Bioelectric Potentials in Bone

In addition, electricity can be induced in bone by means of an electric field with the electric apparatus remaining completely external to the limb; however, the amplitude and frequency of the applied current needs to be increased to effectively cross the cutaneous resistance barrier. The electric field can be inductively or capacitively coupled to the bone. In inductive coupling, a current varying over time within external wire coils produces a time-varying magnetic field, which in turn induces a time-varying direct current electric field within biological tissues contained inside the space between the wire coils. In capacitive coupling, an electric field is induced in bone by an external capacitor (two charged metal plates are placed on either side of the limb and attached to a voltage source). Several studies have shown that both inductive- and capacitive-coupled pulsed electric fields can favorably influence fracture repair in experimental animals and humans.

The mechanism by which electricity induces osteogenesis is unclear. It is known that the cathode consumes oxygen and produces hydroxyl radicals according to the equation 2H2O + O2 + 4e → 4OH. Thus, the oxygen tension (PO2) could be lowered in the local tissue, and pH is raised in the vicinity of the cathode. Studies have also shown that low PO2 in tissue encourages bone formation at the growth plate and within fracture calluses. Other studies have determined that the pH in the growth plate at the calcification front is rather high (7.70 ± 0.05), and this information is consistent with the previous concept.

These local microenvironmental changes in the vicinity of the cathode lead to cellular changes that ultimately result in osteogenesis. Both capacitive- and inductive-coupled pulsed electric fields act directly on bone and cartilage cells resulting in transient elevations in intracellular calcium ions contributed by two sources: (1) the opening of voltage-gated calcium channels allowing external calcium ions to flow into cells and (2) those calcium ions released from endoplasmic reticulum storage depots. In addition, evidence shows that these pulsed electromagnetic treatments activate other intracellular signal transduction pathways in bone and cartilage cells, leading to the stimulation of cell proliferation and/or the production and secretion of additional extracellular matrix. These findings have enabled the application of bioelectricity in one or more of its many forms to modulate growth, maintenance, and repair of bone and cartilage.

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Jul 3, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Bioelectric Potentials in Bone

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