Difference analysis of the glenoid centerline between 3D preoperative planning and 3D printed prosthesis manipulation in total shoulder arthroplasty.

INTRODUCTION: Excessive version and inclination of the glenoid component during total shoulder arthroplasty can lead to glenohumeral instability, early loosening, and even failure. The orientation and position of the central pin determine the version and inclination of the glenoid component. The purpose of this study was to compare the differences in centerline position and orientation obtained using "3D preoperative planning based on the best-fit method for glenoid elements" and the surgeon's manipulation. MATERIALS AND METHODS: Twenty-nine CT images of glenohumeral osteoarthritis of the shoulder were reconstructed into a 3D model, and a 3D printer was used to create an in vitro model for the surgeon to drill the center pin. The 3D shoulder model was also used for 3D preoperative planning (3DPP) using the best-fit method for glenoid elements. The in vitro model was scanned and the version, inclination and center position were measured to compare with the 3DPP results. RESULTS: The respective mean inclinations (versions) of the surgeon and 3DPP were -2.63° ± 6.60 (2.87° ± 5.97) and -1.96° ± 4.24 (-3.21° ± 4.00), respectively. There was no significant difference in the inclination and version of the surgeon and 3DPP. For surgeons, the probability of the inclination and version being greater than 10° was 13.8% (4/29) and 10.3% (3/29), respectively. Compared to the 3DPP results, the surgeon's center position was shifted down an average of 1.63 mm. There was a significant difference in the center position of the surgeon and 3DPP (p < 0.05). CONCLUSION: The central pin drilled by surgeons using general instruments was significantly lower than those defined using 3D preoperative planning and standard central definitions. 3D preoperative planning prevents the version and inclination of the centerline from exceeding safe values (± 10°).

A parametric investigation on traditional and cortical bone trajectory screws for transpedicular fixation.

BACKGROUND: Many studies have been conducted to compare traditional trajectory (TT) and cortical bone trajectory (CBT) screws; however, how screw parameters affect the biomechanical properties of TT and CBT screws, and so their efficacy remains to be investigated. METHODS: A finite element model was used to simulate screws with different trajectories, diameters, and lengths. Responses for implant and tissues at the adjacent and fixed segments were used as the comparison indices. The contact lengths and spanning areas of the inserted screws were defined and compared across the varieties. RESULTS: The trajectory and diameter had a greater impact on the responses from the implant and tissues than the length. The CBT has shorter length than the TT; however, the contact length and supporting area of the CBT within the cortical bone were 19.6%. and 14.5% higher than those of the TT, respectively. Overall, the TT and CBT were equally effective at stabilizing the instrumented segment, except for bending and rotation. The CBT experienced less adjacent segment compensations than the TT. With the same diameter and length, the TT was considerably less stressed than the CBT, especially for flexion and extension. CONCLUSIONS: The CBT may provide less stress at adjacent segments compared with the TT. The CBT may provide more stiffer in osteoporotic segments than the TT due to greater contact with cortical bone and a wider supporting base between the paired screws. However, both entry point and insertion trajectory of the CBT should be carefully executed to avoid vertebral breach and ensure a stable cone-screw purchase.

Gender differences in femoral trochlea morphology.

PURPOSE: This study aimed to analyze the morphology of the anterior femoral condyle using a quantitative three-dimensional reconstruction method. The morphological data were compared between genders. METHODS: Computed tomography scans of femurs were taken from 90 healthy subjects and then reconstructed in 3D modeling software. Coaxial cutting planes were created at 10° increments to measure the lateral and medial anterior condylar heights (LACH and MACH, respectively), lateral and medial trochlear groove widths (LTW and MTW, respectively), and for trochlear groove tracking. The absolute values and normalized data were compared between male and female subjects. The sulcus angle and deepest point of the trochlear groove at each cross-section were also analyzed to determine the differences in the depth of the trochlear groove. RESULTS: The absolute dimensions of LACH, MACH, LTW, and MTW were significantly smaller in the female subjects, by 10.5%, 36.9%, 10.3%, and 11.0%, respectively, than in the males (p < 0.05). After normalization, no significant difference was found in the condylar height between the genders. However, the female subjects had a significantly larger value of approximately 7.9% for the normalized trochlear width. CONCLUSION: Male subjects had greater condylar heights and widths than the female subjects. Although the trajectory of the trochlear groove varied greatly among the subjects, the trochlear groove appeared to be wider and shallower in the female subjects than in the male subjects. These results provide important information for the design of femoral trochlea to fit Asian female patients. LEVEL OF EVIDENCE: III.

