Locking screw-plate interface stability in carbon-fibre reinforced polyetheretherketone proximal humerus plates.

Purpose: Carbon-fibre reinforced polyetheretherketone (CFR-PEEK) plates have recently been introduced for proximal humerus fracture treatment. The purpose of this study was to compare the locking screw-plate interface stability in CFR-PEEK versus stainless steel (SS) proximal humerus plates.
Methods: Locking screw mechanical stability was evaluated independently in proximal and shaft plate holes. Stiffness and load to failure were tested for three conditions: (1) on-axis locking screw insertion in CFR-PEEK versus SS plates, (2) on-axis locking screw insertion, removal, and reinsertion in CFR-PEEK plates, and (3) 10-degree off-axis locking screw insertion in CFR-PEEK plates. Cantilever bending at a rate of 1 mm/minute was produced by an Instron machine and load-displacement data recorded.
Results: Shaft locking screw load to failure was significantly greater in CFR-PEEK plates compared to SS plates (746.4 ± 89.7 N versus 596.5 ± 32.6 N, p < 0.001). The stiffness and load to failure of shaft locking screws was significantly decreased when inserted 10 degrees off-axis compared to on-axis in CFR-PEEK plates (p < 0.001). Stiffness and load to failure did not vary significantly following screw reinsertion in CFR-PEEK plates.
Conclusion: The mechanical stability of locking screws in CFR-PEEK plates is comparable or superior to locking screws in SS plates.