Electric fields and bone loss of disuse

Amelioration of bone fragility by pulsed electromagnetic fields in type 2 diabetic KK-Ay mice involving Wnt/β-catenin signaling

Type 2 diabetes mellitus (T2DM) results in compromised bone microstructure and quality, and subsequently increased risks of fractures. However, it still lacks safe and effective approaches resisting T2DM bone fragility. Pulsed electromagnetic fields (PEMFs) exposure has proven to be effective in accelerating fracture healing and attenuating osteopenia/osteoporosis induced by estrogen deficiency. Nevertheless, whether and how PEMFs resist T2DM-associated bone deterioration remain not fully identified. The KK-Ay mouse was used as the T2DM model. We found that PEMF stimulation with 2 h/day for 8 wk remarkably improved trabecular bone microarchitecture, decreased cortical bone porosity, and promoted trabecular and cortical bone material properties in KK-Ay mice. PEMF stimulated bone formation in KK-Ay mice, as evidenced by increased serum levels of bone formation (osteocalcin and P1NP), enhanced bone formation rate, and increased osteoblast number. PEMF significantly suppressed osteocytic apoptosis and sclerostin expression in KK-Ay mice. PEMF exerted beneficial effects on osteoblast- and osteocyte-related gene expression in the skeleton of KK-Ay mice. Nevertheless, PEMF exerted no effect on serum biomarkers of bone resorption (TRAcP5b and CTX-1), osteoclast number, or osteoclast-specific gene expression (TRAP and cathepsin K). PEMF upregulated gene expression of canonical Wnt ligands (including Wnt1, Wnt3a, and Wnt10b), but not noncanonical Wnt5a. PEMF also upregulated skeletal protein expression of downstream p-GSK-3β and β-catenin in KK-Ay mice. Moreover, PEMF-induced improvement in bone microstructure, mechanical strength, and bone formation in KK-Ay mice was abolished after intragastric administration with the Wnt antagonist ETC-159. Together, our results suggest that PEMF can improve bone microarchitecture and quality by enhancing the biological activities of osteoblasts and osteocytes, which are associated with the activation of the Wnt/β-catenin signaling pathway. PEMF might become an effective countermeasure against T2DM-induced bone deterioration.NEW & NOTEWORTHY PEMF improved trabecular bone microarchitecture and suppressed cortical bone porosity in T2DM KK-Ay mice. It attenuated T2DM-induced detrimental consequence on trabecular and cortical bone material properties. PEMF resisted bone deterioration in KK-Ay mice by enhancing osteoblast-mediated bone formation. PEMF also significantly suppressed osteocytic apoptosis and sclerostin expression in KK-Ay mice. The therapeutic potential of PEMF on T2DM-induced bone deterioration was associated with the activation of Wnt/ß-catenin signaling.

Pulsed electromagnetic fields modify the adverse effects of glucocorticoids on bone architecture, bone strength and porous implant osseointegration by rescuing bone-anabolic actions

Long-term glucocorticoid therapy is known to induce increased bone fragility and impaired skeletal regeneration potential. Growing evidence suggests that pulsed electromagnetic fields (PEMF) can accelerate fracture healing and increase bone mass both experimentally and clinically. However, how glucocorticoid-treated bone and bone cells respond to PEMF stimulation remains poorly understood. Here we tested the effects of PEMF on bone quantity/quality, bone metabolism, and porous implant osseointegration in rabbits treated with dexamethasone (0.5 mg/kg/day, 6 weeks). The micro-CT, histologic and nanoindentation results showed that PEMF ameliorated the glucocorticoid-mediated deterioration of cancellous and cortical bone architecture and intrinsic material properties. Utilizing the new porous titanium implant (Ti2448) with low toxicity and low elastic modulus, we found that PEMF stimulated bone ingrowth into the pores of implants and enhanced peri-implant bone material quality during osseous defect repair in glucocorticoid-treated rabbits. Dynamic histomorphometric results revealed that PEMF reversed the adverse effects of glucocorticoids on bone formation, which was confirmed by increased circulating osteocalcin and P1NP. PEMF also significantly attenuated osteocyte apoptosis, promoted osteoblast-related osteocalcin, Runx2 and Osx expression, and inhibited osteocyte-specific DKK1 and Sost expression (negative regulators of osteoblasts) in glucocorticoid-treated skeletons, revealing improved functional activities of osteoblasts and osteocytes. Nevertheless, PEMF exerted no effect on circulating bone-resorbing cytokines (serum TRAcP5b and CTX-1) or skeletal gene expression of osteoclast-specific markers (TRAP and cathepsin K). PEMF also significantly upregulated skeletal gene expression of canonical Wnt ligands (Wnt1, Wnt3a and Wnt10b), whereas PEMF did not alter non-canonical Wnt5a expression. This study demonstrates that PEMF treatment improves bone mass, strength and porous implant osseointegration in glucocorticoid-treated rabbits by promoting potent bone-anabolic action, which is associated with canonical Wnt-mediated improvement in osteoblast and osteocyte functions. This study provides a new treatment alternative for glucocorticoid-related bone disorders in a convenient and non-invasive manner.

