Osteoarthritis and Cartilage 18 (2010) 1117e1126
Review
Efficacy of ultrasound therapy for the management of knee osteoarthritis:
a systematic review with meta-analysis
A. Loyola-Sánchez*, J. Richardson a, N.J. MacIntyre b
School of Rehabilitation Science, McMaster University, Canada
a r t i c l e i n f o
s u m m a r y
Article history:
Received 5 January 2010
Accepted 17 June 2010
Objective: To assess the efficacy of ultrasound therapy (US) for decreasing pain and improving physical
function, patient-perception of disease severity, and cartilage repair in people with knee osteoarthritis
(OA).
Methods: We conducted a systematic review (to February 2009) without language limits in MEDLINE,
EMBASE, Cochrane Library, LILACS, MEDCARIB, CINAHL, PEDro, SPORT-discus, REHABDATA, and World
Health Organization Clinical Trial Registry. We included randomized controlled trials of people with knee
OA comparing the outcomes of interest for those receiving US with those receiving no US. Two reviewers
independently selected studies, extracted relevant data and assessed quality. Pooled analyses were
conducted using inverse-variance random effects models.
Main results: Six small trials (378 patients) were included. US improves pain [Standardized Mean
Difference (SMD) (95% confidence interval (CI)) ¼ 0.49 (0.79, 0.18), P ¼ 0.002], and tends to improve
self-reported physical function [SMD (CI) ¼ 0.54 (1.19, 0.12), P ¼ 0.11] along with walking performance
[SMD (CI) ¼ 0.81 (0.09, 1.72), P ¼ 0.08]. Results from two trials (128 patients), conducted by the same
group, show a positive effect of US on pain [SMD (CI) ¼ 0.77 (1.15, 0.39), P < 0.001], self-reported
physical function [SMD (CI) ¼ 1.25 (1.69, 0.81), P < 0.001], and walking performance [SMD (CI) ¼
1.47 (1.06, 1.88), P < 0.001] at 10 months after the intervention concluded. Heterogeneity observed
between studies regarding the effect of US on pain was explained by US dose, mode and intensity. The
quality of evidence supporting these effect estimates was rated as low.
Conclusions: US could be efficacious for decreasing pain and may improve physical function in patients
with knee OA. The findings of this review should be confirmed using methodologically rigorous and
adequately powered clinical trials.
Ó 2010 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.
Keywords:
Ultrasound
Osteoarthritis
Knee
Meta-analysis
Introduction
Knee osteoarthritis (OA) is the most common presentation of
OA, with an estimated prevalence between 12% and 35% in the
general population1,2 and is considered the leading cause of
musculoskeletal disability in the elderly population worldwide3.
Physiotherapy is recommended for the management of painful
knee OA4 and ultrasound therapy (US) is one of the most
common physical agents used within physiotherapy practice in
* Address correspondence and reprint requests to: Adalberto Loyola-Sánchez,
School of Rehabilitation Science, IAHS e 403, 1400 Main Street West, Hamilton, ON,
Canada L8S 1C7. Tel: 1-905-525-9140x26410.
E-mail addresses: loyolaa@mcmaster.ca (A. Loyola-Sánchez), jrichard@mcmaster.ca
(J. Richardson), macint@mcmaster.ca (N.J. MacIntyre).
a
Tel: 1-905-525-9140x27811.
b
Tel: 1-905-525-9140x21166.
several countries5. US is based on the application of high
frequency sound waves to the tissues of the body in order to
obtain mechanical or thermal effects6. These effects aim to
enhance soft tissue healing, decrease the inflammatory response,
increase blood flow, increase metabolic activity, and decrease
pain6. Moreover, there is some evidence that ultrasonic energy
stimulates the repair of joint cartilage in animal models of
cartilage injury7e9. Therefore, US could be an effective intervention in the management of pain and disability in people with
knee OA.
