The primary indication for electric- or electromagneticinduced bone stimulation is delayed union or nonunion following fracture, osteotomy, attempted arthrodesis, or infection. Electrical stimulation has been used as the primary modality for treatment in up to 40% of patients with nonunions (42). The use of electric or electromagnetic stimulation on bone may, and should usually, be used as a secondary modality in combination with other measures to enhance healing, including cast or brace immobilization, internal or external fixation, bone grafting, and débridement and concurrent management of infection in bone or soft tissue.

No universal agreement exists as to the precise definition of a nonunion. A general understanding is a situation in which bone has failed to heal and all outward clinical and radiographic evidence of reparative processes has ceased. Previously, the U.S. Food and Drug Administration (FDA) defined a nonunion as being established when a minimum of 9 months had elapsed since injury and the fracture site showed no visibly progressive signs of healing for a minimum of 3 months. After this original definition was released, many clinicians argued that the 9-month time period represented an arbitrary cutoff point that did not reflect the complicated variables present in many fractures, for example, degree of soft tissue damage, alignment of the bone fragments, vascularity, and quality of the underlying bone stock. Other proposed definitions evolved defining a nonunion as being present when the fracture was 3 to 6 months from original healing or simply when serial x-rays fail to show any further healing. Later, the FDA broadened its definition, stating a nonunion is considered to be established when the fracture site shows no visible, progressive signs of healing. Certainly, a clinician’s judgment plays a role in this determination as well. In severe trauma with extensive soft tissue, vascular, and neural injury, there is a higher prevalence of nonunion or delayed union. In these cases, patients should be followed closely with a high level of suspicion for the development of a nonunion (43). Delayed union generally refers to a decelerating of the bone healing process, as identified on serial radiographs. (In contrast, serial radiographs of a nonunion show no evidence of healing.) When lumped together, delayed union and nonunion are sometimes referred to as “ununited fractures.”

The precise differentiation of a delayed union from nonunion may be even more difficult to define clinically and radiographically. Asymptomatic cartilaginous or even fibrous union may occur within a bone that demonstrates the radiographic characteristics of nonunion. Under these circumstances, a reduction in pain or other signs and symptoms that are extraosseous in nature may be used to determine the presence of a radiographically occult union.

Many clinicians have advocated the use of electrical stimulation of bone “as soon as tardy union of bone is identified” (11). Their argument is that the early institution of electrical stimulation of a delayed union will reduce the disability time, as well as the incidence of nonunion (30,44).

A benchmark study of PEMF stimulation in humans was first performed on congenital or acquired pseudarthroses that were previously resistant to surgical treatment. PEMF therapy was used as a last attempt at salvage prior to amputation. The success rate was 73% and 76%, respectively (45). Patients who had failed multiple surgeries healed their acquired pseudarthroses with adjunctive PEMF treatment and long-term assessment showed that the union achieved remained intact. In the less fortunate cases of congenital pseudarthroses, patients would heal with PEMF stimulation but refractured elsewhere (27,46).

A study comparing treatment of tibial nonunions with capacitive coupling, DC, and bone grafting all showed similar rates of healing when there were no other risk factors involved (i.e., duration, atrophic nonunion, comminuted fracture, infection) (33). Bone growth stimulation may be a reasonable option prior to returning to the operating room to surgically repair the nonunion.

Ultrasound has also been successful in the treatment of nonunions, with success rates of ranging from 85% to 100% in multiple, smaller studies. In long-term follow-up, the healed areas remained intact. Not only was time to union significantly shorter in the studies, there was also better maintenance of fracture reduction (12,13,47).

Electrical stimulation may augment the normal incorporation of bone grafts (48), and a synergistic effect of bone grafting and electrical stimulation has been reported (49,50 and 51). Bone grafting, in combination with electrical stimulation, is typically employed if malunion or osseous defects exist, inasmuch as electrical stimulation will not correct osseous malalignment or loss of bone substance (Fig. 89.2).

Bone grafts that may be augmented with electrical bone stimulation include autografts, allografts, and many of the bone substitute grafts that include porous hydroxyapatite.

Electrical stimulation has been used with success for the management of infected nonunions (3,52). Appropriate stabilization, as well as appropriate efforts to eradicate the microorganisms, must be concurrently employed as necessary. Three problems exist that need to be addressed in managing an infected delayed union or nonunion, and these include the infection itself, the osseous instability, and the hindrance of osteogenesis. Management of the infection and the creation of osseous stability, along with the use of a bone stimulator for enhanced osteogenesis, create a more optimized environment for healing an infected nonunion.

In addition to the augmentation of osteogenesis, electrical stimulation may accelerate the resolution of infection by other means. Electrical stimulation has been noted to result in reduction, change in character, and resolution of drainage at the site of an infected nonunion (11). Bone grafting combined with electrical stimulation has been demonstrated to successfully resolve the signs and symptoms associated with infected nonunions (49,53,54). If an infection is present or suspected, a noninvasive PEMF or CMF device may be preferable to an implantable one. Use of PEMF therapy has been shown to increase lymphocytic response in vitro and in vivo, regulating inflammatory response (55,56,57 and 58).