Numerical Simulation of Electroactive Hydrogels for Cartilage-Tissue Engineering

The intrinsic regeneration potential of hyaline cartilage is highly limited due to the absence of blood vessels, lymphatics, and nerves, as well as a low cell turnover within the tissue. Despite various advancements in the field of regenerative medicine, it remains a challenge to remedy articular cartilage defects resulting from trauma, aging, or osteoarthritis. Among various approaches, tissue engineering using tailored electroactive scaffolds has evolved as a promising strategy to repair damaged cartilage tissue. In this approach, hydrogel scaffolds are used as artificial extracellular matrices, and electric stimulation is applied to facilitate proliferation, differentiation, and cell growth at the defect site. In this regard, we present a simulation model of electroactive hydrogels to be used for cartilage–tissue engineering employing open-source finite-element software FEniCS together with a Python interface. The proposed mathematical formulation was first validated with an example from the literature. Then, we computed the effect of electric stimulation on a circular hydrogel sample that served as a model for a cartilage-repair implant.

Pulsed electromagnetic fields partially preserve bone mass, microarchitecture, and strength by promoting bone formation in hindlimb-suspended rats

A large body of evidence indicates that pulsed electromagnetic fields (PEMF), as a safe and noninvasive method, could promote in vivo and in vitro osteogenesis. Thus far, the effects and underlying mechanisms of PEMF on disuse osteopenia and/or osteoporosis remain poorly understood. Herein, the efficiency of PEMF on osteoporotic bone microarchitecture, bone strength, and bone metabolism, together with its associated signaling pathway mechanism, was systematically investigated in hindlimb-unloaded (HU) rats. Thirty young mature (3-month-old), male Sprague-Dawley rats were equally assigned to control, HU, and HU + PEMF groups. The HU + PEMF group was subjected to daily 2-hour PEMF exposure at 15 Hz, 2.4 mT. After 4 weeks, micro-computed tomography (µCT) results showed that PEMF ameliorated the deterioration of trabecular and cortical bone microarchitecture. Three-point bending test showed that PEMF mitigated HU-induced reduction in femoral mechanical properties, including maximum load, stiffness, and elastic modulus. Moreover, PEMF increased serum bone formation markers, including osteocalcin (OC) and N-terminal propeptide of type 1 procollagen (P1NP); nevertheless, PEMF exerted minor inhibitory effects on bone resorption markers, including C-terminal crosslinked telopeptides of type I collagen (CTX-I) and tartrate-resistant acid phosphatase 5b (TRAcP5b). Bone histomorphometric analysis demonstrated that PEMF increased mineral apposition rate, bone formation rate, and osteoblast numbers in cancellous bone, but PEMF caused no obvious changes on osteoclast numbers. Real-time PCR showed that PEMF promoted tibial gene expressions of Wnt1, LRP5, β-catenin, OPG, and OC, but did not alter RANKL, RANK, or Sost mRNA levels. Moreover, the inhibitory effects of PEMF on disuse-induced osteopenia were further confirmed in 8-month-old mature adult HU rats. Together, these results demonstrate that PEMF alleviated disuse-induced bone loss by promoting skeletal anabolic activities, and imply that PEMF might become a potential biophysical treatment modality for disuse osteoporosis.