How do lateral hinge and distraction affect three-dimensional rotation in open wedge high tibial osteotomy?

BACKGROUND: Open-wedge high tibial osteotomy (OWHTO) has extensively been used for the correction of medial knee osteoarthritis. The proximal tibia is osteotomized and distracted to enable the rotation of tibial fragments around the lateral hinge. Both, wedge inclination on the medial side and saw progression near the lateral cortex determine the hinge orientation. This study focused on the interaction between hinge orientation and distraction sites on the coronal, sagittal, and horizontal planes of the distracted plateau. METHODS: Three parameters of wedge inclination, saw progression, and distraction site (i.e., posterior, middle, and anterior) were systematically varied. Using a three-dimensional (3D)-printing technique, the osteotomized tibiae were manufactured as the specimens for the in vitro experiments. In total, 27 variations (3 × 3 × 3) were tested. After distraction, the specimens were scanned by computed tomography and spatially registered with the original tibia to compare the 3D angles of the distracted plateaus. RESULTS: Coronal rotation is the main purpose of OWHTO; therefore, all the values of the coronal angles were positive and significantly higher than the other two. The sagittal and horizontal angles had relatively similar values. Distraction in the middle site seems to have the least impact on sagittal rotation. Large angles of hinge orientation show the superior ability in adjusting the sagittal rotation than small angles. However, the larger the horizontal angles the greater the wedge inclination. CONCLUSIONS: The wedge inclination, saw progression, and distraction site constitute a complex mechanism that affects 3D rotations of the distracted plateau. The coronal angles are sensitive to hinge orientation and distraction site. The intraoperative planning of manipulating hinge orientation is an effective method to adjust sagittal rotation. A large angle of wedge inclination is an indicator of horizontal rotation, and it should be carefully mitigated to reduce the risk of cracking in the lateral hinge.

Traditional and cortical trajectory screws of static and dynamic lumbar fixation- a finite element study.

BACKGROUND: Two types of screw trajectories are commonly used in lumbar surgery. Both traditional trajectory (TT) and cortical bone trajectory (CBT) were shown to provide equivalent pull-out strengths of a screw. CBT utilizing a laterally-directed trajectory engaging only cortical bone in the pedicle is widely used in minimal invasive spine posterior fusion surgery. It has been demonstrated that CBT exerts a lower likelihood of violating the facet joint, and superior pull-out strength than the TT screws, especially in osteoporotic vertebral body. No design yet to apply this trajectory to dynamic fixation. To evaluate kinetic and kinematic behavior in both static and dynamic CBT fixation a finite element study was designed. This study aimed to simulate the biomechanics of CBT-based dynamic system for an evaluation of CBT dynamization. METHODS: A validated nonlinearly lumbosacral finite-element model was used to simulate four variations of screw fixation. Responses of both implant (screw stress) and tissues (disc motion, disc stress, and facet force) at the upper adjacent (L3-L4) and fixed (L4-L5) segments were used as the evaluation indices. Flexion, extension, bending, and rotation of both TT and CBT screws were simulated in this study for comparison. RESULTS: The results showed that the TT static was the most effective stabilizer to the L4-L5 segment, followed by CBT static, TT dynamic, and the CBT dynamic, which was the least effective. Dynamization of the TT and CBT fixators decreased stability of the fixed segment and alleviate adjacent segment stress compensation. The 3.5-mm diameter CBT screw deteriorated stress distribution and rendered it vulnerable to bone-screw loosening and fatigue cracking. CONCLUSIONS: Modeling the effects of TT and CBT fixation in a full lumbosacral model suggest that dynamic TT provide slightly superior stability compared with dynamic CBT especially in bending and rotation. In dynamic CBT design, large diameter screws might avoid issues with loosening and cracking.

Placement-induced effects on high tibial osteotomized construct - biomechanical tests and finite-element analyses.

