Study finds steroid injections into carpal tunnel do not put median nerve at risk

Injections where needle did not move with tendon gliding produced better drug dispersion patterns.

SEATTLE — A study of steroid injections into the carpal tunnel showed the technique used does not injure the median nerve, but fails to consistently allow the drug to disperse freely in a cadaveric model.

Investigators utilized the same technique in 34 cadaver hand/forearm specimens and passively flexed and extended the fingers before actually injecting the drug. They injected the specimens and then dissected them to determine the distribution of the solution and if the median nerve was violated.

"We actually found the injection results in five different distribution patterns," Joseph E. Robison, MD, said in a presentation at the 62nd Annual Meeting of the American Society for Surgery of the Hand.

Steroid and dye

Investigators injected specimens with 1 cc Depo-Medrol (methylprednisolone acetate; Pfizer) with dye via a 5/8-inch 25-gauge needle. To ensure their technique was consistent, they identified the intersection of the wrist flexion crease and midline of the ring finger ray and directed the injection distally in line with the ring finger ray at 45?. They stopped when the needle's hub contacted the skin.

They flexed and extended the fingers noting if the needle moved and then completed the injection, leaving the needle in place to confirm the injection site.

Investigators dissected the carpal tunnel (CT) and found the following solution dispersion patterns and frequencies:

free distribution, 16;
flexor tenosynovium or tendon sheath, 9;
nonspecific tenosynovium, 5;
ulnar sidewall of CT, 3; and
subcutaneous, 1.

Needle motion association

No needle motion occurred in 13 specimens and four had a pattern other than free distribution, "where the injection was actually into the wall of the CT or the subcutaneous tissue," Robison said. If there was no needle motion, there was a more free distribution of the steroid.

Investigators concluded injections were delivered into the CT, that a high percentage resulted in a focal deposit of solution, and that the median nerve is at low risk during the technique.

Limitations of the study were injections may behave differently in live tissue and it only analyzed time-zero after injection. The authors believe that the clinical success of this procedure is based upon the distribution of the steroid in the clinical setting over succeeding days. Also, any of the distribution patterns could possibly provide patients with CT pain relief days or weeks later, Robison said.

For more information:
Jeffrey Lawton, MD, can be reached at department of orthopedic surgery, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195. 216-445-6915; lawtonj@ccf.org. He has no direct financial interest in the products discussed in this article, nor is he a paid consultant for any companies mentioned.
Robison JE, Lawton J, Evans P. Actual delivery location of carpal tunnel injections: A cadaveric study. #19. Presented at the 62nd Annual Meeting of the American Society for Surgery of the Hand. Sept. 27-29, 2007. Seattle.