Key messages

• Pulsed ultrasound could lead to a small decrease in pain in osteoarthritis, but the certainty of the evidence is low.
• It is not clear if the use of pulsed ultrasound produces an improvement in functionality in patients with osteoarthritis, because the certainty of the evi-dence is very low.

What is the evidence.
See evidence matrix  in Epistemonikos later

We found six systematic reviews [1],[2],[3],[4],[5],[6] including eight studies overall, corresponding to randomized controlled trials [7],[8],[9],[10],[11],[12],[13],[14].

What types of patients were included*

All of the trials focused on osteoarthritis of the knee.

Average body mass index (BMI) ranged between 28.75 and 32.2 in four trials [7],[8],[11],[14] and four did not report it [9],[10],[12],[13]. Average age of the participants ranged between 57 and 65 years in the different trials. 

The proportion of women was between 33 and 100% in the different trials.

What types of interventions were included*

All of the trials used pulsed ultrasound.

One trial used ultrasound with a frequency of 1 MHz and potency of 1.5 W/cm2 in sessions of twelve minutes each, for two weeks (10 sessions in total) [7].

One trial used ultrasound with a frequency of 1 MHz and potency of 1.5 W/cm2 in sessions of fifteen minutes each, for eight weeks (24 sessions in total) [9].

One trial used ultrasound with a frequency of 1 MHz and potency of 2.5 W/cm2 in sessions of fifteen minutes each, three times a week for eight weeks (24 sessions in total) [10].

One trial used ultrasound with a frequency of 1 MHz and potency of 0.2 W/cm2 in sessions of nine and a half minutes each, for eight weeks (24 sessions in total) [11].

One trial used ultrasound with a frequency of 2.5 MHz in sessions of fifteen minutes each, for eight weeks (24 sessions in total) [13].

One trial used ultrasound with a frequency of 1 MHz and potency of 2 W/cm2 in sessions of five minutes each, for two weeks (10 sessions in total) [14].

Two trials did not describe the frequency or the power of the pulsed ultrasound, or the amount of sessions or the duration of them [8],[12].

Two trials associated isokinetic exercises to the pulsed ultrasound [9],[10]. 

Four trials compared against placebo or standard therapy [10],[11],[12],[13]. 

Four trials compared against placebo and against continued wave ultrasound [7],[8],[9],[14].

What types of outcomes
were measured

The outcomes, as classified in the identified systematic reviews, were as follows: effect on the intensity of pain (analyzed as a decrease or improvement) according to visual analogue scale; knee osteoarthritis severity index established by Lequesne; and sub-scale of physical functionality established by the Western Ontario and McMaster Universities Arthritis Index (WOMAC).

The average follow-up of the trials was 16 weeks with a range between 2 and 52 weeks.

To whom this evidence does and does not apply

• While the intention of this summary was to include osteoarthritis in general, considering all of the possible affected joints, the trials that were found focused specifically on osteoarthritis of the knee.
• In absence of direct evidence for other joints, we believe that extrapolating the conclusions of this summary could lead to error since the effect of ultrasound depends on the target tissue, and there are other joints deeper(surrounded by more soft tissue) such as hip and shoulder, in which we could assumed a lower intensity of ultrasound and therefore a lesser effect.
• It is important to emphasize that different primary studies evaluating pulsatile ultrasound used different frequencies and intensities, with different application times and total treatment duration. It is not possible with the existing data to make judgments about the effectiveness of some specific type of pulsatile wave ultrasound.

• The outcomes included in this summary are those considered critical for decision-making by the authors of this summary. Furthermore, we conducted a search of the Core Outcome Measures in Effectiveness Trials (COMET) Initiative, finding one relevant article [15] that indicated, through a consensus, the following as the most relevant outcomes: joint pain, functionality, quality of life in relation to health, work situation, mortality, reoperation, hospital readmission, and overall satisfaction with the results of the treatment.

• Although the observed effect over pain is statistically significant, the magnitude of the effect was below the minimally important difference reported in the literature [16]. In the case of functionality by Lequesne index, according to the literature [17] the difference presented in the meta-analysis would be clinically significant, but the certainty of the evidence is very low.
• In terms of safety, adverse effects have not been described in any of the trials included in this summary, therefore we expanded the search to ultrasound in general. One study described the intention of monitoring the incidence of adverse events associated to the use of continued wave ultrasound and reported absence of major complications [18]. Another study reported absence of adverse events during and after the application of continued wave ultrasound [19].

• Although pulsed ultrasound is a widely available therapy and at a cost generally accessible to the majority of the population, it implies a significant amount of time to attend the multiple sessions that are needed.
• Considering the scarce benefit reported, even when the existing evidence shows no adverse effects, the balance between costs and benefits is not favorable.

• Faced with the evidence presented in this summary, most patients and clinicians should lean against the use of this intervention.
• However, without clearly effective therapeutic alternatives, variation could exist in the clinical decisions made by patients and individual clinicians. 

Differences between this summary and other sources

• The reviews included in this summary differ among each other. One review [1] concluded pulsed ultrasound would be better than placebo on pain reduction and functionality improvement, without associated adverse effects. Another review [2] reported pulsed ultrasound could be beneficial in decreasing pain, but it mentions treatment duration as a limitation because it must be defined patient by patient. Four reviews [3],[4],[5],[7] concluded ultrasound could be beneficial in decreasing pain and improving functionality in patients with knee osteoarthritis, but given that the available evidence has methodological limitations and is difficult to compare, new studies of better quality are required. Finally, another review [6] determines ultrasound is ineffective for decreasing pain in knee osteoarthritis because the evidence has low certainty or it is controversial.
• The conclusions of this summary agree with the main international guidelines for osteoarthritis: The Osteoarthritis Research Society International (OARSI) [20] indicates it is uncertain whether therapeutic ultrasound for the treatment of knee osteoarthritis is useful and it is not recommended for the treatment of knee osteoarthritis or multiple joints. The American Academy of Orthopedic Surgeons (AAOS) [21] concludes that given the inconsistency of the findings for multiple physical therapies, including therapeutic ultrasound, they cannot make a recommendation in favor or against its use in patients with symptomatic knee osteoarthritis.

• The probability that the conclusions of this summary change with future trials is high, due to the low and very low certainty of the existing evidence.
• We identify at least four ongoing trials [22],[23],[24],[25] in the International Clinical Trials Registry Platform of the World Health Organization, which could provide relevant information.
• New reviews, especially if they manage to obtain additional information from existing trials, could provide more reliable results. However, we did not identify ongoing reviews in the PROSPERO database.