Finite Element Analysis of Cervical Spine Kinematic Response during Ejection Utilising a Hill-Type Dynamic Muscle Model.

To determine the impact of active muscle on the dynamic response of a pilot's neck during simulated emergency ejection, a detailed three-dimensional (3D) cervical spine (C0-T1) finite element (FE) model integrated with active muscles was constructed. Based on the Hill-type model characterising the muscle force activation mechanics, 13 major neck muscles were modelled. The active force generated by each muscle was simulated as functions of (i) active state (Na), (ii) velocity (Fv(v)), and (iii) length (FL(L)). An acceleration-time profile with an initial acceleration rate of 125 G·s-1 in the 0-80 ms period, reaching peak acceleration of 10 G, then kept constant for a further 70 ms, was applied. The rotational angles of each cervical segment under these ejection conditions were compared with those without muscles and with passive muscles derived from the previous study. Similar trends of segmental rotation were observed with S- and C-curvature of the cervical spine in the 150 ms span analysed. With active muscles, the flexion motion of the C0-C2 segments exhibited higher magnitudes of rotation compared to those without muscle and passive muscle models. The flexion motion increased rapidly and peaked at about 95-105 ms, then decreased rapidly to a lower magnitude. Lower C2-T1 segments exhibited less variation in flexion and extension motions. Overall, during emergency ejections, active muscle activities effectively reduce the variability in rotational angles across cervical segments, except C0-C2 segments in the 60-120 ms period. The role of the active state dynamics of the muscles was crucial to the magnitude of the muscle forces demonstrated. This indicates that it is crucial for pilots to consciously contract their muscles before ejection to prevent cervical spine injuries.

Structural and Organizational Strategies of Locomotor Modules during Landing in Patients with Chronic Ankle Instability.

BACKGROUND: Human locomotion involves the coordinated activation of a finite set of modules, known as muscle synergy, which represent the motor control strategy of the central nervous system. However, most prior studies have focused on isolated muscle activation, overlooking the modular organization of motor behavior. Therefore, to enhance comprehension of muscle coordination dynamics during multi-joint movements in chronic ankle instability (CAI), exploring muscle synergies during landing in CAI patients is imperative. METHODS: A total of 22 patients with unilateral CAI and 22 healthy participants were recruited for this research. We employed a recursive model for second-order differential equations to process electromyographic (EMG) data after filtering preprocessing, generating the muscle activation matrix, which was subsequently inputted into the non-negative matrix factorization model for extraction of the muscle synergy. Muscle synergies were classified utilizing the K-means clustering algorithm and Pearson correlation coefficients. Statistical parameter mapping (SPM) was employed for temporal modular parameter analyses. RESULTS: Four muscle synergies were identified in both the CAI and healthy groups. In Synergy 1, only the gluteus maximus showed significantly higher relative weight in CAI compared to healthy controls (p = 0.0035). Synergy 2 showed significantly higher relative weights for the vastus lateralis in the healthy group compared to CAI (p = 0.018), while in Synergy 4, CAI demonstrated significantly higher relative weights of the vastus lateralis compared to healthy controls (p = 0.030). Furthermore, in Synergy 2, the CAI group exhibited higher weights of the tibialis anterior compared to the healthy group (p = 0.042). CONCLUSIONS: The study suggested that patients with CAI exhibit a comparable modular organizational framework to the healthy group. Investigation of amplitude adjustments within the synergy spatial module shed light on the adaptive strategies employed by the tibialis anterior and gluteus maximus muscles to optimize control strategies during landing in patients with CAI. Variances in the muscle-specific weights of the vastus lateralis across movement modules reveal novel biomechanical adaptations in CAI, offering valuable insights for refining rehabilitation protocols.

Finite element study on the amount of injection cement during the pedicle screw augmentation.

