Dynamic biomechanical investigation of a novel sulcus bicipitalis plate in combination with a conventional locking plate for the treatment of complex proximal humerus fractures

Background: Complex proximal humerus fractures place high demands on osteosynthetic treatment. In some cases, double plating has already been used to increase primary stability of the osteosynthesis. This approach was advanced in the present study by developing an additive plate for the sulcus bicipitalis. To demonstrate the superior primary stability of the newly developed plate osteosynthesis, a biomechanical comparison against a conventional locking plate with an additional calcar screw was performed. Methods: Ten pairs of cadaveric humeri were treated proximally with a locking plate (PENTA plate small frag-ment, INTERCUS). Each had a two-part fracture model with a fracture gap of 10 mm. All right humeri were treated with an additive novel plate that extends along the bicipital sulcus and encircles the lesser tuberosity proximally. First, the specimens were loaded sinusoidally at 250 N in 20 degrees abduction for 5000 cycles. Afterwards quasi-static loading until failure was applied.Findings: The movement at the fracture gap due to the cyclic loading occurred mainly as rotation around the z-axis, corresponding to a tilt medially and distally. The double plate osteosynthesis reduces the rotation by approximately 39%. For all load cycles observed, except 5000 cycles, medial and distal rotation of the head was significantly reduced by the double plate. The failure loads showed no significant differences between the groups.Interpretation: In the tested scenario under cyclic loading, the novel double plate osteosynthesis showed a sig-nificant superiority of primary stability over the conventional treatment with one locking plate. Furthermore, the study showed the advantages of cyclic load application over quasi-static load application until failure.