Reviews & Clinical Evidence

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A systematic review and meta-analysis (Busse et al 2002) has carefully considered the evidence in respect to the effect of low intensity pulsed ultrasound on the time to fracture healing. They conclude that the evidence from randomised trials where the data could be pooled (3 studies, 158 fractures) that the time to fracture healing was significantly reduced in the ultrasound treated groups than in the control groups and the mean difference in healing time was 64 days.

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Warden et al (1999) published a review paper concluded that from animal and human studies, the use of ultrasound could accelerate the rate of fracture repair by a factor of 1.6. The unit utilised for this work (Sonic Accelerated Fracture Healing System – SAFHS) delivers a low intensity (0.03 W cm-2) at 1.5MHz pulsed at a ratio of 1:4. Whilst this dose may be reproducible by standard therapeutic machines, the SAFHS device has a particularly low BNR and thus is considered to be safe to apply with a stationary treatment head, unlike conventional physiotherapy ultrasound machines. This could be an important factor as treatment was for 20 minutes daily, with the patient using the device rather than attending for therapy.

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Heckman et al (1994) demonstrated a 38% reduction in the healing time for tibial fractures using the SAFHS device whilst Kristiansen et al (1997) demonstrated a 30% acceleration in healing for fractures of the radius. Jensen (1998) identifies the beneficial effects of ultrasound in the treatment (as opposed to the diagnosis) of stress fractures with an overall success rate of 96%. The report fails to identify all relevant data for consideration and must therefore be considered with some caution in terms of ‘quality evidence’.

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Mayr et al (2000) report a series of outcomes when using low intensity pulsed ultrasound for patients with delayed unions (n=951) and non unions (n=366). The overall success rate for the delayed unions was 91% for the delayed and 86% for the non unions.

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The authors undertook an interesting stratified analysis of their patients, and identified that those who were using non steroidal anti inflammatory drugs, calcium channel blockers or steroids had a less favourable outcome, a finding that could be considered to be consistent with several research publications that have tried to identify the mechanism by which the ultrasound could bring about fracture healing acceleration and other wider research concerning the adverse influence of NSAID’s on tissue repair (e.g. Tsai et al 2004, Evans & Butcher2004).

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The use of such low doses has been shown to result in non significant increases in tissue temperature. Using higher ultrasound doses could have an adverse effect on the fracture healing process and the low intensity pulsed system is considered to be effective and safe for this patient group. Reher et al (1997) demonstrated a stimulative effect at low dose (0.1 W cm-2) whilst an inhibitory effect at a higher dose (1 – 2 W cm-2). Chang et al (2002) demonstrated that the effect of low intensity pulsed ultrasound in these circumstances was achieved by non thermal mechanisms rather than as a phenomenon secondary to thermal effects.

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The mechanisms by which therapeutic ultrasound can be effective for fracture repair includes nitric oxide (NO) pathways and prostaglandin (PGE2) (Reher et al 2002, Warden et al 2001, Kobubu et al 1999). This too would be consistent with other proposed mechanisms of ultrasound action (ter Haar 1999) and the relationship between the use of NSAID’s and tissue repair following injury.

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Both Tis et al (2002) and Sakurakichi et al (2004) have evaluated the use of ultrasound as a component of treatment (in an animal model) during distraction osteogenesis, and both have demonstrated significant benefits. Cook et al (2001) have demonstrated similar benefits following spinal fusion surgery and Tanzer et al (2001) have shown that the use of ultrasound in combination with porous intramedullary implants is also beneficial. There are many other studies concerning the use of US and bone repair, but essentially the published work shows a consistent benefit, and the use of low intensity pulsed ultrasound for patients with bone related disorders, including normally healing fractures, stress fractures, delayed and non unions and as a post surgical intervention should be considered positively.

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One study (Schortinghuis et al 2004) that employed the SAFHS ultrasound system yet failed to demonstrate a significant effect (following deliberate bone injury – rat model) is probably related to the additional inclusion of a PTFE membrane – a GoreTex® like material). This would almost certainly not enable adequate ultrasound energy transmission due to the porous nature of the material, and the consequent air trapping, leading to ultrasound energy reflection.

The SAFHS system is not the only ultrasound device employed for the clinical management of fractures, and a recent paper (Lerner et al 2004) describes the use of an alternative (Exogen) system with 17 ‘case studies’. The Exogen device is additionally described in several other review papers.

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The Warden et al (1999) paper provides a useful review for therapists wishing to update their knowledge in the area and who want to go beyond the material on these pages.

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