Analysis of the Stress and Displacement Distribution of Inferior Tibiofibular Syndesmosis Injuries Repaired with Screw Fixation: A Finite Element Study

Background

Studies of syndesmosis injuries have concentrated on cadaver models. However, they are unable to obtain exact data regarding the stress and displacement distribution of various tissues, and it is difficult to compare models. We investigated the biomechanical effects of inferior tibiofibular syndesmosis injuries (ITSIs) and screw fixation on the ankle using the finite element (FE) method.

Methodology/Principal Findings

A three-dimensional model of a healthy ankle complex was developed using computed tomography (CT) images. We established models of an ITSI and of screw fixation at the plane 2.5 cm above and parallel to the tibiotalar joint surface of the injured syndesmosis. Simulated loads were applied under three conditions: neutral position with single-foot standing and internal and external rotation of the ankle. ITSI reduced contact forces between the talus and fibula, helped periarticular ankle ligaments withstand more load-resisting movement, and increased the magnitude of displacement at the lower extreme of the tibia and fibula. ITSI fixation with a syndesmotic screw reduced contact forces in all joints, decreased the magnitude of displacement at the lower extreme of the tibia and fibula, and increased crural interosseous membrane stress.

Conclusions/significance

Severe syndesmosis injuries cause stress and displacement distribution of the ankle to change multidirectional ankle instability and should be treated by internal fixation. Though the transverse syndesmotic screw effectively stabilizes syndesmotic diastasis, it also changes stress distribution around the ankle and decreases the joint''s range of motion (ROM). Therefore, fixation should not be performed for a long period of time because it is not physiologically suitable for the ankle joint.     

非刚性内固定治疗踝关节骨折合并下胫腓联合损伤患者术后踝关节功能和生活质量的影响

摘要 目的：探讨非刚性内固定治疗踝关节骨折合并下胫腓联合损伤的临床疗效及对术后踝关节功能和生活质量的影响。方法：回顾性分析2015年1月至2020年6月我院收治的60例踝关节骨折合并下胫腓联合损伤患者的诊治资料。根据内固定方法的不同,将患者分为非刚性组（n=30,采用非刚性内固定治疗下胫腓联合损伤）和传统螺钉组（n=30,采用传统螺钉内固定治疗下胫腓联合损伤）。比较两组的围术期指标和完全负重所需时间、手术前后的下胫腓重叠距离（TBOL）和下胫腓间隙（TBCS）;以美国足踝外科协会（AOFAS）踝-后足评分评估两组的术后踝关节功能,以世界卫生组织生活质量测定简表（WHOQOL-BREF）评估两组的生活质量,并比较两组的术后并发症情况。结果：非刚性组的完全负重所需时间短于传统螺钉组,操作角度大于传统螺钉组（均P<0.05）。两组患者术后6周、12周和6个月的TBOL均大于术前,TBCS均小于术前（均P<0.05）,但两组术后6周、12周和6个月的TBOL和TBCS相比无明显差异（P>0.05）。非刚性组术后12周的AOFAS评分高于传统螺钉组（P<0.05）;两组术后6个月的AOFAS评分均较术后12周升高（P<0.05）,但组间比较无明显差异（P>0.05）。术后6个月,非刚性组的WHOQOL-BREF各项评分及总分均高于传统螺钉组（P<0.05）。两组并发症发生率比较无明显差异（P>0.05）。结论：非刚性与传统螺钉内固定治疗踝关节骨折合并下胫腓联合损伤的临床疗效及康复效果相当,但非刚性固定的操作更加便利,术后恢复较快,患者术后生活质量更高,可较早完全负重。     

Finite Element Analysis of Minimal Invasive Transforaminal Lumbar Interbody Fusion

