Aim: The posterior interosseous nerve (PIN) is often at risk during surgical approaches to the proximal radius. The forearm is pronated during the approach to retract the PIN further away from the dissection. We hypothesized that a fracture of the radius would decrease the protection provided by the pronation maneuver.

Material and Methods: The position of the PIN in cadaveric elbows was measured using CT scans made after the PIN sheath was injected with radiopaque dye. Senventeen elbows were injected and CT scans were made in both full supination and pronation. The same elbows then had a radial osteotomy performed at the proximal-middle third junction and were re-scanned in supination and pronation. Finally the same elbows had the fascia around the osteotomy sutured and were scanned a third time. Measurements on the axial CT scans at the level of the radial head were taken of the angle formed by the olecranon, head, and PIN, as well as of the distance between the PIN and the lateral most aspect of the radial head.

Results: In the control group with intact radii, pronation increased the distance between the lateral radial head and the PIN by 6.44 mm. With radial osteotomy, the mean increase was 3.88 mm. The excursion of the nerve along the long axis of the radius decreased from 29.6 degrees to 23.3 degrees.

Conclusions: Radial osteotomy decreased the excursion of the PIN provided by pronation for the forearm by 40%. The Kocher approach requires additional care in light of a radial shaft fracture, but pronation is still beneficial.