## 4 Discussion  
Vertebroplasty and kyphoplasty have been established in recent decades as minimally invasive techniques for stabilizing osteoporortic vertebral compression fractures [1; 5; 29]. Studies showed that better sagittal profiles were restored with kyphoplasty than with  
Figure 8: Mean stiffness in the intact, EVA®and OsseoFix@groups. Groups with significant differences (\(p<0.05\)) are indicated with the “**” symbol. Figure 9: A typical force versus displacement curve for calculation of compression stiffness in the compression test. Compression stiffness was arbitrarily defined as the slope of the force-displacement curve between 500 N and 1500 N. Forces at 500 N and 1500 N are indicated with the “+” symbol. vertebroplasty [7; 29]. However, VBH recovery was often lost after the balloon was deflated and withdrawn from the catheter [27; 28]. Several intravertebral augmentation systems aimed at the permanent reduction in the fractured vertebral body have been widely used in recent years [21; 30]. Among these vertebral augmentation devices, the Vertebral Body Stenting(r) (VBS) device (Synthes, Soletta, Switzerland) consists of an expandable stent delivered into the vertebral body before bone cement injection. [PERSON] et al. [31] compared VBS device and kyrophoplasty treatments of 24 fresh-frozen human cadaveric spines and found significant VBH restoration in the VBS group and no significance in stiffness or ultimate strength between systems. The SpineJack(r) device (Vexim, SA, Balma, France) consists of two parallel titanium plates, which can be used to elevate the fracture end plates craniocaudally and restore the collapsed vertebrae. It was reported that this device was superior to kyrophplasty in restoring vertebral heights and in decreasing cement leakage [32; 33; 34]. Intravertebral augmentation with polymer and memory alloys has also been widely used in recent years [22; 35; 36; 37]. The KIVA(r) (Benvenue Medical Inc., Santa Clara, CA, USA) system [22] uses a flexible polyetheretherketone (PEEK) to restore the VBH and hold the cement; the Tektona(r) system consists of a flexible lamella nickel-titanium alloy that can be shaped by a vertebral fragment reduction instrument and allows for cement augmentation [35; 37]. Intravertebral augmentation devices have been proven to have a better vertebral height restoration and a comparable biomechanical performance to balloon kyrophoplasty in studies [20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38]; therefore, considering the similar expansion mechanism and material properties, OsseoFix(r) was chosen for comparison with our design [20; 21; 38]. Randomized specimens, controlled implant size, and the same cement volume allowed our biomechanical data to be reliable. Osteoporotic human fresh-frozen vertebrae are the ideal model for vertebral augmentation biomechanical studies. In our study, a BMD of less than 0.7 g/cm\({}^{2}\) of each specimen was observed by DXA measurements [22]. Most of the vertebral compression fractures caused by osteoporosis clinically have an anterior wedge shape of varying degrees [3; 5; 6]. The contact point of axial force was determined for each specimen in the anterior half of the superior end plate to create an anterior 25% compression fracture unit that could present the clinical condition [22; 25; 35]. The mean VBH ratio were efficiently restored to above 94% postoperatively in both groups, which is in agreement with results of other studies using a 25% anterior wedge fractured vertebral model [24; 27; 28]. Vertebral height restoration-induced correction of local kyphosis was believed to be positively correlated with the sagittal vertical axis and improved spinopelvic parameters; thus, long-term satisfactory clinical outcomes were achieved [39; 40; 41]. Controversies exist about the adjacent vertebral fracture resulting from altered biomechanics in the augmented vertebra due to resistant kyphosis [42; 43].