Biomedical subjects

Vijay K Goel

Publications and source records attributed to Vijay K Goel.

31 records · Page 2Linked to original sources

PubMed2004

Contributions of flexion-extension cyclic loads to the lumbar spinal segment stability following different discectomy procedures.

STUDY DESIGN: An in vitro biomechanical cadaveric study. OBJECTIVES To elucidate the effect of flexion-extension cyclic loads on the motion behavior of lumbar spine after different discectomies. SUMMARY OF BACKGROUND DATA: Biomechanical cadaveric studies to evaluate the effect of discectomy have been performed and have indicated the relevance between the volume of removed disc materials and increase of motion in affected intervertebral disc. However, there are no biomechanical studies to investigate the motion behavior of injured intervertebral disc after cyclic loads. METHODS: Twenty-eight lumbar functional spinal units were randomized into fenestration, annulotomy, limited discectomy, and radical discectomy groups. Pure bending moments were applied to simulate various loading modes and determine the resulting displacements before and after surgery, and after cyclic loads of 1,000, 5,000, and 10,000 cycles at a frequency of 0.5 Hz and a force of +/-3.0 Nm. Change of range of motion (ROM) was compared among each group. RESULTS: Following surgery, in the radical discectomy group, the relative change of ROM mostly increased in all motion directions except right lateral bending. On the other hand, during cyclic loads up to 10,000 cycles, in the limited discectomy group, the relative change of ROM mostly increased in all motion directions except right lateral bending. CONCLUSIONS: These results demonstrate that the effect of cyclic loads after discectomy may increase ROM, leading to spinal instability even if the increase in ROM does not occur immediately after surgery for the minimum removal of nucleus pulposus case. Clinically, this may underscore the importance of postoperative lumbar support.

Biomechanical Phenomena↗

PubMed2004

Increased concentrations of lipoprotein(a), circadian rhythms and metabolic reactions evoked by acute myocardial infarction, associated with acute reactions in relation to large breakfasts.

Of 54 patients with acute coronary artery disease (CAD) that were included in this study, 41 patients had acute myocardial infarction (AMI), five patients possible MI, four patients unstable angina and the remaining four angina pectoris. The control subjects (n = 85) were randomly selected from the general population of the city of Moradabad of similar age range after exclusion for CAD (n = 9), diabetes (n = 6) and excess intake of trans fatty acids (n = 20). The incidence of lipoprotein(a) excess (> 30 mg/dl; 42.6 vs 24.7%; P < 0.05) and mean concentration of lipoprotein(a) (Lp[a], 6.4 mg/dl, 95% confidence interval: 2.8-10.5; P < 0.05) was significantly greater in the acute CAD group compared with control subjects. Mean total cholesterol and triglycerides were significantly higher and mean nitrite level lower in the study group as compared with the control group.There was a significant greater incidence of cardiac events in the second quarter of the day compared with the fourth quarter. Lp(a), triglycerides, blood glucose, plasma insulin, malondialdehyde, diene conjugates, TBARS and TNF-alpha and IL-6 levels, which were significantly greater during the acute phase, showed a significant decline and serum nitrite and coenzyme Q demonstrated an increase at 4 weeks of follow-up when the acute reactions evoked by MI had been controlled. Large breakfasts were a predisposing factor for cardiac events in the second quarter of the day and it was significantly associated with metabolic reactions. The findings indicate that acute reactions as a result or as circadian rhythms appear to be important in the pathogenesis of AMI-associated complications and that a large breakfast in association with nitrite deficiency may further trigger the circadian rhythms. However, more studies in a larger number of subjects would be necessary in order to confirm our findings.

Acute Disease↗

PubMed2003

Ability of the finite element models to predict response of the human spine to sinusoidal vertical vibration.

STUDY DESIGN: The study examined the efficacy of the finite element models of various spinal segments in predicting the vibration response of the human spine. OBJECTIVE: To determine the optimal spinal segment finite element model to understand the effects of vibration on its biomechanics. SUMMARY OF BACKGROUND DATA: Several finite element models (one and two motion segments) have been proposed to look into the effects of vibration on the lumbar spine. However, they cannot be used to predict biomechanical parameters in the lumbar spine in response to whole body vibration. METHODS: A finite element model of the upper body from the head to the sacrum (H-S1) was generated. The H-=S1 model was altered to generate models of one motion segment (L3-L4), two motion segments (L3-L5), and the entire thoracolumbar spine and rib cage (T1-S1). The resonant frequencies of these models and effects of the trunk muscles and gravity were studied. RESULTS: The resonant frequencies decreased with the increase in the number of motion segments. However, the decrease plateaued beyond the T1-S1 segment model. The first resonant frequency in the vertical direction for the H-S1 model was 8.32 Hz. Inclusion of the trunk muscles and the preload of self-weight changed it to 8.91 and 6.82 Hz, respectively. CONCLUSIONS: Both the T1-S1 and H-S1 finite element models were able to predict vibration response of the human spine that closely matched in vivo experimental data reported in the literature.

