Biomechanical Effects Research Articles

Effect of force direction and impaction angulation during dilaceration impacted central incisor traction: a finite element analysis

BackgroundThe effects of traction forces at different angles on impacted central incisors(ICI)with varying inverted angles (IA) may be different. The objective of this study was to analyze the biomechanical effects of different force directions (FD) on developmentally inverted ICI with multi-angle variations and to offer insights and guidance for the treatment of inverted ICI.MethodsThree-dimensional finite element method was employed to simulate clinical scenarios of inverted ICI traction. As such, 0.2 N of force (direction: antero-superior angles of 90°, 100°, 110°, 120°, and 130° relative to the long axis of the inverted ICI crown) was applied to the inverted ICI with inverse angles (IA) of 40°, 30°, 20°, 10° and 0°. Inverted ICI apical displacement and Von Mises stress on periodontal ligament (PDL) and alveolar bone were compared.ResultsIA and FD showed minimal influence on the stress distribution in the PDL, as higher stresses were concentrated in the apical region. The higher stresses in the alveolar bone are focused on the cervical and apical regions of the tooth. In particular, IA exerts a more significant impact on stress distribution in the alveolar bone than FD. The influence of IA on the apical displacement of inverted ICI is larger than that of FD.ConclusionsTo promote the health of the root and periodontal tissues, it is recommended to use an angle of 100°-110° relative to the long axis of the ICI crown when dealing with a large IA (> 20°) developmentally inverted ICI. Conversely, an angle of 110°-120° can be used.

Biomechanical effects of posterior lumbar interbody fusion with vertical placement of pedicle screws compared to traditional placement.

The pedicle screw technique is widely employed for vertebral body fixation in the treatment of spinal disorders. However, traditional screw placement methods require the dissection of paraspinal muscles and the insertion of pedicle screws at specific transverse section angles (TSA). Larger TSA angles require more force to pull the muscle tissue, which can increase the risk of surgical trauma and ischemic injury to the lumbar muscles. To study the feasibility of zero-degree TSA vertical pedicle screw technique in the lumbosacral segment. Finite element models of vertebral bodies and pedicle screw-rod systems were established for the L4-S1 spinal segments. A standard axial load of 500 N and a rotational torque of 10 N/m were applied. Simulated screw pull-out experiment was conducted to observe pedicle screw resistance to pull-out, maximum stress, load-displacement ratio, maximum stress in vertebral bodies, load-displacement ratio in vertebral bodies, and the stress distribution in pedicle screws and vertebral bodies. Differences between the 0-degree and 17-degree TSA were compared. At 0-degree TSA, the screw pull-out force decreased by 11.35% compared to that at 17-degree TSA (P < 0.05). At 0-degree and 17-degree TSA, the stress range in the screw-rod system was 335.1-657.5 MPa and 242.8-648.5 MPa, separately, which were below the fracture threshold for the screw-rod system (924 MPa). At 0-degree and 17-degree TSA, the stress range in the vertebral bodies was 68.45-78.91 MPa and 39.08-72.73 MPa, separately, which were below the typical bone yield stress range for vertebral bodies (110-125 MPa). At 0-degree TSA, the load-displacement ratio for the vertebral bodies and pedicle screws was slightly lower compared to that at 17-degree TSA, indicating slightly lower stability (P < 0.05). The safety and stability of 0-degree TSA are slightly lower, but the risks of screw-rod system fracture, vertebral body fracture, and rupture are within acceptable limits.

Biomechanical Motion Changes in Adjacent and Noncontiguous Segments Following Single-Level Anterior Cervical Discectomy and Fusion: A Computed Tomography-Based 3D Motion Capture Study.