STUDY DESIGN: A finite element analysis of the screw pullout procedure for the osteoporotic cancellous bone using screw-bone unit model without cortical layer. OBJECTIVE: The objective is to determine the region of effect (RoE) during the screw pullout procedure and predict the proper amount of injection cement (AIC) in screw augmentation. SUMMARY OF BACKGROUND DATA: For the osteoporotic spine, the AIC is a critical factor for the augmentation screw performance and leakage risk. There are few studies on the proper AIC in literature. METHODS: Three finite element models were established, 2 screw-foam models were used for validation study, and 1 screw-bone model was used for investigation of RoE and AIC. The simulations of screw pullout were conducted. A velocity loading of 0.01 mm/s with a maximum displacement of 2.7 mm was applied on the screw. For the validation, the screw-foam models with 2 different densities were used for comparison of pullout force with those published experimental data. After validation, the screw-bone model was used to investigate the RoE and predict the proper AIC during screw augmentation in spine surgery. RESULTS: In validation, the predicted pullout strengths were 2028.8 N for high-density foam model and 607 N for low-density foam model, respectively. They were in good agreement with those of the published experiment. In the screw-bone model, the simulations demonstrated that the RoE changed with the displacement of screw and reached the maximum when the displacement of screw was 1.8 mm. Similar trend was found for the AIC with the displacement. The proper AIC was 2.6 mL when the displacement of screw was 1.8 mm in this study. CONCLUSIONS: The RoE and proper AIC for augmentation were evaluated in the osteoporotic spine. This information could provide practical reference for screw augmentation in spinal decompression and instrumentation in the spine surgery.

Finite Element Analysis of Head-Neck Kinematics in Rear-End Impact Conditions with Headrest.

A detailed three-dimensional (3D) head-neck (C0-C7) finite element (FE) model was developed and used to dictate the motions of each cervical spinal segment under static physiological loadings of flexion and extension with a magnitude of 1.0 Nm and rear-end impacts. In this dynamic study, a rear-end impact pulse was applied to C7 to create accelerations of 4.5 G and 8.5 G. The predicted segmental motions and displacements of the head were in agreement with published results under physiological loads of 1.0 Nm. Under rear-end impact conditions, the effects of peak pulse acceleration and headrest angles on the kinematic responses of the head-neck complex showed rates of increase/decrease in the rotational motion of various cervical spinal segments that were different in the first 200 ms. The peak flexion rotation of all segments was lower than the combined ROM of flexion and extension. The peak extension rotation of all segments showed variation compared to the combined ROM of flexion and extension depending on G and the headrest angle. A higher acceleration of C7 increased the peak extension angle of lower levels, but the absolute increase was restricted by the distance between the head and the headrest. A change in the headrest angle from 45° to 30° resulted in a change in extension rotation at the lower C5-C6 segments to flexion rotation, which further justified the effectiveness of having distance between the head and the headrest. This study shows that the existing C0-C7 FE model is efficient at defining the gross reactions of the human cervical spine under both physiological static and simulated whiplash circumstances. The fast rate of changes in flexion and extension rotation of various segments may result in associated soft tissues and bony structures experiencing tolerances beyond their material characteristic limits. It is suggested that a proper location and angle of the headrest could effectively prevent the cervical spine from injury in traumatic vehicular accidents.

Effect of Displacement Degree of Distal Chevron Osteotomy on Metatarsal Stress: A Finite Element Method.

BACKGROUND: The stress of foot bone can effectively evaluate the functional damage caused by foot deformity and the results of operation. In this study, the finite element method was used to investigate the degree of displacement of distal chevron osteotomy on metatarsal stress and metatarsophalangeal joint load; Methods: Four finite element models of displacement were established by using the CT images of a patient with moderate hallux valgus (hallux valgus angle and intermetatarsal angle were 26.74° and 14.09°, respectively), and the validity of the model was verified. Each finite element model consisted of bones and various cartilage structures, ligaments, and plantar fascia, as well as encapsulated soft tissue. Except for soft tissue, the material properties of other parts were isotropic linear elastic material, and the encapsulated soft tissue was set as nonlinear hyperelastic material. The mesh was tetrahedral mesh. Link elements were used in ligament and plantar fascia. A ground reaction force with a half-body weight was applied at the bottom of the floor to simulate the ground reaction when standing. The upper surfaces of the encapsulated soft tissue, distal tibia, and distal fibula were fixed. The stress distribution of metatarsals and the stress of cartilage of the first metatarsophalangeal joint were compared and analyzed; Results: Compared with the hallux valgus without osteotomy, the stress of the first metatarsals and second metatarsals of 2-4 mm decreased, and the stress of the interarticular cartilage of the first metatarsophalangeal joint with 4 mm was reduced. In the case of 6 mm, the stress value between the first metatarsal and the first metatarsophalangeal joint increased, and 4 mm was the most suitable distance; Conclusions: Compared with the hallux valgus without osteotomy, the stress of the first metatarsals and second metatarsals of 2-4 mm decreased, and the stress of the interarticular cartilage of the first metatarsophalangeal joint with 4 mm was reduced. In the case of 6 mm, the stress value between the first metatarsal and the first metatarsophalangeal joint increased, and 4 mm was the most suitable distance. For the degree of displacement of the distal chevron osteotomy, the postoperative stability and the stress distribution of metatarsal bone should be considered. Factors such as hallux valgus angle, intermetatarsal angle, patient's age, body weight, and metatarsal width should be considered comprehensively. The factors affecting osteotomy need to be further explored. The degree of displacement of osteotomy can be evaluated by FE method before the operation, and the most suitable distance can be obtained.

