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Study design A biomechanical comparison among the intact C2 to C7 segments, the C5 to C6 segments implanted with fusion cage, and three different artificial disc replacements (ADRs) by finite element (FE) model creation reflecting the entire cervical spine below C2. Objective The aim of this study was to analyze the biomechanical changes in subaxial cervical spine after ADR and to verify the efficacy of a new mobile core artificial disc Baguera C that is designed to absorb shock. Summary of background data Scarce references could be found and compared regarding the cervical ADR devices' biomechanical differences that are consequently related to their different clinical results. Methods One fusion device (CJ cage system, WINNOVA) and three different cervical artificial discs (Prodisc-C Nova (DePuy Synthes), Discocerv (Scient'x/Alphatec), Baguera C (Spineart)) were inserted at C5-6 disc space inside the FE model and analyzed. Hybrid loading conditions, under bending moments of 1 Nm along flexion, extension, lateral bending, and axial rotation with a compressive force of 50 N along the follower loading direction, were used in this study. Biomechanical behaviors such as segmental mobility, facet joint forces, and possible wear debris phenomenon inside the core were investigated. Results The segmental motions as well as facet joint forces were exaggerated after ADR regardless of type of the devices. The Baguera C mimicked the intact cervical spine regarding the location of the center of rotation only during the flexion moment. It also showed a relatively wider distribution of the contact area and significantly lower contact pressure distribution on the core than the other two devices. A "lift off" phenomenon was noted for other two devices according to the specific loading condition. Conclusion The mobile core artificial disc Baguera C can be considered biomechanically superior to other devices by demonstrating no "lift off" phenomenon, and significantly lower contact pressure distribution on core. Level of evidence N/A.

In this study, the effects of medial collateral ligament (MCL) release and the limb correction strategies with pre-existing MCL laxity on tibiofemoral contact force distribution after high tibial osteotomy (HTO) were investigated. The medial and lateral contact forces of the knee were quantified during simulated standing using computational modeling techniques. MCL slackness had a primary influence on contact force distribution of the knee, while there was little effect of simulated limb correction. Anterior and middle bundle release, which involved the partial release of two-thirds of the superficial MCL, was shown to be an optimal surgical method in HTO, achieving balanced contact distribution in simulated weight-bearing standing.

The development of heterotopic ossification (HO) is considered one of the major complications following cervical total disc replacement (TDR). Even though previous studies have identified clinical and biomechanical conditions that may stimulate HO, the mechanism of HO formation has not been fully elucidated. The objective of this study is to investigate whether mechanical loading is a biomechanical condition that plays a substantial role to decide the HO formation. A finite element model of TDR on the C5-C6 was developed, and HO formation was predicted by simulating a bone adaptation process under various physiological mechanical loadings. The distributions of strain energy on vertebrae were assessed after HO formation. For the compressive force, most of the HO formation occurred on the vertebral endplates uncovered by the implant footplate which was similar to the Type 1 HO. For the anteriorly directed shear force, the HO was predominantly formed in the anterior parts of both the upper and lower vertebrae as the Type 2 HO. For both the flexion and extension moments, the HO shapes were similar to those for the shear force. The total strain energy was reduced after HO formation for all loading conditions. Two distinct types of HO were predicted based on mechanically induced bone adaptation processes, and our findings were consistent with those of previous clinical studies. HO formation might have a role in compensating for the non-uniform strain energy distribution which is one of the mechanical parameters related to the bone remodeling after cervical TDR.

Many clinical case series have reported the predisposing factors for C5 palsy and have presented comparisons of the two types of laminoplasty. However, there have been no biomechanical studies focusing on cervical spinal cord and nerve root following laminoplasty. The purpose of this study is to investigate biomechanical changes in the spinal cord and nerve roots following the two most common types of laminoplasty, open-door and double-door laminoplasty, for cervical ossification of the posterior longitudinal ligament (OPLL). A finite element (FE) model of the cervical spine and spinal cord with nerve root complex structures was developed. Stress changes in the spinal cord and nerve roots, posterior shift of the spinal cord, and displacement of the cervical nerve roots were analyzed with two types of cervical laminoplasty models for variations in the degree of canal occupying ratio and shape of the OPLL. The shape and degree of spinal cord compression caused by the OPLL had more influence on the changes in stress, posterior shift of the spinal cord, and displacement of the nerve root than the type of laminoplasty. The lateral-type OPLL resulted in imbalanced stress on the nerve roots and the highest nerve root displacement. Type of laminoplasty and shape and degree of spinal cord compression caused by OPLL were found to influence the changes in stress and posterior displacement of the cervical spinal cord and nerve roots. Lateral-type OPLL might contribute to the development of C5 palsy due to the imbalanced stress and tension on the nerve roots after laminoplasty.

