In vivo dynamic compression has less detrimental effect than static compression on newly formed bone of a rat caudal vertebra.

Fusionless devices are currently designed to treat spinal deformities such as scoliosis by the application of a controlled mechanical loading. Growth modulation by dynamic compression was shown to preserve soft tissues. The objective of this in vivo study was to characterize the effect of static vs. dynamic loading on the bone formed during growth modulation. Controlled compression was applied during 15 days on the 7(th) caudal vertebra (Cd7) of rats during growth spurt. The load was sustained in the "static" group and sinusoidally oscillating in the "dynamic" group. The effect of surgery and of the device was investigated using control and sham (operated on but no load applied) groups. A high resolution CT-scan of Cd7 was acquired at days 2, 8 and 15 of compression. Growth rates, histomorphometric parameters and mineral density of the newly formed bone were quantified and compared. Static and dynamic loadings significantly reduced the growth rate by 20% compared to the sham group. Dynamic loading preserved newly formed bone histomorphometry and mineral density whereas static loading induced thicker (+31%) and more mineralized (+12%) trabeculae. A significant sham effect was observed. Growth modulation by dynamic compression constitutes a promising way to develop new treatment for skeletal deformities.

Effectiveness of braces designed using computer-aided design and manufacturing (CAD/CAM) and finite element simulation compared to CAD/CAM only for the conservative treatment of adolescent idiopathic scoliosis: a prospective randomized controlled trial.

PURPOSE: Clinical assessment of immediate in-brace effect of braces designed using CAD/CAM and FEM vs. only CAD/CAM for conservative treatment of AIS, using a randomized blinded and controlled study design. METHODS: Forty AIS patients were prospectively recruited and randomized into two groups. For 19 patients (control group), the brace was designed using a scan of patient's torso and a conventional CAD/CAM approach (CtrlBrace). For the 21 other patients (test group), the brace was additionally designed using finite element modeling (FEM) and 3D reconstructions of spine, rib cage and pelvis (NewBrace). The NewBrace design was simulated and iteratively optimized to maximize the correction and minimize the contact surface and material. RESULTS: Both groups had comparable age, sex, weight, height, curve type and severity. Scoliosis Research Society standardized criteria for bracing were followed. Average Cobb angle prior to bracing was 27° and 28° for main thoracic (MT) and lumbar (L) curves, respectively, for the control group, while it was 33° and 28° for the test group. CtrlBraces reduced MT and L curves by 8° (29 %) and 10° (40 %), respectively, compared to 14° (43 %) and 13° (46 %) for NewBraces, which were simulated with a difference inferior to 5°. NewBraces were 50 % thinner and had 20 % less covering surface than CtrlBraces. CONCLUSION: Braces designed with CAD/CAM and 3D FEM simulation were more efficient and lighter than standard CAD/CAM TLSO's at first immediate in-brace evaluation. These results suggest that long-term effect of bracing in AIS may be improved using this new platform for brace fabrication. TRIAL REGISTRATION: NCT02285621.

Biomechanical analysis of fracture risk associated with tibia deformity in children with osteogenesis imperfecta: a finite element analysis.

OBJECTIVES: Osteogenesis imperfecta (OI) frequently leads to long-bone bowing requiring a surgical intervention in severe cases to avoid subsequent fractures. However, there are no objective criteria to decide when to perform such intervention. The objective is to develop a finite element model to predict the risk of tibial fracture associated with tibia deformity in patients with OI. METHODS: A comprehensive FE model of the tibia was adapted to match bi-planar radiographs of a 7 year-old girl with OI. Ten additional models with different deformed geometries (from 2° to 24°) were created and the elasto-plastic mechanical properties were adapted to reflect OI conditions. Loads were obtained from mechanography of two-legged hopping. Two additional impact cases (lateral and torsion) were also simulated. Principal strain levels were used to define a risk criterion. RESULTS: Fracture risks for the two-legged hopping load case remained low and constant until tibia bowing reached 15° and 16° in sagittal and coronal planes respectively. Fracture risks for lateral and torsion impact were equivalent whatever the level of tibial bowing. CONCLUSIONS: The finite element model of OI tibia provides an objective means of assessing the necessity of surgical intervention for a given level of tibia bowing in OI-affected children.

