Biomechanical analysis of the rotation-self oriented distraction trauma fixation system

Objective To analyze the mechanical features of rotation-self oriented distraction trauma fixation system (RTS) in fixation of spinal fractures of anterior and median columns. Methods Five fresh calf specimens of thoracolumbar vertebrae (T11 to L6) were made models of spinal fractures of anterior and median columns according to the Gurr's methods. The biomechanical stabilities of the models were measured by axial compression, stretching and torsion tests in the models before (control group) and after (experimental group) fixation with RTS. Next, RTS was fixed onto a titanium rod by a locking force of 10.0 to 11.5 N • m to test its gripping and anti-torsion strengths. The mechanical properties of RTS were compared with similar overseas products. Results The axial compression test showed no significant difference in displacement under 100 to 500 N load between the control and experimental groups (P > 0.05) . The anteflexion test showed no significant difference in displacement under 20 to 100 N load between the control and experimental groups (P > 0.05). The extension test showed significantly greater displacement under 20 to 100 N load in the experimental group than in the control group (P 0.05). RTS was basically similar to the overseas products in the grasping force, but superior in the anti-torsion force. Conclusion Since the fine biomechanical performance of RTS can lead to rigid three-dimensional orthopedic fixation, this self-designed internal fixation system may have a prospect of wide clinical application for spinal fractures of anterior and median columns. Key words: Spinal fractures; Fracture fixation, internal; Bone nails; Biomechanics