Electrical Stimulation

Mechanism of Bone Healing and Electrical Stimulation

Bone is living tissue made up of many different types of cells in an organized structure. Bone is constantly undergoing the process of renewal and repair. When a bone breaks, the body immediately begins the repair process.

Bone heals through a number of phases in a process called remodeling. It has a dynamic (constantly changing) environment. Old bone is removed by cells called osteoclasts, and new bone is formed by osteoblasts. Generally, bones heal better and faster in children than in adults. A solid union (complete healing) of a fracture usually occurs in 3 months. Other factors that affect bone healing include the type and location of the fracture. Bone healing is based on its position and the amount of stress that is put on it. This is known as Wolfe's law. A long bone will return to a shape [Page 422]that is mechanically the most suitable for its function. Examples of long bones include the femur and the tibia in the leg.

Mechanism and History of Electrical Stimulation

Studies suggest that electrical stimulation may activate cellular pathways that promote bone healing. When the correct amount and type of energy are applied to bone, calcification as well as mineralization of the repair are encouraged.

Electrical stimulation has been used for decades to aid healing of fractures that are difficult to heal. In the 1950s, scientists determined that electrical current affects bone healing. Fukada and Yasuda showed that there is a relationship between electricity and the formation of callus. They showed that bone is piezoelectric, meaning that it causes the separation of charge when stressed.

When stress is applied to the bone, the concave (curved in) side has a positive charge, and the convex (curved out) side has a negative charge. This is particularly significant in long bones. When the bone is positively charged, osteoblastic (bone building) activity occurs. When there is a negative charge, osteoclastic (bone absorption) activity occurs. Electrical stimulation changes the electrical potential across the bone to stimulate osteoblastic activity. It therefore replicates the negative potential created at fracture sites by the body's electrical impulses.

Electrical Stimulation and Sports Injuries

Historically, electrical stimulation has been used to heal long-bone fractures. It has also been effective in treating nonunion of carpal navicular fractures. Electrical stimulation has been used after spinal fusions in athletes. Electrical stimulation may also have a role in healing sports-related stress fractures and stress fractures of the foot and the spine. A solid, bony union (complete healing of the fracture) gives the best results. However, some athletes return to sports with a fibrous union (painfree nonunion). It is important to monitor the athlete for recurrent or new symptoms that are problematic.

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