BACKGROUND:Percutaneous retrograde screws and minimally invasive percutaneous plates are extensively used in the treatment of unilateral pubic ramus fractures.However,the above internal fixations have the disadvantages of mistakenly penetrating the hip joint and damaging the medial pelvic trophoblastic artery.A new type of retrograde superior pubic ramus intramedullary nail offers advantages,such as fewer radiographic exposures and shorter surgery times,but the validation of the biomechanical properties of the three endoprostheses is lacking.OBJECTIVE:To compare the biomechanical differences post-treatment of upper and lower pubic ramus fractures using percutaneous retrograde screws,minimally invasive percutaneous plates,and retrograde superior pubic ramus intramedullary nail under various conditions through finite element analysis.METHODS:Pelvic CT data were collected from one volunteer and imported into Mimics 20,Geomagic Wrap 2021,and SolidWorks 2019 to create geometric models of three types of internal fixation for treating unilateral pubic ramus fractures:hollow screw group,plate group,and intramedullary nail group.Each model was imported into Ansys 2022 software,where it was set up in vertical,book-opening,and shear conditions for preprocessing and calculation to compare and analyze the mechanical stability of the implants.RESULTS AND CONCLUSION:(1)In vertical conditions,the biomechanical stability of the hollow screw treatment for unilateral pubic fractures was superior to that of the steel plate and intramedullary nail,with the smallest peak stress in the implant,which was four times lower compared to the other two groups.(2)In book-opening conditions,the steel plate treatment for unilateral pubic fractures showed better biomechanical stability,particularly in reducing stress at the fracture ends of the upper pubic branch,with stress values five times higher in the other two groups.(3)In shear conditions,the intramedullary nail treatment for unilateral pubic fractures exhibited good biomechanical stability,maintaining the best pelvic displacement,with a 25％greater displacement observed in the other two groups.(4)These findings reveal the biomechanical differences of different implants:the peak stress of implants is the smallest under vertical working conditions with percutaneous retrograde screws.Minimally invasive percutaneous plates reduce the stress at the broken end of superior pubic branch under open-book working condition.Retrograde superior pubic ramus intramedullary nail of superior pubic branch maintains pelvic displacement under shear working condition.The surgeon can combine the biomechanical differences of the implants with the actual situation of pubic injury in clinical practice to make the best implant treatment.

BACKGROUND:Percutaneous retrograde screws and minimally invasive percutaneous plates are extensively used in the treatment of unilateral pubic ramus fractures.However,the above internal fixations have the disadvantages of mistakenly penetrating the hip joint and damaging the medial pelvic trophoblastic artery.A new type of retrograde superior pubic ramus intramedullary nail offers advantages,such as fewer radiographic exposures and shorter surgery times,but the validation of the biomechanical properties of the three endoprostheses is lacking.OBJECTIVE:To compare the biomechanical differences post-treatment of upper and lower pubic ramus fractures using percutaneous retrograde screws,minimally invasive percutaneous plates,and retrograde superior pubic ramus intramedullary nail under various conditions through finite element analysis.METHODS:Pelvic CT data were collected from one volunteer and imported into Mimics 20,Geomagic Wrap 2021,and SolidWorks 2019 to create geometric models of three types of internal fixation for treating unilateral pubic ramus fractures:hollow screw group,plate group,and intramedullary nail group.Each model was imported into Ansys 2022 software,where it was set up in vertical,book-opening,and shear conditions for preprocessing and calculation to compare and analyze the mechanical stability of the implants.RESULTS AND CONCLUSION:(1)In vertical conditions,the biomechanical stability of the hollow screw treatment for unilateral pubic fractures was superior to that of the steel plate and intramedullary nail,with the smallest peak stress in the implant,which was four times lower compared to the other two groups.(2)In book-opening conditions,the steel plate treatment for unilateral pubic fractures showed better biomechanical stability,particularly in reducing stress at the fracture ends of the upper pubic branch,with stress values five times higher in the other two groups.(3)In shear conditions,the intramedullary nail treatment for unilateral pubic fractures exhibited good biomechanical stability,maintaining the best pelvic displacement,with a 25％greater displacement observed in the other two groups.(4)These findings reveal the biomechanical differences of different implants:the peak stress of implants is the smallest under vertical working conditions with percutaneous retrograde screws.Minimally invasive percutaneous plates reduce the stress at the broken end of superior pubic branch under open-book working condition.Retrograde superior pubic ramus intramedullary nail of superior pubic branch maintains pelvic displacement under shear working condition.The surgeon can combine the biomechanical differences of the implants with the actual situation of pubic injury in clinical practice to make the best implant treatment.