Biomechanical studies have indicated that the conventional nonanatomic reconstruction techniques for lateral ankle sprain (LAS) tend to restrict subtalar joint motion compared to intact ankle joints. Excessive restriction in subtalar motion may lead to chronic pain, functional difficulties, and development of osteoarthritis (OA). Therefore, various anatomic surgical techniques to reconstruct both the anterior talofibular and calcaneofibular ligaments (CaFL) have been introduced. In this study, ankle joint stability was evaluated using multibody computational ankle joint model to assess two new anatomic reconstruction and three popular nonanatomic reconstruction techniques. An LAS injury, three popular nonanatomic reconstruction models (Watson-Jones, Evans, and Chrisman–Snook) and two common types of anatomic reconstruction models were developed based on the intact ankle model. The stability of ankle in both talocrural and subtalar joint were evaluated under anterior drawer test (150 N anterior force), inversion test (3 N·m inversion moment), internal rotational test (3 N·m internal rotation moment), and the combined loading test (9 N·m inversion and internal moment as well as 1800 N compressive force). Our overall results show that the two anatomic reconstruction techniques were superior to the nonanatomic reconstruction techniques in stabilizing both talocrural and subtalar joints. Restricted subtalar joint motion, which is mainly observed in Watson-Jones and Chrisman–Snook techniques, was not shown in the anatomical reconstructions. Evans technique was beneficial for subtalar joint as it does not restrict subtalar motion, though Evans technique was insufficient for restoring talocrural joint inversion. The anatomical reconstruction techniques best recovered ankle stability.

Several experimental and computational studies have investigated the effect of bone fragment impact on the spinal cord during trauma. However, the effect of the impact velocity of a fragment generated by a burst fracture on the stress and strain inside the spinal cord has not been computationally investigated, even though spinal canal occlusion and peak pressure at various impact velocities were provided in experimental studies. These stresses and strains are known factors related to clinical symptoms or injuries. In this study, a fluid-structure interaction model of the spinal cord, dura mater, and cerebrospinal fluid was developed and validated. The von-Mises stress distribution in the cord, the longitudinal strain, the cord compression and cross-sectional area at the impact center, and the obliteration of the cerebrospinal fluid layer were analyzed for three pellet sizes at impact velocities ranging from 1.5 m/s to 7.5 m/s. The results indicate that stress in the cord was substantially elevated when the initial impact velocity of the pellet exceeded a threshold of 4.5 m/s. Cord compression, reduction in cross-sectional area, and obliteration of the cerebrospinal fluid increased gradually as the velocity of the pellet increased, regardless of the size of the pellet. The present study provides insight into the mechanisms underlying spinal cord injury.

The current study was performed to evaluate a dynamic multibody model developed to characterize the influence of tibial tuberosity realignment procedures on patellofemoral motion and loading. Computational models were created to represent four knees previously tested at 40°, 60° and 80° of flexion with the tibial tuberosity in a lateral, medial and anteromedial position. The experimentally loaded muscles, major ligaments of the knee, and patellar tendon were represented. A repeated measures ANOVA with post-hoc testing was performed at each flexion angle to compare data between the three positions of the tibial tuberosity. Significant experimental trends for decreased patella flexion due to tuberosity anteriorization and a decrease in the lateral contact force due to tuberosity medialization were reproduced computationally. The dynamic multibody modeling technique will allow simulation of function for symptomatic knees to identify optimal surgical treatment methods based on parameters related to knee pathology and pre-operative kinematics.

The development of a biomaterial substitute that can promote bone regeneration in massive defects has remained as a significant clinical challenge even using bone marrow cells or growth factors. Without an active, thriving cell population present throughout and stable anchored to the construct, exceptional bone regeneration does not occur. An engineered micro-channel structures scaffold within each trabecular has been designed to overcome some current limitations involving the cultivation and habitation of cells in large, volumetric scaffolds to repair massive skeletal defect. We created a scaffold with a superior fluid retention capacity that also may absorb bone marrow cells and provide growth factor-containing body fluids such as blood clots and/or serum under physiological conditions. The scaffold is composed of 3 basic structures (1) porous trabecular network (300-400 μm) similar to that of human trabecular bones, (2) micro-size channels (25-70 μm) within each trabecular septum which mimic intra-osseous channels such as Haversian canals and Volkmann's canals with body fluid access, diffusion, nutritional supply and gas exchange, and (3) nano-size pores (100-400 nm) on the surface of each septum that allow immobilized cells to anchor. Combinatorial effects of these internal structures result in a host-adapting construct that enhances cell retention and habitation throughout the 3 cm-height and 4 cm-length bridge-shaped scaffold.

Knowledge of in vivo human lumbar loading is critical for understanding the lumbar function and for improving surgical treatments of lumbar pathology. Although numerous experimental measurements and computational simulations have been reported, non-invasive determination of in vivo spinal disc loads is still a challenge in biomedical engineering. The object of the study is to investigate the in vivo human lumbar disc loads using a subject-specific and kinematic driven finite element approach.Three dimensional lumbar spine models of three living subjects were created using MR images. Finite element model of the L3-4 disc was built for each subject. The endplate kinematics of the L3-4 segment of each subject during a dynamic weight lifting extension was determined using a dual fluoroscopic imaging technique. The endplate kinematics was used as displacement boundary conditions to calculate the in-vivo disc forces and moments during the weight lifting activity.During the weight lifting extension, the L3-4 disc experienced maximum shear load of about 230 N or 0.34 bodyweight at the flexion position and maximum compressive load of 1500 N or 2.28 bodyweight at the upright position. The disc experienced a primary flexion-extension moment during the motion which reached a maximum of 4.2 Nm at upright position with stretched arms holding the weight.This study provided quantitative data on in vivo disc loading that could help understand intrinsic biomechanics of the spine and improve surgical treatment of pathological discs using fusion or arthroplasty techniques.

