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Biomedical subjects

V K Goel

Publications and source records attributed to V K Goel.

At least 19 recordsLinked to original sources
PubMed1992

Dynamic response of the occipito-atlanto-axial (C0-C1-C2) complex in right axial rotation.

The torque-angular deformation in right axial rotation until failure of the ligamentous occipito-atlanto-axial complex subjected to variable loading rate (dynamic) axial torque was characterized using a biaxial MTS system. A special fixture and gear box that permitted right axial rotation of the specimen until failure without imposing any additional constraints were used to obtain the data. The specimens were divided into three groups and tested until failure at three different dynamic loading rates: 50, 100, and 400 degrees/s. A previous study by the authors provided data for quasi-static (4 degrees/s) loading conditions. The torque versus rotation curves can be divided into two straight regions and two transition zones. The plots clearly indicated that at loading rates higher than 4 degrees/s, the specimens became stiffer in the region of steadily increasing resistance prior to failure. The increase in stiffness was maximum at 100 degrees/s. The stiffness decreased somewhat at 400 degrees/s in comparison with 100 degrees/s, but this decrease was not significant. The resulting torque-right axial rotation curves were also examined to estimate the magnitude of maximum resistance (torque) and the corresponding angular rotation value. The average maximum resistance torque increased from 13.6 Nm at 4 degrees/s to 27.8 Nm at 100 degrees/s. The corresponding right angular rotation data (65-78 degrees), however, did not show any significant variation with loading rate. Posttest dissection of the specimens indicated that the type of injury observed was related to the rate of axial loading imposed on a specimen during testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Development of a computer model to predict strains in the individual fibers of a ligament across the ligamentous occipito-atlanto-axial (C0-C1-C2) complex.

A fresh ligamentous occipito-atlanto-axial (C0-C1-C2) complex was appropriately prepared and serially sectioned into thin slices along the transverse planes. The bony outlines from these slices were digitized and assembled in the proper manner to obtain a three-dimensional model of the complex using the AutoCAD system. Various ligaments were identified on the model and strains in individual fibers of a ligament were predicted based on the principles of rigid body mechanics. The ligament behaviors in axial rotation, flexion, and extension modes were analyzed. The capsular ligament fibers were predicted to undergo strains in all modes. Furthermore, these ligaments experienced the largest strain among the ligaments analyzed. Fibers within a ligament were found to respond differently; some were more active than the others and some did not experience any strain at all. A differential behavior in the right and left side alar ligament fibers was also found in axial rotation. The transverse ligament was predicted to wrap around the dens during axial rotation. The strain within a fiber was found to be a function of the initial length (ligament laxity) and its distance from the center of rotation.

Atlanto-Axial Joint↗
PubMed1992

Effect of cavity depth on stresses in a restored tooth.

Restorative procedures commonly replace lost tooth structure, but redistribution of functional stresses after treatment is not fully understood. Many restorative methods are dictated by the integrity of the remaining tooth structure, because sparse tooth structure can lead to fracture. It is essential to prevent fractures by having a clear concept of the designs for cavity preparations, and to anticipate the stresses of mastication on the remaining tooth structure. Knowledge of various internal parameters of cavity designs would facilitate selection of the appropriate cavity preparation for a specific clinical situation. Three cavity designs and restorations were examined in this study for stresses using the finite element technique. After placement of restorative materials, the dentin experienced a dramatic change in stress gradient immediately below the pulpal wall, and this response was magnified in deeper cavity preparations. Enamel also exhibited major alterations in the stress gradient in all three designs of cavity preparations. The combination of the changes can cause cracks in the remaining tooth structure, leading to cusp fracture immediately adjacent to the deepest portion of the cavity.

Alveolar Process↗
PubMed1992

Isolated L4-L5 fusions using the variable screw placement system: unilateral versus bilateral.

Thirty-six patients were retrospectively followed an average of 25.1 months to evaluate the relative effectiveness of unilateral (16 patients) versus bilateral (20 patients) variable screw placement (VSP) instrumentation in isolate L4-L5 fusions. Demographic variables and preoperative diagnoses were similar between treatment groups. Outcome was assessed primarily through evaluation of plain roentgenograms and self-report questionnaires. Use of VSP instrumentation at the L4-L5 level with autogenous posterolateral grafting achieved a successful fusion rate of 97% with minimal complications. Fusion results with unilateral instrumentation were nearly identical to those of bilateral; in both cases, results were better than most historical controls for noninstrumented fusions in situ. Clinical outcome, as obtained through standardized measurement techniques of pain and function, demonstrated 69% excellent and good results. Clinical outcome was similar between treatment groups yet was not significantly related to the fusion status obtained at follow-up.

