Biomechanical Study (biomechanical + study)

Distribution by Scientific Domains

Selected Abstracts

A Microscopic and Biomechanical Study of Skin and Soft Tissue After Repeated Expansion

BACKGROUND Conventional expansion inadequately restores damaged skin for patients with large areas of skin deficiency or who lack sources of normal skin. These patients require repeated skin expansions, but little is known about the outcomes of this procedure. OBJECTIVE To evaluate the microscopic changes and biomechanical properties of skin and soft tissue after repeated expansion. MATERIALS AND METHODS We prepared three groups of six pigs each: a conventional expansion group, a repeated expansion group, and a blank nonsurgical control group. We measured histology, ultrastructure, basic fibroblast growth factor (bFGF), stress,strain, stress relaxation, and stress strength. RESULTS Skin obtained after conventional expansion and repeated expansion was basically healthy, but the microscopic and biomechanical properties differed from those of nonexpanded skin, especially in the repeated expansion group. CONCLUSION Repeated skin expansion involves growth under stress, simultaneous injuries, and further repairs, with fibers showing more injury signs than cells. This article describes the microscopic changes and biomechanical properties that occur after repeated expansion. [source]

A biomechanical study on flexible intramedullary nails used to treat pediatric femoral fractures

Jason K. Green
Abstract Flexible intramedullary nails have been indicated to treat femoral fractures in pediatric patients. The purpose of this study was to examine the stability of simulated transverse fractures after retrograde intramedullary flexible nail fixation. Various nail diameter combinations were tested using composite femurs in bending, torsion, and a combined axial/bending test where a vertical compressive force was applied to the femoral head. The cross-sectional percent area fill of the nails within the femurs was also determined. In 4 point bending, the greatest repair stiffness was 12% of the intact stiffness. In torsion, the greatest stiffness was 1% of the intact stiffness for either internal or external rotation. The greatest repair stiffness was 80% of the intact stiffness for a compressive load applied to the femoral head. Nail combinations with single nail diameters greater than 40% of the mid-shaft canal width, as measured from an AP radiograph, prevented the fracture from being reduced and left a posterior gap. Flexible intramedullary nails may be of value in the treatment of pediatric femoral fractures, but care must be taken to insert nails that are correctly sized for the canal and to protect the healing fracture from high torsional and bending loads. © 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source]

Cranial cruciate stabilitv in the rottweiler and racing greyhound: an in vitro study

C. Wingfield
An in vitro biomechanical study of cadaver stifles from rottweilers and racing greyhounds was undertaken to evaluate the contribution of the cranial cruciate ligament to stifle joint stability. This was performed at differing stifle joint angles, first with the joint capsules and ligaments intact and then with all structures removed except for the cranial cruciate ligament. Craniocaudal laxity increased in both breeds as stifle flexion increased. The rottweiler stifle showed greater craniocaudal joint laxity than the racing greyhound at all joint angles between 150° and 110°, but the actual increases in joint laxity between these joint angles were similar for both breeds. Tibial rotation during craniocaudal loading of the stifle increased craniocaudal laxity in both breeds during joint flexion. The relative contribution of the cranial cruciate ligament to cranial stability of the stifle joint increased as the joint flexed and was similar in both breeds. [source]

Effect of elbow flexion contractures on the ability of people with C5 and C6 tetraplegia to lift

Lisa Harvey
Abstract Background and Purpose It is commonly assumed that minor elbow flexion contractures prevent people with C5,C6 tetraplegia and paralysis of the triceps brachii muscles from bearing full body weight through their upper limbs. The aim of the present study was to determine the effect of simulated bilateral elbow flexion contractures on the ability of these individuals to bear weight through their upper limbs and to determine whether full passive elbow extension is truly critical for lifting body weight. Method A biomechanical study was performed. Body weight lifted was measured under conditions that simulated bilateral elbow flexion contractures. Five people with motor complete C6 tetraplegia and one person with motor complete C5 tetraplegia, all with bilateral paralysis of the triceps brachii muscles, were recruited to the study. Subjects were fitted with bilateral elbow splints that restricted elbow extension but did not restrain elbow flexion nor prevent the elbow from collapsing, and were seated on an instrumented platform that measured vertical forces under the buttocks. Subjects pushed down through their hands and lifted under five different conditions, namely: with no elbow splints; with bilateral elbow splints adjusted to restrict elbow extension by 5,10°; by 15,20°; by 25,30° and with bilateral elbow splints adjusted to allow unrestricted movement of the elbow joint. Maximal weight lifted from under the buttocks, for each condition, was expressed in relation to weight under the buttocks during unsupported sitting (that is, ,seated body weight'). Results Subjects lifted progessively less weight from under their buttocks as passive elbow restriction was progressively restricted. However, one subject lifted all his seated body weight when elbow extension was restricted by 5,10° and another lifted all his seated body weight when elbow extension was restricted by 5,10° and 15,20°. Conclusions Minor elbow flexion contractures will not alone prevent people with tetraplegia and paralysis of the triceps brachii muscles from lifting. Full passive elbow extension is not critical for the performance of this task. Copyright © 2001 Whurr Publishers Ltd. [source]

Influence of surgical technique and surface roughness on the primary stability of an implant in artificial bone with different cortical thickness: a laboratory study

Afsheen Tabassum
Abstract Objective: The aim of this biomechanical study was to assess the interrelated effect of both surface roughness and surgical technique on the primary stability of dental implants. Material and methods: For the experiment, 160 screw-designed implants (Biocomp®), with either a machined or an etched surface topography, were inserted into polyurethane foam blocks (Sawbones®). As an equivalent of trabecular bone, a density of 0.48 g/cm3 was chosen. To mimic the cortical layer, on top of these blocks short-fibre-filled epoxy sheets were attached with a thickness varying from 0 to 2.5 mm. The implant sites were prepared using either a press-fit or an undersized technique. To measure the primary stability of the implant, both the insertion and the removal torques were scored. Results: Independent of the surgical technique used, both implant types showed an increased insertion and removal torque values with increasing cortical thickness, although >2 mm cortical layer no further increase in insertion torque was observed. In the models with only trabecular bone (without cortical layer) and with a 1 mm cortical layer, both implant types showed a statistically higher insertion and removal torque values for undersized compared with the press-fit technique. In addition, etched implants showed a statistically higher insertion and removal torque mean values compared with machined implants. In the models with 2 and 2.5 mm cortical layers, with respect to the insertion torque values, no effect of either implantation technique or implant surface topography could be observed. Conclusion: The placement of etched implants in synthetic bone models using an undersized preparation technique resulted in enhanced primary implant stability. A correlation was found between the primary stability and the cortical thickness. However, at or above a cortical thickness of 2 mm, the effect of both an undersized surgical approach, as also the presence of a roughened (etched) implant surface, had no extra effect. Besides the mechanical aspects, the biological effect of undersized drilling, i.e. the bone response on the extra insertion torque forces should also be elucidated. Therefore, additional in vivo studies are needed. To cite this article: Tabassum A, Meijer GJ, Wolke JGC, Jansen JA. Influence of surgical technique and surface roughness on the primary stability of an implant in artificial bone with different cortical thickness: a laboratory study. Clin. Oral Impl. Res. 21, 2010; 213,220. doi: 10.1111/j.1600-0501.2009.01823.x [source]