Biomechanical evaluation of different internal fixation methods for humerus shaft fractures with medial butterfly fragment (Biomechanical study)

The most crucial problem in medial butterfly fragmented humerus shaft fractures is the healing problem of medial butterfly fragment. The basic reason of this problem in shaft fractures is the existence of a single nutritional artery entering from medial region in mid-distal one-third junction. In this case, implant failure develops in the surgical material used in time due to nonunion. The objective of this study is to compare biomechanical strength of biologic fixation methods that can be implemented without disturbing the circulation of medial butterfly fragment.Butterfly fragments were formed to left twenty-one white cortical shell humerus, similar to AO 12B2 fracture, in a way that its peak point would be in lateral and its bottom would be in medial from 13 cm proximal of medial epicondyle. In a way that each group would consist of seven experimental subjects, antegrade intramedullary nailing, retrograde intramedullary nailing and bridge plating were applied to humeruses. In the study, 9x280 mm expert humeral nail system (synthes) was applied by antegrade and retrograde means to the bones butterfly fragment of which were removed. Distal and proximal lockings were locked with two screws. In the plate group, 10 holed narrow 4.5 mm LC-DCP plate (synthes) were fixed with 20 mm screw locking to eight plates from anterolateral of humerus and not extending to the opposite cortex in a way to bridge the region of fracture.Special assemblies were prepared for bending and rotational overloads. For rotational overload, a constantly increasing overload was applied with an assembly, in a way that pressure speed would be 5 mm/min. up to 320 N, to ensure external rotation to distal part of the humeruses. In rotational tests, 9.6 N/m torque was applied with 320 N load. It was measured that moment= load applied x distance, and at the end of the measurements load (N) ? displacement (mm) curves were obtained. For four-point bending test, axial compression was applied in a way that the speed would be 5 mm/min. up to 500 N at mediolateral direction by means of pressing tool, and load (N) ? displacement curves were obtained. Displacement values obtained in torsion tests are found as follows: mean 37.38 mm (25.75 mm ? 55.68 mm) in the group applied bridge plating, mean 26.55 mm (21.25 mm ? 41.81 mm) in the group applied antegrade nailing, mean 33.23 mm (27.20 mm ? 46.45 mm) in the group applied retrograde nailing. Displacement values obtained in four-point bending test are found as follows: mean 3.27 mm (2.54 mm ? 3.73 mm) in the group applied bridge plating, mean 3.17 mm (2.67 mm ? 3.55 mm) in the group applied antegrade nailing, mean 3.15 mm (2.10 mm ? 4.02 mm) in the group applied retrograde nailing. No meaningful difference was found among the groups in the torsion and bending tests under these results.Medial butterfly fragmented humerus fractures are the most problematic group in humeral fractures. Today, biologic fixation methods not disturbing the blood supply of fracture fragments are being used more commonly. In this study, a biologic fixation model to mimic biologic fixation without fixing the medial fragment was establish, and in this way, antegrade intramedullary nailing, retrograde intramedullary nailing and plate screw systems were compared. It was found that these three methods have no superiority to one another as biomechanical.Key words: Humerus fractures, Biomechanic, Fixation, Intramedullary nailing, Plate