Carpal Tunnel Injection

Carpal tunnel injection with corticosteroid is used to treat the carpal tunnel syndrome in which the median nerve is compressed under wrist flexor retinaculum.

Some of the contraindications to carpal tunnel injections include:

1. Patient refusal,
2. Infection over the injection site,
3. Edema at the injection site.
4. Patients on anticoagulation may undergo carpal tunnel injections, but with careful evaluation for bleeding. 

See Also: Carpal Tunnel Syndrome

Equipment Needed

• Syringe: 1 ml
• Needle: Blue, 23 gauge / 1.25 inches (30 mm)
• Kenalog 40: 20 mg
• Lidocaine: Nil
• Total volume: 0.5 ml

Related Anatomy

The flexor retinaculum of the wrist attaches to four sites – the pisiform, the scaphoid, the hook of hamate and the trapezium. It is approximately as wide as the thumb from proximal to distal, and the proximal edge lies at the distal wrist crease. The median nerve usually lies immediately under the palmaris longus tendon at the midpoint of the wrist and medial to the flexor carpi radialis tendon. If no palmaris longus is present, the patient presses the tip of the thumb onto the tip of the little finger; the crease seen at the midpoint of the palm points to where the median nerve should lie.

Carpal Tunnel Injection Technique

• The patient may be seated or supine during the injection.
• The patient is instructed to place his affected hand with palm up,
• Identify point midway along proximal wrist crease, between flexor carpi radialis and median nerve.
• Insert the needle at this point and then angle it 45 degrees. Slide distally until the needle end lies under the midpoint of retinaculum
• Inject corticosteroid solution as a bolus.

The patient rests until symptoms abate and then resumes normal activities. A night splint helps in the early stages after the infiltration, and the patient is advised to avoid sleeping with the wrists held in full flexion – the dormouse position.

Carpal Tunnel Injection Ultrasound

An ultrasound linear array probe can be used to scan the wrist for any anatomical variants such as volar ganglion cysts, flexor tendon tenosynovitis, and tumors. The probe is then placed transversely at the proximal wrist crease by the entrance to the carpal tunnel.

The goal is to have the pisiform, ulnar nerve, and ulnar artery in view as well as the median nerve. Doppler imaging can aid in determining vascular structures. The median nerve is identified and most often edematous. The injectate is targeted around the nerve in a target sign. The subsynovial tissue may also be injected, which has recently been implicated as the etiology of idiopathic CTS.

Notes

No local anaesthetic is used here because the main symptom is paraesthesia, and more volume increases pressure within the tunnel. Avoid inserting the needle too vertically, when it will go into bone, or too horizontally, when it will enter the retinaculum.

If the patient experiences paraesthesia, the needle is in the median nerve and must be withdrawn slightly and repositioned. The injection can be performed equally well by inserting the needle between the median nerve and the flexor tendons, using the same dose and volume.

Although one injection is often successful, recurrences do occur. Further injections can be given, but if symptoms still recur, surgery may be required. If the patient has continuous numbness and/ or thenar eminence wasting, refer promptly for decompressive surgery.

A comparative study of several locations found that injecting within the flexor carpi radialis tendon proximal to the carpal tunnel might be the safest.

Carpal Tunnel Injection Complications include:

1. Bleeding
2. Elevated blood glucose levels
3. Infection
4. Median nerve injury 
5. Pain
6. Paresthesias

References & More

1. Injection Techniques in Musculoskeletal Medicine. A Practical Manual for Clinicians In Primary And Secondary Care. Fifth Edition.
2. Racasan O, Dubert T. The safest location for steroid injection in the treatment of carpal tunnel syndrome. J Hand Surg Br. 2005 Aug;30(4):412-4. doi: 10.1016/j.jhsb.2005.04.009. PMID: 15950338.
3. Schwartz RH, Urits I, Viswanath O. Carpal Tunnel Injection. [Updated 2022 Jan 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557828/
4. Median Nerve Injuries Caused by Carpal Tunnel Injections – Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/A-Ultrasound-guided-carpal-tunnel-injection-It-shows-transducer-position-for_fig1_261765968 [accessed 15 Nov, 2022]
5. Smith J, Wisniewski SJ, Finnoff JT, Payne JM. Sonographically guided carpal tunnel injections: the ulnar approach. J Ultrasound Med 2008; 27: 1485-90.