Dec 31, 2022
Medicine
Bone Healing
A slightly edited excerpt from Are Electromagnetic Fields Making Me Ill? by Brad Roth
Steady electric fields have been used to heal broken bones. This work was motivated by bone’s piezoelectric property: a mechanical stress produces an electric field, and conversely an electric field produces a mechanical stress. When orthopedic surgeons discovered bone’s piezoelectricity, they wondered if electric fields could cause effects in addition to mechanical ones. In particular, they speculated about electric fields causing bone healing. The original experiments were promising, and doctors began to utilize electrical bone growth stimulators clinically. Now there are over a dozen such devices approved by the Food and Drug Administration for mending long bones (particularly those fractures that failed to heal on their own, called nonunions), and for fusing vertebrae in the spine.
Initial experiments on bone healing in the 1950s used a direct current (DC) electric field, meaning the field was static. This method requires that electrodes be implanted surgically near the fracture. Bone growth was observed at the cathode (negative electrode) and bone absorption at the anode (positive electrode). To avoid absorption, the anode was generally placed in the surrounding tissue, away from the bone itself. Most publications describing the use of DC electric fields for bone healing report the applied current as about 10 microamps. Converting the current to electric field strength is not simple, but the field appears to be on the order of 0.1–1 V/m.
When a metal electrode is in contact with the salt water making up much of our tissue, an electric current results in chemical reactions at the electrode surface (these reactions are necessary in order to transform current carried by electrons in the electrode wires into current carried by ions in the tissue). For alternating current, these often reversible reactions first progress in one direction and then the other, with little net effect. But with a direct current, the products of these reactions accumulate. Researchers believe that these products, rather than the electric field itself, are what stimulate bone growth. The cathode releases hydroxyl radicals, hydrogen peroxide, and other chemicals, which are thought to upregulate growth factors, thereby increasing bone deposition.
A DC electric field has several disadvantages. If too many reaction products amass, they may be toxic. Too much or too little of these chemicals is bad; the amount must just right. Also, implanting or removing the electrodes requires surgery, which is invasive, is usually painful, might cause infection, and could trigger inflammation.
To avoid surgery and other drawbacks, researchers developed two new methods for producing the electric field, based on capacitive and inductive coupling. Both of these techniques use an alternating electric field or brief pulses. These approaches do not require chemical reactions at the surface of an electrode; for capacitive coupling the electrodes are on the skin well away from the bone, and for inductive coupling there are no electrodes at all. Therefore, these methods have a mechanism of interaction with bone that is different from DC stimulation. The healing is caused by the electric field itself, and not by a chemical reaction at the electrode surface. The details are uncertain, but any therapeutic response appears to derive from the electric field causing calcium ions to either enter the cell through channels in the membrane or be released from intracellular stores, initiating a complex biochemical response. The electric field strength employed by these instruments varies widely, but is generally stronger than for DC fields.
Does an electric field (alternating or steady) improve healing in patients with a broken bone? Researchers have performed many clinical trials, and the results are mixed. Several meta-analyses have attempted to sort through all the data. For example, Brent Mollon and his coworkers examined 11 randomized clinical trials, nine of which were blinded to a placebo control. Their analysis was limited to electromagnetic stimulators. They found that “while our pooled analysis does not show a significant impact of electromagnetic stimulation on delayed unions or ununited long bone fractures, methodological limitations and high between-study heterogeneity leave the impact of electromagnetic stimulation on fracture-healing uncertain” (Journal of Bone and Joint Surgery, Volume 90, Pages 2322–2330, 2008). Other meta-analyses, like that of Griffin and Bayat (ePlasty, Volume 11, Pages 303–353, 2011) and Aleem et al. (Scientific Reports, Volume 6, Article 31724, 2016), compared the clinical effectiveness of all three types of devices — DC, capacitive, and inductive — and were cautiously supportive of using electric fields for bone healing. The meta-analysis by Kooistra et al. (Indian Journal of Orthopaedics, Volume 43, Pages 149–155, 2009) concluded that “although preclinical and observational evidence seems to provide a sensible rationale for using [electrical stimulation] in the treatment of long bone nonunions, the current paucity of and heterogeneity in sound clinical evidence prevent orthopedic surgeons from justifiably implementing it.”
What do I make of these results? After decades of research and clinical use, we still are not sure if electric fields help bones heal. The evidence is so puzzling that even meta-analysis cannot make sense of it. Maybe electric fields do help, but maybe they do not. Nevertheless, when half a century of study is not sufficient to determine if a method works, I get suspicious. The technique is plausible, but definitely not proven.
