Therapeutic ultrasound for chronic low‐back pain
Abstract
Background
Chronic non‐specific low‐back pain (LBP) has become one of the main causes of disability in the adult population around the world. Therapeutic ultrasound is frequently used by physiotherapists in the treatment of LBP and is one of the most widely used electro‐physical agents in clinical practice.
Objectives
The objective of this review is to determine the effectiveness of therapeutic ultrasound in the management of chronic non‐specific LBP.
Search methods
Electronic searches were performed using CENTRAL, MEDLINE, EMBASE, PEDro, and PsycLIT databases in October 2013. Reference lists of eligible studies and relevant systematic reviews were checked and forward citation searching was also performed.
Selection criteria
Randomised controlled trials on therapeutic ultrasound for non‐specific chronic LBP were included.
Data collection and analysis
Two review authors independently assessed the risk of bias of each trial and extracted the data. When sufficient clinical and statistical homogeneity existed, a meta‐analysis was performed. The quality of the evidence for each comparison was determined using the GRADE approach.
Main results
Seven small randomised controlled trials involving a total of 362 participants with chronic LBP were included. Two of the studies had a low risk of bias, meeting six or more of the 12 criteria used for assessing risk of bias. All studies were carried out in secondary care settings and most applied therapeutic ultrasound in addition to exercise therapy, at various intensities for six to 18 treatment sessions. There was moderate quality evidence that therapeutic ultrasound improves back‐specific function (standardised mean difference (SMD) [95%CI] ‐0.45 [‐0.84 to ‐0.05]) compared with placebo in the short term. There was low quality evidence that therapeutic ultrasound is no better than placebo for short‐term pain improvement (mean difference (MD) [95%CI] ‐7.12 [‐17.99 to 3.75]; zero to100‐point scale). There was low quality evidence that therapeutic ultrasound plus exercise is no better than exercise alone for short‐term pain improvement (MD [95%CI] ‐2.16 [‐4.66 to 0.34]; zero to 50‐point scale), or functional disability (MD [95%CI] ‐0.41 [‐3.14 to 2.32]; per cent). The studies comparing therapeutic ultrasound versus placebo or versus exercise alone did not report on overall satisfaction with treatment, or quality of life. There was low quality evidence that spinal manipulation reduces pain and functional disability more than ultrasound over the short to medium term. There is also very low quality evidence that there is no clear benefit on any outcome measure between electrical stimulation and therapeutic ultrasound; and that phonophoresis results in improved SF‐36 scores compared to therapeutic ultrasound. None of the included studies reported on adverse events related to the application of therapeutic ultrasound.
Authors' conclusions
No high quality evidence was found to support the use of ultrasound for improving pain or quality of life in patients with non‐specific chronic LBP. There is some evidence that therapeutic ultrasound has a small effect on improving low‐back function in the short term, but this benefit is unlikely to be clinically important. Evidence from comparisons between other treatments and therapeutic ultrasound for chronic LBP were indeterminate and generally of low quality. Since there are few high quality randomised trials and the available trials are very small, future large trials with valid methodology are likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
PICOs
Plain language summary
Therapeutic ultrasound for chronic low‐back pain
Ultrasound is a treatment that uses vibration to deliver heat and energy to parts of the lower back—including spinal muscles, ligaments, tendons and bones. Its goal is to reduce pain and speed healing. Chronic low back pain is low‐back pain that lasts longer than 12 weeks.
Review Question: Is ultrasound a safe and effective treatment for chronic low‐back pain?
We looked for randomised controlled trials (a type of study) that compared ultrasound with other treatments. All the people in these studies were adults (age 18 or over) with chronic “non‐specific back pain”. Chronic “Non‐specific back pain” is back pain with no known cause that lasts more than 12 weeks.
The comparison treatments included exercise, electrical treatments, spinal manipulation and “placebo treatments”. Placebo treatments are also called “dummy treatments”. They are treatments that have no real treatment effect, such as ultrasound with the ultrasound machine turned off.
The patients who received ultrasound in these studies typically had six to 18 sessions of ultrasound therapy.
We wanted to see if ultrasound helped with pain, quality of life, patient satisfaction, and the ability to perform normal activities of daily living, including work.
Background:
Chronic low‐back pain is a common cause of pain and problems carrying out normal activities for people around the world. Chronic back pain often causes people to seek medical care, change their lifestyles, and even miss work.
Therapeutic ultrasound is a widely used treatment for low‐back pain. When a patient has ultrasound therapy, a healthcare provider uses a hand‐held device to rub against the skin over the lower back. The device produces vibration that goes through the skin. The goal is to deliver heat and energy to body parts under the skin, to reduce pain and speed recovery. But it is not clear if ultrasound is a safe and effective treatment or not.
Study Characteristics
We looked for studies (randomised controlled trials) published through to October, 2013. We found seven small studies that included a total of 362 adult patients being treated for chronic low‐back pain. All patients in these studies had “non‐specific back pain”.
Most of the patients had mild to moderate back pain in terms of pain severity and ability to perform daily activities.
All the studies were performed in “secondary care settings”. In other words, the patients all had been assessed by a physician or other healthcare professional before being treated.
The studies in this review compared ultrasound with other treatments.
Most of the studies only provided short‐term follow‐up for the patients being treated. In other words, they followed the patients for only a few days or a few weeks. Ideally, studies of treatments for chronic back pain should follow patients for many months or years.
None of the studies reported being commercially funded.