Effect of Long-Distance Running on Inter-segment Foot Kinematics and Ground Reaction Forces: A Preliminary Study.

Long-distance running has gained massive popularity in recent years, yet the intra-foot adaptations during this event remain unclear. This study aimed to examine the kinematic and ground reaction force alterations induced within the foot following a 5 and 10 km run using the Oxford Foot Model Ten marathon-experienced recreational runners participated in this study. Five-kilometer running led to more rearfoot dorsiflexion, rearfoot eversion, and rearfoot rotation while less forefoot plantarflexion during the stance phase. Increased rearfoot plantarflexion, while decreased forefoot plantarflexion, supination, adduction, and hallux plantarflexion were observed at 10 km. In addition, the forefoot space of footwear was found to play a role in hallux kinematics. Concerning GRFs, only a lesser propulsive force was presented after a 10 km run. Findings of this study showed that 5 km of running would induce excessive foot motion while 10 km of running may gradually change the foot posture and lead to reduced propulsive forces, which could potentially increase the risks of running-related injuries (RRI) due to overuse or fatigue. Nevertheless, further research is warranted, and this study could be used as a preliminary reference to evaluate and predict foot running-related injuries.

The Effect of Concave-Side Intertransverse Ligament Laxity on the Stress of AIS Lumbar Spine Based on Finite Element Method.

(1) Background: Scoliosis has the mechanical characteristic of asymmetric stress distribution, which is one of the reasons for the aggravation of scoliosis. Bracing therapy is the best treatment for AIS, but it is difficult and costly to operate. Is it possible to reduce pressure in the concave side by relaxing the ITL in the concave side of scoliosis, so as to improve the abnormal stress distribution of scoliosis? In this paper, a finite element method was used to simulate the effect of the relaxation of concave-side ITL on the stress of a lumbar spine with scoliosis, which provides some guidance for the treatment of scoliosis. (2) Methods: Using CT images of a patient with scoliosis whose Cobb Angle was 43° and Lordosis Angle was 45, a scoliosis lumbar was established, and Young's modulus of the ITL of the concave-side lumbar spine was reduced by 95% to simulate ligament relaxation. By comparing the stress condition of the model vertebral body with no ligament relaxation, the effect of concave-side ITL relaxation on the mechanical characteristics of scoliosis lumbar spine was explored. (3) Results: An effective and complete model of the lumbar spine was established. The concave ITL relaxed, which only had a great impact on the bending loads. After the ligament was relaxed, the stability of the spine was reduced. Stress concentration on the concave side of vertebrae and the IVD was aggravated. Under loads on the convex side, the maximum stress on the vertebral body and the IVD increased significantly, making lumbar vertebrae more vulnerable to injury. (4) Conclusions: Laxity of the ITL on the concave side of the AIS lumbar only affects the bending load. Laxity of the concave-side ligament will reduce the stability of the lumbar, aggravate the uneven stress distribution of scoliotic lumbar vertebrae, increase the risk of IVD injury, and be unfavorable for the scoliotic lumbar spine. Relaxation of the concave ITL alone is not an effective way to treat scoliosis.

Intracellular Oxidative Stress Induced by Physical Exercise in Adults: Systematic Review and Meta-Analysis.