The Osteoarthritis Research Society International (OARSI)
struck a committee to complete a systematic review of existing
treatment guidelines (2007) in order to develop recommendations for the management of knee and hip OA4. Ultrasound was
not identified as a core treatment modality based on the results of
a systematic review published in 2001 by the Cochrane Collaboration10. The Cochrane systematic review included studies
1063-4584/$ e see front matter Ó 2010 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.joca.2010.06.010
1118
A. Loyola-Sánchez et al. / Osteoarthritis and Cartilage 18 (2010) 1117e1126
available prior to June 200010 while more recent trials evaluating
the effectiveness of US in the management of knee OA were not
reviewed. Since there is a need for effective conservative treatment options for people with knee OA, it is important to confirm
or change current clinical practice guidelines based on best
available evidence. Therefore, the objective of this systematic
review and meta-analysis was to determine the efficacy of US in
decreasing pain and improving physical function in people with
knee OA. Further, we extended the scope of previous systematic
reviews on the topic by evaluating the efficacy of US on patientperception of disease severity, and cartilage repair. We followed
the Preferred Reporting Items for Systematic reviews and MetaAnalyses (PRISMA) recommendations11 in the creation of this
manuscript.
(n ¼ 9) written in their first language (a physical therapist, an engineer, an occupational therapist, a rheumatologist, and a physiatrist).
Data extraction and management
Two reviewers, using a pre-tested data collection form, followed a double extraction method. The reviewers independently
extracted data related to the study population (clinical setting,
diagnostic criteria, joint involvement, sex, age and OA severity),
study design, US intervention (device, frequency, mode, intensity and dose), co-interventions, outcomes (pain, physical function, participant’s perception of disease severity, and cartilage
repair), and the monitoring/reporting of adverse events. The US
dose was calculated using the following formula5:
ðAverage temporal intensityÞ ðTimeÞ ðEffective radiating areaÞ
Energy J=cm2 ¼
Treated surface area
Methods
Search strategy
The Cochrane Central Register of Controlled Trials (fourth Quarter
2008), MEDLINE (1950 to January week 4, 2009), MEDLINE Daily
Update (Feb 5, 2009), MEDLINE In Process & Other non-indexed citations (February 5, 2009), EMBASE (1980e2009 week 6), LILACS
(February 6, 2009), MEDCARIB (February 6, 2009), CINAHL (February 8,
2009), pre CINAHL (February 8, 2009), PEDro (last updated February 2,
2009), AMED (1985 to January 2009), SPORTdiscus (1830 to February 9,
2009), REHABDATA (1956 to February 9, 2009), and World Health
Organization Clinical Trial Registry (February 8, 2009) databases were
searched by one of the authors (AL). In addition, published literature
with restricted distribution was searched through the ISI Web of
Knowledge, Papers First, Proceedings First, and ProQuest for Dissertations and Theses. Authors of an unpublished study reported as
a conference proceeding in the Proceedings First database were contacted via e-mail. A detailed example of the full electronic search
strategy for Ovid MEDLINE is provided in Appendix A. Briefly, the
following medical subject headings (MeSH) were used: Osteoarthritis,
Arthritis, Ultrasonic Therapy, Ultrasonics, Sonication, Diathermy,
Cartilage, and Wound Healing; keywords were osteoarthritis, arthritis
experimental, ultrasound therapy, low intensity pulsed ultrasound,
low intensity ultrasound, and cartilage repair. To increase the search
sensitivity, no date, language, or design limits were included. Duplicates were removed after all databases were searched.
Study selection and eligibility criteria
Two reviewers (AL, JR) independently screened all citations
obtained and retrieved all parallel group randomized controlled
trials involving patients with knee OA that compared US with
placebo or no intervention. Trials that compared US in combination
with another intervention to which the comparison group was
exposed were also included. Studies were excluded from the review
if phonophoresis was the only ultrasonic intervention, US was
combined with another intervention not provided to the comparison group, and samples included subjects having other diagnoses
and results for the subjects with knee OA were not reported separately. Cohen’s unweighted Kappa (k) was used to measure agreement between reviewers12. Observed agreement was fair
(k ¼ 0.57)23. Disagreement was solved by consensus including
a third reviewer (NM). Colleagues translated non-English articles
We defined cartilage repair as all measures that directly or indirectly assess the cartilage formationedegradation process (i.e.,
imaging, arthroscopy, fluid biomarkers). Primary authors were
contacted in the case of missing data or unclear reporting. A
physiatrist with expertise in OA and US (AL) and a physical therapist with expertise in research methodology and OA (NM)
reviewed the papers and extracted the data.
Risk of bias and quality assessment
The risk of bias was assessed for each study by evaluating the
rigor of the randomization process, the treatment allocation
concealment, the blinding process, the completeness of the data,
and the reporting of results following the Cochrane Collaboration
recommendations13. To judge the completeness of the data as
adequate, a dropout rate of less than 15% was required.
