max thickness of nerve fascicles (MTNF) measure short axis *DPN CSA 22.63+/-2.66mmsq and 0.7mm MTNF *DM CSA 14.4 +/-1.7mmsq and 0.4mm MTNF *Control CSA 12.4 +/-1.01mmsq and 0.3mm MTNF K. Singh et al 2017 [ Ref :17] “The morphological changes in peripheral nerves of Type 2 diabetic patients were found before onset of neuropathy and were closely correlated with the severity of diabetic neuropathy” PTN CSA 3cm cephalad to MM Control PTN MTNF 0.213mm “MTNF of both nerves in patients without DN was also greater than controls, and increased depending on DN severity” F. Ishibashi et al 2014 [Ref:15]

MTTS measurement

“The difference in the measured axial CSA of the tibial nerve by ultrasonography b/w the posteromedial tarsal tunnel and 10cm above the tunnel is a key data point for the diagnosis of TTS with and without compressive etiology” *CSA 15mmsq inside Tarsal Tunnel best threshold for TTS Sensitivity 74% 100% specificity *5mmsq difference best threshold (TT to 10cm Prox) Sensitivity 81% 100% specificity O. Fantino et al 2020 [Ref:21] “There was a significant difference in the CSA within tunnel, and CSA proximal tunnel ratio b/w TTS group and controls” Ratio >1 within MTT to Prox MTT 74% sensitivity CSA 19mmsq within MTT optimum

Sensitivity 61% E.A Tawfik et al [Ref:22 ] Decompression

Impaired glucose intolerance creates a peripheral nervous system that is susceptible to chronic nerve compression

● Lower extremity nerve decompression can be performed by releasing : -Common peroneal nerve at the fibular neck -Superficial peroneal nerve in the distal third of the leg -Deep peroneal nerve over the dorsum of the foot -Tibial nerve proximally at the soleus arch -Tibial nerve in the Tarsal Tunnel, and its three branches in medial plantar Tunnel, lateral plantar Tunnel and calcaneal Tunnel A.L. Dellon 2008 [Ref:8] HbA1c levels are index DPN severity Won-Jae Lee et al [Ref:14 ]

Haemodynamic

Diabetic foot infections and related foot amputations are major cause of morbidity in diabetic patients Early diagnosis to alleviate permanent nerve damage, and functional disability Posteror tibial and dorsalis pedis arteries: PI values significantly increased pre op measurements compared to post op measurements RI values significantly decreased pre op measurements compared to post op measurements “In patients with DPN Nerve decompression procedures have a positive effect on the haemodynamic and morphological parameters of the adjacent arteries as they pass through the Tunnels, as well as its positive effects on the neurological functions of the entrapped nerves”

F. Tekin et al 2015 [Ref:3] Treatment for MTTS

Conservative: Rest or restriction of activities ● Medical care to treat disease conditions RA, Hypothyroidism, Diabetes ● Podiatry treatment orthotics devices, splints, and braces ● Physiotherapy exercises to strengthen muscles of lower limb ● NSAIDS U/S guided interventional therapy : Cortisone injection ● Aspiration ganglion/ fluid collection ● Biopsy of mass / Nerve Surgery : open release or endoscopic ● U/S guide selection of patients for surgery ● U/S diagnose site of Nerve injury, tumour, mass ● U/S assist in location of nerves for Decompression surgery ● U/s diagnose post surgical complications

Conclusion Advantages of Ultrasound of MTTS: ● Wide availability, lower cost, and Higher spatial resolution than MRI

● Non invasive, and well tolerated by patients ● Assess anatomy, and dynamics tendons, muscles and nerves

● Diagnose intrinsic and extrinsic pathology ● U/S can be as first line of investigation to diagnose MTTS

● U/S Differentiate MTTS from Peripheral Neuropathy ● Assist in diagnosis and staging of DPN as per Criteria