Key Results
We did not find any convincing evidence that ultrasound is an effective treatment for low‐back pain. There was no high‐quality evidence that ultrasound improves pain or quality of life.
We did find some evidence that ultrasound may improve back‐related function—the ability of people to use their backs. But those effects were so small they may not make any difference to patients’ lives.
The studies in this review did not provide information on the safety of ultrasound treatment in terms of injuries or other harmful events related to ultrasound treatment.
Therefore, we cannot determine the effects of ultrasound on chronic back pain based on these studies.
Quality of the Evidence
The quality of the evidence on ultrasound leaves much to be desired. In this review, we found “moderate” quality evidence regarding back‐related function. The evidence on other outcomes was of “low” or “very low” quality. There is a great need for further research with larger and better studies.
Authors' conclusions
Summary of findings
| Therapeutic ultrasound for chronic low‐back pain | |||||
| Patient or population: Adults with chronic low‐back pain Settings: Secondary care Intervention: Therapeutic ultrasound Comparison: Sham (placebo) ultrasound | |||||
| Outcomes | Illustrative comparative risks* (95% CI) | No of Participants | Quality of the evidence | Comments | |
| Assumed risk | Corresponding risk | ||||
| Placebo | Therapeutic ultrasound | ||||
| Pain intensity Visual analogue scale (100‐point scale); post‐treatment | *The mean outcome for the most representative study (Ebadi 2012) is 30.7 (SD 13.1) | The mean pain intensity in the intervention groups was 7.12 points lower (17.99 lower to 3.75 higher) | 121 (3) | ⊕⊕⊝⊝ | No statistically significant difference |
| Back‐specific functional status Functional Rating Index or Oswestry Disability Questionnaire (higher scores mean worse function); post‐treatment | *The mean outcome for the most representative study (Ebadi 2012) is 31.1 (SD 13.4) | The mean back‐specific functional status in the intervention groups was 0.45 standard deviations lower (0.84 lower to 0.05 higher) | 100 (3) | ⊕⊕⊕⊝ | The magnitude of this difference is small to moderate. |
| Flexion ROM post‐treatment Modified Schober method (cm) or fingertip‐to‐floor method (cm); post‐treatment | *The mean outcome for the most representative study (Ebadi 2012) is 59.8 (SD 17.9) | The mean flexion ROM in the intervention groups was 0.18 standard deviations higher (0.62 lower to 0.98 higher) | 89 (3) | ⊕⊝⊝⊝ | No statistically significant difference |
| Extension ROM post‐treatment Modified Schober method (cm) or degrees; post‐treatment | *The mean outcome for the most representative study (Ebadi 2012) is 24.1 (SD 9.3) | The mean extension ROM in the intervention groups was 0.33 standard deviations lower (0.85 lower to 0.19 higher) | 58 (2) | ⊕⊕⊕⊝ | No statistically significant difference |
| *Of the included trials for this outcome, we chose the study that is a combination of the most representative study population and the lowest risk of bias (Ebadi 2012). This figure represents the mean outcome in the control group of this particular study. CI: Confidence interval; RR: Risk Ratio; SD: Standard Deviation; ROM: Range of Motion | |||||
| GRADE Working Group grades of evidence | |||||
| 1. Total number of events was < 300 2. I2 > 60% 3. Two of the three included trials were rated as having a high risk of bias | |||||
| Therapeutic ultrasound for chronic low‐back pain | |||||
| Patient or population: Adults with chronic low‐back pain Settings: Secondary care Intervention: Therapeutic ultrasound plus exercise Comparison: Exercise | |||||
| Outcomes | Illustrative comparative risks* (95% CI) | No of Participants | Quality of the evidence | Comments | |
| Assumed risk | Corresponding risk | ||||
| Exercise | Therapeutic ultrasound plus exercise | ||||
| Pain intensity Pain Disability Index (70‐point scale); post‐treatment | *The mean change for the most representative study (Durmus 2013) is 10.7 (SD 4.4) | The mean pain intensity in the intervention groups was 2.16 points lower (4.66 lower to 0.34 higher) | 79 (2) | ⊕⊕⊝⊝ | No statistically significant difference |
| Back‐specific functional status Oswestry Disability Questionnaire (percentage); post‐treatment | *The mean change for the most representative study (Durmus 2013) is 8.2 (SD 7.2) | The mean back‐specific functional status in the intervention groups was 0.41 percent lower (3.14 lower to 2.32 higher) | 79 (2) | ⊕⊕⊝⊝ | No statistically significant difference |
| Flexion ROM post‐treatment Lumbar Schober method (cm); post‐treatment | *The mean change for the most representative study (Durmus 2013) is 0.38 (SD 1.41) | The mean flexion ROM in the intervention groups was 0.02 cm higher (0.52 lower to 0.56 higher) | 79 (2) | ⊕⊕⊝⊝ | No statistically significant difference |
| Extension ROM post‐treatment | Not measured | Not measured | Not applicable | Not applicable | |
| *Of the included trials for this outcome, we chose the study that had the lowest risk of bias (Durmus 2013). This figure represents the mean change in the control group of this particular study. CI: Confidence interval; RR: Risk Ratio; SD: Standard Deviation; ROM: Range of Motion | |||||
| GRADE Working Group grades of evidence | |||||
| 1. Total number of events was < 300 2. Both included studies were rated as having a high risk of bias. | |||||
Background
Low‐back pain (LBP) is the most frequent self‐reported type of musculoskeletal pain. It is often recurrent and has important socioeconomic consequences. Estimates of the prevalence of LBP vary considerably between studies and reach 33% for point prevalence, 65% for one‐year prevalence, and 84% for lifetime prevalence. Chronic non‐specific LBP and its resulting disability have become an enormous health and socioeconomic problem (Walker 2000).
