Low-Intensity Pulsed Ultrasound, or LIPUS, is a non-invasive medical technology utilized to encourage the body’s natural healing processes, particularly for bone injuries. This therapy involves applying low-intensity sound waves to a specific area of the body to stimulate tissue repair. Its primary application lies in accelerating bone formation and aiding in the mending of fractures.
The Mechanism of LIPUS
LIPUS operates using ultrasonic energy at a much lower intensity than diagnostic ultrasound, which is typically used for imaging. These mechanical sound waves create subtle micro-stresses at the cellular level within the treated tissue. This gentle mechanical stimulation is then converted into biochemical signals through a process called mechanotransduction.
This conversion triggers a cascade of biological responses within the cells. LIPUS stimulates undifferentiated mesenchymal stem cells to differentiate into osteoblasts, which are the cells responsible for forming new bone. The treatment also increases the expression of certain growth factors and proteins, such as bone morphogenetic protein-2 (BMP-2), osteocalcin, alkaline phosphatase, and Vascular Endothelial Growth Factor (VEGF). These are all essential for bone repair and the formation of new blood vessels (angiogenesis). This enhanced cellular activity promotes increased mineralization and calcium deposition, leading to accelerated bone formation and improved callus quality.
Conditions Treated with LIPUS
LIPUS therapy finds its primary clinical application in the treatment of bone fractures, especially those facing healing complications. It is used for both fresh fractures and, more commonly, for situations where bone healing is impaired. The therapy aims to accelerate the natural repair process.
The treatment is particularly considered for delayed unions, where a fracture is healing slower than anticipated, and for nonunions. A nonunion fracture is defined as a permanent failure of bone healing, meaning the bone will not mend without further intervention. The U.S. Food and Drug Administration (FDA) typically defines a nonunion as a fracture that is at least nine months old and has shown no visible signs of radiographic healing in the last three months. While some studies also show benefit for fresh fractures, LIPUS is most often applied when healing has stalled or is significantly behind schedule.
The Patient Treatment Process
Undergoing LIPUS therapy typically involves a straightforward, at-home routine using a portable device. The equipment usually consists of a small, handheld unit with a transducer head that delivers the ultrasound waves. Patients are instructed on how to properly use the device for daily self-administration.
To begin treatment, a coupling gel is applied to the skin directly over the fracture site. This gel helps ensure optimal contact between the transducer and the skin, allowing ultrasound waves to effectively penetrate the tissue and reach the bone. The transducer head is then placed directly on the gel-covered skin.
Patients typically apply the device for a prescribed duration, often around 20 minutes per day. The overall course of therapy can vary, but it often lasts for several months, depending on the specific fracture and individual healing progress. This consistent daily application is important for stimulating the continuous biological responses needed for bone repair.
Evaluating LIPUS as a Treatment Option
Clinical evidence supports LIPUS for nonunion fractures, offering a non-invasive alternative to surgery. Pooled data from studies on nonunions treated with LIPUS indicate an estimated healing rate of 82% to 87%. For fractures defined as nonunion for at least eight months, the success rate is around 84%. This rate is comparable to surgical outcomes for non-infected nonunions.
LIPUS is considered a safe treatment with a minimal side effect profile. Adverse effects are rare, limited to minor skin irritation from the coupling gel, which resolves upon temporary cessation of treatment. No significant device-related adverse events have been found in studies.
However, there are specific situations where LIPUS should not be used. Contraindications include application over cancerous tumors, near open growth plates in children, or in proximity to the skull or eyes. A large bone gap of 10 mm or more between fracture fragments may reduce the likelihood of successful outcomes.