A physical exercise program is one of the commonly used methods for improving an individual's antioxidative capacity. However, an inappropriate physical exercise program would induce extra oxidative stress (OS), and the relationship between the details of a physical exercise protocol and the severity of intracellular OS is still unclear. A systematic review and meta-analysis of randomized controlled trials were conducted by searching PubMed, Medline, and Web of Science with the eligibility criteria: (1) participants over 18 years old; (2) physical exercise interventions; (3) 8-hydroxydeoxyguanosine, F2-isoprostanes, and protein carbonyls (PCs) as outcome measures; (4) published in English and peer-reviewed. 12 studies were included, and the data of 8 in them were pooled together. The agreement between authors reached a kappa value of 0.73. The results of the meta-analysis showed that: (1) the level of OS did not depend on the absolute intensity of physical exercise but on both the intensity and the volume of exercise; (2) high-intensity aerobic exercise (HIAE) and a combined protocol of HIAE and resistance training had the highest potential to induce large OS in unhealthy people; (3) the OS induced by moderate-to-high intensity aerobic exercise was significantly larger than that induced by ordinary life activities in healthy adults; (4) high-intensity interval training and moderate-intensity aerobic exercise had the lowest and sub-lowest probabilities to induce high intracellular OS for unhealthy adults. activities induce OS in various tissues in the human body, and the severity of OS depends on many factors of physical exercises as well as the health condition of an individual. A high-intensity and high-volume physical exercise program has the largest possibility of inducing severe OS, while a moderate-intensity aerobic exercise program and a high-intensity interval training program with a relatively low volume might be beneficial to the redox balance for unhealthy individuals. In conclusion, continuous aerobic exercise under moderate-intensity or high-intensity interval training could be recommended to enhance the body's capacity for maintaining redox balance, especially for unhealthy individuals. The PROSPERO Registration Number is CRD42022349687.

The Influence of Heel Height on Strain Variation of Plantar Fascia During High Heel Shoes Walking-Combined Musculoskeletal Modeling and Finite Element Analysis.

The therapeutic benefit of high heel shoes (HHS) for plantar fasciitis treatment is controversial. It has been suggested that plantar fascia strain can be decreased by heel elevation of shoes which helps in body weight redistribution throughout the length of the foot. Yet it is a fact that the repetitive tension caused by HHS wearing resulting in plantar fasciitis is a high-risk disease in HHS individuals who suffer heel and plantar pain. To explore the biomechanical function on plantar fascia under HHS conditions, in this study, musculoskeletal modeling (MsM) and finite element method (FEM) were used to investigate the effect of heel height on strain distribution of plantar fascia. Three-dimensional (3D) and one-dimensional (1D) finite element models of plantar fascia were generated to analyze the computed strain variation in 3-, 5-, and 7-cm heel heights. For validation, the computed foot contact pressure was compared with experimental measurement, and the strain value on 1D fascia was compared with previous studies. Results showed that the peak strain of plantar fascia was progressively increased on both 3D and 1D plantar fascia as heel elevated from 3 to 7 cm, and the maximum strain of plantar fascia occurs near the heel pain site at second peak stance. The 3D fascia model predicted a higher strain magnitude than that of 1D and provided a more reliable strain distribution on the plantar fascia. It is concluded that HHS with narrow heel support could pose a high risk on plantar fasciitis development, rather than reducing symptoms. Therefore, the heel elevation as a treatment recommendation for plantar fasciitis is questionable. Further studies of different heel support structures of shoes to quantify the effectiveness of heel elevation on the load-bearing mechanism of plantar fascia are recommended.

Health View to Decrease Negative Effect of High Heels Wearing: A Systemic Review.

