The posterior interosseous nerve (PIN) is at risk during surgery that involves the proximal radius when using dorsal approach. Multiple cadaveric studies have looked at anatomic relationships. This study looks at PIN variations associated with a simulated diaphyseal fracture of the proximal radius and a radial neck fracture with an Essex-Lopresti injury.
Twenty cadaveric upper extremities were used to measure the distance from radiocapitellar joint to crossing point of the PIN on radius during a Thompson approach. Distances were recorded with the forearm in supination (3.2 cm), neutral (4.2 cm), and pronation (5.6 cm). Osteotomy or radial head excision was used to simulate either diaphyseal fracture or radial neck fracture with Essex-Lopresti. Simulated diaphyseal fracture decreased the effect of forearm rotation creating a much less significant difference from supination to pronation in terms of distance of the PIN from the radiocapitellar joint. Change in nerve position normally from pronation to supination averaged 2.13 cm, but with diaphyseal osteotomy this decreased to 0.24 cm. Also radial head resection allowed proximal migration of the radius and the nerve.
This article brings up some interesting points about the position of the PIN in the associated injuries looked at in this study. Most all other studies looking at the variation of the PIN based on forearm position have found that pronation increases the distance of the nerve from the radiocapitellar joint. This study however gives two good examples when the PIN can be at increased risk of injury even with pronation of the forearm due to shorter distance of the nerve from radiocapitellar joint. Therefore, in these two instances, it is especially important to visualize and retract the PIN appropriately to decrease risk of injury.
Weaknesses of the study include the fact that no soft tissue injury was taken into account, such as supinator tearing or forearm deformities. The small sample size of 20 cadaveric upper extremities is also a weakness to keep in mind when interpreting the results. Also the measurements taken were only with the elbow at 90 degrees so the effect on the PIN may be different in different positions of the elbow. However, the article does give a baseline understanding of the PIN variations in the two associated traumas, and it does stress the importance of proper visualization and retraction of the PIN in proximal radius surgeries using a dorsal approach.