Effectiveness of SplashGuard Caregiver prototype in reducing the risk of aerosol transmission in intensive care unit rooms of SARS-CoV-2 patients: a prospective and simulation study.

BACKGROUND: The contagiousness of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is known to be linked to the emission of bioaerosols. Thus, aerosol-generating procedures (AGPs) could increase the risk of infection among healthcare workers (HCWs). AIM: To investigate the impact of an aerosol protection box, the SplashGuard Caregiver (SGGC) with suction system, by direct analysis of the presence of viral particles after an AGP, and by using the computational fluid dynamics (CFD) simulation method. METHODS: This prospective observational study investigated HCWs caring for patients with SARS-CoV-2 admitted to an intensive care unit (ICU). Rooms were categorized as: SGCG present and SGCG absent. Virus detection was performed through direct analysis, and using a CFD model to simulate the movement dynamics of airborne particles produced by a patient's respiratory activities. FINDINGS: Of the 67 analyses performed, three samples tested positive on quantitative polymerase chain reaction: one of 33 analyses in the SCCG group (3%) and two of 34 analyses in the non-SGCG group (5.9%). CFD simulations showed that: (1) reduction of the gaps of an SGCG could decrease the number of emitted particles remaining airborne within the room by up to 70%; and (2) positioning HCWs facing the opposite direction to the main air flow would reduce their exposure. CONCLUSIONS: This study documented the presence of SARS-CoV-2 among HCWs in a negative pressure ICU room of an infected patient with or without the use of an SGCG. The simulation will help to improve the design of the SGCG and the positioning of HCWs in the room.

The Rib Vertebra Angle Difference and its Measurement in 3D for the evaluation of early onset scoliosis.

The Rib Vertebra Angle Difference (RVAD) as defined by Mehta (1972) is used to predict the progression of early onset scoliosis. No clear physical significance has been established for this measurement. The purpose of this study was to evaluate the RVAD along the thoracic spine and the equivalent measurement on 3D reconstructions of the spine and rib cage of early onset scoliosis patients in order to determine their relationship with the geometry of the chest wall and evolution along the spine. The RVAD was measured on PA radiographs of 42 infantile scoliotic patients (Cobb >20°) from T4 to T10 according to the method described by Mehta. The RVAD 3D was computed using the same landmarks from the 3D reconstruction generated from the calibrated biplanar radiographs. Cases were divided into Phase I and Phase II using Mehta's classification based on the rib head overlap with the apical vertebral body on coronal plane radiographs. A linear relationship exists between the Metha (2D) and 3D RVAD for both Phase I (r = 0.87) and Phase II (r = 0.78) patients. For more severe deformities (RVAD 3D ≥ 35°), a relationship was found between RVAD 3D and the axial rotation of the thoracic vertebrae (r = 0.51) in Phase II patients. However, no significant relationship exists between axial rotation and RVAD 3D for Phase I patients as well as Mehta's RVAD. Maximal RVAD measurements were located 2 ½ levels above the apical vertebra. Results indicated that RVAD 3D provides additional information to Mehta's RVAD on the torsional nature of the deformity. Considering the importance of clinical indices to assess the progression of early onset scoliosis, this study raises some questions on looking solely at the RVAD measured on radiographs at the apical vertebra of Phase I patients and suggests considering also levels above the apex of the scoliotic curve and 3D measurements. Further investigation is required to fully understand the 3D nature of the spine and rib cage deformities.

Credibility assessment of patient-specific biomechanical models to investigate proximal junctional failure in clinical cases with adult spine deformity using ASME V&V40 standard.

