The posterior interosseous nerve crosses the radial head midline and increases its distance from bony structures with supination of the forearm

Background: This study investigated whether forearm movements change the relative position of the posterior interosseous nerve (PIN) with respect to the midline of the radial head (Rh) under direct arthroscopic observation. Methods: The PIN was identified in 10 fresh frozen cadaveric specimens dissected under arthroscopy. The forearm was moved first in full pronation and then in full supination, and the displacement of the PIN from medial to lateral with respect to the midline of the Rh was recorded. The shortest linear distance between the nerve and the most anterior part of the Rh was measured with a graduated calliper inserted via the midlateral portal with the forearm in neutral position, full pronation, and full supination. Results: The PIN was identifiable in all specimens. In all cases the PIN crossed the Rh midline with forearm movements, moving from medial in full pronation to lateral in full supination. The distance between the PIN and Rh is significantly greater in supination than in the neutral position and pronation (P =.0001). Conclusions: This study confirms that the PIN movement described in open surgery (medialization with pronation) also occurs during arthroscopy. The role of pronation in protecting the PIN in extra-articularprocedures is therefore confirmed. Supination, however, increases the linear distance between the PIN and Rh and should therefore be considered to increase the safe working volume whenever intra-articular procedures are performed on the anterolateral aspect of the elbow.