The main objectives of treatment for LBP are for the patient to return to their desired level of activity and participation and to prevent chronic complaints and recurrences (Bekkering 2003). The fact that there are many types of treatment for LBP, each of which has multiple subcategories, is testament that no single approach has been able to demonstrate its superiority (Haldeman 2008). Evidence shows that the effectiveness of some interventions is supported (e.g. exercise) (Hayden 2005) while other interventions are not effective for LBP (e.g. traction) (Gay 2001; Wegner 2013). This situation makes it very challenging for clinicians, policy makers, insurers, and patients to make decisions regarding which treatment is the most appropriate for chronic LBP.
The effectiveness of ultrasound for musculoskeletal problems remains controversial. Two systematic reviews on the effects of ultrasound therapy for different musculoskeletal disorders found that there are few studies on this topic and that there is a dearth of evidence regarding its usefulness in the treatment of shoulder disorders, degenerative rheumatic disorders, and myofascial pain (Robertson 2001; van der Windt 1999). The effectiveness of ultrasound for LBP is also still debated (Airaksinen 2006; Ebadi 2011; NICE 2009).
Description of the condition
LBP is defined as pain and discomfort in the lumbosacral region, below the last rib and above the gluteal crease. According to the recommended diagnostic triage, three types of LBP can be defined: 1) non specific LBP; 2) LBP with nerve root symptoms; and 3) LBP resulting from serious pathology (e.g. malignancy, fracture, ankylosing spondylitis). Non‐specific LBP, in which there is no recognised patho‐anatomical cause, is usually a benign, self‐limiting condition. Using the traditional classification system, LBP is also categorised according to its duration as acute (shorter than six weeks), sub‐acute (six to 12 weeks) and chronic (longer than 12 weeks) (Krismer 2007; Waddell 2004).
Description of the intervention
Therapeutic ultrasound is frequently used by physiotherapists in the treatment of LBP and is almost certainly the most widely used electro‐physical agent in current clinical practice (Blanger 2010). Ultrasound is also commonly used for musculoskeletal disorders by other health professionals such as osteopaths, chiropractors, and sports therapists.
The hypothesis is that therapeutic ultrasound delivers energy to deep tissue sites through ultrasonic waves, to produce increases in tissue temperature or non‐thermal physiologic changes (Allen 2006). Unlike ultrasound for medical imaging (which transmits ultrasonic waves and processes a returning echo to generate an image), therapeutic ultrasound is a one‐way energy delivery which uses a crystal sound head to transmit acoustic waves at 1 or 3 MHz and at amplitude densities between 0.1 watts/cm² and 3 watts/cm² (Allen 2006; Robertson 2006).
Therapeutic ultrasound can be delivered in two modes, continuous or pulsed. Continuous ultrasound involves the delivery of non‐stop ultrasonic waves throughout the treatment period; while in pulsed ultrasound the delivery of is intermittently interrupted (Robertson 2006). Traditionally, continuous ultrasound is used for its thermal effects. Pulsed ultrasound is thought to minimise the thermal effects, however, it is not possible to truly isolate the thermal and non‐thermal effects as both effects occur with ultrasound application (Robertson 2006).
How the intervention might work
Ultrasound refers to vibrations that are essentially the same as sound waves but of a higher frequency, beyond the range of human hearing. Therapeutic ultrasound is assumed to have thermal and mechanical effects on the target tissue that results in an increased local metabolism, circulation, extensibility of connective tissue, and tissue regeneration (Robertson 2006).
When acoustic energy is absorbed as it penetrates soft tissues, it causes molecules to vibrate under repeated cycles of compression waves and rarefaction waves. The higher the intensity of the ultrasonic beam and the more continuous the emission of acoustic waves, the more vigorous the molecular vibration or kinetic energy. The more vigorous the micro‐friction, the more frictional heat is generated in the tissue (Dyson 1976). Tissue heating is presumed to enhance tissue cell metabolism, which in turn is believed to promote soft‐tissue healing. Tissue heating is clearly of value in numerous clinical conditions, through mechanisms of pain relief and improving tissue flexibility, but the evidence does not fully support the use of ultrasound as an efficient thermal intervention (Watson 2008).
Historically, ultrasound has been widely employed for its thermal effects, but it has been argued more recently that the ‘non‐thermal’ effects of this energy form are more effective (Watson 2008). The physical mechanisms thought to be involved in producing these non‐thermal effects include cavitation and acoustic streaming (micro‐massage). Cavitation is triggered by the absorption of acoustic energy and begins when minute gas pockets that infiltrate most biological fluids develop into microscopic bubbles, thus causing cavities in these fluids and the surrounding soft tissues. Under the sustained influence of acoustic radiation, these microscopic bubbles expand and contract (pulsate or oscillate) at the same carrier frequency at which the acoustic waves are produced. Microstreaming is the minute flow of fluid in the vicinity of the pulsating bubbles and is triggered by stable cavitation. These two phenomena are proposed to cause increased cell permeability and affect the course of cell growth, which in turn can improve tissue healing (O'Brien 2007).