The purpose of our study is to develop and validate three-dimensional finite element models of transforaminal lumbar interbody fusion, and explore the most appropriate method of fixation and fusion by comparing biomechanical characteristics of different fixation method. We developed four fusion models: bilateral pedicle screws fixation with a single cage insertion model (A), bilateral pedicle screws fixation with two cages insertion model (B), unilateral pedicle screws fixation with a single cage insertion model (C), and unilateral pedicle screws fixation with two cages insertion model (D); the models were subjected to different forces including anterior bending, posterior extension, left bending, right bending, rotation, and axial compressive. The von Mises stress of the fusion segments on the pedicle screw and cages was recorded. Angular variation and stress of pedicle screw and cage were compared. There were differences of Von Mises peak stress among four models, but were within the range of maximum force. The angular variation in A, B, C, and D decreased significantly compared with normal. There was no significant difference of angular variation between A and B, and C and D. Bilateral pedicle screws fixation had more superior biomechanics than unilateral pedicle screws fixation. In conclusion, the lumbar interbody fusion models were established using varying fixation methods, and the results verified that unilateral pedicle screws fixation with a single cage could meet the stability demand in minimal invasive transforaminal interbody fusion.     

An efficient and accurate prediction of the stability of percutaneous fixation of acetabular fractures with finite element simulation

Posterior wall fracture is one of the most common fracture types of the acetabulum and a conventional approach is to perform open reduction and internal fixation with a plate and screws. Percutaneous screw fixations, on the other hand, have recently gained attention due to their benefits such as less exposure and minimization of blood loss. However their biomechanical stability, especially in terms interfragmentary movement, has not been investigated thoroughly. The aims of this study are twofold: (1) to measure the interfragmentary movements in the conventional open approach with plate fixations and the percutaneous screw fixations in the acetabular fractures and compare them; and (2) to develop and validate a fast and efficient way of predicting the interfragmentary movement in percutaneous fixation of posterior wall fractures of the acetabulum using a 3D finite element (FE) model of the pelvis. Our results indicate that in single fragment fractures of the posterior wall of the acetabulum, plate fixations give superior stability to screw fixations. However screw fixations also give reasonable stability as the average gap between fragment and the bone remained less than 1 mm when the maximum load was applied. Our finite element model predicted the stability of screw fixation with good accuracy. Moreover, when the screw positions were optimized, the stability predicted by our FE model was comparable to the stability obtained by plate fixations. Our study has shown that FE modeling can be useful in examining biomechanical stability of osteosynthesis and can potentially be used in surgical planning of osteosynthesis.     

Biomechanical effects of posterior pedicle fixation techniques on the adjacent segment for the treatment of thoracolumbar burst fractures: a biomechanical analysis

Abstract

Posterior pedicle fixation technique is a common method for treating thoracolumbar burst fractures, but the effect of different fixation techniques on the postoperative spinal mechanical properties has not been clearly defined, especially on adjacent segments. A finite element model of T10-L2 with moderate T12 vertebra burst fracture was constructed to investigate biomechanical behavior of three posterior pedicle screw fixation techniques. Compared with traditional short-segment 4 pedicle screw fixation (TS-4) and intermediate long-segment 6 pedicle screw fixation (IL-6), mono-segment 4 pedicle screw fixation (MS-4) provides a safer surgical selection to prevent the secondary degeneration of adjacent segments in the long-term.     

Biomechanical differences of Coflex-F and pedicle screw fixation combined with TLIF or ALIF – a finite element study

Lumbar interbody fusion is a common procedure for treating lower back pain related to degenerative disc diseases. The Coflex-F is a recently developed interspinous spacer, the makers of which claim that it can provide stabilisation similar to pedicle screw fixation. Therefore, this study compares the biomechanical behaviour of the Coflex-F device and pedicle screw fixation with transforaminal lumbar interbody fusion (TLIF) or anterior lumbar interbody fusion (ALIF) surgeries by using finite element analysis. The results show that the Coflex-F device combined with ALIF surgery can provide stability similar to the pedicle screw fixation combined with TLIF or ALIF surgery. Also, the posterior instrumentations (Coflex-F and pedicle screw fixation) combined with TLIF surgery had lower stability than when combined with ALIF surgery.     