Given the objective of this systematic review, we identified
randomization, treatment allocation concealment, blinding, and
completeness of data as key domains for establishing risk of bias.
For each included study, risk of bias was determined to be low
when all key domains were performed adequately, unclear when
one or more key domains were not clearly described, and high
when one or more key domains were inadequate. Across studies,
the risk of bias was considered low if all studies had low risk,
unclear when more than 75% of the studies had unclear or low risk
and less than 25% of the studies had high risk of bias, and high
when more than 25% of the studies had high risk of bias. Observed
agreement was fair (k ¼ 0.56)23 and disagreement was resolved by
consensus and inclusion of a third reviewer, who is a physical
therapist with research methodology expertise (JR).
The quality of the evidence for each outcome was determined by
considering the risk of bias, the heterogeneity of the findings, the
use of surrogate measurements for outcome assessment, and the
precision of the effect estimates as recommended by the Grading of
Recommendations, Assessment Development and Evaluation
(GRADE) working group14.
Statistical analyses
An inverse-variance random effects model15 was used to calculate pooled standardized mean differences (SMDs) using Review
Manager (RevMan [computer program] Version 5.0 Copenhagen:
The Nordic Cochrane Centre, The Cochrane Collaboration, 2008,
Oxford, UK). The SMD is a ratio between the differences observed
A. Loyola-Sánchez et al. / Osteoarthritis and Cartilage 18 (2010) 1117e1126
between groups and the standard deviation (SD) of the outcomes
among participants (Hedges’ adjusted g). The 95% confidence
interval (CI) was calculated and a Z test was performed with significance set at P < 0.05. Heterogeneity among studies was assessed
with a c2 test with significance set at P < 0.10 and an inconsistency
test (I2) which represents the percentage variability in the effect
estimates that is due to heterogeneity rather than chance. Inconsistency (I2) > 40% was considered significantly high16.
Two studies17,18 reported different subgroups of US, so the
means and SDs of these subgroups were pooled using the following
formulas19:
Meanpooled ¼
ðX1 n1Þ ðX2 n2Þ ðX3 n3Þ ðX. n.Þ
n1 þ n2 þ n3 þ n.
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
s1 n11 þ s22 n21 þ s23 n31 þ s2n n1
SDpooled ¼
ðn11Þþðn21Þþðn31Þþðn.1Þ
where X ¼ mean for each group, SD ¼ standard deviation,
s2 ¼ variance, and n ¼ number of participants in that group.
Three studies17,18,20 reported the results of pain outcomes by
knee rather than by patient. Therefore, we included the number of
patients (n ¼ 35 instead of n ¼ 70) in each group during the pooled
analysis, in order to account for the intercorrelation of measurements taken from the knees of the same patient.
In order to express the effect estimates as percentage change relative to the control groups, the SMDs were back transformed to mean
differences (MD) using SDs reported in observational studies21,22
(Appendix B). Heterogeneity was explored through subgroup
1119
analyses following a priori hypotheses that considered factors such as
disease severity, US mode/intensity/dose, co-interventions, number of
sessions provided, and methodological adequacy.
Results
Twenty-three studies, out of 1119 citations identified, fulfilled
the inclusion criteria and were retrieved for full text review (see
Fig. 1). Of these, only six studies were included and considered in the
final analysis. The remaining 17 studies were excluded because the
samples included persons with diagnoses other than knee OA24e26;
compared US with short wave diathermy27e29, diadynamic
currents/magnetotherapy30, or phonophoresis31, without a control
group with similar exposure; compared different frequencies/
modes of US32e34, or used US in combination with other physical
modalities35 without a control group; four articles were case series
reports36e39; and one study was performed in vitro40.
Description of included studies
The six small, English-language, randomized controlled trials17,18,20,41e43 included in this review are summarized in Table I. In
one study18, unpublished data were provided by the primary
author. All trials included people with knee OA who met the
American College of Rheumatology diagnostic criteria44 and the
mean age of participants was over 53 years. All trials delivered
ultrasonic energy at a frequency of 1 MHz. For the study by Falconer
et al.42, tabulated results were extracted. Five studies reported
sufficient information for the dose calculation17,18,20,42,43. Three
trials17,18,20 conducted by the same group reported a peak intensity
Fig. 1. Flowchart of study selection.
