A Novel Calcium Phosphate–Based Nanocomposite for Augmentation of Cortical Bone Trajectory Screw Fixation

Yuetian Wang,1,&ast; Chun Liu,2,&ast; Huiling Liu,3 Haoyong Fu,1 Chunde Li,1 Lei Yang,3,4 Haolin Sun1 1Department of Orthopedics, Peking University First Hospital, Beijing, People’s Republic of China; 2Medical Research Centre, Changzhou Second People’s Hospital Affiliated to Nanjing Medical University, Jiangsu, People’s Republic of China; 3Institute of Orthopedics, Department of Orthopedics, Soochow University, Suzhou, People’s Republic of China; 4Center for Health Sciences and Engineering (CHSE), School of Health Sciences and Biomedical Engineering, Hebei University of Technology, Tianjin, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Lei Yang; Haolin Sun, Tel +86 13681146156, Email ylei@hebut.edu.cn; sunhaolin@vip.163.comPurpose: To evaluate the effect of cement augmentation of cortical bone trajectory (CBT) screws using a novel calcium phosphate–based nanocomposite (CPN).Material and Methods: CBT screws were placed into cadaveric lumbar vertebrae. Depending on the material used for augmentation, they were divided into the following three groups: CPN, polymethylmethacrylate (PMMA), and control. Radiological imaging was used to evaluate the cement dispersion. Biomechanical tests were conducted to measure the stability of CBT screws. A rat cranial defect model was used to evaluate biodegradation and osseointegration of the CPN.Results: After cement augmentation, the CPN tended to disperse into the distal part of the screws, whereas PMMA remained limited to the proximal part of the screws (P < 0.05). As for cement morphology, the CPN tended to form a concentrated mass, whereas PMMA arranged itself as a scattered cement cloud, but the difference was not significant (P > 0.05). The axial pullout test showed that the average maximal pullout force (Fmax) of CPN-augmented CBT screws was similar to that of the PMMA group (CPN, 1639.56 ± 358.21 N vs PMMA, 1778.45 ± 399.83 N; P = 0.745) and was significantly greater than that of the control group (1019.01 ± 371.98 N; P < 0.05). The average torque value in the CPN group was higher than that in the control group (CPN, 1.51 ± 0.78 N∙m vs control, 0.97 ± 0.58 N∙m) and lower than that in the PMMA group (1.93 ± 0.81 N∙m), but there were no statistically significant differences (P > 0.05). The CPN could be biodegraded and gradually replaced by newly formed bone tissue after 12 weeks in a rat cranial defect model.Conclusion: The biocompatible CPN could be a valuable augmentation material to enhance CBT screw stability.Keywords: cement augmentation, CBT screws, osteoporotic spine, PMMA, CPN