Biomedical subjects

V K Goel

Publications and source records attributed to V K Goel.

At least 73 records · Page 4Linked to original sources

PubMed1995

Biomechanical testing of the spine. Load-controlled versus displacement-controlled analysis.

Mechanical testing of the spine can be carried out in either a load-controlled or a displacement-controlled manner. Each method requires certain assumptions and offers different advantages. Dr. W. Thomas Edwards believes that displacement-controlled testing most accurately reflects the in vivo environment, while Drs. Vijay Goel, David Wilder, and Malcolm Pope support the use of the load-controlled method as most logical and easily standardized.

Biomechanical Phenomena↗

PubMed1995

Assessment of unicortical and bicortical fixation in a quasistatic cadaveric model. Role of bone mineral density and screw torque.

STUDY DESIGN: The stabilizing potential of the Caspar Trapezial Osteosynthetic Plate was studied using unicortical and bicortical screw placement in cadaveric cervical spines. OBJECTIVE: To determine if Caspar plates secured with unicortical screws provide the same degree of stability as those anchored with unlocked bicortical screws. SUMMARY OF BACKGROUND DATA: Previous work has demonstrated that bicortical cervical vertebral screws are superior to unicortical screws in terms of pullout strength and decreased wobble. However, these two methods of plate fixation have not been directly compared in a clinically relevant cadaveric model. METHODS: The immediate and post-fatigue stabilizing potential of Caspar plates secured with unicortical or bicortical screws was assessed using a model of complete segmental instability. RESULTS: Unicortical screw placement resulted in inadequate stabilization in half of the cervical specimens. CONCLUSIONS: Our results suggest that, for the Caspar screw, bicortical fixation provides greater flexion-extension stability.

Biomechanical Phenomena↗

PubMed1995

Applications of the finite element method to thoracolumbar spinal research--past, present, and future.

The finite element method has been used in spine biomechanics research for nearly a quarter of a century. Recent developments have made it possible to simulate a variety of clinical situations in an increasingly realistic manner, and have elevated the finite element method into a fully complementary partnership with experimental approaches for investigating clinical problems of the spine. The impact of several of these new developments on present and future spine biomechanics research is addressed in this update.

Biomechanical Phenomena↗

PubMed1995

Interlaminar shear stresses and laminae separation in a disc. Finite element analysis of the L3-L4 motion segment subjected to axial compressive loads.

STUDY DESIGN: This study analyzed interlaminar shear stresses across the laminae of a ligamentous L3-L4 motion segment. A three-dimensional finite element model of the motion segment was developed and its response in axial compression mode was predicted. OBJECTIVES: The contributions of "mechanical" factors in producing laminae separation in a disc are not well understood, especially when the nucleus is still gel-like in appearance (stage 1 of disc degeneration). All types of stresses are likely to contribute to laminae separation. The authors believe it is partially due to the interlaminar shear stresses at the laminae interfaces in specific regions of an intact disc because the disc is a composite structure. The effects of anular tears on the interlaminar shear stresses were also investigated. These tears can be circumferential or radial in nature, and commonly occur in the aged, degenerated disc. SUMMARY OF BACKGROUND DATA: A large number of biomechanical studies dealing with the role of the disc vis-a-vis other spinal components have been reported in the literature. The role of mechanical factors, however, in producing laminae separation, especially when the nucleus is still gel-like in appearance (stage 1 of disc degeneration), is not entirely clear. METHODS: A three-dimensional nonlinear finite element model of an intact L3-L4 lumbar motion segment, based on the use of a special type of element for the disc anulus, was created to investigate the interlaminar shear stresses in the anulus. The effects of radial "out-in," radial "in-out," and "circumferential" injuries were analyzed. Injury was modeled as element removal in the posterolateral portion of the disc. Models subjected to axial compressive loads, ranging from 200 N to 2000 N, were analyzed. In addition to the interlaminar shear stresses, disc bulge, and displacements including coupled motions were predicted. RESULTS: The theoretical disc bulge predictions for the radial in-out injury case were in agreement with the disc bulge data obtained experimentally. Displacements, disc bulge, and coupled motions increased with injury, as expected. The interlaminar shear stresses were highest in the posterolateral portions of the intact disc model. Interlaminar shear stresses, in general, increased with injury. Also, a slight increase in circumferential injury was sufficient to see a substantial increase in interlaminar shear stresses. CONCLUSIONS: The interlaminar shear stresses being higher in the posterolateral regions of the intact disc reinforces that, from clinical studies, tears originate in the posterolateral portion of the disc. The large interlaminar shear stresses, caused by asymmetry in the disc structure due to injury, along with chemical and structural changes in the disc with age, may be an important cause of further degeneration through laminae separation. This is the case for traditional composite laminates. This study points out the importance of interlaminar shear stresses to gain further understanding of the role of mechanical factors in producing disc degeneration, especially delamination of the anulus. Clinical relevance of the findings and possible relationship to the aging process are explored.

