Search PubMed⌕ Search

Biomedical subjects

V K Goel

Publications and source records attributed to V K Goel.

At least 109 records · Page 6Linked to original sources
PubMed1990

Stimulation of dorsal root ganglia and degradation of rabbit annulus fibrosus.

The authors sought to determine whether narrowing of the intervertebral neural foramen, by itself and in association with vibration, would stimulate the mechanosensitive dorsal root ganglia and result in degradation of proteoglycan and collagen of the annulus fibrosus, as proposed in their working model of dorsal root ganglia-neuropeptide-mediated degeneration of the spinal motion segment. Degradation of proteoglycan and collagen of rabbit annulus was observed when there was narrowing of the neural foremen and the degradation process was accelerated by vibration. Vibration alone, in the absence of structural abnormalities of the spinal motion segment, did not induce matrix degradation probably because of a less pronounced stimulation of the dorsal root ganglia. Biological events similar to those postulated here, fomented by a combination of structural abnormalities and environmental factors, could be involved in human disc degeneration.

Animals↗
PubMed1990

Ligamentous laxity across C0-C1-C2 complex. Axial torque-rotation characteristics until failure.

The axial torque until failure of the ligamentous occipito-atlanto-axial complex (C0-C1-C2) subjected to axial angular rotation (theta) was characterized using a biaxial MTS system. A special fixture and gearbox that permitted right axial rotation of the specimen until failure without imposing any additional constraints were designed to obtain the data. The average values for the axial rotation and torque at the point of maximum resistance were, respectively, 68.1 degrees and 13.6 N-m. The specimens offered minimal resistance (approximately 0.5 N-m), up to an average axial rotation of 21 degrees across the complex. The torque-angular rotation (T-theta) curve can be divided into four regions: regions of least and steadily increasing resistances, a transition zone that connects these two regions, and the increasing resistance region to the point of maximum resistance. The regions of least and steadily increasing resistances may be represented by two straight lines with average slopes of 0.028 and 0.383 N-m/degree, respectively. Post-test dissection of the specimens disclosed the following. The point of maximum resistance corresponded roughly to the value of axial rotation at which complete bilateral rotary dislocation of the C1-C2 facets occurred. The types of injuries observed were related to the magnitude of axial rotation imposed on a specimen during testing. Soft-tissue injuries alone (like stretch/rupture of the capsular ligaments, subluxation of the C1-C2 facets, etc.) were confined to specimens rotated up to or close to the point of maximum resistance. The specimens that were subjected to rotations up to the point of maximum resistance of the curve spontaneously reduced completely on removal from the testing apparatus. Spontaneous reduction was not possible for specimens tested slightly beyond their points of maximum resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed1990

Possible role of stresses in inducing spinal stenosis--a long term complication following disk excision.

A three-dimensional finite element model of an intact ligamentous lumbar motion segment (L3-4) was used to predict stresses in the pars interarticularis regions of the modeled vertebral bodies. The changes in stresses following disk excision, as compared to the intact model, also were computed. The predicted results show an increase in stresses in the posterior bony elements following disk excision. In some patients over a long period of time this increase in stresses, in association with other clinical factors, may lead to bony hypertrophy of the structures that surround the nerve roots. Ultimately, over a long period of time the increase in pressure on the entrapped nerve root may induce recurrent pain and other complications reported in the literature.

Biomechanical Phenomena↗
PubMed1989

Evaluation of effectiveness of a facet wiring technique: an in vitro biomechanical investigation.

The effects of facet wiring procedure commonly used for stabilizing cervical spines after laminectomy or bilateral facet dislocation on the motion behavior of whole cervical spines are investigated using a Selspot II system. A fresh human ligamentous intact specimen was potted at T1/T2 vertebra and clinically relevant loads applied to the topmost vertebra (C2) of the specimen. The resulting three rotational components of each of the five vertebral bodies (C3-C7) were recorded. Specimen was injured to mimic total laminectomies at C5 and C6 vertebral levels and tested again. The injured specimen was stabilized, using a facet wiring construct, across C4-C7 segment before testing for the final time. The injured specimens, compared to the intact specimens, demonstrated an increase in flexion-extension of about 10%. Facet wiring imparted stability to the cervical spine by stiffening segments up to roughly four times intact values.

