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

Abstract

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. 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 1mm/minute was produced by an Instron machine and load-displacement data recorded. Shaft locking screw load to failure was significantly greater in CFR-PEEK plates compared to SS plates (746.4±89.7N versus 596.5±32.6N, 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. The mechanical stability of locking screws in CFR-PEEK plates is comparable or superior to locking screws in SS plates.