Biomechanical Phenomena↗

PubMed2003

Comparative biomechanical analysis of a cervical cage made of an unsintered hydroxyapatite particle and poly-L-lactide composite in a cadaver model.

STUDY DESIGN: A new cage made from a forged composite of unsintered hydroxyapatite particles and poly-L-lactide (F-u-HA/PLLA) is compared biomechanically with the Ray threaded fusion cage. OBJECTIVES: To compare the stability imparted to the human cadaveric spine by two different threaded cervical cages and the effect of cyclic loading on construct stability. SUMMARY OF BACKGROUND DATA: Threaded cages have been developed for use in anterior cervical interbody fusions to provide initial stability during the fusion process. However, metallic instrumentation has several limitations. Recently, totally bioresorbable bone fixation devices made of F-u-HA/PLLA have been developed, including a cage for spinal interbody fusion. However, no biomechanical study has compared the F-u-HA/poly-L-lactide (PLLA) cage with metallic cages. METHODS: For this study, 12 fresh ligamentous human cervical spines (C4-C7) were used. After anterior discectomy across C5-C6, stabilization was achieved with the F-u-HA/PLLA cage in six spines and with the Ray threaded fusion cage in the remaining six spines. Biomechanical testing of the spines was performed with six degrees of freedom before and after stabilization, and after cyclic loading of the stabilized spines (5000 cycles of flexion-extension at 0.5 Nm). RESULTS: The specimens stabilized with either the F-u-HA/PLLA cage or the Ray cage were significantly more stable than the discectomy case in all directions except in extension. In extension, both groups were stiffer, although not at a significant level (P > 0.05). After fatigue, the stiffness, as compared with that in the prefatigue case, decreased in both groups, although not at a significant level. The Ray cage group exhibited better stability than the F-u-HA/PLLA cage group in all directions, although a significant difference was found only in right axial rotation. CONCLUSIONS: The F-u-HA/PLLA cage has the possibility to supplant the use of metallic devices in interbody fusions of the cervical spine.

Biomechanical Phenomena↗

PubMed2003

Biomechanical evaluation of cervical double-door laminoplasty using hydroxyapatite spacer.

STUDY DESIGN: In vitro three-dimensional kinematic changes after double-door cervical laminoplasty, with and without spacer, and laminectomy were studied in a human cadaveric model. OBJECTIVES: To evaluate the effects of multilevel double-door laminoplasty and laminectomy as compared with the intact and to assess the influence of the spinous process spacer on the stability of the cervical spine. SUMMARY OF BACKGROUND DATA: Double-door type cervical laminoplasty has been widely used in the treatment of multisegmental stenotic conditions. However, its biomechanical advantages over laminectomy remain controversial. Also, the biomechanical effects of spacers between the split laminae have not been investigated. METHODS: Using fresh cadaveric C2-T1 specimens, sequential injuries were created in the following order: intact, double-door laminoplasty (C3-C6) with insertion of hydroxyapatite spacers, laminoplasty without spacer, and laminectomy. Motions of each vertebra in each injury status were measured in six loading modes: flexion, extension, right and left lateral bending, and right and left axial rotation.RESULTS Cervical laminectomy showed significant increase in motion compared with intact control in flexion [25% (P < 0.001)], extension [19% (P < 0.05)], and axial rotation [24% (P < 0.001)] at maximum load. Double-door laminoplasty with hydroxyapatite spacer indicated no significant difference in motion in all loading modes compared with intact. Laminoplasty without spacer showed intermediate values between laminoplasty with spacer and laminectomy in all loading modes. Initial slack of each injury status showed trends similar to that of maximum load, although mean percent changes of laminectomy and laminoplasty without spacer were greater than that of maximum load. CONCLUSIONS: Double-door laminoplasty with hydroxyapatite spacer appears to restore the motion of the decompressed segment back to its intact state in all loading modes. The use of HA spacers well contributes to maintaining the total stiffness of cervical spine. In contrast, laminectomy seems to have potential leading postoperative deformity or instability.

Adult↗

PubMed2003

An advanced approach for computer modeling and prototyping of the human tooth.