Computational models are increasingly used to assess spine biomechanics and support surgical planning. However, varying levels of model verification and validation, along with characterization of uncertainty effects limit the level of confidence in their predictive potential. The objective was to assess the credibility of an adult spine deformity instrumentation model for proximal junction failure (PJF) analysis using the ASME V&V40:2018 framework. To assess model applicability, the surgery, erected posture, and flexion movement of actual clinical cases were simulated. The loads corresponding to PJF indicators for a group of asymptomatic patients and a group of PJF patients were compared. Model consistency was demonstrated by finding PJF indicators significantly higher for the simulated PJF vs. asymptomatic patients. A detailed sensitivity analysis and uncertainty quantification were performed to further establish the model credibility.

Interferon regulatory factor 5 gene variants and pharmacological and clinical outcome of Interferonß therapy in multiple sclerosis.

Interferon-ß (IFNß) therapy is effective in approximately half of the patients with relapsing-remitting multiple sclerosis (RRMS). Clinical non-responders were characterized by an increased expression of IFN response genes before the start of therapy, and a lack of a pharmacologically induced increase in IFN response gene activity. Because Interferon Regulatory Factor 5 (IRF5) is a master regulator of IFN-activity, we carried out a candidate gene study of IRF5 gene variants in relation to the pharmacological and clinical response upon IFNß treatment. We found that patients with the IRF5 rs2004640-TT and rs47281420-AA genotype exerted a poor pharmacological response to IFNß compared with patients carrying the respective G-alleles (P=0.0006 and P=0.0023, respectively). Moreover, patients with the rs2004640-TT genotype developed more magnetic resonance imaging (MRI)-based T2 lesions during IFNß treatment (P=0.003). Accordingly, an association between MRI-based non-responder status and rs2004640-TT genotype was observed (P=0.010). For the rs4728142-AA genotype a trend of an association with more T2 lesions during IFNß treatment and MRI-based non-responder status was observed (P=0.103 and P=0.154, respectively). The clinical relevance of the rs2004640-TT genotype was validated in an independent cohort wherein a shorter time to first relapse was found (P=0.037). These findings suggest a role for IRF5 gene variation in the pharmacological and clinical outcome of IFNß therapy that might have relevance as biomarker to predict the response to IFNß in multiple sclerosis.

Concave or convex rod translation first in adolescent idiopathic scoliosis instrumentation with differential rod contouring?

The objective was to assess deformity correction and bone-screw force associated respectively with concave manipulation first, convex manipulation first, and different differential rod contouring configurations. Instrumentation scenarios were computationally simulated for 10 AIS cases with mean thoracic Cobb angle (MT) of 54±8°, apical vertebral rotation (AVR) of 19±2° and thoracic kyphosis of 21±9°. Instrumentations with major correction maneuvers using the concave side rod were first simulated; instrumentations with major correction maneuvers using the convex side rod were then simulated. Simulated correction maneuvers were concave/convex rod translation followed by apical vertebral derotation and then convex/concave rod translation. There were no significant differences in deformity corrections and bone-screw forces between concave rod translation first and convex rod translation first with differential rod contouring. Increasing differential rod contouring angle and concave rod diameter improved AVR correction and increased the TK and bone-screw forces; the effect on the MT Cobb angle was not clinically significant.

The impact of immediate in-brace 3D corrections on curve evolution after two years of treatment: preliminary results.

For the brace treatment of adolescent idiopathic scoliosis (AIS), in-brace correction and brace-wear compliance are well-documented parameters associated with a greater chance of treatment success. However, the number of studies on the impact of sagittal and transverse correction on curve evolution in the context of bracing is limited. The objective of this work was to evaluate how immediate inbrace correction in the three anatomical planes is related to long-term curve evolution after two years of bracing. We performed a retrospective analysis on 94 AIS patients followed for a minimum of two years. We analyzed correlations between in-brace correction and two-year out-of-brace evolution for Cobb and apical axial rotations (ARs) in the medial thoracic and thoraco-lumbar/lumbar regions (MT & TL/L). We also studied the association between the braces' kyphosing and lordosing effect and the evolution of thoracic kyphosis (TK) and lumbar lordosis (LL) after two years. Finally, we separated the patients into three groups based on their curve progression results after two years (corrected, stable and progressed) and compared the 3D in-brace corrections and compliance for each group. Coefficients were statistically significant for all correlations. They were weak for Cobb angles (MT: -0.242; TL/L: -0.275), low for ARs (MT: -0.423; TL/L: -0.417) and moderate for sagittal curves (TK: 0.549; LL: 0.482). In-brace coronal correction was significantly higher in corrected vs stable patients (p=0.004) while compliance was significantly higher in stable vs progressed patients (p=0.026). This study highlights the importance of initial in-brace correction in all three planes for successful treatment outcomes.

