Streaming potentials in gap osteotomy callus and adjacent cortex. A pilot study.
This study documented streaming potentials generated in vivo by maturing osteotomy calluses in 10 canine tibiae. Gap osteotomies were allowed to heal for 6 or 12 weeks and were stabilized by an external fixator. Then, with the dogs under anesthesia, electrical measurements were made from 3 silver-silver chloride electrodes placed surgically in direct contact with the callus, with adjacent cortical bone, and with the medullary canal (reference electrode). Streaming potentials were recorded during step loading and sinusoidal bending (0.1-30 Hertz) as the tibia was deformed by 2 threaded pins coupled to a servohydraulic device. Streaming potentials were generated at callus and adjacent cortical sites, but the magnitude was greater on the immature, flexible callus, where bending strain was concentrated; as the callus became increasingly rigid, strain and streaming potential magnitude were distributed more evenly over the callus and adjacent cortical fragments. When normalized to surface strain, mean streaming potential per strain was less dependent on the microscopic structure, although on individual specimens streaming potential per strain at callus and adjacent cortical bone sites tended to increase with decreasing porosity. Despite a wide variation in data in this pilot series, these observations are consistent with the natural history of callus maturation: the maximum magnitude of streaming potentials in callus appears to decrease as the strain gradient across the site decreases, whereas streaming potentials normalized to strain increase as bone matures and becomes more dense.