Electrode-oxygen consumption and its effects on tissue-oxygen tension. A study by mass spectrometry

A theory for the mechanism of electrical bone stimulation proposes that passage of an electric current reduces the local PO2 and raises the pH near the cathode, thereby creating a favorable environment for osteogenesis. To study the effects of electric current passage on the PO2, PCO2 and pH in the vicinity of the electrodes in vivo, a wire electrode spiralled around the catheter of a clinical mass spectrometer was placed in dog muscle. Electrodes were made of stainless steel or platinum. With a cathode located in the tissue, a 20-microA direct constant current caused a drop in PO2 of 5-10 mmHg and a drop in PCO2 of 2-6 mmHg, both reaching plateaus again within five to 20 minutes. The time required to reach this new equilibrium was shorter for platinum than for stainless steel. When the electric current was turned off, PO2 and PCO2 reversed to their original values. Because of the high buffer capacity of tissue, it is highly unlikely that 20-microA current would induce a change in pH.     

Electrical stimulation of bone growth with direct current

Electrical stimulation of osteogenesis was studied in rabbit femora in: (A) a transcortical electric field with a cortex-depolarizing or hyperpolarizing orientation derived from an intramedullary electrode and a ring-shaped counter electrode encircling the femoral shaft; and (B) an electric field derived from an electrode located in the medullary canal and the counter electrode in the abdominal wall. Electrodes were made of platinum. A direct current of 20 microA was applied during six weeks. Contralateral femora with dummy electrodes served as controls. Results were analyzed by optical densitometry of roentgenograms and histomorphometry of histologic slides. Under the conditions of these experiments bone growth was not stimulated by applying a cortex-depolarizing electric field. Significant stimulation of bone growth was only observed at an intramedullary cathode, when the anode was placed at a distance.     

Electrical osteogenesis by low direct current

A constant direct current cathode was employed in the medullary canal of the rabbit tibia to investigate electrical osteogenesis at low current levels. Currents of 0.015 or 0.075 μA were delivered to the bone and the biological response was compared with contralateral controls receiving 20 μA. This investigation was performed to determine if electrical osteogenesis occurs at current levels below the previously studied range of 1–100 μA with stainless steel electrodes. New bone formed by 0.015 μA cathodes was statistically comparable with that found around inactive cathodes from an earlier pertinent study. The osteogenic response to 0.075 μA cathodes was significantly elevated above that to inactive ones, thus substantiating electrical osteogenesis for currents below 1 μA. However, it is evident that this does not demonstrate a further stimulatory range but that currents near 0.075 μA probably approach the lower significant limit for electrically induced bone growth with stainless steel electrodes.     

Appearance of osteoclasts and osteoblasts in electrically stimulated bones cultured on chorioallantoic membranes

Tibial shafts from 15-day-old chick embryos were cultured on chorioallantoic membranes of chick embryos. These bones were stimulated by either constant-direct or constant-alternating current via platinum wire electrodes. Around the anodes of 10 microA constant direct-current stimulation, the number of osteoclasts was significantly larger than that of the control, and numerous osteoblasts were observed. Around the cathodes of this current, periosteum was thickened and accompanied by proliferation of osteoblasts. Slight bone resorption in the immediate vicinity of the cathodes was also observed. The periosteum between the two electrodes was significantly thickened by this current. The comparative study between equivalent constant direct-current and alternating-current stimulation showed a dominance of direct current. This model could be useful in investigations on electrical stimulation of bone in vivo. It produces fewer artifacts and shows activation of osteoclasts in association with activation of osteoblasts in electrically induced reactions of bone tissue.     

Bone formation near direct current electrodes with and without motion.

The osteogenesis induced in the medullary canal of rabbits by the implantation of moving and stationary wire electrodes was studied with and without the simultaneous application of 20-microA constant direct cathodic current. After 3 weeks, the formation of new trabecular bone in the canal was studied and measured microscopically. Electrically stimulated osteogenesis was not observed at stationary electrodes. As in previous studies with this model, a movable electrode alone stimulated new bone formation whose area was 7-10% of the canal area. The amount of this bone was not statistically increased by the addition of cathode current. Movable, electrically active cathodes were associated, however, with fluid-filled spaces incorporated within the new trabecular bone. When mechanical stimuli were controlled, we were not able to demonstrate that the direct current stainless steel cathode acts either as an inducer or a substantial enhancer of medullary osteogenesis.     