1120
Table I
Summary of included randomized controlled trials evaluating the effectiveness of US in people with knee OA
Characteristics of subjects
Intervention group
Comparison group
Outcomes
Follow-up
Risk of bias
Cetin et al.41
(Turkey)
100% Women with mild
to severe bilateral knee
OA; w58 (8) years.
n* ¼ 17
Standardized warm up, isokinetic
exercises and hotpack.**
Pain-VASz
Physical function-LSIx
Walking speed-time to walk
50 m in seconds)
8 Weeks
High
Falconer et al.42
(USA)
w72% Women with
severity not specified;
w67.5 (11) years.
n* ¼ 35
Sham US (start button not pushed).**
Pain-VAS
Walking speed-50 ft walk time
(converted to m/min)
4e6 Weeks
High
Huang et al.18
(Taiwan)
w33% Women with
mild to severe bilateral knee
OA; w60 (9) years.
n* ¼ 18
Sonopulus 590 US device, continuous
mode, 1.5 W/cm2 intensity, 180 J/cm2 dosey,
24 ten-min sessions in 8 weeks.
Also: standardized warm up, isokinetic
exercises, and hotpack.
n* ¼ 34
Chattanooga Intellect 200 US device,
continuous mode{, 1.7 W/cm2 intensity,
26 J/cm2 dose, 12 twelve-min sessions
in 4e6 weeks.
n* ¼ 30
Sonopulus 590 US device; pulsed mode
(duty cycle: 25%), 2.5 W/cm2
intensity, 112 J/cm2 dose, 24 fifteen-min
sessions in 8 weeks.
n* ¼ 30
Sham US.**
8 Weeks
Unclear
Huang et al.17
(Taiwan)
w81% Women with
mild knee OA;
w62 (17) years.
n* ¼ 25
Standardized warm up, isokinetic
exercises and hotpack**
(home exercise program following 8 weeks).
8 Weeks and
12 months
High
Huang et al.20
(Taiwan)
w81% Female with
mild knee OA,
w65 (13) years.
n* ¼ 30
Standardized warm up, isokinetic
exercises and hotpack**
(home exercise program following 8 weeks).
Pain-VASz
Physical function-LSIx
Walking speed-50 ft walk time
(converted to m/min)
8 Weeks and
12 months
High
Ozgonenel et al.43
(Turkey)
w80% Women with
mild to moderate knee
OA; w55 (7.5) years.
Group 1: n* ¼ 27; Continuous mode,
1.5 W/cm2 intensity, 270 J/cm2 dose.
Group 2: n* ¼ 30; Pulsed mode
(duty cycle: 25%), 2.5 W/cm2
intensity, 112.5 J/cm2 dose.
Both groups used a Sonopulus
590 US device, 24 fifteen-min
sessions in 8 weeks.
Also: standardized warm up, isokinetic
exercises and hotpack
(home exercise program
following 8 weeks).
n* ¼ 32
Sonopulus 590 US device, pulsed mode
(duty cycle: 25%),
2.5 W/cm2 intensity, 112 J/cm2 dose,
24 fifteen-min sessions in 8 weeks.
Also: standardized warm up, isokinetic
exercises and hotpack
(home exercise program following 8 weeks).
n* ¼ 34
Peterson .250 US device, continuous mode,
1 W/cm2 intensity,
150.72 J/cm2 dose, 10 five-min
sessions in 2 weeks.
Pain-VASz
Physical function-LSIx
Walking speed-50 ft walk time
(converted to m/min)
Arthritis Severity Index ¼ ratio
of 99mTechnetium uptake#
knee/99mTechnetium uptake middle
third ipsilateral femur
Pain-VASz
Physical function-LSIx
Walking speed-50 ft walk time
(converted to m/min)
n* ¼ 31
Sham US (applicator disconnected from device).**
Pain-VASz
Physical function-WOMACk
Walking speed-time to walk 50 m
(seconds)
2 Weeks
High
*
y
z
x
k
{
#
**
Sample size of subjects whose data were included in the present metaanalysis.
Treated surface area was not reported and US dose was calculated using a value of 25 cm2 reported in 1 similar trial17.
Visual Analogue Scale (VAS) from 0 cm (no pain) to 10 cm (most intense pain).
LSI scale from 0 (better) to 26 (worst).
Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) physical function subscale from 0 (better) to 68 (worst).
The ultrasonic mode was not reported, we assumed it was continuous based on the way the intensity of the energy was delivered (“from 0 W/cm2 to maximal tolerable dose not exceeding 2.5 W/cm2 ”).