Biomechanical differences of Coflex-F and pedicle screw fixation combined with TLIF or ALIF--a finite element study

Lumbar interbody fusion is a common procedure for treating lower back pain related to degenerative disc diseases. The Coflex-F is a recently developed interspinous spacer, the makers of which claim that it can provide stabilisation similar to pedicle screw fixation. Therefore, this study compares the biomechanical behaviour of the Coflex-F device and pedicle screw fixation with transforaminal lumbar interbody fusion (TLIF) or anterior lumbar interbody fusion (ALIF) surgeries by using finite element analysis. The results show that the Coflex-F device combined with ALIF surgery can provide stability similar to the pedicle screw fixation combined with TLIF or ALIF surgery. Also, the posterior instrumentations (Coflex-F and pedicle screw fixation) combined with TLIF surgery had lower stability than when combined with ALIF surgery.     

人工半骨盆假体置换联合腰椎椎弓根螺钉固定术后生物力学的有限元分析

目的:建立人工半骨盆假体置换与联合腰椎椎弓根螺钉固定后的三维有限元模型,评价腰骶段生物力学改变后半骨盆假体力学结构的特点。方法:采用CT薄层扫描采集原始数据,分别建立正常骨盆、半骨盆假体置换术后以及半骨盆假体置换联合腰椎椎弓根螺钉固定术后骨盆的三维有限元模型,分别在第4腰椎上终板平面施以500 N的垂直纵向载荷,分析不同骨盆模型的应力分布特点。结果:与正常骨盆有限元模型相比,半骨盆假体置换术后健侧骨盆应力分布以骶髂关节、髋臼窝及耻骨为主,置换侧半骨盆假体以耻骨连接棒、髋臼杯及髂骨座为主,最大应力出现在耻骨连接棒,应力峰值为65.62 MPa。联合腰椎椎弓根螺钉固定后健侧应力相对减小,置换侧髂骨固定座与骶骨固定处应力相对减小,应力分布以腰椎椎弓根钉棒、耻骨连接棒及髋臼杯为主,最大应力出现在椎弓根螺钉,应力峰值为107 MPa。结论:半骨盆假体置换联合腰椎椎弓根螺钉固定后钉棒分担了半骨盆置换后健侧骨盆及置换侧髂骨固定座与骶骨固定处附近的部分应力,缓解应力集中现象,降低术后骨盆破坏风险,一定程度上增加了半骨盆置换后骨盆的稳定性。     

Biomechanical comparison of conventional and optimised locking plates for the fixation of intraarticular calcaneal fractures: a finite element analysis

Intraarticular calcaneal fractures can result in poor prognosis. Although operative fixation can improve the functional outcomes in most cases, surgical complications such as loss of reduction and wound healing problems may increase the risk of reoperation. Hence, this study aimed to design calcaneal locking plate with a lower profile and better biomechanical performance and to compare the redesigned plate with the traditional calcaneal plate via the finite element method. A Sanders’ type II-C intraarticular calcaneal fracture was simulated. Two fixation models utilising the branch-like calcaneal locking plate and the full plate were constructed. Topology optimisation was conducted to generate a new calcaneal plate design. A biomechanical comparison among the three groups of plates was performed using the finite element method. For the fracture simulated in this study, the optimised plate was superior to the traditional plate in terms of fixation stability and safety but was reduced in volume by approximately 12.34%. In addition, more rational stress distributions were observed in the redesigned plate, underscoring the superiority of this new design in terms of fatigue strength. These results demonstrate that the topology optimisation can be used to design a new implant with a minimised profile and no loss of fixation stability.     

Titanium Elastic Nail (TEN) versus Reconstruction Plate Repair of Midshaft Clavicular Fractures: A Finite Element Study