Temporal course of bone formation in response to constant direct current stimulation

Reactive, post-traumatic bone formation in response to intramedullary insertion of a polytetrafluorethylene-coated, 28 gauge stainless steel wire was compared with the sequential bone formation seen in response to an identical intramedullary stainless steel cathode delivering 20 microA constant direct current. Animals were studied at days 1, 2, 3, 4, 5, 7, 9, 11, 14, 17, and 21 after wire insertion. Point count analysis revealed progressive bone formation beginning as early as day 3 on the constant direct current-stimulated side, progressing steadily through day 21. Control tibia, however, began to show bone formation on day 5 with peaking at day 9 and subsequent bone resorption. The osteogenic response at the 20 microA cathode was statistically elevated above that seen at the control on days 11, 17, and 21.     

The bone growth chamber for quantification of electrically induced osteogenesis

A dividable titanium implant was inserted in the tibial metaphysis of rabbits, which permitted a numerical evaluation of ingrowing bone. The implant on the test side was used as cathode and was connected to a subcutaneously located stimulator delivering constant current of either 5 microA, 20 microA, or 50 microA. A corresponding control implant was inserted in the other tibia of the same animal and treated likewise, but was not connected to the stimulator. Distally to each implant, a platinum-iridium screw was inserted into the cortex and connected on the test side to the stimulator to serve as the anode. The results showed a 2.4-fold increase in bone formation with 5 microA. In the 20-microA group, there was 2.6-fold more bone in the test chambers. Direct current (DC) stimulation with 50 microA caused a clear decrease of bone volume, with an average of 48% less bone in the test implants. The results indicate that 5 and 20 microA direct current enhance bone ingrowth into a titanium implant that is used as a cathode. The osteogenesis seemed to be more pronounced in the case where the chamber was used as a cathode compared to earlier experiments in which the cathode was placed at a distance of 5 mm from the implant.     

Effect of direct current stimulation on bone growth after distraction epiphysiolysis of the rabbit tibia

The effect of direct current stimulation on bone formation during limb lengthening was tested in a lower leg lengthening model in the rabbit. Limb lengthening was performed by distraction epiphysiolysis. A specially designed external distraction device was placed at the tibia. The distractor allowed 10 mm of lengthening in 4 weeks. Two weeks after starting the distraction, a platinum electrode was passed through the anterior cortex below the tibial tuberosity and advanced via the medullary cavity so that the tip rested in the elongated zone. Stimulation started at the time of placement of the electrodes and was continued for 3 weeks. The electrode in the elongated zone served as the cathode; the anode was placed subcutaneously. A 20 microA stimulus was selected. A control group received the same treatment without stimulation. Bone formation in the elongated zone was evaluated by histology and scintigraphy. The data from this experiment show that direct current stimulation in the early phase of a limb lengthening procedure had no effect on the extent of bone formation in the elongated zone.     

The relationship between electrical callus formation and the amount of electricity

Electrical stimulation to enhance callus formation has been in use for some time now. This experiment was undertaken to find the relationship between electrical callus formation and the amount of electricity. In this experiment, the long bones of canines were stimulated by direct current and observed microscopically for callus formation. Moreover, distribution patterns of electric potential and current density were calculated theoretically by finite element method. The results are summarized as follows: Electrical callus formation was observed in the medullary canal with 8.7-20 microA direct current. Electrical callus is fibrous ossification and the peak of callus formation is from fourteen to twenty one days. There is no difference in volume and/or speed of callus formation between the simple and the constant direct current. Using platinum electrodes, the amount of callus formed around the cathode and anode is the same. To prevent electrolysis of the tissues, distance between electrodes must be kept at a minimum. On the other hand, the surface area of the electrodes must be widen to keep the electric potential at the minimum level. The area of callus formation is related to 5-10 microA/cm2 of electric current density.     

Calcification of cartilaginous matrix in culture by constant direct-current stimulation

Forty-six femora of nine-day-old chick embryos were stimulated by 10 microA of constant direct current via platinum wire electrodes inserted into the diaphyses as cathodes in tissue culture. Apparent calcification in the hypertrophic cartilaginous region of the diaphyses was induced by the electric stimulation. This calcification was most remarkable on both ends of the diaphyses, where fine granules were observed in electron micrographs of the cartilaginous matrix. These granules were aggregates of fine needlelike crystals containing calcium and phosphorous demonstrable by X-ray microanalysis. Incorporation of 45Ca into the femora was significantly increased by the stimulation of up to 247% of the control. This matrix calcification was of interest because it occurred in avian embryonic cartilage that is normally resorbed uncalcified before it is replaced by bone.     