Influence of force volume indentation parameters and processing method in wood cell walls nanomechanical studies.

Since the established correlations between mechanical properties of a piece of wood at the macroscopic scale and those of the cell wall at the submicron scale, techniques based on atomic force microscopy (AFM) have become widespread. In particular Peak Force tapping, allowing the differentiation of various layers, has become the new standard for wood cell wall's nanomechanical characterization. However, its use requires fully elastic indentation, a good knowledge of stiffness of the probe and assumes a perfect tip shape of known radius (sphere) or angle (cone). Those strong hypotheses can result in large approximations in the extracted parameters for complex, nanostructured, and stiff and viscous materials such as wood. In this work, we propose a reliable and complementary alternative based on AFM force-volume indentation by refining the Oliver and Pharr nanoindentation processing and calibration procedure for AFM cantilever and tip. The introduced area-function calibration (AFC) method allows to considerably reduce these approximations and provides semi-quantitative measurements. No prior knowledge of the tip shape and cantilever stiffness are required and viscoplasticity is investigated through a qualitative index. Indentation parameters variations are shown to impact the resulting measurements, i.e., indentation modulus, viscoplasticity index, adhesion force and energy. AFC method, applied to map regions of tension wood, provides very stable mechanical parameters characteristic of each region, which makes this method of high interest for plant cell wall studies.

Mechanical loading effects on isthmic spondylolytic lumbar segment: finite element modelling using a personalised geometry.

Biomechanics of the isthmic spondylolysis was investigated by using a nonlinear 3D-finite element model (FEM). A personalised in vivo pediatric geometry of L5-S1 low-grade spondylolisthesis patient was used to develop a L5-pelvis motion segment model that took into consideration vertebrae, disc and ligaments. The stress distribution in the affected motion segment under axial force only, and for a combination of flexion and extension was evaluated. Predicted results showed that, under all loading conditions, stresses were much higher on the pedicle and in the dorsal wall of the pars interarticularis due to the abnormal geometry which is consistent with clinical observations.

Optical Lace for Synthetic Afferent Neural Networks.

While vision dominates sensing in robots, animals with limited vision deftly navigate their environment using other forms of perception such as touch. Efforts have been made to apply artificial skins with tactile sensing to robots for similarly sophisticated mobile and manipulative skills. The ability to functionally mimic the afferent sensory neural network, required for distributed sensing and communication networks throughout the body is still missing. This limitation is partially due to the lack of cointegration of the mechanosensors in the body of the robot. In this paper, lacings of stretchable optical fibers distributed throughout 3D printed elastomer frameworks create a cointegrated body, sensing, and communication network. This soft, functional structure can localize deformation with sub-millimeter positional accuracy (Err = 0.71 mm), and sub-Newton force resolution (~0.3 N).

Influence of correction objectives on the optimal scoliosis instrumentation strategy: a preliminary study.