BackgroundThe biomechanical characteristics of midshaft clavicular fractures treated with titanium elastic nail (TEN) is unclear. This study aimed to present a biomechanical finite element analysis of biomechanical characteristics involved in TEN fixation and reconstruction plate fixation for midshaft clavicular fractures.MethodsFinite element models of the intact clavicle and of midshaft clavicular fractures fixed with TEN and with a reconstruction plate were built. The distal clavicle displacement, peak stress, and stress distribution on the 3 finite element models were calculated under the axial compression and cantilever bending.ResultsIn both loading configurations, TEN generated the highest displacement of the distal clavicle, followed by the intact clavicle and the reconstruction plate. TEN showed higher peak bone and implant stresses, and is more likely to fail in both loading configurations compared with the reconstruction plate. TEN led to a stress distribution similar to that of the intact clavicle in both loading configurations, whereas the stress distribution with the reconstruction plate was nonphysiological in cantilever bending.ConclusionsTEN is generally preferable for treating simple displaced fractures of the midshaft clavicle, because it showed a stress distribution similar to the intact clavicle. However, TEN provides less stability, and excessive exercise of and weight bearing on the ipsilateral shoulder should be avoided in the early postoperative period. Fixation with a reconstruction plate was more stable but showed obvious stress shielding. Therefore, for patients with a demand for early return to activity, reconstruction plate fixation may be preferred.     

Biomechanical measurements on scaphoid bone screws in an experimental model

A number of screws commonly used for internal fixation in scaphoid bone fractures and nonunions are compared regarding biomechanical properties and clinical applicability. The experiments were carried out on models made of ash-wood, representing a reconstruction and fixation as is performed in a cortico-cancellous inlay bone graft for scaphoid non-union. For fixation use was made of 2.7 and 3.5 AO/ASIF cortical screws respectively, 4.0 AO/ASIF cancellous screws, Herbert screws, and a newly designed screw called the three components screw (D.K.S.). The models with implanted screws were tested for bending strength, tensile strength and torsion stability. No large differences between the various screws were found regarding the measured parameters, so that a small intra-osteal implant such as the Herbert screw and the D.K.S., which can be inserted easily and which gives a certain amount of interfragmentary compression, will be sufficient for osteosynthesis of the scaphoid bone. In case an intra-osteal implant is not available a single 3.5 AO/ASIF cortical screw, inserted following lag-screw principles, is recommended.     

Reasons why dynamic compression plates are inferior to locking plates in osteoporotic bone: a finite element explanation

While locking plate fixation is becoming increasingly popular for complex and osteoporotic fractures, for many indications compression plating remains the standard choice. This study compares the mechanical behaviour of the more recent locking compression plate (LCP) device, with the traditional dynamic compression plates (DCPs) in bone of varying quality using finite element modelling. The bone properties considered include orthotropy, inhomogeneity, cortical thinning and periosteal apposition associated with osteoporosis. The effect of preloads induced by compression plating was included in the models. Two different fracture scenarios were modelled: one with complete reduction and one with a fracture gap. The results show that the preload arising in DCPs results in large principal strains in the bone all around the perimeter of the screw hole, whereas for LCPs large principal strains occur primarily on the side of the screw proximal to the load. The strains within the bone produced by the two screw types are similar in healthy bone with a reduced fracture gap; however, the DCP produces much larger strains in osteoporotic bone. In the presence of a fracture gap, the DCP results in a considerably larger region with high tensile strains and a slightly smaller region with high compressive strains. These findings provide a biomechanical basis for the reported improved performance of locking plates in poorer bone quality.     

Finite Element Analysis of Tibial Implants — Effect of Fixation Design and Friction Model

Abstract

A three dimensional nonlinear finite element model was developed to investigate tibial fixation designs and friction models (Coulomb's vs nonlinear) in total knee arthroplasty in the immediate postoperative period with no biological attachment. Bi-directional measurement-based nonlinear friction constitutive equations were used for the bone-porous coated implant interface. Friction properties between the polyethylene and femoral components were measured for this study. Linear elastic isotropic but heterogeneous mechanical properties taken from literature were considered for the bone. The Tensile behaviour of polyethylene was measured and subsequently modeled by an elasto-plastic model. Based on the earlier finite element and experimental pull-out studies, pegs and screws were also realistically modeled. The geometry of every component was obtained through measurement. The PCA tibial baseplate with three different configurations was considered; one with three screws, one with one screw and two short inclined porous-coated pegs, and a third one with no fixation for the sake of comparison. The axial load of 2000N was applied through the femoral component on the medial plateau of articular insert. It was found that Coulomb's friction significantly underestimates the relative micromotion at the bone-implant interface. The lowest micromotion and lift-off were found for the design with screws. Relative micromotion and stress transfer at the bone-implant interface depended significantly on the friction model and on the baseplate anchorage configuration. Cortical and cancellous bones carried, respectively, 10–13% and 65–86% of the axial load depending on the fixation configuration used. The remaining portion was transmitted as shear force by screws and pegs. Normal and Mises stresses as well as contact area in the polyethylene insert were nearly independent of the baseplate fixation design. The Maximum Mises stress in the polyethylene exceeded yield and was found 1–2 mm below the contact surface for all designs.     