Anterior cervical discectomy and fusion (ACDF) is known to elicit adverse biomechanical effects on immediately adjacent segments; however, its impact on the kinematics of the remaining nonadjacent cervical levels has not been understood. This study aimed to explore the biomechanical impact of ACDF on kinematics beyond the immediate fusion site. We hypothesized that compensatory motion following single-level ACDF is not predictably distributed to adjacent segments due to compensation from noncontiguous levels. Six fresh-frozen cervical spines (C2-T1) underwent fluoroscopic screening and sagittal and coronal reformats from computed tomography scans and were utilized to grade segmental degeneration. Each specimen was tested to 30° of flexion and extension intact and following single-level ACDF at the C5-C6 level. The motions of each vertebral body were tracked using 3-dimensional (3D) motion capture into an inverse kinematics model, facilitating correlations between the 3D reconstruction from computed tomography images and the 3D motion capture data. This model was used to calculate each level's flexion/extension range of motion (ROM). Single-level fusion at the C5-C6 level across all specimens resulted in a significant motion reduction of -6.8° (P = 0.002). No significant change in ROM occurred in the immediate adjacent segments C4-C5 (P = 0.07) or C6-C7 (P = 0.15). Hypermobility was observed in 2 specimens (33%) exclusively in adjacent segments. In contrast, the other 4 spines (66%) displayed hypermobility at noncontiguous segments. Hypermobility occurred in 42% (5/12) of the adjacent segments, 28% (5/18) of the noncontiguous segments, and 50% (3/6) of the cervicothoracic segments. Single-level ACDF impacts ROM beyond adjacent segments, extending to noncontiguous levels. Compensatory motion, not limited to adjacent levels, may be influenced by degenerative changes in noncontiguous segments. Surprisingly, hypermobility may not occur in adjacent segments after ACDF. Overall, the multifaceted biomechanical effects of ACDF underscore the need for a comprehensive understanding of cervical spine dynamics beyond immediate adjacency, and it needs to be taken into consideration when planning single-level ACDF.

The Influence of Medial and Lateral Forefoot Height Discrepancy on Lower Limb Biomechanical Characteristics during the Stance Phase of Running

Previous research has predominantly focused on the biomechanical effects of anterior–posterior foot motion during running, with comparatively less attention given to medial–lateral foot motion and its impact on lower limb biomechanical characteristics. We recruited 18 healthy runners who wore five different types of running shoes: regular shoes (NS), those with a 6 mm and 9 mm medial–lateral height difference in the forefoot (M6, M9), and those with a 6 mm and 9 mm lateral–medial height difference (L6, L9). Biomechanical parameters of lower limb joints during the stance phase of running, including range of motion, peak angular velocity, peak moment, power, and work, were analyzed. We used paired-sample t-tests and one-dimensional statistical parametric mapping (SPM1D) to compare joint biomechanics between shoes with varying height differences and NS. Under the L6 condition, notable differences occurred in the hip and knee flexion–extension moments during landing and push-off, accompanied by a significant increase in ankle dorsiflexion work and a significant decrease in inversion–eversion work. In contrast, the M9 condition resulted in decreased hip flexion–extension peak moment, power, and work in the sagittal plane. These findings indicate that varying forefoot medial–lateral height differences in running shoes significantly impact lower limb joint dynamics during the stance phase, particularly the L6 condition, potentially reducing knee injury risk and aiding gait improvement for overpronators. The findings offer valuable insights for sports injury prevention and athletic footwear design. However, further research is needed to understand the underlying mechanisms and practical implications for sports injury prevention and performance enhancement.

Biomechanical effects of hemin and sildenafil treatments on the aortic wall of chronic-hypoxic lambs.

Introduction: Gestation under chronic hypoxia causes pulmonary hypertension, cardiovascular remodeling, and increased aortic stiffness in the offspring. To mitigate the neonatal cardiovascular risk, pharmacological treatments (such as hemin and sildenafil) have been proposed to improve pulmonary vasodilation. However, little is known about the effects of these treatments on the aorta. Therefore, we studied the effect of hemin and sildenafil treatments in the aorta of lambs gestated and raised at highlands, thereby subjected to chronic hypoxia. Methods: Several biomechanical tests were conducted in the descending thoracic aorta (DTA) and the distal abdominal aorta (DAA), assessing 3 groups of study of hypoxic animals: non-treated (Control) and treated either with hemin or sildenafil. Based on them, the stiffness level has been quantified in both zones, along with the physiological strain in the unloaded aortic duct. Furthermore, a morphological study by histology was conducted in the DTA. Results: Biomechanical results indicate that treatments trigger an increment of axial pre-stress and circumferential residual stress levels in DTA and DAA of lambs exposed to high-altitude chronic hypoxia, which reveals a vasodilatation improvement along with an anti-hypertensive response under this characteristic environmental condition. In addition, histological findings do not reveal significant differences in either structure or microstructural content. Discussion: The biomechanics approach emerges as a valuable study perspective, providing insights to explain the physiological mechanisms of vascular function. According to established results, alterations in the function of the aortic wall may not necessarily be explained by morphostructural changes, but rather by the characteristic mechanical state of the microstructural components that are part of the studied tissue. In this sense, the reported biomechanical changes are beneficial in mitigating the adverse effects of hypobaric hypoxia exposure during gestation and early postnatal life.

