Biomechanical assessment of polyaxial combination-hole locking plates for screw push-out strength and three-point...

Polyaxial locking plate systems and combination-hole designs expand implant adaptability during fracture fixation; however, limited data exist regarding their mechanical behavior. This study evaluated screw push-out strength and three-point bending performance of a 3.5-mm polyaxial combination-hole locking plate.

Axial screw push-out testing was performed on 31 screws inserted into three 12-hole plates and tightened to 2.0 Nm. Screws were loaded at 0° angulation under quasi-static conditions until failure. Three-point bending was conducted following ASTM F382 using a 90-mm support span to determine flexural stiffness, flexural modulus, flexural strength, and maximum load to failure. Area moment of inertia (AMI) was estimated from bending data to provide geometric context for structural performance. Data were reported descriptively. No statistical comparisons were performed.

Mean screw push-out forces ranged from 2,839 ± 471 N to 3,119 ± 274 N. Three-point bending yielded flexural strengths of 641-697 MPa, flexural moduli of 55,655-63,732 MPa, flexural stiffness values of 133-141 N/mm, and maximum loads to failure of 0.63-0.65 kN. Estimated AMI values ranged from 32.4 to 38.0 mm⁴. Results indicate that the combination-hole configuration did not adversely affect the locking mechanism of the plate under the conditions tested. Mechanical responses were consistent across plates, demonstrating uniform screw-plate engagement and predictable bending behavior.

Observed screw retention and bending responses were uniform across plates and fell within ranges reported for other veterinary locking plate systems. Results represent baseline mechanical characteristics of the screw-plate interface and plate bending behavior under controlled testing conditions. Interpretation is limited by testing at 0° angulation, a plate-only construct, and differences in testing methodologies across previously reported studies.

This study provides foundational mechanical data for a 3.5-mm polyaxial combination-hole locking plate, demonstrating that incorporation of a combination-hole interface does not compromise locking screw engagement or bending behavior under baseline testing conditions. Further investigation using standardized test configurations, cyclic loading, fracture-gap models, and variable screw angulation is warranted to define comparative performance and clinical relevance.