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Biomedical subjects

A Simkin

Publications and source records attributed to A Simkin.

At least 19 recordsLinked to original sources
PubMed2003

Dynamic force distribution during level walking under the feet of patients with chronic ankle instability.

OBJECTIVES: To examine changes in the pattern of force transfer between the foot and the floor associated with chronically sprained ankles by measuring the peak forces and their timing under several regions of the feet during level walking. METHODS: Twelve young male subjects (mean (SD) age 21 (2) years) with recurrent ankle sprains were studied. Seven of them had unilateral and bilateral chronic instability and laxity, and five had bilateral instability. Twelve healthy men (without orthopaedic or medical disease) served as a control group. Subjects walked at their own pace along a 7 m walkway, which included a Mini-EMED pressure distribution measuring system. The variables measured were relative peak force (fraction of body weight) and relative timing (fraction of stance time). These variables were measured under six regions of interest in each foot print: heel, midfoot, medial, central, and lateral forefoot, and toes. RESULTS: (a) A significant delay to the time of peak force under the central and lateral forefoot and toes in subjects with chronic ankle instability. (b) A significant decrease in the relative forces under the heel and toes and an increase in the relative forces under the midfoot and lateral forefoot in subjects with chronic ankle instability. (c) In the patients with unilateral instability, there were no significant differences in any of the variables between the injured and non-injured foot. CONCLUSIONS: In patients with chronic ankle instability, there is a slowing down of weight transfer from heel strike to toe off, a reduced impact at the beginning and end of the stance phase, and a lateral shift of body weight.

Adult↗
PubMed2001

A home exercise program for tibial bone strengthening based on in vivo strain measurements.

OBJECTIVE: To compare the strain and strain rates generated during lower limb calisthenics with walking, an exercise that has been found to have only minimal effect on bone mass. Strengthening of bone, while it still has adaptive ability, can be achieved by exercise. Mechanical loading during physical activity produces strains and strain rates within the bones. It is thought that strain and strain rates higher than the usual provide the stimulus for the bones' adaptation. DESIGN: Three strain-gauged bone staples were inserted percutaneously in a 30 degrees rosette pattern in the medial aspect of the midtibial diaphysis of two volunteers. The principal compression, tension, shear strains, and strain rates were measured during various lower limb calisthenics and compared with those of jogging and walking. RESULTS: Zig-zag hopping was in the grouping of exercises with the highest principal compression, tension, and shear strains and compression strain rates, whereas walking was in the lowest or next-to-the-lowest grouping for all principal strain or strain rates. CONCLUSION: Zig-zag hopping, based on the high strain and strain rates that it produces, may be an optimal tibial bone-strengthening exercise.

Adult↗
PubMed2001

The effect of shoe sole composition on in vivo tibial strains during walking.

To test the hypothesis that shoe sole composition can affect the level of bone strain and strain rates that contribute to the development of stress fractures, in vivo tibial strain measurements were made during treadmill walking while wearing four shoes which differed only in their sole composition. Soles of 65 Shore A polyurethane with an embedded heel air cell had significantly lower compression and shear strains and shear strain rates than soles of 65, 75 and a composite of 40/65 Shore A polyurethane with no embedded air cells. A sole composed of 65 Shore A polyurethane with an embedded air cell can potentially be protective against stress fracture in a walking shoe.

Adult↗
PubMed2001

Optical processing of radiographic trabecular pattern versus bone mineral density of proximal femur as measures of bone strength.

The purpose of the present study was to evaluate a noninvasive method that utilizes optical processing to analyze the trabecular pattern on bone radiographs. The trabecular network on proximal femur radiographs of 17 intact cadaveric femora was analyzed by optical Fourier transform, yielding a trabecular bone index (TBI) at several locations. The bone mineral density (BMD) of the proximal femur was measured by dual X-ray absorptiometry. Dimensions of the proximal femur were obtained from the radiograph. The bones were fractured in a "fall configuration" to yield the fracture load. A multiple regression model, combining only radiograph- derived parameters-bone dimensions and the TBI at the intertrochanteric region and at the greater trochanter-yielded a correlation of 0.938 with the fracture load. A model combining the BMD at the greater trochanter and at the neck yielded a correlation of 0.928 with the fracture load. When all the variables were introduced into a combined analysis, the correlation with the fracture load was 0.973. The TBI obtained by optical processing of the trabecular bone pattern on femoral radiographs together with bone dimensions derived from these radiographs may serve as an effective estimate for hip fracture risk.

Absorptiometry, Photon↗
PubMed2000

Effect of microwave oven induced mild hyperthermia on bone viability and strength.