Biomechanical analysis of stabilization for thoracolumbar anterior spinal failure caused by osteolytic lesions, a finite element comparison of direct lateral corpectomy and posterior long segment instrumentation

BACKGROUND CONTEXTOsteolytic lesions caused by infection or metastatic disease of the spine can induce instability. Different surgical strategies are available to restore stability in this scenario, however little is known how various reconstruction techniques affect spinal biomechanics. PURPOSETo analyze and quantify the biomechanical effects of three different surgical reconstruction techniques in the treatment of a T12 osteolytic model. STUDY DESIGN/SETTINGFinite element analysis of the thoracic spine with a T12 osteolytic lesion. METHODSUsing CT scans from a 20-year-old man without structural deformity, simulation of an osteolytic lesion with a 50% defect at the posterior aspect of T12 vertebral body was created by a 490 N vertical force to T9. Next, three common instrumentation techniques treating the osteolytic lesion were modeled and biomechanically tested. These included: Model A, corpectomy with short segment fixation (T11-L1) and two long-segment instrumentations; Model B long segment fixation with triple rod construct; Model C long segment fixation with dual rod construct. A load of 480N was then applied on the spine models in vertically downward direction on T9. Von Mises stresses were measured (MPa) in the discs, vertebrae, and implants. RESULTSModel A demonstrated the lowest stress on construct material, adjacent vertebral bodies, and discs but increased stress on the instrumented vertebrae. Model B was more rigid and demonstrated lower construct stress compared to Model C. However, Model C had the lowest vertebral body stress in flexion, extension, and lateral bending in the most upper instrumented vertebral body, but the highest screw pull-out stress when compared to Model A and Model B. CONCLUSIONSThis osteolytic T12 model provides unique biomechanical data that can help to tailor surgical strategies in select scenarios. While optimal outcomes are best achieved with a construct tailored to a specific patient's need for stabilization, our findings can be generalized for instances of cancerous lesions, low bone density, and infectious causes. CLINICAL RELEVANCEThe results of this study can help with the choice of appropriate surgical reconstruction technique based on patient-specific characteristics.

Biomechanical Effects of Stem Extension of Tibial Components for Medial Tibial Bone Defects in Total Knee Arthroplasty: A Finite Element Study.

The aim of this study was to investigate the biomechanical effects of stem extension with a medial tibial bone defect in primary total knee arthroplasty (TKA) on load distribution and stress in the proximal tibia using finite element (FE) analysis.FE simulations were performed on the tibia bone to evaluate the stress and strain on the tibia bone and bone cement. This was done to investigate the stress shielding effect, stability of the tibia plate, and the biomechanical effects in TKA models with various medial defects and different stem length models.The results demonstrated that in the bone defect model, the longer the stem, the lower the average von Mises stress on the cortical and trabecular bones. In particular, as the bone defect increased, the average von Mises stress on cortical and trabecular bones increased. The average increase in stress according to the size of the bone defect was smaller in the long stem than in the short stem. The maximal principal strain on the trabecular bone occurred mainly at the contact point on the distal end of the stem of the tibial implant. When a short stem was applied, the maximal principal strain on the trabecular bone was approximately 8% and 20% smaller than when a long stem was applied or when no stem was applied, respectively.The findings suggest that a short stem extension of the tibial component could help achieve excellent biomechanical results when performing TKA with a medial tibial bone defect.

Biomechanical Effects of Titanium and Carbon Fiber Reinforced PEEK as Dental Implant Material: A Finite Element Analysis.

