Smooth and partially threaded 3.12 mm (W inch) trochar-tipped Steinmann pins were inserted transversely through both diaphyseal cortices of eight mature canine tibias using five methods. Angular velocity (revolutions per minute) during insertion and temperature elevation due to friction during penetration of the second cortex were recorded. The force required for extraction of the pins from the bone and the histologic appearance of the bone-pin interface were determined for one-half of the pins 2 days after insertion and for one-half of the pins 56 days after insertion. The increase in temperature was similar for all methods of insertion except high speed power, which was significantly greater (p < 0.05). The force required for axial pin extraction was similar for pins inserted by hand chuck, predrllled, and low speed power methods after both 2 and 56 days. Pins inserted by high speed power and hand drill required force similar to the others for extraction after 2 days but significantly less force (p < 0.05) for extraction after 56 days. The partially threaded pins required significantly greater force (p < 0.01) extraction after both 2 and 56 days. Hlstologic examination revealed increased mechanical bone damage surrounding hand chuck inserted pins, increased bone necrosis surrounding high speed power inserted pins, and increased inflammatory changes surrounding hand drill inserted pins.

The strength and holding power of four pin designs for use with half pin (type I) external skeletal fixation were evaluated. Pins that were tested were fully threaded, nonthreaded, two cortices partially threaded, and one cortex partially threaded. The study involved three parts: (1) resistance of the pins to axial extraction immediately after insertion; (2) resistance of the pins to axial extraction 8 weeks after being inserted into the tibiae of live dogs; and (3) resistance of the pins to bending load. Pins with threads engaging two cortices were more resistant to axial extraction than nonthreaded pins in both the acute (p less than 0.0001) and chronic (p less than 0.0001) studies. Nonthreaded pins were more resistant to bending than fully threaded and two cortices partially threaded pins (p less than 0.0005). One cortex partially threaded pins possessed similar bending strength to nonthreaded pins (p = 0.21) and had 5.3 times more resistance to axial extraction in the acute study (p less than 0.0001) and 6.9 times more in the chronic study (p less than 0.0001). Though one cortex partially threaded pins were not as resistant to axial extraction as pins with threads engaging two cortices (p less than 0.0001), they were more resistant to bending loads (p less than 0.0005). Loss of holding power and pin failure are two of the most serious problems associated with fracture stabilization using external skeletal fixation. The results of this study suggest that one cortex partially threaded pins are better at maintaining holding power and resisting bending and breaking than nonthreaded pins.(ABSTRACT TRUNCATED AT 250 WORDS)

A method was developed to determine the elastic behavior of large blood vessels in terms of their transmission characteristics for small sinusoidal pressure signals. The method is new insofar as it utilizes transient signals of the form of finite trains of sine waves that are superimposed on the naturally occurring pressure fluctuations and are generated by an electrically driven impactor or by a pump. Its application to the thoracic aortas of 18 mature mongrel dogs anesthetized with pentobarbital has shown that dispersion and attenuation data for frequencies between 40 and 200 cps can be obtained without requiring either Fourier transform computations or resolution of reflection interference. For the frequency range considered, the descending aorta is only mildly dispersive but exhibits strong attenuation that must be attributed primarily to dissipative mechanisms in the vessel wall. At normal blood pressure levels, the wave speed during diastole can have a value between 4 and 6 m/sec. For all frequencies tested the amplitude ratio of the waves exhibits the same exponential decay pattern with distance measured in wavelengths. A marked increase in wave speed observed from diastole to systole can be associated with an increase in mean flow and with a stiffening of the aortic wall due to the rise in pressure. This phenomenon implies that the aortas of anesthetized dogs should exhibit nonlinear properties with respect to large amplitude pulse waves such as those generated by the heart.

Data on wave speed acquired from 20 anesthetized dogs showed that the thoracic aorta was essentially nondispersive for small artificially generated pressure waves traveling in the downstream or the upstream direction and having frequencies between 40 and 120 Hz. The amplitude of these waves decayed exponentially with the distance traveled. The attenuation was independent of frequency and pressure if the distance was measured in wavelengths. The logarithmic decrement of the downstream waves ranged between 0.7 and 1.0, whereas that of the retrograde waves was between 1.3 and 1.5. The discrepancy in the attenuation for the two directions appeared to be due to the taper of the thoracic aorta. Simultaneous measurements of the transmission times of waves traveling downstream and upstream indicated that small pressure perturbations were convected with a speed that was approximately equal to the mean flow velocity. The speed of such perturbations depended strongly on the aortic pressure level at which they were generated. For normal pressure pulses generated by the heart, the speed of small perturbations at systole might be 30% higher than that at diastole. Theoretical studies have shown that such changes in wave speed due to variations in pressure and flow produce marked nonlinear effects in hemodynamics. KEY WORDSnonlinear properties of aorta phase velocity convection of pressure signals wave transmission characteristics dissipative mechanisms elastic behavior of blood vessels retrograde wavesFrom the

The measurement of blood velocity fields, volume flow, and arterial wall motion in the descending thoracic aorta provides essential hemodynamic information for both research and clinical diagnosis. The close proximity of the esophagus to the aorta in the dog makes it possible to obtain such data nonsurgically using an ultrasonic esophageal probe; however, the accuracy of such a probe is limited if the angle between the sound beam and the flow axis, known as the Doppler angle, is not precisely known. By use of a pulsed Doppler velocity meter (PUDVM) and a triangulation procedure, accurate empirical measurement of the Doppler angle has been obtained, allowing quantification of blood velocity scans across the aorta. Volume flow is obtained by integration of blood velocity profiles and arterial wall motion is measured with an ultrasonic echo tracking device. Accuracy of the probe was substantiated by comparison with ultrasonic and electromagnetic implanted flow cuff measurements. Use of the probe in measurement of blood velocity, volume flow and arterial wall motion at various locations along the 8- and 10-cm length of the descending thoracic aorta in adult beagle dogs is detailed. The simplicity, accuracy, and nontraumatic aspect of the technique should allow increasing use of such a probe in numerous research and clinical applications.

Half-pin (type 1) external skeletal fixators with four, three, and two fixation pins and an intramedullary pin, and four-pin external skeletal fixators without an intramedullary pin were applied to prepared canine femurs. Load to failure, load to yield, safe load, and stiffness under compressive and torsional loads were calculated. When tested in compression, all measurements for the four-pin fixators with an intramedullary pin were significantly higher than for the two-pin fixators with an intramedullary pin. The values for all parameters except load to yield were significantly higher for the four-pin fixators with an intramedullary pin than for the four-pin fixators without an intramedullary pin. When tested in torsion, all measurements for the four-pin fixators with an intramedullary pin were significantly higher than for the two or three-pin fixators with an intramedullary pin.

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