What are the recommended landmarks for a carpal tunnel syndrome injection?

Carpal Tunnel Injection Landmarks

For carpal tunnel injections using anatomic landmarks, insert the needle just ulnar to the palmaris longus tendon (or at the radial border of the median nerve) at the wrist crease, though ultrasound guidance significantly improves accuracy and safety when available.

Optimal Injection Technique

Landmark-Based Approach

Primary recommended site:

• Insert the needle at the wrist crease, just ulnar to the palmaris longus (PL) tendon 1, 2
• Alternative landmark: inject through the flexor carpi radialis (FCR) tendon, as the median nerve extends medially beyond the PL tendon in 88% of cases 3
• The median nerve lies approximately 3 mm ulnar to the palmaris longus and 9.57 mm ulnar to the FCR tendon 4

Critical safety zone:

• Avoid injection within 1 cm of either edge of the palmaris longus tendon, as this risks median nerve injury 3
• The median nerve averages 7.85 mm in width and typically lies ulnar to both the palmaris longus and the midpoint of the wrist 4
• If injecting between tendons, aim midway between the palmaris longus and flexor carpi ulnaris, just proximal to the transverse carpal ligament, in line with the ring finger superficialis tendon 2

Alternative Distal Approach

A novel technique uses injection 2-3 cm distal to the wrist crease (rather than the traditional 3-4 cm proximal), which demonstrates comparable efficacy with significantly reduced procedure time (8.5 vs 26.7 seconds) and potentially less pain 5

Ultrasound Guidance Superiority

Ultrasound guidance should be used when available, as it significantly improves accuracy and outcomes 6:

• The American Institute of Ultrasound in Medicine notes ultrasound-guided injections show significant improvement in severity over 12 weeks compared with landmark-guided injections 6
• Landmark-based injection accuracy is only 75.7% for proper carpal tunnel placement, with 8.7% resulting in median nerve penetration 1
• This accuracy is lower than previously reported rates of 82-100%, indicating landmark injection may be less reliable than historically thought 1

Critical Safety Considerations

Stop and redirect immediately if the patient experiences any paresthesias during injection 2:

• Direct median nerve injection can cause permanent damage requiring neurolysis 2
• The ulnar neurovascular bundle is at risk with injections placed too far medially 3

Aseptic technique is mandatory:

• Use surgical gloves and skin preparation with alcohol, iodine, or chlorhexidine 7
• Change needles between drawing medication and injecting 7
• Risk of septic arthritis is 0.035% (3 per 7,900 procedures) 7

Timing Considerations

Do not inject within 3 months of planned surgery, as this increases infection risk 8, 6:

• The American Academy of Orthopaedic Surgeons specifically advises against corticosteroid injection in the pre-surgical window 8, 6
• Limit to maximum 2-3 injections total 6

When to Avoid Landmark-Based Injection

Consider ultrasound guidance or referral when:

• Patient anatomy is unclear or atypical 6
• Previous injection attempts have failed 6
• Severe obesity obscures landmarks 6
• Pregnancy (though conservative splinting should be attempted first) 9