Pathophysiology of Peripheral Nerve Lesions Part 3: Lower Extremity Entrapment Syndromes

1. Pathophysiology of Peripheral Nerve LesionsPart 3: Lower Extremity Entrapment Syndromes David A. Lake, PT, PhD Department of Physical Therapy Armstrong Atlantic State University Savannah, GA

2. Obturator Nerve • Obturator Nerve Anatomy • Arises from anterior division of L2-4 spinal nerves • Passes along the medial edge of the psoas and over the sacroiliac joint • Passes through the obturator canal (foramen) to enter the medial thigh

3. Obturator Nerve • Obturator Nerve Entrapment results from: • Abdominal tumors • Endometriosis • Obturator hernias • Abdominal trauma & surgery • Symptoms • Pain along medial thigh

4. Obturator Nerve • Symptoms of Obturator neuropathy reported by patient include: • Pain along medial thigh - “obturator neuralgia” common • Numbness along medial thigh also common • Occassionally report gait abnormalities • Rarely do patients report weakness

5. Obturator Nerve • Neurologic findings of Obturator damage include: • Weakness in thigh adduction • Circumduction of thigh when walking • Occassionally wide stance • Positive EMG signs of denervation in adductor muscles

6. Femoral Nerve • Anatomy of the Femoral nerve • Posterior division of L2-L4 spinal nerves • Passes over and innervates the psoas and iliacus • Passes under the inguinal ligament to enter the anterior thigh

7. Femoral Nerve • Injury most commonly occurs in one of two places • In the retroperitoneal space • Under the inguinal ligament • Less commonly as a stretch injury from hip hyperextension

8. Femoral Nerve • Injury in the retroperitoneal space • Most common secondary to abdominal surgery and retroperitoneal hematomas • Estimated that in up to 7.5% of hysterectomies there is femoral nerve damage

9. Femoral Nerve • Injury under the inguinal ligament • Most common secondary to nerve compression during lithotomy positioning • Estimated that femoral nerve damage occurs in up to 2.3% of total hip surgeries particularly in complicated revisions • Less common from inguinal hematomas resulting from femoral vessel catheterization

10. Femoral Nerve • Symptoms of nerve injury reported by patients • Most commonly unilateral but can be bilateral after lithotomy • Weakness in quadriceps femoris muscles • Knee buckling on weightbearing • Easy loss of balance and falling • Numbness on anteromedial thigh & leg • Pain usually only with retroperitoneal hematomas

11. Femoral Nerve • Diagnosis of femoral nerve injury • Weakness of quads with diminished or eliminated patellar tendon reflex • Thigh adduction and ankle dorsiflexion strength is normal • MR & CT for presumed space occupying lesion • NCV studies of CMAP of femoral nerve and SNAP of saphenous nerve show  amplitudes and conduction velocities • Spontaneous activity and  recruitment of MUAPs of quadriceps femoris

12. Femoral Nerve • Terminology note: • Saphenous nerve is the sensory branch of the femoral nerve • NCV - nerve conduction velocity but also includes amplitude in of the compound action potentials from surface recordings • CMAP - compound motor action potentials • SNAP - sensory nerve action potentials • MUAPs - motor unit action potentials recorded with needle electrodes in the muscle

13. Saphenous Nerve • Anatomy of Saphenous Nerve: • Saphenous nerve branches from the femoral nerve in the groin and travels distally though the subsartorial (Hunter’s or adductor) canal • Becomes subcutaneous medial to the patella to innervate skin over anterior patella • Continues along medial leg

14. Saphenous Nerve • Anatomy of Saphenous Nerve: • Saphenous nerve terminal branches innervate the skin of: • The medial knee • The medial leg down to the medial malleolus • A small area of the medial arch of the foot

15. Saphenous Nerve • Neuropathies of Saphenous nerve occur: • Occasionally through entrapment as it exits the subsartorial canal next to the pes anserine bursa as a result of bursitis or other narrowing of the canal • Most commonly the result of damage with: • Varicose vein surgery • Removal of the saphenous vein for coronary artery bypass grafting • Arthroscopic surgery of the knee

16. Saphenous Nerve • Primary symptoms of nerve damage reported by patients include: • Paresthesia, hyperthesias and pain along the medial leg • Knee pain is also common and if only the infrapatellar branch is damaged , there may only be anterior knee numbness

17. Saphenous Nerve • Diagnosis is done with the following findings: •  SNAP of saphenous nerve • No weakness in quadriceps femoris muscles • Normal EMG findings in quadriceps femoris, hip adductors and iliacus • Occasionally + Tinel sign over subsartorial canal

18. Lateral Femoral Cutaneous Nerve • Anatomy of the Lateral Femoral Cutaneous Nerve (LFCN): • Arises from L2 & L3 • Passes through abdomen over iliacus • Emerges under inguinal ligament next to anterior superior iliac spine • Penetrates fascia lata to ramify over lateral thigh