Extracorporeal hyperthermia treatment of bone followed by reimplantation may be an option for treating bone tumors. However, intensive heat treatment, such as autoclaving, causes a decline of mechanical and biologic functions of bone tissue. In the current study, a microwave oven was used for minimal hyperthermic treatment, and it was found that complete eradication of all viable cells in rat bone could be achieved with minimal reduction in mechanical function. When the cells were evaluated histologically by special lactate dehydrogenase activity staining, complete bone cell death occurred after 60 seconds of heating in an empty Petri dish and after 30 seconds when heated in a Petri dish containing normal saline. Mechanical stiffness and strength of the bones, tested in three-point bending, showed no decrease after this heating. Microwave oven induced hyperthermia eradication of viable cells without significant damage to the mechanical properties may have clinical relevance in limb salvage tumor surgery.

Animals↗
PubMed2000

Plant genome complexity may be a factor limiting in situ the transfer of transgenic plant genes to the phytopathogen Ralstonia solanacearum.

The development of natural competence by bacteria in situ is considered one of the main factors limiting transformation-mediated gene exchanges in the environment. Ralstonia solanacearum is a plant pathogen that is also a naturally transformable bacterium that can develop the competence state during infection of its host. We have attempted to determine whether this bacterium could become the recipient of plant genes. We initially demonstrated that plant DNA was released close to the infecting bacteria. We constructed and tested various combinations of transgenic plants and recipient bacteria to show that the effectiveness of such transfers was directly related to the ratio of the complexity of the plant genome to the number of copies of the transgene.

Betaproteobacteria↗
PubMed2000

Do high impact exercises produce higher tibial strains than running?

BACKGROUND: Bone must have sufficient strength to withstand both instantaneous forces and lower repetitive forces. Repetitive loading, especially when bone strain and/or strain rates are high, can create microdamage and result in stress fracture AIM: To measure in vivo strains and strain rates in human tibia during high impact and moderate impact exercises. METHODS: Three strain gauged bone staples were mounted percutaneously in a rosette pattern in the mid diaphysis of the medial tibia in six normal subjects, and in vivo tibial strains were measured during running at 17 km/h and drop jumping from heights of 26, 39, and 52 cm. RESULTS: Complete data for all three drop jumps were obtained for four of the six subjects. No statistically significant differences were found in compression, tension, or shear strains with increasing drop jump height, but, at the 52 cm height, shear strain rate was reduced by one third (p = 0.03). No relation was found between peak compression strain and calculated drop jump energy, indicating that subjects were able to dissipate part of the potential energy of successively higher drop jumps by increasing the range of motion of their knee and ankle joints and not transmitting the energy to their tibia. No statistically significant differences were found between the principal strains during running and drop jumping from 52 cm, but compression (p = 0.01) and tension (p = 0.004) strain rates were significantly higher during running. CONCLUSIONS: High impact exercises, as represented by drop jumping in this experiment, do not cause higher tibial strains and strain rates than running and therefore are unlikely to place an athlete who is accustomed to fast running at higher risk for bone fatigue.

Adult↗
PubMed2000

In-vivo strain measurements to evaluate the strengthening potential of exercises on the tibial bone.

Mechanical loading during physical activity produces strains within bones. It is thought that these forces provide the stimulus for the adaptation of bone. Tibial strains and rates of strain were measured in vivo in six subjects during running, stationary bicycling, leg presses and stepping and were compared with those of walking, an activity which has been found to have only a minimal effect on bone mass. Running had a statistically significant higher principal tension, compression and shear strain and strain rates than walking. Stationary bicycling had significantly lower tension and shear strains than walking. If bone strains and/or strain rates higher than walking are needed for tibial bone strengthening, then running is an effective strengthening exercise for tibial bone.

Adult↗
PubMed1999

Do axial dynamic fixators really produce axial dynamization?

The use of dynamic external fixators for the treatment of long bone fracture is widespread and well accepted. It is claimed that dynamization, i.e. small micromovements of compression/distraction at the fracture site, can be produced by allowing sliding of an inner rod within an outer housing. However, as the forces on the fixator are not direct but transferred from the bone via bone pins, there is a bending moment on the fixator. This produces "self-locking" and effectively prevents axial movements. We have studied the effect of this moment on the binding properties of the Orthofix system. The amount of movement at a simulated fracture site allowed before this locking occurs was measured and its implications discussed. It would appear that true axial dynamization does not take place using this system.

External Fixators↗
PubMed1998

FRACAS: a system for computer-aided image-guided long bone fracture surgery.

This article describes FRACAS, a computer-integrated orthopedic system for assisting surgeons in performing closed medullary nailing of long bone fractures. FRACAS's goal is to reduce the surgeon's cumulative exposure to radiation and surgical complications associated with alignment and positioning errors of bone fragments, nail insertion, and distal screw locking. It replaces uncorrelated, static fluoroscopic images with a virtual reality display of three-dimensional bone models created from preoperative computed tomography and tracked intraoperatively in real time. Fluoroscopic images are used to register the bone models to the intraoperative situation and to verify that the registration is maintained. This article describes the system concept, software prototypes of preoperative modules (modeling, nail selection, and visualization), intraoperative modules (fluoroscopic image processing and tracking), and preliminary in vitro experimental results to date. Our experiments suggest that the modeling, nail selection, and visualization modules yield adequate results and that fluoroscopic image processing with submillimetric accuracy is practically feasible on clinical images.

