Nerve Conduction Studies- Lower Leg

This presentation describes the common conditions, anatomy and the ideal ways to do and perform nerve conduction studies in lower limbs. It is nicely depicted with self explanatory pictures.

1. NCV OF THE LOWER LIMBS BY- DR SAUMYA MITTAL 18 th NOVEMBER 2014

2. Lumbar Plexus L1-L4

3. LUMBAR PLEXUS Formed by the ANTERIOR RAMI of L1-4. Anterior rami join to form OBTURATOR N. Posterior divisions of the rami join to form FEMORAL N.

4. OTHER NERVES Other nerves include- LATERAL CUTANEOUS NERVE OF THIGH (pure sensory). ILIOHYPOGASTRIC N ILIOINGUINAL N GENITOFEMORAL N

5. Lumbar plexopathy Abrupt onset pain in anterior aspect of thigh. Muscle wasting and weakness in 2-3 weeks. Absent knee reflexes. Tender femoral N Positive femoral stretch sign Clinical features Signs

6. Sensory symptoms are partial and seen in 1/3 rd patients. NCV shows normal nerves- femoral, peroneal, sural and saphenous N. May show reduced amplitude. EMG may show changes of denervation and renervation . Recovery may be spontaneous over months-years.

7. Femoral N From dorsal portion of anterior rami of L2-L4 Mixed Nerve Normal femoral conduction velocity – 70.0 ± 5.5 m/S

8. Femoral Nerve In intraabdominal course, supplies the iliopsoas muscle. Divides to anterior and posterior division after crossing Inguinal ligament.

9. Femoral Nerve Medial cut N Supplies medial thigh Intermediate cut N Supplies anterior thigh Supply to Pectineus and Sartorius Supplies Knee and hip joint Quadriceps musc . Terminates as Saphenous N Anterior Division Posterior Division

10. Femoral Neuropathy Causes Weakness of Quadri . Wasting of Quadri . Loss of knee reflexes Sensory loss in medial aspect of thigh and leg Causes Diabetes mellitus Intrapelvic collection Pelvic surgery Hip arthroplasty Tumor of vertebra Cannulation of Femoral vein/artery Inguinal lig compression in lithotomy Renal transplant

11. Electrophysiology Surface recording electrode: belly of vastus medialis Reference electrode prox to patella. Stimulating electrode: lateral to femoral artery.

12. NCV Slowing of conduction velocity Small CMAP amplitude. Conduction block (if compressed at inguinal lig ) Saphenous vein can be used to evaluate sensory loss. Normal femoral conduction velocity – 70.0 ± 5.5 m/S

13. Saphenous Nerve Largest and longest pure sensory branch of Femoral N . Supplies skin over medial aspect of leg and foot. Normal Saphenous conduction velocity- 49.03 ± 3.36 m/s. SNAP Amplitude- 3.54 ± 1.52 µV

14. Saphenous N Arises from posterior division of Femoral N Becomes superficial just above medial condyle Continues down to head of 1 st metatarsal

15. Saphenous Neuropathy Uncommon Follows Laceration injuries Entrapment in subsartorial canal Surgery for varicose veins Causes sensory impairment in medial aspect of knee, leg and foot.

16. Saphenous Nerve Conduction Stimulate 1 cm above inferior border of patella between gracilis and sartorius . Recording electrode- 15 cm distal on medial border of tibia.

17. Stimulate between medial head of gastrocnemius and tibia, 12- 14 cm proximal to med malleolus Recording electrode is placed anterior to medial malleolus Normal Saphenous conduction velocity- 49.03 ± 3.36 m/s. SNAP Amplitude- 3.54 ± 1.52 µV

18. Lateral Femoral Cutaneous Nerve of Thigh L2-3. Sensory supply to Anterolateral aspect of thigh. Latency and Amplitude of SNAP above Inguinal Lig - 2.8±0.4ms and 6±1.5 µV

19. Meralgia Paresthetica Entrapment of the nerve at Inguinal tunnel Seat belts Obesity Unknown Proximal lesions Psoas abscess Retroperitoneal tumor Post op scarring Pain & paresthesia over lateral surface of thigh. Symptoms increase on standing and prolonged walking. Sensory loss is in area smaller than supplied by the nerve NCV- abnormal conduction in Lat Cut N of Thigh EMG- normal study of paraspinal , iliopsoas , quadriceps.

20. Nerve conduction- Lat Cut n of thigh Surface Electrode- 17-20 cm distal to Ant Supr Iliac Spine (ASIS). Reference electrode- 3 cm distal to surface electrode. Antidromic stimulation above inguinal ligament 1 cm medial to ASIS Latency and Amplitude of SNAP above Inguinal Lig - 2.8±0.4ms and 6±1.5 µV

21. SACRAL PLEXUS L4-S3 roots

22. Sacral Plexus Branches Sup Gluteal N(L4-S1) Gluteus medius Gluteus minimus Tensor facsia lata Inf Gluteal N(L5-S1) Gluteux maximus Sciatic N ( L4-S3)

23. SACRAL PLEXOPATHY Abrupt onset pain in posteror aspect of the thigh and buttocks. Weakness of knee flexor Absent reflexes. Sciatic N tenderness Positive SLR test.