Cathodic oxygen consumption and electrically induced osteogenesis.

Small amounts of electric current stimulate bone formation in the region of a cathode. The purpose of this experiment is to compare changes in oxygen and hydroxyl ion concentration that occur at the cathode at current levels known to be capable of inducing osteogenesis (10-20 muamps) with those changes that occur at current levels known to be toxic to bone (100 muamps). An oxygen consumption chamber containing an oxygen electrode is fitted with two stainless steel electrodes which are connected to a constant current source. At the cathode, with a current of 100 muamps, oxygen is consumed at nearly stoichiometric rates. At higher current (100 muamps) levels, cathodic oxygen consumption gives way to hydrogen evolution. Cathodic hydroxyl ion production is directly proportional to current. It is concluded from these in vitro experiments that at 10-20 muamps the oxygen tension in the vicinity of the cathode is lowered and the pH is moderately increased. At 100 muamps the oxygen tension is not lowered, but the pH is increased dramatically. If these same changes occur in the vicinity of a cathode in vivo, then lowering the local tissue oxygen tension and raising the local pH may be mechanisms operative in electrically induced bone formation.     

Experimental study on the effect of direct currents on the internal remodeling of a long bone cortex

The effects of direct currents on internal remodeling were examined using femurs of 21 adult mongrel dogs. The left femurs of all dogs, used as a control, were inserted electrodes only, which were not electrically stimulated. In Group 1, no surgery was done on the right femur. In Group 2, 1 microA continuous direct current (D. C.) was applied for 6 weeks; in Group 3, 10 microA for 2 weeks; in Group 4, 10 microA for 4 weeks; in Group 5, 10 microA for 6 weeks; in Group 6, 10 microA for 16 weeks; and in Group 7 100 microA for 6 weeks. Each group was composed of three dogs. The following histomorphometric parameters were measured to evaluate the effects of electrical stimulation: number of resorption cavities (Ar), number of secondary osteons with osteoid seam (osAf), linear rate of mineralization of osteoid seam (Mo), perimeter of osteoid seam (Sf), cross-sectional area of secondary osteon (Ah) and bone formation rate (Vf). The following results were obtained: In Group 1, resorption cavities and secondary osteon with osteoid seam were observed more in the left femur than in the right. Then, mechanical stimulation of periosteal stripping or cortical drilling enhanced internal remodeling of cortical bone. In other groups (electrical stimulation was applied on the right femur), it seems that internal remodeling, especially activation frequency, was enhanced by D. C. No significant change was noted in the linear rate of mineralization of osteoid seam and cross-sectional area of the secondary osteons. Bone formation rate in the right femur showed increment when length of stimulating period had increased from 2 to 6 weeks. In Group 6 and 7, the enhanced area of bone formation has increased in cross-section, although in Group 7, bone necrosis was observed around the electrode in the right femur. Therefore, the optimum current of electrical stimulation may be just or slightly more than 10 microA. Bone formation rate was correlated with volume of callus in the marrow cavity within the period of six weeks.     

Effect of weak direct current with silver electrodes on bacterial growth

The author studied the effect of weak direct current on bacterial growth in vitro and in vivo. In vitro, electric current was applied 20 or 100 micro A/cm2 of direct current using electrode of carbon, silver or platinum. Its inhibitory effect was observed on the growth curve of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa in the anode bath respectively. A silk thread that adsorbed Staphylococcus aureus was inserted into the intramedullary space of the tibia of Wistar rats to induce osteomyelitis. Silver electrodes were placed to apply 100 microA/cm2 of direct current for two weeks. The therapeutic effect was then evaluated in terms of X-ray findings, histological findings and changes in the viable count of Staphylococcus aureus in the intramedullary space of the tibia. It was found that application of electric current using a silver electrode was most effective for the inhibition of bacterial growth both in vivo and in vitro, and seemed to be clinically useful for treating osteomyelitis.     

