Bone displacement and the role of longitudinal ligaments during balloon vertebroplasty in traumatic thoracolumbar fractures

Study Design. In a human cadaveric burst fracture model with and without longitudinal ligament damage, the amount of anterior and posterior bone displacement (ABD, PBD) during balloon vertebroplasty after pedicle-screw instrumentation was investigated quantitatively. Objectives. To investigate, in a burst fracture model with and without longitudinal ligament damage, the amount of ABD, PBD, and cement leakage at various phases during balloon vertebroplasty in combination with pedicle-screw instrumentation. Summary of Background Data. The role of intact longitudinal ligaments in traumatic spine fractures, for prevention of bone retropulsion and subsequent reduction, has been discussed in several studies but is still up for debate. In a recent human cadaveric burst fracture study, inflatable bone tamps and calcium phosphate cement were used for the augmentation of the anterior column after pedicle-screw instrumentation. The additional balloon vertebroplasty procedure was found to be feasible and safe, but no data pertaining to unwarranted bone displacement or cement leakage during the procedure are available for burst fractures with damaged longitudinal ligaments. Methods. Ten thoracic and 10 lumbar burst fractures, with rotation or flexion components, were created, and balloon vertebroplasty with calcium phosphate cement was performed after pedicle-screw instrumentation. Volumetric datasets ( using the 3-dimensional (3D) rotational x-ray imaging technique) of the fractures were obtained during the following phases: intact, fractured, after reduction and stabilization with pedicle-screws, after inflation of the balloons, after deflation and removal of the balloons, and after injection of the cement. The amount of ABD and PBD was measured on reconstructed sagittal images and recorded together with the presence of extracorporal cement leakage. The continuity of the longitudinal ligaments was assessed after anatomic dissection. Results. During the balloon vertebroplasty procedure, a significant ( P < 0.05) increase of ABD ( at both thoracic and lumbar level) and PBD ( thoracic level) occurred after inflation of the balloons. After deflation and subsequent injection of the cement, however, the ABD and PBD returned to the preinflation levels. The absolute amount of ABD and PBD (< 1 mm) during inflation was considered of little clinical importance. No differences in ABD or PBD were observed for specimens with or without continuity of the corresponding longitudinal ligament, irrespective of the level, at any of the phases during the experiment (P > 0.5 in all cases). A small amount of cement leakage was observed in the psoas compartment of one specimen with intact longitudinal ligaments. Conclusions. It is suggested that balloon vertebroplasty after pedicle-screw instrumentation may safely be used, in terms of bone displacement and cement leakage, in fracture types where damage to longitudinal ligaments is to be expected.