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Biomedical subjects

V K Goel

Publications and source records attributed to V K Goel.

At least 55 records · Page 3Linked to original sources
PubMed1997

A protocol to evaluate semi-rigid pedicle screw systems.

The objective of the current study was to develop an in vitro testing protocol to evaluate semi-rigid pedicle screw devices. A corpectomy model protocol exists to evaluate rigid spinal implants; however, semi-rigid devices are contraindicated for this condition. This paper describes a technique that simulates more closely the conditions a semi-rigid device would see in vivo. Finally, the new testing protocol is used to evaluate the DDS pedicle screw-cable system. Benefits and shortcomings of the new protocol are discussed.

Bone Screws↗
PubMed1997

Bone registration method for robot assisted surgery: pedicle screw insertion.

A registration method that identifies bone geometry with respect to a robotic manipulator arm is presented. Although the method is generally applicable to many orthopaedic internal fixation procedures, it was only demonstrated for the insertion of pedicle screws in vertebral bodies for spine fixation. The method relies upon obtaining an impression of the vertebral bodies. Computerized tomography (CT) scans of both vertebrae and mould are reconstructed using a computer aided engineering (CAE) system. From the reconstructions, the surgeon is able to do preoperative planning including selection of pedicle screw diameter, direction of screw through pedicle, point of entry and length of engagement. The three-dimensional models are than meshed to determine positions of the surgeon's preoperative plan relative to the mould. Intra-operative positions are defined in space by a mechanical fixture rigidly attached to the mould and designed to allow a manipulator end-effector to recognize the global coordinates of the in vivo spine. The theory and methodology were validated using a five-axis manipulator arm. This initial presentation assumes and allows no relative motion between vertebrae in vivo.

Bone Screws↗
PubMed1997

Basic science of spinal instrumentation.

A wide variety of spinal implants are available to the clinician for the surgical treatment of spinal disorders. Most of the implants are associated with fusion--they are designed either to promote fusion, or, in the case of the newer devices such as artificial discs and disc implants, to offset the perceived disadvantages of fusion. The contributions of biomechanics to the improvement of spinal implant design and clinical implementation are detailed. Benchtop tests of device components and assemblies, in vitro studies of spinal constructs using osteoligamentous spinal segments, and analytical (finite element) and animal models are reviewed. Through these studies, the quantification of parameters such as stresses and strains within the spinal structures and within the fixation devices has permitted a better understanding of the relationship between the clinical observations after surgery and the mechanical factors. However, despite improvements in fusion techniques that have reduced the pseudarthrosis rate, there is still room for improvement. New concepts such as the biological enhancement of spinal fusion and alternatives to fusion such as the artificial disc are currently the subjects of intense, multidisciplinary study, but await the ultimate test of clinical trial with long term followup.

Animals↗
PubMed1996

Muscular response to sudden load. A tool to evaluate fatigue and rehabilitation.

STUDY DESIGN: Subjects were exposed to fatiguing and restorative interventions to assess their response to sudden loads. OBJECTIVES: To investigate the erector spinae and rectus abdominis response characteristics to "sudden load" and the effect of fatigue and rehabilitation. SUMMARY OF BACKGROUND DATA: Unexpected loads which people often experience, can lead to high forces in the spine and may be a cause of low back injury. METHODS: Muscle responses to sudden load were mediated by fatigue, walking, expectation, method of load application, exposure to vibration, and cognitive-behavioral rehabilitation in patients with chronic low back pain. A novel technique, perfected in this work, called wavelet analysis, was used to analyze these data. RESULTS: Reaction time was affected by fatigue and expectation. Vibration exposure significantly increased the muscle response time. Walking was able to ameliorate that effect. Back muscles responded differently, depending on whether loads were applied to the back through the hands or through the trunk. Electromyographic reaction time and magnitude decreased in patients after a 2-week rehabilitation program. CONCLUSIONS: Sudden loads can exacerbate fatigue effects. Walking after driving reduces the risk to the back caused by handling unpredictable loads. Vibration exposure guidelines should be more conservative. Patients have longer response times than healthy subjects, but patients can improve their response to sudden loads via rehabilitation. Patients exhibit a flexion-extension oscillation at 5 Hz in response to a sudden load, suggesting that the 5-Hz, seated, natural frequency observed during whole-body vibration may result from neurophysiologic control limits.

