Peripheral Nerve Injuries: Diagnosis

• Differential diagnosis focuses on the peripheral nervous system

Objectives

• Review common injury mechanisms of peripheral nerve injuries in extremities
• Describe diagnostic findings with various peripheral nerve injuries
• Identify risk factors of specific peripheral nervous system entrapments

Symptoms of Peripheral Nerve Involvement

• General nerve injury symptoms include numbness, tingling, and radiating pain
• Pain is described as burning, shooting, or piercing
• Hyperalgesia or allodynia is possible
• Weakness may occur
• Symptoms follow the nerve's distribution
• Possible sympathetic response or ischemic pain may occur

Common Causes of Injury

• Axillary nerve injuries result from shoulder dislocations or surgical neck fractures of the humerus
• Musculocutaneous nerve injuries are from lacerations or projectile wounds
• Median nerve injuries include impingement in the hypertrophied pronator teres or compression in the carpal tunnel
• Ulnar nerve injuries involve impingement at the cubital tunnel, impingement between heads of flexor carpi ulnaris, compression in tunnel of Guyon, or trauma at the elbow
• Radial nerve injuries are caused by shoulder dislocations, mid-humerus fractures, or compression at the axilla
• Femoral nerve injuries stem from pelvis or upper femur fractures, pressure during forceps delivery, reduction of congenital hip dislocation, or surgical complications
• Obturator nerve injury is rare in isolation, may result from pelvis and femur fractures, or damage during childbirth
• Sciatic nerve injuries are caused by compression from the piriformis muscle or hip dislocation/reduction
• Tibial nerve injuries can result from trauma at the knee or medial malleolus

Upper Extremity Peripheral Nerve Injuries

• Axillary nerve (C5,6) injury leads to impaired shoulder abduction (ABD) and external rotation (ER), plus deltoid atrophy, causing a "square shoulder" appearance
• Musculocutaneous nerve (C5,6, C7) injury causes weakness in elbow flexion, especially when the forearm is supinated, and atrophy of the flexor surface of the upper arm
• Median nerve (C6-8, T1) injury results in weakness in forearm pronation, weak grip, impaired thumb opposition & abduction, and atrophy of the thenar eminence
• Ulnar nerve (C8, T1) injury causes loss of 4th and 5th digit function for cylindrical and spherical grip, impaired thumb adduction and finger ABD/ADD, and atrophy of hypothenar eminence and ulnar drift of the 5th finger
• Radial nerve (C5-8, T1) injury can result in triceps weakness (higher lesions), weak supination, difficulty forming a fist or gripping unless the wrist is stabilized in extension, and weakness of wrist extensors and finger extensors

Lower Extremity Peripheral Nerve Injuries

• Femoral nerve (L2-4) injury causes hip flexion and knee extension weakness, anterior thigh atrophy, difficulty controlling the knee during loading response (buckling), and difficulty with hip flexion to initiate swing phase (circumduction/hiking)
• Obturator nerve (L2-4) injury leads to hip adduction and rotation difficulties, plus medial thigh atrophy
• Sciatic nerve (L4-5, S1-3) injury results in weak knee flexion, impacts foot/ankle control, "sciatica" pain radiating to posterior thigh and calf, and atrophy of posterior thigh, leg and foot
• Tibial nerve (L4-S3) injury causes weakened plantarflexion and toe flexion, calf atrophy, impaired "push-off" at terminal stance; may develop claw toes or pes cavus with injury to medial and lateral plantar nerves
• Common Peroneal nerve (L4-S2) injury causes weakness of dorsiflexors and toe extensors (deep peroneal branch) and evertors (superficial peroneal branch) that results in foot slap/drop and steppage gait or pes valgus/ equinovarus

Nerve Entrapment Conditions: Thoracic Outlet Syndrome (TOS)

• The subclavian artery, subclavian vein, and/or brachial plexus is compressed
• Repetitive upper extremity activities, especially overhead motions at high intensity, are risk factors
• Bony anomalies like cervical ribs or clavicle anomalies can increase risk
• Fibromuscular abnormalities like scar tissue or muscle hypertrophy is also a risk
• Prior trauma to the cervicothoracic or shoulder region and faulty posture are risk factors