An approximate model for cancellous bone screw fixation

This paper presents a finite element (FE) model to identify parameters that affect the performance of an improved cancellous bone screw fixation technique, and hence potentially improve fracture treatment. In cancellous bone of low apparent density, it can be difficult to achieve adequate screw fixation and hence provide stable fracture fixation that enables bone healing. Data from predictive FE models indicate that cements can have a significant potential to improve screw holding power in cancellous bone. These FE models are used to demonstrate the key parameters that determine pull-out strength in a variety of screw, bone and cement set-ups, and to compare the effectiveness of different configurations. The paper concludes that significant advantages, up to an order of magnitude, in screw pull-out strength in cancellous bone might be gained by the appropriate use of a currently approved calcium phosphate cement.     

Finite Element Analysis of Tibial Implants - Effect of Fixation Design and Friction Model

A three dimensional nonlinear finite element model was developed to investigate tibial fixation designs and friction models (Coulomb's vs nonlinear) in total knee arthroplasty in the immediate postoperative period with no biological attachment. Bi-directional measurement-based nonlinear friction constitutive equations were used for the bone-porous coated implant interface. Friction properties between the polyethylene and femoral components were measured for this study. Linear elastic isotropic but heterogeneous mechanical properties taken from literature were considered for the bone. The Tensile behaviour of polyethylene was measured and subsequently modeled by an elasto-plastic model. Based on the earlier finite element and experimental pull-out studies, pegs and screws were also realistically modeled. The geometry of every component was obtained through measurement. The PCA tibial baseplate with three different configurations was considered; one with three screws, one with one screw and two short inclined porous-coated pegs, and a third one with no fixation for the sake of comparison. The axial load of 2000N was applied through the femoral component on the medial plateau of articular insert. It was found that Coulomb's friction significantly underestimates the relative micromotion at the bone-implant interface. The lowest micromotion and lift-off were found for the design with screws. Relative micromotion and stress transfer at the bone-implant interface depended significantly on the friction model and on the baseplate anchorage configuration. Cortical and cancellous bones carried, respectively, 10-13% and 65-86% of the axial load depending on the fixation configuration used. The remaining portion was transmitted as shear force by screws and pegs. Normal and Mises stresses as well as contact area in the polyethylene insert were nearly independent of the baseplate fixation design. The Maximum Mises stress in the polyethylene exceeded yield and was found 1-2 mm below the contact surface for all designs.     

Enhanced bone screw fixation with biodegradable bone cement in osteoporotic bone model

Purpose: The purpose of this study was to study the potential of novel biodegradable PCL bone cement to improve bone screw fixation strength in osteoporotic bone. Methods: The biomechanical properties of bone cement (ε-polycaprolactone, PCL) and fixation strength were studied using biomechanical tests and bone screws fixed in an osteoporotic bone model. Removal torques and pullout strengths were assessed for cortical, self-tapping, and cancellous screws inserted in the osteoporotic bone model (polyurethane foam blocks with polycarbonate plate) with and without PCL bone cement. Open cell and cellular rigid foam blocks with a density of 0.12 g/cm3 were used in this model. Results: Removal torques were significantly (more than six-fold) improved with bone cement for cancellous screws. Furthermore, the bone cement improved pullout strengths three to 12 times over depending on the screw and model material.?Conclusions: Biodegradable bone cement turned out to be a very potential material to stabilize screw fixation in osteoporotic bone. The results warrant further research before safe clinical use, especially to clarify clinically relevant factors using real osteoporotic bone under human body conditions and dynamic fatigue testing for long-term performance.     