Adult↗
PubMed1996

Effects of muscle dysfunction on lumbar spine mechanics. A finite element study based on a two motion segments model.

STUDY DESIGN: A combined finite element and optimization approach was developed to investigate the clinically relevant biomechanical parameters of the muscular lumbar spine under five quasistatic back-lifting conditions. OBJECTIVES: To quantify the effects of muscle "dysfunction" on the mechanical behavior of the lumbar spine. SUMMARY OF BACKGROUND DATA: Trunk muscles have been proven to play an important role in the normal functioning of the spine. Although passive structures of the spine are believed to be subjected increasingly to mechanical stresses when muscular support is inadequate, supportive quantitative data have been lacking. METHODS: External loads at L3-L4 for various lifting tasks were estimated experimentally and partitioned to the disc and muscles across the L3-L4 segment using an optimization scheme. These forces were incorporated into a finite element model of the ligamentous L3-L5 lumbar spine. Muscle "dysfunction" was simulated by decreasing the computed muscle forces. RESULTS: The range of motion intradiscal pressure forces in ligaments, and load across facets increased nonlinearly with the increases in trunk flexion and the load held in hands. At higher loads or at larger flexed postures, muscles were found to play a more crucial role in stabilizing the spine compared with the passive structures. Muscle "dysfunction" destabilized the spine, reduced the role of facet joints in transmitting load, and shifted loads to the discs and ligaments. CONCLUSIONS: Muscle dysfunction disturbs the normal functioning of other spinal components and may cause spinal disorders.

Biomechanical Phenomena↗
PubMed1996

Effect of specimen fixation method on pullout tests of pedicle screws.

STUDY DESIGN: Experimental axial pullout tests of a new type of pedicle screw were done on cadaveric lumbar vertebrae. The manner in which specimens were secured in the testing apparatus was varied to determined influence of specimen fixation method on the maximum pedicle screw pullout force. OBJECTIVES: To determine the appropriateness of embedding (i.e., potting) spinal specimens in polymer resin (e.g., bone cement or Plastic Padding [Plastic Padding Ltd., High Wycombe, Buckinghamshire, England]) for axial pullout tests of pedicle screws. Several different specimen fixation methods were examined to make recommendations for the standardization of future experimental testing protocols. SUMMARY OF BACKGROUND DATA: Axial pullout of transpedicular screws, although not a likely clinical mode of failure, is a popular experimental testing mode for evaluating screw-bone biomechanics. A wide variety of techniques for securing a vertebral specimen to counter the axial pullout force has been reported (including the use of polymer resin) with a correspondingly wide range in the resulting axial pullout strengths. The possible influence of the specimen fixation method on pedicle screw axial pullout strength has not been addressed previously. METHODS: Axial pullout tests of pedicle screws (DDS, Plus Endoprothetik, Rotkreuz, Switzerland) from the pedicles of 21 isolated lumber vertebral bodies were done using a Model 810 MTS Universal Testing Machine (MTS Systems, Inc., Minneapolis, Minnesota). The specimens were secured in a custom-made vise fixture either as is or after the vertebral bodies were potted in Plastic Padding up to the pedicle origin. Some of the potted specimens were wrapped first in latex to prevent polymer resin intrusion, and the others were unprotected. Pullout tests were attempted on both the left and right pedicles of each specimen, and the maximum pedicle screw pullout force was recorded. Measurement of bone mineral density by means of dual energy x-ray absorptiometry, in addition to macroscopic and scanning electron microscopy histologic analyses, microradiography, and energy dispersive X-ray spectroscopy, was done post-test to assist in the interpretation of the data. RESULTS: The maximum pedicle screw pullout force was found to be dependent on both the bone mineral density and the mode of fixation of the vertebrae. Embedding in polymer resin without protection of the specimen (i.e., latex wrapping) led to several instances of well-documented polymer resin intrusion; in these specimens, mean maximum pedicle screw pullout force was significantly greater than that of specimens secured without polymer resin and that of embedded specimens for which intrusion did not occur. CONCLUSIONS: Polymer resin intrusion can have a significant effect on the biomechanical characteristics of the bone-pedicle screw interface. When polymer resins are used to secure vertebral specimens for in vitro biomechanical tests of the bone-pedicle screw interface, it is important to either prevent intrusion (e.g., with a latex wrapping) or document post-test (e.g., through the methods described in this article) that intrusion did not occur for the specimens included in the analysis.