The aim of this study is to examine the stresses on the peri-implant bone under occlusal forces of 30% Carbon fiber reinforced PEEK (Cfr-PEEK) and 60% Cfr-PEEK materials that can be used as an alternative to titanium dental implants by finite element analysis. Single-tooth implants of 30% Cfr-PEEK, 60% Cfr-PEEK and titanium were modeled in each of the maxillary anterior, maxilla posterior, mandibular posterior regions. As a result of the applied vertical and oblique forces; Von Misses stress, maximum principal stress and minimum principal stress values and stress distributions in the implant, cortical bone and spongious bone in each of the models were examined. 30% Cfr-PEEK implants stress in the surrounding bone was higher than titanium and 60% Cfr-PEEK implants. The 60% Cfr-PEEK material displayed lower stress distribution on both cortical and spongious peri-implant bone in all models. Titanium and 60% Cfr- PEEK implants exhibited biomechanically similar behavior and these implants conducted stresses to bone more homogeneous than the 30% Cfr-PEEK implants. Overall, oblique forces had more destructive effect than vertical forces and denser bone structure showed better stress distribution against incoming forces. For the routine use of Cfr-PEEK material as dental implant material; animal and long-term clinical studies are needed.

Beyond CREA: Evolutionary patterns of non-allometric shape variation and divergence in a highly allometric clade of murine rodents.

The shared functions of the skull are thought to result in common evolutionary patterns in mammalian cranial shape. Craniofacial evolutionary allometry (CREA) is a particularly prominent pattern where larger species display proportionally elongate facial skeletons and smaller braincases. It was recently proposed that CREA arises from biomechanical effects of cranial scaling when diets are similar. Thus, deviations from CREA should occur with changes in cranial biomechanics, for example due to dietary change. Here, we test this using 3D geometric morphometric analysis in a dataset of Australian murine crania, which are highly allometric. We contrast allometric and non-allometric variation in the cranium by comparing evolutionary mode, allometry, ordinations, as well as allometry, integration, and modularity in functional modules. We found evidence of stabilising selection in allometry-containing and size-free shape, and substantial non-allometric variation aligned with dietary specialisation in parallel with CREA. Integration among cranial modules was higher, and modularity lower, with size included, but integration between rostrum and cranial vault, which are involved in the CREA pattern, dropped dramatically after size removal. Our results thus support the hypothesis that CREA is a composite arising from selection on cranial function, with substantial non-allometric shape variation occurring alongside CREA where dietary specialisation impacts selection on gnawing function. This emphasises the need to research mammalian cranial evolution in the context of allometric and non-allometric selection on biomechanical function.

Force magnitude and distribution during impacts to the hip are affected differentially by body size and body composition

Hip fractures are a severe health concern among older adults. While anthropometric factors have been shown to influence hip fracture risk, the low fidelity of common body composition metrics (e.g. body mass index) reduces our ability to infer underlying mechanisms. While simulation approaches can be used to explore how body composition influences impact dynamics, there is value in experimental data with human volunteers to support the advancement of computational modeling efforts. Accordingly, the goal of this study was to use a novel combination of subject-specific clinical imaging and laboratory-based impact paradigms to assess potential relationships between high-fidelity body composition and impact dynamics metrics (including load magnitude and distribution and pelvis deflection) during sideways falls on the hip in human volunteers.Nineteen females (<35 years) participated. Body composition was assessed via DXA and ultrasound. Participants underwent low-energy (but clinically relevant) sideways falls on the hip during which impact kinetics (total peak force, contract area, peak pressure) and pelvis deformation were measured. Pearson correlations assessed potential relationships between body composition and impact characteristics.Peak force was more strongly correlated with total mass (r = 0.712) and lean mass indices (r = 0.510–0.713) than fat mass indices (r = 0.401–0.592). Peak deflection was positively correlated with indices of adiposity (all r > 0.7), but not of lean mass. Contact area and peak pressure were positively and negatively associated, respectively, with indices of adiposity (all r > 0.49). Trochanteric soft tissue thickness predicted 59 % of the variance in both variables, and was the single strongest correlate with peak pressure. In five-of-eight comparisons, hip-local (vs. whole body) anthropometrics were more highly associated with impact dynamics.In summary, fall-related impact dynamics were strongly associated with body composition, providing support for subject-specific lateral pelvis load prediction models that incorporate soft tissue characteristics. Integrating soft and skeletal tissue properties may have important implications for improving the biomechanical effectiveness of engineering-based protective products.