In three recent studies we have shown how different correction objectives from a group of experienced spine surgeons add to the variability in AIS instrumentation strategies. This study examined the effect of correction objectives of three surgeons on the optimal instrumentation strategy. An optimization method using six instrumentation design parameters (e.g. limits of the instrumented segment, number, type and location of implants and rod shape) that were manipulated in a uniform experimental design framework was linked to a patient-specific biomechanical model to analyze the effects of a specific instrumentation configuration. The optimization cost function was formulated to maximize correction in the three anatomic planes and with minimal number of instrumented levels. Three surgeons from the Spinal Deformity Study Group provided their respective correction objectives for a single patient (56 degrees thoracic and 38 degrees lumbar Cobb angle). For each surgeon, 702 surgical configurations were iteratively simulated using a biomechanical model. The influence of the three different correction objectives on the optimal surgical strategy was evaluated. The resulting optimal fusion levels were T2-L4, T4-L2, and T4-L1. A Wilcoxon non parametric test analysis showed that fusion levels and the location of implants significantly were influenced by the correction objectives strategies (p<0.05). The optimal number of implants although different (12 vs.11 vs.10) was not statistically significant (p>0.1). Thus different surgeon-specified correction objectives produced different optimal instrumentation strategies for the same patient.

The relationship between hip flexion/extension and the sagittal curves of the spine.

The objective of this study was to develop a finite element model (FEM) in order to study the relationship between hip flexion/extension and the sagittal curves of the spine. A previously developed FEM of the spine, rib cage and pelvis personalized to the 3D reconstructed geometry of a patient using biplanar radiographs was adapted to include the lower limbs including muscles. Simulations were performed to determine: the relationship between hip flexion / extension and lumbar lordosis / thoracic kyphosis, the mechanism of transfer between hip flexion / extension and pelvic rotation, and the influence that knee bending, muscle stiffness, and muscle mass have on the degree to which sagittal spinal curves are modified due to lower limb positioning. Preliminary results showed that the model was able to accurately reproduce published results for the modulation of lumbar lordosis due to hip flexion; which proved to linearly decrease 68% at 90 degrees of flexion. Additional simulations showed that the hamstrings and gluteal muscles were responsible for the transmission of hip flexion to pelvic rotation with the legs straight and flexed respectively, and the important influence of knee bending on lordosis modulation during lower limb positioning. The knowledge gained through this study is intended to be used to improve operative patient positioning.

Biomechanical modelling of a direct vertebral translation instrumentation system: preliminary results.

Many new spine instrumentation concepts were introduced in recent years, like the incremental direct vertebral translation. The objective was to develop a biomechanical model in order to analyze the biomechanics of this instrumentation system. The patient-specific spine model was built using the 3D reconstruction based on bi-planar radiographs of a scoliotic patient (thoraco-lumbar Cobb: 49 degrees ). The mechanical properties were derived from literature, experiments on cadaver spines and patient's side bending radiographs. Each screw construct was modelled by four rigid bodies connected each other by kinematic joints. The screw-vertebra flexible joint was represented by 3 experimentally derived non-linear springs, and the rods by non-linear flexible elements. The correction manoeuvres were simulated by lowering the rod, tightening the crimps (incremental segmental translation) and applying secondary correction manoeuvres (direct vertebra derotation, compression, distraction and construct tightening). The simulations showed that the system allows a good force distribution among implants. The long post pushing and pulling contributed, to a great extent, to a global correction in the coronal plane, while the crimp tightening had more important effect in the sagittal plane. The preliminary results illustrated the effectiveness of local correction by a direct vertebra translation technique. Our next step is to validate the model and compare the performance of this strategy with other spinal instrumentation systems.

Quantification of intervertebral efforts during walking: comparison between a healthy and a scoliotic subject.

The accurate quantification of internal efforts in the human body is still a challenge in biomechanics. The aim of this study is to quantify the intervertebral efforts along the spine during walking, in order to compare the dynamical behaviours between a healthy and a scoliotic subject. Practically, one healthy subject, one scoliotic patient before an instrumentation surgery (Cobb 41 degrees ) and after this instrumentation (Cobb 7.5 degrees ) walked on a treadmill at 4 km/h. The acquisition system included optokinetic sensors, recording the 3D-joint coordinates, a treadmill equipped with strain gauges, measuring the external forces independently applied to both feet, and bi-planar radiographs, enabling the 3D reconstruction of the spine from C7 to L5, using a free form interpolation technique. The intervertebral efforts were computed using an inverse dynamical model of the human body in 3D. As results, significant differences of the spine kinematics were recorded which lead to different internal effort behaviour in magnitude, shift, coordination and pattern when normalized to the subject mass. Particularly, the normalized antero-posterior intervertebral torques are less uniform for the scoliotic patient (from min -2.5 to max 1.9 Nm/kg) than the healthy subject (from -1.5 to 1.5 Nm/kg). This disequilibrium in the left-right balance of the scoliotic patient is a bit rectified after surgery (from -1.3 to 1.1 Nm/kg).