Aged↗
PubMed1996

European Spine Society--the AcroMed Prize for Spinal Research 1995. Unexpected load and asymmetric posture as etiologic factors in low back pain.

Unexpected loads, which often occur in the working environment, can lead to high forces in the spine and, thus, may be a cause of low back injury. This paper discusses the effect of "sudden load" on the erector spine reaction and amplitude. Muscle responses were mediated by several factors, including fatigue, posture, expectation and rehabilitation, in chronic low back pain patients. The subjects were fatigued by holding a 20% maximum voluntary contraction for 1 min. A functional restoration program was tested for its efficacy in reducing reaction time and EMG amplitude in chronic low back pain patients. Reaction time was longer and EMG amplitude lower in patients than in their matched controls. EMG reaction time and magnitude decreased in patients after a 2-week rehabilitation program, including specific training of coordination and posture control. The results of the modelling showed higher spinal compressive load and lower shear forces when the load was expected than when the load was unexpected. The effect of sudden loads can be exacerbated if a worker is not standing on a flat surface or is fatigued. Chronic low back pain patients have less ability to protect themselves from sudden loads, but they can be trained to improve their response by means of an appropriate rehabilitation program.

Adult↗
PubMed1996

A study of the control of disc movement within the temporomandibular joint using the finite element technique.

PURPOSE: A two-dimensional finite element model was developed to simulate and study the in vivo biomechanics and mechanisms of the human temperomandibular joint (TMJ) over the range of normal motion. MATERIALS AND METHODS: A nonlinear model was developed and run using the commercially available ABAQUS software with slide line elements that allowed large displacements and arbitrary contact of surfaces. The three main components of the model were the mandibular condyle, articular disc, and glenoid fossa region of the temporal bone, which were all modeled as deformable bodies. Continuous motion was simulated by doing a static analysis for each of many small steps. A parametric study was performed by determining the maximum stress in each of the three main components as a function of the elasticity of the articular disc. RESULTS: The articular disc was found to move along with condyle in a lifelike manner, even when there were no attachments to the disc. Stress distribution plots showed relatively high stresses deep in the glenoid fossa for most steps. There was a direct, although nonlinear, relationship between maximum stress for all three components and the stiffness of the disc. CONCLUSIONS: This model suggests that muscle contraction is not required to maintain proper disc position. Normal motion results in relatively high stresses deep in the glenoid fossa. The elasticity of the in vivo articular disc may be closer to the lower end of the reported values.

Biomechanical Phenomena↗
PubMed1996

Cervical spine motion with direct laryngoscopy and orotracheal intubation. An in vivo cinefluoroscopic study of subjects without cervical abnormality.

