Biomedical subjects

Hsiang-Ho Chen

Publications and source records attributed to Hsiang-Ho Chen.

11 recordsLinked to original sources

PubMed2006

Compressive loading at the end plate directly regulates flow and deformation of the basivertebral vein: an analytical study.

BACKGROUND: Metastatic diseases and infections frequently involve the spine. This is the result of seeding of the vertebral body by tumor cells or bacteria delivered by venous blood from Batson's plexus, which is hypothesized to enter the vertebral body via the epidural veins. Isolated spinal segments deform significantly at the bony end plate when under compression. This deformation could cause a volume change of the vertebral body and may be accompanied by retrograde flow of venous blood. To date, this process has not been investigated quantitatively. The purpose of this study was to determine the volume changes of the vertebral body and basivertebral vein for a vertebral body under compression. METHODS: A three-dimensional finite element mesh model of the L4 segment with both adjacent discs was modified from a 3-D computed tomography scan image. An octagon representing the basivertebral vein was introduced into the center of the vertebral body in the model. Four compressive orientations (1500 N) were applied on the top disc. The volume change of the vertebral body model and the basivertebral vein were then computed. RESULTS: The volume change of the vertebral body was about 0.1 cm3 (16.3% of the basivertebral vein) for the four loading conditions. The maximum cross-sectional area reductions of the basivertebral vein and volume reduction were 1.54% and 1.02%, for uniform compression. CONCLUSION: Our study quantified the small but significant volume change of a modeled vertebral body and cross-sectional areas and that of the basivertebral vein, due to the inward bulging of the end plate under compression. This volume change could initiate the reverse flow of blood from the epidural venous system and cause seeding of tumors or bacterial cells.

Journal Article↗

PubMed2006

Transpedicle body augmenter in painful osteoporotic compression fractures.

Osteoporotic compression fractures (VCFs) can result in progressive kyphosis and chronic pain. Polymethylmethacrylate has been used for augmentation of VCFs; however, there are cement complications, and long-term fracture healing is unknown. The transpedicle body augmenter (TpBA), a porous titanium spacer, has been reported as an internal support to reconstruct the vertebral body combining short segment fixation in burst fracture. We retrospectively reviewed radiographic and clinical results of TpBA vertebroplasty for single symptomatic VCF in 80 patients. Manual reduction and TpBA vertebroplasty via a paramedian incision with blunt dissection was done. Mean age was 72.3 years (range 51-87 years), and female-male ratio was 66:14. The mean symptom duration was 5 months, and follow-up 44 months. Peri-operative variables and radiographic and clinical results were evaluated. The average operation time was 26.1 min, blood loss 92 cc, and hospitalization 2.3 days. No patient had neurological deterioration. TpBA was found sinking into vertebral body initially, then locked by residual cortex, and finally stabilized within the vertebra. There was no dislodgement of TpBA in the final visit. Sixty-two patients (77.5%) could walk within 3-6 h after operation and the others within 24 h. The anterior vertebral restoration was 8.0 mm initially and 6.1 mm at final follow-up. Wedge angle correction was 11.5 degrees initially and 9.4 degrees at final follow-up. Pain, by the visual analog scale, was 8.6 pre-operatively, 2.5 at day 7 follow-up, and 2.9 at final follow-up. By the questionnaire, 72 of 76 respondents reported a decrease in discomfort after TpBA vertebroplasty, and 63 of 76 patients reported a return to normal activity after operation. The final satisfaction rate was 93.4%. TpBA vertebroplasty led to early and medium-term clinical improvement and anatomic restoration of painful VCFs.

Aged↗

PubMed2005

Biomechanical analysis of unilateral fixation with interbody cages.

