Cement Augmentation in a Thoracolumbar Fracture Model

Study Design. In vitro biomechanical investigation. Objective. To assess differences in kyphosis after balloon kyphoplasty (BKP) or vertebral body stenting (VBS). Summary of Background Data. Cement augmentation techniques allow early mobilization in patients with osteoporotic thoracolumbar fractures. Biomechanically, the grade of reduction and preservation are as important as in nonosteoporotic fractures. With BKP, negative effects of balloon deflation on the reduction and whether specific combinations of materials may preserve the reduction are as yet unclear. Methods. Twelve bisegmental human thoracolumbar specimens (6 x T12 L2, 6 x L3 L5; age at death, 76.3 yr; range, 63 89 yr; female: male ratio, 3: 3; bone mineral density, 68.1 g/cm(3); mean, 12.9 g/cm(3)) were tested in a spine simulator with pure moments of 7.5 Nm to assess primary and secondary stability. After flexibility testing of the intact specimens, an eccentric compression force induced standardized fractures, which were reduced using either BKP or VBS against a flexional moment of 2.5 Nm. Primary and secondary stability were assessed using range of motion in a spine tester. The specimens were tested after each of 3 periods of cyclic flexion loading. The kyphotic angle of the index vertebra was measured radiographically. Results. The 2 techniques achieved comparable reduction against a relatively high bending moment in this model. Neither technique restored the stability of the intact state; with increasing loads, the range of motion continuously increased to the level of fractured specimen to the level of the fractured specimen. Although the deflation effect on the kyphotic angle was lower with VBS ( P <= 0.05), there were no significant differences between the techniques relative to angle restoration. Conclusion. Both augmentation techniques are able to restore vertebral body height after thoracolumbar fractures. The deflation effect on the kyphotic angle was less with VBS than with BKP. High flexion moments during implantation limit the effectiveness of reduction using cement augmentation methods.