Moderate-intensity rotating magnetic fields do not affect bone quality and bone remodeling in hindlimb suspended rats

Abundant evidence has substantiated the positive effects of pulsed electromagnetic fields (PEMF) and static magnetic fields (SMF) on inhibiting osteopenia and promoting fracture healing. However, the osteogenic potential of rotating magnetic fields (RMF), another common electromagnetic application modality, remains poorly characterized thus far, although numerous commercial RMF treatment devices have been available on the market. Herein the impacts of RMF on osteoporotic bone microarchitecture, bone strength and bone metabolism were systematically investigated in hindlimb-unloaded (HU) rats. Thirty two 3-month-old male Sprague-Dawley rats were randomly assigned to the Control (n = 10), HU (n = 10) and HU with RMF exposure (HU+RMF, n = 12) groups. Rats in the HU+RMF group were subjected to daily 2-hour exposure to moderate-intensity RMF (ranging from 0.60 T to 0.38 T) at 7 Hz for 4 weeks. HU caused significant decreases in body mass and soleus muscle mass of rats, which were not obviously altered by RMF. Three-point bending test showed that the mechanical properties of femurs in HU rats, including maximum load, stiffness, energy absorption and elastic modulus were not markedly affected by RMF. µCT analysis demonstrated that 4-week RMF did not significantly prevent HU-induced deterioration of femoral trabecular and cortical bone microarchitecture. Serum biochemical analysis showed that RMF did not significantly change HU-induced decrease in serum bone formation markers and increase in bone resorption markers. Bone histomorphometric analysis further confirmed that RMF showed no impacts on bone remodeling in HU rats, as evidenced by unchanged mineral apposition rate, bone formation rate, osteoblast numbers and osteoclast numbers in cancellous bone. Together, our findings reveal that RMF do not significantly affect bone microstructure, bone mechanical strength and bone remodeling in HU-induced disuse osteoporotic rats. Our study indicates potentially obvious waveform-dependent effects of electromagnetic fields-stimulated osteogenesis, suggesting that RMF, at least in the present form, might not be an optimal modality for inhibiting disuse osteopenia/osteoporosis.

Influence of electromagnetic fields on bone fracture in rats: role of CAPE

OBJECTIVE

To study the effects of radiation emitted by mobile phones on bone strength and caffeic acid phenethyl ester (CAPE) on the changes induced by radiation.

METHODS

Forty-eight Sprague-Dawley rats were divided into five groups. Rats in the control group (first group) were left within the experimental setup for 30 min/day for 28 days without radiation exposure. Nine hundred MHz radiation group was broke down into 2 subgroups (group 1/2). Both subgroups were exposed to radiation for 28 days (30 min/day). The next group was also divided into 2 subgroups (group 3/4). Each was exposed to 1800 MHz of radiation for 28 days (30 min/day). The third and fifth groups were also treated with CAPE for 28 days. Treatment groups received ip caffeic acid phenethyl ester (10 micromol/kg per day) before radiation session. Bone fracture was analyzed.

RESULTS

Breaking force, bending strength, and total fracture energy decreased in the irradiated groups but increased in the treatment groups.

CONCLUSION

Radiation and CAPE can significantly improve bone.

Mechanotherapy: how physical therapists' prescription of exercise promotes tissue repair

Mechanotransduction is the physiological process where cells sense and respond to mechanical loads. This paper reclaims the term “mechanotherapy” and presents the current scientific knowledge underpinning how load may be used therapeutically to stimulate tissue repair and remodelling in tendon, muscle, cartilage and bone.

The purpose of this short article is to answer a frequently asked question “How precisely does exercise promote tissue healing?” This is a fundamental question for clinicians who prescribe exercise for tendinopathies, muscle tears, non-inflammatory arthropathies and even controlled loading after fractures. High-quality randomised controlled trials and systematic reviews show that various forms of exercise or movement prescription benefit patients with a wide range of musculoskeletal problems.1^–4 But what happens at the tissue level to promote repair and remodelling of tendon, muscle, articular cartilage and bone?

The one-word answer is “mechanotransduction”, but rather than finishing there and limiting this paper to 95 words, we provide a short illustrated introduction to this remarkable, ubiquitous, non-neural, physiological process. We also re-introduce the term “mechanotherapy” to distinguish therapeutics (exercise prescription specifically to treat injuries) from the homeostatic role of mechanotransduction. Strictly speaking, mechanotransduction maintains normal musculoskeletal structures in the absence of injury. After first outlining the process of mechanotransduction, we provide well-known clinical therapeutic examples of mechanotherapy–turning movement into tissue healing.