BACKGROUND: High tibial osteotomy (HTO) with a medially opening wedge has been used to treat osteoarthritic knees. However, the osteotomized tibia becomes a highly unstable structure and necessitates the use of plate and screws to stabilize the medial opening and enhance bone healing. A T-shaped plate (e.g. TomoFix) with locking screws has been extensively used as a stabilizer of the HTO wedge. From the biomechanical viewpoint, however, the different plate sites and support bases of the HTO plate should affect the load-transferring path and wedge-stabilizing ability of the HTO construct. This study uses biomechanical tests and finite-element analyses to evaluate the placement- and base-induced effects of the HTO plates on construct performance. METHODS: Test-grade synthetic tibiae are chosen as the standard specimens of the static tests. A medial wedge is created for each specimen and stabilized by three plate variations: hybrid use of T- and I-shaped plates (TIP), anteriorly placed TomoFix (APT), and medially placed TomoFix (MPT). There are five tests for each variation. The failure loads of the three constructs are measured and used as the load references of the fatigue finite-element analysis. The residual life after two hundred thousand cycles is predicted for all variations. RESULTS: The testing results show no occurrence of implant back-out and breakage under all variations. However, the wedge fracture consistently occurs at the opening tip for the APT and MPT and the medially resected plateau for the TIP, respectively. The testing results reveal that both failure load and wedge stiffness of the TIP are the highest, followed by the MPT, while those of the APT are the least (P < 0.05). The fatigue analyses predict comparable values of residual life for the TIP and MPT and the highest value of damage accumulation for the APT. Both experimental and numerical tests show the biomechanical disadvantage of the APT than their counterparts. However, the TIP construct without locking screws shows the highest stress at the plate-screw interfaces. CONCLUSIONS: This study demonstrates the significant effect of placement site and support base on the construct behaviors. The TIP provides a wider base for supporting the HTO wedge even without the use of locking screws, thus significantly enhancing construct stiffness and suppressing wedge fracture. Compared to the APT, the MPT shows performance more comparable to that of the TIP. If a single plate and a smaller incision are considered, the MPT is recommended as the better alternative for stabilizing the medial HTO wedge.

Effects of stemmed and nonstemmed hip replacement on stress distribution of proximal femur and implant.

BACKGROUND: Despite improvements in shape, material, and coating for hip stem, both stress shielding and aseptic loosening have been the major drawbacks of stemmed hip arthroplasty. Some nonstemmed systems were developed to avoid rasping off the intramedullary canal and evacuating the bone marrow due to stem insertion. METHODS: In this study, the finite-element models of one intact, one stemmed, and two nonstemmed femora with minimal removal of the healthy neck were investigated to evaluate their biomechanical effects. The resurfacing (ball-shaped) and fitting (neck-shaped) systems were respectively selected as the representative of the ready- and custom-made nonstemmed implants. The stress distribution and interface micromotion were selected as the comparison indices. RESULTS: The results showed that stress distributions of the two nonstemmed femora are consistently more similar to the intact femur than the stemmed one. Around the proximal femur, the stem definitely induces the stress-shielding phenomenon of its counterparts. The fitting system with the anatomy-shaped cup can make intimate contact with the neck cortex and reduce the bone-cup micromotion and the implant stress. Comparatively, the reamed femoral head provides weaker support to the resurfacing cup causing higher interfacial micromotion. CONCLUSIONS: The reserved femoral neck could act as the load-transferring medium from the acetabular cup, femoral neck, to the diaphysial bone, thus depressing the stress-shielding effect below the neck region. If the hip-cup construct can be definitely stabilized, the nonstemmed design could be an alternative of hip arthroplasty for the younger or the specific patients with the disease limited only to the femoral head.

Biomechanical comparison of static and dynamic cervical plates in terms of the bone fusion, tissue degeneration, and implant behavior.

