The incidence of adjacent segment degeneration (ASD) after lumbar spinal fusion have not been precisely verified. In the presence of mild degeneration in the proximal segment adjacent to the fused segment, selection of additional fusion is not agreed upon. Muscle activity change and ASD after fusion was analyzed with a developed three-dimensional finite element model of musculoskeletal system. The paraspinal muscle activities were calculated based on a hypothesis, the intervertebral disc was assumed to have a transducer function and the muscle is activated according to a sensor driven control mechanism to maintain the stability of the lumbar spine. Simulation was conducted for erect standing and 60° isometric forward flexed posture. Total muscle force produced in each deep muscle group was similar however activity of some muscle fascicles which inter-connected to the vertebrae above the fused segment showed increased value. In the presence of mild degeneration in the proximal adjacent segment, muscle activity across the degenerated segment was reduced. Despite changes in muscle activity, nucleus pressure at adjacent segment was increased in both cases. This change would eventually lead to the ASD.

Spinal stability is controlled by two interrelated systems: the spinal column including ligaments and the muscular control system. In addition to these systems, the thoracolumbar fascia (TLF) also interacts with the muscular system to maintain the stability of the spine. The effects of the tensioning of TLF on the spinal stability was investigated using computational analysis. The stability of the spine was analyzed with a three-dimensional finite element model of musculoskeletal system including TLF. The paraspinal muscle activities were calculated based on a hypothesis: the intervertebral disc was assumed to have a transducer function and the muscle is activated according to a sensor driven control mechanism to maintain stability of the lumbar spine. Muscle forces were calculated in examining 40o isometric forward flexed and erect standing postures. As a result, the fascial tension induced a decrease in superficial muscle activity while maintaining the spinal stability.

In this study, modal analysis and equivalent static load analysis for valve supports of 26" gas piping in gas stations were conducted and the existing straight and inclined types of valve supports were compared using seismic performance testing. Also, a new valve support shape was suggested by optimizing position of fastener holes, width and thickness of the support, and size of bracket. Improvement in seismic performance by design optimization was verified through equivalent static load analysis. The seismic performance of the newly proposed valve support was greatly improved and the maximum displacement and maximum stress of the seismic load was about 20% lower than those of the existing valve support.

Recently, we have proposed a hypothesis that spinal structures have a stress sensor driving feedback mechanism. In the human spine, spinal structure could react to modify muscular action in such a way so as to equalize stress at the disc, therefore reduce the risk of injury. In this analysis, abdominal muscle and abdominal pressure, which were not included in the previous study, were added to identify those effects in spine stability during upright stance posture for the case where the intervertebral disc plays the role of mechanoreceptor. The musculoskeletal FE model was consisted with detailed whole lumbar spine, pelvis, sacrum, coccyx and simplified trunk model. Muscle architecture with 46 local muscles containing paraspinal muscle and 6 rectus abdominal muscles were assigned according to the acting directions. The magnitude of 4㎪ was considered for abdominal pressure. Minimization of the nucleus pressure deviation and annulus fiber average tension stress deviation was chosen for cost function. Developed model provide nice coincidence with in-vivo measurement (nucleus pressure). Analysis was conducted according to existence of co-activation of abdominal muscle and abdominal pressure. Antagonistic activity of abdominal muscle produced stability of spinal column with relatively small amount of total muscle force. In contrast to the abdominal muscle, effect of abdominal pressure was not clear that was partly depending on the assumption of constant abdominal pressure.

For stability analysis of the lumbar spine, the hypothesis presented is that the disc has stress sensors driving feedback mechanism, which could react to the imposed loads by adjusting the contraction of the muscles. Fusion in the motion segment of the lumbar spinal column is believed to alter the stability of the spinal column. To identify this effect finite element (FE) models combined with optimization technique was applied and quantify the role of each muscle and reaction forces in the spinal column with respect to the fusion level. The musculoskeletal FE model was consisted with detailed whole lumbar spine, pelvis, sacrum, coccyx and simplified trunk model. Vertebral body and pelvis were modeled as a rigid body and the rib cage was constructed with rigid truss element for the computational efficiency. Spinal fusion model was applied to L3-L4, L4-L5, L5-S1 (single level) and L3-L5 (two levels) segments. Muscle architecture with 46 local muscles was used as acting directions. Minimization of the nucleus pressure deviation and annulus fiber average axial stress deviation was selected for cost function. As a result, spinal fusion produced reaction changes at each motion segment as well as contribution of each muscle. Longissimus thoracis and psoas major muscle showed dramatic changes for the cases of L5-S1 and L3-L5 level fusion. Muscle force change at each muscle also generated relatively high nucleus pressure not only at the adjacent level but at another level, which can explain disc degeneration pattern observed in clinical study.