Additional TOS subtypes

• Neurogenic TOS is more common in females with typical onset age 20 to 40 years, deep aching pain in the neck/shoulder/chest region, and arm/forearm/finger pain; tingling/numbness in arm/hand and symptoms are worse at night plus arm/hand fatigue and a sensation of heaviness, loss of dexterity, cold intolerance, or headaches are additional symptoms
• Venous TOS is more common in males with onset age 20-30 years, include effects such as Paget-Schroetter syndrome (effort thrombosis of UE), pain in affected arm (strenuous use), UE numbness/tingling, arm/hand swelling, veins of shoulder and chest appear more visible or distended
• Arterial TOS affects males and females equally with onset at age 20-30 years, includes pain at rest & with UE activity, UE numbness/tingling, hand appears pale, arm/hand is cool to touch, decreased UE pulses, blood pressure differential >20 mmHg

TOS Activity Limitations

• Sleep disturbances
• Difficulty carrying heavy objects with shoulder strap
• Difficulty maintaining prolonged overhead positions or repetitive overhead tasks
• Difficulty with sustained computer/desk work or driving for prolonged periods

Cubital Tunnel Syndrome

• Entrapment/compression of the ulnar nerve at the elbow
• Risk factors include prior fracture or dislocation of the elbow, bone spurs/arthritis of the elbow, swelling/inflammation around the elbow joint and cysts near the elbow joint

Symptoms of Cubital Tunnel Syndrome

• Aching on the medial aspect of the elbow and tenderness (TTP) just distal to the medial epicondyle
• Numbness & tingling in 4th and 5th fingers increases when the elbow is bent in driving, holding the phone, sleeping
• Severe compression leads to grip impairment, difficulty with finger coordination, atrophy of intrinsics

Other Sources of Ulnar Nerve Irritation at Elbow

• Subluxation of the nerve from behind the medial epicondyle with elbow flexion
• Tissue usually traps the nerve and alters mobility which can lead to further nerve irritation and damage over time
• Nerve compression from leaning on the elbow for long periods or elbow swelling may compress the nerve and medial epicondylitis can cause this
• Direct blow to inside of the elbow causes irritation as well

Ulnar Nerve Compression at Ulnar Tunnel

• Guyon's canal contains a fibro-osseous compartment localized at the ulnar side of the palmar aspect of the wrist that is ~4cm long
• It begins at the proximal aspect of the transverse carpal ligament & extends to the aponeurotic arch of the hypothenar muscles

Ulnar Nerve Compression - Zones of Injury

• Zone 1 has mixed motor and sensory disruption
• Zone 2 has motor only disruption
• Zone 3 has sensory only disruption

More Information on Ulnar Nerve Compression

• Most common non-traumatic cause stems from ganglion cyst near wrist joint compresses the nerve
• Trauma, repetitive trauma, chronic pressure, fracture to hook of hamate, dislocation of pisiform, inflammatory arthritis, or bony anomaly are other causes
• Symptoms will greatly depend upon zone of injury with symptoms often worsened by repetitive gripping and increasing numbness
• Weakness in 5th finger and the degree of weakness & numbness depend on site of compression while pain can be present or not
• Progression leads to difficulty opening jars, or/ difficulty holding objects & coordinating the fingers or partial claw hand deformity and atrophy of hypothenar eminence & intrinsics of

Radial Tunnel Syndrome (RTS)

• Radial tunnel extends from radial head to inferior border of supinator located at Boundaries formed by supinator, ECRL, ECRB, & brachioradialis

• Compression may occur at 5 sites along the tunnel with the most common site being location Arcade of Frohse (superior border of superficial layer of supinator muscle)

• Pain is primary symptoms and often mimics lateral epicondylitis

  • Lateral epicondylitis has point tenderness over the epicondyle
  • RTS has localized tenderness over the radial nerve 5 cm distal to the lateral epicondyle

• Pain increased with actively extending wrist or supinating, especially against resistance or increased pain with wrist flexion, ulnar deviation, and pronation

Radial Nerve Entrapment

• Posterior Interosseous Nerve (PIN) related with
  • Weakness of wrist extensors and finger extensors
  • Grip is impacted if unable to attain appropriate wrist position
• Superficial Branch
  • Sensory Issues only

Carpal Tunnel Syndrome (CTS)