Why it is important to do this review
Despite the widespread use of ultrasound in the field of physiotherapy for LBP patients, there is still insufficient evidence of its effectiveness, appropriate intensity and dosage for LBP patients (Airaksinen 2006; Ebadi 2011; NICE 2009). This is the first systematic review to evaluate the effectiveness of therapeutic ultrasound for patients with chronic LBP.
Objectives
The objective of this review is to determine the effectiveness of therapeutic ultrasound in the management of chronic non‐specific low‐back pain (LBP). We compared ultrasound (either alone or in combination with another treatment) with placebo, no treatment, or other interventions for chronic LBP. A secondary objective was to determine the most effective dosage and intensity of therapeutic ultrasound for chronic LBP.
Methods
Criteria for considering studies for this review
Types of studies
Only randomised controlled trials (RCTs) that evaluated the use of therapeutic ultrasound as a treatment in patients with chronic LBP and that were published as full reports (i.e. not abstracts or conference proceedings) were considered for inclusion in this systematic review. Only studies with a follow‐up longer than one day were included.
Types of participants
Studies were included if they recruited adult patients with chronic non‐specific LBP. Studies of post‐operative patients and patients in whom a specific cause for their LBP had been determined (e.g. vertebral fracture, malignancy) were excluded.
Types of interventions
All RCTs that had compared ultrasound therapy (continuous or pulsed) with other interventions or placebo for chronic LBP were included. Studies were excluded if ultrasound was one part of a treatment package and for which it was not possible to determine the effectiveness of ultrasound alone. For example, we did not include a study that compared aerobic exercise + home exercise to hot pack + ultrasound + TENS (transcutaneous electrical nerve stimulation), but included a study comparing an exercise program with ultrasound to the same exercise program without ultrasound.
Types of outcome measures
Primary outcomes
Primary outcome measures were: symptoms (e.g. pain), overall improvement or satisfaction with treatment, back‐specific functional status (e.g. measured with the Roland Morris Questionnaire, Oswestry Disability Index), well‐being (e.g. quality of life measured with the SF‐36, SF‐12, EuroQol), and disability (e.g. ability to perform activities of daily living, return‐to‐work status, work absenteeism) (Furlan 2009). The timing of outcome measurements was reported as short term (closest to four weeks), intermediate term (closest to six months), and long term (closest to one year).
Secondary outcomes
Secondary outcome measures included lumbar range of motion, muscle strength and endurance.
Search methods for identification of studies
Electronic searches
To identify all relevant RCTs that met the inclusion criteria a search of CENTRAL (The Cochrane Library, October 2013), MEDLINE (1966 to October 2013), EMBASE (1988 to October 2013), PEDro (up to October 2013), and PsycLIT (1974 to October 2013) databases was performed, using the search strategy recommended by the Cochrane Back Review Group (Furlan 2009). A highly sensitive search strategy to retrieve controlled trials (Appendix 1) was used in conjunction with a specific search for low‐back pain and therapeutic ultrasound. Studies published in all languages were considered for inclusion.
Searching other resources
To supplement the electronic search strategy, reference lists from relevant publications and reviews were screened and Science Citation Index was used to perform citation tracking of the RCTs identified by the first step. Additionally, we contacted experts in the field of therapeutic ultrasound to identify other relevant articles which may have been missed by the electronic search.
Data collection and analysis
Selection of studies
Two review authors (SE & NH) screened the titles and abstracts of all retrieved studies to identify those meeting the inclusion criteria. The studies were selected independently and the results discussed to make the final selection. A final decision was made for each study after reading the full text of all potentially eligible articles. In cases of disagreement, a third review author (MvT) was consulted.
Data extraction and management
A standardised data extraction form was used to extract data from the included papers. Extracted data included study characteristics (e.g. country, recruitment modality, study funding, risk of bias), patient characteristics (e.g. number of participants, age, sex, severity of LBP), description of the experimental and control interventions, co‐interventions, duration of follow‐up, outcomes assessed, and results. The same two review authors who conducted the study selection independently extracted the data. All disagreements were discussed and a third review author was consulted if necessary.
Assessment of risk of bias in included studies
Two review authors (SE & NH) independently assessed the risks of bias in each included study using the updated Cochrane Back Review Group criteria which are shown in Appendix 2 and are based on the criteria in the updated Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). In cases of disagreement, a third review author (MvT) was consulted. Attempts were made to obtain additional information from authors of the studies regarding any items that remained unclear. Studies meeting at least six of the 12 criteria and having no serious flaws were considered to have a "low" risk of bias (Furlan 2009).
Measures of treatment effect
Continuous outcomes were analysed by calculating the mean difference (MD) with 95% confidence intervals (CI) when studies used the same outcome measure, or the standardised mean difference (SMD) with 95% CI when studies used different outcome measures for the same construct. If dichotomous outcomes has been reported, we would have calculated the risk ratio (RR) as the effect measure. In cases where more than two interventions were evaluated in the same study, a single "pair‐wise" comparison was made. This was necessary to correct for error introduced by "double‐counting" of participants in the meta‐analyses. For each treatment comparison, an effect size and a 95% CI were calculated and displayed as forest plots. All analyses were conducted in Review Manager v.5.1.
Dealing with missing data
Where any required data were missing, multiple attempts to contact corresponding authors of the studies were made. Where no contact was possible with the authors, these studies were excluded from the meta‐analyses.