Objective:To investigate the biomechanical stabilities of different internal screw fixations for Sanders type ⅡB calcaneal fractures using finite element analysis.Methods:Based on the CT scan data of a male volunteer's calcaneus (26 years old, 173 cm tall, weighing 70 kg), a three-dimensional finite element model of the calcaneus was established using digital medical software such as Mimics 22.0, Geomagic 12.0, Solidworks 2019, and ANSYS Workbench 2022. A three-dimensional finite element model of Sanders type ⅡB calcaneal fracture was also established. The following 3 kinds of screws were used: ① longitudinal screws: from the calcaneal tuberosity to the anterior part; ② transverse screws: from the lateral wall of the calcaneus to the sustentaculum tali; ③ vertical screws: from the base of the calcaneus to the talar dome, perpendicular to the posterior articular surface. The scheme of screw configuration was as follows: the longitudinal screws were divided into the upper, middle, and lower groups based on their entry points from the upper, middle, and lower parts of the calcaneal tuberosity. Based on different configurations (double transverse screws + single vertical screw, single transverse screw + single vertical screw, double transverse screws without a vertical screw, and single transverse screw without a vertical screw) 4 subgroups were further subdivided, resulting in a total of 12 models (a, b, c, d, e, f, g, h, i, j, k, l). Forces of 420 N and 200 N were applied to the posterior and middle subtalar joints, respectively, to simulate the load on the calcaneus during single-leg standing in adults. In each model, total deformation displacement, relative displacement of the sustentaculum tali fracture gap, relative displacement of the anterior fracture gap, relative displacement of the articular surface fracture gap, peak stress at the fracture ends and peak screw stress were analyzed.Results:The total deformation displacement was the lowest in models i and j, while models k and l exhibited the highest deformation displacement. The maximum deformation values in the remaining models varied only slightly. The average relative displacement of the sustentaculum tali fracture gap was the lowest in the upper group (0.27 mm) and relatively higher in the lower group, with the greatest variation seen in models k and l. The average relative displacement of the anterior fracture gap was the smallest in the lower group (0.16 mm), with models i and k performing the best. The relative displacement of the articular surface fracture gap remained at a low level across all models. The upper group had the lowest average peak stress at the fracture ends (60.20 MPa), while the middle and lower groups had similar values (103.88 MPa and 99.76 MPa, respectively). The upper group had the lowest average screw stress peak value (222.77 MPa), whereas models k and l in the lower group had the highest stress peaks, reaching 331.48 MPa and 349.82 MPa, respectively.Conclusions:Model i (inferior longitudinal screw + double transverse screws + single vertical screw) can be recommended in clinic because it demonstrates balanced performance in displacement and stress and a notable advantage in reducing overall deformation displacement and anterior fracture gap displacement. As longitudinal, vertical, and transverse screws each play their distinct role in calcaneal fracture fixation, surgeons should select an appropriate screw configuration based on the patient's needs.

Objective:To evaluate the clinical efficacy of the preoperative digital design combined with three-dimensional(3D) printing models to assist percutaneous kyphoplasty (PKP) treatment for thoracolumbar compression frac-tures.Methods:From January 2018 to August 2020,we obtained data of 99 patients diagnosed thoracolumbar com-pression fractures.These patients were divided into control group (n =50) underwent traditional PKP surgery,and observation group (n =49) underwent preoperative digital design combined with 3D printing model assisted PKP treatment.The clinical efficacy was evaluated with five parameters,including operation time,number of intraoperative radiographs,visual analogue scale (VAS) score,Cobb Angle change,and high compression rate of injured vertebrae.Results:There were statistically significant differences of operation time and number of intraoperative radio-graphs between the two groups (P ＜ 0.05).For VAS score,Cobb Angle change and vertebral height compression rate,all of these three parameters were significantly improved when the patients accepted surgery treatment in two groups (P ＜ 0.05).However,there were no significant differences between control group and observation group for these three parameters either before or after surgery (P ＞ 0.05).Conclusions:Through the design of preoperative surgical guide plate and the application of 3D printing model to guide the operation,the precise design of preoperative surgical puncture site and puncture Angle of the injured vertebra was realized,the number of intraoperative radiographs was reduced,the operation time was shortened and the operation efficiency was improved.