This paper presents a systematic and practical method for constructing accurate computer and physical models that can be employed for the study of human tooth mechanics. The proposed method starts with a histological section preparation of a human tooth. Through tracing outlines of the tooth on the sections, discrete points are obtained and are employed to construct B-spline curves that represent the exterior contours and dentino-enamel junction (DEJ) of the tooth using a least square curve fitting technique. The surface skinning technique is then employed to quilt the B-spline curves to create a smooth boundary and DEJ of the tooth using B-spline surfaces. These surfaces are respectively imported into SolidWorks via its application protocol interface to create solid models. The solid models are then imported into Pro/MECHANICA Structure for finite element analysis (FEA). The major advantage of the proposed method is that it first generates smooth solid models, instead of finite element models in discretized form. As a result, a more advanced p-FEA can be employed for structural analysis, which usually provides superior results to traditional h-FEA. In addition, the solid model constructed is smooth and can be fabricated with various scales using the solid freeform fabrication technology. This method is especially useful in supporting bioengineering applications, where the shape of the object is usually complicated. A human maxillary second molar is presented to illustrate and demonstrate the proposed method. Note that both the solid and p-FEA models of the molar are presented. However, comparison between p- and h-FEA models is out of the scope of the paper.

Anatomy, Cross-Sectional↗

PubMed2003

Comparison of stabilities between obliquely and conventionally inserted Bagby and Kuslich cages as posterior lumbar interbody fusion in a cadaver model.

BACKGROUND: The Bagby and Kuslich (BAK) cage as posterior lumbar interbody fusion (PLIF) is reported to give satisfactory results in restoring spinal stability. Moreover, correction by obliquely inserting a single BAK cage has the advantages of reducing exposure, precise implantation, and lower cost. However, biomechanical data on this procedure are not abundant. This study was designed to compare the stability imparted by the cages placed using an oblique and posterior approaches and to determine the effects of supplementary posterior instrumentation. METHODS: After affixing nine human cadaveric spines (L2-S1) within a testing frame, load testing in several clinically relevant modes was performed sequentially for the intact and the following procedures across the L4-5 segments: posterior destabilization, stabilization using 2 parallel BAK cages (CBAK group) or 1 oblique BAK cage (OBAK group), and additional stabilization with posterior instrumentation. Spatial locations of vertebral bodies were recorded after each loading step using a 3-D motion measurement system. RESULTS: Except the OBAK group that had a lower stability in left axial rotation, there were no significant differences in the stability between both groups in all loading modes for the stabilization using cages alone. Compared with the intact cases, CBAK cages provide significant improvement in the stability in 5 displacement modes and OBAK cage may restore the stabilities of the specimens to the intact state in 5 modes and provide significant improvement in flexion. Addition of supplementary posterior instrumentation significantly reduced the angular displacements in both groups. CONCLUSIONS: Both methods of cage insertion have similar stability. Both implantations, alone or with posterior instrumentation, may improve the stability of the spine, although posterior instrumentation may further strengthen the stability. The oblique insertion is more favorable since it requires less exposure, enables precise implantation, and is less expensive.

Cadaver↗

PubMed2002

An analysis of bone stresses and fixation stability using a finite element model of simulated distal radius fractures.

A 3-dimensional finite element model was used to study pin fixation in simulated unstable extra-articular distal radius fractures. Bone geometry and material properties were generated from computed tomography. The model was validated in cadaver testing. The model is robust and an accurate predictor of bone stresses and fracture stability under pure axial load. Three different pinning configurations and 3 different pin materials were evaluated. Crossed pinning provided greater fracture stability and a broader distribution of bone stresses than pinning through the radius styloid alone. Steel pins provided greater fracture stability; however, bioabsorbable pins produced lower stress concentration in the bone near the pins. A finite element model is useful in showing differences between various pin constructs in the treatment of distal radius fractures.

Aged↗

PubMed2002

In vitro biomechanical studies of an anterior thoracolumbar implant.

After L1 corpectomy in T11-L3 human cadaveric spine, anterior thoracolumbar instrumentation with strut grafting restores spinal stability. T12-L2 angular rotation was measured in response to moments of 0.0, 1.5, 3.0, 4.5, and 6.0 Nm in flexion, extension, lateral bending, and axial rotation, respectively. The spines were tested: 1) intact; 2) after partial L1 corpectomy, grafting, and instrumentation (Profile plate, DePuy-AcroMed, Raynham, MA), with the wooden dowel graft screwed to the plate; 3) without graft screw fixation; and 4) after flexion-extension cyclic fatiguing for 5000 cycles at a load of +/-3.0 Nm. Before and after fatiguing, the instrumented spine was significantly (p <or= 0.05) stiffer than the intact spine in flexion, extension, and right and left lateral bending but not in axial rotation. There were no significant differences between the constructs with or without graft-to-plate fixation before or after fatigue. The instrumented spines were more rigid in bending away from the implant than bending toward the implant. Anterior spinal instrumentation with the Profile implant augments stiffness in the sagittal and coronal planes but not in the axial plane. Although graft-to-plate fixation may prevent graft migration into the canal, it does not contribute to spinal rigidity.