A recent prospective study utilizing PEMF stimulation in a patient population that included primary and revisional arthrodesis, showed an increased rate of radiographic union (59). Whether or not a bone stimulator is indicated in a primary fusion remains debatable, but in all subgroups studied, the time to radiographic union was significantly decreased.

Patients who have reduced healing potential, such as those in an immunocompromised state due to comorbidities and/or steroid usage, and those with impaired vascularity due to peripheral vascular disease or tobacco use, could benefit from an adjunctive device. Nicotine abuse has been shown to cause a decreased rate of bone healing, in addition to complications during healing. In assessing the healing of distal radial and tibial fractures in nonsmoking and smoking patients who either used a low-intensity, pulsed ultrasonic device or a placebo device, there were no statistical differences found in healing time between smokers and nonsmokers who used the active ultrasound device (60).

Arthrodesis procedures are common salvage procedures used in Charcot deformity, arthritic conditions, and failed nonarthrodesis surgeries. Unfortunately, many of the patients undergoing arthrodesis are high-risk patients with past medical histories that prove a challenge for bone fusion. Some conditions include diabetes mellitus, rheumatoid arthritis or connective tissue disorders, peripheral vascular disease, obesity, smoking, immunosuppressive therapy, and alcoholism. In these instances, it may be beneficial to primarily use an implantable bone stimulator during the initial arthrodesis surgery (61).

Electrical stimulation may be used to resolve symptoms associated with failed arthrodesis procedures, with a reported success rate of approximately 85% (62,63). The most important aspect in the use of electrical stimulation for failed arthrodesis is to identify the delayed union or nonunion and to take appropriate steps to reinitiate the reparative process. If the arthrodesis site is failing, this must be identified in such a way as to classify it as a delayed union, partial union, or complete nonunion site. Identifying where any fibrocartilaginous nonunion has occurred is equally important since surgical reduction and revision may be necessary prior to using electrical bone stimulation. Electrical bone stimulation can be either a primary treatment or a secondary
adjunctive treatment for a failed arthrodesis of the foot or ankle. The delayed union or nonunion must be hypertrophic (i.e., not an atrophic nonunion), and capable of potential healing, for electrical bone stimulation to be considered alone. If the delayed union or nonunion is atrophic and/or not capable of healing (e.g., due to the gap distance present), then surgical treatment must be performed, and if desired, combined with invasive or noninvasive electrical bone growth stimulation (Fig. 89.3). In a small case series, using an implantable bone stimulator as an adjunct to rigid external fixation in revisional arthrodesis procedures led to fusion in all 10 patients studied. While the success of fusion cannot be attributed solely to the use of bone growth stimulation, the study also showed that no patients had complications or problems arising from the implantable stimulator (64).

Electrical stimulation has been reported as effective in the management of neuropathic (Charcot) joint disease associated with diabetes mellitus or alcoholic neuropathy (41,65,66,67 and 68). Traditionally, acute Charcot osteoarthropathy is treated with rigid immobilization and edema reduction measures. These modalities may potentially be enhanced with the use of bone growth stimulation and used as an adjunct in this way; bone growth stimulation may result in a more expedient reduction of joint inflammation and edema and earlier foot stability (69). Hanft et al (66) performed a study with patients using CMF stimulation in patients with acute Charcot arthropathy, and consolidation occurred 12.8 weeks sooner in the group receiving bone growth stimulation than in the control group.

Charcot joint disease is characterized by progressive bone resorption and increased osteoclastic activity, with both processes reduced by electrical stimulation of bone because of a decrease in the cellular response to parathyroid hormone (70). In addition, improvement in ulcer healing rates and sensation related to electrical field-triggered alterations in neural regeneration and axon transport rates have been reported (71,72 and 73).

Low-intensity ultrasound has also been proposed as an adjunctive treatment for patients with acute Charcot osteoarthropathy based on its positive supportive role in healing a limited number of reported cases (74).

A variety of osteonecroses may affect the foot and ankle, including posttraumatic or nontraumatic avascular necrosis of the talus, second metatarsal head (Freiberg disease), navicular (Köhler disease), or dysvascular change after any fracture or osteotomy. Electrical stimulation of bone has been shown to increase angiogenesis while promoting osteogenesis. In addition, electrical bone growth stimulation diminishes the osteoclastic resorption of bone associated with osteonecrosis, which is responsible for the bone collapse and fragmentation.

Electrical stimulation has been shown to be an effective, conservative alternative to arthroplasty for the management of avascular necrosis of the hip. A significantly higher percentage of success was found in patients treated with PEMF stimulation rather than surgical decompression. PEMF therapy, by decreasing bone resorption and therefore maintaining bone mass, was more successful in preventing collapse of the femoral head and preventing further progression of the condition (75,76,77,78 and 79). Its use may be helpful following distal first metatarsal surgery with suspected avascular necrosis of the capital fragment, thus potentially avoiding the development of overt collapse and deformity, at which point resection arthroplasty or arthrodesis may be necessary.