Influence of Electromagnetic Fields and Protective Effect of CAPE on Bone Mineral Density in Rats

BACKGROUND

Most mobile phones emit electromagnetic radiation at 900 MHz or 1800 MHz. An electromagnetic field has some biological effects on the behavior of the cell population of bone. The aim of this work is to evaluate the effects of the radiation emitted by mobile phones on bone mineral density (BMD). The effects of caffeic acid phenethyl ester (CAPE) on the radiation-induced changes were also investigated.

METHODS

In the study, 48 Sprague Dawley rats were used. Rats were divided into five groups as follows: control, irradiated with 900 MHz, irradiated with 900 MHz and treatment, irradiated with 1800 MHz, irradiated with 1800 MHz and treatment groups. The rats in the control group (first group) were left within the experimental setup during 30 min/day for 28 days without radiation exposure. Nine hundred-MHz radiation group was exposed to irradiate both second and third groups for 28 days (30 min/day); 1800-MHz radiation group was exposed to irradiate both fourth and fifth groups for 28 days (30 min/day). Third and fifth groups were also treated by CAPE for 28 days. Treatment groups received 10 microml/kg/day CAPE i.p. before the irradiation. Bone mineral densities were determined in all groups.

RESULTS

BMD was found to be decreased in the irradiated groups and to be increased in the treatment groups.

CONCLUSIONS

The changes were not significant (p >0.05).

Formation of osteoclast-like cells is suppressed by low frequency, low intensity electric fields

With use of a solenoid to generate uniform time-varying electric fields, the effect of extremely low frequency electric fields on osteoclast-like cell formation stimulated by 1,25(OH)2D3 was studied in primary murine marrow culture. Recruitment of osteoclast-like cells was assessed by counting multinuclear, tartrate-resistant acid phosphatase positive cells on day 8 of culture. A solenoid was used to impose uniform time-varying electric fields on cells; sham exposures were performed with an identical solenoid with a null net electric field. During the experiments, both solenoids heated interiorly to approximately 1.5 degrees C above ambient incubator temperature. As a result of the heating, cultures in the sham solenoid formed more osteoclast-like cells than those on the incubator shelf (132 +/- 12%). For this reason, cells exposed to the sham solenoid were used for comparison with cultures exposed to the active coil. Marrow cells were plated at 1.4 x 10(6)/cm2 in square chamber dishes and exposed to 60 Hz electric fields at 9.6 muV/cm from days 1 to 8. Field exposure inhibited osteoclast-like cell recruitment by 17 +/- 3% as compared with sham exposure (p < 0.0001). Several variables, including initial cell plating density, addition of prostaglandin E2 to enhance osteoclast-like cell recruitment, and field parameters, were also assessed. In this secondary series, extremely low frequency fields inhibited osteoclast-like cell formation by 24 +/- 4% (p < 0.0001), with their inhibitory effect consistent throughout all variations in protocol. These experiments demonstrate that extremely low intensity, low frequency sinusoidal electric fields suppress the formation of osteoclast-like cells in marrow culture. The in vitro results support in vivo findings that demonstrate that electric fields inhibit the onset of osteopenia and the progression of osteonecrosis; this suggests that extremely low frequency fields may inhibit osteoclast recruitment in vivo.

Suspension osteopenia in mice: whole body electromagnetic field effects

Whole-body fields were tested for their efficacy in preventing the osteopenia caused by tail suspension in mice. The fields had fundamental frequencies corresponding to the upper range of predicted endogenous impact-generated frequencies (0.25-2.0 kHz) in the long bones. Three distinct whole-body EMFs were applied for 2 weeks on growing mice. Structural, geometric, and material properties of the femora, tibiae, and humeri of suspended mice were altered compared to controls. Comparison of suspended mice and mice subjected to caloric restriction indicates that the changes in caloric intake do not explain either the suspension or the field-induced effects. In agreement with past studies, rather, unloading appears to cause the suspension effects and to be addressed by the EMFs. The EMF effects on bone properties were apparently frequency dependent, with the lower two fundamental frequencies (260 and 910 Hz) altering, albeit slightly, the suspension-induced bone effects. The fields are not apparently optimized for frequency, etc., with respect to therapeutic potential; however, suspension provides a model system for further study of the in vivo effects of EMFs.