Biomechanical Phenomena↗

PubMed2002

The biomechanical effects of multilevel posterior foraminotomy and foraminotomy with double-door laminoplasty.

The aim of this study is to evaluate the biomechanical effects of multilevel foraminotomy and foraminotomy with double-door laminoplasty compared with foraminotomy with laminectomy. Using fresh human cadaveric specimens (C2-T1), sequential injuries were created in the following order: intact, bilateral foraminotomies (C3-C4, C4-C5, C5-C6), laminoplasty (C3-C6) using hydroxyapatite spacer, removal of the spacers, and laminectomy. Changes in the rotations of each vertebra in each injury status were measured in six loading modes: flexion, extension, right and left lateral bending, and right and left axial rotation. Foraminotomy alone and following laminoplasty showed no significant differences in motion compared with intact except in axial rotation. After removal of the spacers and following laminectomy, the motion increased significantly in flexion and axial rotation. The ranges of initial slack showed similar trends when compared with the results at maximum load. Clinical implications of these observations are presented.

Aged↗

PubMed2002

Natural history of extruded lumbar intervertebral disc herniation.

We studied the natural history of extruded lumbar intervertebral discs using MRI. Forty-nine patients with lumbar disc herniation were included in this study. Ages ranged from 19 to 57. On the T2-weighted sagittal MR image, the signal intensity in the herniated mass was measured and the ratio to that in the original nucleus (i.e., nucleus pulposus from which they extruded) was calculated (signal intensity ratio; SIR). The relationship with SIR and duration of illness was evaluated. In ten patients who were re-examined by MRI after conservative treatment, the size of the herniation measured by T1-weighted axial MR image was compared before and after treatment. The signal intensity of HNP became higher than that of the original nucleus immediately following herniation and thereafter decreased with time, suggesting that initial hydration of the HNP occurred shortly after herniation followed by dehydration of the HNP. The size of the HNP with a SIR value of 1.2 and higher on T2-weighted MR images decrease with time, however, the HNP with a SIR below 1.2 did not show any size reduction. The SIR of 1.2 and higher is a good indicator predicting spontaneous reduction of the HNP. Dehydration in the HNP may play an important role in the reduction of the lumbar disc herniation.

Adult↗

PubMed1997

Biomechanical changes in the low back following reduction mammaplasty surgery.

OBJECTIVE: To give evidence of the mechanical consequences of reduction mammaplasty (RM) on the low back. DESIGN: A repeated-measures analysis was implemented to test the effect of RM on the external loads and angular velocity of the back during both static and dynamic lifting tasks. BACKGROUND: Patient follow-up surveys have documented a decrease in the frequency of low back pain following RM, but there is no quantitative data regarding biomechanical changes following surgery. METHODS: Patients were evaluated before and 4-8 weeks following RM. Flexion moment, compression and shear forces at L3-L4 were quantified for isometric flexion angles between 0 and 40 degrees. External loads and angular velocities of the back were studied during rapid dynamic lifting tasks. RESULTS: Isometric external flexion moments at L3-L4 decreased following RM. RM did not effect the applied flexion moment in the lumbar spine, but a trend suggested that RM resulted in increased lifting velocity. CONCLUSIONS: RM does act to reduce the loads on the lumbar spine during simple isometric tasks. During dynamic tasks, subjects may be able to lift faster without generating larger loads.

Journal Article↗

PubMedDate not supplied

Artificial disc prosthesis: design concepts and criteria.

Clinical and biomechanical objectives of disc arthroplasty are reviewed in this paper. The available literature relative to these criteria for nucleus and total disc replacement where relevant is also reviewed. Clinical criteria include: pain relief, functional recovery, lower morbidity than spinal fusion, shorter recuperation, and ease of implantation and revision. Biomechanical criteria include: preservation of motion in compression-bending and compression-torsion, shock absorption, relief of abnormal stresses within and adjacent to the motion segment, stability, and alignment. A review of devices with these criteria in mind is reported.

Arthroplasty, Replacement↗