When Iwao Yasuda, MD was a medical student at the Kyoto Prefectural University of Medicine in Kyoto, Japan, he showed a keen interest in the study of physics and electronics. This became the start of a lifelong, personal investigative journey into the electrical properties of bone. Yasuda was one of the first people to measure the electrical fields generated in bone in response to mechanical stimulation. Said another way he discovered that bone produces an electrical field or charge when weight is applied such as walking or running. His discovery was a monumental breakthrough in the understanding of how bones work and in turn was instrumental in the creation of electrical stimulation devices used to promote fracture and bone healing used throughout the world today.
Dr. Yasuda happened to discover the piezoelectricity of bone in a laboratory that was built into his house. At first he thought the phenomenon was a kind of noise, but it did not take much time before he firmly believed that the bone produced an electrical field. Initially Dr. Yasuda presented his work to the Japanese orthopedic community but few shared his excitement. Through persistence he managed to get his work published in 1953 in a rather obscure Japanese medical journal. Two decades later after his work was validated as a great contribution to bone research it was translated into English and published around the world.
In the article, he described the theories and methods behind his discovery. He hypothesized that active regions in biologic tissues are always electronegative compared to resting regions; therefore, portions of bone under compression would be electronegative. To test this theory he did the following experiment. One end of a long tubular bone was fixed to a stationary stand while a weight was placed on the other to bend the bone. Yasuda, using a voltmeter, measured the electrical potential where the bone was bent the most. He discovered the concave side of the bone, which was under compression, was electronegative while the convex side, which was under tension carried a positive charge. Therefore, it can be said that when bone is stressed electricity is produced. This phenomenon is called piezoelectricity of bone.
Yasuda then tried to use this understanding of how bones work to explain how a fractured bone heals. Initially he thought the callus or new bone that forms around a fracture produced electricity but further experimentation proved this wrong. His additional work showed that stress on bone produced electricity that in turn caused the callus to form and the bone to heal. From this he went on to conclude that the quality and quantity of bone healing should be controllable, and that the application of electricity in the treatment of fractures and bone and joint diseases will soon follow – and follow it.
Today electrical devices that stimulate bone healing – commonly called bone stimulators – are routinely used to increase bone-healing potential under many circumstances. Bone stimulators are used in complex fractures that are slow to heal, in spine surgery to increase the rate of bone fusion, and in sports medicine to get athletes back quicker. In fact just a few years ago when Duke was on its way to another national championship, Elton Brand returned to play just 5 weeks after a serious foot fracture rather than 8 or 10 weeks thanks in part to a bone stimulator.