Design and biomechanical study of a new system for anterior thoracolumbar internal fixation

Abstract

Objective To evaluate the biomechanical performance of a self-designed new complex rod-plate system (D-rod) for anterior thoracolumbar internal fixation.Methods Eighteen specimens of pig spine (T12-L3) were allocated to 3 groups (n=6 each) by random digits table.Bone mineral density (BMD) in each group was measured and compared.Models of L1 bust fracture were created in each group,titanium mesh cage was implanted for vertebral reconstruction,and then fixed respectively with D-rod system (group A),Z-plate system (group B) and Ventrofix system (group C).Range of motion on relative angular displacement in T12-L2 under 6.0 Nm pure moment of couple was measured for specimens in each group at six motions (anterior flexion,posterior extension,left lateral bending,right lateral bending,left axial rotation and right axial rotation).Stability was compared among 3 groups.Results The BMD for groups A,B and C was respectively(1.265±0.073) g/cm2,(1.126±0.082) g/cm2 and (1.403±0.095) g/cm2,with no significant between-group difference(P＞0.05).D-rod and Ventrofix yielded significantly greater stability than Z-plate at anterior flexion,posterior extension,left and right lateral bending (all P＜0.05).D-rod and Z-plate yielded significantly greater stability than Ventrofix at axial rotations (both P＜0.05).Conclusions The selfdesigned D-rod system,as a locking system with low profile and greater adjustability,can result in adequate stability for anterior thoracolumbar reconstruction. Key words: Internal fixators; Spinal fractures; Biomechanics; Combined rod-plate system