| Summary: | Zhenyu Dai,1,* Yue Li,2,* Yonggang Yan,3 Ruijie Wan,1 Qiang Ran,1 Weizhong Lu,1 Bo Qiao,4 Hong Li3 1Department of Orthopedics, Chongqing Traditional Chinese Medicine Hospital, Chongqing, People’s Republic of China; 2Department of Clinical Laboratory, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People’s Republic of China; 3College of Physical Science and Technology, Sichuan University, Chengdu, People’s Republic of China; 4Department of Orthopedics, the First Affiliated Hospital, Chongqing Medical University, Chongqing, People’s Republic of China *These authors contributed equally to this work Objective: To evaluate the internal fixation effect of nano-calcium-deficient hydroxyapatite/poly-amino acid (n-CDHA/PAA) composite screws in the intraarticular fracture model. Materials and methods: A total of 35 New Zealand White rabbits were used in a bilateral femoral intercondylar fracture model and randomly divided into two groups. n-CDHA/PAA screws were used in the experimental group, and medical metal screws were used in the control group. The fracture condition, range of motion, and the screw push-out strength were assessed, and an arthroscopic examination of knee joint was performed at 4, 8, and 12 weeks after surgery. The biodegradation of the n-CDHA/PAA screws in vivo was tested through weighing, and changes in screw structure were assessed by X-ray diffraction at 12 weeks after surgery. Results: The general situation of all animals was good and showed no incision infection and dehiscence after surgery. X-ray scanning showed that significant callus growth was present in both groups at 4 weeks after surgery, and there was no significant difference (P>0.05) in the Lane-Sandhu score between the experimental and control groups at all time points after surgery. There were no statistically significant differences (P>0.05) in the range of motion and Oswestry Arthroscopy Score of arthroscopic examination of the knee joints between the two groups. The screw push-out strength of the control group was stronger than that of the experimental group at 4 weeks after surgery (P<0.05), but after that, there was no significant difference between the groups (P>0.05). The degradation tests showed that the n-CDHA/PAA screws degraded gradually after implantation, and the weight loss rate was approximately 16% at 12 weeks after surgery. The X-ray diffraction results showed that the crystal structure of the outer surface of the n-CDHA/PAA screw has changed at 12 weeks after surgery. Conclusion: The n-CDHA/PAA screw is an effective and safe implant as a potential internal fixation device for an intercondylar fracture of the femur, and its internal fixation effect was similar to that of medical metal screw. Keywords: n-CDHA/PAA screw, internal fixation, intraarticular fracture, biocompatibility, bioactivity
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