Optimization of electric field parameters for the control of bone remodeling: exploitation of an indigenous mechanism for the prevention of osteopenia

The discovery of piezoelectric potentials in loaded bone was instrumental in developing a plausible mechanism by which functional activity could intrinsically influence the tissue's cellular environment and thus affect skeletal mass and morphology. Using an in vivo model of osteopenia, we have demonstrated that the bone resorption that normally parallels disuse can be prevented or even reversed by the exogenous induction of electric fields. Importantly, the manner of the response (i.e., formation, turnover, resorption) is exceedingly sensitive to subtle changes in electric field parameters. Fields below 10 microV/cm, when induced at frequencies between 50 and 150 Hz for 1 h/day, were sufficient to maintain bone mass even in the absence of function. Reducing the frequency to 15 Hz made the field extremely osteogenic. Indeed, this frequency-specific sinusoidal field initiated more new bone formation than a more complex pulsed electromagnetic field (PEMF), though inducing only 0.1% of the electrical energy of the PEMF. The frequencies and field intensities most effective in the exogenous stimulation of bone formation are similar to those produced by normal functional activity. This lends strong support to the hypothesis that endogenous electric fields serve as a critical regulatory factor in both bone modeling and remodeling processes. Delineation of the field parameters most effective in retaining or promoting bone mass will accelerate the development of electricity as a unique and site-specific prophylaxis for osteopenia. Because fields of these frequencies and intensities are indigenous to bone tissue, it further suggests that such exogenous treatment can promote bone quantity and quality with minimal risk or consequence.

Field distributions in the rat tibia with and without a porous implant during electrical stimulation: a parametric modeling

Expeditious post-operative ingrowth of bone is necessary for clinically successful fixation of porous joint prostheses. Electrical or electromagnetic fields to stimulate bone growth into porous implants have been used; however, they produced nonconvincing data. This was partially attributable to the lack of quantification of the localized electric fields produced in the pores of the implants. Therefore, this study set out: i) to quantify the local electric field values induced into the surface pores of nonconducting implants by "capacitive" coupling and to determine the magnitude of the macroscopically applied capacitively coupled electrical currents to induce specific electric field amplitudes in the pores, ii) to identify the important dielectric properties of the implant-tissue interface, and iii) to create the basis for successfully applying electrical fields in an animal model to stimulate bone ingrowth. A finite element method was used to calculate the electric field gradients and current densities present in a rat tibia modeled with a porous intramedullary implant when capacitively stimulated. Results indicated that while the current density in the pores are reduced in comparison to the region just outside the pore by about one order of magnitude, a significant current density still exists in the pore region. Furthermore, the presence of the implant increases the current densities in the trabecular bone while decreasing these values in the cortical bone. Replacing the trabecular bone in the pore by saline increases the current density in the pore by three-fold, but decreases the voltage gradient by a similar factor.

Modulation of bone loss during disuse by pulsed electromagnetic fields

The effect of pulsed electromagnetic fields (PEMFs) on bone loss associated with disuse was investigated by applying 1.5 Hz repetitions of 30 ms bursts of asymmetric pulses, varying from +2.5 to -135 mV, to bones deprived of their normal functional loading. The proximal portion of one fibula in each of a group of ovariectomised adult female beagle dogs was isolated from functional loading in vivo by proximal and distal osteotomies. Comparison of these prepared bones with their intact contralateral controls after 12 weeks, showed a 23% reduction in cross-sectional area. In similarly prepared bones exposed to PEMFs for 1 h per day, 5 days per week, this bone loss was substantially and significantly reduced to 9% (p = 0.029). There was no evidence of any new bone formation on the periosteal surface of prepared fibulae in treated or untreated situations. PEMF treatment was not associated with any significant change in number of osteons per mm2 formed within the cortex of the bones, their radial closure rate, or their degree of closure. The modulation in loss of bone area associated with exposure to PEMFs can, therefore, be inferred to be due to a reduction in resorption on the bone surface.

