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To compare the advantages and disadvantages of biodegradable and non-degradable implants in orthopedic fractures. Recent original articles about biodegradable and non-degradable implants for fracture fixation were reviewed extensively, and a comprehensive retrospective analysis was performed. Standard orthopedic treatment is to use non-degradable metal implants to fixate the fracture site. This kind of treatment not only causes rejection and stress shielding, but also requires a second surgery to remove the metal implants. In addition, this kind of treatment increases physical pain and is a serious financial burden to patients. However, biodegradable implants do not require a second surgery for removal and have good biocompatibility and osteoconductivity. Biodegradable implants do not require a second surgery for removal and have good biocompatibility and osteoconductivity. Consequently, they are an ideal treatment and are increasingly used for orthopedic surgical patients. The most common indications for biodegradable implants include craniofacial reconstruction, anterior cruciate ligament reconstruction, meniscus repair, ankle fracture treatment, and tibia and fibula fracture treatment.

Objective To compare the biomechanical stability of transsacral-transiliac screw fixation and lumbopelvic fixation for “H”- and “U”-type sacrum fractures with traumatic spondylopelvic dissociation. Methods Finite element models of “H”- and “U”-type sacrum fractures with traumatic spondylopelvic dissociation were created in this study. The models mimicked the standing position of a human. Fixation with transsacral-transiliac screw fixation, lumbopelvic fixation, and bilateral triangular fixation were simulated. Biomechanical tests of instability were performed, and the fracture gap displacement, anteflexion, rotation, and stress distribution after fixation were assessed. Results For H-type fractures, the three kinds of fixation ranked by stability were bilateral triangular fixation > lumbopelvic fixation > transsacral-transiliac screw fixation in the vertical and anteflexion directions, bilateral triangular fixation > transsacral-transiliac S1 and S2 screw fixation > lumbopelvic fixation in rotation. The largest displacements in the vertical, anteflexion, and rotational directions were 0.57234 mm, 0.37923 mm, and 0.13076 mm, respectively. For U-type fractures, these kinds of fixation ranked by stability were bilateral triangular fixation > lumbopelvic fixation > transsacral-transiliac S1 and S2 screw fixation > transsacral-transiliac S1 screw fixation in the vertical, anteflexion, and rotational directions. The largest displacements in the vertical, anteflexion, and rotational directions were 0.38296 mm, 0.33976 mm, and 0.05064 mm, respectively. Conclusion All these kinds of fixation met the mechanical criteria for clinical applications. The biomechanical analysis showed better bilateral balance with transsacral-transiliac screw fixation. The maximal displacement for these types of fixation was less than 1 mm. Percutaneous transsacral-transiliac screw fixation can be considered the best option among these kinds of fracture fixation.

In recent years, a combination of traction and vibration therapy is usually used to alleviate low back pain (LBP) in clinical settings. Combining head-down tilt (HDT) traction with vibration was demonstrated to be efficacious for LBP patients in our previous study. However, the biomechanics of the lumbar spine during this combined treatment is not well known and need quantitative analysis. In addition, LBP patients have different grades of degeneration of the lumbar spinal structure, which are often age related. Selecting a suitable rehabilitation therapy for different age groups of patients has been challenging. Therefore, a finite element (FE) model of the L1-L5 lumbar spine and a vibration dynamic model are developed in this study in order to investigate the biomechanical effects of the combination of HDT traction and vibration therapy on the age-related degeneration of the lumbar spine. The decrease of intradiscal pressure is more effective when vibration is combined with traction therapy. Moreover, the stresses on the discs are lower in the "traction+vibration" mode than the "traction-only" mode. The stress concentration at the posterior part of nucleus is mitigated after the vibration is combined. The disc deformations especially posterior disc radial retraction is improved in the "traction+vibration" mode. These beneficial effects of this therapy could help decompress the discs and spinal nerves and therefore relieve LBP. Simultaneously, patients with grade 1 degeneration (approximately 41-50 years old) are able to achieve better results compared with other age groups. This study could be used to provide a more effective LBP rehabilitation therapy.