Assessment of heterogeneity
Clinical heterogeneity of the included RCTs was assessed by considering whether the studies were similar for the setting, participants, interventions and outcomes. Methodological heterogeneity was evaluated by examining the variability in study design and risk of bias. Statistical heterogeneity was checked using the Chi² test with the level of significance at 0.05. Values of I² that are greater than 80% show a very high level of heterogeneity, in which case, pooling of studies was not performed. If values of I² were 40% to 79%, studies were pooled using a random‐effects model; in cases of low or no heterogeneity, studies were pooled using a fixed‐effect model.
Data synthesis
Where possible, the outcome measures from the individual RCTs were combined through meta‐analysis provided sufficient homogeneity (i.e. I² < 80%) existed between studies. The clinical relevance of the results was evaluated using five criteria (Appendix 3) and considered in the 'Summary of the findings' table. The criteria include items on the reporting of patients, interventions and treatment settings, as well as assessing likely treatment benefits in relation to potential harms. An improvement of 30% on LBP or function was considered as a clinically important change (Ostelo 2005).
The overall quality of the evidence was evaluated using the GRADE approach (Guyatt 2008). The quality of the evidence for a specific outcome was based on performance against five principal domains: 1) limitations (due to risk of bias), 2) consistency of results, 3) directness (i.e. generalisability), 4) precision (sufficient data with narrow confidence intervals) and 5) other (e.g. publication bias). Single studies were considered to provide "low" or "very low" quality evidence, depending upon whether they were associated with a low or high risk of bias, respectively. The following levels of the quality of the evidence were applied.
-
High quality: Further research is very unlikely to change the level of evidence.
-
Moderate quality: Further research is likely to have an important impact on confidence in the estimate of effect and may change the estimate.
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Low quality: Further research is very likely to have an important impact on confidence in the estimate of effect and is likely to change it.
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Very low quality: We are very uncertain about the estimate.
Results
Description of studies
Results of the search
The search strategy for the current review identified 868 references from electronic databases and 42 records from additional sources (Figure 1). After removal of duplicates, 910 unique articles were screened for inclusion. After screening the titles and abstracts, full text copies of 58 trials were retrieved. The reference lists of previous reviews were checked but did not result in the identification of any further relevant studies. After reviewing the full text of the 58 selected trials, both review authors (SE, NH) agreed on the inclusion of seven trials and exclusion of 51 trials.
Study flow diagram.
Included studies
Six articles published in English and one Croatian article (which was translated by a native speaker) were included in this systematic review. Outcome measures and intervention details are described below as well as in the Characteristics of included studies table. All studies were performed in secondary care settings, usually in outpatient physiotherapy departments. The seven included studies had mostly small sample sizes, with only one study (Mohseni‐Bandpei 2006) having more than 25 participants per treatment arm. One study with three arms compared ultrasound to no treatment and electrical stimulation (Durmus 2010b), one study compared ultrasound plus exercise to phonophoresis plus exercise and exercise alone (Durmus 2013), four studies compared therapeutic ultrasound to placebo or sham ultrasound (i.e. application of ultrasound with the machine turned off) (Ansari 2006, Durmus 2010a, Ebadi 2012, Grubisic 2006), and one study compared ultrasound to spinal manipulation (Mohseni‐Bandpei 2006). All studies except for one (Ansari 2006) used stretching or strengthening exercise as an additional intervention to ultrasound therapy while Durmus 2010a also provided hot packs to both groups.
All studies used 1 MHz continuous ultrasound at intensities between 1 W/cm2 and 2.5 W/cm2. The duration of intervention was diverse between studies. Two studies (Ansari 2006, Ebadi 2012) used Gray’s formula (Allen 2006) for calculation of the application time, while the others applied ultrasound for 5 to 10 minutes. The number of treatment sessions varied between studies, from 6 sessions (Mohseni‐Bandpei 2006) to 18 sessions (Durmus 2010b, Durmus 2013).
Excluded studies
Further details of some excluded studies are presented in the Characteristics of excluded studies table. The most common reasons for exclusion were that the ultrasound therapy was used as part of a combination treatment and its effect could not be separated from other therapies, or patients had specific causes of low back pain (such as spinal stenosis).
Risk of bias in included studies
The final results of the 'Risk of bias' assessment are shown in Figure 2. Two studies (29%) had a low risk of bias, meeting six or more of the 12 criteria .
'Risk of bias' summary: review authors' judgements about each risk of bias item for each included study.
Allocation
Only two studies clearly described the randomisation procedure and only one reported a concealed allocation procedure. Most studies did not report sufficient details on either the method of randomisation or allocation, thus they were judged as "unclear" for these items.
Blinding
Participants were blinded to group allocation in four studies (Ansari 2006; Durmus 2010a; Ebadi 2012; Grubisic 2006) through the use of sham ultrasound (i.e. application of ultrasound with the machine turned off or output set to zero). In the three studies that compared ultrasound with other treatments (Durmus 2010b, Durmus 2013, Mohseni‐Bandpei 2006), blinding of patients was not carried out. In no study was the care provider blinded to group allocation. Because the primary outcome measure in all studies was self‐reported, the risk of outcome assessor bias was low in the studies in which patients were blinded.
Incomplete outcome data
In five studies (Durmus 2010a, Durmus 2010b, Durmus 2013, Ebadi 2012, Mohseni‐Bandpei 2006) dropout rates were explained and acceptable. The rate of dropout in the study by Ansari 2006 was 30% of the (already very small) sample size, which renders a high risk of attrition bias. In three studies (Ansari 2006, Durmus 2010b, Durmus 2013) participants who dropped out were excluded from the analysis. Two studies (Durmus 2010a; Ebadi 2012) reported that an intention‐to‐treat analysis was performed.
