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Pedicle screw instrumentation of thoracolumbar burst fractures: Biomechanical evaluation of screw configuration with pedicle screws at the level of the fracture

Michael J. Bolesta, MD,1 Troy Caron, DO,2 Suresh R. Chinthakunta, MSc,3 Pedram Niknam Vazifeh, BS,3 Saif Khalil, PhD3
1The University of Texas Southwestern Medical Center, Dallas, TX 2St John's Orthopedic Clinic, Springfield, MO 3Globus Medical, Inc., Audubon, PA

Abstract 

Background

Posterior fixation alone may not be adequate to achieve and maintain burst fracture reduction. Adding screws in the fractured body may improve construct stiffness. This in vitro study evaluates the biomechanical effect of inserting pedicle screws in the fractured body compared with conventional short- and long-segment posterior fixation.

Methods

Stable and unstable L2 burst fractures were created in 8 calf spines (aged 18 weeks). Constructs were tested at 8 Nm in the intact state and then with instrumentation consisting of long- and short-segment posterior fixation with and without screws in the fractured L2 vertebral body after (1) stable burst fracture and (2) unstable burst fracture. Range of motion was recorded at L1-3 for flexion-extension, lateral bending, and axial rotation. Statistical analysis was performed with repeated-measures analysis of variance, with significance set at P < .05. The data were normalized to the intact state (100%).

Results

Both long- and short-segment constructs with screws in the fractured body significantly reduced motion compared with the stable and unstable burst fracture in flexion-extension and lateral bending. Fracture screws enhanced construct stability by 68% (on average) relative to conventional short-segment posterior fixation and were comparable to long-segment posterior fixation.

Conclusions

Screws at the fracture level improve construct stiffness. Short-segment constructs may suffice for stable burst fractures. More severe injuries may benefit from fracture screws and can be considered as an alternative treatment to long-segment constructs.

keywords: 
Thoracolumbar fractures, Posterior fixation, Fracture screws, Index level screw
Volume 6
doi: 
10.1016/j.ijsp.2012.09.002