Bone Nails↗
PubMed1998

Effect of moderate bone hyperthermia on cell viability and mechanical function.

Extracorporeal hyperthermia treatment of bone followed by its reimplantation may be an optional treatment of bone tumors. In this study, the authors examined the minimal hyperthermic condition in which complete eradication of all viable cells in rat bone can be achieved and the mechanical effect of this treatment on the tested bone. When the results were evaluated histologically by special lactate dehydrogenase activity staining, it was found that complete bone cell death occurred after 30 minutes of heating at 60 degrees C. Cartilage cells, including those of the epiphysis, were more resistant to thermal damage. When the ability of the specimens to proliferate in cell cultures was tested, no growth was observed after heating at temperatures of 50 degrees C or greater. The mechanical stiffness tested in the Instron machine showed decreased bone stiffness at 70 degrees C but no change in the breaking load of the bones. Controlled hyperthermia's ability to eradicate viable cells without significant damage to the mechanical properties may have clinical relevance in limb salvage tumor surgery.

Animals↗
PubMed1998

A comparison of the effect of shoes on human tibial axial strains recorded during dynamic loading.

Percutaneous axial extensometers were mounted on the medial cortex of the midtibial diaphysis in seven male volunteers and the effect of three different shoes on in vivo peak-to-peak axial compression-tension strains measured during dynamic loading. Zohar shoes had lower axial strains and strain rates during treadmill walking than Nike Air Max running shoes or Israeli infantry boots. During running on a running track, there was no statistically significant difference between the axial strains or strain rates between the shoes tested. Shoe gear can modify tibial strains and strain rates that contribute to the development of tibial stress fractures.

Adult↗
PubMed1996

In vivo measurement of human tibial strains during vigorous activity.

Our understanding of mechanical controls on bone remodeling comes from studies of animals with surgically implanted strain gages, but in vivo strain measurements have been made in a single human only once. That study showed that strains in the human tibia during walking and running are well below the fracture threshold. However, strains have never been monitored in vivo during vigorous activity in people, even though prolonged strenuous activity may be responsible for the occurrence of stress fractures. We hypothesized that strains > 3000 microstrain could be produced on the human tibial midshaft during vigorous activity. Strains were measured on the tibiae of two subjects via implanted strain gauges under conditions similar to those experienced by Israeli infantry recruits. Principal compressive and shear strains were greatest for uphill and downhill zigzag running, reaching nearly 2000 microstrain in some cases, about three times higher than recorded during walking. Strain rates were highest during sprinting and downhill running, reaching 0.050/sec. These results show that strain is maintained below 2000 microstrain even under conditions of strenuous activity. Strain rates are higher than previously recorded in human studies, but well within the range reported for running animals.

Analysis of Variance↗
PubMed1996

The effect of shoe gear on human tibial strains recorded during dynamic loading: a pilot study.

The study was conducted to test the hypothesis that alterations in shoe gear can affect tibial strains in the human during dynamic loading. Rosette strain gauges were mounted on the medial border of the mid-diaphysis in two human subjects with a new strain gauge bonding technique using methyl methacrylate. Strain measurements were made at this site, the most frequent location for stress fractures in the Israeli Army during treadmill walking and free running while wearing various sport shoes (Rockport ProWalkers and New Balance NBX 900) and army boots (light Israeli infantry, double layered sole Israeli infantry, and Zohar infantry boots). Data were analyzed for only one of the subjects because strain gauge bonding was found to be inadequate at the time of surgical removal in the other subject. No single shoe lowered both the principal tibial compression and tensile strains, and the shear strains. The Zohar boot had the lowest principal compression strains during treadmill walking and mobile running, despite its relatively higher weight and sole durometry.

Biomechanical Phenomena↗
PubMed1993

Measurement of the impulsive bone motion by skin-mounted accelerometers.

A measurement system was designed to investigate longitudinal wave propagation through the lower extremity generated from foot strikes. The principal goal of the design was to eliminate measurement time lag and amplitude reduction, such that the acceleration measured by Skin Mounted Accelerometer--SMA is equal to the actual acceleration of the bone measured by Bone Mounted Accelerometer--BMA. For accurate dynamic measurement, it is important that the gain and phase of the measurement system are as close as possible to a constant and zero, respectively, for the frequency range being covered. An in vitro experiment was carried out to simultaneously measure skin and bone accelerations. The obtained information was used for identification of a linear spring/damper model representing the interface between the BMA and the SMA. The present work showed that the SMA overestimated the BMA by 12 percent in the signals between 15-30 Hz.

Acceleration↗