19. Lateral Femoral Cutaneous Nerve • Neuropathy of the LFCN: • Termed Meralgia Paresthetica and most commonly due to compression under the inguinal ligament • Contributing factors can include: • Pregnancy • Obesity • Wearing a heavy tool belt or very tight belt • Automobile accident restrained by seatbelt • Chronic leaning against object such as gymnastic bars

20. Lateral Femoral Cutaneous Nerve • Symptoms patients report with LFCN neuropathy: • Pain (burning), numbness, paresthesia or occasion-ally hyperesthesia along the lateral thigh - where a pants pocket is • Sometimes worse with standing, walking, running, turning in bed • May improve with hip flexion

21. Lateral Femoral Cutaneous Nerve • Diagnosis of LFCN neuropathy: • History of precipitating factor • Pattern of pain, numbness, paresthesias along lateral thigh •  SNAP amplitude and conduction velocity • Lack of quadriceps or adductor weakness or sensory loss over femoral or obturator distributions

22. Lateral Femoral Cutaneous Nerve • Some evidence for physical therapy intervention effectiveness from case study: • Thermal US & mobilization to inguinal ligament followed by icepack • 3 treatments/week for 3 weeks reduced pain from 6/10 to 2/10 • Lasted until patient started running again • Subsequent treatments reduced pain again

23. Sciatic Nerve • Anatomy of Sciatic Nerve • Arises from L5, S1 & S2 • Composed of lateral division, the common peroneal nerve, and the medial division, the tibial nerve, in a common sheath • Leaves the pelvis through the greater sciatic notch • Rise just inferior to the piriformis to run deep to the gluteus maximus

24. Sciatic Nerve • Anatomy of Sciatic Nerve • However in 10-30% of subjects, either all or part of the sciatic nerve penetrates the piriformis muscle (b or d in picture)

25. Sciatic Nerve • Neuropathies of the Sciatic Nerve can result from: • Entrapment by the piriformis • Posterior dislocation of the hip joint • Acetabular fracture, repair of femoral neck fracture or hip arthoplasty

26. Sciatic Nerve • Neuropathies of the Sciatic Nerve can result from: • Prolonged compression of the buttock or posterior thigh • Inappropriately administered intramuscular injection in the buttock • Small vessel disease blocking vessel to nerve

27. Sciatic Nerve • Symptoms reported by patients with Sciatic Neuropathies include: • Loss of muscle strength of all muscles below the knee and the hamstrings and adductor magnus • Paresthesias, numbness or pain in all areas below the knee except the medial leg area served by the saphenous nerve

28. Sciatic Nerve • In partial injury common peroneal nerve more vulnerable because • fewer axons than tibial nerve • more exposed to traction injury being tightly secured at fibular head and sciatic notch.

29. Sciatic Nerve • Differential diagnosis of sciatic neuropathy • Easy from distribution of motor and sensory loss • Foot drop • NCV & EMG studies to confirm diagnosis • Differentiate from L5 & S1 radiculopathy by pattern of muscle impairment and sensory loss

30. Sciatic Nerve • Differential diagnosis of sciatic neuropathy • Motor L4-L5 loss is hip extensor/knee flexor weakness • Motor L5 loss is foot drop & no heal walking and weakness in toe extension • Motor S1 loss is lack of plantar flexion & toe walking

31. Common Peroneal Nerve • Anatomy of the Common Peroneal Nerve • Splits from the Tibial Nerve at some point before the popliteal fossa • The lateral cutaneous nerve of the calf and the lateral sural nerve arise in the popliteal fossa

32. Common Peroneal Nerve • Anatomy of the Common Peroneal Nerve • It curves lateral around the neck of the fibula through the “fibular tunnel” made by the fibula and tendon of the peroneus longus • It then splits into the deep and superficial peroneal nerves

33. Common Peroneal Nerve • Peroneal Nerve Neuropathies • Most common site of injury is the fibular neck where it can suffer different forms of injury including: • Traction • Compression • Other forms of trauma

34. Common Peroneal Nerve • Peroneal Nerve Neuropathies • Compression • Lying on with pressure on fibular head (coma, anesthesia) • Pressure wrapping around knee including: casts, AFOs, compression stockings, & pneumatic splints • Recent loss of weight and loss of fat padding around the fibular head added risk

35. Common Peroneal Nerve • Peroneal Nerve Neuropathies • Traction • Prolonged squating such as crop harvesting, yoga meditation and exercises • Lithotomy positioning for prolonged periods such as in childbirth • Ankle sprains • Trauma • Blunt trauma as well as open wounds • Fibular fractures or dislocations • Surgical procedures such as arthroscopic or open knee procedures

36. Common Peroneal Nerve • Peroneal Nerve Neuropathies • Other factors • Diabetics and others with polyneuropathies are particularly prone to injury at this point • Prolonged (> 30 min) cold applied to the knee has been shown to produce irreversible injury to the common peroneal nerve at this point as well