Research Purpose: To compare the stability of sacral fracture fixation with three kinds of internal fixations by using finite element method. Proposed Methods: The L4-L5 and pelvic models were intercepted from previously established and validated complete lumbar pelvic model and modified to simulate the U-shaped sacral fracture model, and fixed using the following three fixation methods. (1) screw with S1S2 passed through, (2) L4L5 pedicle screw + screw for wing of ilium, (3) L4L5 pedicle screw + screw with S1 passed through + screw for wing of ilium. A 500N force was applied for point of action where is in central position of L4 superior end-plate and coupled with superior end-plate surface, then compared the stress, strain and fracture gap separation value of different fixation methods. Results: There is no significant difference on fracture gap separation value and strain on fracture surface in above three fixation methods, however the maximum stress (101.1MPa) produced by the first fixation method is less than the one (291.1MPa) produced by the second method and the one (197.1MPa) produced by the third fixation method. Conclusions: For U-shaped sacral fracture, the prior adoption is the first fixation method to make fix.

INTRODUCTION Modern super agile fighter aircraft are capable of producing an increasing multiaxial acceleration environment which can adversely affect the pilot. An evaluation of the performance of the restraint system during flight maneuvers will benefit restraint designs and, thus, the safety of pilots. METHODS A finite element model of a mannequin with PCU-15/P harness restraint was used in this study to investigate how the factors, such as strap material stiffness, friction, and belt tension, affect the performance of restraint systems during impact along the -Gx, -Gy, and -Gz directions. The corresponding maximum displacement of the mannequin's torso was computed. RESULTS The mannequin moved beyond 74 mm sideways. The change in friction coefficient (FC) from 0.1 to 0.4 decreased the displacement of the lower torso by less than 6.7%. The displacement of the torso decreased as the stiffness of the strap or tension increased. Displacement decreased by 9.3%, 6.0%, and 2.7% for the lower torso under the Gx impact, as the tightening force increased from 20 N to 80 N gradually. However, this changed slightly when the stiffness arrived at 1 E or the tension increased to 60 N. DISCUSSION PCU-15/P harness has the poorest performance during side impact and friction plays an unimportant role in affecting its performance. The stiffness of the webbing used in the PCU-15/P harness is sufficiently high. The lap belt has more effect on limiting the movement of the pilot than the shoulder straps, and a tension of 60 N during the adjustment may be enough for conventional flight maneuvers.

A 3-dimensional finite element investigation.To compare the biomechanical performances of different rotation centers (RCs) in the prevalent artificial cervical discs.Various configurations are applied in artificial discs. Design parameters may influence the biomechanics of implanted spine. The RC is a primary variation in the popular artificial discs.Implantation of 5 prostheses was simulated at C5-C6 on the basis of a validated finite element cervical model (C3-C7). The prostheses included ball-in-socket design with a fixed RC located on the inferior endplate (BS-FI) and on the superior endplate (BS-FS), with a mobile RC at the inferior endplate (BS-MI), dual articulation with a mobile RC between the endplates (DA-M), and sliding articulation with various RCs (SA-V). The spinal motions in flexion and extension served as a displacement loading at the C3 vertebrae.Total disc replacements reduced extension moment. The ball-in-socket designs required less flexion moment, whereas the flexion stiffness of the spines with DA-M and SA-V was similar to that of the healthy model. The contributions of the implanted level to the global motions increased in the total disc replacements, except in the SA-V and DA-M models (in flexion). Ball-in-socket designs produced severe stress distributions in facet cartilage, whereas DA-M and SA-V produced more severe stress distribution on the bone-implant interface.Cervical stability was extremely affected in extension and partially affected in flexion by total disc replacement. With the prostheses with mobile RC, cervical curvature was readjusted under a low follower load. The SA-V and BS-FS designs exhibited better performances in the entire segmental stiffness and in the stability of the operative level than the BS-MI and BS-FI designs in flexion. The 5 designs demonstrated varying advantages relative to the stress distribution in the facet cartilages and on the bone-implant interface.5.

Objective To compare the biomechanical stability of four different kinds of percutaneous screw fixation in two types of unilateral sacroiliac joint dislocation. Methods Finite element models of unstable Tile type B and type C pelvic ring injuries were created in this study. Modelling was based on fixation with a single S1 screw (S1-1), single S2 screw (S2-1), two S1 screws (S1-2) and a combination of a single S1 and a single S2 screw (S1–S2). The biomechanical test of two types of pelvic instability (rotational or vertical) with four types of percutaneous fixation were compared. Displacement, flexion and lateral bend (in bilateral stance) were recorded and analyzed. Results Maximal inferior translation (displacement) was found in the S2-1 group in type B and C dislocations which were 1.58 mm and 1.90 mm, respectively. Maximal flexion was found in the S2-1 group in type B and C dislocations which were 1.55° and 1.95°, respectively. The results show that the flexion from most significant angulation to least is S2-1, S1-1, S1-2, and S1–S2 in type B and C dislocations. All the fixations have minimal lateral bend. Conclusion Our findings suggest single screw S1 fixation should be adequate fixation for a type B dislocation. For type C dislocations, one might consider a two screw construct (S1–S2) to give added biomechanical stability if clinically indicated.

