Biomechanical evaluation of calcium phosphate-based nanocomposite versus polymethylmethacrylate cement for percutaneous kyphoplasty.

Abstract

BACKGROUND CONTEXT\nPolymethylmethacrylate (PMMA) is the most commonly used filling material when performing percutaneous kyphoplasty (PKP) for the treatment of osteoporotic vertebral compression fractures. However, there are some inherent and unavoidable drawbacks with the clinical use of PMMA. PMMA bone cement tends to leak during injection, which can lead to injury of the spinal nerves and spinal cord. Moreover, the mechanical strength of PMMA-augmented vertebral bodies is extraordinary and this high level of mechanical strength might predispose to adjacent vertebral fractures. A novel biodegradable calcium phosphate-based nanocomposite (CPN) for PKP augmentation has recently been developed to potentially avoid these issues.\n\n\nPURPOSE\nBy comparison with PMMA, the leakage characteristics, biomechanical properties, and dispersion of CPN were evaluated when used for PKP.\n\n\nSTUDY DESIGN\nBiomechanical evaluation and studies on the dispersion and anti-leakage properties of CPN and PMMA cements were performed and compared using cadaveric vertebral fracture model, sheep vertebral fracture model and simulated rigid foam model.\n\n\nMETHODS\nSheep vertebral bodies were decalcified by ethylenediaminetetraacetic acid disodium salt (EDTA-Na2) to simulate osteoporosis, in vitro. After compression to create wedge-shaped fractures using a self-designed fracture creation tool, human cadaveric vertebrae and decalcified sheep vertebrae underwent PKP augmentation. In addition, three L5 vertebral bodies from human cadavers were used in a contrast vertebroplasty (VP) augmentation experiment. Occurrence of cement leakage was observed and compared between CPN and PMMA during the process of vertebral augmentation. Open-cell rigid foam model (Sawbones®#1522-507) was used to create a simulated leakage model for the evaluation of the leakage characteristics of CPN and PMMA with different viscosities. The augmentation effects of CPN and PMMA were evaluated in human cadaveric and decalcified sheep vertebral models and then compared to the results from solid rigid foam model (Sawbones®#1522-23). The dispersion abilities of CPN and PMMA were evaluated via three methods as follows. The dispersion volume and dispersion ratio were calculated by three-dimensional reconstruction using human vertebral body CT scans; the ratio of cement area to injection volume was calculated in three sections of micro-CT scans of a sheep vertebra; and the micro-CT images of cement dispersion in an open cell rigid foam model (Sawbones®#1522-507) were compared between CPN and PMMA. This study was funded by the National Natural Science Foundation of China (No.81622032, 190000 dollars and No.51672184, 90600 dollars), Principal Project of Natural Science Research of Jiangsu Higher Education Institutions (No.17KJA180011, 22,000 dollars) and Jiangsu Innovation and Entrepreneurship Program (146000 dollars).\n\n\nRESULTS\nThere was no significant difference in vertebral height between CPN and PMMA during PKP augmentation and both cements restored the vertebral height after augmentation. In PKP augmentation experiment, posterior wall leakage occurred in 75% of human vertebrae augmented with PMMA, however, no leakage occurred in human vertebrae augmented with CPN. Anterior leakage occurred in all vertebrae augmented by PMMA, while in only 75% of vertebra augmented by CPN. Furthermore, CPN and PMMA had completely different leakage patterns in the simulated model whether administered at the same injection speed or under the same injection force, suggesting that CPN has anti-leakage characteristics. The augmentation force in human cadaveric vertebrae was lower with CPN compared to PMMA (1668±816 N vs. 2212±813 N, P=0.459, respectively), but this difference was not significant. The force in sheep vertebral bodies reached 1393±433 N when augmented with PMMA, but only 1108±284 N when augmented with CPN. However, the difference was not significant (P=0.057). The dispersion of CPN was better, and the dispersion volume and ratio were greater, with CPN than with PMMA. Imaging of the open cell rigid foam model showed completely different dispersion modes for CPN and PMMA. After injection, the PMMA cement formed a contracted clump in the open cell rigid foam model. However, the CPN cement extended many antennae outward, appearing to spread to the surrounding area. The surface areas of the CPN cement blocks with different L/S ratios were significantly larger than the surface area of the PMMA cement in the open cell rigid foam model (P<0.05).\n\n\nCONCLUSIONS\nCPN has anti-leakage properties, which might be related to its high viscosity and viscoplasticity. CPN had a slightly lower augmentation force than PMMA when used in cadaveric vertebrae, decalcified sheep vertebrae and in the standard rigid foam model. However, CPN diffused more easily into cancellous bone than did PMMA and encapsulated bone tissue during the dispersion process. The excellent dispersion of CPN generated better interdigitation with cancellous bone, which may be why the augmentation effect of CPN is similar to that of PMMA.\n\n\nCLINICAL SIGNIFICANCE\nBiodegradable CPN is a potential alternative to PMMA cement in PKP surgery, in which CPN is likely to reduce the cement leakage during the surgery and avoid the post-surgery complications caused by excessive strengths and non-degradability of PMMA cement.