Effect of localized pulsed electromagnetic fields on tail-suspension osteopenia in growing mice

Pulsed magnetic fields (PEMFs) have been used effectively to treat bone fractures and sciatic-nerve-section-induced osteopenias. Properly applied PEMFs are presumed to stimulate osteogenesis. Mouse-tail suspension has been implemented as a means of inducing an osteopenic response in the long bones of the hind limbs. To evaluate localized PEMF effects, the mouse-suspension model was modified to accommodate the use of miniature wire coils affixed directly to the rear legs. Laterally and axially orientated PEMF effects were compared. Three test groups of mice included (C) control mice, (S) tail-suspended mice with treatment apparatus attached, and (SF) tail-suspended mice with apparatus attached and PEMFs delivered. The SF group was divided into mice receiving axial or lateral PEMFs. Significant bone changes occurred in suspended as compared with control mice after a 2-week test period. The PEMF mice showed significantly fewer osteopenic effects than did untreated, suspended mice. These findings are based on biomechanical measures of stiffness, strength, ductility, and energy as well as whole-bone mass and porosity. The effects of PEMFs on these properties differ for axial and lateral exposures. The results are discussed in terms of mechanisms underlying PEMF effects.

Frequency specific modulation of bone adaptation by induced electric fields

A frequency specificity for the response of bone tissue to a physical stimulus is proposed. This is obtained by comparing the spectral power of exogenously induced electric fields to the efficacy of those fields to inhibit immobilization induced bone loss in an in vivo model of skeletal adaptation. Analysis of a family of related waveforms shows that the effectiveness of the induced electric fields could be related to the induced spectral power below approximately 75 Hz. The analysis suggests that bone tissue may be extremely sensitive to induced power levels at or below this frequency, as amplitude variations of less than a factor of two within this range correspond to significantly different bone remodeling responses. The analysis also suggests that bone tissue may be strongly frequency selective, with bone capable of responding specifically to induced power in this osteogenic frequency band, even though the band includes less than 0.1% of the total induced power. As normal functional activity generates strain components encompassing this osteogenic frequency band, a distinct frequency selectivity may indicate that the tissue response is tuned to a specific endogenous stimulus. A detailed characterization of the frequency response of bone tissue could well point to the primary source for the control of the cells responsible for functional adaptation in the skeleton.

Field distributions in vertebral bodies of the rat during electrical stimulation: a parametric study

The electrical field and current density distributions were found in the various tissues of a mathematical model of the experimental rat used to study systemic osteoporosis. The finite element method was used to solve the boundary value problem derived from Maxwell's equations using a quasistatic approximation for a 60 kHz external output signal applied via skin electrodes. A parametric study was done initially to determine the principle factors which effect the solution of the field in the vertebral bodies. Grid coarseness, model length, and intervertebral space width had little effect on the solution while trabecular bone and abdominal cavity conductivity values had strong effects. The two pair of transversely placed electrodes spaced by at least three vertebral bodies produced the most uniform field distributions and was used in the experimental rat model. The range of current density values in the trabecular bone was determined to be 3.0-5.0 microA/cm2 at the external output signal where evidence of a reversal of bone loss due to castration osteoporosis had been found in the experimental rat.

Treatment of denervation/disuse osteoporosis in the rat with a capacitively coupled electrical signal: effects on bone formation and bone resorption

Utilizing a sciatic neurectomy model of disuse osteoporosis, the effects on rates of bone formation and bone resorption were examined when a capacitively coupled electrical signal was applied to the denervated tibia in the rat. It was found that a low-voltage, symmetrical sine wave, 60-kHz, capacitively coupled signal had no significant effect on the amount of bone resorption occurring in denervated right tibiae in rats previously labeled with [3H]tetracycline. This was true whether the signal was applied while osteoporosis was developing (prevention of osteoporosis) or after it had been established (treatment of osteoporosis). If a similar capacitively coupled signal was applied to rats in which osteoporosis was well established, and the rats were labeled with [3H]tetracycline daily during a 12-day treatment period, it was found that there was statistically significant enhancement of the amount of new bone formation (increased [3H]tetracycline incorporation) in the tibiae that received the signal as compared with that of the controls. These results indicate that prevention or amelioration of disuse osteoporosis that occurs with a capacitively coupled electrical signal is due not to a change in the rate of bone resorption, but to an increase in the rate of bone formation.