The aim of this study is to investigate the dynamic response of a multi-segment model of the thoracolumbar spine and determine how the sitting posture affects the response under the impact of ejection. A nonlinear finite element model of the thoracolumbar-pelvis complex (T9-S1) was developed and validated. A multi-body dynamic model of a pilot was also constructed so an ejection seat restraint system could be incorporated into the finite element model. The distribution of trunk mass on each vertebra was also considered in the model. Dynamics analysis showed that ejection impact induced obvious axial compression and anterior flexion of the spine, which may contribute to spinal injuries. Compared with a normal posture, the relaxed posture led to an increase in stress on the cortical wall, endplate, and intradiscal pressure of 43%, 10%, 13%, respectively, and accordingly increased the risk of inducing spinal injuries.

ObjectiveTo investigate the biomechanical effects of the lumbar posterior complex on the adjacent segments after posterior lumbar interbody fusion (PLIF) surgeries.MethodsA finite element model of the L1-S1 segment was modified to simulate PLIF with total laminectomy (PLIF-LAM) and PLIF with hemilaminectomy (PLIF-HEMI) procedures. The models were subjected to a 400N follower load with a 7.5-N.m moment of flexion, extension, torsion, and lateral bending. The range of motion (ROM), intradiscal pressure (IDP), and ligament force were compared.ResultsIn Flexion, the ROM, IDP and ligament force of posterior longitudinal ligament, intertransverse ligament, and capsular ligament remarkably increased at the proximal adjacent segment in the PLIF-LAM model, and slightly increased in the PLIF-HEMI model. There was almost no difference for the ROM, IDP and ligament force at L5-S1 level between the two PLIF models although the ligament forces of ligamenta flava remarkably increased compared with the intact lumbar spine (INT) model. For the other loading conditions, these two models almost showed no difference in ROM, IDP and ligament force on the adjacent discs.ConclusionsPreserved posterior complex acts as the posterior tension band during PLIF surgery and results in less ROM, IDP and ligament forces on the proximal adjacent segment in flexion. Preserving the posterior complex during decompression can be effective on preventing adjacent segment degeneration (ASD) following PLIF surgeries.

Orthopedic insole was important for partial foot amputation (PFA) to achieve foot balance and avoid foot deformity. The inapposite insole orthosis was thought to be one of the risk factors of reamputation for foot valgus patient, but biomechanical effects of internal tissues on valgus foot had not been clearly addressed. In this study, plantar pressure on heel and metatarsal regions of PFA was measured using F-Scan. The three-dimensional finite element (FE) model of partial foot evaluated different medial wedge angles (MWAs) (0.0°-10.0°) of orthopedic insole on valgus foot. The effect of orthopedic insole on the internal bone stress, the medial ligament tension of ankle, plantar fascia tension, and plantar pressure was investigated. Plantar pressure on medial heel region was about 2.5 times higher than that of lateral region based on the F-Scan measurements. FE-predicted results showed that the tension of medial ankle ligaments was the lowest, and the plantar pressure was redistributed around the heel, the first metatarsal, and the lateral longitudinal arch regions when MWA of orthopedic insole ranged from 7.5° to 8.0°. The plantar fascias maintained about 3.5% of the total load bearing on foot. However, the internal stresses from foot bones increased. The simulation in this study would provide the suggestion of guiding optimal design of orthopedic insole and therapeutic planning to pedorthist.

We observed the effect of vibration parameters on lumbar spine under different vibration conditions using finite element analysis method in our laboratory. In this study, the CT-images of L1-L5 segments were obtained. All images were used to develop 3D geometrical model using the Mimics10. 01 (Materialise, Belgium). Then it was modified using Geomagic Studio12. 0 (Raindrop Geomagic Inc. USA). Finite element (FE) mesh model was generated by Hypermesh11. 0 (Altair Engineering, Inc. USA) and Abaqus. Abaqus was used to calculate the stress distribution of L1-L5 under different vibration conditions. It was found that in a vibration cycle, tensile stress was occurred on lumbar vertebra mainly. Stress distributed evenly and stress concentration occurred on the left rear side of the upper endplate. The stress had no obvious changes under different frequencies, but the stress was higher when amplitude was greater. In conclusion, frequency and amplitude parameters have little effect on the stress distribution in vertebra. The stress magnitude is positively correlated with the amplitude.