INTRODUCTION: Using an anterior cervical fixation device in the anterior cervical discectomy and fusion (ACDF) has evolved to various systems of static and dynamic cervical plates (SCP and DCP). Dynamic cervical plates have been divided into three categories: the rotational (DCP-R), translational (DCP-T), and hybrid (DCP-H) joints. However, little studies have been devoted to systematically investigate the biomechanical differences of dynamic cervical plates. MATERIALS AND METHODS: The biomechanical tests of load-deformation properties and failure modes between the SCP and DCP systems are implemented first by using the UHMWPE blocks as the vertebral specimens. The CT-based C2-C7 model simulates the strategies of cervical plate in ACDF surgery is developed with finite-element analyses. One intact, one SCP and two DCP systems are evaluated for their biomechanical properties of bone fusion and tissue responses. RESULTS: In the situation of biomechanical test, The mean values of the five ACDSP constructs are 393.6% for construct stiffness (p < 0.05) and 183.0% for the first yielding load (p < 0.05) less than those of the SCP groups, respectively. In the situation of finite-element analysis, the rigid-induced ASD is more severe for the SCP, followed by the DCP-H, and the DCP-R is the least. DISCUSSION AND CONCLUSIONS: Considering the degenerative degree of the adjacent segments and osteoporotic severity of the instrumented segments is necessary while using dynamic system. The mobility and stability of the rotational and translational joints are the key factors to the fusion rate and ASD progression. If the adjacent segments have been degenerative, the more flexible system can be adopted to compensate the constrained mobility of the ACDF segments. In the situation of the osteoporotic ACDF vertebrae, the stiffer system is recommended to avoid the cage subsidence.

Development of a simulation system for femoroacetabular impingement detection based on 3D images.

Image-based criteria have been adopted to diagnose femoroacetabular impingement (FAI). However, the overlapping property of the two-dimensional X-ray outlines and static and supine posture of taking computed tomography (CT) and magnetic resonance imaging images potentially affect the accuracy of the criteria. This study developed a CT image-based dynamic criterion to effectively simulate FAI, thereby providing a basis for physicians to perform pre-operative planning for arthroscopic surgery. Post-operative CT images of 20 patients with satisfactory surgical results were collected, and 10 sets of models were used to define the flexion rotation centre (FRC) of the three-dimensional FAI model. First, let these 10 groups of models simulate the FAI detection action and find the best centre offset, and then FRC is the result of averaging these 10 groups of best displacements. The model was validated in 10 additional patients. Finally, through the adjustment basis of FRC, the remaining 10 sets of models can find out the potential position of FAI during the dynamic simulation process. Rotational collisions detected using FRC indicate that the patient's post-operative flexion angle may reach 120° or greater, which is close to the actual result. The recommended surgical range of the diagnostic system (average length of 6.4 mm, width of 4.1 mm and depth of 3.2 mm) is smaller than the actual surgical results, which prevents the doctor from performing excessive resection operations, which may preserve more bones. The FRC diagnostic system detects the distribution of FAI in a simple manner. It can be used as a pre-operative diagnosis reference for clinicians, hoping to improve the effect and accuracy of debridement surgery.

Investigating the Effect of Design Parameters on the Mechanical Performance of Contact Wave Springs Designed for Additive Manufacturing.

Additive manufacturing (AM) enables design freedom to fabricate functionally graded wave springs designed by varying design parameters, which are not possible in traditional manufacturing. AM also enables optimization of the wave spring design for specific load-bearing requirements. Existing wave springs are manufactured by metal with constant dimensions (width and thickness of the strip, diameter) using customized traditional machines in which design variations are almost impossible. This study aims to investigate the effect of wave height, the overlap between the two consecutive coils, and the number of waves per coil on the mechanical properties, for example, load-bearing capacity, stiffness, and energy absorption of contact wave springs. Two designs, that is, rectangular and variable thickness wave springs, were chosen and the design of experiment was devised using Minitab software, resulting in 24 samples. HP MultiJet Fusion (MJF) printer was used to manufacture the samples for performing uniaxial compression tests up to 10 cycles and 90% of the compressible distance to study the variation in mechanical properties due to changes in parameters. Experimental and simulation results showed that variable thickness wave springs have better load bearing, stiffness, and energy absorption compared with the rectangular counterparts. In addition to that, the number of waves per coil and the overlap are directly proportional to the load-bearing capacity as well as stiffness of the wave springs, while the constant wave height is responsible for more uniformly distributed stresses throughout the coils. Load-bearing capacity was increased by 62%, stiffness by 37%, and energy absorption by 20% once the number of waves per coil is increased from 5 to 6 in rectangular wave springs. Overall, the parametric variations significantly affect the performance of wave springs; thus, designers can choose the optimized values of investigated parameters to design customized wave springs for specific applications as per load/stiffness requirements.