Adult↗
PubMed1992

Meniscus-like synovial fold in the atlantoaxial (C1-C2) joint.

Some of the synovial joints in the human body have a fibrocartilaginous disc interposed between the joint surfaces to absorb or evenly distribute loads. Examples of fibrocartilagenous discs include the intervertebral disc, knee joint meniscus, and triangular fibrocartilages in the distal radioulnar joint and the acromioclavicular joints. The joint capsule and the surrounding tissue from nine cervical spines (18 C1-C2 joints) were dissected and prepared for gross examination and histology. We found meniscus-like synovial folds in 13 of the 18 atlantoaxial joints. These folds were located at the anteromedial and posteromedial aspect of the joint. Each synovial fold was of semilunar shape, with a thickened outer edge and thin inner edge giving a wedge-shape cross section. In one case, the synovial fold was grossly similar in appearance to a knee joint meniscus, and on histological examination there was evidence of cartilagenous metaplasia in part of the fold. The findings are compared with the limited data reported in the literature.

Aged↗
PubMed1992

CT-based geometric data of human spine musculature. Part I. Japanese patients with chronic low back pain.

Mechanical factors are considered to play a dominant role in low back problems. Various spinal structures, including muscles, act in unison to resist the external load, including the body segments. An estimation of the forces in these requires a knowledge of the orientation, location, and area of cross-section of the muscles to complete the information for the formulation of a truly three-dimensional biomechanical mathematical model of the spine in the lumbar region. Computed tomography scans of 10 Japanese patients suffering from chronic low back pain were obtained to determine the geometric data of the abdominal and back muscles from the 12th thoracic vertebral to the first sacral vertebral level. The mean age +/- 1 SD of the group was 40.1 +/- 14.12 years (range, 24-70), 573 +/- 88.5 N of body weight (range, 441-705), and 1.63 +/- 0.09 m tall (range, 1.44-1.74). The geometric parameters quantified were the line of action, and the centroid and physiologic area of cross-section of each muscle as a function of the spinal level. The effective/physiological area of cross-section of each muscle changed along the length of the spine because of the change in the line of action of the muscle. The centroidal approach adopted for quantifying the lines of action of various muscles was found unsuitable for the abdominal muscles, excluding the rectus abdominis, because of the associated anatomic complexities. Alternatives are proposed to complete the data base. The application of the data for the formulation of a truly three-dimensional biomechanical model of the spine at the L3-4 level is briefly presented. Application to nonlinear optimization-based force predictions in various spinal structures is discussed.

Adult↗
PubMed1992

Comparison of stress transmission in the IMZ implant system with polyoxymethylene or titanium intramobile element: a finite element stress analysis.

Using the finite element method, this study modeled a 4.0 x 13.0-mm IMZ implant, restored with a cast gold crown, to examine the influence of the polyoxymethylene (POM) intramobile element (IME) on the transmission of vertical and oblique forces. Stress concentrations in the bone and in components of the implant system were much greater under a 30-degree load than under an equal vertical load. Stress transmission to bone occurred chiefly in the crestal region, and these stresses were not reduced when the IME was modeled in POM rather than in titanium. Maximum stress concentrations occurred in the fastening screw.

Alveolar Process↗
PubMed1992

A study of nerve conduction velocity in patients on diphenylhydantoin therapy.

Peripheral nerve conduction studies were performed in 30 epileptics, treated with DPH and results were compared with age and sex matched controls. There was significant reduction in the amplitude of sensory nerve action potential of median (26.65 +/- 14.71 mu v) and superficial radial nerve (25.65 +/- 10.08 mu v) (p < 0.001) in DPH treated group as compared to controls, (median nerve 42.64 +/- 15.93 uv and superficial radial nerve 40.72 +/- 24.74 mu v). The results suggest that DPH causes a subclinical distal axonal neuropathy in therapeutic dosage.

Action Potentials↗
PubMed1991

Stresses at the dentinoenamel junction of human teeth--a finite element investigation.

A three-dimensional, linear, elastic finite element model of a maxillary first premolar from longitudinal ground sections was developed to investigate stress variation in the enamel and dentin adjacent to the dentinoenamel junction (DEJ). The effect of regional variation in the contour of the DEJ on the stress patterns for enamel and dentin was also analyzed. The normal (compressive or tensile) and shear stresses in the dentin and enamel surfaces of the DEJ were computed for a vertical load of 170 N acting on the entire occlusal surface of the model. The normal stresses in dentin and enamel were maximum on the occlusal surface of the model and diminished along the buccal and lingual surfaces of the DEJ. However, the magnitude of the normal stresses increased at the cervical enamel, which also showed increased values for shear stress distribution. The normal and shear stresses were markedly affected by the contour of the DEJ and the thickness of enamel in the occlusal third on the buccal and lingual surfaces. The results suggested that because the mechanical interlocking between enamel and dentin in the cervical region is weaker than in other regions of the DEJ, enamel in this region may be susceptible to belated cracking that could eventually contribute to the development of cervical caries.