Other potential sources of bias
None of the studies reported on compliance with the intervention. Three studies (Ansari 2006; Durmus 2013; Ebadi 2012) controlled for co‐interventions, and all studies assessed their outcomes at similar time intervals for all groups. No study mentioned any conflict of interest in regard to commercial funding.
Effects of interventions
See: Summary of findings for the main comparison ; Summary of findings 2
Therapeutic ultrasound versus placebo
Four studies (Ansari 2006; Durmus 2010a; Ebadi 2012; Grubisic 2006) compared therapeutic ultrasound with placebo ultrasound.
Three studies (n = 121) provided post‐treatment data on pain intensity (Durmus 2010a; Ebadi 2012; Grubisic 2006). There was low quality evidence (imprecision, inconsistency) that therapeutic ultrasound provides no significant improvement in pain intensity when compared to placebo (mean difference (MD) [95%CI] ‐7.12 [‐17.99 to 3.75]) (Figure 3, Analysis 1.1).
Forest plot of comparison: 1 Ultrasound vs. sham ultrasound, outcome: 1.1 Pain (VAS) post‐treatment.
Three studies (n = 100) provided post‐treatment data on back‐specific function (Ansari 2006; Durmus 2010a; Ebadi 2012). There was moderate quality evidence (imprecision) that therapeutic ultrasound improves back‐specific function when compared to placebo (standardised mean difference (SMD) [95%CI] ‐0.45 [‐0.84 to ‐0.05]) (Figure 4, Analysis 1.2).
Forest plot of comparison: 1 Ultrasound vs. sham ultrasound, outcome: 1.2 Back‐specific functional status post‐treatment.
Three studies (n = 89) provided post‐treatment data on lumbar flexion range of motion (ROM) (Ansari 2006; Ebadi 2012; Grubisic 2006). There was very low quality evidence (limitations in design, imprecision, inconsistency) that therapeutic ultrasound provides no improvement in flexion ROM when compared to placebo (SMD [95%CI] 0.18 [‐0.62 to 0.98]) (Analysis 1.3).
Two studies (n = 58) provided post‐treatment data on lumbar extension ROM (Ansari 2006; Ebadi 2012). There was moderate quality evidence (imprecision) that therapeutic ultrasound provides no improvement in extension ROM when compared to placebo (SMD [95%CI] ‐0.33 [‐0.85 to 0.19]) (Analysis 1.4).
Therapeutic ultrasound plus exercise versus exercise alone
Two small (n = 59; n = 60) studies (Durmus 2010b; Durmus 2013) compared therapeutic ultrasound in addition with an exercise program and compared this with the exercise program alone.
Both studies (n = 79) provided post‐treatment data on pain intensity measured with the Pain Disability Index. There was low quality evidence (imprecision, limitations in design) that therapeutic ultrasound in addition to exercise provides no significant improvement in pain intensity when compared to exercise alone (MD [95%CI] ‐2.16 [‐4.66 to 0.34]) (Figure 5, Analysis 2.1).
Forest plot of comparison: 2 Ultrasound in addition to exercise vs. exercise alone, outcome: 2.1 Pain (PDI) post‐treatment.
Both studies (n = 79) provided post‐treatment data on back‐specific functional status measured with the Oswestry Disability Questionnaire. There was low quality evidence (imprecision, limitations in design) that therapeutic ultrasound in addition to exercise provides no significant improvement in functional status when compared to exercise alone (MD [95%CI] ‐0.41 [‐3.14 to 2.32]) (Figure 6, Analysis 2.2).
Forest plot of comparison: 2 Ultrasound in addition to exercise vs. exercise alone, outcome: 2.2 Back‐specific functional status post‐treatment.
Both studies (n = 79) also provided post‐treatment data on flexion ROM measured with the Lumbar Schober method. There was low quality evidence (imprecision, limitations in design) that therapeutic ultrasound in addition to exercise provides no significant improvement in flexion ROM when compared to exercise alone (MD [95%CI] 0.02 [‐0.52 to 0.56]) (Analysis 2.3).
Therapeutic ultrasound versus other treatments
Three studies (Durmus 2010b; Durmus 2013; Mohseni‐Bandpei 2006) compared therapeutic ultrasound with other treatments for chronic low back pain. There is very low quality evidence that there is no significant post‐treatment difference on any outcome measure between electrical stimulation and therapeutic ultrasound (Durmus 2010b). There is very low quality evidence that phonophoresis results in improved SF‐36 scores compared to therapeutic ultrasound (Durmus 2013). There is low quality evidence that spinal manipulation results in a significantly greater reduction in pain intensity and functional disability, as well as improved lumbar flexion and extension than therapeutic ultrasound post‐treatment and after six months (Mohseni‐Bandpei 2006).
