Biomechanical evaluation of a modified proximal humeral locking plate application for distal extra-articular diaphyseal humeral fractures.

The extra-articular distal humerus locking plate (EADHP) is widely used for distal extra-articular diaphyseal humeral fracture fixation. However, it occasionally causes skin prominence and discomfort. The upside-down use of a proximal humerus internal locking system (PHILOS) plate is suggested as an alternative option, but it lacks biomechanical evidence. The purpose of this study was to compare the biomechanical performance between two different fixation methods: the modified use of the PHILOS plate on the anterior cortex versus conventional use of an EADHP on the posterior cortex. Twelve pairs of fresh-frozen cadaveric humeri were used and 7 mm gap osteotomy was performed at 50 mm proximal to the lateral epicondyle to simulate an AO/OTA 12-C1.3 fracture type. Single load to failure was measured after five stiffness tests of the plate-bone constructs in anterior/posterior bending, internal/external torsion, and axial compression. There were no significant differences in metrics between the two groups, except for the load to failure in posterior bending, which was significantly higher for PHILOS (1589.3 ± 234.5) compared to EADHP (1430.1 ± 188.6), p < .023. In conclusion, the modified use of the PHILOS plate showed comparable biomechanical performance compared to the conventional EADHP. The new fixation method offers potential clinical advantages, considering the patient's position and surgical approach at the time of surgery as well as postoperative soft tissue irritation. Therefore, this could be an option for distal humeral extra-articular diaphyseal fracture fixation when the use of EADHP is not suitable or preferred.