In-plane Deformation Research Articles

A hyperelastic model considering the coupling of shear-compression for the forming simulation of 3D orthogonal composite preforms

The shear-compression coupling phenomenon is vital in the forming process of complex 3D woven composite components, but has not been effectively considered in existing macroscopic material models. A hyperelastic material model considering shear-compression coupling is developed here. Firstly, in-plane shear tests on pre-compressed specimens and compression tests on pre-sheared specimens were carried out, respectively. The results show that pre-compression can hinder and promote the in-plane shear deformation before and after shear locking occurs in the fabric, respectively. In-plane shear can contribute to compression. Then, a nonlinear hyperelastic constitutive model is presented and implemented in an Abaqus/Explicit user subroutine. Finally, a simulation study of the hemispherical forming of 3D orthogonal woven fabric was conducted using this model. The simulation results considering shear-compression coupling show more accurate in-plane shear angles and edge shapes compared to those without considering coupling. Moreover, since the shear-compression coupling is considered, the friction between the fabric and the tool needs to be reasonably discussed in the moulding simulation.

Buckling of planar curved beams with finite prebuckling deformation

The serpentine structure with a sufficiently thick cross section has recently been proposed as an important design concept in stretchable electronics, which features mechanically stable in-plane deformation mechanism and very low electrical resistance, bringing unique advantages for devices compared with the traditional thin ribbon layout. However, unduly increasing the thickness is well known to sacrifice the overall flexibility and functionality of devices. Such a contradiction leads to challenges in structural stability, as a relatively thick but insufficient serpentine structure may eventually undergo the out-of-plane buckling after significant in-plane prebuckling deformation and appreciable alterations in initial configuration, which is ignored by most conventional buckling theories (CBTs) and linear buckling analysis in commercial finite element analysis software, producing intolerable errors when predicting the critical loads. In this paper, a systematic and straightforward theory considering the finite prebuckling deformation (FPD buckling theory) is established to investigate the underlying mechanism. Two sets of governing equations related to the prebuckling and FPD buckling behavior are obtained. Four representative examples, including two classical problems of planar curved beams and two typical loading conditions of serpentine structures, have been carefully studied. Comparisons with the accurate geometrically-nonlinear-analysis-based (GNAB) buckling analysis have amply demonstrated the validity of our theory in predicting the reinforcement effect of prebuckling deformation on the buckling resistance of structures. Key dimensionless geometric parameters that govern this effect have also been identified, providing direct and effective guidance for the design and optimization of stretchable electronic devices.

Influence of hydrogen on deformation and embrittlement mechanisms in a high Mn austenitic steel: In-Situ neutron diffraction and diffraction line profile analysis

Austenitic steels have relatively high resistance to hydrogen embrittlement and play a critical role in hydrogen service applications. In particular, high Mn austenitic steels are considered economically viable alloy alternatives for these applications. The current study employed in-situ and ex-situ neutron diffraction techniques combined with diffraction line profile analysis (DLPA) to investigate the influence of hydrogen on deformation and embrittlement mechanisms in a high Mn (approximately 30 wt pct) austenitic steel. Investigation using both neutron diffraction and electron backscatter diffraction revealed the presence of extensive deformation twins and stacking faults within the steel microstructure after tensile deformation in the non-charged condition. These microstructural features suggest planar deformation behavior, which is expected from the relatively low stacking fault energy (SFE) of the alloy (approximately 29 mJ/m2). Hydrogen pre-charging resulted in apparent increases in both dislocations and stacking faults, contributing to macroscopic hardening and embrittlement mechanisms. Overall, numerical parameters obtained through neutron DLPA were used to elucidate the underlying mechanisms associated with hydrogen effects on the mechanical behavior, i.e. macroscopic strengthening, strain hardening rate, and embrittlement.

