The load-sharing classification of thoracolumbar fractures: an in vitro biomechanical validation.

Study Design: An in vitro biomechanical investigation.
Objectives: The purpose of this study was to investigate the association between various load-sharing score and the acute flexibility of thoracolumbar fractures by measuring the 3-dimensional flexibility data.
Summary of Background Data: The load-sharing classification is a way to describe the injury severity of a spinal fracture and can be very useful in determining successful candidates for the choice of operative approaches. However, this classification needs to be validated by biomechanical and more clinical studies before its widespread use. To date, no biomechanical study was available.
Methods: Eighteen fresh bovine T12-L3 specimens were harvested and divided into 3 groups, and subjected to axial compressive impact with 63.8, 107.8, and 137.2 J energy, respectively. Radiograph films and computed tomography scans of the experimental spine were taken in neutral posture after trauma. Multidirectional flexibility of each specimen was measured under flexion-extension, right/left lateral bending, and right/left axial rotation before and after trauma. The association between the multidirectional instabilities and the vertebral injuries to each of load-sharing point score was analyzed.
Results: The load-sharing score of a fracture increased with the level of impact energy. Significant positive correlations were found between the load-sharing score and the motion parameters (average R = 0.434, average P = 0.004). Fractures with mild comminution (< or =6 points) showed more stability as compared to those with more comminution (> or =7 points) (P < or = 0.016).
Conclusion: This study confirms that assessing the load-sharing score should be helpful in evaluating the acute instability of thoracolumbar fractures, and justifies the use of load-sharing classification in the thoracolumbar fractures.