37. Common Peroneal Nerve • Symptoms of Peroneal Nerve Neuropathies include: • Complete or partial footdrop • Paresthesias or numbness on the anterio-lateral leg & dorsum of the foot • Mild, deep “boring” pain around the lateral leg and knee may be reported

38. Common Peroneal Nerve • Diagnosis of Peroneal Nerve Neuropathies include: • History generally is related to a sudden onset with a single episode of trauma or compression • 3-fold higher incidence in males • Generally unilateral (approx 10% bilateral) • Weakness in ankle dorsiflexion & toe extension with retention of ankle plantar flexion, inversion, toe flexion and ankle eversion

39. Common Peroneal Nerve • Diagnosis of Peroneal Nerve Neuropathies include: • Normal quadriceps and plantar flexor reflexes (patellar & achilles tendon reflexes) • NCV studies involve CMAP from tibialis anterior and extensor digitorum brevis, SNAP from sensory component and spontaneous activity and  MUAP recruitment

40. Common Peroneal Nerve • Differential Diagnosis of Peroneal Nerve Neuropathies require: • Distinguish from flail foot - peripheral neuropathy has just weakness while flail foot is total incoordination of all movements • Distinguish from upper motoneuronal injury (head injury or stroke) - normal plantar flexor and knee extension reflexes in neuropathy but changed in upper motoneuronal disorders • Distinguish from sciatic mononeuropathy

41. Tibial Nerve • Anatomy of the Tibial Nerve: • Originates primarily from L4-S2 after formation in the posterior thigh it continues along the midline posteriorly through the popliteal fossa • In the popliteal fossa it gives off the medial sural cutaneous nerve and motor branches to the popliteus, plantaris, gastrocnemius & soleus

42. Tibial Nerve • Anatomy of the Tibial Nerve: • The tibial nerve then runs beneath the fibrous arch of the soleus and at this point is commonly referred to as the posterior tibial nerve • Innervates tibialis posterior, flexor digitorum longus & flexor hallucis longus as it runs with these muscles • Exits the leg through the tarsal tunnel inferior to the medial malleolus

43. Tibial Nerve • Anatomy of the Tibial Nerve: • Tarsal tunnel has osseous base and roof is the flexor retinaculum • Exits the tarsal tunnel & gives off the medial calcaneal nerve. • But the medial calcaneal nerve often branches proximal to the tarsal tunnel • It splits into the medial and lateral plantar nerves

44. Tibial Nerve • Anatomy of the Tibial Nerve: • The medial and lateral plantar nerves enter the foot through the fascial origin of the abductor hallicus longus which is referred to as the abductor tunnel

45. Tibial Nerve • Tibial Neuropathies: • Damage in or around the popliteal fossa • Damage in the tarsal tunnel (tarsal tunnel syndrome)

46. Tibial Nerve • Tibial Neuropathies: • The popliteal fossa is the most common site of tibial nerve injury (48% in a recent study) followed by distal to it - mostly in the tarsal tunnel (27%) and then proximal to it (25%) • Most common etiology is trauma (56%) followed by ischemia (19%) & neoplasms (17%) • Lesions proximal to the popliteal fossa most commonly from cast compression or blunt trauma

47. Tibial Nerve • Tibial Neuropathies: • Popliteal lesions of the tibial nerve occur mostly from penetrating and non-penetrating trauma, tibial dislocations during knee injury and only very rarely following surgical procedures • Tibial nerve lesions distal to the popliteal fossa are primarily the result of tibial fractures, posterior compartment syndrome, and entrapment in the tendinous arch of the soleus or in fibrous bands between heads of gastrocnemius

48. Tibial Nerve • Tibial Neuropathies: • Most common cause of tarsal tunnel syndrome injury is secondary to trauma • Displaced fracture of distal tibia • Fracture of tarsal bones • Fracture of the calcaneous • Medial ankle sprains • Tenosynovitis of tendons in tarsal tunnel (tibialis posterior, flexor hallucis longus, flexor digitorum longus • Perineurial fibrosis secondary to trauma

49. Tibial Nerve • Tibial Neuropathies: • Other non-traumatic causes of tarsal tunnel syndrome • Space occupying lesions such as tumors, ganglia • Foot deformities such as varus heel with pronated forefoot or valgus heel with abducted forefoot (pes planus) • Rarely but seen with patients with diabetes and inflammatory arthritis

50. Tibial Nerve • Symptoms: • Sensory disturbances in the distribution of the sural, medial & lateral plantar and medial calcaneal nerves - posteromedial leg (calf), lateral ankle, on the lateral aspect, sole and heel of the foot • If damage proximal to popliteal fossa weakness in ankle plantar flexion and inversion and toe flexion • Weakness of knee flexion may be seen if denervation of gastrocnemius