The electrical treatment of scaphoid nonunion

Seventy-one percent (12 out of 17) of the previously treated nonunions united within 12 weeks by a semi-invasive technique of electrical stimulation. The electrodes are stainless steel and Teflon-coated except for the 1 cm bare tip. The power source is a 7.5 volt battery in circuit with resistors and transistors such that a constant continuous current of 20 muamp is applied to each electrode. Three or four cathodes are implanted percutaneously, using local or regional anesthesia with radiographic control, usually an image intensifier. A long-arm cast is used for three weeks and then reduced to a short-arm cast which is used for nine additional weeks. The indication for this technique is failure of previous bone grafting. The contraindications are wrist arthritis and an avascular proximal pole. Patient acceptance of this electrode technique was high and morbidity was less than in those patients treated by iliac bone grafting. The treatment of nonunion of the scaphoid by this semi-invasive electrical stimulation technique is a reasonable alternative to bone grafting and provides a salvage procedure when bone grafting or other therapeutic modalities have failed.     

Failure of the rabbit tibial growth plate to respond to the long-term application of a capacitively-coupled electrical field

A continuous 5-V peak-to-peak, 60 kHz capacitively-coupled sine wave signal was applied to the proximal tibial growth plate in fifteen 9-week-old male New Zealand white rabbits for 6 weeks. A pair of flexible stainless steel "injectrodes" was held in place medially and laterally on the surface of the proximal hindlimb in each rabbit by means of tape wrappings. The electrodes were connected to a 9-V battery-operated power unit carried in a dorsal pouch in a body vest worn by each rabbit. Control animals wore the identical apparatus, only the power unit was inactive. Small Tantalum markers were inserted into the anteromedial aspect of the proximal tibial metaphysis 1 cm distal to the proximal tibial growth plate in all of the animals, control and experimental, 2 weeks prior to the onset of electrical stimulation. The distance between the proximal lateral tibial spine and the Tantalum marker, between the Tantalum marker and the apex of the distal tibial intercondylar notch, and between the proximal tibial spine and the distal notch was measured from roentgenograms made at the time of bone marker insertion, at the time of electrode application to the limb, and at the end of the stimulation period. Results indicate that there was no significant difference in tibial lengths between the stimulated and control groups. There was significantly less total body weight gain in both the experimental and control animals than that which occurred in paired normal animals during the same period of time. This failure to thrive may be responsible for the resultant lack of longitudinal growth stimulation of the capacitive coupling.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in bioelectric potentials on bone associated with direct current stimulation of osteogenesis

This study was designed to determine whether changes occur in the bioelectric potentials on bone during and after bone stimulation with a 20-microA direct current (DC) and whether the variations in bioelectric potentials are related to the variations in bone formation. The bioelectric potentials were recorded at different times on the rabbit distal tibial surface, during (current-on state) and after (current-off state) DC stimulation with a cathode implanted within the medullary canal. The new bone formed at the end of the experiment was quantitated and related to the bioelectric potentials recorded at current-on and current-off states, respectively. Direct current stimulation resulted in electronegative potential spike centered on the cathode tip while current was applied. After electrical stimulation was turned off, the residual potentials at the end of the experiment did not significantly differ from the initial values. Conversely, the time sequence of the changes was significantly different from the control to the experimental group. The variations in the induced potentials at current-on state were significantly related to the variations in bone formation. This study suggests the existence of a relationship among bioelectric potentials, DC stimulation, and osteogenesis.     

Preliminary report of localization of spinal cord blood supply by hydrogen during aortic operations

One source of paraplegia after aortic operations is the failure to reattach the spinal cord blood supply, the origins of which are not evident at operation. This report is concerned with a rapid new method of identifying these vessels intraoperatively. In 9 pigs, a specially designed catheter with platinum and stainless steel electrodes was inserted intrathecally. Saline solution saturated with hydrogen was injected sequentially into arterial ostia at T-15 to L-4 inclusive, and the generated current impulses from the conditioned platinum electrode were recorded. Of 90 potential segmental arteries supplying the spinal cord, 28 gave rise to spinal radicular arteries. Hydrogen-induced current impulses correctly located 25 of the radicular arteries and all those larger than 180 microns in diameter. When injected with indigo carmine, the vessels localized by the hydrogen-induced current impulses filled the entire anterior spinal artery from the low thoracic to the sacral region, whereas injection of the other vessels did not show filling. After refinement and testing for safety, this method has been employed clinically to rapidly localize and reattach routes of critical cord circulation.     