Distal Tibial Dome Osteotomy With Ilizarov Fixation in Correction of Ankle Deformity Resulting From Malunited Ankle Fusion

Background: Distal tibial osteotomy is used in the treatment of ankle deformities. Many methods of fixation of this osteotomy were described, including plates, pins, and ilizarov. Dome osteotomy is a cylindrical osteotomy with no bone loss, with the axis of bone is rotated around the center of the circle. We conducted a case series of treatment of ankle deformity due to malunited ankle fusion with distal tibial dome osteotomy. Methods: Eight patients with a history of poliomyelitis with ankle deformity due to a malunited ankle fusion underwent distal tibial dome osteotomy with ilizarov fixation for deformity correction. Postoperative follow up was done up to 12 months postoperatively. We intended to follow up the union of the osteotomy, the axis of the limb, the external clinical appearance, and patient satisfaction. Results: Deformity correction was achieved in all patients regarding the clinical alignment, with no apparent clinical residual deformity in coronal, sagittal plane, or rotational deformity, the limb was cosmetically straight with a plantigrade foot satisfactory to the patients with improving quality of gait. The osteotomy fully united in all patients in a period of 8 to 11 weeks with an average of 9.3 weeks, after which frame was removed. No patient had nonunion or delayed union of the osteotomy. Three patients had pin tract infection during the period of the fixator which was treated by local dressings and antibiotics. Conclusion: Distal tibial focal dome osteotomy fixed by ilizarov is an effective treatment option in malunited ankle fusion deformities.

Analyzing the back-face deformation of curved UHMWPE composite laminate under high-speed impact

Ballistic protection extensively employs curved ultra-high-molecular-weight polyethylene (UHMWPE) laminates to conform to protective targets. However, ballistic tests have indicated that the curvature of laminates increases back-face deformation, diminishing ballistic performance, while the mechanism behind this curvature effect on back-face deformation remains unclear. In this paper, the back-face deformation of curved UHMWPE laminates, including apex displacement and the boundary of the deformation region, are systematically studied through numerical simulation and theoretical analysis. Firstly, a numerical model of curved UHMWPE laminates under the high-speed impact is established. The numerical results indicate that as the curvature increases, the deformation region becomes more concentrated, resulting in a larger apex displacement. Secondly, as the curvature increases from zero, the deformation mode of curved laminates changes from membrane stretching dominated to a combination of membrane stretching and bending. Finally, considering the change in the deformation mode, a theoretical analysis for the propagation of bending waves in an orthotropic curved plate is conducted to reveal the relationship between curvature and back-face deformation. The theoretical analysis shows that increasing curvature slows bending wave speed, reducing in-plane deformation region movement, thus increasing apex displacement. This study is expected to help design curved UHMWPE laminates with better ballistic performance.

The role of the interfaces and cross-links on the mechanical behavior of mineralized collagen fibrils. A numerical approach

Mechanical properties of bone tissue are highly dependent on its hierarchical structure. The presence of microcracks and diffuse damage in lamellar bone is correlated with the failure of the collagen-mineral interface in mineralized collagen fibrils (MCF). The main goal of this work is to evaluate the mechanical behavior of the interfaces and quantify the stiffness loss of the MCF associated with different failure mechanisms, under controlled in-plane displacement. Additionally, we aim to study the role of the cross-links on the fibril mechanical response, beyond the interface failure. Inter- and intra-microfibrilar cross-links are analyzed. In order to address the first issue, a detailed representative volume of the MCF is analyzed by means of the finite element method, under the assumption of plane strain and periodic boundary conditions. In this model the interfaces between constituents are modeled with an exponential cohesive law. Enzymatic cross-links, located at the molecular terminals connecting each 4D (D=67nm) staggered molecules, are represented by non-linear springs. Three in-plane controlled deformations are applied. The results of this work provide the anisotropic stiffness loss of the tissue involved in the different failure mechanisms at the nano-scale length. The initiation of microcracks and the presence of damage zones are compatible with the failure mechanisms observed at interfaces. Interface failure entails a progressive stiffness loss, bringing a non-linear behavior of bone. The strength obtained for the longitudinal maximum deformation is more than 20 times the transverse strength and 3.5 times the shear strength. The quantification of the reduction percentage in the elastic moduli and the shear stiffness when the fibril is damaged, has a potential application in improving failure criteria based on degradation of elastic constants. When longitudinal elongation is applied, the mechanical contribution of the cross-links in delaying the failure initiation of the interface is shown. Likewise, results of this work confirm the scarce influence of the cross-links in the strain range analyzed. Additionally, a three-dimensional numerical model of several microfibrils is defined with the aim of analyzing the mechanical relevance of inter- and intra-microfibrilar cross-links, beyond the interface failure. Results confirm that cross-links transfer the load when strain increases, being highlighted the mechanical competence of the trivalent cross-links.