Adolescent↗

PubMed1995

Loads in the spinal structures during lifting: development of a three-dimensional comprehensive biomechanical model.

Epidemiological studies have shown that loads imposed on the human spine during daily living play a significant role in the onset of low back pain. The loads applied to the lumbar spine are shared by a number of structures: muscles; posterior elements, including facets and ligaments; and the disc of a ligamentous motion segment. In vivo, it is not practical to determine forces in these structures using experimental techniques. Biomechanical models, based on an optimization technique of electromyographic activities of the trunk muscles, have been proposed to predict forces in the load transmitting structures. The mathematical models reported in the literature are based on information collected from a wide variety of sources, of which the subject that takes part in the experiment is only one. The present study describes techniques developed in our laboratory to collect from the subjects themselves all the data needed for the formulation of a biomechanical model. The results demonstrated that back lifting with 0 N (no load), 90 N, and 180 N in the hands created maximum external flexion moments respectively of 109.6 Nm, 137.9 Nm, and 161.7 Nm, at the L3-4 disc level. The corresponding external axial compression forces on the disc were 469.5 N, 511.8 N, and 601.5 N. The predicted disc compression varied from 3.4 to 5.0 times the body weight. In comparison to the static lifting mode, the dynamic lifting task caused an increase in the disc compression force ranging from 15.8% to 39.4% depending on the load being lifted (e.g., 3256 N for the dynamic mode vs. 2516 N for the static mode when the subject lifted 90 N). The salient features of the entire protocol developed by the authors and the need for further improvements are also presented.

Adult↗

PubMed1995

A three-dimensional finite-element stress analysis of an endodontically prepared maxillary central incisor.

This study is an application of a three-dimensional Finite-Element Method to investigate the changes in stress characteristics of a prepared maxillary central incisor. The purpose of this study was to analyze stress distributions in this tooth after simulated canal preparation and static loading. A maxillary central incisor was embedded in acrylic, sectioned, photographed, and digitized. A three-dimensional finite-element model was generated by a computer and appropriately modified to simulate canal preparation. Data identified the highest stress magnitudes to be located between the middle and coronal thirds of the root; an area clinically observed to be prone to fracture during treatment. In addition, the magnitude of generated stresses was directly correlated with the simulated prepared canal diameter. The development of a validated three-dimensional finite-element method could identify areas that may predispose a tooth to structural failure during condensation loads.

Computer Simulation↗

PubMed1995

Cancellous bone Young's modulus variation within the vertebral body of a ligamentous lumbar spine--application of bone adaptive remodeling concepts.

Bone remodeling theory based on strain energy density (SED) as the feedback control variable was used in conjunction with the finite element method to analyze the shape of the vertebral bodies within the ligamentous motion segment. The remodeling theory was once again applied to the altered two motion segments model to predict the Young's modulus distribution of the cancellous bone within the vertebral bodies. A three-dimensional finite element model of the two motion segments ligamentous lumbar spine (L3-5) was developed. Bone remodeling response (external as well as internal) of the motion segments to a uniaxial compressive load of 424.7 N was studied. The external shape of the converged model matched the normal shape of a vertebral body. The internal remodeling resulted in regional cancellous bone Young's moduli (or bone density) distributions similar to those reported in the literature; posterocentral regions of the vertebrae were predicted to have greater values of the elastic modulus than that of the outer regions. The results of the present study suggest that vertebral body assumes an adequate/optimum structure in terms of both its shape and its elastic moduli distribution within the cancellous region in response to the applied load. Extensions of the present model and its clinically relevant applications are discussed.

