[Treatments and prognostic factors of cancer of the pancreas based on the data of three cancer registries].
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Female↗
Biomedical subjects
D Pienkowski
Publications and source records attributed to D Pienkowski.
Comparison of asymmetrical and symmetrical pulse waveforms in electromagnetic stimulation.
Pulsing electromagnetic field (PEMF) stimulation is a noninvasive therapeutic modality that has been successfully used to stimulate healing of surgically resistant human bone fracture nonunions. Asymmetry of the stimulus pulse waveform was thought to be necessary for therapeutic effectiveness, but asymmetrical pulses require significant electrical energy that constrains clinical delivery systems to suboptimal designs. Development of low-energy consuming stimuli will enable clinical device improvements and may provide additional information about the interaction of electromagnetic fields with tissues. The objectives of this study were (a) to determine if asymmetry of the stimulus pulse waveform is needed for efficacy and (b) to determine if symmetrical pulse waveform stimuli also can produce a beneficial therapeutic response. The rabbit fibular osteotomy model was used to answer these questions and to identify which components of the clinically used asymmetrical PEMF produce the therapeutic response. The results suggest that asymmetry is not necessary and that a narrow pulse width, symmetrical square wave signal can also stimulate stiffness increases in this model. The data also suggest that the high-amplitude, narrow-pulse portion of the asymmetrical PEMF is the principal component of the signal pulse that is responsible for the clinical therapeutic effect.
Animals↗
Field distributions in the rat tibia with and without a porous implant during electrical stimulation: a parametric modeling.
Expeditious post-operative ingrowth of bone is necessary for clinically successful fixation of porous joint prostheses. Electrical or electromagnetic fields to stimulate bone growth into porous implants have been used; however, they produced nonconvincing data. This was partially attributable to the lack of quantification of the localized electric fields produced in the pores of the implants. Therefore, this study set out: i) to quantify the local electric field values induced into the surface pores of nonconducting implants by "capacitive" coupling and to determine the magnitude of the macroscopically applied capacitively coupled electrical currents to induce specific electric field amplitudes in the pores, ii) to identify the important dielectric properties of the implant-tissue interface, and iii) to create the basis for successfully applying electrical fields in an animal model to stimulate bone ingrowth. A finite element method was used to calculate the electric field gradients and current densities present in a rat tibia modeled with a porous intramedullary implant when capacitively stimulated. Results indicated that while the current density in the pores are reduced in comparison to the region just outside the pore by about one order of magnitude, a significant current density still exists in the pore region. Furthermore, the presence of the implant increases the current densities in the trabecular bone while decreasing these values in the cortical bone. Replacing the trabecular bone in the pore by saline increases the current density in the pore by three-fold, but decreases the voltage gradient by a similar factor.
Animals↗
Pulsing electromagnetic field stimulation of the in vitro growth plate.
Specific pulsing electromagnetic fields (PEMFs) have been used to stimulate growth and repair of osteogenic tissues; however, the basis for this specificity is unknown. Previously, we determined the relevant electromagnetic field parameters of the clinically used PEMF and independently verified the beneficial effects of PEMFs on the rabbit fibula fracture healing model. The goal of the present study was to develop an in vitro model that would permit the effectiveness of various electric and magnetic field components of the PEMF to be determined. The costochondral junction (CCJ) of the 21-day-old rat was exposed in vitro to PEMFs with various electric and magnetic field component amplitudes. Response of this model to PEMFs was determined by nondestructive macrophotographic measurement of CCJ growth. Preliminary data indicated that temperature effects were present in this in vitro system. Subsequent experiments designed to separate the effects of temperature and PEMFs on the growth of CCJs in tissue culture were performed. Results indicate that accurate and frequent temperature measurements must be made for in vitro models being used to study effects of PEMFs. Small temperature differences induced by the coils used to produce PEMFs in the CCJ experimental system can have significant stimulatory effects, and the combined effects of temperature and PEMFs are not linearly additive in this model. Furthermore, our results suggest that thermal and PEMF stimuli could affect macrophotographically measured growth of the CCJ by separate mechanisms or could have a synergistic effect. Therefore, PEMF stimulation experiments should be performed under strictly "athermal" conditions.
Animals↗
The electric double layer in bone and its influence on stress-generated potentials.
Stress-generated potential (SGP) studies in fluid-filled bone have been interpreted in terms of streaming potential theory. Variations in fluid conductivity and viscosity are in agreement with this theory. Experimental results also indicate that the zeta potential of bone is dependent upon the ion concentration of the fluid. In fact, the zeta potential is seen to reverse polarity at sufficiently high concentrations of NaCl and KCl. This observation indicates that the electric double layer at the fluid-bone matrix interface is an important region contributing to electromechanical effects in bone. The double layer may also have an effect on piezoelectric studies in dry bone since the charged species remain on the matrix after the bone specimens are dried.