24. Sciatic Nerve L4-S3 Comes out of sciatic notch Supplies all hamstrings (medial trunk) except short head of biceps femoris All muscles distal to knee Normal Sciatic N Conduction velocity- 52.75±4.66 m/s

25. Sciatic neuropathy Causes include- Trauma Fracture/ disloc of hip joint Injection Puncture wound Muscle scarring Vasculitis Compression Anesthesia Coma Lymphoma & tumours Symptoms Involvement of hamstrings Involvement of muscles below knee Variable sensory loss. Needs motor conduction studies of Peroneal N Post Tibial N Sural N Sup Peroneal N EMG

26. Sciatic N Conduction Difficult d/t deep location. Surface Electrode on distal peroneal innervated muscle eg abd hallucius Stimulation- Just below gluteal fold Medial trunk- apex of popliteal fossa Lateral trunk- head of fibula NCV

27. EMG Helps differentiate the condition and levels Denervation in paraspinal muscle + normal sural snap s/o L5/S1 radiculopathy Involvement of gluteal muscles- involvement prior to sciatic notch Peroneal neuropathy v/s sciatic neuropathy- Lat trunk- short head of biceps Med trunk- hamstrings and other tibial supp muscles Normal Sciatic N Conduction velocity- 52.75±4.66 m/s

28. Common Peroneal Nerve Lateral trunk of Sciatic N descends as Common Peroneal N

29. Course & Branches Branches- Lat Cut N of Calf Supplying anterior, lateral and posterior surface of leg Superficial Peroneal N Also supplies lateral and dorsal portion of leg and dorsum of foot. Deep Peroneal N

30. Common Peroneal Neuropathy Occurs due to compression around head of fibula. In sleep/coma Anesthesia Plaster/tight bandage Cross legging Fracture of fibula Callus/cyst/ lipoma Vasculitis Leprosy Weakness of Dorsiflexion of foot and toes Eversion of foot Cause foot drop and slapping gait Sensory loss In distribution of superficial peroneal N or lat cut N of calf, depending on level of lesion

31. Electrophysiology Evaluation by conduction study of Different segments of common peroneal nerve Superficial peroneal nerve EMG of peroneal nerve innervated muscles. Sural conduction and EMG of short head of biceps differentiate from sciatic neuropathy

32. PERONEAL NERVE CONDUCTION Surface recording- ext digi brev Stimulation – 2cm distal to fibular neck, At fibular neck 5-8cm above fibular neck Conduction velocity Below knee segment-48.3±3.9ms Above knee segment-52±6.2ms Latency on ankle stimulation 3.77±0.86ms Distal CMAP amplitude 5.1±2.3mV

33. SUPERFICIAL PERONEAL NERVE CONDUCTION Active electrode Just above junction of lateral third of a line connecting the malleoli . Reference electrode 3cm distal to active electrode. Stimulation 10-15cm proximal to upper edge of lateral malleolus anterior to peroneus longus Normal peroneal nerve conduction velocity-49±3.4ms and amplitude of SNAP 3.5±1.5µV

34. In peroneal neuropathy conduction block and reduction in motor nerve conduction velocity >10ms across head of fibula localizes the lesion at this site. In common peroneal neuropathy muscles supplied by the deep branch are frequently/severely affected. Common peroneal nerve and lateral trunk of sciatic nerve- EMG of short head of biceps are useful

35. Sural Nerve S1 and S2 Medial derived from Tibial N Lateral derived from Peroneal N Pure sensory N Sural N conduction velocity- 50.9±5.4 m/s, amplitude of SNAP 18±10.5µV

36. Sural Neuropathy Uncommon Part of generalised neuropathies Compression Baker’s cyst Against hard object Tendon sheath ganglia Scar tissue # 5 th metatarsal Presents with Numbness and paresthesia in supplied region Low conduction velocity and amplitude in NCV

37. Sural Leg should be relaxed and in lateral position. Surface Electrode- between lateral malleolus and tendoachilles . Stimulated 10-16 cm proximal to recording electrode, distal to lower border of gastrocnemius at the junction of middle and lower third of leg. Sural N conduction velocity- 50.9±5.4 m/s, amplitude of SNAP 18±10.5µV

38. Tibial Nerve Continuation of medial trunk of sciatic nerve

39. TIBIAL NEUROPATHY Damage at popliteal fossa uncommon. Causes- Baker’s cyst Nerve sheath ganglia Popliteal A Aneurysm Leprosy Weakness of plantar flexors Invertors Intrinsic foot muscles Sensory loss in sole

40. TARSAL TUNNEL SYNDROME Rare picture Pain and paresthesia of sole Weakness of intrinsic foot muscles (rare) Causes Ill-fitting footwear Tight plaster cast Post traumatic fibrosis Tenosynovitis RA Hypothyroidism Idiopathic

41. ELECTROPHYSIOLOGY Needs tibial N conduction, medial and lateral plantar N conduction, EMG. Tibial N conduction- Surface recording-abductor hallucis /abductor digiti quinti below and ant to navicular tuberosity . Stimulation behind and proximal to medial malleolus /in popliteal fossa .

42. Motor conduction of medial and lateral plantar N Recording electrode (M)- abductor hallucis (belly) Recording electrode (L)-abductor digiti quinti Nerve stimulation- behind and above medial malleolus

43. Sensory conduction of medial and lateral plantar nerves: Stimulation- 1 st and 5 th toes- M and L respectively. Recording electrode- just below medial malleolus .

44. In Tarsal Tunnel Syndrome Conduction block and latency prolongation across tarsal tunnel Accurate localisation by inching technique (1cm) -abrupt prolongation in latency. Normal conduction velocity of Tibial N-48.3±4.5ms Motor conduction Latency for medial plantar nerve-3.8±0.5ms Latency for lateral plantar nerve-3.9±0.5ms Sensory conduction for Latency for medial plantar nerve-2.4±0.2ms, 3.2±0.3ms, 4±0.2ms (10,14 and 18 cm segment). Latency for lateral plantar nerve-3.2±0.3ms,4±0.3ms (14 and 18 cm segment).

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