Clinical Relevance
All included studies described the parameters (intensity, duration, frequency) for ultrasound application. Most described the patients in sufficient detail and reported on at least one relevant outcome measure (e.g. pain, functional disability). However, very few of the included studies reported intermediate‐ or long‐term outcomes. In addition, no study showed a clinically significant effect size in favour of ultrasound and in light of the potential for harm associated with the application of ultrasound, the benefits could not be clinically justified (Table 1).
| Study | Patients described in detail | Interventions described | Relevant outcomes reported | Size of the effect | Benefit/harm |
| Yes | Yes | No | No | No | |
| Yes | Yes | Yes | No | No | |
| Yes | Yes | Yes | No | No | |
| Yes | Yes | Yes | No | No | |
| Yes | Yes | Yes | No | No | |
| No | Yes | Yes | No | No | |
| Yes | Yes | Yes | No | No |
Discussion
Summary of main results
Seven small randomised controlled trials (362 participants) met the inclusion criteria for this review (Ansari 2006; Durmus 2010a; Durmus 2010b; Durmus 2013, Ebadi 2012; Grubisic 2006; Mohseni‐Bandpei 2006). From three trials (n = 100) there was moderate quality evidence that therapeutic ultrasound improves back‐specific function (SMD = ‐0.45) compared with placebo in the short term. From two trials (n = 58) there was moderate quality evidence that ultrasound provides no improvement in extension ROM compared with placebo in the short term.
There was low quality evidence from two trials (n = 79) that therapeutic ultrasound in addition to exercise does not significantly reduce pain intensity or improve back‐specific function or flexion ROM when compared with exercise alone. There was also low quality evidence (three studies; n = 121) that therapeutic ultrasound is not better than placebo with regards to short‐term pain improvement; and that spinal manipulation significantly reduces pain and functional disability more than ultrasound post‐treatment and after six months (one study; n = 112).
For all other comparisons and follow‐up time points there was either very low quality evidence or no evidence.
Overall completeness and applicability of evidence
The lack of intermediate‐ and long‐term outcome assessment in most of the studies included in this review restricts our ability to comment on whether any effects of therapeutic ultrasound were maintained. In most of the included studies, therapeutic ultrasound was evaluated in combination with some form of exercise therapy, which limits any conclusions on the effectiveness of ultrasound as a uni‐modal treatment. Within the included studies, not all recommended outcome measures for studies on low‐back pain (LBP) (such as pain and back‐specific function) were measured by all studies (Furlan 2009). The reporting of ultrasound application parameters and dose was inconsistently reported in the included studies, which meant that no conclusions on the most effective dose could be made. No study reported on calibration of the ultrasound device prior to or between treatment sessions.
Quality of the evidence
The small sample sizes in the included studies led to a downgrading of the evidence (i.e. imprecision) for most of the treatment comparisons. As a result, there was mostly low to very low quality evidence to support the use of therapeutic ultrasound. Most studies were affected by poor reporting, which made assessment of the risk of bias difficult. While most studies blinded the patient or outcome assessor, no study was able to appropriately blind the caregiver (therapist). In addition, there was a lack of information from all studies about compliance with therapeutic ultrasound or adverse events.
Potential biases in the review process
All attempts were made to reduce the bias involved with the review process. Where any of the review authors were also authors of one of the included studies, external reviewers were consulted to apply the eligibility criteria, extract the data, and perform the 'Risk of bias' assessment. In the case of missing data, attempts were made to gather the information from authors of the included studies.
'Risk of bias' summary: review authors' judgements about each risk of bias item for each included study.
Forest plot of comparison: 1 Ultrasound vs. sham ultrasound, outcome: 1.1 Pain (VAS) post‐treatment.
Forest plot of comparison: 1 Ultrasound vs. sham ultrasound, outcome: 1.2 Back‐specific functional status post‐treatment.
Forest plot of comparison: 2 Ultrasound in addition to exercise vs. exercise alone, outcome: 2.1 Pain (PDI) post‐treatment.
Forest plot of comparison: 2 Ultrasound in addition to exercise vs. exercise alone, outcome: 2.2 Back‐specific functional status post‐treatment.
Comparison 1 Ultrasound vs. sham ultrasound, Outcome 1 Pain (VAS) post‐treatment.
Comparison 1 Ultrasound vs. sham ultrasound, Outcome 2 Back‐specific functional status post‐treatment.
Comparison 1 Ultrasound vs. sham ultrasound, Outcome 3 Flexion ROM post‐treatment.
Comparison 1 Ultrasound vs. sham ultrasound, Outcome 4 Extension ROM post‐treatment.
Comparison 2 Ultrasound in addition to exercise vs. exercise alone, Outcome 1 Pain (PDI) post‐treatment.
Comparison 2 Ultrasound in addition to exercise vs. exercise alone, Outcome 2 Back‐specific functional status post‐treatment.
Comparison 2 Ultrasound in addition to exercise vs. exercise alone, Outcome 3 Flexion ROM post‐treatment.
