Bone streaming potentials and currents depend on anatomical structure and loading orientation.

Bone streaming potentials (SPs) and streaming currents (SCs) may be a remodeling signal to cells, and might also be used to probe bone pore structure and fluid flows. For SPs or SCs to serve as either a remodeling signal or as a probe for pore structure, they must depend on bone structure. This study was undertaken to address two related questions. First, will differences in Haversian and laminar bone structure and fluid flow direction produce measurable differences in SP and SC? Second, do differences in SP or SC relate to differences in macroscopic bone impedance or large pore structure? SPs and SCs were measured across Haversian and laminar bone specimens with fluid flow driven in different directions by sinusoidal four-point bending. Data were grouped by bone type and flow direction (Haversian tissue, laminar tissue with radial flow, and laminar tissue with tangential flow) and flow direction alone (tangential and radial). SPs were larger for Haversian tissue and for laminar tissue with radial flow than for laminar tissue with tangential flow. SP and SC magnitude, and impedance were larger for radial than tangential flow. No difference in SC magnitude, SP or SC kinetics, or macroscopic bone impedance was observed between Haversian tissue, laminar tissue with radial flow, and laminar tissue with tangential flow. Thus, since laminar tissue with tangential flow had more vascular connections in the direction of fluid flow, SP was smallest for greatest vascular connectivity. The relation between SP or SC and impedance was inconclusive.

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.

Intraarterial protamine sulfate reduces the magnitude of streaming potentials in living canine tibia.

Using previously described techniques, transcortical streaming potentials were measured at two middiaphyseal sites on one tibia of each of nine anesthetized canines during sinusoidal bending (approximately 0 to -200 mu epsilon periosteal surface strain) at 2 Hz. Measurements were made for 60 minutes prior to and up to 180 minutes following bolus injection of protamine sulfate (42-126 mg/kg) dissolved in Hanks Balanced Salt Solution, directly into the femoral artery without interrupting circulation. Shortly after injection, the protamine sulfate caused a clear reduction in the magnitude of streaming potentials. Subsequent injections of additional protamine sulfate resulted in further reductions, and in several instances, voltage sign reversals. This study represents the first observation that circulating proteins may alter electromechanical transduction in living bone, and suggests the possibility that specific agents, which are known to affect bone remodeling, may do so, in part, by altering these endogenous electrical potentials.