Features April 2006 Issue

Bone Fracture: Heal Thyself

Electronic stimulators help mend broken bones, but they’re not for everyone.

Bones break. It’s how they heal that’s important. Even when a bone has begun to mend, healing may stop prematurely and won’t continue without medical intervention. Studies indicate that as many as five to 10 percent of fractures will not heal properly.

Patients who may be at risk of delayed healing following a bone break can take advantage of a new technology called bone-growth stimulation.

“This technology is effective, it helps lead to greater chances of success with bone healing—especially with difficult cases—and it can help a patient get back to an active lifestyle faster and more predictably,” says Brian Donley, M.D., vice-chairman of the Department of Orthopaedic Surgery at The Cleveland Clinic.

The healing process  
Fractured bones heal in stages. In the days after fracture, the inflammatory process begins to move debris away from the fracture site. A collection of blood—a hematoma—forms. Next, tissue begins to fill the space between the bone fragments. Osteoblasts—cells that secrete protein which forms new bone—make their way to the fracture site, where they absorb the hematoma. As the hematoma is absorbed, collagen begins to form around the site, and a callus develops over the fracture on the outside and inside of the bone. Eventually, this process creates cartilage and more bone. 

Bone growth requires the stimulation of cells. Normally, cells are stimulated through natural biomechanical processes at the cellular level. But in some people, when bone growth stops prematurely these cells need a boost. Enter bone-growth stimulators, which create changes at the cellular level as the bone heals. By delivering an electrical impulse to the site of the injury, a bone stimulator causes cells to produce more bone, either for patients with bone fractures or for those who need to undergo spinal fusion in their vertebrae. Research has shown that electrical charges activate bone-forming osteoblasts in areas of bone growth.

Currently, five types of bone-growth stimulators exist. One delivers acoustic signals, through ultrasound; four use low-dose electrical and electromagnetic signals.

Easy healing. Bone-growth stimulators, such as the DonJoy OL1000, use electric “pulsing” to stimulate cell growth and mend fractured bones.

The first bone stimulators, developed in the 1960s, were surgically implanted devices. While this invasive technology still exists, it is less common than other methods because it requires surgical removal later. Doctors place today’s more popular bone stimulators externally over the fracture site, with the majority delivering electrical and electromagnetic pulses. They can also be used over a cast. Bone stimulators that use ultrasound, such as the Exogen 2000, weaken as they travel through tissue, do not penetrate as deeply as those using electrical and electromagnetic signals, and cannot penetrate metal. They must be applied directly on top of the fracture site or, if the patient is in a cast, to the fracture site through a hole drilled into the cast. Because ultrasound-based bone stimulators also do not penetrate muscle and fat as well as electrical stimulators do, they are more effective for fractures close to the skin.

Different approaches
Within the class of electric bone stimulators, there are also differences in how the electrical impulses travel.

Electromagnetic energy travels in waves, and devices using pulsed electromagnetic fields—the Orthofix Physio-Stim and the EBI BHS—feature a control which produces waveforms and monitors the patient’s use. Both devices create a magnetic field within the device, and the stimulator sends random pulses of electromagnetic energy. Similar to the way physical therapists often urge patients to alternate between heat and ice for treating an injury, these “pulsing” devices serve to train and rest the cells healing the bone, thereby stimulating growth. 

Bone stimulators such as the DonJoy OL1000 employ combined magnetic fields, using direct and alternating current (DC and AC) to produce static and alternating magnetic fields. Other electrical stimulators include the Biolectron Orthopak and the EBI OsteoGen.   The Orthopak uses electrodes that remain on the skin all day in order to deliver sinusoidal electrical impulses. The OsteoGen relies on surgically implanted electrodes to deliver DC electrical current to the site; it may be surgically removed once the fracture has healed.

While studies show that the effects of all bone-growth stimulators are universal—every bone stimulator works to some degree—doctors usually have a preference. This may be based on cost and the amount of time required for treatment each day. Exogen’s ultrasound device is used for the shortest amount of time—20 minutes a day—while DonJoy’s stimulator is typically used for 30 minutes each day. Treatments with the two units using pulsed electromagnetic fields—the Orthofix and EBI BHS—last for three hours and 10 hours, respectively. Treatments with the Bioelectron Orthopak and EBI’s implanted device continue for 24 hours a day. Recommended wearing times are based on the manufacturers’ effectiveness studies, and each device is approved by the Food and Drug Administration (FDA) with those timeframes in mind. Patients will typically use any of these devices for three months, or until their doctor sees that their fracture or fusion is healed.

Low risk, high price
According to Dr. Donley, there are no risks or disadvantages, other than cost, associated with the use of a bone-growth stimulator. “There are no significant side effects,” he says. Often, he says, the patient is unaware that the stimulator is turned on.

Cost is a factor, which means these devices aren’t for everyone. In general, bone stimulators, available only by prescription, cost between $2,500 and $4,950. They are normally covered by health-care insurers, but you must obtain pre-approval from your provider before purchase. While Dr. Donley says that just about every patient with a fracture or spinal fusion would benefit from the use of bone stimulators—they are typically used for tibia, wrist, foot, and stress fractures—based on their prohibitive price, not every patient is a candidate. Instead, bone-growth stimulators are typically used only for patients considered at high risk for not healing. Patients in those groups typically include diabetics, smokers, and people with a history of fractures that don’t heal properly. 

Bottom line: All bone-growth stimulators have been proven to be effective by the FDA, and all have demonstrated significant clinical success. It all comes down to patient compliance, and the trend to increasingly shorter treatment times with these devices may be the path to greater compliance.