In this study, a new method of applying follower load in finite element (FE) model of lumbar spine was presented. The effect of follower load on the range of motions (ROM) in lumbar spine was also investigated. A three-dimensional nonlinear FE model of lumbar spine (L1-S1) has been developed and validated. Connector elements between each pair of endplates were created to apply follower load. The endpoints of each connector were close to the center of endplate. The follower load of 0N, 500N , 800N, 1200N were respectively applied to explore their influence on the motion response of lumbar spine to the moment of 7.5NM in three principle planes (extension, flexion, right bending, left bending, right torsion, left torsion). The results showed that the direction of follower load was almost along with the curvature of spine and induced very small segmental motion. The follower load made the ROM of lumbar spine slightly increase in extension, while produced the decrease in ROM in other five moments. This stiffening effect became more obvious with an increase in the follower load. The largest percent decrease in motion of lumbar spine due to pre-load was in left torsion (47%),and then right torsion(42%), right lateral bending (21%) , left lateral bending(20%), flexion(11%).

Foot inversion was the most common injury of lower limb injury, it seriously affected the foot balance and posture control during standing and walking. The purpose of this study was to describe the rationality of biomechanical modeling for foot inversion. Plantar pressure measurements and foot roentgenogram had been reported. However, direct measurement of the internal tissues stress was difficult. A three-dimensional finite element model of foot inversion was developed to investigate the region of foot inversion injury. Compared with normal foot, the results showed that subtalar joint region was mainly weight-bearing region. Peak von Mises stress of the internal bones was transferred to the lateral longitudinal arch. The simulation in this study would provide the suggestion of therapeutic planning to foot inversion.

Pilots have been often sustained ejection-induced spine trauma and investigation of dynamic response of spine benefit for the insight of injury mechanism and design of protective device under ejection condition. This study developed a nonlinear finite element (FE) model of the thoracolumbar spine and a multi-body dynamic model of dummy respectively. The kinetic data of multi-body model and stress information of FE model have been analyzed. It can be found that ejection impact induces obvious axial compression and anterior flexion of the spine, which may contribute to the incidence of spinal injury. The high stress was located in T1 and L1 which has more risk of injury during impact loading. The combination of FE method and multi-body dynamic approach provides a convenient tool for studying occupants restrained by seat belts, such as drives, aviators, etc.

Blunt impact on the eye could results in lens capsular rupture that allows foreign substances to enter into the lens and leads to cataract formation. This paper aimed to investigate the mechanism of lens capsular rupture using finite element (FE) method. A FE model of the human eye was developed to simulate dynamic response of the lens capsule to a BB (a standard 4.5-mm-diameter pellet) impact. Sensitivity studies were conducted to evaluate the effect of the parameters on capsular rupture, including the impact velocity, the elastic modulus of the lens, the thickness and the elastic modulus of the lens capsule. The results indicated that the lens was subjected to anterior compression and posterior intension when the eye was stricken by a BB pellet. The strain on the posterior capsule (0.392) was almost twice as much as that on the anterior capsule (0.207) at an impact velocity of 20 m/s. The strain on the capsule was proportional to the impact velocity, while the capsular strain showed no significant change when the lens modulus elastic varied with age. The findings confirmed that blunt traumatic capsular rupture is the result of shockwave propagation throughout the eye. The posterior capsule is subjected to greater tension in blunt trauma, which is the main cause that ruptures are more commonly found on the posterior capsule than the anterior capsule. Also, thinner thickness and lower elastic modulus would contribute to the posterior capsular rupture.

The aim of this study is to investigate the dynamic response of a multi-segment model of the thoracolumbar spine and determine how the sitting posture affects the response under the impact of ejection. A nonlinear finite element model of the thoracolumbar-pelvis complex (T9-S1) was developed and validated. A multi-body dynamic model of a pilot was also constructed so an ejection seat restraint system could be incorporated into the finite element model. The distribution of trunk mass on each vertebra was also considered in the model. Dynamics analysis showed that ejection impact induced obvious axial compression and anterior flexion of the spine, which may contribute to spinal injuries. Compared with a normal posture, the relaxed posture led to an increase in stress on the cortical wall, endplate, and intradiscal pressure of 43%, 10%, 13%, respectively, and accordingly increased the risk of inducing spinal injuries.