Stress and stability comparison between different systems for high tibial osteotomies.

BACKGROUND: High tibial osteotomy (HTO) with a medial opening wedge has been used to treat medial compartment osteoarthritis. However, this makes the proximal tibia a highly unstable structure and causes plate and screws to be the potentials sources for mechanical failure. Consequently, proper design and use of the fixation device are essential to the HTO especially for overweight or full weight-bearing patients. METHODS: Based on the CT-based images, a tibial finite-element model with medial opening was simulated and instrumented with one-leg and two-leg plate systems. The construct was subjected to physiological and surgical loads. Construct stresses and wedge micromotions were chosen as the comparison indices. RESULTS: The use of locking screws can stabilize the construct and decrease the implant and bone stresses. Comparatively, the two-leg design provides a wider load-sharing base to form a force-couple mechanism that effectively reduces construct stresses and wedge micromotions. However, the incision size, muscular stripping, and structural rigidity are the major concerns of using the two-leg systems. The one-leg plates behave as the fulcrum of the leverage system and make the wedge tip the zone of tension and thus have been reported to negatively affect the callus formation. CONCLUSIONS: The choice of the HTO plates involved the trade-off between surgical convenience, construct stability, and stress-shielding effect. If the stability of the medial opening is the major concern, the two-leg system is suggested for the patients with heavy load demands and greater proximal tibial size. The one-leg system with locking screws can be used for the majority of the patients without heavy bodyweight and poor bone quality.

Biomechanical comparison of three stand-alone lumbar cages--a three-dimensional finite element analysis.

BACKGROUND: For anterior lumbar interbody fusion (ALIF), stand-alone cages can be supplemented with vertebral plate, locking screws, or threaded cylinder to avoid the use of posterior fixation. Intuitively, the plate, screw, and cylinder aim to be embedded into the vertebral bodies to effectively immobilize the cage itself. The kinematic and mechanical effects of these integrated components on the lumbar construct have not been extensively studied. A nonlinearly lumbar finite-element model was developed and validated to investigate the biomechanical differences between three stand-alone (Latero, SynFix, and Stabilis) and SynCage-Open plus transpedicular fixation. All four cages were instrumented at the L3-4 level. METHODS: The lumbar models were subjected to the follower load along the lumbar column and the moment at the lumbar top to produce flexion (FL), extension (EX), left/right lateral bending (LLB, RLB), and left/right axial rotation (LAR, RAR). A 10 Nm moment was applied to obtain the six physiological motions in all models. The comparison indices included disc range of motion (ROM), facet contact force, and stresses of the annulus and implants. RESULTS: At the surgical level, the SynCage-open model supplemented with transpedicular fixation decreased ROM (>76%) greatly; while the SynFix model decreased ROM 56-72%, the Latero model decreased ROM 36-91%, in all motions as compared with the INT model. However, the Stabilis model decreased ROM slightly in extension (11%), lateral bending (21%), and axial rotation (34%). At the adjacent levels, there were no obvious differences in ROM and annulus stress among all instrumented models. CONCLUSIONS: ALIF instrumentation with the Latero or SynFix cage provides an acceptable stability for clinical use without the requirement of additional posterior fixation. However, the Stabilis cage is not favored in extension and lateral bending because of insufficient stabilization.

Biomechanical comparisons of dynamic fixators with rod-rod and screw-spacer joints on lumbar hybrid fixation.