齿状突几何参数、骨密度与生物力学性质的相关性研究

目的:齿状突骨折是颈椎的严重损伤,其中大部分需要行前路螺钉内固定术治疗,齿状突的几何参数对螺钉的选择起决定性作用,其骨密度则影响螺钉对骨质的把持力,齿状突固有的生物力学性质对齿状突骨折固定效果进而对骨折愈合有较大影响,基于以上考虑,本课题分析并比较了几何参数、骨密度与生物力学性质的相关性,评价其指导临床应用的意义。方法:将15例经福尔马林浸泡的国人枢椎标本剔除周围软组织,分别测量并分析各个标本的几何参数、骨密度以及扭转刚度、剪切刚度、拉伸刚度等生物力学性质的特点,并比较它们之间的相关性。结果:齿状突为一椭球形结构,难以容纳两枚内固定螺钉,齿状突的几何参数、骨密度和生物力学性质之间没有相关性。结论:临床上在对齿状突骨折采用螺钉内固定前需要了解齿状突的解剖结构并据此选取适当尺寸的螺钉,应根据齿状突基底部的横径选择螺钉的直径,根据基底部到前唇的距离选择螺钉光滑段的长度,根据枢椎高度选择螺钉长度,齿状突的几何参数、骨密度和齿状突的生物力学性质之间并无相关性,并不能根据齿状突几何参数、骨密度来预测其生物力学强度进而预测内固定的初始稳定性。     

Investigation of fixation screw pull-out strength on human spine

For the purpose of fixation and stabilizing the spine, the pull-out strength of the screw is one of the most important factors to be considered. The material properties of the bone, coupled with the principal dimensions of the screw such as major diameter, minor diameter, pitch and purchase length, may affect the pull-out strength of the fixation screw. In this study, the effects of various factors on the bone screw pull-out strength were studied using finite element method of analysis. A three-dimensional finite element model simulating the threaded connection of bone and surgical screw was constructed. The behavior of both the bone and the screw during screw pull-out were analyzed and discussed. The effect of the screw parameters on the screw pull-out strength was also investigated. The results showed that failure of the connection was due to bone shearing which occurred along a cylindrical surface determined by the outer perimeter of the screw and penetrated length. The distribution of the shear stress along the threaded length in the bone was nearly uniform. The effect of the major diameter on the screw pull-out strength was more significant than those of the minor diameter and the pitch. The minor diameter hardly affected the pull-out strength.     

Biomechanical interactions of different mini-plate fixations and maxilla advancements in the Le Fort I Osteotomy: a finite element analysis

This study investigates the biomechanical interaction of different mini-plate fixation types (shapes/sizes and patterns) with segmental advancement levels on the Le Fort I osteotomy using the non-linear finite element (FE) approach. Nine models were generated under a standard 1-piece LeFort I osteotomy for advancement with 3, 6 and 9 mm distances and four mini-plates with three fixation patterns including LL, LI, and II patterns placed on the maxillae models by integrating computed tomography images and computer-aided design system. The axial and oblique occlusal forces were 250 N applied to each premolar/molar and 125 N applied at 30° inclination to the tooth long axis and from palatal to buccal, respectively. The relative micro-movement values between the two maxillary bone segments and maximum mini-plate stress increased obviously with maxilla advancement increment and the increasing trend can be fitted by exponential curve. The corresponding values in II mini-plate fixation presented apparently high values in all simulated cases. The mini-plate stress concentration locations were found at the bending regions to increase high fracture risk. The mini-plate yield strength can be mapped to a critical (limited) advancement for three types of fixations for safe consideration. This study concluded that L-shaped mini-plates with lateral fixation are recommended to provide better stability. The risk for mini-plate fracture and bone relapse increases when maxillary advancement is larger than a critical value of 5 mm in the Le Fort I osteotomy.