Effective recommendations about how to decrease adverse effects of high heels (HH) need to be provided, since wearing HH is inevitable for most women in their daily life, regardless of their negative impacts on the foot morphology. The main purpose of this systematic review was to summarize studies which have provided specific information about how to effectively offset the negative effects of wearing HH, in the case of women, by means of examining heel height, insole, and heel base support (HBS). Some evidence indicate the following: (i) the range of appropriate heel height for HH shoes is 3.76 cm to 4.47 cm; (ii) compared to small HBS, the larger ones effectively increase gait stability, reduce risk of ankle injury, and improve comfort rating during HH walking; and (iii) the use of a total contact insert (TCI) significantly decreases plantar pressure and the impact on the foot, resulting in higher perceived comfort. It must be noted that these results are based on short-term research; therefore, any conclusions with regard to effects in the long term should be taken with a grain of salt. Nevertheless, future studies should be aimed at combining numerical and experimental methods, in order to provide personal recommendations for HH shoes by considering heel height and HBS size, based on the individual characters (weight, height, and age).

A Mixed Comparisons of Aerobic Training With Different Volumes and Intensities of Physical Exercise in Patients With Hypertension: A Systematic Review and Network Meta-Analysis.

It is essential for patients with hypertension to effectively reduce and maintain appropriate blood pressure levels. As one of the non-pharmacological and invasive methods, physical exercise seems to improve blood pressure of the patients with hypertension. However, different volumes and intensities of physical exercise on the improvement of hypertension are different. To understand the effects of the type of exercise training on blood pressure and the other health status of patients with hypertension, a network meta-analysis was used to compare the mixed effects of different types of exercise training. This systematic review includes all eligible randomized controlled trials of PubMed, Medline, Cochrane Library, and CINAHL. Twelve studies met the inclusion criteria (n = 846 participants at the end of the study). The results show that a medium-intensity training (MIT) is best in improving the blood pressure of patients with hypertension, while a high-volume high-intensity interval training (HVHIIT) is better in reducing body mass and resting heart rate. In addition, the analysis of the exercise capacity shows that HVHIIT has a better effect on the improvement of patients with hypertension. Noticeably, long-term high-volume and appropriate intensity exercise can effectively improve the health status of patients with hypertension. In short, for patients with high blood pressure, MIT seems to be better at lowering blood pressure, while HVHIIT can better improve exercise ability and physical fitness. However, larger randomized controlled trials with a longer duration than those included in this meta-analysis are needed to confirm these results.

A Simulation Analysis of Maternal Pelvic Floor Muscle.

Pelvic floor disorder (PFD) is a common disease affecting the quality of life of middle-aged and elderly women. Pelvic floor muscle (PFM) damage is related to delivery mode, fetal size, and parity. Spontaneous vaginal delivery causes especially great damage to PFM. The purpose of this study was to summarize the characteristics of PFM action during the second stage of labor by collecting female pelvic MRI (magnetic resonance imaging) data and, further, to try to investigate the potential pathogenetic mechanism of PFD. A three-dimensional model was established to study the influence factors and characteristics of PFM strength. In the second stage of labor, the mechanical responses, possible damage, and the key parts of postpartum lesions of PFM due to the different fetal biparietal diameter (BPD) sizes were analyzed by finite element simulations. The research results showed that the peak stress and strain of PFM appeared at one-half of the delivery period and at the attachment point of the pubococcygeus to the skeleton. In addition, during the simulation process, the pubococcygeus was stretched by about 1.2 times and the levator ani muscle was stretched by more than two-fold. There was also greater stress and strain in the middle area of the levator ani muscle and pubococcygeus. According to the statistics, either being too young or in old maternal age will increase the probability of postpartum PFM injury. During delivery, the entire PFM underwent the huge deformation, in which the levator ani muscle and the pubococcygeus were seriously stretched and the attachment point between the pubococcygeus and the skeleton were the places with the highest probability of postpartum lesions.

Current Evidence on Traditional Chinese Exercise for Cancers: A Systematic Review of Randomized Controlled Trials.

Traditional Chinese exercise (TCE) has gradually become one of the widespread complementary therapies for treatment and recovery of cancers. However, evidence based on the systematic evaluation of its efficacy is lacking, and there appears to be no conclusion regarding the setting of TCE interventions. The purpose of this systematic review is to summarize the current randomized controlled trials (RCTs) that outline the effects of TCE on cancer patients. Relevant studies were searched by GOOGLE SCHOLAR, SCIENCEDIRECT, and WEB OF SCIENCE using "traditional Chinese exercise" and "cancer." Only RCTs published in peer-reviewed English journals were included. A total of 27 studies covering 1616 cancer patients satisfied the eligibility criteria for this review. Despite the methodological limitation and relatively high risk of bias possessed by some included studies, positive evidence was still detected on the effects of TCE on these cancer-related health outcomes in physical, psychological, and physiological parameters. The 60-min or 90-min course of TCE intervention for two to three times per week for 10 to 12 weeks was found to be the most common setting in these studies and has effectively benefited cancer patients. These findings add scientific support to encourage cancer patients to practice TCE during or after conventional medical treatment. Nevertheless, future well-designed RCTs with improved methodology and larger sample size on this field are much warranted for further verification.