Animals↗
The origin of stress-generated potentials in fluid-saturated bone.
The objective of this study was to determine the origin of stress-generated potentials (SGPs) in fluid-saturated bone. Stress-generated potentials were studied as a function of the conductivity, NaCl concentration, and viscosity of the fluid contained within cortical human and bovine bone. Bone samples were soaked in solutions in which NaCl and sucrose concentrations were systematically varied. Macroscopic SGPs and their relaxation times were measured as a function of these properties. Stress-generated potentials were also measured as a function of conductivity and NaCl concentration by using a microelectrode. The results of this study confirmed that the properties of the fluid in bone have a great influence on the magnitude and time dependence of the SGP. Especially notable was the observation that solutions of high NaCl concentration consistently reversed the polarity of the SGP. These results are consistent with streaming potential theory. Although fluid-saturated bone may retain some piezoelectric properties, SGPs are predominantly caused by streaming potentials.
Adult↗
A mechanical comparison of subtrochanteric femur fracture fixation.
OBJECTIVE: To determine whether the mechanical properties of first-generation interlocking femoral nails are different from those of second-generation interlocking femoral nails in a subtrochanteric femur fracture model. DESIGN: Randomized laboratory investigation using a synthetic subtrochanteric femur fracture model. SETTING: Simulated stable and unstable fractures were created at three levels in the subtrochanteric region of synthetic femora. Instrumented specimens were tested elastically in a biomaterials testing system. INTERVENTION: Synthetic femora were instrumented with either a statically locked first-generation femoral nail or a statically locked second-generation femoral nail. MAIN OUTCOME MEASUREMENTS: Elastic stiffness for both the stable and unstable fracture groups was measured in both compression and torsion. Unstable fracture specimens were tested to failure in compression, and load to failure was measured. RESULTS: Throughout the subtrochanteric region, second-generation femoral nail constructs were consistently stiffer in compression and torsion than were statically locked first-generation femoral nail constructs. In general, second-generation constructs also withstood larger loads to failure in the unstable fracture model. CONCLUSIONS: Second-generation nails provided significantly enhanced mechanical stiffness compared with first-generation femoral nails when used to treat both stable and unstable subtrochanteric femur fractures. Although these results were obtained by using a well-controlled, mechanically consistent model, clinical validation of an increased incidence of fracture unions or of decreased time to union is required before we can recommend that second-generation nails be used routinely to treat subtrochantenic femur fractures.
Analysis of Variance↗
Interference screw fixation strength of a quadrupled hamstring tendon graft is directly related to bone mineral density and insertion torque.
The purpose of this study was to determine whether bone mineral density of the host bone, measured using conventional dual photon absorptiometry techniques, and insertion torque can predict part of the ultimate failure strength of interference screw fixation of quadrupled hamstring tendon grafts. The semitendinosus and gracilis tendons were harvested from 10 human cadaveric knees, mean age 66.5 years (range, 53 to 81). The bone tunnel was sized within 0.5 mm of the graft. The graft was fixed with a biodegradable screw (7 x 25 mm for the femur, and 9 x 25 mm for the tibia) directly against the tendon and at the joint surfaces. Tibial fixation and femoral fixation were tested to failure using a materials testing system. Bone mineral density was measured in the metaphyseal region of the tibia and femur. The results of multiple regression analyses showed that both insertion torque and bone mineral density were related to the maximum load the graft withstood. These two variables explained 77.1% of the maximum load observed. We concluded that bone mineral density measurements of the host bone site are an important determinant of postoperative graft strength and thus have an important, but previously unrecognized, clinical role in establishing individual postsurgery rehabilitation protocols. Insertion torque in this study was a useful predictor of graft fixation strength.
Aged↗
The effect of ankle stabilizers on athletic performance. A randomized prospective study.
The ankle is the site of more than one third of all injuries that occur to male basketball players. Although ankle bracing may prevent injury, many players believe that braces restrict athletic performance. This belief discourages use of braces and obviates the injury protection that bracing provides. The objectives of this study were to 1) determine whether athletic performance (in four basketball-related activities) was affected by three ankle brace designs (Universal, Kallassy, and Air-Stirrup ankle training brace), 2) determine whether specific braces are better for specific athletic activities, and 3) determine whether athletic performance changes with brace use. Twelve high school basketball players wore each brace type while vertical jumping, standing long jumping, cone running, and 18.3-meter shuttle running at two test times (initially and after 1 week of acclimation). Our data showed that these braces had no significant effects on athletic performance. No brace affected athletic performance in one specific activity more than another, and athletic performance did not change with brace use. We concluded that prophylactic ankle bracing does not inhibit athletic performance.
Adaptation, Physiological↗