BACKGROUND: Hybrid fixators with quite different joint design concepts have been widely to suppress adjacent segment degeneration problems. The kinematic and kinetic responses of the adjacent and transition segments and contact behaviors at the bone-screw interfaces served as the objective of this study. METHODS: The moderately degenerated L4/L5 and mildly degenerative L3/L4 segments were respectively immobilized by a static fixator and further bridged by the rod-rod (Isobar) and screw-spacer (Dynesys) fixator. The joint stiffness and mobility of the rod-rod system and the cable pretension of the screw-spacer system were systematically varied. FINDINGS: The flexion of the screw-spacer system provided higher mobility to the transition segment, reducing adjacent-segment problems. The cable pretension had a minor effect on the construct behavior. However, due to limited joint mobility, the rod-rod system showed higher constraints to the transition segment and induced more adjacent-segment compensations. The increased mobility of the rod-rod joint caused it to behave as a more dynamic fixator that increased adjacent-segment compensations at the transition segment. Comparatively, increasing the joint mobility showed more significant effects on the construct behaviors than decreasing the joint stiffness. Furthermore, increased constraint by the rod-rod joint induced higher stress and risk of loosening at the bone-screw interfaces INTERPRETATION: If the protection of the transition segment is the major concern, the rod-rod system can be used to constrain the intervertebral motion and share the higher loads through the fixator. Otherwise, the screw-spacer system is recommended in situations where higher loads onto the transition disc are allowable.

Flexural Properties of Periodic Lattice Structured Lightweight Cantilever Beams Fabricated Using Additive Manufacturing: Experimental and Finite Element Methods.

Lattice structures are a type of lightweight structure that is more commonly being applied to engineering systems as a way to reduce mass and enhance mechanical properties. The cantilever beam case is one of the primary modes of loading in many engineering applications, where light-weighting is also crucial. However, lightweight lattice structured cantilever beams have not been investigated considerably due to design and manufacturing limitations. Therefore, the aim of this study was to investigate the response of four different lattice structured cantilever beams comprising of unit cells made from Schwarz-P, Schwarz-D, Gyroid, and Octet-truss structures fabricated using Multi Jet Fusion additive manufacturing technology. An investigation into the cross-sections of these structures leads to a conclusion that the beams made from such structures are non-prismatic in nature as a result of variation in cross-sections. This led to the development of equations for the moment of inertia of these structures, which helped in calculating symmetric and un-symmetric bending. These beams were subjected to cantilever loading until failure, which provided insights into flexural properties such as flexural stress, stiffness, and strain energy. Experimental results indicate that the surface-based structures, due to better surface-area-to-volume ratio, have better ability in transferring loads and hence perform better than the beam-based Octet-truss beam. The Schwarz-D beam had performed the best among all the beams, which is further supported in literature due to its stretch-dominated topology that results in higher values of modulus. The finite element analysis (FEA) findings also validate these findings in which the distribution of stresses can be seen to be better transmitted than the other structures. The FEA validation shows that the distribution of Von-Mises stress and their position in experimental tests and failure of these structures is also very close, which provides validation to the experimental setup and the testing of beams.

A Review of Critical Issues in High-Speed Vat Photopolymerization.

Vat photopolymerization (VPP) is an effective additive manufacturing (AM) process known for its high dimensional accuracy and excellent surface finish. It employs vector scanning and mask projection techniques to cure photopolymer resin at a specific wavelength. Among the mask projection methods, digital light processing (DLP) and liquid crystal display (LCD) VPP have gained significant popularity in various industries. To upgrade DLP and LCC VPP into a high-speed process, increasing both the printing speed and projection area in terms of the volumetric print rate is crucial. However, challenges arise, such as the high separation force between the cured part and the interface and a longer resin refilling time. Additionally, the divergence of the light-emitting diode (LED) makes controlling the irradiance homogeneity of large-sized LCD panels difficult, while low transmission rates of near ultraviolet (NUV) impact the processing time of LCD VPP. Furthermore, limitations in light intensity and fixed pixel ratios of digital micromirror devices (DMDs) constrain the increase in the projection area of DLP VPP. This paper identifies these critical issues and provides detailed reviews of available solutions, aiming to guide future research towards developing a more productive and cost-effective high-speed VPP in terms of the high volumetric print rate.

Biomechanical comparison of unilateral and bilateral pedicle screws fixation for transforaminal lumbar interbody fusion after decompressive surgery--a finite element analysis.