Finite element application in implant research for treatment of lumbar degenerative disc disease.

Surgical treatment for disc degeneration can be roughly grouped as fusion, disc replacement and dynamic stabilization. The clinical efficacy and biomechanical features of the implants used for disc degenerations can be evaluated through short- or long-term follow up observation, in vitro and in vivo experiments and computational simulations. Finite element models are already making an important contribution to our understanding of the spine and its components. Models are being used to reveal the biomechanical function of the spine and its behavior when healthy, diseased or damaged. They are also providing support in the design and application of spinal instrumentation. The article reviewed the most recent studies in the application of FE models that address the issue of implant research for treatment of low back pain. The published studies were grouped and reviewed thoroughly based on the function of implants investigated. The considerations of the finite element analysis in these studies were further discussed.

Finite element analysis of head-neck kinematics under simulated rear impact at different accelerations.

The information on the variation of ligament strains over time after rear impact has been seldom investigated. In the current study, a detailed three-dimensional C0-C7 finite element model of the whole head-neck complex developed previously was modified to include T1 vertebra. Rear impact of half sine-pulses with peak values of 3.5g, 5g, 6.5g and 8g respectively were applied to the inferior surface of the T1 vertebral body to validate the simulated variations of the intervertebral segmental rotations and to investigate the ligament tensions of the cervical spine under different levels of accelerations. The simulated kinematics of the head-neck complex showed relatively good agreement with the experimental data with most of the predicted peak values falling within one standard deviation of the experimental data. Under rear impact, the whole C0-T1 structure formed an S-shaped curvature with flexion at the upper levels and extension at the lower levels at early stage after impact, during which the lower cervical levels might experience hyperextensions. The predicted high resultant strain of the capsular ligaments, even at low impact acceleration compared with other ligament groups, suggests their susceptibility to injury. The peak impact acceleration has a significant effect on the potential injury of ligaments. Under higher accelerations, most ligaments will reach failure strain in a much shorter time immediately after impact.

A numerical study of the effect of axial acceleration on the responses of the cervical spine during low-speed rear-end impact.

A detailed, three-dimensional, head-neck (vertebral segments CO to C7) finite element model - developed and validated previously on the basis of the actual geometry of a cadaveric specimen - was used to evaluate the effect of cranial acceleration on the response of the cervical spine during low-speed, rear-end impact. Analyses were carried out to compare the predicted overall and segmental rotations, peak disc stresses, and capsular ligament strains of each motion segment during whiplash with or without cranial acceleration applied on the C7 inferior surface. The results show that, in the first 150 ms, the variation curves of predicted segmental rotational angles, disc stresses, and capsular strains for each motion segment overlapped well under the two conditions. However, after 150 ms, the capsular strains of C2 to C6 without cranial acceleration applied on C7 were all obviously lower than those with cranial acceleration applied, but the segmental rotational angles and disc stresses remain unaffected. It was implied that, although without cranial acceleration applied on C7, the relatively simple head-neck model could be used to reflect effectively the biomechanical response of the cervical spine during the initial stage (i.e. 150 ms) under low-speed, rear-end impact as well as the whole-human-body dummy model.

Application of Taguchi method in optimization of cervical ring cage.