Biomechanical effects of different instrumented segments and trunk shifts on distal adjacent segments after congenital scoliosis posterior hemivertebrectomy: Preliminary results of a single case

ObjectiveThe present study aims to discuss the biomechanical effects of the sagittal vertical axis and different instrumented segments on distal adjacent segments after congenital scoliosis posterior hemivertebrectomy. MethodA case of congenital scoliosis caused by hemivertebra was selected for the reconstruction of the preoperative and postoperative 3D computed tomography data of the full spine. A finite element model of different fusion lengths and postoperative trunk shift (TS) values was established using the finite element method to compare the biomechanical effects of different models on the distal adjacent segment. ResultIn the L1–L3 and T12–L1–L3–L4 fusion modes, the horizontal shift of the 1st vertebra below the lowest instrumented vertebra (LIV) increased with the trunk shift (TS) expansion after operation, and the imbalance between the left and right vertical stress of the 1st intervertebral disc below the LIV increased. With the decrease in fused segments in cases of TS = 10 mm and TS = 5 mm, the 1st vertebra below the LIV was subjected to a greater unbalanced force in the horizontal direction, and the 1st intervertebral disc below the LIV was subjected to a smaller imbalance between the left and right vertical stress after operation. ConclusionWhen treating congenital scoliosis with hemivertebrectomy and pedicle screw fixation, fused segments can be properly extended and the postoperative TS shortened with a view of reducing the imbalance between the left and right stress of the 1st intervertebral disc below the LIV as well as the horizontal shift of the 1st vertebra below the LIV.

Effect of different lumbar–iliac fixation and sacral slope for Tile C1.3 pelvic fractures: a biomechanical study

BackgroundLumbar–iliac fixation (LIF) is a common treatment for Tile C1.3 pelvic fractures, but different techniques, including L4–L5/L5 unilateral LIF (L4–L5/L5 ULIF), bilateral LIF (BLIF), and L4–L5/L5 triangular osteosynthesis (L4–L5/L5 TOS), still lack biomechanical evaluation. The sacral slope (SS) is key to the vertical shear of the sacrum but has not been investigated for its biomechanical role in lumbar–iliac fixation. The aim of this study is to evaluate the biomechanical effects of different LIF and SS on Tile C1.3 pelvic fracture under two-legged standing load in human cadavers.MethodsEight male fresh-frozen human lumbar–pelvic specimens were used in this study. Compressive force of 500 N was applied to the L4 vertebrae in the two-legged standing position of the pelvis. The Tile C1.3 pelvic fracture was prepared, and the posterior pelvic ring was fixed with L5 ULIF, L4–L5 ULIF, L5 TOS, L4–L5 TOS, and L4–L5 BLIF, respectively. Displacement and rotation of the anterior S1 foramen at 30° and 40° sacral slope (SS) were analyzed.ResultsThe displacement of L4–L5/L5 TOS in the left–right and vertical direction, total displacement, and rotation in lateral bending decreased significantly, which is more pronounced at 40° SS. The difference in stability between L4–L5 and L5 ULIF was not significant. BLIF significantly limited left–right displacement. The ULIF vertical displacement at 40° SS was significantly higher than that at 30° SS.ConclusionsThis study developed an in vitro two-legged standing pelvic model and demonstrated that TOS enhanced pelvic stability in the coronal plane and cephalad–caudal direction, and BLIF enhanced stability in the left–right direction. L4–L5 ULIF did not further improve the immediate stability, whereas TOS is required to increase the vertical stability at greater SS.

Three-dimensional finite element analysis of lumbar disc herniation under different body positions

To campare biomechanical effects of different postural compression techniques on three-dimensional model of lumbar disc herniation (LDH) by finite element analysis. Lumbar CT image of a 48-year-old female patient with LDH (heighted 163 cm, weighted 53 kg) was collected. Mimics 20.0, Geomagic Studio, Solidwords and other software were used to establish three-dimensional finite element model of LDH on L4,5 segments. Compression techniques under horizontal position, 30° forward bending and 10° backward extension were simulated respectively. After applying the pressure, the effects of compression techniques under different positions on stress, strain and displacement of various tissues of intervertebral disc and nerve root were observed. L4, 5 segment finite element model was successfully established, and the model was validated. When compression manipulation was performed on the horizontal position, 30° flexion and 10° extension, the annular stress were 0.732, 5.929, 1.286 MPa, the nucleus pulposus stress were 0.190, 1.527, 0.295 MPa, and the annular strain were 0.097, 0.922 and 0.424, the strain sizes of nucleus pulposus were 0.153, 1.222 and 0.282, respectively. The overall displacement distance of intervertebral disc on Y direction were -3.707, -18.990, -4.171 mm, and displacement distance of nerve root on Y direction were +7.836, +5.341, +3.859 mm, respectively. The relative displacement distances of nerve root and intervertebral disc on Y direction were 11.543, 24.331 and 8.030 mm, respectively. Compression manipulation could make herniated intervertebral disc produce contraction and retraction trend, by increasing the distance between herniated intervertebral disc and nerve root, to reduce symptoms of nerve compression, to achieve purpose of treatment for patients with LDH, in which the compression manipulation is more effective when the forward flexion is 30°.

