A biomechanical study of monosegmental fixation by pedicle instrumentation in the management of thoracolumbar fractures

Abstract

Objective To test the biomechanical stability of fixation of thoracolumbar burst fractures (A 3.1 by AO classification) with monosegmental pedicle instrumentation (MSPI). Methods Six specimens of T10-L2 thoracolumbar spine segment were harvested from human donors ranging in age from 27 to 46 years (mean,39 years).Incomplete burst fractures (A3.1 by AO classification) were made at the level of T12 in the specimens using a mechanical dropping hammer.The fractures were fixated with MSPI in the specimens sequentially to restore spinal stability.The specimens in conditions of integrity,fracture and MSPI fixation were tested on the mechanical testing system for biomechanical assessment of the segmental stability.Range of motions (ROM) in flexion-extension and lateral bending were recorded by a 2-camera VICON motion measurement system.The rotational stability was tested by a computer torsional testing machine. Results The ROMs of MSPI specimens in flexion,extension,left and right lateral bending were respectively 0.14°± 0.02°,0.07° ± 0.02°,0.73 ° ± 0.22° and 0.74° ± 0.13°,significantly lower than those of fracture specimens (0.84° ± 0.10°,1.94° ± 0.30°,2.33° ± 0.56° and 2.54° ± 0.44° ) and those of intact specimens (0.46° ±0.05°,1.01° ±0.23°,1.34° ± 0.24° and 1.30° ± 0.31°) ( P ＜ 0.05).The torsional force needed in MSPI specimens was 3103.00 ± 213.11 N,which was not significantly different from that in intact specimens (2654.75 ± 122.90 N) ( P ＞ 0.05) but significantly higher than that in fracture specimens ( 1519.60 ± 100.82 N) ( P ＜ 0.05). Conclusion In the treatment of thoraeolumbar burst fractures (A3.1 by AO classification),MSPI can reconstruct the spinal stability. Key words: Spinal fracture; Fracture fixation, internal; Bone nail; Biomechanics