Evaluation of the loads on lumbar intervertebral discs (IVD) is critically important since it is closely related to spine biomechanics, pathology and prosthesis design. Non-invasive estimation of the loads in the discs remains a challenge. In this study, we proposed a new technique to estimate in vivo loads in the IVD using a subject-specific finite element (FE) model of the disc and the kinematics of the disc endplates as input boundary conditions. The technique was validated by comparing the forces and moments in the discs calculated from the FE analyses to the in vitro experiment measurements of three corresponding lumbar discs. The results showed that the forces and moments could be estimated within an average error of 20%. Therefore, this technique can be a promising tool for non-invasive estimation of the loads in the discs and may be extended to be used on living subjects.

In this study, a multibody dynamic model of the cervical spine was developed for a virtual in-vitro cadaveric experiment. The dynamic cervical spine model was reconstructed based on Korean CT images and the material properties of joints and soft tissue obtained from in-vitro experimental literature. The model was validated by comparing the inter-segmental rotation, multi-segmental rotations, load-displacement behavior, ligament force, and facet contact force with the published in-vitro experimental data. The results from the model were similar to published experimental data. The developed dynamic model of the cervical spine can be useful for injury analysis to predict the loads and deformations of the individual soft-tissue elements as well as for virtual in-vitro cadaveric experiments.

We have developed a hydroxyapatite-based scaffold with micro-channels and nano-pores (MCNP) using a polyurethane template coating method to overcome some of the limitations by addressing fluid absorbance and retention via capillary action. The novel scaffold has 3 basic structures. First, the scaffold has a porous trabecular network similar to that of human trabecular bones (300–400 um) which are mechanically matched to the strength of native trabecular bone (2–12 MPa). Second, it has micro-sized channels (25–70 um) within each trabecular septum which exhibit highly effective fluid absorption via capillary action. Third, the surface of each septum has nano-sized pores (100–400 nm) that allow immobilized cells to anchor. The surface area of the scaffold with micro-channels was significantly (+42.0%) higher than the scaffold without micro-channels as calculated using computer aided design (CAD) software, while overall porosity did not change significantly (+8.8%). Combinatorial effects of these internal structures result in a host-adapting construct that enhances cell ingress and retention from the host bone marrow throughout the entire scaffold.

Unbalanced contact force on the tibial component has been considered a factor leading to loosening of the implant and increased wear of the bearing surface in total knee arthroplasty. Because it has been reported that good alignment cannot guarantee successful clinical outcomes, the soft tissue balance should be checked together with the alignment. Finite element models of patients' lower extremities were developed to analyse the medial and lateral contact force distribution on the tibial insert. The distributions for four out of five patients were not balanced equally, even though the alignment angles were within a clinically acceptable range. Moreover, the distribution was improved by changing soft tissue release and ligament tightening for the specific case. Integration of the biomechanical modelling, image matching and finite element analysis techniques with the patient-specific properties and various dynamic loading would suggest a clinically relevant pre-operative planning for soft tissue balancing.

The consideration of biomechanical alterations due to intervertebral disc (IVD) degeneration is crucial for the accurate analysis of spine biomechanics. In this study, finite element (FE) models of the L4-L5 motion segment with full coverage of the degeneration grades from healthy IVD to severe degeneration were developed. The effects of IVD degeneration on spine biomechanics were analyzed under physiological loading conditions using compressive forces and bending moments. The FE models of all degeneration grades were consistent with published data in terms of the ranges of motion. Severe IVD degeneration showed lower inter-segmental rotations in flexion-extension and lateral bending, lower intradiscal pressure in all motions, higher facet joint forces in lateral bending and axial rotation, and higher von-Mises stress in annulus ground substance in all motions versus the healthy IVD. These findings could provide fundamental information for understanding the characteristics of the biomechanical behaviors of degenerated lumbar motion segments.

Post-operative C5palsies are among the most common complications seen after cervical surgery for ossification of the posterior longitudinal ligament (OPLL). Although C5 palsy is a well-known complication of cervical spine surgery, its pathogenesis is poorly understood and depends on many other factors. In this study, a finite element model of the cervical spine and spinal cord-nerve roots complex structures was developed. The changes in stress in the cord and nerve roots, posterior shift of the spinal cord, and displacement and elongation of the nerve roots after laminectomy for cervical OPLL were analyzed for three different cervical sagittal alignments (lordosis, straight, and kyphosis). The results suggest that high stress concentrated on the nerve roots after laminectomy could be the main cause of C5 palsy because ossification of ligaments increases spinal cord shifting and root displacement. The type of sagittal alignment had no influence on changes in cord stress after laminectomy, although cases of kyphosis with a high degree of occupying ratio resulted in greater increases in nerve root stress after laminectomy. Therefore, kyphosis with a high OPLL occupying ratio could be a risk factor for poor surgical outcomes or post-operative complications and should be carefully considered for surgical treatment.

A golf-related ACL injury can be linked with excessive golf play or practice because such over-use by repetitive golf swing motions can increase damage accumulation to the ACL bundles. In this study, joint angular rotations, forces, and moments, as well as the forces and strains on the ACL of the target-side knee joint, were investigated for ten professional golfers using the multi-body lower extremity model. The fatigue life of the ACL was also predicted by assuming the estimated ACL force as a cyclic load. The ACL force and strain reached their maximum values within a short time just after ball-impact in the follow-through phase. The smaller knee flexion, higher internal tibial rotation, increase of the joint compressive force and knee abduction moment in the follow-through phase were shown as to lead an increased ACL loading. The number of cycles to fatigue failure (fatigue life) in the ACL might be several thousands. It is suggested that the excessive training or practice of swing motion without enough rest may be one of factors to lead to damage or injury in the ACL by the fatigue failure. The present technology can provide fundamental information to understand and prevent the ACL injury for golf players.

