Introduction: Local anesthetic blockade of the posterior interosseous nerve (PIN) and anterior interosseous nerve (AIN) can be helpful in evaluating the effectiveness of wrist denervation pre-operatively. A description and analysis of the technique has not been reported to our knowledge. We describe and compare two methods of injecting a dyed tracer in a cadaver model.

Methods: For PIN and AIN injection a needle was advanced from dorsal to volar starting at 1cm ulnar and 3cm proximal to Lister’s tubercle. The needle was advanced until the interosseous membrane was encountered. One ml of 0.5% methylene blue was injected on the dorsal surface of the interosseous membrane to saturate the PIN. The needle was then advanced across the interosseous membrane and an additional 1ml of methylene blue was injected to saturate the AIN. PIN injection alone was done by advancing a needle from dorsal to volar at a site 1cm ulnar to the proximal end of Lister’s tubercle. The needle was advanced until the dorsal surface of the radius was encountered. 0.5ml of 0.5% methylene blue was then injected. A successful injection was defined as a stained PIN and/or AIN. A digital picture (Olympus 3030z) was taken of the resected nerves on a white background. The density (color intensity) of staining was measured using the Image Pro Plus graphics program (Media Cybernetics). The density of staining reflected the nerves concentration of dye.

Results: For each injection maximum density, mean density and area stained were analyzed. For both techniques methylene blue was accurately delivered to the PIN in 100% of the samples. Methylene blue was accurately delivered to the AIN in 100% of samples in which it was injected.

For PIN and AIN injections the average maximum density of staining for the PIN and AIN were 2.04 and 2.01 respectively. For PIN injection alone the average maximum density of staining was 1.97. The difference in PIN injections was not statistically significant (P<0.53). The average area of staining for the PIN and AIN in proximal PIN/AIN injections was 83.97mm² and 82.87 mm² respectively. The average area stained in distal PIN injections was 33.41 mm^2. The difference in PIN area stained was statistically significant (P<0.05).

Conclusions: Our techniques successfully saturated the PIN and AIN or PIN alone and may be useful as a diagnostic and therapeutic tool in the work up of chronic wrist pain as well as for pre-operative outcome assessment for wrist denervation.