Biomedical subjects

A F Tencer

Publications and source records attributed to A F Tencer.

99 records · Page 6Linked to original sources

PubMed1984

Development of a variable stiffness external fixation system for stabilization of segmental defects of the tibia.

The mechanical properties of a variable stiffness external fixation system were explored. Initial testing of a unilateral fixator configuration demonstrated that system rigidity could be increased by maximizing pin separation distance in the fracture component and the number of pins used while minimizing pin separation distance across the fracture site and the sidebar offset distance from bone. A triangulated system composed of half pin frames mounted anteriorly and medially on the tibial aspects and linked by crossbars was devised. Progressive disassembly of the frame was shown to result in progressive decreases in fixator rigidity in all planes.

Biomechanical Phenomena↗

PubMed1984

A biomechanical comparison of various methods of stabilization of subtrochanteric fractures of the femur.

Subtrochanteric femoral fractures with and without bony contact were simulated in cadaver specimens, fixed with one of seven different types of intramedullary or plate implants, and tested biomechanically. The implants used were Enders pins, Zickel nail, compression hip screw, AO angled blade plate, and intramedullary locked nail systems of the Klemm-Schellman, Brooker-Wills, and Grosse-Kempf types. Femur-implant constructs using intramedullary devices were a maximum of 5% as stiff in torsion as intact cadaveric femora tested in the same manner, while plate-fixed fractures were nearly 50% as stiff. In bending, all devices except the Enders pins were approximately 80% as stiff as intact femora. Loss of bony contact at the fracture site had little effect on stiffness except in the case of the keyless compression hip screw, where the screw rotated freely in the barrel. In combined bending and compression to failure, a test to simulate forces due to body weight, the intramedullary locked rods were found to support between 300 and 400% of body weight while the plate systems failed at loads between 100 and 200% of body weight.

Biomechanical Phenomena↗

PubMed1984

Use of noninvasive techniques for quantification of spinal range-of-motion in normal subjects and chronic low-back dysfunction patients.

Quantitative measures of physical function (range of motion, strength, stability) are critical to musculoskeletal care of the extremities, yet such objective measures in the spine are currently unavailable. In this paper, the authors present a simple, single inclinometer modification of the method of Loebl, which offers the opportunity to separate the components of the compound motion of hip and spine. Analysis of the motion in normal and chronic low-back pain patients allows differentiation of the groups, demonstration of progress in rehabilitation programs, determination of impairment, and provides tests of patient compliance and level of motivation.

Adult↗

PubMed1983

Soft tissue strain and facet face interaction in the lumbar intervertebral joint--Part I: Input data and computational technique.

A numerical simulation was devised to determine ligament strains, facet face interaction, and disk fiber strain in the lumbar intervertebral joint under load. This technique uses experimentally derived load deflection and morphologic data from lumbar cadaver specimens from which initial and displaced soft tissue attachment points can be calculated. This allows the strain data to be derived. The effect of disk bulge is also considered. The calculated strains of most ligaments except the facet capsular ligaments were found to be insensitive to anatomical measurement variability of +/- 1 mm.

Adolescent↗

PubMed1983

Soft tissue strain and facet face interaction in the lumbar intervertebral joint--Part II: Calculated results and comparison with experimental data.

A numerical simulation of soft-tissue strain and facet face interaction in the lumbar intervertebral joint under load was performed. The results, compared with a previous experimental sectioning study, showed that disk fiber strain was the main mechanism in shear resistance, except posterior shear, where the facets were main load bearing members. In axial compression, compression of the annulus was found, with a significant decrease in compressive strain resulting from annulus bulging, but no contact was found in the facet joints. The posterior ligaments, except for the facet capsules and ligamentum flavum, were found to be active only in flexion and lateral bending, while the facets and the disk both played major roles in resisting axial torsion moments.

Biomechanical Phenomena↗

PubMed1982

Some static mechanical properties of the lumbar intervertebral joint, intact and injured.

The in-vitro static load-displacement properties of the intact and the injured human lumbar intervertebral joint have been investigated in a loading apparatus which allows entirely unconstrained relative displacement between the joint members. The spatial relative displacement produced by a given load, alone or in combination with another load (preload), were measured using 14 specimens and emphasizing strict control of the secondary variables which are known to affect the results. An attempt has been made to interpret the results in terms of the relative load-bearing roles of the disk, the facets and the posterior ligaments as a function of the type of load. The results indicate that the disk is the major load-bearing element in lateral and anterior (with respect to fixed superior vertebra) shears, axial compression and flexion, while the facets play a major role in posterior shear and axial torque.

Biomechanical Phenomena↗

PubMed1981

The role of secondary variables in the measurement of the mechanical properties of the lumbar intervertebral joint.

A general method is proposed for the testing of the structural properties of lumbar intervertebral joints. The apparatus designed includes a loading jig capable of applying any wrench resultant load while allowing unconstrained motion of the specimen and a three-dimensional displacement transducer for measurement of principal and coupled displacements. Four secondary independent variables, load axis position, nucleus pressure, the number of initial cycles and the load duration are shown to significantly affect the dependent variable, displacement. When performing this type of experiment, these secondary variables must be standardized and controlled.

Adolescent↗

PubMedDate not supplied

A biomechanical study of thoracolumbar spinal fractures with bone in the canal. Part I. The effect of laminectomy.

A simulation of thoracolumbar spinal fractures with bone in the canal was performed using fresh cadaver spines. In the study, a hole was drilled anterior to posterior in vertebral body T12 to accommodate a microload cell and displacement transducer that was then manually pushed into the canal to simulate the compressive effect of retropulsed bone on the spinal cord. In this part of the study, measurements were made pre- and postlaminectomy. The results indicated that laminectomy had no decompressive effect with up to 35% occlusion of the canal. Measurements of dural wall deflection during penetration of the load cell indicated that the anterior wall deformed locally due to penetration of the load cell with minimal displacement of the posterior wall occurring.

Adult↗

PubMedDate not supplied

A biomechanical study of thoracolumbar spinal fractures with bone in the canal. Part II. The effect of flexion angulation, distraction, and shortening of the motion segment.

In the second part of this biomechanical study of thoracolumbar spinal fractures with bone in the neural canal contract force on the spinal cord--meningeal complex was measured with relation to varying fracture wedge depth, flexion angulations, and distraction and shortening of the fracture model motion segment. The removal of progressively deeper vertebral body wedges did not change the measured contact force/depth of penetration characteristics, however, the resistance to flexion angulation was decreased. Distraction of the motion segment an average of 5.2 mm increased significantly the contact force at the same depth of penetration compared with the case of normal vertebral body height. Shortening an average of 3.2 mm did not have a significant effect. Flexion angulation to 20 degrees did not change the depth/force characteristic in either the shortened or distracted case.

Adult↗