Individuals with lower extremity amputation must adapt the mechanical interactions between the feet and ground to account for musculoskeletal function loss. However, it is currently unknown how individuals with amputation modulate three-dimensional ground reaction forces (GRFs) when running. This study aimed to understand how running with running-specific prostheses influences three-dimensional support forces from the ground. Eight individuals with unilateral transtibial amputations and 8 control subjects ran overground at 2.5, 3.0, and 3.5 m/s. Ten force plates measured GRFs at 1000 Hz. Peak and average GRFs and impulses in each plane were compared between limbs and groups. Prosthetic limbs generated reduced vertical impulses, braking forces and impulses, and mediolateral forces while generating similar propulsive impulses compared with intact and control limbs. Intact limbs generated greater peak and average vertical forces and average braking forces than control subjects’ limbs. These data indicate that the nonamputated limb experiences elevated mechanical loading compared with prosthetic and control limbs. This may place individuals with amputation at greater risk of acute injury or joint degeneration in their intact limb. Individuals with amputation adapted to running-specific prosthesis force production limitations by generating longer periods of positive impulse thus producing propulsive impulses equivalent to intact and control limbs.

We have developed the computer-aided and robot-assisted system for anterior cruciate ligament (ACL) reconstruction surgery. The surgical robot system includes the pre-planning module, registration and navigation module and automatic tunnel drilling module. The sawbone experiments were performed for both of single-bundle and double-bundle ACL reconstruction surgery. The experimental results were compared with the planning results in terms of the position and angle accuracies, and safety angles. The experiment accuracies were in clinically acceptable range. The developed surgical robot system would be further investigated by performing cadaver studies for future clinical trials.

Recently, commercially available computer-aided surgical robot systems have been introduced to enable surgeons to improve the accuracy of cutting and alignment in total knee arthroplasty (TKA). The minimal invasive surgery (MIS) in the TKA has been increased since MIS can improve the surgical outcomes such as the recovery time and hospital stay by reducing the incision in surgery. However, current surgical robot systems do not provide the MIS TKA capability. In this study, we developed a laboratory-level surgical robot system to cut the bone from the lateral direction of the knee joint to provide MIS TKA. TKA experiments with saw bones of femur were compared between the conventional approach and the MIS approach. The incision length for the working space of the cutting tool and bone cutting time were decreased in lateral direction bone cutting. In addition, the cutting surface was smoother and the ranges of motion of all six joints were decreased in lateral direction bone cutting. Moreover, the cutting accuracy in terms of the lengths and angles of five cutting planes in femur were smaller in lateral approach than those in conventional approach. Therefore, consideration of bone cutting from the lateral direction in robotic TKA surgery should be necessary to improve the surgical outcomes in knee arthroplasty. The developed surgical robot system could be a platform of various orthopedic robotic surgeries.

This study investigated synergistic actions of hand-pen contact forces during circle drawing tasks in three-dimensional (3D) space. Twenty-four right-handed participants drew thirty concentric circles in the counterclockwise (CCW) and clockwise (CW) directions. Three-dimensional forces acting on an instrumented pen as well as 3D linear and angular positions of the pen were recorded. These contact forces were then transformed into the 3D radial, tangential, and normal force components specific to circle drawing. Uncontrolled manifold (UCM) analysis was employed to calculate the magnitude of the hand-pen contact force synergy. Three hypotheses were tested. First, hand-pen contact force synergies during circle drawing are dependent on the angular position of the pen tip. Second, hand-pen contact force synergies are dependent on force components in circle drawing. Third, hand-pen contact force synergies are greater in CCW direction than CW direction. The results showed that the strength of the hand-pen contact force synergy increased during the initial phase of circle drawing and decreased during the final phase. The synergy strength was greater for the radial and tangential components as compared to the normal component. Also, the circle drawing in CW direction was associated with greater hand-pen contact force synergy than the CCW direction. The results of this study suggest that the central nervous system (CNS) prioritizes hand-pen contact force synergies for the force components (i.e., radial and tangential) that are critical for circle drawing. The CNS modulates hand-pen contact force synergies for preparation and conclusion of circle drawing, respectively.

The hip joint diseases have various kinds of origination, and they have multifarious forms according to the originations. One of the major concerns to plan the surgical operation for the hip diseases is the alternation of biomechanical environment, such as joint force and contact pressure. In this study, we analyzed the biomechanical effects of surgical techniques of the hip joint diseases by finite element analysis. We developed the finite element models of the pre-operative and post-operative hip joints for four children patients who have hip joint disease with abnormal joint anatomy. The models consist of two bones (pelvis and femur) reconstructed from CT images, and the articular cartilages on acetabulum and femoral head. Bones and cartilages were assumed having linear elastic material properties. The resultant joint force and the abductor force were calculated from 3-D static equilibrium in one-leg standing position. The calculated joint force was applied on the pelvis, the inferior plate of femur was fixed in all directions, and the medial edge of pelvis was constrained in vertical direction. Mechanical values such as contact force, pressure, and contact area on the hip joint were measured. The results of the finite element analysis were similar with those clinically estimated. The present non-destructive biomechanical evaluation method could be clinically useful for the optimal planning and selecting of surgical method by the rearrangement of contact pressure in the hip joint.