Total ankle arthroplasty in valgus ankle osteoarthritis

The valgus total ankle replacement (TAR) presents a considerable challenge and tests the skill and ingenuity of even the most accomplished foot and ankle surgeon. Coronal plane deformity used to be considered a relative contra-indication for TAR, however with implant innovation and greater surgical understanding, the indications for TAR in deformity continue to expand. Success requires a bespoke approach to each patient to ensure that intra- and extraarticular deformities and imbalance are adequately addressed to avoid TAR failure. The overall goal in TAR surgery is achieving a well aligned and stable ankle with a well aligned and stable foot below. This article presents some of our strategies to achieve this when considering TAR in the valgus ankle.10.1016/j.fuspru.2024.08.002

Anterior Column Release: With Great Lordosis Comes Great Risk of Complications-A Case Series.

Retrospective review. We sought to characterize complications associated with anterior column release (ACR). Correction of positive sagittal imbalance was traditionally completed with anterior column grafts or posterior osteotomies. ACR is a minimally invasive technique for addressing sagittal plane deformity by restoring lumbar lordosis. We conducted a retrospective review of consecutive patients who underwent ACR in a prospectively kept database at a tertiary care academic center from January 2012 to December 2018. The prespecified complications were hardware failure (rod fracture, hardware loosening, or screw fracture), proximal junctional kyphosis, ipsilateral thigh numbness, ipsilateral femoral nerve weakness, arterial injury requiring blood transfusion, bowel injury, and abdominal pseudohernia. Thirty-eight patients were identified. Thirty-five patients had ACR at L3-4, 1 had ACR at L4-5, and 1 patient had ACR at L2-3 and L3-4. Eighteen patients (47.4%) had one of the prespecified complications (10 patients had multiple). Ten patients developed hardware failure (26.3%); 8 patients (21.1%) had rod fracture, 4 (10.5%) had screw fracture, and 1 (2.6%) had screw loosening. At discharge, rates of ipsilateral thigh numbness (37.8%) and hip flexor (37.8%)/quadriceps weakness (29.7%) were the highest. At follow-up, 6 patients (16.2%) had ipsilateral anterolateral thigh numbness, 5 (13.5%) suffered from ipsilateral hip flexion weakness, and 3 patients (5.4%) from ipsilateral quadriceps weakness. Arterial injury occurred in 1 patient (2.7%). Abdominal pseudohernia occurred in 1 patient (2.7%). There were no bowel injuries observed. ACR is associated with a higher than initially anticipated risk of neurological complications, hardware failure, and proximal junctional kyphosis.

Focal Dome Osteotomy Combined with Ilizarov Technique for Treating Femoral Multiplanar Deformity.

The management of femoral multiplanar deformity remains a great challenge for orthopaedic surgeons. The focal dome osteotomy (FDO) combined with Ilizarov technique is a theoretically ideal method for treating femoral multiplanar deformity, but the clinical evidence is limited. The aim of this study is to assess the clinical and radiological outcomes of this combined strategy for correcting femoral multiplanar deformities. A retrospective analysis was conducted to analyze 20 patients (29 limbs) with femoral multiplanar deformities treated by FDO combined with Ilizarov external fixation in our limb deformity center between 2017 and 2022. Preoperative and postoperative radiographical parameters were measured, including lateral proximal femoral angle (LPFA), mechanical lateral distal femoral angle (mLDFA), middle diaphysis angle (MDA), anatomic posterior distal femoral angle (aPDFA), mechanical axis deviation (MAD), and limb length discrepancy (LLD). Clinical assessments included a self-made questionnaire for exercise capacity score (ECS), visual analog scale (VAS), and the 36-Item Short-Form Health Survey (SF-36) score. There were eight males and 12 females, with a mean age of 32.8 years (14-61 years). All patients completed follow-up with a mean follow-up duration of 41.5 (27-81) months. The mean EFT was 8.9 (1.4-20.2) months. At final follow-up, significantly improvement was noted regarding mean LLD (from 1.8 to 0.4 cm, p < 0.05), MDA (from 31.8° to 10.4°, p < 0.05), aPDFA (from 97.6° to 91.8°, p < 0.05), MAD (from 22.4 to 5.3 mm, p < 0.05), CORA on the true deformity plane (from 32.4° to 6.8°, p < 0.05). The mean VAS was decreased from 4.03 (2.0-6.0) preoperatively to 1.38 (0-3.0) at final follow-up (p < 0.05). The mean score of each item of SF-36 was significantly improved at final follow-up (p < 0.05). The mean ECS was improved from 8.2 (5-12) preoperatively to 11.4 (8-13) at final follow-up (p < 0.05). During the follow-up, one patient underwent pin exchange. One patient underwent internal fixation to replace the Ilizarov fixation 1.4 months after the first surgery. Residual LLD (>0.5 cm) was noted in four patients but without significant symptoms. No serious complications occurred. The strategy of FDO combined with Ilizarov fixation could provide powerful ability and good flexibility for correcting femoral multiplanar deformities without significant complications.