BACKGROUND: Little is known about the biomechanical effectiveness of transforaminal lumbar interbody fusion (TLIF) cages in different positioning and various posterior implants used after decompressive surgery. The use of the various implants will induce the kinematic and mechanical changes in range of motion (ROM) and stresses at the surgical and adjacent segments. Unilateral pedicle screw with or without supplementary facet screw fixation in the minimally invasive TLIF procedure has not been ascertained to provide adequate stability without the need to expose on the contralateral side. This study used finite element (FE) models to investigate biomechanical differences in ROM and stress on the neighboring structures after TLIF cages insertion in conjunction with posterior fixation. METHODS: A validated finite-element (FE) model of L1-S1 was established to implant three types of cages (TLIF with a single moon-shaped cage in the anterior or middle portion of vertebral bodies, and TLIF with a left diagonally placed ogival-shaped cage) from the left L4-5 level after unilateral decompressive surgery. Further, the effects of unilateral versus bilateral pedicle screw fixation (UPSF vs. BPSF) in each TLIF cage model was compared to analyze parameters, including stresses and ROM on the neighboring annulus, cage-vertebral interface and pedicle screws. RESULTS: All the TLIF cages positioned with BPSF showed similar ROM (<5%) at surgical and adjacent levels, except TLIF with an anterior cage in flexion (61% lower) and TLIF with a left diagonal cage in left lateral bending (33% lower) at surgical level. On the other hand, the TLIF cage models with left UPSF showed varying changes of ROM and annulus stress in extension, right lateral bending and right axial rotation at surgical level. In particular, the TLIF model with a diagonal cage, UPSF, and contralateral facet screw fixation stabilize segmental motion of the surgical level mostly in extension and contralaterally axial rotation. Prominent stress shielded to the contralateral annulus, cage-vertebral interface, and pedicle screw at surgical level. A supplementary facet screw fixation shared stresses around the neighboring tissues and revealed similar ROM and stress patterns to those models with BPSF. CONCLUSIONS: TLIF surgery is not favored for asymmetrical positioning of a diagonal cage and UPSF used in contralateral axial rotation or lateral bending. Supplementation of a contralateral facet screw is recommended for the TLIF construct.

Improvement in the clinical practicability of roentgen stereophotogrammetric analysis (RSA): free from the use of the dual X-ray equipment.

After total knee replacement, the monitoring of the prosthetic performance is often done by roentgenographic examination. However, the two-dimensional (2D) roentgen images only provide information about the projection onto the anteroposterior (AP) and mediolateral (ML) planes. Historically, the model-based roentgen stereophotogrammetric analysis (RSA) technique has been developed to predict the spatial relationship between prostheses by iteratively comparing the projective data for the prosthetic models and the roentgen images. During examination, the prosthetic poses should be stationary. This should be ensured, either by the use of dual synchronized X-ray equipment or by the use of a specific posture. In practice, these methods are uncommon or technically inconvenient during follow-up examination. This study aims to develop a rotation platform to improve the clinical applicability of the model-based RSA technique. The rotation platform allows the patient to assume a weight-bearing posture, while being steadily rotated so that both AP and ML knee images can be obtained. This study uses X-ray equipment with a single source and flat panel detectors (FPDs). Four tests are conducted to evaluate the quality of the FPD images, steadiness of the rotation platform, and accuracy of the RSA results. The results show that the distortion-induced error of the FPD image is quite minor, and the prosthetic size can be cautiously calibrated by means of the scale ball(s). The rotation platform should be placed closer to the FPD and orthogonal to the projection axis of the X-ray source. Image overlap of the prostheses can be avoided by adjusting both X-ray source and knee posture. The device-induced problems associated with the rotation platform include the steadiness of the platform operation and the balance of the rotated subject. Sawbone tests demonstrate that the outline error, due to the platform, is of the order of the image resolution (= 0.145 mm). In conclusion, the rotation platform with steady rotation, a knee support, and a handle can serve as an alternative method to take prosthetic images, without the loss in accuracy associated with the RSA method.

Design for Additive Manufacturing and Investigation of Surface-Based Lattice Structures for Buckling Properties Using Experimental and Finite Element Methods.