Bicuspid↗
PubMed1991

In vitro comparative biomechanical analysis of transpedicular screw instrumentations in the lumbar region of the human spine.

An analysis of the load-displacement behavior of stabilized spines in comparison with intact spines was undertaken using fresh human cadaveric spines (T12/L1--sacrum). The three-dimensional load-displacement data of the five vertebral bodies of an intact specimen in clinically relevant loading cases were recorded using the Selspot II motion measuring system. After testing the intact specimen, an instability was created at the L4-5 level. The unstable motion segment was stabilized sequentially with three transpedicular screw instrumentations. The stabilized specimens were tested, and the data for the stabilized tests were normalized with respect to the intact data to determine the degree of stabilization achieved in various loading modes as a function of the three devices. The results showed that the three transpedicular devices included in this study were effective in imparting stability to the injured ligamentous spinal segment at a p less than 0.01 level of significance. The differences among the devices were not significant.

Aged↗
PubMed1991

Effect of disc degeneration at one level on the adjacent level in axial mode.

Nonlinear three-dimensional finite element models of a ligamentous two motion segments spine specimen (L3-L4-L5) were developed to investigate the effects of disc degeneration, simulated at the L4-L5 level, on the biomechanical behavior of the adjacent intact L3-L4 motion segment. The disc degeneration was simulated by removing the hydrostatic capabilities of the nucleus and making the L4-L5 disc stiffer than a normal disc. The results of the degenerated model were compared with the predictions for a model in which the L4-L5 disc was left intact. The loads on the facets decreased, and intradiscal pressure in the intact L3-L4 disc increased as a result of disc degeneration compared with the intact model. The predicted increase in the intradiscal pressure and the associated increase in the disc bulge in the posterior region over time may trigger the degenerative process at the L3-L4 motion segment. This is in accordance with the Wolff's law; living tissue responds to chronic changes in stresses and strains. The limitations of the present two motion segments model and the potentials of multisegmental models are discussed.

Cadaver↗
PubMed1991

Effects of rigidity of an internal fixation device. A comprehensive biomechanical investigation.

Internal fixation with instrumentation often accompanies surgical fusion to augment spinal stability, provide temporary fixation while the surgical fusion mass unites, and enhance postoperative mobilization of a patient. Some surgeons, however, feel that the existing plate-screw designs are too rigid and are the primary cause of "iatrogenic" adverse effects clinically observed. A three-part study, involving in vitro experimental protocol, analytical finite-element-based models, and an in vivo canine investigation, was undertaken to study the role of decreasing rigidity of a device on the biomechanical response of the stabilized segments. Two alternatives--the use of one variable screw placement (Steffee plate [unilateral, 1VSP model]) as opposed to two VSP plates (bilateral, 2VSP model) and two VSP plates with polymer washers placed in between the integral nut and plate (2MVSP model)--were considered for achieving a reduction in the rigidity of the conventional VSP system. The load-displacement data obtained from the in vitro experiments and the stress distributions within the stabilized and intact models predicted by the finite-element models revealed that the unilateral VSP system is less rigid and is likely to reduce stress shielding of the vertebral bodies compared with the 2VSP model. The undesirable effects associated with the use of the 1VSP plate system are the presence of coupled motions due to the inherent asymmetry and the likely inability to provide enough rigidity for decompression procedures requiring a complete excision of the disc. The use of two MVSP plates overcomes these deficiencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Clinical implications of the response of enamel and dentin to masticatory loads.

The success of restorative procedures is dependent on comprehension of the responses of enamel and dentin, including responses to masticatory forces. The regional variation resulting from masticatory forces is critical because clinically it relates to the thickness of enamel and dentin occlusogingivally. Three-dimensional finite element models of an intact mandibular molar were developed to analyze stresses in enamel and dentin occlusogingivally, buccolingually, and mesiodistally. There were dramatic regional variations in the magnitude and character of different stresses caused by masticatory forces, and despite being organically "bonded," enamel and dentin responded independently. This unique behavior with regional variations of these tissues could have serious clinical implications during restorative procedures.

Bite Force↗
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↗