Comparison of needle position proximity to the median nerve in 2 carpal tunnel injection methods: a cadaveric study.

Purpose: Steroid injections are commonly performed by hand surgeons for relief of symptoms associated with carpal tunnel syndrome. The purpose of this study is to examine the relationship of the needle to the median nerve within the carpal tunnel and to the palmar cutaneous branch, using 2 injection techniques.
Methods: Simulated carpal tunnel injections were performed on 15 cadaveric arms using 2 methods. The first injection used a widely accepted approach in which the needle is inserted at the wrist crease, just ulnar to the palmaris longus, and directed at a 30 degrees angle to the horizontal. In the second method, the needle is positioned just ulnar to the palpable ulnar border of flexor carpi radialis and angled 30 degrees to the horizontal. Specimens were dissected using an open carpal tunnel release. Calipers measured the distance from each needle to the median nerve within the carpal tunnel and to the palmar cutaneous branch.
Results: Using the first injection method, the needle pierced the median nerve in 4 specimens, and its mean distance from the nerve measured 1.34 mm +/- 1.83 mm. With the second injection method, the median nerve was pierced in 1 specimen, and the needle averaged a distance of 4.79 mm +/- 3.96 mm from the nerve. In the first approach, the needle averaged 9.47 mm +/- 4.11 mm from the palmar cutaneous branch, compared to 1.74 mm +/- 1.59 mm with the second technique.
Conclusions: Physicians must exercise caution when performing carpal tunnel injections to avoid intraneural injection. The needle was a statistically significant shorter distance to the median nerve with the traditional injection method; however, the alterative method risks injury to the palmar cutaneous branch of the median nerve.