Without an active, thriving cell population that is well-distributed and stably anchored to the inserted template, exceptional bone regeneration does not occur. With conventional templates, the absence of internal micro-channels results in the lack of cell infiltration, distribution, and inhabitance deep inside the templates. Hence, a highly porous and uniformly interconnected trabecular-bone-like template with micro-channels (biogenic microenvironment template; BMT) has been developed to address these obstacles. The novel BMT was created by innovative concepts (capillary action) and fabricated with a sponge-template coating technique. The BMT consists of several structural components: inter-connected primary-pores (300-400 µm) that mimic pores in trabecular bone, micro-channels (25-70 µm) within each trabecula, and nanopores (100-400 nm) on the surface to allow cells to anchor. Moreover, the BMT has been documented by mechanical test study to have similar mechanical strength properties to those of human trabecular bone (~3.8 MPa)12. The BMT exhibited high absorption, retention, and habitation of cells throughout the bridge-shaped (Π) templates (3 cm height and 4 cm length). The cells that were initially seeded into one end of the templates immediately mobilized to the other end (10 cm distance) by capillary action of the BMT on the cell media. After 4 hr, the cells homogenously occupied the entire BMT and exhibited normal cellular behavior. The capillary action accounted for the infiltration of the cells suspended in the media and the distribution (active migration) throughout the BMT. Having observed these capabilities of the BMT, we project that BMTs will absorb bone marrow cells, growth factors, and nutrients from the periphery under physiological conditions. The BMT may resolve current limitations via rapid infiltration, homogenous distribution and inhabitance of cells in large, volumetric templates to repair massive skeletal defects.

Computational musculoskeletal models have been developed to predict mechanical joint loads on the human spine, such as the forces and moments applied to vertebral and facet joints and the forces that act on ligaments and muscles because of difficulties in the direct measurement of joint loads. However, many whole-spine models lack certain elements. For example, the detailed facet joints in the cervical region or the whole spine region may not be implemented. In this study, a detailed cervico-thoraco-lumbar multibody musculoskeletal model with all major ligaments, separated structures of facet contact and intervertebral disk joints, and the rib cage was developed. The model was validated by comparing the intersegmental rotations, ligament tensile forces, facet joint contact forces, compressive and shear forces on disks, and muscle forces were to those reported in previous experimental and computational studies both by region (cervical, thoracic, or lumbar regions) and for the whole model. The comparisons demonstrated that our whole spine model is consistent with in vitro and in vivo experimental studies and with computational studies. The model developed in this study can be used in further studies to better understand spine structures and injury mechanisms of spinal disorders.

Clinically, spinal cord injuries (SCIs) are radiographically evaluated and diagnosed from plain radiographs, computed tomography (CT), and magnetic resonance imaging. However, it is difficult to conclude that radiographic evaluation of SCI can directly explain the fundamental mechanism of spinal cord damage. The von-Mises stress and maximum principal strain are directly associated with neurological damage in the spinal cord from a biomechanical viewpoint. In this study, the von-Mises stress and maximum principal strain in the spinal cord as well as the cord cross-sectional area (CSA) were analyzed under various magnitudes for contusion, dislocation, and distraction SCI mechanisms, using a finite-element (FE) model of the cervical spine with spinal cord including white matter, gray matter, dura mater with nerve roots, and cerebrospinal fluid (CSF). A regression analysis was performed to find correlation between peak von-Mises stress/peak maximum principal strain at the cross section of the highest reduction in CSA and corresponding reduction in CSA of the cord. Dislocation and contusion showed greater peak stress and strain values in the cord than distraction. The substantial increases in von-Mises stress as well as CSA reduction similar to or more than 30% were produced at a 60% contusion and a 60% dislocation, while the maximum principal strain was gradually increased as injury severity elevated. In addition, the CSA reduction had a strong correlation with peak von-Mises stress/peak maximum principal strain for the three injury mechanisms, which might be fundamental information in elucidating the relationship between radiographic and mechanical parameters related to SCI.

In this study, trigonelline, a niacin-related compound was incorporated into chitosan nanoparticles through ion-complex formation between anionic carboxylic acid group of trigonelline and cationic amine group of chitosan. Morphology of trigonelline-incorporated chitosan nanoparticles have spherical shape with less than 500 nm in size and thier size distribution showed quite unimodel phase. Even though trigonelline and trigonelline-incorporated chitosan nanoparticles were not significantly affected to the proliferation of tumor cells, invasion of tumor cells was effectively inhibited by trigonelline-incorporated chitosan nanoparticles. We suggested that trigonelline-incorporated chitosan nanoparticles are promising candidate for inhibition of tumor cell invasion.