Effects of different tooth movement patterns and aligner thicknesses on maxillary arch expansion with clear aligners: a three-dimensional finite element study.

The objective of this study was to investigate the biomechanical effects of different tooth movement patterns and aligner thicknesses on teeth and periodontal tissues during maxillary arch expansion with clear aligners, to facilitate more precise and efficient clinical orthodontic treatments. Three-dimensional models including teeth, maxilla, periodontal ligament, and aligner were constructed and subjected to finite element analysis. Tooth displacement trends and periodontal ligament stresses were measured for seven tooth displacement patterns (divided into three categories including overall movement of premolars and molars with gradually increasing molar expansion in each step; distributed movement of premolars and molars; and alternating movement between premolars and molars at intervals) and two aligner thicknesses (0.5mm and 0.75mm) during maxillary arch expansion with clear aligners. When expanding the maxillary arch with clear aligners, the effective expansion of the target teeth mainly showed a tilting movement trend. Increasing the amount of molar expansion increased the buccal displacement of the first molar but decreased the buccal displacement of the premolars. The mean buccal displacement of the target teeth was greater in the posterior teeth interval alternating movement group (0.026mm) than in the premolar/molar distributed movement group (0.016mm) and the overall movement group (0.015mm). Increasing aligner thickness resulted in greater buccal displacement of the crowns and increased stress on the periodontal ligaments. Increasing the amount of molar expansion reduces the efficiency of premolar expansion. Alternating movement of premolars and molars at intervals achieves a higher arch expansion efficiency, but attention should be paid to the anchorage of adjacent teeth. Increasing the thickness of the aligner increases the expansion efficiency but may also increase the burden on the periodontal tissues.

Research progress of Chinese unique Inlay Bristow (Cuistow surgery) using suture button fixation

To explore the research progress of the coracoid transfer surgery using suture button fixation, particularly focusing on the technique known as Chinese unique Inlay Bristow (Cuistow surgery). Extensive literature review was conducted to summarize and analyze the utilization of suture button fixation in the Cuistow surgery, comparing its biomechanical and clinical outcomes with those of traditional screw fixation. Utilizing suture button fixation in coracoid transfer surgery helps circumvent certain metal-related complications associated with traditional screw fixation. While its biomechanical stability and effectiveness have been preliminarily confirmed, debates persist regarding its graft healing rate and postoperative recurrence rate compared to traditional screw fixation. The Cuistow surgery based on the Inlay structure is a solution to improve the healing rate of graft after suture button fixation. Suture button fixation, as a novel approach in coracoid transfer surgery, remains to have its advantages and disadvantages compared to traditional screw fixation not entirely elucidated, underscoring the need for further in-depth clinical and fundamental research. Cuistow surgery is the Chinese experience of coracoid transfer surgery, and its biomechanical stability and clinical advantages have been preliminarily confirmed.

Ex vivo biomechanical investigations of combined extra- and intracapsular stabilization in canines with cranial cruciate ligament deficiency.