Adaptation, Physiological↗

PubMed1995

Finite element methods in spine biomechanics research.

The finite element method has been used in spine biomechanics research for nearly a quarter of a century. Recent developments have made it possible to simulate a variety of clinically relevant situations in an increasingly realistic manner, elevating the finite element method into a fully complementary partnership with experimental approaches for the investigation of clinical problems in the spine. These new developments are presented in a historical context to evaluate their potential impact on future spine biomechanics research.

Age Factors↗

PubMed1995

Biomechanical analysis of bone mineral density, insertion technique, screw torque, and holding strength of anterior cervical plate screws.

The bone mineral density (BMD) of 99 cadaveric cervical vertebral bodies (C3-7) was determined using dual x-ray absorptiometry. The vertebral bodies were randomly assigned to receive either a unicortical (51 bodies) or bicortical (48 bodies) Caspar cervical plating screw. The initial insertion torque was measured using a digital electronic torque wrench, and the force required to withdraw the screw from the vertebral body was determined. The mean BMD for the total group of 99 was 0.787 +/- 0.154 g/cm2, the mean insertion torque was 0.367 +/- 0.243 newton-meters, and the mean pullout force was 210.4 +/- 158.1 newtons. A significant correlation was noted between BMD and torque (p < 0.0001, r = 0.42), BMD and pullout force (p < 0.0001, r = 0.54), and torque and pullout force (p < 0.0001, r = 0.88). Although the BMD of the unicortical and biocortical groups was equivalent (p = 0.92), the insertion torque and pullout force differed significantly (p = 0.02 and p = 0.008, respectively) for the unicortical and bicortical groups. A holding index for each screw and insertion technique was defined as the product of the BMD and insertion torque. The calculated holding index and resultant pullout force were significantly correlated for both techniques of screw insertion (r = 0.92), and a significant difference in holding index was observed with unicortical versus bicortical screw placement (p = 0.04). The determination of BMD and measurement of insertion torque to create a unique holding index provides an assessment of bone-screw interaction and holding strength of the screw, both of which impact on the resultant stability of cervical instrumentation. As the number of cervical plating systems increases, the determination of a holding index for various screws and insertion techniques may assist in the comparison of cervical instrumentation.

Absorptiometry, Photon↗

PubMed1994

Spinal motion after cervical fusion. In vivo assessment with roentgen stereophotogrammetry.

STUDY DESIGN: A roentgen stereophotogrammetric (RS) technique using metallic markers was used to determine in vivo three-dimensional (3-D) motion data in the post-operative cervical spine. Two patients were examined with RS following fusion for up to 12 months at scheduled intervals. OBJECTIVES: The study was designed to develop a technique and provide an in vivo assessment of the fusion process following surgery. Besides the researchers and surgeons, this type of information is of particular interest to the FDA and implant manufacturers. SUMMARY OF BACKGROUND DATA: The high accuracy of the roentgen stereophotogrammetric (RS) technique using metallic markers to predict displacements across body joints, including spinal joints, has been well established in the literature. Its applications in the lumbar region to assess the fusion process as a function of time following surgery have also been reported. Similar in vivo applications (and results) dealing with the cervical region are lacking. METHODS: A roentgen stereophotogrammetric (RS) technique using metallic markers was developed. Appropriate in vitro studies were undertaken to assess its accuracy for in vivo applications in the cervical spine region. Following this, three Vitallium beads were surgically implanted in anatomically appropriate positions in of each the exposed vertebrae of two patients at the time of surgery. The patients were followed with RS serially for 12 months after surgery at scheduled intervals. At each RS session, roentgen stereo pairs of the cervical spine in neutral, maximum voluntary flexion, and maximum voluntary extension were obtained using a biplanar radiographic system. The metallic beads on the radiographs were digitized using an in-house software package to determine vertebral motions across the fused segments. RESULTS: In patient 1 (atlantoaxial fusion), the flexion-extension range of rotational motion decreased with time while the corresponding AP translation at the fusion level increased from 6 mm at 3 months post-op to 13 mm at 6 and 12 months postoperatively. The abnormal AP translation at 6 months and beyond was evident on extension/extension lateral radiographs, but the AP translation at 3 months was not visually evident. In patient 2 (anterior discectomy and interbody fusion), motions of small magnitude were observed at the fused level in all three axes. These motions actually increased over the one year observation period, but were never large enough to be visually detectable on lateral extension/extension radiographs. Patient 2 had a good clinical result despite these small motions. CONCLUSIONS: Roentgen stereophotogrammetry may detect motion in the in vivo cervical spine with a sensitivity heretofore unavailable. In patient 1, we were able to detect motion before it was visually manifest. In patient 2, small motions were detected at the level of a successful anterior cervical fusion, the significance of which remain uncertain.