The purpose of this study was to examine if the application of custom-made porous titanium membranes combined with bone graft materials promotes exophytic bone formation in rabbit calvaria. For this purpose, round decorticated calvaria sites were created using a round carbide bur. In the control group, rectangular parallelepiped-shaped porous titanium membranes (RPTMs) were placed on the decorticated sites and fixed with metal pins. In the experimental groups, RPTMs were filled with one of the following bone graft materials prior to fixing with metal pins: bovine bone mineral (BBM), demineralized freeze-dried human cortical bone (DFDB) or freeze-dried human cancellous bone (FDB). Animals were sacrificed at 8 and 12 weeks after surgery, and new bone formation was assessed by histomorphometric as well as statistical analysis. The results indicate that at 8 and 12 weeks, all the experimental groups demonstrated exophytic bone formation. At 12 weeks, DFDB group revealed the most new bone formation (p

Finite element contact analyses of dysplastic hip joints were performed based on CT and MR images as a surgical planning tool of the shelf operation. The 3-D cartilage thickness was approximated using MRI, and the joint contact force was calculated from a 3-D expansion of the Ninomiya’s method. After surgical planning, the anatomical parameters including the CE angle, the AC angle, the sharp angle and the spheric sector angle were improved to normal hips. The mechanical parameters including the maximum contact pressure, the contact area and the quality of contact pressure distribution also were improved. The present models and the results can be used as a computer simulation tool for optimal pre-operative planning of the shelf operation in hip dysplasia.

Finite element (FE) model studies have made important contributions to our understanding of functional biomechanics of the lumbar spine. However, if a model is used to answer clinical and biomechanical questions over a certain population, their inherently large inter-subject variability has to be considered. Current FE model studies, however, generally account only for a single distinct spinal geometry with one set of material properties. This raises questions concerning their predictive power, their range of results and on their agreement with in vitro and in vivo values. Eight well-established FE models of the lumbar spine (L1-5) of different research centres around the globe were subjected to pure and combined loading modes and compared to in vitro and in vivo measurements for intervertebral rotations, disc pressures and facet joint forces. Under pure moment loading, the predicted L1-5 rotations of almost all models fell within the reported in vitro ranges, and their median values differed on average by only 2° for flexion-extension, 1° for lateral bending and 5° for axial rotation. Predicted median facet joint forces and disc pressures were also in good agreement with published median in vitro values. However, the ranges of predictions were larger and exceeded those reported in vitro, especially for the facet joint forces. For all combined loading modes, except for flexion, predicted median segmental intervertebral rotations and disc pressures were in good agreement with measured in vivo values. In light of high inter-subject variability, the generalization of results of a single model to a population remains a concern. This study demonstrated that the pooled median of individual model results, similar to a probabilistic approach, can be used as an improved predictive tool in order to estimate the response of the lumbar spine.

A protocol to choose the graft diameter attachment point of each bundle has not yet been determined since they are usually dependent on a surgeon’s preference. Therefore, the influence of bundle diameters and attachment points on the kinematics of the knee joint needs to be quantitatively analyzed. A three-dimensional knee model was reconstructed with computed tomography images of a 26-year-old man. Based on the model, models of double bundle anterior cruciate ligament (ACL) reconstruction were developed. The anterior tibial translations for the anterior drawer test and the internal tibial rotation for the pivot shift test were investigated according to variation of bundle diameters and attachment points. For the model in this study, the knee kinematics after the double bundle ACL reconstruction were dependent on the attachment point and not much influenced by the bundle diameter although larger sized anterior-medial bundles provided increased stability in the knee joint. Therefore, in the clinical setting, the bundle attachment point needs to be considered prior to the bundle diameter, and the current selection method of graft diameters for both bundles appears justified.

Carbon fiber running-specific prostheses (RSPs) have allowed individuals with lower extremity amputation (ILEA) to participate in running. It has been established that as running speed increases, leg stiffness (Kleg) remains constant while vertical stiffness (Kvert) increases in able-bodied runners. The Kvert further depends on a combination of the torsional stiffnesses of the joints (joint stiffness; Kjoint) and the touchdown joint angles. Thus, an increased understanding of spring-like leg function and stiffness regulation in ILEA runners using RSPs is expected to aid in prosthetic design and rehabilitation strategies. The aim of this study was to investigate stiffness regulation to various overground running speeds in ILEA wearing RSPs. Eight ILEA performed overground running at a range of running speeds. Kleg, Kvert and Kjoint were calculated from kinetic and kinematic data in both the intact and prosthetic limbs. Kleg and Kvert in both the limbs remained constant when running speed increased, while intact limbs in ILEA running with RSPs have a higher Kleg and Kvert than residual limbs. There were no significant differences in Kankle, Kknee and touchdown knee angle between the legs at all running speeds. Hip joints in both the legs did not demonstrate spring-like function; however, distinct impact peaks were observed only in the intact leg hip extension moment at the early stance phase, indicating that differences in Kvert between limbs in ILEA are due to attenuating shock with the hip joint. Therefore, these results suggest that ILEA using RSPs has a different stiffness regulation between the intact and prosthetic limbs during running.

Ossification of the posterior longitudinal ligament (OPLL) and ossification of the ligamentum flavum (OLF) have been recognized as causes of myelopathy due to thickening of the ligaments resulting in narrowing of the spinal canal and compression of the spinal cord. However, few studies have focused on predicting stress distribution under conditions of OPLL and OLF based on clinical aspects such as the relationship between level of stress and severity of neurologic symptoms because direct in vivo measurement of stress is very restrictive. In this study, a three-dimensional finite element model of the spinal cord in T12-L1 was developed based on MR images. The von-Mises stresses in the cord and the cross-sectional area of the cord were investigated for various grades and shapes of spinal cord compression in OPLL and OLF. Substantial increases in maximum stresses resulting in the manifestation of spinal cord symptoms occurred when the cross-sectional area was reduced by 30-40% at 60% compression of the antero-posterior diameter of the cord in OPLL and at 4mm compression in OLF. These results indicate that compression greater than these thresholds may induce spinal symptoms, which is consistent with clinical observations.