Intracapsular reconstruction (ICR) has long been recommended as a treatment for cranial cruciate ligament deficiency (CCLD) in dogs, but it has fallen out of favor due to its inferior long-term functional outcomes. These outcomes may be attributed to the poor stiffness and strength of the graft in the early period before ligamentization is completed. Additional placement of extracapsular sutures to mechanically protect the graft during the ligamentization process may be a viable method to address this problem. However, the biomechanical effect of this combined surgical approach remains unknown. This study aimed to evaluate the 3D kinematics of the CCLD stifle in dogs in response to ICR and combined extra- and intracapsular reconstruction (CEICR). Twelve hindlimbs were collected from nine cadavers of mature dogs. The limbs were tested using a custom-made testing apparatus that reproduces their sagittal plane kinematics during the stance phase. Four statuses of stifle joints were tested, namely, (a) cranial cruciate ligament (CCL) intact; (b) CCLD; (c) CCLD stifle stabilized by CEICR; and (d) CCLD stifle stabilized by ICR only. Three-dimensional stifle kinematics at the 5 instances of the stance phase were measured with an optoelectronic system. The results showed that ICR marginally corrects the increased adduction, internal rotation, and caudodistal stifle joint center displacement that occur as a result of CCLD. CEICR led to better restoration of the stifle kinematics, especially with respect to the internal rotation and cranial translation stabilities. Furthermore, CEICR only resulted in minor excessive restraints on other motion components. The findings indicated that the additional lateral fabellotibial suture offers immediate stability to the stifle, consequently lowering the risk of graft over-elongation in the short term postoperatively. Considering the propensity for the extracapsular suture to degrade over time, further in vivo studies are warranted to explore the long-term effects of the CEICR procedure.

Biomechanical analysis of adjacent segments after correction surgery for adult idiopathic scoliosis: a finite element analysis

The biomechanical aspects of adjacent segment degeneration after Adult Idiopathic Scoliosis (AdIS) corrective surgery involving postoperative changes in motion and stress of adjacent segments have yet to be investigated. The objective of this study was to evaluate the biomechanical effects of corrective surgery on adjacent segments in adult idiopathic scoliosis by finite element analysis. Based on computed tomography data of the consecutive spine from T1–S1 of a 28-year-old male patient with adult idiopathic scoliosis, a three-dimensional finite element model was established to simulate the biomechanics. Two posterior long-segment fixation and fusion operations were designed: Strategy A, pedicle screws implanted in all segments of both sides, and Strategy B, alternate screws instrumentation on both sides. The range of motion (ROM), Maximum von Mises stress value of intervertebral disc (IVD), and Maximum von Mises stress of the facet joint (FJ) at the fixation adjacent segment were calculated and compared with data of the preoperative AdIS model. Corrective surgery decreased the IVD on the adjacent segments, increased the FJ on the adjacent segments, and decreased the ROM of the adjacent segments. A greater decrease of Maximum von Mises stress was observed on the distal adjacent segment compared with the proximal adjacent segment. The decrease of Maximum von Mises stress and increment of Maximum von Mises stress on adjacent FJ in strategy B was greater than that in strategy A. Under the six operation modes, the change of the Maximum von Mises stress on the adjacent IVD and FJ was significant. The decrease in ROM in the proximal adjacent segment was greater than that of the distal adjacent segment, and the decrease of ROM in strategy A was greater than that in strategy B. This study clarified the biomechanical characteristics of adjacent segments after AdIS corrective surgery, and further biomechanical analysis of two different posterior pedicle screw placement schemes by finite element method. Our study provides a theoretical basis for the pathogenesis, prevention, and treatment of adjacent segment degeneration after corrective surgery for AdIS.

How athletes’ biomechanical running characteristics effect running economy during the use of running shoes with and without carbon inserts

To maximise running economy (RE), shoe manufacturers placed carbon plates within the midsole of shoes. Shoe technology research is limited on understanding the variability of individual responses to carbon-plated shoes and how these responses vary across running velocities. Little research on same shoe characteristics with and without a stiff element has been completed. This study aimed to investigate how running shoes with carbon versus without a carbon composite stiff element alter individual running biomechanics and the metabolic cost of running. Ethical approval was gained from Cardiff Metropolitan University Ethics Committee. Ten male athletes (69 ± 9 kg; 174 ± 4 cm; 28 ± 9 years) completed two submaximal incremental treadmill runs. One test was completed in a shoe without carbon (C1), the other test was completed in carbon shoes (C2), the order of testing for each shoe were randomised. Running velocity started at 9 km/h and increased by 1 km/h every four mins, blood lactate samples were taken after every stage. Once 4 mmol·L−1 (OBLA; the second lactate turn point) had been reached one more stage was completed. Gas exchange was analysed throughout the whole test. The first 15 s of the final 2 minutes of each stage was recorded using Theia3D markerless motion capture software (Theia3Dv2022.1.0.2309, Theia Markerless, Inc., Kingston, ON, Canada). Data were analysed in 4 stages, the initial stage, pre-OBLA, OBLA and post-OBLA. Physiology data were averaged over the final two mins of each stage. Discrete joint angles were taken from each stage, and an average of the 15 s recording was taken for spatiotemporal measure. Data were analysed using a four-way repeat measures ANOVA, to show individual differences. Non-parametric data were analysed using Wilcoxon signed-rank test. Hedges g calculations were completed to calculate effect size (ES). Results showed significant increase in flight time (FT; P = 0.04, ES = 0.20) in the pre-OBLA stage when using C2. Metatarsophalangeal joint (MTP) dorsiflexion showed significant increase during the initial stage in C2 (P = 0.05, ES = 0.8), and ankle dorsiflexion had significant increase in the post-OBLA stage in C2 (P = 0.03, ES = 0.2). The were no significant differences present in the physiology data. Across the physiological, spatiotemporal and kinematics, high dispersions around the mean were exhibited. Findings suggest that to improve RE, mechanical and spatiotemporal changes need to be present when using C2. Further findings show carbon shoes elicit highly individual responses to both RE and mechanics of running.