Atlanto-Axial Joint↗

PubMed1994

A method for the fatigue testing of pedicle screw fixation devices.

Spinal devices/instrumentation are used to augment the stability of a decompressed spinal segment during surgery. Like any other mechanical component, the device can fail. A standard in vitro test protocol, was developed to determine load vs number of cycles to failure curve for a pedicle screw-plate/rod type spinal device. The protocol based on the use of an 'artificial spine' model, is clinically relevant. The protocol was used to characterize the load-carrying capacities and failure modes of a specific pedicle screw-rod type fixation device to demonstrate its appropriateness. The devices (Kaneda) were tested in the quasi-static as well as fatigue bending modes. In the bending fatigue mode, the devices failed at loads significantly smaller than the corresponding quasi-static failure load magnitude (806 N). The device exhibited an endurance limit in the fatigue bending mode. The device is not likely to exhibit failure if subjected to cyclic loads which cause less than 380 N axial compression (and an accompanying bending moment relative to the device of less than 13.57 Nm). The failures observed in specimens subjected to the fatigue tests ranged from complete to partial breakage of the paraspinal rods as opposed to failure due to permanent deformation (yielding) of the rods in the quasi-static bending test specimens. The protocol developed can be used for any other screw-plate/rod type spinal instrumentation. The use of a standard protocol by researchers would enable a comparison of various devices currently available in the market. Such comparative data would be useful for the scientific community, and agencies such as the FDA and ASTM.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Plates↗

PubMed1994

Stress analysis of a canine spinal motion segment using the finite element technique.

Canine models have been frequently employed to investigate the in vivo effects of a surgical procedure. Various studies indicate that canine models can provide a successful in vivo biological model for these studies. Use of canine models for the biomechanical studies of the spine, however, have been questioned because of different loading conditions on the canine and human spines originated from posture differences between canine and human. Similarities between the stress distributions within the canine and human motion segments under physiological loads will strengthen the use of canine models for the studies of spine biomechanics. In the present study, finite element models of the canine intact and stabilized motion segments were developed to investigate these aspects. Comparison of model predicted flexion angle, axial stiffness, and facet contact force for the canine intact L6-L7 motion segment revealed good agreement with the corresponding parameters experimentally measured under the similar loading conditions. Similar stress distributions within the intact canine and human models were found from the predicted results in response to the physiological load. Stabilizing and stress-shielding effects of a pedicle screw-plate-type fixation device [variable spinal plating (VSP)] on the stabilized motion segment were also similar for the canine and human stabilized models. Furthermore, maximum stresses in the pedicle screws were found at the junction between the bone screw and the integrated nut of the inferior screw in both the canine and human stabilized models. This corresponds to the location of pedicle screw breakage reported in the literature. These findings suggest that a canine is a suitable model for the biomechanical studies of the lumbar spine.

Animals↗

PubMed1994

A comparison of stress-induced porosity due to conventional and a modified spinal fixation device.

A hypothesis that device-related osteopenia can be reduced by decreasing the rigidity of a fixation device was tested through a canine study. Polymer washers were interposed between the integral nut and plate of the variable spinal plating (VSP) system to reduce its rigidity. A solid fusion was observed 6 months postoperatively in all of the animals using VSP or modified systems. The stabilized segment using both systems showed similar load-displacement behaviors immediately after surgery and 6 months postoperatively. Although not significant, 5.6 and 1.8% decreases in volumetric density of mineralized bone were found in the stabilized segments due to VSP and modified systems, respectively. The modified system also increased bone growth around screws. The new concept of using polymer washers, to decrease rigidity of the fixation device over time, may reduce device-related osteopenia.

