P8. Evaluation of Bone Cement Deposition with Plasma-Mediated Radiofrequency Ablation and Cement Augmentation for Advanced Metastatic Spine Lesions

Proceedings of the NASS 24th Annual Meeting / The Spine Journal 9 (2009) 1S-205S PURPOSE: It is hypothesized that topping off fusion with a posterior dynamic stabilization (PDS) system may diminish the increased stress and ROM and subsequently, reduce the incidence of adjacent level disc disease. The objective of this work was therefore to determine the biomechanical effect of PDS by measuring the stress and the ROM of a segment adjacent to a fusion prior and after PDS instrumentation. STUDY DESIGN/SETTING: Finite Element Model PATIENT SAMPLE: N/A OUTCOME MEASURES: N/A METHODS: A three-dimensional nonlinear finite element model (FEM) of the human osseo-ligamentous lumbar spine was developed and validated based on experiments conducted on human cadavers. The model was adapted to simulate fusion at L4-L5 and a PDS topping the fusion at L3-L4 (Figure 1). The fusion was simulated using bone graft spacer and pedicle screws with 5.5 mm titanium rod. The PDS was simulated using a pedicle screw based system with a flexible rod having a stiffness equivalent to that of an intact spinal segment, thus permitting 50% of load sharing with the segment structural element. Imposed displacements in flexion (20 ), extension (15 ) was applied to the intact, fusion and PDS topping off models while under a 200 N follower load and 260 N upper body weight. Facet loads, disc pressure, ROM and screw loosening associated with these modalities were evaluated.

Figure. FE-Model of PDS topping off fusion.

RESULTS: All results were expressed relative to a normal spinal segment (referred to as ‘‘intact’’), without adjacent instrumentation. Analyses included ROM as well as facet loads and intradiscal pressures, as shown in Table 1.With regard to bone screw loading, the PDS system reduced the screw bending load by 40%, as compared to that observed using a rigid titanium rod. CONCLUSIONS: PDS topping off a fusion was shown in this model to relieve facet loading and reduce intradiscal pressure on adjacent segments. Assuming that these stresses contribute to adjacent-level disc disease, these data indicate that PDS topping off a fusion may provide some protection against fusion-induced adjacent-level degeneration. In addition, reduced

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bone screw interface loading further suggests that PDS may be an option to avoid adjacent segment decompensation. FDA DEVICE/DRUG STATUS: PDS: Not approved for this indication. doi: 10.1016/j.spinee.2009.08.265 P8. Evaluation of Bone Cement Deposition with Plasma-Mediated Radiofrequency Ablation and Cement Augmentation for Advanced Metastatic Spine Lesions Bassem Georgy, MD; University of California, San Diego, San Diego, CA, USA BACKGROUND CONTEXT: The combination of percutaneous plasma-mediated radiofrequency ablation and vertebral body augmentation offers an alternative treatment to surgical intervention options for vertebral body compression fractures (VCFs) caused by advanced metastatic spine lesions, and is particularly useful for cases with cortical destruction and/or epidural extension. These advanced cases are considered relative contraindications for conventional PVP (percutaneous vertebroplasty) or PVA (percutaneous vertebral augmentation). PURPOSE: This study evaluated bone cement deposition patterns and extravasation in treated vertebral bodies in relation to the metastatic lesion to assess effectiveness of using this combined approach. STUDY DESIGN/SETTING: Prospective case series from a private health care clinic. PATIENT SAMPLE: The study group consisted of 37 patients between the ages of 34 and 89 years who were consecutively treated for painful vertebral body compression fractures (VCF) due to metastatic lesions in the lower thoracic region (T6 and below) and lumbar spine. All lesions demonstrated cortical disruption, epidural or paraspinal extension, or a combination of these findings. OUTCOME MEASURES: Computed Tomography imaging was performed immediately before and after the procedure. Pain alleviation was measured using visual analogue scale (VAS) scores. METHODS: A void was created in the anterior portion of the tumor-infiltrated vertebral body by using a bipolar plasma radiofrequency-based wand (ArthroCare Corporation, Austin, TX) to ablate channels in the malignant mass along several different orientations. A total of 3-6 passes were sufficient to complete this cavity. Bone cement (Zimmer, Warsaw, IN) was then injected into the ablated cavity under fluoroscopic guidance. On average, 3–6 mL of bone cement was found to be sufficient to fill the ablated tumor cavity. Evaluation of cement deposition was performed using a standard PACS system. The amount of cement present in the anterior twothirds of the vertebral body was visually estimated in increments of 5%, and the estimate was confirmed in the axial and coronal planes. This process was performed on all levels and repeated twice. Cement deposition in relation to the metastatic lesion was also recorded. Cement extravasation was evaluated in all three planes. Pain relief was evaluated using the VAS (Visual Analogue Scale) both pre- and post-operatively. RESULTS: In 19 (43%) levels, 90-100% of the cement was deposited in the anterior 2/3 of the vertebral body. In 34 levels (77%), 75% or more of the cement was deposited in the anterior 2/3 of the vertebral body. In 13 of 15 (86%) levels with posterior lesions, cement was deposited anterior to the lesion. Two clinically insignificant incidences of epidural extravasation were noted. Pain relief after the procedure was reported by 25 of the 28 (89.5%) patients with available data. CONCLUSIONS: Plasma-mediated radiofrequency ablation may allow greater cement deposition control, increasing likelihood of successfully stabilizing the anterior 2/3 of the vertebral body. The deposition pattern heightens the stability of the vertebral body and may be an effective minimally-invasive replacement for more extensive surgical stabilization techniques. This combined technique appeared particularly useful in cases with posteriorly-located lesions. Incidence of cement extravasation was relatively high but clinically insignificant. FDA DEVICE/DRUG STATUS: Cavity Spine Wand: Approved for this indication. doi: 10.1016/j.spinee.2009.08.266