• Compression of the median nerve
• Numbness & tingling in thumb, index and middle fingers (radial half of ring finger), wrist pain, weakness of thumb
• Decreased grip strength that is often worse at night, driving, or prolonged flexed or extended wrist position
• Heredity, female sex, or repetitive hand are contributing factors
• Hormonal changes, age or medical conditions of DM, RA, thyroid dysfunction

Further Information on Carpal Tunnel Syndrome (CTS)

• Can be affected by obesity or pregnancy (fluid retention)

• Local tumor and oral contraceptives may be implicated as well as diabetes mellitus and hormonal imbalance from menopause

• Systemic illness like Amyloidosis or Arthritis (rheumatoid, gout, polymyalgia rheumatica) or dermatomyositis can be factors

• Systemic Lupus or Alcohol abuse are examples of systemic illnesses that lead to CTS

• Chemotherapy (delayed, long-term effect) or Vitamin/nutritional deficiency (vitamin B6; folic acid)

Anterior Interosseous Nerve (AIN) Syndrome

• Includes weakness of thumb opposition and flexion as well as weakness of finger flexion and difficulty making full fist
• No parathesias will be present
• The flexor pollicis longus and lateral half of flexor digitorum profundus as well as pronator muscles are impacted

Piriformis Syndrome

• Compression of the sciatic nerve by the piriformis muscle can stem from muscle tightness
• Pain results in the buttocks that has numbness and tingling in the legs following the distribution of the sciatic nerve
• Primary piriformis syndrome from pathology inside the piriformis itself
• Secondary piriformis syndrome is a pelvic outlet syndrome
  • It is related to tumor and leg length discrepancy and total hip arthroplasty(THA)

Common findings associated with Piriformis Syndrome

• H/o trauma to the SI and/ or gluteal region as well as pain in the region of the SI joint, greater sciatic notch, and/or piriformis muscle
• Increased pain with lifting or Palpating of spasms and TTP over the piriformis or a positive straight leg raise
• The person will have gluteal atrophy (chronic & severe cases), pain and/or weakness with resisted hip ER and hip ABD alongside Increased symptoms with walking and prolonged sitting

Tarsal Tunnel Syndrome

• Neuralgia of the tibial nerve or any of its terminal branches with tarsal tunnel

• Roof: flexor retinaculum and Floor: medial surfaces of the talus and calcaneus

  • Medial plantar artery is in this same area!

• From anterior to posterior: -Tibialis posterior tendon and flexor digitorum longus tendon

  • The tibial nerve and flexor hallucis longus tendon are also in this space

Common Causes of Tarsal Tunnel Syndrome

• Idiopathic in 50% of presentations and Ganglion cysts are also associated
• Bone deformity from calcaneal fractures or varicosities can be the issue with Tenosynovitis of the flexor tendons alongside tumors being presented
• The person may have a hypertrophied abductor hallucis muscle or synovial hypertrophy plus a hind-foot valgus or post-traumatic fibrosis

Typical presentation of Tarsal Tunnel Syndrome

• The person will have to pain & paresthesia in toes, volar aspect of foot, and/or medial ankle/heel with Burning pain associated with this

• The pain is often exacerbated with overpressure into DF with EV

• Distal calf pain, with Claw toe deformity and weakness of intrinsic toe flexors can be associated

Soleal Sling Syndrome

• Compression of proximal tibial nerve that tunnels between with superficial & deep components of posterior leg at the point of origin of soleus
• Foot and calf pain with associated numbness or tingling in the plantar foot
• Posterior lower leg pain can occur that can be palpated ~ 9 cm below flexion crease of the knee alongside Tinel's at area
• Active plantarflexion can greatly increase pain and weakness of toe flexion (especially FHL) and possibly gastroc

"Double Crush" Syndrome

• Controversial condition that refers to the possibility multiple location of compression along just a single peripheral nerve
• Requires using strict diagnostic criteria (EMG/NCV testing) and anatomic criteria and has very low incidence
• It is mostly see in those with those with CTS and cervical root and is associated with systemic and vascular factors with systemic disease

Differentiating Radiculopathy from More Peripheral Entrapment

• One should clinically start at the spine and move peripherally

• For radiculopathy the pattern is myotomal/dermatomal while nerve entrapment is more localized

• Positive Spurlings test while using the ULTT median. Test is also useful alongside cervical rotation