| Therapeutic ultrasound for chronic low‐back pain | |||||
| Patient or population: Adults with chronic low‐back pain Settings: Secondary care Intervention: Therapeutic ultrasound Comparison: Sham (placebo) ultrasound | |||||
| Outcomes | Illustrative comparative risks* (95% CI) | No of Participants | Quality of the evidence | Comments | |
| Assumed risk | Corresponding risk | ||||
| Placebo | Therapeutic ultrasound | ||||
| Pain intensity Visual analogue scale (100‐point scale); post‐treatment | *The mean outcome for the most representative study (Ebadi 2012) is 30.7 (SD 13.1) | The mean pain intensity in the intervention groups was 7.12 points lower (17.99 lower to 3.75 higher) | 121 (3) | ⊕⊕⊝⊝ | No statistically significant difference |
| Back‐specific functional status Functional Rating Index or Oswestry Disability Questionnaire (higher scores mean worse function); post‐treatment | *The mean outcome for the most representative study (Ebadi 2012) is 31.1 (SD 13.4) | The mean back‐specific functional status in the intervention groups was 0.45 standard deviations lower (0.84 lower to 0.05 higher) | 100 (3) | ⊕⊕⊕⊝ | The magnitude of this difference is small to moderate. |
| Flexion ROM post‐treatment Modified Schober method (cm) or fingertip‐to‐floor method (cm); post‐treatment | *The mean outcome for the most representative study (Ebadi 2012) is 59.8 (SD 17.9) | The mean flexion ROM in the intervention groups was 0.18 standard deviations higher (0.62 lower to 0.98 higher) | 89 (3) | ⊕⊝⊝⊝ | No statistically significant difference |
| Extension ROM post‐treatment Modified Schober method (cm) or degrees; post‐treatment | *The mean outcome for the most representative study (Ebadi 2012) is 24.1 (SD 9.3) | The mean extension ROM in the intervention groups was 0.33 standard deviations lower (0.85 lower to 0.19 higher) | 58 (2) | ⊕⊕⊕⊝ | No statistically significant difference |
| *Of the included trials for this outcome, we chose the study that is a combination of the most representative study population and the lowest risk of bias (Ebadi 2012). This figure represents the mean outcome in the control group of this particular study. CI: Confidence interval; RR: Risk Ratio; SD: Standard Deviation; ROM: Range of Motion | |||||
| GRADE Working Group grades of evidence | |||||
| 1. Total number of events was < 300 2. I2 > 60% 3. Two of the three included trials were rated as having a high risk of bias | |||||
| Therapeutic ultrasound for chronic low‐back pain | |||||
| Patient or population: Adults with chronic low‐back pain Settings: Secondary care Intervention: Therapeutic ultrasound plus exercise Comparison: Exercise | |||||
| Outcomes | Illustrative comparative risks* (95% CI) | No of Participants | Quality of the evidence | Comments | |
| Assumed risk | Corresponding risk | ||||
| Exercise | Therapeutic ultrasound plus exercise | ||||
| Pain intensity Pain Disability Index (70‐point scale); post‐treatment | *The mean change for the most representative study (Durmus 2013) is 10.7 (SD 4.4) | The mean pain intensity in the intervention groups was 2.16 points lower (4.66 lower to 0.34 higher) | 79 (2) | ⊕⊕⊝⊝ | No statistically significant difference |
| Back‐specific functional status Oswestry Disability Questionnaire (percentage); post‐treatment | *The mean change for the most representative study (Durmus 2013) is 8.2 (SD 7.2) | The mean back‐specific functional status in the intervention groups was 0.41 percent lower (3.14 lower to 2.32 higher) | 79 (2) | ⊕⊕⊝⊝ | No statistically significant difference |
| Flexion ROM post‐treatment Lumbar Schober method (cm); post‐treatment | *The mean change for the most representative study (Durmus 2013) is 0.38 (SD 1.41) | The mean flexion ROM in the intervention groups was 0.02 cm higher (0.52 lower to 0.56 higher) | 79 (2) | ⊕⊕⊝⊝ | No statistically significant difference |
| Extension ROM post‐treatment | Not measured | Not measured | Not applicable | Not applicable | |
| *Of the included trials for this outcome, we chose the study that had the lowest risk of bias (Durmus 2013). This figure represents the mean change in the control group of this particular study. CI: Confidence interval; RR: Risk Ratio; SD: Standard Deviation; ROM: Range of Motion | |||||
| GRADE Working Group grades of evidence | |||||
| 1. Total number of events was < 300 2. Both included studies were rated as having a high risk of bias. | |||||
| Study | Patients described in detail | Interventions described | Relevant outcomes reported | Size of the effect | Benefit/harm |
| Yes | Yes | No | No | No | |
| Yes | Yes | Yes | No | No | |
| Yes | Yes | Yes | No | No | |
| Yes | Yes | Yes | No | No | |
| Yes | Yes | Yes | No | No | |
| No | Yes | Yes | No | No | |
| Yes | Yes | Yes | No | No |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 1 Pain (VAS) post‐treatment Show forest plot | 3 | 121 | Mean Difference (IV, Random, 95% CI) | ‐7.12 [‐17.99, 3.75] |
| 2 Back‐specific functional status post‐treatment Show forest plot | 3 | 100 | Std. Mean Difference (IV, Fixed, 95% CI) | ‐0.45 [‐0.84, ‐0.05] |
| 3 Flexion ROM post‐treatment Show forest plot | 3 | 89 | Std. Mean Difference (IV, Random, 95% CI) | 0.18 [‐0.62, 0.98] |
| 4 Extension ROM post‐treatment Show forest plot | 2 | 58 | Std. Mean Difference (IV, Fixed, 95% CI) | ‐0.33 [‐0.85, 0.19] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 1 Pain (PDI) post‐treatment Show forest plot | 2 | 79 | Mean Difference (IV, Fixed, 95% CI) | ‐2.16 [‐4.66, 0.34] |
| 2 Back‐specific functional status post‐treatment Show forest plot | 2 | 79 | Mean Difference (IV, Fixed, 95% CI) | ‐0.41 [‐3.14, 2.32] |
| 3 Flexion ROM post‐treatment Show forest plot | 2 | 79 | Mean Difference (IV, Fixed, 95% CI) | 0.02 [‐0.52, 0.56] |