Curve progression following selective and nonselective spinal fusion for adolescent idiopathic scoliosis: are selective fusions stable?

PurposeThe purpose of this study is to compare postoperative outcomes between selective and non-selective fusions longitudinally over the first five postoperative years.MethodsPatient parameters were retrieved from a multicenter, prospective, database. Patients with Lenke 1–6, B and C deformities were included. Patients were stratified into 2 groups: selective fusion (SF), if the last instrumented vertebra (LIV) was at or cranial to the lumbar apex, or non-selective fusion (NSF). Differences in coronal and sagittal radiographic outcomes were assessed with generalized linear models (GLMs) at 1-, 2- and 5- year postoperative outcomes. Five-year postoperative categorical radiographic outcomes, flexibility, scoliosis research society scores (SRS), and reoperation rates were compared between groups. Matched cohorts were created for subgroup analysis.Results416 (SF:261, NF:155) patients, including 353 females were included in this study. The mean preoperative thoracic and lumbar Cobb angles were 57.3 ± 8.9 and 45.3 ± 8.0, respectively. GLMs demonstrated greater postoperative coronal deformity in the SF group (p < 0.01); however, the difference between groups did not change overtime (p > 0.05) indicating a relatively stable postoperative deformity correction. The SF group had a greater incidence of lumbar Cobb ≥ 26 degrees (p < 0.01). The NSF group demonstrated worse forward and lateral flexibility at 5-year postoperative outcome (p < 0.05). There was no difference in postoperative SRS scores between the SF and NSF groups. Reoperation rates were similar between groups.ConclusionSelective fusion results in greater coronal plane deformity; however, this deformity does not progress significantly over time compared to non-selective fusion. Selective spinal fusion may be a beneficial option for a larger subset of patients than previously identified.Level of evidenceIII.

Optimizing Outcomes in Distal Tibial Deformity Correction: The Role of Supramalleolar Osteotomy with Computer-assisted Hexapod External Fixator.

Distal tibial deformities can significantly impact patients if left uncorrected, often leading to pain, alterations in gait, and the eventual development of post-traumatic arthritis. The criteria for surgical correction in these patients continues to be a subject of debate, while supramalleolar osteotomy (SMO) is an effective method for correcting distal tibial deformities. The purpose of this study was to evaluate and compare the clinical results of SMO using internal fixation or using computer-assisted hexapod external fixator in the treatment of distal tibial deformity. A retrospective study was conducted on 290 patients who underwent SMO between June 2015 and January 2023. Forty-four patients met the inclusion and exclusion criteria. Among the participants, 19 underwent SMO combined with a computer-assisted hexapod external fixator, while 25 received SMO with plate and screw internal fixation. The tibial anterior surface (TAS) angle, tibial lateral surface (TLS) angle, the tibiotalar (TT) angle and the talocrural (TC) angle were assessed on weight-bearing X-ray films. Functional assessments were performed according to the American Orthopedic Foot and Ankle Society (AOFAS) ankle-hindfoot score. The study followed patients for an average duration of 31.7 ± 15.3 months, with a range from 12 to 67 months. Successful bone union was achieved in all cases. For patients treated with the computer-assisted hexapod external fixator, significant improvements were observed: the mean deviation in sagittal plane deformity parameters decreased from 14.3 ± 10.4 degrees preoperatively to 2.8 ± 3.8 degrees postoperatively (p < 0.05). Similarly, coronal plane deformity parameters showed a reduction from 25.9 ± 22.5 degrees preoperatively to 5.9 ± 11.0 degrees postoperatively (p < 0.05). The AOFAS ankle-hindfoot score improved markedly from 66.0 ± 14.9 to 86.1 ± 11.7 points (p < 0.05). For patients undergoing internal fixation, the absolute difference in coronal plane parameters improved from 15.4 ± 12.6 degrees preoperatively to 3.7 ± 3.4 degrees postoperatively (p < 0.05). A significant enhancement in AOFAS ankle-hindfoot score was also noted, increasing from 68.3 ± 14.3 points to 79.4 ± 13.5 points (p < 0.05). There were no significant differences in gender, side, follow-up time, postoperative deviation of deformity, pre- or postoperative AOFAS between the two groups. In conclusion, comprehensive preoperative planning of SMO combined with either internal fixation or a hexapod external fixator for treating distal tibial deformities can achieve satisfactory outcomes. The utilization of a computer-assisted hexapod external fixator facilitates a gradual and precise correction process, which proved to be an effective and relatively safe method.

