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Biomedical subjects

G W Pratt

Publications and source records attributed to G W Pratt.

8 recordsLinked to original sources
PubMed1997

Model for injury to the foreleg of the Thoroughbred racehorse.

A discussion is presented of contributing factors to the injury to the foreleg of the Thoroughbred racehorse. The critical part of the step is taken to be the first 10-20 ms after ground contact as the hoof slides forward and stops. Large nonaxial loads associated with the deceleration of the hoof are shown to arise. Results of accelerometer measurements on the hoof of a horse running at racing speed are presented as well as mechanical properties of the racing surface. The mechanical properties of the track surface, the type of shoe, and the degree of fatigue of the horse all work together to determine the level of risk.

Acceleration↗
PubMed1988

Ultrasonic measurement of immobilization-induced osteopenia: an experimental study in sheep.

An animal model was used to examine the use of noninvasive transmission ultrasound to measure changes in bone mass which occur following disuse. Unilateral achilles tenectomy was performed on the left leg of eight adult sheep. Following a 12-week period of nonweight bearing, presacrifice transmission ultrasound measurements were taken across the calcanei of the intact and the experimental limbs and compared with those values taken postoperatively. Following specimen harvest, cross-sectional areas of the bones were quantified by microradiography and stereology, and compared with the in vivo ultrasound measurements. There was an average of 8.6% less total bone area, and 18.0% less trabecular volume fraction in the experimental nonweight-bearing limbs as compared with control intact calcanei. The difference in bone mass was associated with a 9.0% decrease in the velocity of sound from the postoperative to the presacrifice ultrasound measurements taken from the experimental calcanei, and a 2.3% increase in the control calcanei. The velocity of sound was found by the Student's t test to be a highly reliable discriminator between the experimental and control limbs.

Animals↗
PubMed1987

The use of ultrasound in vivo to determine acute change in the mechanical properties of bone following intense physical activity.

The velocity of ultrasound was measured transcutaneously across the patella and tibia in 98 volunteers both before and after running the 26 mile Boston Marathon. Absolute sound velocities were 2.9% higher in those runners finishing before 3 h when compared to runners finishing after 3 h. Tibial velocities in males were 8.8% higher than in female runners. The mean velocity across the patella of three wheelchair racers was 28% lower than the mean combined patella velocity measured in all runners. These data suggest that 'faster' velocities are associated with bone that is better suited for high functional demands. Surprisingly, when pre- and post-race velocities were compared in each runner, there was a 1.6% increase in ultrasonic velocity across the tibia, and a 3.5% increase across the patella. An increase in ultrasonic velocity following extreme physical activity suggests that adaptive mechanisms exist in healthy bone to withstand, or possibly avoid, the microdamage which might be caused by repetitive cyclic loading.

Adult↗
PubMed1978

A relationship between gait and breakdown in the horse.

A biomechanical model of running has been presented. A basic premise has been that the swing time is nearly independent of speed. In fact, both the racehorse and the trotter have nearly equal swing times. Consequently, as speed increases and the stance phase becomes shorter, the horse must compensate by increasing his extension or the length of the airborne phase (or both). The safe speed which allows the horse adequate preparation time for contact of a leg with the ground is calculated, using a stride-by-stride analysis of the motion of the horse. This is seen to be a very sensitive function of the overlap time in the gait. The overlap between the legs appears to affect both the ultimate performance potential of the horse and also his prospects for soundness.

Animals↗
PubMed1976

Force plate studies of equine biomechanics.

The force plate can measure a wide range of effects in the horse. The same instrument can record forces from more than a ton in the galloping animal to 25 g associated with the action of the heart. In all probability, the force plate will develop into a valuable clinical instrument.

Animals↗
PubMed1975

Colles' fractures. Functional bracing in supination.

The classic position of immobilization of Colles' fractures with the elbow in flexion, the forearm in pronation, and the wrist in volar flexion and ulnar deviation is probably the main reason for the common and rapid recurrence of the original deformity. Such a position places the brachioradialis muscle, a strong flexor of the elbow and the only muscle attached to the distal fracture fragment, in an ideal physiological position to exert a deforming force on the fracture fragments. Based on this assumption, further supported by electromyographic studies, a method of treatment was developed which calls for the initial immobilization of the arm in an above-the-elbow cast with the elbow in flexion, the forearm in supination, and the wrist inmoderate ulnar and volar flexion. This cast is changed a few days after application for an Orthoplast brace that permits motion of the elbow and volar flexion of the wrist while preventing pronation and supination of the forearm and dorsiflexion of the wrist. The proposed method did not prevent collapse of the fragments in all instances. However, the degree of collapse was minimum. The position of supination of the forearm and the freedom of motion of all joints seemed to reduce the swelling, stiffness, and incapacitation frequently found during active treatment of these fractures.

Braces↗