Purpose: Based on rapid modeling 1 year after intramedullary nailing, personalized finite element modeling analysis was performed to predict whether the broken ends of fractured bones would break again after nail dislodgement. Methods: A total of 10 male volunteers with femur fractures who had undergone intramedullary nailing were selected 1 year after fixation and were divided into healing ([Formula: see text][Formula: see text]5) and non-healing ([Formula: see text][Formula: see text]5) groups based on X-ray analysis. We modeled each femoral fracture and performed finite element analyses after the intramedullary nail was dislodged. Static loads and constraints were applied to each model to simulate a person standing on one leg. Results: In the healing group, the von Mises stress concentrations and stress concentration point distribution were located outside the bone healing area, indicating that the stress was not concentrated at the fracture site. In the non-healing group, the maximum von Mises stress for various materials was located in the broken ends of the fractured bone, indicating that the stress was concentrated at the fracture site. Conclusion: Personalized modeling can be used to analyze bone healing before removal of a fixator to predict the stability of the fractured bone after fixator removal and to rapidly decide whether slow walking could refracture the broken ends.

In contrast to numerous researches on static or quasi-static stiffness of cervical spine segments, very few investigations on their dynamic stiffness were published. Currently, scale factors and estimated coefficients were usually used in multi-body models for including viscoelastic properties and damping effects, meanwhile viscoelastic properties of some tissues were unavailable for establishing finite element models. Because dynamic stiffness of cervical spine segments in these models were difficult to validate because of lacking in experimental data, we tried to gain some insights on current modeling methods through studying dynamic stiffness differences between these models. A finite element model and a multi-body model of C6-C7 segment were developed through using available material data and typical modeling technologies. These two models were validated with quasi-static response data of the C6-C7 cervical spine segment. Dynamic stiffness differences were investigated through controlling motions of C6 vertebrae at different rates and then comparing their reaction forces or moments. Validation results showed that both the finite element model and the multi-body model could generate reasonable responses under quasi-static loads, but the finite element segment model exhibited more nonlinear characters. Dynamic response investigations indicated that dynamic stiffness of this finite element model might be underestimated because of the absence of dynamic stiffen effect and damping effects of annulus fibrous, while representation of these effects also need to be improved in current multi-body model. Copyright © 2015 John Wiley & Sons, Ltd.

Ball-and-socket disc prostheses are the leading type of artificial disc replacement (ADR) and are typically used to treat degenerative cervical spine instability. Previous publications focused on the influence of different ProDisc-C design parameters in view of biomechanics. However, more beneficial data could be gathered if the implant was implanted prior to testing. Therefore, this study aimed to estimate the effect of different ProDisc-C arthroplasty designs and alignments when implanted at the C5-6 segment. This research can provide advice on the design of artificial discs as well as optimal placement. The geometry of the vertebrae was developed based on computed tomography (CT) images of a 32-year-old healthy male (170 cm height and 68 kg weight) with a slice thickness of 0.625 mm. A finite element (FE) model of intact C5–C6 segments including vertebrae and disc was developed and validated. A ball-and-socket artificial disc prosthesis model (ProDisc-C, Synthes) was implanted into the validated FE model. The curvature of the ProDisc-C prosthesis as well as the implanted position was varied. All models were loaded with a 74 N compressive force and pure moments of 1.8 Nm in flexion-extension, bilateral bending and axial torsion. The radius of the artificial disc influenced the ROM, facet joint force and capsule ligament tension only in flexion, while the position influenced these aspects in all loading conditions. The disc with a 6 mm radius had a greater ROM in flexion, and lower stress on the polyethylene (PE) insert without apparent stress concentrations, but it had a greater facet joint force and ligament tension compared to other radii. For all the designs, the implant position in the anterior–posterior direction had a significant influence on the disc biomechanics. Disc design and surgical procedure, such as implantation position, are important factors in postoperative rehabilitation, especially regarding the ROM in flexion/extension and implant stress. Thus, a suitable disc design should consider preserving an adequate range of motion (ROM) as well as a moderate facet joint force or stress, and proper implant positioning along the anterior–posterior direction should be monitored.