[Biomechanical analysis of four internal fixations for Pauwels â ¢ femoral neck fractures with defects].

OBJECTIVE: To investigate the biomechanical characteristics of different internal fixations for Pauwels type Ⅲ femoral neck fracture with defect, and provide reference for the treatment of femoral neck fracture. METHODS: Three-dimensional (3D) finite element models of femoral neck fractures were established based on CT images, including fracture and fracture with defects. Four internal fixations were simulated, namely, inverted cannulated screw(ICS), ICS combined with medial buttress plate, the femoral neck system (FNS) and FNS combined with medial buttress plate. The von Mises stress, model stiffness and fracture displacements of fracture models under 2 100 N axial loads were measured and compared. RESULTS: When femoral neck fracture was fixed by ICS and FNS, the peak stress was mainly concentrated on the surface of the screw near the fracture line, and the peak stress of FNS is higher than that of ICS;When the medial buttress plate was combined, the peak stress was increased and transferred to medial buttress plate, with more obvious of ICS fixation. For the same fracture model, the stiffness of FNS was higher than that of ICS. Compared with femoral neck fracture with defects, fracture model showed higher stiffness in the same internal fixation. The use of medial buttress plate increased model stiffness, but ICS increased more than FNS. The fracture displacement of ICS model exceeded that of FNS. CONCLUSION: For Pauwels type Ⅲ femoral neck fracture with defects, FNS had better biomechanical properties than ICS. ICS combined with medial buttress plate can better enhance fixation stability and non-locking plate is recommended. FNS had the capability of shear resistance and needn't combine with medial buttress plate.

Modified Ni-Nail and C-Nail systems for intra-articular fractures of the calcaneus: A biomechancial study.

OBJECTIVES: We have proposed a novel intramedullary nail (Ni-Nail) by incorporating a sustentaculum tali screw to improve the fixation stability of minimally invasive treatment for calcaneal fractures. This study aimed to evaluate the biomechanical characters of the Ni-Nail system and compare it with traditional C-Nail system. METHODS: A finite element model of a Sanders type-IIIAB calcaneal fracture was reconstructed and fixed using two intramedullary nail systems, which was validated by a cadaver study. A vertical loading of 700 N was applied to the subtalar joint surfaces, and 525 N Achilles tendon tension was applied to the superior border of the Achilles tuberosity. The von Mises stresses and fracture displacements of both fixation models were evaluated. RESULTS: The maximum von Mises stress of the screws of Ni-Nail and C-Nail were 27.92 MPa and 57.42 MPa, respectively, while that of the main nail were 67.44 MPa and 53.01 MPa. In addition, the maximum fracture displacement of the Ni-Nail was larger than that of C-Nail by 15.6% (0.37 mm vs.0.32 mm). CONCLUSIONS: Our static simulation analysis showed that both Ni-Nail and C-Nail demonstrated similar biomechanical stability for calcaneal fixation. The Ni-Nail features a simple structure that is easier to operate and less traumatizing. Future studies may consider to further evaluate the clinical effectiveness by clinical trials and follow-ups.

[Characteristics of femoral neck fractures in young and middle-aged adults based on fracture mapping technology].

Objective: To analyze the characteristics of femoral neck fractures in young and middle-aged adults by means of medical image analysis and fracture mapping technology to provide reference for fracture treatment. Methods: A clinical data of 159 young and middle-aged patients with femoral neck fractures who were admitted between December 2018 and July 2019 was analyzed. Among them, 99 patients were male and 60 were female. The age ranged from 18 to 60 years, with an average age of 47.9 years. There were 77 cases of left femoral neck fractures and 82 cases of right sides. Based on preoperative X-ray film and CT, the fracture morphology was observed and classified according to the Garden classification standard and Pauwels' angle, respectively. Mimics19.0 software was used to reconstruct the three-dimensional models of femoral neck fracture, measure the angle between the fracture plane and the sagittal plane of the human body, and observe whether there was any defect at the fracture end and its position on the fracture surface. Through reconstruction, virtual reduction, and image overlay, the fracture map was established to observe the fracture line and distribution. Results: According to Garden classification standard, there were 6 cases of type Ⅰ, 61 cases of type Ⅱ, 54 cases of type Ⅲ, and 38 cases of type Ⅳ. According to the Pauwels' angle, there were 12 cases of abduction type, 78 cases of intermediate type, and 69 cases of adduction type. The angle between fracture plane and sagittal plane of the human body ranged from -39° to +30°. Most of them were Garden type Ⅱ, Ⅳ and Pauwels intermediate type. The fracture blocks were mainly in the form of a triangle with a long base and mainly distributed below the femoral head and neck junction area. Twenty-six cases (16.35%) were complicated with bone defects, which were mostly found in Garden type Ⅲ, Ⅳ, and Pauwels intermediate type, located at the back of femoral neck and mostly involved 2-4 quadrants. The fracture map showed that the fracture line of the femoral neck was distributed annularly along the femoral head and neck junction. The fracture line was dense above the femoral neck and scattered below, involving the femoral calcar. Conclusion: The proportion of displaced fractures (Garden type Ⅲ, Ⅳ) and unstable fractures (Pauwels intermediate type, adduction type) is high in femoral neck fractures in young and middle-aged adults, and comminuted fractures and bone defects further increase the difficulty of treatment. In clinical practice, it is necessary to choose treatment plan according to fracture characteristics. Anatomic reduction and effective fixation are the primary principles for the treatment of femoral neck fracture in young and middle-aged adults.

[Biomechanical analysis of Magic screw fixation for acetabular posterior column fracture].

This study aims to analyze the biomechanical stability of Magic screw in the treatment of acetabular posterior column fractures by finite element analysis. A three-dimensional finite element model of the pelvis was established based on the computed tomography (CT) and magnetic resonance imaging (MRI) data of a volunteer and its effectiveness was verified. Then, the posterior column fracture model of the acetabulum was generated. The biomechanical stability of the four internal fixation models was compared. The 500 N force was applied to the upper surface of the sacrum to simulate human gravity. The maximum implant stresses of retrograde screw fixation, single-plate fixation, double-plate fixation and Magic screw fixation model in standing and sitting position were as follows: 114.10, 113.40 MPa; 58.93, 55.72 MPa; 58.76, 47.47 MPa; and 24.36, 27.50 MPa, respectively. The maximum stresses at the fracture end were as follows: 72.71, 70.51 MPa; 48.18, 22.80 MPa; 52.38, 27.14 MPa; and 34.05, 30.78 MPa, respectively. The fracture end displacement of the retrograde tension screw fixation model was the largest in both states, and the Magic screw had the smallest displacement variation in the standing state, but it was significantly higher than the two plate fixations in the sitting state. Magic screw can satisfy the biomechanical stability of posterior column fracture. Compared with traditional fixations, Magic screw has the advantages of more uniform stress distribution and less stress, and should be recommended.