Anatomical mismatch between the proximal humerus and PHILOS plate could result in varus malreduction

This study aims to investigate the anatomical incongruity between the proximal humerus and the PHILOS plate, which may lead to varus malreduction when this plate is used for indirect reduction. Fifty Asian cadaveric human humeri were included in the study. Three-hole and five-hole PHILOS plates were appropriately positioned on the lateral cortex of the proximal humerus. The gap distance between the plate and the lateral surface of the proximal humerus at each screw hole was measured using a digital vernier caliper. A Kirschner wire was inserted into the humeral head, guided by the locking sleeve. The angle between the plate and the lateral cortex was then measured. Differences in plate-bone distance and angles between the different plate lengths were analyzed using a paired t-test. The correlation between demographic variables and mismatched data was evaluated using Pearson correlation. All measurements were conducted by two observers to assess inter-observer reliability. In all specimens, the maximum gap distance was observed at the most proximal screw hole. The average plate-bone distance at this location was 2 mm for the 3-hole plate and 3 mm for the 5-hole plate. The average plate-bone angle was 2.9 degrees for the 3-hole plate and 3.2 degrees for the 5-hole plate. No correlation was found between total humeral length and either the plate-bone distance or the plate-bone angle. Due to the anatomical mismatch between the PHILOS plate and the proximal humerus, caution is advised when using the plate for indirect reduction, as it may lead to secondary varus malreduction.