A new risk to the axillary nerve during percutaneous proximal humeral plate fixation using the Synthes PHILOS aiming system

Background Percutaneous aiming arms have been developed to minimize injury during placement of submuscular proximal humerus plates. The purpose of this study was to determine the risk of axillary nerve injury during percutaneous proximal humeral plate fixation using the Synthes PHILOS aiming system. Methods By use of 10 fresh-frozen cadavers (20 shoulders), a 3.5-mm locking compression proximal humeral plate was fixated percutaneously to the humerus through a lateral deltoid-splitting approach using the PHILOS aiming guide. Dissection of the axillary nerve was then carried out, and measurements of its relation to the screw holes in row A through row G of the plate were taken. The lateral acromion–to–axillary nerve distance was also measured. Results The axillary nerve traversed row D in every shoulder, whereas it crossed over row C in 11 shoulders and both holes in row E in 16 shoulders. The closest distance to the axillary nerve achieved was 4.5 mm, corresponding to the distal (left) screw in row B. A significant negative correlation was found for the distance from the nerve to the closest proximal and distal screws (row B and row G, respectively) in both right shoulders (ρ = –0.797; 95% confidence interval, –0.916 to –0.548) and left shoulders (ρ = –0.615; 95% confidence interval, –0.831 to –0.237). Conclusion The axillary nerve traverses rows C, D, and E of the proximal humeral plate using the PHILOS aiming system. Importantly, our study is the first to demonstrate that the axillary nerve crosses over row C. Left-sided plate screws also came in closer proximity to the axillary nerve than right-sided plate screws.