Bone stimulation devices — designed to accelerate fracture healing through electromagnetic or ultrasonic energy — are commonly prescribed in foot and ankle surgery for fractures at risk of delayed healing, established delayed unions, and nonunions. Despite decades of use, their evidence base is more nuanced than manufacturer marketing suggests. This guide provides an accurate summary of what bone stimulators can and cannot do.

How Bone Stimulators Work

Two primary technologies are used:

• Pulsed electromagnetic field (PEMF) stimulation: Generates time-varying electromagnetic fields around the fracture site using coils placed over the skin. The electromagnetic fields are thought to stimulate osteoblast activity, growth factor expression, and angiogenesis at the fracture site by activating mechanotransduction pathways. Devices are worn for specified periods (typically 3–10 hours per day) over external coils.
• Low-intensity pulsed ultrasound (LIPUS): Delivers low-intensity ultrasonic waves (1.5 MHz, 30 mW/cm²) through a transducer applied directly to skin overlying the fracture. LIPUS activates integrin signaling pathways and promotes angiogenesis and chondrogenesis at the fracture callus. Typically used 20 minutes per day. The Exogen device (Smith & Nephew) is the most widely prescribed LIPUS device in the United States.

What the Evidence Shows

The evidence base is stronger for some applications than others:

• Established nonunion (fractures not healed at 6+ months): PEMF and LIPUS both have reasonable evidence for improving nonunion healing rates. A Cochrane review found PEMF increased the probability of nonunion healing, though study quality was variable. Healing rates of 70–80% for established nonunions treated with bone stimulation have been reported in multiple series.
• High-risk stress fractures: The navicular and fifth metatarsal (Jones fracture zone) are considered “high-risk” stress fractures with notoriously poor healing due to tenuous blood supply. LIPUS is commonly prescribed as an adjunct for these fractures, with some evidence suggesting reduced healing time and lower nonunion rate. A prospective trial by Josza et al. found significantly faster navicular stress fracture healing with LIPUS versus conservative management alone.
• Routine stress fractures and fresh fractures: Evidence is considerably weaker for routine fractures with normal healing prognosis. Several high-quality trials have failed to demonstrate meaningful reduction in healing time for fresh metatarsal fractures or low-risk stress fractures compared to standard management.

When Bone Stimulators Are Appropriately Prescribed

Appropriate indications for bone stimulation in the foot and ankle:

• Delayed union (fracture not progressing toward healing at expected rate) at 3–4 months post-injury
• Established nonunion (fracture not healed at 6 months)
• High-risk stress fractures (tarsal navicular, zone II fifth metatarsal Jones fracture) as adjunctive therapy
• Post-surgical fusion with slow radiographic progression (tibiotalar, subtalar, or first MTP arthrodesis)
• Patient with risk factors for impaired healing: smoker, osteoporosis, diabetic, high training volume

Insurance coverage typically requires documentation of delayed or non-union status before approving bone stimulators. Coverage for prophylactic use in fresh fractures is limited.

Limitations and Practical Considerations

Bone stimulators are adjuncts to — not replacements for — appropriate fracture management. Continued weight-bearing on a nonunion reduces bone stimulator efficacy. Patient compliance with daily device use is the most significant practical limitation. For PEMF devices, the electromagnetic coils must be positioned accurately over the fracture; for LIPUS, the transducer must be applied through a coupling gel directly over the fracture site.