Aged↗
PubMed1989

Stress distribution in the ulna following a hinged elbow arthroplasty. A finite element analysis.

The failure rates for total elbow arthroplasty, in comparison to those for hip arthroplasty, are quite high, and a precise understanding of the underlying causes still remains elusive. The presence of abnormal stresses is a known factor that accelerates loosening of hip and knee arthroplasties. Although a large number of biomechanical studies have led to a better understanding of elbow joint kinetics, very little is known about the stress distribution in this joint. The implantation of a Coonrad humeral component increases stresses in the bone and cement adjacent to the stem tip and hinge regions. An analysis of implanted ulnar stresses and a comparison of those stresses to implanted humeral stresses would improve our understanding of hinged elbow arthroplasty. For this reason, the distribution of mechanical stresses in the ulna are investigated in this study. Using a specially developed casting and sectioning technique, three-dimensional finite element meshes were obtained from an intact human cadaver ulna and an ulna fitted with a Coonrad prosthesis. The material properties were derived from values presented in the literature. Stress distributions in response to axial compression, axial torque, and anteroposterior (AP) force were computed. The cancellous bone and cement regions adjacent to the stem tip of the prosthesis exhibited higher stresses than those in the same regions of the intact case. The higher stresses in the ulna with an implanted prosthesis, as compared to the intact model, might initiate loosening or failure of the prosthesis. The stresses in the cortical bone region adjacent to the prosthesis head were decreased. This is consistent with the clinical observations of bone atrophy following total elbow arthroplasty.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Kinematics of the cervical spine following discectomy and stabilization.

The immediate biomechanical stability of the cervical spine following discectomy and stabilization is described. Fresh human ligamentous spines (C2-T2) were potted, and clinically relevant loads were applied by a loading frame attached to the C2 vertebra of each specimen. A set of three infrared light-emitting diodes (LEDs) were attached rigidly to each of four vertebrae (C4 to C7) to record their spatial locations after each load step application using a Selspot II (Selcom Selective Electronic, Inc., Valdese, North Carolina) system. The specimen was tested in the intact state, following discectomy at the C5-6 intervertebral level, following insertion of a bone graft in the intervertebral space, and following the application of an anterior metal plate. The load-deformation data of the injured and stabilized tests were normalized with regard to the corresponding results of the intact specimens. At the injured level (C5-6), the load-deformation results indicated a highly significant increase in motion in flexion (66.6%), extension (69.5%), lateral bending (41.3%), and axial rotation (37.9%). After the insertion of the bone graft, a significant decrease in motion was seen in the effected segment in extension (-45.9%), with similar reductions in lateral bending and axial rotation and a smaller reduction in flexion. The application of an anterior metal plate in addition to the bone graft at the injured level provided significant reduction in motion (-70%) in all load modalities. This data may have clinical relevance regarding the role of internal fixation in cases of severe spine instability.

Biomechanical Phenomena↗
PubMed1988

Kinematics of the cervical spine: effects of multiple total laminectomy and facet wiring.

The effect of multiple-level total laminectomies followed by stabilization on the load-deformation behavior of the cervical spine is described. Fresh human ligamentous cervical spines (C2-T2) were potted and clinically relevant load types applied via a loading frame attached to the C-2 vertebra of the specimen. A set of three infrared light-emitting diodes (LEDs) were attached rigidly to each of five vertebrae (C3-7) to record their spatial locations after each load step application, using a Selspot II system. The specimen was tested again after total laminectomy performed on C5. The supraspinous, interspinous, and flavum ligaments between the C4-5 and C5-6 motion segments were cut; thereafter, the vertebral arch was removed. The specimen testing was resumed after inducing injury at C-6 in a similar fashion. The specimen was stabilized, using a facet wiring construct, across the C4-7 segment before testing for the final time. The load-deformation data of the injured and stabilized tests were normalized with regard to the corresponding results of the intact test. In flexion-extension mode, an increase in motion of about 10% after laminectomies was observed. Facet wiring was found to be an effective technique to stabilize injured cervical spines (approximately equal to 80% reduction in motion, compared with intact spines, was observed.