In this study, lower extremity joint kinematics and kinetics and lumbar lordosis were investigated for two different symmetrical lifting techniques(squat and stoop) using the three-dimensional motion analysis. Twenty-six male volunteers lifted boxes weighing 5, 10 and 15㎏ by both squat and stoop lifting techniques. There were not significant differences in maximum lumbar joint moments between the two techniques. The hip and ankle contributed the most part of the support moment during squat lifting, and the knee flexion moment played an important role in stoop lifting. The hip, ankle and lumbar joints generated power and only the knee joint absorbed power in the squat lifting. The knee and ankle joints absorbed power, the hip and lumbar joints generated power in the stoop lifting. The bi-articular antagonist muscles' co-contraction around the knee joint during the squat lifting and the eccentric co-contraction of the gastrocnemius and semitendinosus were found to be important for straightening up during the stoop lifting. At the time of lordotic curvature appearance in the squat lifting, there were significant correlations in all three lower extremity joint moments with the lumbar joint. Differently, only the hip moment had significant correlation with the lumbar joint in the stoop lifting. In conclusion, the knee extension which is prominent kinematics during the squat lifting was produced by the contributions of the kinetic factors from the hip and ankle joints(extensor moment and power generation) and the lumbar extension which is prominent kinematics during the stoop lifting could be produced by the contributions of the knee joint kinetic factors(flexor moment, power absorption, bi-articular muscle function).

To investigate the bone remodeling phenomenon around implant device, 3-D mathematical simulation model was developed. Strain energy density from the finite element method was chosen for the indicator for remodeling process. Recursive calculations continued until converged results between FEM and mathematical model. For a osteo-integration example, bone-remodeling process in a implanted tibia of beagle was adapted. Calculated results indicated that the bone densities around screw pitch were increased which indicates firm fixations between the bone and implant. Screw design parameters have an influence on initial stability of the implant rather than remodeling process.

Although several artificial disc designs have been developed for the treatment of discogenic low back pain, biomechanical changes with its implantation were rarely studied. To evaluate the effect of artificial disc implantation on the biomechanics of functional spinal unit, a nonlinear three-dimensional finite element model of L4-L5 was developed with 1-mm CT scan data. Biomechanical analysis was performed for two different types of artificial disc having constrained and unconstrained instant center of rotation(ICR), ProDisc and SB Charite III model. The implanted model predictions were compared with that of intact model. Angular motion of vertebral body, forces on the spinal ligaments and facet joint, and stress distribution of vertebral endplate for flexion-extension, lateral bending, and axial rotation with a compressive preload of 400 N were compared. The implanted model showed increased flexion-extension range of motion compared to that of intact model. Under 6Nm moment, the range of motion were 140%, 170% and 200% of intact in SB Charite III model and 133%, 137%, and 138% in ProDisc model. The increased stress distribution on vertebral endplate for implanted cases could be able to explain the heterotopic ossification around vertebral body in clinical observation. As a result of this study, it is obvious that implanted segment with artificial disc suffers from increased motion and stress that can result in accelerated degenerated change of surrounding structure. Unconstrained ICR model showed increased in motion but less stress in the implanted segment than constrained model.

Unexpected postoperative changes, such as growth in rib hump and shoulder unbalance, have been occasionally reported after corrective surgery for scoliosis. However there has been neither experimental data for explanation of these changes, nor the suggestion of optimal correction method. Therefore, the numerical study was designed to investigate the post-operative changes of vertebral rotation and rib cage deformation after the corrective surgery of scoliosis. A mathematical finite element model of normal spine including rib cage, sternum, both clavicles, and pelvis was developed with anatomical details. In this study, we also developed a special program which could convert a normal spine model to a desired scoliotic spine model automatically. A personalized skeletal deformity of scoliosis model was reconstructed with X-ray images of a scoliosis patient from the normal spine structures and rib cage model. The geometric mapping was performed by translating and rotating the spinal column with an amount analyzed from the digitized 12 built-in coordinate axes in each vertebral image. By utilizing this program, problems generated in mapping procedure such as facet joint overlapping, vertebral body deformity could be automatically resolved.

Scoliosis is a complex musculoskeletal dieses requiring 3-D treatment with surgical instrumentation. To investigate the effects of correction surgery, a finite element model of personalized model of the scoliotic spine that will allow the design of clinical test providing optimal estimation of the post-operation results was developed. Three dimensional skeletal parts, such as vertebrae, clavicle and scapular were modeled as rigid bodies with keeping their morphologies. Kinematical joints and spring elements were adapted to represent the inter-vertebral disc and ligaments respectively. With this model, two types of surgery procedure, distraction procedure with Harrington device and rod derotation procedure with pedicle screw and rod system had been carried out. The obtained simulation results were comparatively corresponding to the post operational outcomes and successfully demonstrated qualitative analysis of surgical effectiveness. From this analysis, it has been found that the preparing of appropriate rod curvature and its insertion was more important than just performing the excessive derotation for scoliosis correction.