Sacral vertebral augmentation: confirmation of fluoroscopic landmarks by open dissection

Sacral insufficiency fractures are a more commonly recognized cause of spine pain among osteoporotic patients, and are now treatable by sacroplasty using percutaneous instillation of PMMA cement. Sacroplasty may be performed using only fluoroscopic landmarks; however, the bony anatomy of the sacrum is complex and the cement deposition based on these landmarks has not been specifically confirmed. In this report we determined the precise fluoroscopic landmarks for cannula placement in a specially prepared excised sacral cadaveric specimen with metal surface markers. The cannulas were placed using the usual dorsal approach, and where the tip was visually seen to breach the cortical surface, fluoroscopic images were obtained and the boundaries of the sacrum were carefully determined. A fluoroscopic cortical "breach" area emerged where a cannula tip would likely be outside the cortical boundaries of the sacrum. With simple sacral vertebroplasty there is no direct control of cement deposition after the PMMA leaves the tip of the cannula. The use of vertebral augmentation devices may be of use to help control cement delivery in performing sacroplasty. We evaluated 2 such devices in cadaver specimens to determine their suitability in performing a sacral vertebral augmentation. Using these same landmarks, a sacral balloon Kyphoplasty was performed and the cadaveric specimen was subsequently bivalved to visually confirm the deposition of cement. On direct inspection the PMMA cement was found to be confined within the sacral cortical boundaries and there was no extravasation near or into the sacral foramen. Based on these fluoroscopic landmarks, the Arcuplasty device was tested in an intact cadaver to determine the optimal cannula placement and locations for creating osteotomies within the sacral trabecular bone prior to PMMA cement deposition. The cement deposition was observed to remain closely confined to the areas where the osteotomies were performed. In the balloon Kyphoplasty specimen the cement deposition was visually confirmed to be confined within the cortical boundaries by open dissection, and both devices have been found successful in creating a more controlled deposition of PMMA cement for performing sacral vertebral augmentation under fluoroscopic imaging.