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BACKGROUND: Treatment strategies for femoral neck fractures include cannulated screw fixation, dynamic hip screw fixation, intramedullary nail fixation, locking plate fixation, and hip replacement. However, the best treatment for Pauwels type III femoral neck fractures is still controversial. OBJECTIVE: To analyze the biomechanical characteristics of a novel femoral neck system for unstable femoral neck fractures by using a three-dimensional finite element analysis method. METHODS: The CT imaging data of the femur of a healthy volunteer were selected and imported into the medical three-dimensional reconstruction software Mimics 21.0 to obtain the original three-dimensional model of the femur. The model was exported to an STL format file and imported into the Geomagic Wrap2017 software for optimization so as to construct femoral cortical bone and cancellous bone structure. The optimized model was imported into Solidworks2017 software, and the 3D model of Pauwels type III femoral neck fracture was reconstructed through Boolean operation. The Pauwels angles are set to 50°, 60° and 70°, respectively. Solidworks2017 software was used to establish three types of internal fixation models (femoral neck system, positive triangular hollow screw, and inverted triangular hollow screw) based on clinical fixation procedures and engineering geometric data modeling. Finally, Abaqus2017 software was used for meshing. After applying load and data calculation, the stress distribution, peak stress and maximum displacement of femur and internal fixation were analyzed in each model. RESULTS AND CONCLUSION: (1) No matter what the angle of the fracture, the stress of the proximal femur in the three internal fixation models was mainly distributed near the medial femoral talus and spread to the surroundings. Among them, the inverted-triangular hollow screw group had the largest stress. The femoral neck system group had the smallest stress. (2) Regardless of the angle of the fracture, the stress of the internal fixation device in the three internal fixation models was mainly distributed on the middle surface of the screw near the fracture line, and the inverted triangle hollow screw group had the least stress, and the femoral neck system group had the largest stress. (3) No matter what the angle of the fracture, the peak displacement of the femur in the three internal fixation models was mainly concentrated on the top of the femoral head. Among them, the peak displacement was the largest in the inverted triangular hollow screw group, and the smallest in the femoral neck system group. (4) No matter what angle of fracture, the peak displacement of the internal fixation device in the three internal fixation models was mainly at the top of the screw. The peak displacement was the largest in the positive triangle hollow screw group, and the smallest in the femoral neck system group. (5) The results show that the biomechanical stability of the femoral neck system for the treatment of unstable femoral neck fractures is better than that of hollow screws, and the risk of internal fixation failure is lower than that of hollow screws. [ABSTRACT FROM AUTHOR]

BACKGROUND: With the development of three-dimensional (3D) printing technology, it has been widely used in spinal surgery. However, whether 3D printing-assisted surgery for lumbar spondylolisthesis has an advantage over traditional surgery is still controversial. OBJECTIVE: To compare the clinical efficacy and safety of 3D printing-assisted versus conventional surgery for the treatment of lumbar spondylolisthesis using system evaluation. METHODS: Randomized controlled trials about 3D printing technology for lumbar spondylolisthesis in CNKI, Wanfang database, CBM, VIP, PubMed, Cochrane Library, Embase, and Web of Science were searched via computer from inception to November 16, 2019. The retrieved literatures were screened according to predefined inclusion and exclusion criteria, and quality evaluation was performed. Then, the available data were extracted and analyzed with the Stata 11.0 software. RESULTS AND CONCLUSION: (1) Six randomized controlled trials including 394 cases were included. Among them, 201 cases were assigned to the 3D printing-assisted group and 193 cases to the conventional group. (2) Meta-analysis results showed that the 3D printing-assisted group proved significantly superior to the conventional group regrading the operation time [WMD=-38.17, 95%CI(-43.93, -32.41), P=0.00], intraoperative blood loss [WMD=-61.61, 95%CI(-69.19, -54.03), P=0.00], the frequency of fluoroscopy [WMD=-4.89, 95%CI(-6.38, -3.41), P=0.00] and the screw placement accuracy [OR=3.89, 95%CI(2.43, 6.25), P=0.00]. (3) However, in terms of the postoperative visual analogue scale scores [WMD=-0.47, 95%CI(-1.21, 0.27), P=0.215], Oswestry disability index [WMD=-1.41, 95%CI(-2.87, 0.05), P=0.058], Japanese Orthopaedic Association scores [WMD=1.02, 95%CI(-0.68, 2.72), P=0.240] and the rate of complications [OR=0.37, 95%CI(0.12, 1.11), P=0.075], no statistically significant differences were found between the two groups. (4) In conclusion, the application of 3D printing technology in the surgical treatment of lumbar spondylolisthesis has the advantage of shortening the operation time, reducing intraoperative blood loss and frequency of fluoroscopy and improving the accuracy of the screw placement. [ABSTRACT FROM AUTHOR]