Effects of different intrusion patterns during anterior teeth retraction using clear aligners in extraction cases: an iterative finite element analysis.

Overtreatment design of clear aligner treatment (CAT) in extraction cases is currently primarily based on the clinical experience of orthodontists and is not supported by robust evidence on the underlying biomechanics. This study aimed to investigate the biomechanical effects of overtreatment strategies involving different maxillary anterior teeth intrusion patterns during anterior teeth retraction by CAT in extraction cases. A finite element model of the maxillary dentition with the first premolar extracted was constructed. A loading method of clear aligners (CAs) based on the initial state field was proposed. The iterative method was used to simulate the long-term orthodontic tooth movement under the mechanical load exerted by the CAs. Three groups of CAs were utilized for anterior teeth retraction (G0: control group; G1: incisors intrusion group; G2: anterior teeth intrusion group). Tooth displacement and occlusal plane rotation tendency were analyzed. In G0, CAT caused lingual tipping and extrusion of the incisors, distal tipping and extrusion of the canines, mesial tipping, and intrusion of the posterior teeth. In G1, the incisors showed minimal extrusion, whereas the canines showed increased extrusion and distal tipping tendency. G2 showed the smallest degree of posterior occlusal plane angle rotation, while the inclination tendency of the canines and second premolars decreased. 1. In CAT, tooth displacement tendency may change with increased wear time. 2. During anterior teeth retraction, the incisor intrusion pattern can provide effective vertical control for the lateral incisors but has little effect on the central incisors. Anterior teeth intrusion patterns can alleviate the inclination of canines and second premolars, resulting in partial relief of the roller-coaster effect.

Topping-Off a Long Thoracic Stabilization With Semi-Rigid Constructs May Have Favorable Biomechanical Effects to Prevent Proximal Junctional Kyphosis: A Biomechanical Comparison.

In-vitro cadaveric biomechanical study. Long posterior spinal fusion is a standard treatment for adult spinal deformity. However, these rigid constructs are known to alter motion and stress to the adjacent non-instrumented vertebrae, increasing the risk of proximal junctional kyphosis (PJK). This study aimed to biomechanically compare a standard rigid construct vs constructs "topped off" with a semi-rigid construct. By understanding semi-rigid constructs' effect on motion and overall construct stiffness, surgeons and researchers could better optimize fusion constructs to potentially decrease the risk of PJK and the need for revision surgery. Nine human cadaveric spines (T1-T12) underwent non-destructive biomechanical range of motion tests in pure bending or torsion and were instrumented with an all-pedicle-screw (APS) construct from T6-T9. The specimens were sequentially instrumented with semi-rigid constructs at T5: (i) APS plus sublaminar bands; (ii) APS plus supralaminar hooks; (iii) APS plus transverse process hooks; and (iv) APS plus short pedicle screws. APS plus transverse process hooks had a range of motion (ie, relative angle) for T4-T5 and T5-T6, as well as an overall mechanical stiffness for T1-T12, that was more favourable, as it reduced motion at adjacent levels without a stark increase in stiffness. Moreover, APS plus transverse process hooks had the most linear change for range of motion across the entire T3-T7 range. Present findings suggest that APS plus transverse process hooks has a favourable biomechanical effect that may reduce PJK for long spinal fusions compared to the other constructs examined.