Determination of the physiological loads in the human lumbar spine is critical for understanding the mechanisms of lumbar injuries and diseases as well as for designing surgical techniques for treatment of lumbar pathologies, such as disc replacement and spinal fusion [1–4]. Numerous experimental studies, both in vitro and in vivo, have attempted to investigate the biomechanics of the spinal system [5–10]. However, it is always difficult to mimic the physiological conditions in in vitro experiments such as including muscle forces [5,6]. On the other hand, due to technical limitations, there are only few in vivo studies that tried to measure the joint forces directly using telemeterized implant techniques [5–8] and indirectly from the measurement of intra-discal pressure using pressure transducer [9,10]. Many computational models have been proposed to provide an alternative way to estimate the physiological loads of the spine during various functional activities [1,2,4,11–20]. For example, Stokes and Gardner-Morse investigated the activation synergies of the lumbar spinal muscle using an inverse dynamic optimization method [19]. Kim et al. reported lumbar joint and muscle forces using a finite element model [15–17]. Shirazi-Adl et al. reported changes of spinal joint and muscle forces, and stability in various standing and loading postures using a finite element model and an optimization algorithm [1,2,4,11,12]. Han et al. reported that the joint forces, which correspond to the same direction as the spinal lordosis (i.e., a follower load), could be generated by spinal muscles using a static numerical model [13]. These modeling studies made various assumptions on physiological factors of the spinal system, such as the intra-abdominal pressure (IAP) [12,20,21], centers of mass (COMs) of the upper body and the lumbar segments [1,2,4,11–20], as well as the vertebral centers of rotation (CORs) [13,17]. A widely used mathematical model of the lumbar spine [18] has assumed a “ball and socket” joint between two vertebral bodies to calculate the spinal joint and muscle forces. When a “ball and socket” joint is used, no moment was transmitted through the joint center. Generally, joint reaction forces and moments were calculated at the midpoint of the intervertebral disc (IVD) in the human articular joint models [18,22]. However, if the selected geometric center is not a real COR, the reaction joint moments are not actually zero at the selected center [22]. A systematic knowledge of how these assumptions affect the prediction of the spinal biomechanics is important for improved accuracy of computational spine biomechanics. In this study, we developed a subject-specific numerical model of the healthy lumbosacral spine to calculate the lumbar joint forces and muscle forces using a global convergence optimization procedure [22,23]. A parametric study was performed to examine the effects of the changing IAP magnitude and the COMs locations on the spine biomechanical responses. Further, we calculated the locations of the CORs of the lumbar spinal motion segments using a global convergence optimization procedure when the spine was under different loading conditions.

This study investigates the role of cutaneous feedback on maximum voluntary force (MVF), finger force deficit (FD) and finger independence (FI). FD was calculated as the difference between the sum of maximal individual finger forces during single-finger pressing tasks and the maximal force produced by those fingers during an all-finger pressing task. FI was calculated as the average non-task finger forces normalized by the task-finger forces and subtracted from 100 percent. Twenty young healthy right-handed males participated in the study. Cutaneous feedback was removed by administering ring block digital anesthesia on the 2nd, 3rd, 4th and 5th digits of the right hands. Subjects were asked to press force sensors with maximal effort using individual digits as well as all four digits together, with and without cutaneous feedback. Results from the study showed a 25% decrease in MVF for the individual fingers as well as all the four fingers pressing together after the removal of cutaneous feedback. Additionally, more than 100% increase in FD after the removal of cutaneous feedback was observed in the middle and ring fingers. No changes in FI values were observed between the two conditions. Results of this study suggest that the central nervous system utilizes cutaneous feedback and the feedback mechanism plays a critical role in maximal voluntary force production by the hand digits.

Recently, computer-aided robotic systems, such as Robodoc® system and Makoplasty® system, have been used to enable surgeons to improve the accuracy of cutting and alignment in knee and hip arthroplasty [1,2,3]. The incision is normally done at the anterior part of the knee and the cutting is performed from the frontal direction during the TKA because enough working space of the tools is required during cutting process. Currently minimal invasive surgery (MIS) is the most popular keyword in the arthroplasty [4], and at this moment the MIS could not be performed common in the TKA using the robotic system. This MIS TKA could be achieved in lateral direction, and different cutting process also changes the robot configuration, which mainly affect the system accuracy. In this study, we investigated what additional advantages could be achieved in the bone cutting process laterally using laboratory-level less-invasive TKA surgical robot system.Copyright © 2011 by ASME