The Taguchi method is a statistical approach to overcome the limitation of the factorial and fractional factorial experiments by simplifying and standardizing the fractional factorial design. The objective of the current study is to illustrate the procedures and strengths of the Taguchi method in biomechanical analysis by using a case study of a cervical ring cage optimization. A three-dimensional finite element (FE) model of C(5)-C(6) with a generic cervical ring cage inserted was modelled. Taguchi method was applied in the optimization of the cervical ring cage in material property and dimensions for producing the lowest stress on the endplate to reduce the risk of cage subsidence, as in the following steps: (1) establishment of objective function; (2) determination of controllable factors and their levels; (3) identification of uncontrollable factors and test conditions; (4) design of Taguchi crossed array layout; (5) execution of experiments according to trial conditions; (6) analysis of results; (7) determination of optimal run; (8) confirmation of optimum run. The results showed that a cage with larger width, depth and wall thickness can produce the lower von Mises stress under various conditions. The contribution of implant materials is found trivial. The current case study illustrates that the strengths of the Taguchi method lie in (1) consistency in experimental design and analysis; (2) reduction of time and cost of experiments; (3) robustness of performance with removing the noise factors. The Taguchi method will have a great potential application in biomechanical field when factors of the issues are at discrete level.

Finite element analysis of head-neck kinematics during motor vehicle accidents: analysis in multiple planes.

In this study, a detailed three-dimensional head-neck (C0-C7) finite element (FE) model developed previously based on the actual geometry of a human cadaver specimen was used. Five simulation analyses were performed to investigate the kinematic responses of the head-neck complex under rear-end, front, side, rear- and front-side impacts. Under rear-end and front impacts, it was predicted that the global and intervertebral rotations of the head-neck in the sagittal plane displayed nearly symmetric curvatures about the frontal plane. The primary sagittal rotational angles of the neck under direct front and rear-end impact conditions were higher than the primary frontal rotational angles under other side impact conditions. The analysis predicted early S-shaped and subsequent C-shaped curvatures of the head-neck complex in the sagittal plane under front and rear-end impact, and in the frontal plane under side impact. The head-neck complex flexed laterally in one direction with peak magnitude of larger than 22 degrees and a duration of about 130 ms before flexing in the opposite direction under both side and rear-side impact, compared to the corresponding values of about 15 degrees and 105 ms under front-side impact. The C0-C7 FE model has reasonably predicted the effects of impact direction in the primary sagittal and frontal segmental motion and curvatures of the head-neck complex under various impact conditions.

Finite element analysis of moment-rotation relationships for human cervical spine.

A comprehensive, geometrically accurate, nonlinear C0-C7 FE model of head and cervical spine based on the actual geometry of a human cadaver specimen was developed. The motions of each cervical vertebral level under pure moment loading of 1.0 Nm applied incrementally on the skull to simulate the movements of the head and cervical spine under flexion, tension, axial rotation and lateral bending with the inferior surface of the C7 vertebral body fully constrained were analysed. The predicted range of motion (ROM) for each motion segment were computed and compared with published experimental data. The model predicted the nonlinear moment-rotation relationship of human cervical spine. Under the same loading magnitude, the model predicted the largest rotation in extension, followed by flexion and axial rotation, and least ROM in lateral bending. The upper cervical spines are more flexible than the lower cervical levels. The motions of the two uppermost motion segments account for half (or even higher) of the whole cervical spine motion under rotational loadings. The differences in the ROMs among the lower cervical spines (C3-C7) were relatively small. The FE predicted segmental motions effectively reflect the behavior of human cervical spine and were in agreement with the experimental data. The C0-C7 FE model offers potentials for biomedical and injury studies.

Effect of bilateral facetectomy of thoracolumbar spine T11-L1 on spinal stability.

Spinal stenosis can be found in any part of the spine, though it is most commonly located on the lumbar and cervical areas. It has been documented in the literature that bilateral facetectomy in a lumbar motion segment to increase the space induces an increase in flexibility at the level at which the surgery was performed. However, the result of bilateral facetectomy on the stability of the thoracolumbar spine has not been studied. A nonlinear three-dimensional finite element (FE) model of thoracolumbar T11-L1 was built to explore the influence of bilateral facetectomy. The FE model of T11-L1 was validated against published experimental results under various physiological loadings. The FE model with bilateral facetectomy was evaluated under flexion, extension, lateral bending and axial rotation to determine alterations in kinematics. Results show that bilateral facetectomy causes increase in motion, considerable increase in axial rotation and least increase in lateral bending. Removal of facets did not result in significant change in the sagittal motion in flexion and extension.