24. Does coronal plane deformity matter for cervicothoracic kyphosis surgery? The incidence of cervical scoliosis and influence on the outcomes of cervical deformity surgery

24. Does coronal plane deformity matter for cervicothoracic kyphosis surgery? The incidence of cervical scoliosis and influence on the outcomes of cervical deformity surgery

Outcomes of the Modified Dunn Procedure Versus Delayed Imhauser Osteotomy for Moderate to Severe Stable Slipped Capital Femoral Epiphysis.

Traditional management of moderate to severe stable slipped capital femoral epiphysis (SCFE) has been in situ fixation followed by reconstructive surgery if symptoms arise. This delayed approach may lead to irreversible intra-articular damage of the hip over time. The purpose of this study was to compare radiographic and clinical outcomes of the modified Dunn procedure (MDP) versus in situ fixation followed by delayed Imhauser osteotomy (DIO). This was a retrospective study from a single institution between 2001 and 2021. Among 250 patients diagnosed with SCFE, a total of 18 (18 hips) treated with MDP and 16 (18 hips) treated with DIO for moderate to severe stable SCFE were included. Most patients who underwent DIO either had concomitant (11/18 hips) or subsequent (2/18 hips) open osteochondroplasty. Mean follow up was 4.7 years (range: 1 to 12.8y). Radiographs were reviewed to measure Southwick angle, anteroposterior and lateral alpha (α) angles, and femoral head-neck offset ratio preoperatively and at latest follow up. Charts were reviewed for demographics, subsequent surgeries, complications, and Heyman-Herndon clinical outcomes. The amount of deformity correction was greater in the MDP than DIO group based on anteroposterior α angles (mean: 22.3 vs. 11.9 degrees, P =0.046) and femoral head-neck offset ratios (mean: 0.26 vs. 0.12, P =0.001). There was no significant difference in Heyman-Herndon scores (both 16/18, 88.9% good to excellent outcomes, P >0.999). Less reoperations were performed in the MDP than DIO group (2/18, 11.1% vs. 9/18, 50%; P =0.004). AVN occurred in 2/18 hips (11.1%) in the MDP group with both surgeries performed early in the series and underwent prior in situ screw fixation compared with 0/18 hips (0%) in the DIO group ( P =0.486). One patient in the DIO group was later diagnosed with osteoarthritis. MDP resulted in more anatomic coronal and sagittal plane deformity correction, less reoperations, and similar Heyman-Herndon clinical outcomes compared with DIO. AVN occurred in the MDP group whereas osteoarthritis occurred in the DIO group. These complications must be weighed against improved long-term clinical results for patients who would otherwise be at risk for premature degenerative joint disease due to residual proximal femoral deformity. Level III-retrospective comparative study.

Thoracolumbar fusions for adult lumbar deformity show superior QALY gain and lower costs compared with upper thoracic fusions.