STUDY DESIGN: An in vitro biomechanical study of the stabilizing effects of a different combination of cages and transpedicular instrumentation on experimental degenerative disc disease. OBJECTIVES: To evaluate the biomechanical efficacy of the interbody fusion cage and unilateral posterior instrumentation on the stability of the spine-device construct. SUMMARY OF BACKGROUND DATA: Posterior lumbar interbody fusion (PLIF) has become a clinically established and increasingly popular procedure since its introduction and subsequent modification. Recently, unilateral fixation was reported to have comparable efficacy to bilateral fixation in two- to three-segment posterior instrumentation. This study has been designed to compare biomechanical properties among various spinal fixations, including bilateral versus unilateral fixation with PLIF and cages. METHODS: Thirty porcine L3-L6 spines were separated into six groups. The utilization of one or two cages and unilateral or bilateral instrumentations were reciprocally combined to stabilize the spine with the L4-L5 discectomy, simulating degenerative disc disease. A serial of biomechanical tests, including flexion (5 N-m), extension (5 N-m), compression (250 N), lateral bending (5 N-m), and axial rotation (5 N-m, 25 mm/min), were conducted at the displacement rate of 25 mm/min in five cycles. Stiffness values were derived from loading curves for comparison of spinal stability. RESULTS.: In axial compression, the stiffness of bilateral fixation (BF) and unilateral fixation with two-cage (UF2C) groups were almost identical and only less than that of the bilateral fixation with two cages (BF2C) group. In the flexion, the BF, UF2C, and unilateral fixation with one cage (UF1C) group incurred comparable stiffness to that of the Intact group. In extension, the UF2C group had a comparable stiffness to the BF2C group. In lateral bending, the BF2C group and the UF2C group were the constructs incurring most stiffness. In torsion, the BF group and the UF2C group were less stiff than the BF2C group, but that was statistically insignificant CONCLUSIONS: In the group of unilateral fixation combining PLIF with two cages, the anterior support of cages enabled unilateral instrumentation to restore torsional stiffness and other spinal stability indexes. Considering the initial stability and the load-sharing effect, this study showed that the unilateral fixation combining PLIF and two cages might be a good alternative to spinal fixation.

Animals↗

PubMed2005

The effect of acute smoking on spinal fusion: an experimental study among rabbits.

BACKGROUND: The establishment of an environment to force animals to inspire cigarette smoke is mandatory to study the true effects of smoking. This model has been used to study long-bone healing but has not yet been used to study spinal fusion. METHODS: Forty male rabbits were divided into four equal groups. All the animals underwent bilateral intertransverse-process fusion at L5-L6 using the 1995 fusion model of Boden et al. The first (C8-week) group did not undergo cigarette smoke inhalation and individual rabbits were killed at 8 weeks; the second (S8-week) group underwent intermittent cigarette smoke inhalation and individual rabbits were killed at 8 weeks; the third (C6-week) group did not undergo cigarette smoke inhalation, and animals were killed at 6 weeks; and the fourth (S6-week) group underwent intermittent smoke inhalation and group-included rabbits were killed at 6 weeks. Subsequent to the animals having been killed, the fusion masses were harvested for a series of studies including manual palpation, biomechanical testing, radiographic examination, and histologic analysis. RESULTS: Six rabbits died shortly after the operation. Of the remaining 34 rabbits, the lumbar spine specimen was harvested for study. Manual palpation, radiographic examination, and histologic analysis of the fusion masses revealed no statistically significant difference in fusion results between the control and the corresponding smoking group killed at either 8 weeks or 6 weeks. Biomechanical testing of the fusion masses also revealed no statistically significant difference in fusion results between the control and the smoking group killed at 8 weeks, although it did indicate that smoking resulted in a 44% decrease in mean flexion stiffness and a 32% decrease in mean extension stiffness among the animals killed at 6 weeks. The former (decrease in flexion stiffness) was statistically significant (p < 0.05). CONCLUSION: The results of the biomechanical testing conducted as a part of the current study demonstrate that acute cigarette smoke inhalation delays but does not prevent the spinal fusion process for rabbits.

Animals↗

PubMed2004

Biomechanical effects of the body augmenter for reconstruction of the vertebral body.

