Inflatable brace-related streaming potentials in living canine tibias

In a canine osteotomy model, application of a pressurized brace increased the density of periosteal bone and, at 12 weeks postfracture, yielded a stronger union compared with fractures treated by conventional cast, as determined by biomechanical testing. Pulsatile transcortical electric potentials were caused by the fluctuations in intramedullary pressure that result from active circulation. This report describes a collaborative effort designed to determine whether pressure fluctuations within an inflatable brace, placed over a canine calf, can affect endogenous transcortical electric potentials. Pressure within a brace placed over a canine hindlimb was observed to oscillate between 20 and 52 mm Hg during normal ambulation in 3 dogs. Manual pulsatile inflation of a similar brace, causing brace pressure fluctuations between 12 mm Hg and 130 mm Hg, produced fluctuating transcortical electric potentials ranging from 1.2 microvolts to 87 microvolts in anesthetized canines. These electric potentials were proportional to intramedullary pressures between 3.4 mm Hg and 59 mm Hg. Transcortical electric potentials resulting from the application of a pressurized brace, rather than conventional casting, may be part of the mechanism by which the changes in fracture healing are achieved.