Purpose of the study: Neurolysis is required for the treatment of non-regressive posttraumatic or spontaneous palsy of the anterior interosseous nerve. This technique is difficult because of the anatomic variability of the nerve and the neighbouring structures. The purpose of this study was to determine the imperative elements for neurolysis by analysing the anatomic relations of the anterior interosseous nerve and identifying the potentially compressive musculo-aponeurotic and vascular structures.

Material and methods: Twelve fresh anatomic specimens were dissected unilateral; the subjects (six male, six female) were aged 82.6 years on average at death. Emergences of the anterior interosseous nerve and its division branches were studied. The relations with the following structures and their anatomic variations were analysed: the lacertus fibrosus, the fibrous arcades of the pronator teres, and the flexor digitorum superficialis, the accessory head (if present) of the flexor pollicis longus (Gantzer muscle) and the vascular structures in close contact with the nerve. The topographic landmarks were noted in relation to the bi-epicondylar line.

Results: Emergence of the anterior interosseous nerve was situated, on average 54.5 mm below the bi-epicondylar line, on the posterior (n=9) or ulnar (n=3) aspect of the median nerve. The relative situations of its division branches were variable. A fibrous arcade was found between the lacertus fibrosus and the pronator teres in two specimens. Nine specimens had two arcades at the pronator teres and the flexor digitalis superficialis, but three specimens only had one. The presence of an accessory head within the flexor digitalis superficialis was a configuration with risk of nerve compression. The Gantzer muscle was present in six specimens and crossed the nerve superficially. Two types of potentially compressive vascular arcades were found in eight specimens.

Discussion: Sites of compression of the anterior interosseous nerve were found a various positions and in variable numbers in the different anatomic specimens. The presence of several sites of compression in the same individual could explain why the electromyogram fails to identify the level of the nerve compression in certain cases, leading to the standardised neurolysis technique recalled here.

Conclusion: This study demonstrates that several sites of potential compression of the anterior interosseous nerve can coexist in the same patient. The surgeon should be perfectly aware of these “at risk” sites when performing neurolysis.