Stepwise resection of the posterior ligamentous complex for stability of a thoracolumbar compression fracture: An in vitro biomechanical investigation

Abstract

To quantify the mechanical contribution of posterior ligamentous structures to the stability of thoracolumbar compression fractures.Twelve fresh human T11-L3 spinal specimens were harvested in this study. The 1/3 L1 vertebral body was resected in a wedged shape. After the preinjury had been created, the specimens were subjected to flexion-compression to create a fracture model. Resection of the ligaments was performed in a sequential manner from the bilateral facet capsule ligament (FCL), interspinous ligament, and supraspinous ligament (SSL) to the ligamentum flavum at the T12-L1 level. Then, for the intact specimen, fracture model, and ligament disruption steps, the range of motion (ROM) and neutral zone (NZ) of T12-L1 and L1-L2 were collected for each simulated movement.Sequential transection of the posterior ligamentous complex (PLC), ROM, and NZ were increased in all movements at the T12-L1 segment. In the flexion-extension (FE), the ROM and NZ demonstrated significant increases after the fracture model and resection of SSL and LF. In lateral bending (LB), the ROM increased after the fracture and removal of the LF, while the NZ showed a slight increase. In axial rotation, the fracture model and removal of the LF resulted in a significant increase in the ROM, and the NZ showed a slight change after step reduction. For the L1-L2 segment, resection of the FCL led to an increased ROM in LB.With rupture of SSL or LF, the stability of the segment decreased significantly compared with the intact and fracture model, particularly in FE motion, the function of the PLC was considered to be incompetent.

Figure 1

Experimental setup. Motion was applied to the thoracolumbar spine specimens (T11–L3). The cranial (T11) and caudal (L3) were mounted in Plexiglas casts. The caudal was fixed to the table vice, and the cranial was fixed to the loading jig. Axial rotation and flexion–extension were applied in the same direction. Lateral bending required a 90° rotation (A). To capture these motions, 4 fluorescent markers were inserted in each vertebral plane and a 3-dimensional model was reconstructed through computer software (B).

Figure 2

A diagram of the test machine and laser scanners for motion analysis. The loading jig was balanced with a counterweight. The 2 forces applied to the loading jig were parallel, opposite, and equal. Laser scanners connected with a computer used the fluorescent signal to create a 3-dimensional model.

Figure 3

Percentage of range of motion to the intact stage for the fracture model and sequential resection of the posterior ligamentous complex in the T12–L1 segment.

Figure 4

Percentage of range of motion to the fracture model for sequential resection of the posterior ligamentous complex in the T12–L1 segment.