Adult spinal deformity (ASD) patients with sagittal plane deformity (N) or structural lumbar/thoraco-lumbar (TL) curves can be treated with fusions stopping at the TL junction or extending to the upper thoracic (UT) spine. This study evaluates the impact on cost/cumulative quality-adjusted life year (QALY) in patients treated with TL vs UT fusion. ASD patients with > 4-level fusion and 2-year follow-up were included. Index and total episode-of-care costs were estimated using average itemized direct costs obtained from hospital records. Cumulative QALY gained were calculated from preoperative to 2-year postoperative change in Short Form Six-Dimension (SF-6D) scores. The TL and UT groups comprised patients with upper instrumented vertebrae (UIV) at T9-T12 and T2-T5, respectively. Of 566 patients with type N or L curves, mean age was 63.2 ± 12.1years, 72% were female and 93% Caucasians. Patients in the TL group had better sagittal vertical axis (7.3 ± 6.9 vs. 9.2 ± 8.1cm, p = 0.01), lower surgical invasiveness (- 30; p < 0.001), and shorter OR time (- 35min; p = 0.01). Index and total costs were 20% lower in the TL than in the UT group (p < 0.001). Cost/QALY was 65% lower (492,174.6 vs. 963,391.4), and 2-year QALY gain was 40% higher, in the TL than UT group (0.15 vs. 0.10; p = 0.02). Multivariate model showed TL fusions had lower total cost (p = 0.001) and higher QALY gain (p = 0.03) than UT fusions. In Schwab type N or L curves, TL fusions showed lower 2-year cost and improved QALY gain without increased reoperation rates or length of stay than UT fusions. III.

A continuum model for the mechanics of elastomeric sheets reinforced with extensible bidirectional fibers resistant to lateral pressure

We investigate the concurrent three-dimensional (in-plane and out-of-plane) deformations of fiber-reinforced composite (FRC) sheets undergoing lateral pressure. This involves the utilization of the Neo-Hookean strain energy model for the matrix material and computing the strain energy of bidirectional fibers by accounting for the stretching, bending, and twisting responses of the fibers. The kinematics of FRC are formulated within the framework of differential geometry on FRC surfaces, including the computations of the first and second gradient of deformation. By employing the variational principles, we derive the Euler equations describing the mechanics of the fiber–matrix composite system subjected to lateral pressure. The resulting three-dimensional continuum model theoretically predicts the deformation of the matrix material and it is found that the maximum deformation of matrix material occurs in the diagonal direction of the domain, yet, the center of the domain suffers weak in-plane deformation because of surface tension equilibrium. In addition, the stretching, bending, and twisting kinematics of fiber units are computed to investigate the effects of the individual fiber’s kinematics on the overall deformation of fiber meshwork. Lastly, it is found that the lateral pressure on the FRC surface induces fiber flexure in the vicinity of domain boundaries and fiber stretch inside the domain, corresponding to the intensified shrinking strain near the edges and stretching strain in the middle of the domain. The theoretical results provide phenomenologically meaningful insights into comprehending the damage patterns of the fiber-reinforced building material, the hemispherical dome shaping results of bamboo Poly (lactic) acid (PLA) composites and the out-of-plane deformation of woven fabric.

Modified solution for a harmonic hole in a soft elastic solid under plane deformation

Modified solution for a harmonic hole in a soft elastic solid under plane deformation

Relevance of instrumented gait analysis in the prediction of the rebound phenomenon after guided growth intervention

Predictors of rebound after correction of coronal plane deformities using temporary hemiepiphysiodesis (TH) are not well defined. The following research questions were tested: (1) Is the dynamic knee joint load useful to improve rebound prediction accuracy? (2) Does a large initial deformity play a critical role in rebound development? (3) Are BMI and a young age risk factors for rebound? Fifty children and adolescents with idiopathic knee valgus malalignment were included. A deviation of the mechanical femorotibial angle (MFA) of ≥ 3° into valgus between explantation and the one-year follow-up period was chosen to classify a rebound. A rebound was detected in 22 of the 50 patients (44%). Two predictors of rebound were identified: 1. reduced peak lateral knee joint contact force in the first half of the stance phase at the time of explantation (72.7% prediction); 2. minor initial deformity according to the MFA (70.5% prediction). The best prediction (75%) was obtained by including both parameters in the binary logistic regression method. A TH should not be advised in patients with a minor initial deformity of the leg axis. Dynamic knee joint loading using gait analysis and musculoskeletal modeling can be used to determine the optimum time to remove the plates.

