Bone stimulators are essentially tools that aid in healing and recovery. They emit a series of electrical impulses or ultrasound waves that create pressure on the tissue of the bone. This pressure stimulates bone-forming cells to create and mineralize new bone through the process of remodeling. As new bone tissue forms along the affected bone, it eventually calcifies, surrounding the bone-forming cell, also known as an osteoblast. Once enclosed in the bone tissue, these cells change from bone-forming cells to actual bone cells, becoming part of the matrix and repairing the damage.
Though a growth stimulator can theoretically aid in healing any fractured or damaged bone, they're more commonly used to mend or repair certain areas of the body more than others. Vertebrae fused within the spine are probably the most common, but you may also see stimulators employed to support or accelerate recovery from fractures in the hand or lower leg. They may also be used on bones of the feet, upper leg, arm, shoulder and even pelvis.
Stimulators come in two basic forms: internal and external. With internal stimulators, the device is usually implanted during the surgical procedure that's being used to correct the bone issue at hand. Electrodes are fastened near the bone (or bones) and connected to the battery pack responsible for the impulses. Both the electrodes and battery pack are placed under the skin, and set to release intermittent impulses.
With external stimulators, you're fitted with a device that is worn outside the body. It could be a corset or splint-like device that contain the electrodes and battery pack or free standing electrodes that you manually attach to the affected area. And much like the internal stimulator, electrical impulses or ultrasounds are delivered to the bone to stimulate new growth.
The reason one device is chosen over the other really comes down to a number of factors, including your age, health, medical history and bones affected by the damage, so there aren't necessarily any hard and fast rules. You and your doctor will discuss the options, and together you'll decide on the best option.