Bone Healing with the Use of Ultrasound
Bone Healing using ultrasound can significantly accelerate bone repair.
Bone fractures or ‘breaks’ are one of the most common bone ailments. The number of fractures treated every year is steadily increasing. For the most part, treating bone fractures is a simple procedure involving setting and aligning the broken bones, and immobilizing the area with a cast. Over time, the fracture gap is bridged with bone. A majority of fractures respond well to this procedure.
However, in several cases, the broken bones do not heal properly (achieve ‘union’) or take unacceptably long times to heal. In the US itself, 5–10 % of all fractures fail to heal or have delayed healing.Moreover, patients with open fractures, smokers, diabetics, end-stage renal disease patients have compromised fracture healing ability.
In such cases, the use of ultrasound therapy has been found to be of use in healing the bones, by stimulating the body’s natural healing process. Scientists report that the use of Low Intensity Pulsed Ultrasound (LIPUS) has definite benefits in accelerating fracture healing. The ultrasound waves are administered through a small device or probe that is worn on the skin over the fracture. The treatment lasts for about 20 minutes per day, over a period of 20 days.
Low intensity ultrasound therapy has already been approved by the US FDA for clinical use. There is one commercial device (EXOGEN®, GmbH) which is being used for treatment of fresh fractures. The use of this device increased the fracture healing rates by up to 38% for fresh fractures, and up to 86% for fractures that were slow in achieving union. This treatment is not recommended for fractures of the skull and vertebrae.
Bone Healing using Ultrasound therapy
High frequency, high intensity ultrasound has also been used for medical applications, and mostly causes a thermal effect, due to heating of tissues. It is important to note that the beneficial effects in bone healing are observed only with low intensity, low frequency ultrasound. In fact, there is some literature evidence that high intensities of ultrasound can actually damage bones and/or delay fracture healing.
On the other hand, low frequency/low intensity ultrasound has been shown to produce the opposite effect. The mode of action of low intensity ultrasound is mostly through mechanical action, and not through thermal effect on the tissues. Low intensity ultrasound has a frequency of 20- 120 kHz and power of 0.05-1.0 W/cm2. This low frequency/low intensity ultrasound vibration is mostly attenuated in the skin surface. Only a small portion of the ultrasound energy transmitted reaches deeper tissue layers, which is why the major effect is mechanical.
How Bone Healing using Ultrsound Works
Ultrasound energy is known to cause cellular and enzymatic changes in the body. While more in-depth research is required to identify the exact mechanism of bone repair through ultrasound, literature evidence on the effects of ultrasound indicate that the following processes are likely involved in the bone repair process:
- Stimulation of calcium turnover and ossification
- Improvement in Prostaglandin production
- Up-regulation of COX-2
- Gene regulation
- Chondrocyte and osteocyte differentiation processes
The above effects of ultrasound are likely involved in tandem to accelerate the healing process. Bone healing involves a fairly complex network of cellular processes, so the effect of ultrasound on any one or more of these processes is likely to affect the other.
The timing of the ultrasound treatment also plays a role in the acceleration of the fracture healing. Scientists report that when fractured rat fibulae are exposed to ultrasound during the early proliferative stages of bone repair soon after the fracture occurred, direct ossification was observed and healing was accelerated. On the other hand, if the ultrasound procedure was delayed until the late proliferative phase, cartilage growth was stimulated. This indicates that the sooner the ultrasound therapy is administered following the bone fracture, faster will be the healing.
Ultrasound treatment of bone fractures clearly has a lot of potential, especially for patients whose bone healing abilities are lower (elderly patients, diabetics, etc.). However, more investigation and clinical trials are required, leading to a better understanding of this treatment process.