A carpal tunnel injection with corticosteroids is used to treat carpal tunnel syndrome, a condition where the median nerve becomes compressed beneath the flexor retinaculum of the wrist.
Patients on anticoagulation therapy may still receive a carpal tunnel injection, but careful monitoring for bleeding is required.
The flexor retinaculum of the wrist attaches at four points: the pisiform, scaphoid, hook of the hamate, and trapezium. It is approximately as wide as the thumb from proximal to distal, and its proximal edge aligns with the distal wrist crease. The median nerve typically lies directly beneath the palmaris longus tendon in the center of the wrist, just medial to the flexor carpi radialis tendon. If the palmaris longus is absent, ask the patient to press the tip of their thumb against the tip of their little finger; the crease in the center of the palm indicates where the median nerve should be located.
After the injection, the patient should rest until symptoms subside, then resume normal activities. A night splint can help in the early stages following infiltration. Advise the patient to avoid sleeping with wrists fully bent (the “praying” or “sleeping” position).
Using a linear array ultrasound probe, the wrist can be examined for anatomical variations such as ganglion cysts, flexor tenosynovitis, and tumors. Position the probe transversely at the proximal wrist crease, at the entrance of the carpal tunnel.
The goal is to visualize the pisiform, ulnar nerve, and ulnar artery alongside the median nerve. Doppler imaging can help identify vascular structures. The median nerve is identified and is often swollen. The injectate is placed precisely around the nerve in a targeted pattern. A subsynovial injection may also be performed, as this area has recently been considered a potential cause of idiopathic carpal tunnel syndrome.
No local anesthetic is used here, as the primary symptom is paresthesia, and adding more volume would increase pressure within the tunnel. Avoid inserting the needle too vertically (which can hit bone) or too horizontally (which can puncture the retinaculum).
If the patient experiences paresthesia during the procedure, the needle is in the median nerve and must be slightly withdrawn and repositioned. The injection can also be performed by inserting the needle between the median nerve and the flexor tendons, using the same dose and volume.
While an injection is often successful, repeat injections may be needed. However, if symptoms persist despite further injections, surgery may be required. If the patient experiences persistent numbness and/or thenar muscle weakness, promptly refer them for surgical decompression.
A multi-site comparative study suggested that injection into the flexor carpi radialis tendon proximal to the carpal tunnel may be the safest approach.
