Carpal Tunnel Injection

Other Names

• Carpal Tunnel Injection
• Median Nerve Injection

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Background

Illustration of the carpal tunnel overlying an MRI of the wrist

Key Points

• Use a high frequency, linear transducer
• Needle: 25-27 gauge, 0.5 to 1 inch needle
• In plane view is recommended using an ulnar-to-radial approach

Anatomy of the Carpal Tunnel

• Carpal tunnel anatomic borders
  • Radial: Scaphoid tubercle, Trapezium
  • Ulnar: Hook of Hamate, Pisiform
  • Floor: Proximal carpal row (as above)
  • Roof: Transverse Carpal Ligament
• Transmits
  • Four tendons of flexor digitorum superficialis
  • Median Nerve, Found somewhat lateral to midline
  • The tendon of flexor pollicis longus (laterally)
  • Four tendons of flexor digitorum profundus

Palpation Guidance vs Ultrasound Guidance

• We recommend ultrasound guidance for injection of the carpal tunnel
• Farfour et al compared blind to ultrasound guided injections and found both groups improved, however the US guided injections produced statistically significantly better responses than the palpation guided group
• Roh found similar outcomes between groups with slightly better relief at 4 weeks in the ultrasound group and fewer cases of median nerve irritation as well
• Evers looked at retrospective data comparing blind and ultrasound guided injections and found US guided patients had better relief and reduced odds of retreatment at 1 year
• Injection accuracy of palpation guidance is around 75-80%

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Indications

• Carpal Tunnel Syndrome

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Contraindications

• Absolute
  • Anaphylaxis to injectates
  • Overlying cellulitis, skin lesion or systemic infection
• Relative
  • Can be treated with less invasive means
  • Hyperglycemia or poorly controlled diabetes
  • Lack of symptom improvement with previous injection

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Procedure

Short axis, in plane approach. (A) Transducer in short axis and in-plane needle approach. (B) US showing needle in plane adjacent to carpal tunnel. Arrows indicate flexor retinaculum, Asterisk: anechoic injectate, N: needle, MN: median nerve, T: flexor tendons

Short axis, out of plane approach. (A) shows needle and transducer position. (B) US showing median nerve (n) with needle target (*)

Long axis, in plane approach. (A) shows needle and transducer position. (B) US showing needle trajectory (arrow) over the median nerve (N)

Palpation guided approach. Clinical markup of the palpation guided approach

Equipment

• Sterile prep (i.e. chloraprep, chlorhexidine, iodine, etc)
• Gloves
• Needle: typically 21-25 gauge, 1.5 inch
• Syringe: 5-10 mL
• Gauze
• Ethyl Chloride
• Bandage
• Injectate
  • Local anesthetic
  • Corticosteroid
• Sterile probe cover

Ultrasound Findings

• Use high frequency, linear transducer
• Median nerve can be identified volar to the flexor tendons
  • Use anisotropy to distinguish tendon from nerve
• Median neuropathy in Short axis
  • swelling of the nerve can be seen
  • Cross sectional area greater than 11 mm considered pathologic
• Median neuropathy in Long axis
  • Notch sign: swelling proximal to the tunnel

Technique: Short Axis, In Plane

• Patient Position
  • Seated or supine
  • Wrist is in slight extension on a rolled towel
• Transducer position
  • Short axis to median nerve at the carpal tunnel
• Needle Approach/ Orientation
  • In plane
  • Ulnar to radial
• Target
  • Deep/superficial to median nerve
• Pearls and Pitfalls
  • Identify the radial artery, ulnar artery and nerve to avoid these structures
  • Visualize needle tip during the entire procedure
  • You can create a window with anesthetic away from the nerve in which to inject the steroid

Technique: Short Axis, Out of Plane

• Patient Position
  • Seated or supine
  • Wrist is in slight extension on a rolled towel
• Transducer position
  • Short axis to median nerve at the carpal tunnel
• Needle Approach/ Orientation
  • In plane
  • Proximal to distal
• Target
  • Ulnar to median nerve
• Pearls and Pitfalls
  • Be careful with this technique as the needle tip will not be visualized past the transducer

Technique: Long Axis, In Plane

• Patient Position
  • Seated or supine
  • Wrist is in slight extension on a rolled towel
• Transducer position
  • Long axis to median nerve at the carpal tunnel
• Needle Approach/ Orientation
  • In plane
  • Proximal to distal
• Target
  • Superficial to median nerve
• Pearls and Pitfalls
  • Identify the radial artery, ulnar artery and nerve to avoid these structures
  • Visualize needle tip during the entire procedure
  • You can create a window with anesthetic away from the nerve in which to inject the steroid

Technique: Palpation Guided

• Patient Position
  • Seated or supine
  • Wrist resting on table
• Needle Approach/ Orientation
  • Proximal to distal
• Target
  • Carpal tunnel adjacent to median nerve
• Description
  • Ask the patient to flex
  • Identify the palmaris longus tendon (blue line)
  • Mark the entry point: 1 cm ulnar to palmaris longus, ~0.5-1 cm proximal to palmar crease
  • Insert needle at 30-45 degree angle above the skin
  • Angle slightly towards the thumb
  • Advance the needle ~1 cm
  • Aspirate to confirm you are not in a vessel
  • Inject your injectate which should flow freely without resistance

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Aftercare

• No significant restrictions
• Can augment with ice, NSAIDS
• Consider temporary cock up wrist splint after procedure

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Complications

• Skin: Subcutaneous fat atrophy, skin atrophy, skin depigmentation
• Painful local reaction
• Infection
• Hyperglycemia
• Tendon, nerve or blood vessel injury

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See Also

• Procedures Main
• Ultrasound Main
• Wrist Pain Main

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