Nailing of diaphyseal ulna fractures in adults—biomechanical evaluation of a novel implant in comparison with locked plating

Abstract Background Adult forearm fractures require surgical treatment in most cases. Open reduction and internal fixation with plate osteosynthesis is the therapy of choice. Intramedullary fixation offers several advantages compared to plate fixation but is not routinely used. The aim of our study was to compare a newly designed ulna nail with angular stable plating in a biomechanical testing setup of an ulna shaft fracture with a diaphyseal defect. Methods Ten pairs of sawbones with a defect osteotomy of the ulna shaft (OTA 2U2C3) were fixed with an interlocked nail or locked plate osteosynthesis. The constructs were tested under four-point bending, torsional loading and axial loading in a servo-pneumatic testing machine to compare the stiffness of both stabilization methods. Results The nail constructs show lower yet sufficient bending stiffness (62.25 ± 6.64 N/mm) compared to the plate constructs (71.2 ± 5.98 N/mm, p = 0.005). The torsional loading test shows superior stiffness of the plate constructs (0.24 ± 0.03 Nm/deg vs. 0.1 ± 0.01 Nm/deg; p < 0.001), while the axial loading shows superior stiffness of the nail constructs (1028.9 ± 402.1 N/mm vs. 343.9 ± 112.6 N/mm; p < 0.001). Conclusions Intramedullary nailing of ulna shaft fractures obtains sufficient but lower stability in bending and torsional loading when compared to rigid angular stable plating and could be an alternative technique to plate fixation. The lower stability and the closed stabilization technique allow for a rapid periosteal healing, which is not present in stiffer constructs.