STUDY DESIGN: An in vitro biomechanical study of the stabilizing effects of the body augmenter and posterior instrumentation on experimental thoracolumbar fractures with vertebral defects. OBJECTIVE: To evaluate the effects of the body augmenter and instrumentation on the stability of the spine-device construct. SUMMARY OF BACKGROUND DATA: Posterior instrumentations alone are widely used to accomplish spinal reduction and provide stability for an injured spine; however, implant failure rates have been reported to be approximately 20%. Transpedicular discectomy and bone graft has reported only 33% fusion rates. Combined anterior bony strut and posterior instrumentation was a challenge to geriatric patients with vulnerable medical conditions and possible vascular and pulmonary complications. Therefore, a new design, the body augmenter, tries to reconstruct the vertebral body through internal mechanical support and also encourage bony fusion. This study is to evaluate its initial mechanical effects. METHODS: Twenty fresh porcine T11-L3 vertebrae were harvested. The L1 vertebra with one third or one half corpectomy was performed to simulate a fracture injury with vertebral defects. Posterior instrumentation alone (PI group), posterior instrumentation with body augmenters (BA group), and anterior instrumentation with tricortical bony strut and DCP 1 level above and 1 level below the fracture site (DCP group) were applied as treatment strategies. Load-displacement and torque-angle plots were generated and used to calculate axial stiffness and torsional rigidity for these constructs with vertebral fracture at the L1 vertebrae. Axial compression, extension, and flexion tests were performed at intact and spine-device constructs to document spinal stability. RESULTS: The construct stability had a complex association to the device applied. In the one third corpectomy group, the BA group had significantly higher compression stiffness than the PI group. In the one half corpectomy group, the flexion and compression stiffness of the BA group became significantly greater than the PI group, and the extension stiffness is significantly higher than the DCP group. CONCLUSIONS: The body augmenters combined with posterior instrumentation increased the spinal construct stability during compression, flexion, and extension. According to results in this study, the body augmenter could provide a better initial stability of construct and prevent the implant failure of posterior instrumentation and may be a feasible substitute for the anterior role in the future.

Animals↗

PubMed2004

Shock wave treatment shows dose-dependent enhancement of bone mass and bone strength after fracture of the femur.

Shock wave treatment is believed to improve bone healing after fracture. The purpose of this study was to evaluate the effect of shock wave treatment on bone mass and bone strength after fracture of the femur in a rabbit model. A standardized closed fracture of the right femur was created with a three-point bending method in 24 New Zealand white rabbits. Animals were randomly divided into three groups: (1) control (no shock wave treatment), (2) low-energy (shock wave treatment at 0.18 mJ/mm2 energy flux density with 2000 impulses), and (3) high-energy (shock wave treatment at 0.47 mJ/mm2 energy flux density with 4000 impulses). Bone mass (bone mineral density (BMD), callus formation, ash and calcium contents) and bone strength (peak load, peak stress and modulus of elasticity) were assessed at 12 and 24 weeks after shock wave treatment. While the BMD values of the high-energy group were significantly higher than the control group (P = 0.021), the BMD values between the low-energy and control groups were not statistically significant (P = 0.358). The high-energy group showed significantly more callus formation (P < 0.001), higher ash content (P < 0.001) and calcium content (P = 0.003) than the control and low-energy groups. With regard to bone strength, the high-energy group showed significantly higher peak load (P = 0.012), peak stress (P = 0.015) and modulus of elasticity (P = 0.011) than the low-energy and control groups. Overall, the effect of shock wave treatment on bone mass and bone strength appears to be dose dependent in acute fracture healing in rabbits.

Animals↗

PubMed2004

An electromyographic assessment of the anti-G straining maneuver.

BACKGROUND: The anti-G straining maneuver (AGSM), used by aircrew to enhance their +Gz tolerance and to reduce the potential risk of G-induced loss of consciousness, has been recognized as an effective technique. The purpose of this study was to establish an objective tool to evaluate the effectiveness of an aircrew member's AGSM. METHODS: There were 20 healthy subjects who participated in the study, including 8 senior aviation physiological trainers and 12 trainees. The former were familiar with the anti-G maneuver and had experienced high +Gz exposure, the latter had never been exposed to any high +Gz stress before the study. The analytic method of electromyography (EMG) was used to investigate the physical characteristics of the L-1 AGSM. RESULTS: Comparison of the EMG data from the two groups indicated that the mean duration of a breathing cycle of the trainer group was significantly longer than that of the trainee group (p < 0.001). The buccinator was the muscle that had the most rapid firing rate in both groups (p < 0.001). The trainer group had a significantly faster firing rate of the buccinator than the trainee group (p = 0.03). In addition, the trainee group performed the AGSM with a firing sequence of muscles that was different from that of the trainer group. CONCLUSIONS: An automated and quantitative system based on EMG can be used during AGSM training to augment or replace the current subjective evaluation of the trainee's performance.

