Skill Checkup: Carpal Tunnel Steroid Injection

Carpal tunnel syndrome (CTS) is a common mononeuropathy resulting from entrapment of the median nerve in the carpal tunnel. Symptoms include hand paresthesia, numbness, and pain in the median nerve distribution of the hand. Conservative treatment options, in addition to carpal tunnel steroid injection, include rest, splinting, oral steroids, ultrasound, yoga, physical or occupational therapy, and ergonomic modification. Surgical intervention is reserved for severe symptoms.

Carpal tunnel steroid injection has been shown to reduce short-term symptoms prior to definitive surgical intervention. Local steroid injection and surgical decompression are effective treatments at 2-year follow-up, with surgical intervention having some additional benefit.

Indications

Electromyographic studies consistent with mild to moderate median nerve entrapment
Symptoms not relieved with other conservative measures

Procedure

Landmark procedure

Have the patient seated or in supine position, with affected wrist supinated and resting on a small, rolled towel allowing for wrist dorsiflexion.

Identify the flexor carpi radialis (FCR) (radial) and palmaris longus (ulnar) tendons. Prep the skin using antiseptic solution. Some patients lack a palmaris longus. In this case, the ulnar landmark is the flexor digitorum superficialis (FDS), which is typically deep to the palmaris longus in patients who have one.

Using a 25- or 27-gauge needle, make a skin wheal with 1% lidocaine just ulnar to the FCR tendon and approximately 1 cm proximal to the wrist crease.

In a separate syringe, draw up the steroid and enter the skin at the skin wheal just ulnar to the FCR tendon, using a 25- or 27-gauge needle. Direct the needle toward the third digit at a 30° angle. Advance the needle approximately 1.5-2 cm. Aspirate to verify that the needle is not intravascular, and inject the steroid with little or no resistance. If the patient feels paresthesias, retract the needle and redirect in either an ulnar or radial direction and then inject.

Remove the needle and place the wrist in a gravity-dependent position, advising the patient to move the fingers for several minutes to facilitate even distribution of the solution. The landmark procedure is shown in the video below.

Several approaches to ultrasound-guided carpal tunnel injections have been described.

For the out-of-plane approach/short-axis view, using a high-frequency ultrasound transducer held transverse across the wrist, the median nerve is identified under the flexor retinaculum. The needle is advanced out of plane, proximal to the ultrasound transducer and directed toward the third digit. Once under the flexor retinaculum, the steroid solution is injected with low resistance to surround the median nerve.

For the in-plane approach/short-axis view, using a high-frequency ultrasound transducer, the wrist is imaged by placing the probe transverse across the dorsiflexed wrist. The median nerve and ulnar artery are identified. At the level of the distal wrist crease, the needle is passed into the skin, superficial to the ulnar artery, penetrating the flexor retinaculum. The needle is advanced toward the median nerve. The steroid solution is injected just under the flexor retinaculum and then retracted and redirected deeper to the ulnar side of the median nerve. This allows the median nerve to be completely surrounded with the steroid solution.

See the images below.

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Figure 1.

Short-axis view ultrasound probe placement

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Figure 2.

In-plane approach with block needle

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Figure 3.

Short-axis view

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Figure 4.

Short-axis view with Doppler

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