Biomechanical Comparison of Expandable Cages for Vertebral Body Replacement in the Thoracolumbar Spine

Abstract

Biomechanical results indicate that design variations of expandable cages for vertebral body replacement are of little importance. Additionally, no significant difference could be determined between the biomechanical properties of expandable and nonexpandable cages. After corporectomy, isolated implantation of expandable cages plus anterior plating was not able to restore normal stability of the motion segment. Therefore, isolated anterior stabilization using cages plus Locking Compression Plate should not be used for vertebral body replacement in the thoracolumbar spine.

En bloc spondylectomy reconstructions in a biomechanical in-vitro study

“…Despite these different implant features and material properties the results of the present study demonstrated only minimal differences in the postimplantational stability between expandable and nonexpandable VBRs. Similar results have been shown for rather more stable corpectomy models [31,43] and indeed, for the defect situation after en bloc resections [38], we also were not able to reveal an advantage of the expandability of an VBR. However, it seems conceivable that expandability of a VBR implant may decrease secondary VBR dislocation [21,30].…”

“…This finding may reflect the fact that the protective effect of additional antero-lateral angular stable plating on short posterior fixation is masked by the primary stabilizing effect of a long posterior construct. Thus, the biomechanical advantage of an optional anterior plate fixation in previous studies needs to be seen differentially as it may depend on the length of posterior fixation [43,63]. However, a simple comparison of the results obtained in the present en bloc spondylectomy study with corpectomy studies seems not appropriative [28].…”

“…By leaving the posterior spinal structures untouched during corpectomy, more than one third of overall segment stability [27] remains intact. On the contrary, the most radical resection technique of en bloc spondylectomy with complete spinal discontinuity, ultimately leads to a defect situation with a maximum degree of biomechanical instability that is different from previously described corpectomy models [28,31,43,63]. In contrast to the widely used corpectomy models only a few authors have biomechanically investigated thoracolumbar spinal reconstructions after en bloc spondylectomy.…”

“…Load sharing, in turn, promotes delay and decrease in early implant failure and loosening. Accordingly, several studies using more stable corpectomy models [25,31,43,49,63] showed an improvement of overall construct stability by multisegmental posterior fixations. These results are further underlined when compared to similar single anterior reconstruction techniques [63].…”

Biomechanical analysis of a new expandable vertebral body replacement combined with a new polyaxial antero-lateral plate and/or pedicle screws and rods

“…However, isolated posterior instrumentations are often accompanied by complications like a loss of correction or implant failure. Therefore, especially in thoracolumbar burst fractures, an anterior approach for reconstruction and stabilization of the anterior vertebral column is often necessary to restore regular spinal column loading [3,10,15,17,25,26,32,33]. Additional anterior approaches to the spine and the 360°fusion are also reasonable from the biomechanical point of view: different biomechanical studies, dealing with a total corpectomy defect model to simulate a rotationally instable fracture, reported the highest stiffness in all motion planes for this kind of fractures treated with 360°fusion [15,17,25].…”