An Instrumented Pendulum System for Measuring Energy Absorption During Fracture Insult to Large Animal Joints in Vivo

Abstract

For systematic laboratory studies of bone fractures in general and intraarticular fractures in particular, it is often necessary to control for injury severity. Quantitatively, a parameter of primary interest in that regard is the energy absorbed during the injury event. For this purpose, a novel technique has been developed to measure energy absorption in experimental impaction. The specific application is for fracture insult to porcine hock (tibiotalar) joints in vivo, for which illustrative intraoperative data are reported. The instrumentation allowed for the measurement of the delivered kinetic energy and of the energy passed through the specimen during impaction. The energy absorbed by the specimen was calculated as the difference between those two values. A foam specimen validation study was first performed to compare the energy absorption measurements from the pendulum instrumentation versus the work of indentation performed by an MTS machine. Following validation, the pendulum apparatus was used to measure the energy absorbed during intraarticular fractures created in 14 minipig hock joints in vivo. The foam validation study showed close correspondence between the pendulummeasured energy absorption and MTSperformed work of indentation. In the survival animal series, the energy delivered ranged from 31.5 to 48.3 Js (41.3 آ±â€‰4.0, mean آ±â€‰s.d.) and the proportion of energy absorbed to energy delivered ranged from 44.2% to 64.7% (53.6% آ±4.5%). The foam validation results support the reliability of the energy absorption measure provided by the instrumented pendulum system. Given that a very substantial proportion of delivered energy passed—unabsorbed—through the specimens, the energy absorption measure provided by this novel technique arguably provides better characterization of injury severity than is provided simply by energy delivery.