Abdomen↗

PubMed2003

A biomechanical study of the cortex-anchorage vertebral screw.

OBJECTIVE: To obtain a comprehensive understanding on the effect of the improvement of fixation strength and on the optimal design in various geometrical parameters of a new screw system through biomechanical analyses. DESIGN: A new screw with the cortex-anchorage was designed and manufactured to improve the fixation of the instrumentation for osteoporotic spine. There were four expandable wings distributed around the screw after insertion. BACKGROUND: Screw loosening or loss of correction caused by insufficient mechanical stability on the bone-screw interface is frequently found in osteoporotic subjects. Similarly, the removal and replacement of a screw in a revision procedure substantially decreases its mechanical fixation. Since cortex is the most rigid part in the vertebral body, emphasis on the cortex-anchorage may offer an optimal fixation of screws. METHODS: The biomechanical evaluation that consists of the pullout test and the finite element analysis was applied to identify the stabilizing effect and the optimal design for the new screw system. In the pullout experiment, the porcine vertebral body with a hollow block of cancellous bone was proposed to simulate an osteoporotic spine. This osteoporotic model was specially simulated the degeneration and destruction of the cancellous bone in vertebrae. In the finite element analysis, the reduction of elastic modulus was used in various levels of vertebral degeneration. RESULTS: Pulling screws out of vertebral bodies with a hollow block of cancellous bone, the mean pullout force was 729 (SD 159) N for the conventional screws, and 1072 (SD 179) N for the new screw system. The finite element analysis showed that the longer screw with bi-cortex fixation was the better option in reducing the bony stress and increased the stability. As the height of wings changed, the stress distributed on vertebral body indicated the lowest in fixation by a screw with the largest wings. Nevertheless, there existed a least displacement of vertebral body and moderately low stress on wings' lateral end when assembled with the middle size wings. CONCLUSION: The stabilization function of expansive wings of the new screw system was enhanced in the osteoporotic vertebra and better than that of a conventional screw. The finite element analysis showed a middle size wing could help the screw to reduce the risk of failure and to improve the vertebral stability. RELEVANCE: Screw loosening or loss of correction caused by insufficient mechanical stability on the bone-screw interface is frequently found in osteoporotic subjects. From the biomechanical point of view, this study had shown that a new design of screw could improve the fixation of the instrumentation for osteoporotic spine. With further investigations that includes the clinical proof and the development of a cortex-anchorage vertebral screw may provide a valuable alternative to the spinal instrumentation for the patients with osteoporosis.

Animals↗

PubMed1998

Biomechanical evaluation of a new anterior spinal implant.

OBJECTIVE: To biomechanically evaluate the construct of a new anterior spinal implant for osteoporotic patients. DESIGN: Mechanical tests and finite element analysis were designed to evaluate the spinal implant. BACKGROUND: Many osteoporotic thoracolumbar spine fractures often need surgical intervention to relieve pains, stabilize progressive kyphosis or improve neurologic impairment. Progressive kyphosis, instrumentation failure and pseudoarthrosis are often seen post-operatively. These results may be due to insufficient bonding between the screw and the vertebral body. As the end-plate is the most rigid part of the vertebral body, the spinal implant was designed so that the end-block would fix onto the end-plates of the vertebral bodies. METHODS: Two biomechanical evaluations of the new anterior spinal implant were conducted to evaluate the construct stiffness and the bonding strength between the spinal implant and the vertebral body. In the evaluation of the construct stiffness, the biomechanical tests between the new spinal implant and the Kaneda device were performed on six fresh intact porcine spines at the thoracolumbar region. In the prediction of the loading transfer between the spinal implant and the vertebral body, a three-dimensional finite element model (FEM) was built to simulate the osteoporotic vertebral body and the new anterior spinal implant. RESULTS: The results of the mechanical tests showed that the compressive stiffnesses of the Kaneda device and the new implant were 357 +/- 37 N mm(-1) and 297 +/- 98 N mm(-1). Their flexional stiffnesses were 0.339 +/- 0.126 N-m mm(-1) and 0.364 +/- 0.107 N-m mm(-1), respectively. Their torsional stiffnesses were 6.37 +/- 0.28 N-m deg(-1) and 5.30 +/- 0.71 N-m deg(-1), respectively. There were no significant differences (p > 0.01). The results of FEM showed that the new implant had high stress concentration on the junction of the screw and plate, screw and end-blocks, and between the end-plate and the end-blocks. CONCLUSIONS: The stabilization effect of the new implant was similar to that of the Kaneda device. With less rigid mechanical properties, the new implant can be more beneficial to the remodeling process of the spinal structure after instrumentation. The new anterior spinal implant showed a high potential for application to osteoporotic patients.