Animals↗

PubMed1994

Investigation of vibration characteristics of the ligamentous lumbar spine using the finite element approach.

A nonlinear, three-dimensional finite element model of the ligamentous L4-S1 segment was developed to analyze the dynamic response of the spine in the absence of damping. The effects of the upper body mass were simulated by including a mass of 40 kg on the L4 vertebral body. The modal analyses of the model indicated a resonant frequency of 17.5 Hz in axial mode and 3.8 Hz in flexion-extension mode. Accordingly, the predicted responses for the cyclic load of -400 +/- 40 N applied at four different frequencies (5, 11, 16.5, and 25 Hz) were compared with the corresponding results for axial compressive static loads (-360, and -440 N). As compared to the static load cases, the predicted responses were higher for the cyclic loading. For example, the effect of cyclic load at 11 Hz was to produce significant changes (9.7-19.0 percent) in stresses, loads transmitted through the facets, intradiscal pressure (IDP), disk bulge, as compared to the static load predictions. The responses were found to be frequency dependent as well; supporting the in vivo observations of other investigators that the human spine has a resonant frequency. For example, the 11 Hz model (DYN11) compared to the DYN5 model showed an increase in majority of the predicted parameters. The parameters showed an increase with frequency until 17.5 Hz (resonant frequency of the model); thereafter a decrease at 25 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗

PubMed1993

A combined finite element and optimization investigation of lumbar spine mechanics with and without muscles.

A combined finite element and optimization approach to study the effects of muscles on the biomechanics of the lumbar spine was initiated. Briefly, a three-dimensional, nonlinear, finite element model of a ligamentous L3-4 motion segment was formulated (LIG model) for the predictions of stresses, etc., in the motion segment. A separate, biomechanical optimization-based force model with experimental input was developed to predict the forces in muscles and disc across the L3-4 segment in response to a person holding 90 N in his hands with spine flexed 30 degrees, and knees straight. The predicted muscle forces from the optimization model were then incorporated into the L3-4 finite element model as nodal forces to simulate the muscle action (MUS model). The predicted responses from the muscles active (MUS) finite element model were compared to the corresponding results from the ligamentous (LIG) finite element model subjected to an equivalent load. The biomechanical parameters compared were: translation and rotation of L3, disc bulge, intervertebral foramen gap, intradiscal pressure, facet loading, ligament tension, compressive disc load, and stresses in the vertebral body. The addition of muscular forces in the MUS model led to a decrease in the anteroposterior translation and flexion rotation (displacements in the sagittal plane) of the segment compared to the corresponding LIG model predictions. Thus, the muscles imparted stability to the ligamentous segment. The presence of muscles also led to a decrease in stresses in the vertebral body, the intradiscal pressure and other mechanical parameters of importance. However, the load bearing of the facets increased compared to the ligamentous model. Thus, facets play a significant role in transmitting loads in a normal intact spine. These results, for the first time, provide quantitative data on the stabilizing effects of muscles on the mechanics of a ligamentous spine. The results also provide a scientific explanation in support of the "degenerative cascade" concept proposed in the literature. The model predictions, in conjunction with the degenerative cascade concept, also support the observation that the osteoarthritis of facets may follow disc degeneration. Future research directions based on the current model are presented.

Biomechanical Phenomena↗

PubMed1993

Thoracolumbar burst fractures. The clinical efficacy and outcome of nonoperative management.