Prevention and treatment of sciatic denervation disuse osteoporosis in the rat tibia with capacitively coupled electrical stimulation

Osteoporosis in the sciatic-denervated rat tibia was both prevented and reversed with a capacitively coupled electrical field. In both the prevention of the development of osteoporosis and the reversal of a previously established osteoporosis, a statistically significant enhancement of wet weight, dry weight, ashed weight, ultimate strength, cortical area, cortical thickness, and a concomitant decrease in cortical porosity occurred in the stimulated, denervated tibiae of the experimental animals compared with the nonstimulated, denervated tibiae of the control animals. These effects exhibited dose-response characteristics. A 60 kHz symmetrical sinewave signal was effective in preventing osteoporosis at a range of 5-10 peak-to-peak, and it was effective in reversing osteoporosis at 10 V peak-to-peak. Reversal of a well-established osteoporosis in laboratory animals has not been reported previously. Continued investigation into the use of a capacitively coupled electrical field in the prevention and treatment of osteoporosis seems warranted from these studies.

Fracture healing in the rabbit fibula when subjected to various capacitively coupled electrical fields

The effect of capacitively coupled electrical stimulation on the healing of midshaft transverse osteotomies of the rabbit fibula is assessed roentgenographically, mechanically, and histologically. The results show that a dose-response curve for capacitive coupling and fracture healing exists and that a 220 mV, 250 microA, 60 kHz applied electrical signal (0.33 V/cm internal electric field) is the most effective signal for fracture stimulation in this model.

Amelioration of oxygen-induced osteoporosis in the in vitro fetal rat tibia with a capacitively coupled electrical field

Near-term fetal rat tibiae were grown in M.E.M. Eagle/NCTC 135/15% newborn calf serum in 5% carbon dioxide and 5, 10, 21, 35, 60, and 90% oxygen for 3, 7, 10, and 14 days. Linear growth of the explants, as measured from macrophotographs of the explants at day zero and each of the days above, was greatest in the lower oxygen concentrations and least in the higher oxygen concentrations. Breaking strengths of the tibial diaphyses were significantly reduced in those explants grown in 60 and 90% oxygen. When the fetal rat tibiae were grown in 60% oxygen for 7 days and were subjected to a capacitively coupled electrical signal (sine wave, 60 kHz, 10 V peak-to-peak output signal; current density and field in the culture dish calculated to be 5.2 microA/cm2 and 0.32 mV/cm, respectively), the breaking strengths and middiaphyseal widths were statistically significantly greater than control tibiae grown in 60% oxygen alone. It is concluded that an appropriate capacitively coupled electrical field can inhibit an oxygen-induced osteoporosis in an in vitro mammalian long bone model.

The effects of pulsed magnetic fields of the type used in the stimulation of bone fracture healing

The main impression received by us whilst writing this review is the scarcity of technical data in the clinical studies and the total absence of controlled trials. The spatial patterns of the stimulus have not been measured, and no experiments have proved that there is an effect from the magnetic field itself. Control experiments using dummy stimulators must be done, since the orthopaedic management of the stimulated patients is different from conventional management and this may have significant and beneficial clinical effects. There is no clinical study at present which shows a direct therapeutic benefit due solely to the application of the magnetic field component of the overall treatment regime. The in vivo animal experiments suggest that there may be effects due to the magnetic fields used but results are very scarce compared with the accumulated data from direct current stimulation. In vitro studies are far removed from the clinical situation, but could nonetheless prove useful if the opportunity of controlling the stimulus can be taken. In the majority of experiments, approximately spatially uniform magnetic fields have been applied, but temporal changes in the magnetic field and both spatial and temporal variation in electric field lead to non-uniform stimulation. Little attempt has been made to assess or control the induced fields by defining the system geometry. Hence it is still unknown whether effects are due to the magnetic field, the induced extracellular electric field or to fields induced at cellular level by regions of different conductivity. In conclusion, we believe that, unlike steady current work, the pulsed magnetic field treatment of fractures has not been sufficiently well investigated and, although some of the animal experiments suggest significant effects, the benefit of using magnetic fields in the clinical management of non-union and delayed union has still to be proven. Double blind trials are essential and, if these do prove that there is a definite effect of the fields, the mechanisms must then be studied using a combination of theoretical, in vivo and in vitro techniques.

