A novel calcium phosphate-based nanocomposite for the augmentation of cement-injectable cannulated pedicle screws fixation: A cadaver and biomechanical study.

BACKGROUND/

objectiveBoth polymethylmethacrylate (PMMA) and traditional calcium phosphate-based cements have some deficiencies as augmentation materials for pedicle screw fixation. Here, a novel calcium phosphate-based nanocomposite (CPN) for the augmentation of pedicle screw fixation was developed based on previous study, and the handling properties, biomechanical performance, and biodegradation behaviour of CPN were evaluated and compared with clinical PMMA by means of a cadaver study and animal tests.

methodsBone mineral density of the lumbar vertebrae was tested. Pedicle screws were placed into the lumbar vertebrae under the guidance of three dimensionally printed templates; each of which was designed based on computed tomography (CT) reconstruction of each vertebrae ​and augmented with either PMMA or CPN. X-ray and CT scan were used to evaluate the accuracy of screw placement and dispersion as well as interdigitation of bone cement. The axial pull-out strength and maximum torque were tested using a mechanical testing machine. Degradation behaviour of CPN was evaluated by in vitro immersion tests for 8 weeks and in vivo rabbit femur defect model for up to 6 months, respectively.

resultsStandard mechanical tests revealed that PMMA was much stronger than CPN after setting (compressive strength 95 vs. 49 ​MPa, respectively,

conclusionA new nanocomposite cement CPN, designed for replacing the nondegradable PMMA cement and overcoming the mechanical inferiority of calcium phosphate cement, was evaluated for its biomechanical and biodegradation behaviours in cement-injectable cannulated pedicle screws (CICPS) application. Although CPN is a mechanically weaker material than PMMA, CPN demonstrates similar biomechanical properties to PMMA in the application of augmentation for CICPS fixation in cadaveric vertebrae. This improvement in biomechanical property is attributed to a better dispersion and interdigitation mode of CPN. In addition, the animal study results suggest the in vivo absorption of CPN is slow enough and matches the bone ingrowth. THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: This work reports a cadaveric and biomechanical study of novel CPN for the application in the augmentation of CICPS. The results suggest that CPN has equivalent or better biomechanical and interdigitation performance compared with PMMA. Together with the biodegradability and ossointegration capability, CPN reveals high translational potential as a new bone cements for load-bearing bone fixation and repair.