There continues to be considerable controversy regarding the management of thoracolumbar burst fractures. Most feel that failure of the middle osteoligamentous complex, particularly with retropulsion of fragments into the spinal canal, is an indication for operative management. Others advocate postural reduction and prolonged bedrest for such injuries. The purpose of this study was to 1) review the clinical outcome and efficacy of closed management of thoracolumbar burst fractures; and 2) quantify what, if any, remodeling occurs in the bony canal as measured by serial CT. Forty-one patients who presented with a burst fracture of the thoracolumbar spine without neurologic deficit were reviewed clinically and radiographically following nonoperative management. At injury, canal compromise averaged 37% (range, 16-66%); 26 patients had at least 30% canal compromise. During treatment, one patient developed neurologic deterioration that prompted surgery; all other patients remained neurologically intact. At average follow-up of 2 years, an overall outcome evaluation indicated that 49% of the patients had excellent outcomes relative to pain and function; 17%, good; 22%, fair; and 12%, poor. Approximately 90% of the patients had a satisfactory work status relative to factors associated with their burst fracture. Serial roentgenograms documented significant progression in body collapse, which averaged 8% (P < 0.0001) from injury to follow-up. On the other hand, serial CTs documented significant improvement from injury to follow-up for canal compromise and midsagittal diameter. Average improvements in canal compromise and midsagittal diameter were 22% (P < 0.0001) and 11% (P < 0.0001), respectively. Only three patients had canal compromise greater than 30%, no patients had canal compromise greater than 40%, and no patients experienced canal area deterioration over time. On average, nearly two-thirds of the fragment occluding the canal resorbed, with most remodeling complete within one year. For patients with burst fractures presenting neurologically intact, we obtained the following findings: 1) nonoperative management yields acceptable results; 2) following nonoperative management, bony deformity (i.e., kyphosis and body collapse) progresses marginally relative to the rate of canal area remodeling; 3) incidence of subsequent neurologic deficits is quite low; and 4) initial radiographic severity of injury or residual deformity following closed management does not correlate with symptoms at follow-up. This pattern of results suggests nonoperative management as the preferred treatment in these circumstances.

Adult↗

PubMed1993

Effects of seated posture on erector spinae EMG activity during whole body vibration.

The purpose of this study was to evaluate the electromyographic (EMG) response of the erector spinae to whole body vibration in three different unsupported seated postures: neutral upright, forward lean, and posterior lean. Subjects were 11 healthy college-age men. EMG was collected using bipolar surface electrodes placed bilaterally over the erector spinae at the L4 level. A modified chair with attached accelerometer was affixed to an induction type vibrator. Subjects were vibrated vertically at 4.5 Hz and 6.21 m.s-2 RMS. Data were collected in each of the three postures for 30 s pre- and post-vibration and for 2 min during vibration. Mean EMG values were determined for each sampling period and compared using ANOVA. The mean value for anterior lean was significantly larger (p < 0.05) than that for posterior lean and neutral. EMG data analysed by triggered averaging showed a phase-dependent response to the vibratory cycle for the forward leaning and neutral upright postures. The results of this study indicate that the magnitude of the vibration synchronous response of the erector spinae musculature is dependent upon body posture. This response may be an important factor in the onset of muscular fatigue and the increased incidence of back disorders among individuals exposed to whole body vibration.

Adult↗

PubMed1993

In vivo kinematics of the cervical spine. Part I: Development of a roentgen stereophotogrammetric technique using metallic markers and assessment of its accuracy.

A technique for simultaneous roentgen stereophotogrammetry (RS) was developed, and its accuracy was assessed. In vitro models fabricated from dried cadaveric C4 and C5 vertebrae were used to simulate the motion behavior of the cervical spine. Metallic markers made of Vitallium beads (diameter < 0.3 mm) were implanted into the posterior and anterior surfaces of each vertebra at surgically accessible locations to simulate the bead placement for both posterior and anterior surgical approaches to the cervical spine. A series of roentgen stereo pairs were obtained to systematically assess the accuracy (validity) of displacement measurements in anteroposterior (AP) translation, axial rotation, and flexion/extension. In addition, the effects of soft tissue density on the accuracy of the system were investigated by obtaining a series of roentgen stereo pairs with the experimental model immersed in a water bath. The coordinates of the metallic markers on the radiographs were then digitized by two raters who were not informed of the actual motion (i.e., blind study). The results indicated a high accuracy throughout the study. Overall root mean square errors were 0.07 mm for AP translation, 0.08 degrees for axial rotation, and 0.14 degrees for flexion/extension. The corresponding accuracy estimates (R2 values by linear regression analysis) were very high (0.992, 0.998, and 0.995) when the measurement results were compared with the actual displacements. The water bath did not affect measurement accuracy, indicating that soft tissue density should have little effect on the accuracy of the technique for in vivo applications. This system appears to be an accurate and reliable method for assessment of simulated in vivo cervical spine motion, regardless of the rater. The technique has been further used in in vivo assessment of cervical spine kinematics in one patient to confirm the efficacy of the developed technique.

Atlanto-Axial Joint↗