The influence of electric field exposure on bone growth and fracture repair in rats

Rats were exposed to a 60-Hz electric field at an unperturbed field strength of 100 kV/m to determine its affect on bone growth and fracture repair. Exposure of immature male and female rats for 20 h/day for 30 days did not alter growth rate, cortical bone area, or medullary cavity area of the tibia. In another experiment, midfibular osteotomies were performed and the juvenile rats were exposed at 100 kV/m for 14 days. Evaluation by resistance to deformation and breaking strength indicated that fracture repair was not as advanced in the exposed animals as in the sham-exposed animals. In another experiment measurements of resistance to deformation were made in adult rats at 16, 20, and 26 days after osteotomy. Fracture repair was slower in exposed compared to control animals at day 20 and, to a lesser extent, at day 16, but not at day 26.

[Bone healing and dynamic interferential current (DIC) (author's transl)]

In the course of supplementary physical and chemical investigations of the influence of Dynamic Interferential Current (DIC) on bone healing 24 black-head sheep were subjected to transversal osteotomy of the radius. After an instable osteosynthesis the site was exposed to repeated therapy with DIC of varying mA intensity. (Methodological details are described in part I). DIC therapy resulted in altering the temperatures in the treated tissue, dependent on the mA intensity. Further associations were verified between DIC intensity and the occurrence of hydroxyprolin, and amino acid specific collagen, which also reflected increased calcifying activity. Measurement of the calcium and phosphorus levels in the regenerated (newly forming) bone tissue documented full mineralization in the DIC-treated animals at a much earlier date than in the untreated controls that had undergone similar operations. Whether DIC specifically stimulates osteogenesis within "healing" bones is still unclear.

Electrical phenomena associated with bones and fractures and the therapeutic use of electricity in fracture healing

Living bones have small electrical potentials on their surfaces, the magnitudes of which change only slightly with the reaching of adulthood. When using a limb stresses are put on the bones inside, and these create piezo-electric potentials which may themselves cause bone growth along the lines of stress, hence making the bone stronger. Voltages also appear at fracture sites and may be important in causing the bone to heal its wound. Fractures that have not healed properly can be stimulated into repair by the passage of small electric currents through them. The factors involved in these processes are discussed.

[The influence of the electromagnetic field on the activity of alkaline phosphatase in immobilised children (author's transl)]

This paper reports the influence of a changing electromagnetic field on the alkaline phosphatase-activity in the sera of immobilised children. The enzyme activity which was considerably reduced in immobilised children, increased significantly after treatment with an electromagnetic field, whereas the acid phosphatase-activity was not changed. A possible influence of the magnetic field on osteoblastic activity is discussed.

The effect of electric fields on osteoporosis of disuse

An experiment originally done by McElhaney et al. was repeated to obtain additional information about the effects of electrical fields on osteoporosis of disuse. The right femurs of 35 male rats were immobilized in plaster casts. Sixteen rats were treated with transcutaneous electrical fields of 30 Hz and approximately 100 V/cm for periods of 2 or 8 h a day. While the right femurs of the untreated rats were found to be atrophic with respect to the opposite limb, in the treated rats the immobilized femur was made larger than the opposite bone. Longer daily treatments exaggerated this effect. The tumors found in the previous study were not seen in our experiments. Other similarities and differences in the 2 studies are discussed.

Electrical modification of disuse osteoporosis

Localized electrical stimulation of the immobilized hind limb of young rabbits resulted in dramatically more bone in the tuber calcis (heel bone) compared to the severe loss of bone (osteoporosis) seen in unstimulated, immobilized controls. Detailed histological evaluation using microradiography and fluorescence and polarization microscopy showed that the increase was probably due to an overall inhibition of surface cortical bone loss )endosteal resorption) and an increase in the quantity of the new immature bone. There was also evidence of increased osteonal resorption in the stimulated animals.

Augmentation of bone repair by inductively coupled electromagnetic fields

Pulsing electromagnetic fields of low frequency and strength have been inductively coupled across skin, directly to bone, to enhance the repair of canine osteotomies. The induced voltage field in bone appears to increase the organization and strength of the repair process at 28 days after "fracture."

Bone growth in organ culture modified by an electric field

Unidirectional pulsating electric fields caused changes in the patterns of growth in rat calvaria grown in organ culture. Morphologic pattern variations were studied by radioautographic techniques. The changes occurred at the negatively charged bone surface. In a strong field, the growth pattern became disoriented.