Additive Manufacturing (AM) is rapidly evolving due to its unlimited design freedom to fabricate complex and intricate light-weight geometries with the use of lattice structure that have potential applications including construction, aerospace and biomedical applications, where mechanical properties are the prime focus. Buckling instability in lattice structures is one of the main failure mechanisms that can lead to major failure in structural applications that are subjected to compressive loads, but it has yet to be fully explored. This study aims to investigate the effect of surface-based lattice structure topologies and structured column height on the critical buckling load of lattice structured columns. Four different triply periodic minimal surface (TPMS) lattice topologies were selected and three design configurations (unit cells in x, y, z axis), i.e., 2 × 2 × 4, 2 × 2 × 8 and 2 × 2 × 16 column, for each structure were designed followed by printing using HP MultiJet fusion. Uni-axial compression testing was performed to study the variation in critical buckling load due to change in unit cell topology and column height. The results revealed that the structured column possessing Diamond structures shows the highest critical buckling load followed by Neovius and Gyroid structures, whereas the Schwarz-P unit cell showed least resistance to buckling among the unit cells analyzed in this study. In addition to that, the Diamond design showed a uniform decrease in critical buckling load with a column height maximum of 5193 N, which makes it better for applications in which the column's height is relatively higher while the Schwarz-P design showed advantages for low height column maximum of 2271 N. Overall, the variations of unit cell morphologies greatly affect the critical buckling load and permits the researchers to select different lattice structures for various applications as per load/stiffness requirement with different height and dimensions. Experimental results were validated by finite element analysis (FEA), which showed same patterns of buckling while the numerical values of critical buckling load show the variation to be up to 10%.

Mechanical Performance of Lightweight-Designed Honeycomb Structures Fabricated Using Multijet Fusion Additive Manufacturing Technology.

Cellular structures including three-dimensional lattices and two-dimensional honeycombs have significant benefits in achieving optimal mechanical performance with light weighting. Recently developed design techniques integrated with additive manufacturing (AM) technologies have enhanced the possibility of fabricating intricate geometries such as honeycomb structures. Generally, failure initiates from the sharp edges in honeycomb structures, which leads to a reduction in stiffness and energy absorption performance. By material quantity, these hinges account for a large amount of material in cells. Therefore, redesigning of honeycomb structures is needed, which can improve aforementioned characteristics. However, this increases the design complexity of honeycombs, such that novel manufacturing techniques such as AM has to be employed. This research attempts to investigate the optimal material distribution of three different topologies of honeycomb structures (hexagonal, triangular, and square) with nine different design configurations. To achieve this, higher amount of material was distributed at nodes in the form of fillets while keeping overall weight of the structure constant. Furthermore, these design configurations were analyzed in terms of stiffness, energy absorption, and the failure behavior by performing finite element analysis and experimental tests on the samples manufactured using Multijet fusion AM technology. It was found that adding material to the edges can improve the mechanical properties of honeycombs such as stiffness and energy absorption efficiency. Furthermore, the failure mechanism is changed due to redistribution of material in the structure. The design configurations without fillets suffer from brittle failure at the start of the plastic deformation, whereas the configurations with increased material proportion at the nodes have larger plastic deformation zones, which improves the energy absorption efficiency.

Supportless Lattice Structure for Additive Manufacturing of Functional Products and the Evaluation of Its Mechanical Property at Variable Strain Rates.

This study proposes an innovative design solution based on the design for additive manufacturing (DfAM) and post-process for manufacturing industrial-grade products by reducing additive manufacturing (AM) time and improving production agility. The design of the supportless open cell Sea Urchin lattice structure is analyzed using DfAM for material extrusion (MEX) process to print support free in any direction. The open cell is converted into a global closed cell to entrap secondary foam material. The lattice structure is 3D printed with Polyethylene terephthalate glycol (PETG) material and is filled with foam using the Hybrid MEX process. Foam-filling improves the lattice structure's energy absorption and crash force efficiency when tested at different strain rates. An industrial case study demonstrates the importance and application of this lightweight and tough design to meet the challenging current and future mass customization market. A consumer-based industrial scenario is chosen wherein an innovative 3D-printed universal puck accommodates different shapes of products across the supply line. The pucks are prone to collisions on the supply line, generating shock loads and hazardous noise. The results show that support-free global closed-cell lattice structures filled with foam improve energy absorption at a high strain rate and enhance the functional requirement of noise reduction during the collision.