Ultrastructure of electrically induced osteogenesis in the rabbit medullary canal

The ultrastructural changes in the medullary canal of the adult male New Zealand white rabbit associated with the trauma of the insertion of an inactive cathode were compared to that associated with electrically induced osteogenesis from an active cathode delivering 20 microA constant direct current. In the vicinity of both an inactive and an active cathode, the medullary canal cellular content was replaced first by polymorphic cells and later by osteoblastic new bone formation. The polymorphic cells always appeared in the immediate vicinity of a capillary or other blood vessel. With time, the new bone formation in the medullary canal surrounding the inactive cathode disappeared, while new formation surrounding the active cathode progressively increased in amount. When the new bone formation in the medullary canal surrounding an inactive cathode disappeared, it was replaced by a network of polymorphic cells. When direct current was then applied to such an inactive electrode, the polymorphic cells were again rapidly replaced by bone. The close association of polymorphic cells with osteoblasts suggests that the former may be a precursor cell of the latter.     

Direct electrical stimulation of the cochlear nucleus: surface vs. penetrating stimulation.

Prosthetic stimulation of the cochlear nucleus (CN) has been used for rehabilitation of profoundly deaf patients who are not suitable candidates for cochlear implants. The goal of this article was to assess the relative effectiveness of surface vs. penetrating stimulation of the CN. Electrophysiologic and autoradiographic measures were used to study central auditory system activation elicited by direct stimulation of the CN. Eighteen pigmented guinea pigs, divided into three groups, underwent acute implantation of bipolar electrodes in the CN. One group was not stimulated and acted as a control (n = 7). Electrodes were placed on the surface of the CN in one test group (n = 4) and within the CN in a second test group (n = 7). Thresholds for electrically evoked middle latency responses (EMLR) were determined and input/output (I/O) functions were obtained. The two test groups were then pulsed with [14C]-2-Deoxyglucose (2-DG) intramuscularly and stimulated for 1 hour with biphasic; charge-balanced pulses having a total duration of 400 microseconds, a repetition rate of 100/sec, and an amplitude of 200 microA. After stimulation, animals were killed and brains were harvested and prepared for autoradiography using standard techniques. Threshold current for EMLRs in the surface-stimulated group had a mean of 67.5 +/- 23.9 microA (range, 40 to 100 microA). Thresholds for in-depth stimulated group had a mean of 11.4 +/- 3.5 microA (range, 10 to 20 microA). The saturation level of the I/O function for the surface-stimulated group had a mean of 287.5 +/- 41.5 microA (range, 250 to 350 microA). The saturation level for the in-depth stimulated group had a mean of 192.9 +/- 49.5 mciroA (range, 100 to 250 microA). The dynamic range for the surface electrodes had a mean of 13.1 +/- 2.7 dB (range, 9.9 to 15.9 dB), whereas the dynamic range for the penetrating electrodes had a mean of 24.5 +/- 2.6 dB (range, 20 to 28.0 dB). Autoradiographs generated by CNS tissue from stimulated animals demonstrated no significant difference in metabolic activity of the CN between surface and in-depth stimulated groups. However, there were highly significant differences in 2-DG uptake in the contralateral superior olivary complex, contralateral inferior colliculus, and ipsilateral and contralateral lateral lemniscus, with greater uptake in in-depth stimulated preparations. Electrophysiologic and autoradiographic data suggest that a penetrating CN prosthesis is capable of activating the auditory tract at a lower threshold, with a relatively wider dynamic range than a surface prosthesis.(ABSTRACT TRUNCATED AT 400 WORDS)     

Treatment of nonunion with constant direct current.

Laboratory experiments show the following relationships between electricity and bone: (1) stressed bone exhibits electronegativity in areas of compression, (2) living, nonstressed bone exhibits electronegativity in areas of bone growth and healing, and (3) the application of low magnitude direct current to bone induces osteogenesis at the negative electrode or cathode. Based on the above principles, a clinical study was performed in which 10-20 microamperes of constant direct current was used in treating nonunion in 57 patients. The results suggest that specific electrical parameters are required for successful osteogenic stimulation in patients. When these electrical parameters are met, a successful healing rate of 70 per cent can be achieved in treating nonunion with direct current. As experience is gained with this new technique in the treatment of nonunion, the results should improve even further. Basic studies exploring the mechanism(s) whereby electricity induces osteogenesis are opening new vistas into our understanding of bone growth and repair. The extension of these basic studies has far-reaching clinical implications.