BACKGROUND: Cervical spine kinetics during airway manipulation are poorly understood. This study was undertaken to quantify the extent and distribution of segmental cervical motion produced by direct laryngoscopy and orotracheal intubation in human subjects without cervical abnormality. METHODS: Ten patients without clinical or radiographic evidence of cervical spine abnormality underwent laryngoscopy using a #3 Macintosh blade while under general anesthesia and neuromuscular blockade. Cervical motion was recorded with continuous lateral fluoroscopy. The intubation sequence was divided into distinct stages and the corresponding fluoroscopic images were digitized. Segmental motion, occiput through C5, was calculated for each stage using the digitized data. RESULTS: During exposure and laryngoscope blade insertion, minimal displacement of the skull base and rostral cervical vertebral bodies was observed. Visualization of the larynx created superior rotation of the occiput and C1 in the sagittal plane, and mild inferior rotation of C3-C5. C2 maintained nearneutral posture. This pattern of displacement resulted in extension at each motion segment, with the most significant motion produced at the occipitoatlantal and atlantoaxial joints (mean = 6.8 degrees and 4.7 degrees, respectively). Intubation created slight additional superior rotation at the occiput and C1, without substantial alteration in the posture of C2-C5. After laryngoscope removal, position trended toward baseline at all levels, although exact neutral posture was not regained. CONCLUSIONS: This investigation quantifies the behavior of the normal cervical spine during direct laryngoscopy with a Macintosh blade. With this maneuver, the vast majority of cervical motion is produced at the occipitoatlantal and atlantoaxial joints. The subaxial cervical segments (C2-C5) are displaced only minimally. This study establishes a highly reliable and reproducible method for analyzing cervical motion in real time.

Adult↗
PubMed1996

Biomechanical evaluation of Caspar and Cervical Spine Locking Plate systems in a cadaveric model.

There exist two markedly different instrumentation systems for the anterior cervical spine: the Cervical Spine Locking Plate (CSLP) system, which uses unicortical screws with a locking hub mechanism for attachment, and the Caspar Trapezial Plate System, which is secured with unlocked bicortical screws. The biomechanical stability of these two systems was evaluated in a cadaveric model of complete C5-6 instability. The immediate stability was determined in six loading modalities: flexion, extension, right and left lateral bending, and right and left axial rotation. Biomechanical stability was reassessed following fatigue with 5000 cycles of flexion-extension, and finally, the spines were loaded in flexion until the instrumentation failed. The Caspar system stabilized significantly in flexion before (p < 0.05) but not after fatigue, and it stabilized significantly in extension before (p < 0.01) and after fatigue (p < 0.01). The CSLP system stabilized significantly in flexion before (p < 0.01) but not after fatigue, and it did not stabilize in extension before or after fatigue. The moment needed to produce failure in flexion did not differ substantially between the two plating systems. The discrepancy in the biomechanical stability of these two systems may be due to differences in bone screw fixation.

Adult↗
PubMed1996

Clinical profile of stroke in relation to glycaemic status of patients.

Present study was undertaken in fifty consecutive patients of acute stroke to assess the role of glycemic status on clinical profile of stroke. Majority of patients (76%) were in age group of 41-70 years. The patients were classified into four groups: euglycemics (33), known diabetics (8), newly diagnosed diabetics (6) and stress hyperglycemics (3). Diabetics as well as stress hyperglycemics had higher prevalence of larger sized severe haemorrhagic stroke with poor outcome and there was positive correlation between them.

Acute Disease↗
PubMed1995

Biomechanics of fusion and stabilization.

STUDY DESIGN: Literature review. OBJECTIVES: To assess the state of the art in the biomechanics of fusions, fusion materials, and the use of instrumentation by critically reviewing the literature as modified by group discussion. SUMMARY OF BACKGROUND DATA: A considerable body of knowledge addresses these issues based on in vitro biomechanical testing and mathematical models. Much biomechanical information is available regarding the biomechanical behavior of the graft material, the fusion, and the instrumentation. Biomechanical testing and finite element analyses remain to be done on semirigid devices, interbody spacers, and artificial discs. METHODS: The literature was reviewed to analyze papers written on the following topics: graft material, in vitro tests of instrumentation, device evaluation using artificial spine models, in vivo human studies, animal models, finite element studies, effects of rigidity, and bone adaptive remodeling. RESULTS: One hundred forty-one modern articles were reviewed and their data analyzed. Much important insight has come from biomechanical studies. CONCLUSIONS: Fusions are largely successful. Biomechanical data is complete except for some of the latest devices.

Biomechanical Phenomena↗