Journal Article↗

PubMed1998

A three-dimensional mathematical model for predicting spinal joint force distribution during manual liftings.

OBJECTIVE: A three-dimensional dynamic mathematical model was developed to discover what loads are imposed on the lumbar structures by performance of asymmetric manual liftings. DESIGN: An external model was used to estimate the intersegmental resultant forces and moments at the L(5)/S(1) joint in this dynamic biomechanical model. Using an optimization algorithm, an internal model then distributed the intersegmental resultants to forces of muscle, disc, facet joints, and ligaments. BACKGROUND: To study the relation between large loads and low-back disorders, many biomechanical models have been developed. Most of the models were two-dimensional models discussed with symmetric activities. Some three-dimensional biomechanical models were static models or only included limited elements of the disc and muscles in the model. METHODS: A healthy young male subject was asked to perform asymmetric lift with bent knees. Dynamic data of body motion and ground reaction forces were monitored, and the EMG of six muscles were recorded simultaneously. A Newtonian equation was used to calculate the joint intersegmental resultant forces and moments. In the internal model, three components of the disc force, eight muscle forces, two ligament forces and two facet joint forces were computed. RESULTS: The correlation between the reaction moments from the upper and lower models of the external part were generally above 0.94, and the root mean square differences were below 19 Nm. In this internal model, the maximal disc compression was close to the data showed on the literature, and the estimation of muscle forces corresponded to the EMG activities. CONCLUSIONS: A three-dimensional biomechanical model has been developed and evaluated to estimate the spinal joint force distribution during asymmetric manual lifting activities.

Journal Article↗

PubMedDate not supplied

Effects of knee position, graft tension, and mode of fixation in posterior cruciate ligament reconstruction: a cadaveric knee study.

PURPOSE: Many knees exhibit residual ligament laxity after posterior cruciate ligament (PCL) reconstruction, which is believed to be technique related. The purpose of this study was to investigate the optimal graft tension, the best angle of knee flexion, and the mode of fixation in PCL reconstruction. TYPE OF STUDY: Anatomic biomechanical study. METHODS: A testing apparatus with frictionless bearing that allows other degrees of freedom except for flexion and extension of the knee joint was designed. The normal PCL tension at different angles of knee flexion was measured with a force transducer, and the optimal tension of the PCL graft that allows full range of knee motion was studied with a tensiometer in 12 cadaver knees. The modes of fixation failure between interference screw fixation and post fixation were studied with an Instron (Canton, MA) machine in 8 cadaver knees. RESULTS: The lowest PCL tension in normal knees was noted at 20 degrees to 30 degrees of knee flexion and the highest at 90 degrees. The optimal tension of PCL graft, which allows full range of knee motion, was 15 lb (68 N). The average load of graft failure was 417 (179-730) N with interference screw fixation and 367 (149-701) N with post fixation when the patellar bone-tendon-bone graft was tested. There was no statistical difference in the failure load between interference screw fixation and post fixation (P =.753); however, the modes of failure differ. The sites of failure for interference screw fixation were 25% caused by rupture of ligament substance and 75% bone plug pullout; those of post fixation were 25% caused by rupture of ligament substance, 37.5% caused by fracture, and 37.5% as a result of suture breakage. CONCLUSIONS: The results of this study suggested that a 15-lb tension to the graft at 20 degrees to 30 degrees of knee flexion is optimal in PCL reconstruction. There was no statistical difference in the failure load between interference fixation and post fixation despite different modes of fixation failure.

Biomechanical Phenomena↗