Cadaveric Analysis of Proximal Humerus Locking Plate Fit: Contour Mismatch May Lead to Malreduction

Objectives: To investigate proximal humerus locking plate fit in a large sample of human proximal humeri. Methods: A total of 97 cadaveric human humeri were selected. Humerus length, head diameter, and neck-shaft angle were measured. Three-hole and 5-hole 3.5-mm proximal humerus locking compression plates were affixed. A digital caliper was used to measure the maximum gap distance from the plate to the bone. Analysis of variance and student's t tests were conducted to evaluate differences in plate-bone distance between the 2 plate lengths, gender, race, age, and laterality. Correlation between plate-bone distance and humerus length, head diameter, and neck-shaft angle were determined. Results: Mean plate-bone distance for the 3-hole plate was 1.5 +/- 0.6 mm (range 0.3-2.9 mm), and for the 5-hole plate was 2.5 +/- 0.9 mm (range 0.7-5.0 mm) (P = 0.01). Female and right-sided humeri were shown to have significantly larger plate-bone gap distance when compared with counterparts (P = 0.01). No correlation was found between plate-bone gap distance and humeral length (R-2 = 0.03), head diameter (R-2 = 0.05), or neck-shaft angle (R-2 = 0.08). Conclusion: The proximal humerus locking plate was under-contoured and spanned all 97 specimens. Greater plate-bone distance was observed with the 5-hole plate versus the 3-hole plate. Applying the plate flush to bone may lead to medial displacement of the humeral head at the calcar increasing risk of loss of fracture fixation. In fractures with any metaphyseal comminution, malreduction will be more pronounced. Caution should be exercised when using the proximal humerus locking plate as a reduction aide.