Biomechanical Phenomena↗
PubMed1988

Moment-rotation relationships of the ligamentous occipito-atlanto-axial complex.

The relationships between applied pure moments at the occiput (C0) and the resulting rotations at the atlanto-occipital (C0-C1) and atlanto-axial (C1-C2) joints are quantified. In axial twist, with a moment of 0.3 Nm, a mean rotation of about 2.5 degrees and 23.3 degrees was observed at C0-C1 and C1-C2 units respectively. Both the atlas and axis contributed to produce lateral bending motion. The ratio between extension and flexion rotations at C0-C1 was 2.5:1. Lateral bending and axial rotations were strongly coupled to each other. The occipito-atlanto-axial complex exhibited a large 'neutral zone' compared to lower cervical spine segments. The likely clinical significance of these findings are discussed.

Aged↗
PubMed1988

Response of the ligamentous lumbar spine to cyclic bending loads.

The effect of a "pure" cyclic flexion bending moment on the three-dimensional load-displacement behavior of fresh ligamentous lumbar spine was investigated. The load-displacement behavior, for 11 L1-sacrum specimens, pre- and post-cyclic fatigue bending tests were quantified using a Selspot II system. A special fixture was designed to mount the specimen within the MTS system to administer "pure" cyclic flexion bending, under displacement control, for 5 hours. The testing was accomplished in a 100% humidity chamber at 0.5 Hz. The maximum cyclic bending moment, based on the literature dealing with loads experienced by the spine during activities involving lifting, was set at 3.0 Nm. An increase in motion of the order of 10% in the extension loading mode was observed. The increase in motion in other loading modes was not significant. In the extension loading mode, the increase in the anteroposterior displacement (retrodisplacement) in general was higher than the corresponding rotation component. The results suggest that the bending moment of low magnitude, usually experienced by the spine during activities of daily living, alone may not trigger the mechanical failure processes in the disc. The presence of high axial compressive loads on the disc seems to be the main contributing factor in this process. The presence of bending moments and axial twist along with axial compressive load may accelerate the unstable processes leading to low back pain.

Humans↗
PubMed1988

An analytical investigation of the mechanics of spinal instrumentation.

Three-dimensional nonlinear finite element models of the intact L4-5 one motion segment/two-vertebrae and L3-5 two motion segments/three-vertebrae were developed using computed tomography (CT) films. The finite element mesh of the L4-5 motion segment model was modified to simulate bilateral decompression surgery. The mesh was further altered to achieve stabilization, using an interbody bone graft and a set of Steffee plates and screws. The model behavior of the intact specimen in all loading modes and of the stabilized model in compression, flexion, and extension modes were studied. The stresses in the cancellous bone region were found to decrease. The interbody bone graft, due to an overall decrease in stresses in the bone below the screw, transmits about 80% of the axial load as compared with 96% transmitted by an intact disc in an intact model. Thus, the use of a fixation device induces a stress shielding effect in the vertebral body. The results indicate that although the bone graft transmits lesser loads than the intact disc, it is active in transmitting loads. The presence of low stresses in the cancellous bone region and high localized stresses in the cortical pedicle region surrounding the screw, compared with the intact case, suggests that the screws are likely to become loose over time. The use of an interbody bone graft alone or in combination with any existing fixation device also induces higher stresses at the adjacent levels. This may be responsible for the adverse iatrogenic effects seen clinically.

Biomechanical Phenomena↗
PubMed1987

A technique to evaluate an internal spinal device by use of the Selspot system: an application to Luque closed loop.

