gms | German Medical Science

Objective: The possibility to treat a traumatic vertebral body fracture in osteoporosis by kyphoplasty is controversially discussed. Here, the reconstruction of height of the fractured vertebral body should also reactivate the ligamentous stabilizers and thus stabilize the injured segment. This suggests the goal of erecting of the vertebral body as completely as possible. However, the potential consequences of such an erection, including fractures to adjacent vertebral bodies, are still not completely understood. The aim of the present study is to evaluate the influence of the erection of the fractured vertebral body and the associated cement volume in kyphoplasty for the development of adjacent fractures in a cyclic stress test.

Methods: The study was performed on 13 osteoporotic spine preparations (Th11 - L3). An incomplete burst fracture was generated according to the standardized protocol in the vertebral body LWK 1. Subsequently, the kyphoplasty of the fractured vertebral body was performed under X-ray control. The balloon erection and the subsequent augmentation of the vertebral body were carried out in the same way as in clinical practice according to the surgeon using X-ray diagnostics. Both the extent of erection and the volume of amount of cement used were documented. A cyclic load test was carried out in 20 stages with linearly increasing axial load (maximum load of the last stage 1.3kN). One stage consisted of 500 cycles. After each step, a radiological control was performed. The occurrence of an adjacent fracture was detected either radiologically or on the basis of the load deformation curve.

Results: The experimental fracture generation resulted in all cases in a detectable reduction in the height of both the fore- (Hv, median -5.6mm, -29%) and trailing edge (Hh, median -2mm, -8%) and the central vertebral height (Hz Median -6mm, -30%). Balloon kyphoplasty reconstruction resulted in vertebral body height reconstruction by Hv + 12%, Hm + 11% and Hh + 3%. A loss of height after kyphoplasty compared to the native state of both the fore- (Hv, median -2,7mm, -10%) and trailing edge (Hh, median -1,4mm, -5%) and the central vertebral height (Hz; Median -3.1mm, -12%) after kyphoplasty was noticed. The balloon volume used was median 10 ml (Q1: 9, Q3: 12.25), the median cement volume was 9.6 ml (Q1: 9, Q3: 12 ml). The subsequent cyclical testing revealed an approximately linear negative correlation between the cement volume used and the load required to induce a terminal pathology.

Conclusion: The goal of an anatomical reconstruction of the vertebral body height often requires a relatively large volume of cement. In the used biomechanical model, the vertebral body height was reconstructed recognizable but not to the native extend. However, there was a negative correlation between the volume of cement used and the force needed to induce adjacent fractures under cyclic loading.

Figure 1 [Fig. 1]