Biomechanical Evaluation of a Novel Expandable Vertebral Augmentation System Using Human Cadaveric Vertebrae

Abstract

Unacceptable sagittal alignment and cement leakage are major concerns of percutaneous vertebroplasty when treating patients with painful vertebral osteoporotic compression fractures. To maintain the restored vertebral height and reduce the reliance on cement as the major stabilizer, an expandable vertebral augment system (EVA®) made of titanium alloy consisting of a rigid tube encased by a barrel with an anterior expansion mechanism was developed. The aim of the current study was to determine whether this novel design is as effective as existing procedures in terms of height restoration and biomechanical performance. Eight osteoporotic vertebrae (T12-L3) confirmed by dual-energy X-ray absorptiometry from two fresh-frozen human cadavers (70- and 72-year-old females) were used. Twenty-five percent reduced anterior wedge vertebral compression fractures were created using a material testing machine. Four randomized specimens were augmented with EVA® (Chang Gu Biotechnology Co. Ltd., Taipei city, Taiwan), and another four randomized specimens were augmented with OsseoFix® (AlphaTec Spine Inc., Carlsbad, CA, USA). The implant size and cement volume were controlled. The anterior vertebral body height (VBH) ratio and pre/postaugmented ultimate strength and stiffness were measured and compared. The mean anterior VBH restoration ratio was 8.54% in the EVA® group and 8.26% in the OsseoFix® groups. A significant difference from augmentation was measured in both groups (p < 0.05), but there was no significant difference between the EVA® and OsseoFix® groups in anterior VBH restoration. The ultimate strengths of the EVA® and OsseoFix® groups were 6071.4 ± 352.6 N and 6262.9 ± 529.2 N, respectively, both of which were statistically significantly higher than that of the intact group (4589.9 ± 474.6 N) (p < 0.05). The stiffnesses of the EVA®, OsseoFix®, and intact groups were 1087.2 ± 176.9, 1154.9 ± 168.9, and 1637.3 ± 340.8 N/mm, respectively, indicating that the stiffness was significantly higher in the intact group than in both the EVA® and OsseoFix® groups (p < 0.05). No significant differences were observed between the two augmentation procedures in height restoration or ultimate strength and stiffness. This novel EVA® system showed comparable height restoration and biomechanical performance to those of existing implants for human cadaveric osteoporotic compression fractures. Potential advantages of preventing cement posterior leakage and promoting cement interdigitation are expected with this ameliorated design.