Circumferential correction of spinal deformity and instability secondary to bacterial spondylodiscitis

BackgroundSpinal deformity as a sequela of non-tuberculous spondylodiscitis is a rarely discussed clinical entity. Sagittal plane deformity, segmental instability, and persistently active infection overlap in these patients resulting in severe restriction in activity and quality of life. The presence of multiple medical co-morbidities restricts surgical options but nonoperative care may be ineffective and result in persistent, refractory discitis for years. We describe our experience with vertebrectomy and long-segment fixation for patients with post-infectious thoracic or lumbar deformity. MethodsA retrospective chart review of 23 consecutive patients who underwent vertebrectomy and long-segment fixation for thoracic or lumbar deformity secondary to nontuberculous bacterial spondylodiscitis was performed. Pre-, peri- and postoperative data is compiled and analyzed with a focus on the perioperative management algorithm to safely perform an extensive reconstruction in this very sick patient population. ResultsExtremely low preoperative quality of life was evident with 87% (20/23) of patients bedridden primarily due to pain despite 70% (16/23) of patients being strong enough to ambulate (Frankel D or E). Most patients (87%) already had an identified infection under adequate treatment either through blood cultures, prior biopsy or decompressive surgery. A single-stage posterior-only was the primary surgical approach utilized in the majority (83%) of cases. Complications were present in 100% of patients, most commonly perioperative anemia and hypotension requiring vasopressor support and aggressive blood product replacement. One in-hospital mortality occurred secondarily to pulmonary embolism. Mean preoperative segmental angle was 18±10 degrees of kyphosis which was corrected to 1±9 degrees of lordosis (p=0.001). The mean correction of the segmental angle was 19 degrees (standard deviation 23 degrees). Visual analogue scale scores improved from a pre-operative value of 8.8±0.9 to a post-operative value of 2.5±1.4 (p<0.001), which was obtained at the last outpatient follow-up (mean 631 days after surgery). Full self-care including ambulation was achieved in 18/23 (78%) patients, and the infection was successfully treated in 22/23 (96%) patients after long-term antibiotics. ConclusionsPatients with refractory spondylodiscitis on appropriate care and antibiotics are typically considered extremely poor surgical candidates despite non-operative care often being ineffective. Post-infectious deformity may also be so severe as to preclude a limited surgical treatment strategy. This study suggests that extensive circumferential reconstruction for deformity secondary to bacterial spondylodiscitis can be effective in restoring these extremely sick patients to self-care and ambulatory status.

In-plane deformation behavior and energy absorption characteristics of a straight-arc coupled auxetic metamaterial inspired by arch bridges

The microstructure and material properties of auxetic honeycomb metamaterials significantly influence their deformation behavior and energy absorption. Inspired by the arch bridge, new types of straight-arc coupled structure (SACS) and the reverse SACS (R-SACS) auxetic metamaterials are designed to enhance the energy absorption capacity (EAC). The quasi-static compression and dynamic impact responses of honeycomb metamaterials are studied numerically under large deformation. A theoretical model is further developed to estimate the average platform stress (σp) of the R-SACS honeycomb, which is verified by the numerical results. For R-SACS--3 with Nylon 12 and Al-alloy, the relative errors of the finite element model compared with the theoretical model are − 5.56 % and − 3.21 %, respectively. Two kinds of basic materials, Nylon 12 and Al-alloy, are employed to analyze the deformation mode of the SACS and R-SACS honeycomb with the same geometric parameters under quasi-static load and impact load. The influence of basic material is discussed, and the structure with Al-alloy exhibits more stability owing to segmented deformation. The creation of additional plastic angles shows an improved σp and specific energy absorption (SEA) compared to the re-entrant structure (RES). σp and SEA of SACS are both 1.3 times as much as those of RES. The peak stress of the R-SACS cellular metamaterial is always smaller than the SACS under impact load, and the maximum reduction is 63 %, which has better a buffering effect.

Fractional Sobolev isometric immersions of planar domains

We discuss $C^1$ regularity and developability of isometric immersions of flat domains into $\mathbb R^3$ enjoying a local fractional Sobolev $W^{1+s, \frac2s}$ regularity for $2/3 \le s< 1 $, generalizing the known results on Sobolev and Holder regimes. Ingredients of the proof include analysis of the weak Codazzi-Mainardi equations of the isometric immersions and study of $W^{2,\frac2s}$ planar deformations with symmetric Jacobian derivative and vanishing distributional Jacobian determinant. On the way, we also show that the distributional Jacobian determinant, conceived as an operator defined on the Jacobian matrix, behaves like determinant of gradient matrices under products by scalar functions.