● Compare to contralateral side ● Colour and Power Doppler

● Guide interventional therapy ● U/S assist pre and post Surgical Treatment

References 1. C. Martonoli. S. Bianchi Ultrasound of Musculoskeletal System Springer Ch 16 p773-883 2. Frank H Netter Atlas of Human anatomy 6th Edition 3. F. Tekin et al The ultrasonographic evaluation of Haemodynamic changes in patients with Diabetic afterTarsal Tunnel Decompression Aug 2015 Microsurgery 35:457-462 4. J.Macare van Maurik et al Ultrasound findings after surgical decompression of the Tarsal Tunnel in Patients with painful Diabetic Polyneuropathy: A prospective randomized study diabetes care 2014;37:767-772 American Diabetes association 5. S. Riazi et al Can ultrasound of the Tibial nerve detect Diabetic Peripheral Neuropathy? Diabetes Care 2012 Dec:35(12):2575-2579 American Diabetes Association 6. O. Fantino et al Role of ultrasound in posteriormedial Tarsal Tunnel Syndrome: 81 cases Journal Ultrasound 2014 Jun: 17(2):99-112 Official Journal of the Italian Society of Ultrasonology in Medicine and Biology 7. Jung Im Suk et al Ultrasound of peripheral nerves Curr Neurol Neurosci Rep 2013 Feb 13( 2) 328 8. A.L. Dellon The Dellon Approach to Neurolysis in the Neuropathy Patient with chronic nerve compression Handchir Plast chir 2008: 40, 1-10

References

9. E. Locati et al Tarsal tunnel Syndrome www. Physiopaedia.com/TTS 10. A.K. Therimadasamy et al Combination of ultrasound and NCS in the Diagnosis of Tarsal tunnel Syndrome india April 2011 vol 59 issue 2 11. A.D Lawande et al role of ultrasound in evaluation of peripheral nerves. Indian Journal of radiol Imaging 2014 Sep 24(3):254-258 12. M.De Maeseneer et al Sonography of the normal ankle: A Target approach using skeletal refernce points. American journal of roentgenology Feb 2009 vol 192 issue 2 13. E.Gallardo et al Ultrasound in the diagnosis of peripheral neuropathy: structure meets function in the neuromuscular clinic. Journal of neurointerventional surgery 2017 vol 86 14. Won-Jae Lee MD et al. Correlation between the severity of DPN and HbA1c Levels:A quantitative study 15. Fukashi Ishibashi et al Morphological changes of the peripheral nerves evaluated by high-resolution ultrasonography are associated with the severity of Diabetic Neuropathy, ...Journal of Diabetes investigation Oct 2014 16. P. Ponnapula et al Lower Extremity changes experienced during Pregnancy. The journal of Foot & ankle surgery 49 (2010)452-458

References

17. K. Singh et al High resolution ultrasonography of the Tibial nerve in Diabetic peripheral Neuropathy Dec 2017 Journal ultrasonography 17:246-25 18. L.K. Koop et al Neuroanatomy, sensory nerves. NCBI Bookshelf A service of the National Library of Medicine, National Institutes of Health Jan 2020 19. J. Jacobson et al Sonographic characterisation of peripheral nerve sheath tumours AJR:182 March 2004 20. J.Ah Ryu et al Sonographic differentiation between schwannoma and neurofibroma in the musculoskeletal system Journal of ultrasound in Medicine vol 34 Nov 2015 21. O. Fantino et al Can the axial CSA of the tibial nerve be used to diagnose tarsal tunnel syndrome? An ultrasonography study Orthopaedic & Traumatology: Surgery & Research July 2020 22. E.A Tawfik et al Proposed Sonographic Criteria for the diagnosis of Idiopathic Tarsal Tunnel Syndrome 23. C.Wright et al Who develops CTS during pregnancy: An analysis of obesity, gestational weight gain, and parity, Obestetric medicine vol 7, 2014