A technique to study the effects of spinal injury and stabilization in terms of load-deformation behavior is described. Fresh human cadaveric ligamentous spine segments (T12-sacrum) were potted and clinically relevant loads applied through the loading frame attached to the topmost vertebra of the specimen. The resulting three-dimensional motion responses of each vertebra for the normal specimen were recorded with the Selspot II System. The specimen was injured at the L4-5 motion segment to represent a typical surgical decompression used in treating patients with spinal stenosis and tested again. The decompressed (or injured) motion segment was stabilized with a Luque closed-loop (Luque rectangle) system before repeating the test protocol. The data of these tests indicate that the injury (surgical decompression) at the L4-5 motion segment leads to a significant increase in motion--in flexion, extension, and axial modes--indicating the possible necessity for stabilization of the injured segment. The closed-loop system reduces the motion at the injured level, with respect to normal specimen behavior, by 35%. Therefore, the system does not provide complete immobilization (100% reduction with respect to normal specimen behavior). The stabilizing effects of the closed loop in lateral bending are not significant and are marginal in axial motion. The motion across the L3-4 motion segment in flexion increases significantly after stabilization. The clinical implications and the need for further studies are also discussed.

Adult↗
PubMed1987

Load sharing among spinal elements of a motion segment in extension and lateral bending.

A linear optimization model was formulated using a semi-experimental protocol to estimate the forces in the spinal elements of a lumbar motion segment subjected to an extension or lateral bending moment with and without a 120 N compressive preload. A morphometer was used to acquire the three-dimensional locations of the disk center, facet centers and ligament origin and insertion sites with the specimen in a "neutral" position. The relative motion of the superior vertebra, under the loading conditions tested, was monitored using a Selspot II system. These data allowed the formulation of the static equilibrium equations for the superior vertebra at each of the loading conditions mentioned above. A linear optimization technique was used, along with a suitable cost function, to find an optimum solution for the set of equations and imposed constraints. Results showed that for 6.9 Nm of extension moment, each facet carried a load of 52 N, with the disk carrying an axial tensile load of 104 N. At the 6.9 Nm extension moment coupled with 120 N preload, each facet carried a load of 77.2 N and the disk an axial tensile load of 37 N. In right lateral bending, with and without preload, the load was distributed among the right facet, the disk, the left ligamentum flavum and the left capsular ligament. At the 6.9 Nm load step without preload the right facet carried an axial load of 127.01 N with the disk carrying an axial compressive load of 7.8 N. Ligament forces for this step for the left ligamentum flavum and capsular ligament, respectively, were 61.03 N and 65.14 N. The addition of 120 N of preload reduced the load on the right facet to 83.5 N. The compressive load in the disk increased to 107.5 N. The corresponding ligament forces were 43.2 N (left ligamentum flavum) and 50.7 N (left capsular ligament).

Biomechanical Phenomena↗
PubMed1987

Left ventricular performance in cases with chronic renal failure. A study of systolic time intervals.

Left ventricular (LV) functions as reflected in systolic time intervals (STIs) were studied in 28 patients with chronic renal failure (CRF) and in an equal number of age and sex matched normal controls. Measurement of STIs revealed that mean total electromechanical systole (QS2) and left ventricular ejection time (LVET) were significantly decreased, whereas isovolumic contraction time (IVCT) was significantly increased in patients with CRF as compared to controls. Mean PEP/LVET ratio did not show any significant change. Eleven cases of CRF had congestive heart failure, and in 9 of them the PEP/LVET ratio was normal. Seven cases of CRF had evidence of left ventricular dysfunction (PEP/LVET greater than 0.4). In 6 cases, STIs were also recorded following dialysis, and revealed an increase in PEP, IVCT and PEP/LVET and a decrease in QS2 and LVET, but none of these changes were statistically significant. It is concluded that only a small percentage of cases of renal failure show LV dysfunction. However, signs of congestion are seen in a greater number of cases. These are not necessarily indicative of LV dysfunction but may be due to fluid and electrolyte overloading.

Adult↗
PubMed1986

Mechanical properties of lumbar spinal motion segments as affected by partial disc removal.

The changes in the three-dimensional motion behavior of the lumbar motion segments, as affected by partial discectomy, are presented. The injured specimens, when subjected to flexion, extension, lateral bending, or axial torsional loads, showed significant increases in their major motions when compared with the corresponding intact specimen. No significant increases in the coupled motions were observed. These results suggest that it is better to excise as little of the nucleus as possible at surgery, since it may limit the increase in motion due to the injury.

Aged↗