Biomechanical evaluation of low-modulus bone cement for enhancing applicability in vertebroplasty - An experimental study in porcine model

Polymethylmethacrylate (PMMA) bone cement has been widely used in vertebroplasty to treat osteoporotic vertebral compression fracture. However, the high compression stiffness of PMMA is suspected to induce adjacent vertebral fracture following vertebroplasty. In the current study, modified low-modulus cement was prepared by combining PMMA with castor oil to solve this problem. The percentage of height recovery and compression stiffness of vertebral bodies was compared after injection of standard PMMA or low-modulus cement. This study aims to investigate whether low-modulus cement is as effective as standard PMMA for storing the initial vertebral height; while lowering the compression stiffness in treatment of osteoporotic vertebral compression fractures. A total of 20 fresh porcine lumbar vertebrae were assigned into two groups (10 per group): standard and low-modulus. All specimens received a four-week decalcification to mimic human osteoporotic vertebrae. The standard and low-modulus groups received a simulated compression fracture followed by treatment of standard and low-modulus cement augmentation, respectively. The low-modulus cement was prepared by combining standard PMMA with 15% weight fractions of castor oil. For all the 20 specimens, vertebral compression fracture was created by reducing the vertebral height of 25% using a material testing machine. The compression stiffness determined from the creation of compression fracture was defined as the intact group (20 specimens). The fractured vertebrae were then treated with standard and low-modulus cement augmentation. The vertebral height was measured pre-And post-Treatment, and the percentage of vertebral height recovery was compared between two cementing groups. Following cement augmentation, axial compression test was conducted to compare compression stiffness among three groups. The results indicated that there is no significant difference in percentage of vertebral height between standard (83.42-11.60%) and low-modulus (88.50-6.15%) groups (p > 0:05). Moreover, the compression stiffness were 1166.49-392.91 N/mm, 1795.85-247.45N/mm and 1362.57-236.92N/mm for intact, standard and low-modulus groups, respectively. There is significant difference among three groups (p < 0:05). We concluded that the modified low-modulus cement is as effective as standard PMMA for storing the initial vertebral height while lowering the compression stiffness in treatment of osteoporotic vertebral compression fractures. These reduce the risks of adjacent vertebral body fracture following vertebroplasty.