Anatomical analysis of different helical plate designs for proximal humeral shaft fracture fixation.

Objectives: Helical plates are preferably used for proximal humeral shaft fracture fixation and potentially avoid radial nerve irritation.

Aims: Safety of applying four different long plate designs (straight, 45°-, 90°-helical and ALPS) with MIPO technique as well as assessment and comparison of their distances to adjacent anatomical structures.

Methods: MIPO was performed in 16 human cadaveric humeri using either a straight (group 1), a 45°-helical (group 2), a 90°-helical (group 3) plate, or an ALPS (group 4). Applying CT angiography, distances between brachial arteries and plates were evaluated. All specimens were dissected and distances to the axillary, radial and musculocutaneous nerve were evaluated.

Results: No specimens demonstrated injuries of the anatomical structures at risk after MIPO with all investigated plate designs. Closest overall distance (mean (range); mm) between each plate and the radial nerve was 1 (1-3) in group 1, 7 (2-11) in group 2, 14 (7-25) in group 3 and 6 (3-8) in group 4. It was significantly bigger in group 3 and significantly smaller in group 1 compared to all other groups, p < 0.001. Closest overall distance between each plate and the musculocutaneous nerve was 16 (8-28) in group 1, 11 (7-18) in group 2, 3 (2-4) in group 3 and 6 (3-8) in group 4. It was significantly bigger in group 1 and significantly smaller in group 3 compared to all other groups, p < 0.001.

Conclusions: MIPO with 45°- and 90°-helical plates as well as with ALPS is safely feasible and demonstrates significantly bigger distances to the radial nerve compared to straight plates. However, the distances remain small and attention must be paid to the musculocutaneous nerve and the brachial artery when MIPO is applied using ALPS, 45°- and 90°-helical implants.