Study design A biomechanical comparison between the intact C2-C7 segments and the C5-C6 segments implanted with two different constrained types (fixed and mobile core) of artificial disc replacement (ADR) using a three-dimensional nonlinear finite element (FE) model. Objective To analyze the biomechanical changes in subaxial cervical spine after ADR and the differences between fixed- and mobile-core prostheses. Summary of background data Few studies have investigated the changes in kinematics after cervical ADR, particularly in relation to the influence of constrain types. Methods A FE model of intact C2-C7 segments was developed and validated. Fixed-core (Prodisc-C, Synthes) and mobile-core (Mobi-C, LDR Spine) artificial disc prostheses were integrated at the C5-C6 segment into the validated FE model. All models were subjected to a follower load of 50 N and a moment of 1 Nm in flexion-extension, lateral bending, and axial torsion. The range of segmental motion (ROM), facet joint force, tension on major ligaments, and stress on the polyethylene (PE) cores were analyzed. RESULTS.: The ROM in the intact segments after ADR was not significantly different from those of the normal cervical spine model. The ROM in the implanted segment (C5-C6) increased during flexion (19% for fixed and 33% for mobile core), extension (48% for fixed and 56% for mobile core), lateral bending (28% for fixed and 35% for mobile core) and axial torsion (45% for fixed and 105% for mobile core). The facet joint force increased by 210% in both fixed and mobile core models during extension and the tension increased (range, 66%-166%) in all ligaments during flexion. The peak stress on a PE core was greater than the yield stress (51 MPa for fixed and 36 MPa for mobile core). Conclusion The results of our study presented an increase in ROM, facet joint force, and ligament tension at the ADR segments. The mobile-core model showed a higher increase in segmental motion, facet force, and ligament tension, but lower stress on the PE core than the fixed-core model.

It has been reported that the center of rotation of each vertebral body is located posterior to the vertebral body center. Moreover, it has been suggested that an optimized follower load (FL) acts posterior to the vertebral body center. However, the optimal position of the FL with respect to typical biomechanical characteristics regarding spinal stabilization, such as joint compressive force, shear force, joint moment, and muscle stress, has not been studied. A variation in the center of rotation of each vertebra was formulated in a three-dimensional finite element model of the lumbar spine with 117 pairs of trunk muscles. Then, the optimal translation of the FL path connecting the centers of rotations was estimated by solving the optimization problem that was to simultaneously minimize the compressive forces, the shear forces, and the joint moments or to minimize the cubic muscle stresses. An upright neutral standing position and a standing position with 200 N in both hands were considered. The FL path moved posterior, regardless of the optimization criteria and loading conditions. The FL path moved 5.0 and 7.8 mm posterior in upright standing and 4.1 mm and 7.0 mm posterior in standing with 200 N in hands for each optimization scheme. In addition, it was presented that the optimal FL path may have advantages in comparison to the body center FL path. The present techniques may be important in understanding the spine stabilization function of the trunk muscles.

Three-dimensional patient-specific bone models have been used in computer-aided planning and biomechanical analysis of orthopaedic surgeries. Reconstruction methods using X-ray images have been developed recently. However, these reconstruction methods have limited ability to generate femur models with severe rotational deformities. In this study, a new X-ray-based reconstruction method was proposed using the free form deformation method with two X-ray images and three CT images. The obtained femur model is closer to a CT-based 3D femur model in comparison with the reconstruction method using only X-ray images. This method will have benefits for many clinical and biomechanical applications.

High tibial osteotomy (HTO) for medial compartment knee osteoarthritis is preferred in the activity patient since it allows patients to return to sports and recreational activities similar to the preoperative level. The purpose of this study was to mathematically formulate medial and anteromedial opening gaps in the medial opening wedge HTO to achieve a targeted tibial posterior slope. The change of posterior slope angle was mathematically derived in terms of the medial and anteromedial opening gaps, and the medial opening angles. The derived equations were validated by comparing them with those directly measured by performing simulated HTOs. In the triangular geometries of osteotomy planes, measured from three-dimensional osteotomy models of 30 knee patients, the mean anteromedial, medial, and lateral included angles were 92.4 degrees, 53.9 degrees, and 33.7 degrees, respectively, and the mean lateral-medial edge length was 53.3 mm. The ratio of the anteromedial opening gap to the posterior opening gap should be "sin(the medial included angle)xcos(the lateral included angle)/sin(the anteromedial included angle)" to maintain an intact posterior tibial slope angle. With the derived equations, surgeons can estimate the opening gaps and opening angles to get a targeted posterior tibial slope with a medial opening angle.

Recently, experimental results have demonstrated that the load carrying capacity of the human spine substantially increases under the follower load condition. Thus, it is essential to prove that a follower load can be generated in vivo by activating the appropriate muscles in order to demonstrate the possibility that the stability of the spinal column could be maintained through a follower load mechanism. The aim of this study was to analyze the coordination of the trunk muscles in order to understand the role of the muscles in generating the follower load. A three-dimensional finite element model of the lumbar spine was developed from T12 to S1 and 117 pairs of trunk muscles (58 pairs of superficial muscles and 59 pairs of deep muscles) were considered. The follower load concept was mathematically represented as an optimization problem. The muscle forces required to generate the follower load were predicted by solving the optimization problem. The corresponding displacements and rotations at all nodes were estimated along with the follower forces, shear forces, and joint moments acting on those nodes. In addition, the muscle forces and the corresponding responses were investigated when the activations of the deep muscles or the superficial muscles were restricted to 75% of the maximum activation, respectively. Significantly larger numbers of deep muscles were involved in the generation of the follower load than the number of superficial muscles, regardless of the restriction on muscle activation. The shear force and the resultant joint moment are more influenced by the change in muscle activation in the superficial muscles. A larger number of deep trunk muscles were activated in order to maintain the spinal posture in the lumbar spine. In addition, the deep muscles have a larger capability to reduce the shear force and the resultant joint moment with respect to the perturbation of the external load or muscle fatigue compared to the superficial muscles.