Finite element modeling of vertebral body stapling applied for the correction of idiopathic scoliosis: preliminary results.

Endoscopic vertebral body stapling is an innovative technique intended to treat adolescent idiopathic scoliosis, but the optimal instrumentation design is not yet established. The objective was to simulate the immediate correction obtained from two stapling configurations. A parametric finite element model of a typical right thoracic scoliotic spine (Cobb 21 degrees ) was developed using geometrical and mechanical data from the literature. Staple insertion and closing were modeled. The intra-operative lateral decubitus and standing positions were taken into account. Two implant configurations, varying the number of staples per vertebra, were simulated. The major correction (9 degrees ) came by simulating the intra-operative posture. The immediate Cobb angle correction due to the staples alone was less then 1 degrees for both configurations. However, the staples helped maintain the correction obtained by the intra-operative posture when the post-operative standing position was simulated. Next steps are to validate the model using surgical cases, implement growth modulation modeling, improve lateral decubitus modeling, and analyze different vertebral stapling strategies for different scoliotic curves.

Simulation of progressive spinal deformities in Duchenne muscular dystrophy using a biomechanical model integrating muscles and vertebral growth modulation.

BACKGROUND: Ninety percent of Duchenne muscular dystrophy patients develop scoliosis in parallel with evident muscular and structural impairment. Altered muscular spinal loads acting on growing vertebrae are likely to promote a self-sustaining spinal deformation process. The purpose of this study was to simulate the effect of asymmetrical fat infiltration of the erector spinae muscles combined with vertebral growth modulation over a period of growth spurt. METHODS: A finite element model of the trunk was built. It integrates (1) longitudinal growth of vertebral bodies and its modulation due to mechanical stresses, (2) muscles and control processes generating muscle recruitment and forces. Three different impairments of the erector spinae muscles were considered and their actions over 12 consecutive cycles representing a span of 12 months were analyzed. FINDINGS: When asymmetrical muscle degeneration was simulated and weaker erector spinae muscles were located on the convex side of the curve, mild scoliosis (Cobb angle of 8-19 degrees ) was induced in the frontal plane and the kyphosis increased from 72 degrees to 110 degrees in all simulations. Those changes were accompanied by a substantial increase of muscle activity in the Rectus Abdominus and Obliquus Internus. INTERPRETATION: Scoliosis as documented in the literature were induced through an asymmetrical activity in the erector spinae muscles and it can be hypothesized that the Rectus Abdominus and Obliquus Internus have a role in maintaining balance and counteracting against spine torsion. This study demonstrated the feasibility of the modeling approach to investigate a musculo-skeletal deformation process based on a neuromuscular deficit.

Finite-element analysis of geometrical factors in micro-indentation of pollen tubes.

Micro-indentation is a new experimental approach to assess physical cellular properties. Here we attempt to quantify the contribution of geometrical parameters to a cylindrical plant cell's resistance to lateral deformation. This information is important to correctly interpret data obtained from experiments using the device, such as the local cellular stiffness in pollen tubes. We built a simple finite-element model of the micro-indentation interacting partners - micro-indenter, cell (pollen tube), and underlying substratum, that allowed us to manipulate geometric variables, such as geometry of the cell, cell radius, thickness of the cell wall and radius of the indenting stylus. Performing indentation experiments on this theoretical model demonstrates that all four parameters influence stiffness measurement and can therefore not be neglected in the interpretation of micro-indentation data.