99m
Technetium uptake was measured by bone scan (TOSHIBA GCA-90 g-camera) 3 h after administrating the radioisotope.
Same number of sessions and period of time as in the intervention group.
A. Loyola-Sánchez et al. / Osteoarthritis and Cartilage 18 (2010) 1117e1126
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A. Loyola-Sánchez et al. / Osteoarthritis and Cartilage 18 (2010) 1117e1126
1121
Table II
Risk of bias assessment of the included randomized controlled trials
Trials
Key domains
Group allocation
concealment
Randomization
Blinding of treatment
provider
Blinding of
participants
Completeness of data
Cetin et al.41
Falconer et al.42
Unclear
Unclear
Unclear
Unclear
No
No
No
Yes
Yes
Yes
Huang et al.18
Huang et al.17
Unclear
No
Unclear
No
Unclear
No
Unclear
No
Huang et al.20
Ozgonenel et al.43
No
Unclear
No
Unclear
No
No
No
Yes
Yes
Yes (8 weeks)
No (12 months)
Yes
Yes
value followed by the statement: “The intensity of sonication was
adjusted to the level at which the patient felt a warm sensation or
a mild sting”. It can be inferred from this statement that the output
intensity was modified for each US application and the calculated
dose would be inaccurate. Communication with the primary author
confirmed that the intensity output was fixed and only the speed of
the sound head varied during the US application. Thus, US dose
could be calculated.
One trial42 did not report the mode of US, however the author
confirmed the use of continuous US (personal communication).
For the trial by Cetin et al.41, the therapeutic dose was calculated
using the size of the treated surface area (25 cm2) reported in
a trial that used the same US device17. Only two trials17,20, which
were conducted by the same research group, reported outcomes of
pain and physical function at 12 months (10 months after
completing the interventions) and this information was analyzed
separately.
Risk of bias and quality assessment
The risk of bias was unclear for one study18 and high for five
studies17,20,41e43 (Table II). Thus, the evidence included in this
review has a high risk of bias overall.
The quality of evidence is low for pain and physical function
outcomes because of the high risk of bias (Table II), and the heterogeneity observed in results across trials [I2 ¼ 51e92%, Figs. 2(A), 3(A)
and 4(A)] (Appendix B). The quality of evidence is considered low for
cartilage repair because the only trial18 that reported this outcome
had an unclear risk of bias (Table II) and used a surrogate measure
(99mTechnetium uptake) to assess cartilage status (Appendix B).
Reporting of outcomes
complete
Risk of bias
Yes
No-final walking
performance not
reported by group
Yes
Yes
High
High
Yes
Yes
High
High
Unclear
High
Effect of US on physical function
Self-reported physical function
Five studies included self-reported physical function
measurements: four used the Lequesne Severity Index (LSI)
score17,18,20,41; one used the Western Ontario and McMaster
Universities Osteoarthritis Index (WOMAC) physical function
subscale score43 (Table I). The effect estimate observed favored
the US intervention, however the difference between groups was
not statistically significant [SMD (CI) ¼ 0.54 (1.19, 0.12),
P ¼ 0.11] [Fig. 3(A)]. Heterogeneity was high (c2 ¼ 29.11, P < 0.001,
I2 ¼ 86%), and predefined subgroup analyses were performed.
Inconsistency was not explained satisfactorily by any of the
subgroup analyses performed. Data pooled from two trials17,20
showed an improvement at 12 months (10 months after
completing the interventions) in the self-reported physical
function of people who received US [SMD (CI) ¼ 1.25 (1.69,
0.81), P < 0.001] [Fig. 3(B)].
Walking performance
Five studies reported walking performance: two studies
measured the time taken to walk 50 m in minutes41,43; three
studies measured walking speed (m/min)17,18,20 (Table I). There was
no significant improvement in the walking performance in the US
group [SMD (CI) ¼ 0.81 (0.09, 1.72), P ¼ 0.08] [Fig. 4(A)]. High
heterogeneity was observed (c2 ¼ 52.2, P < 0.001, I2 ¼ 92%), and the
subgroup analyses did not explain this inconsistency. Pooling the
results of two studies17,20, by the same research group, showed that
walking speed at 12 months (10 months after completing the
interventions) was improved in the US group [SMD (CI) ¼ 1.47 (1.06,
1.88), P < 0.001] [Fig. 4(B)].
Effect of US on patient-perception of disease severity
Effect of US on pain
All included trials assessed pain using a Visual Analog Scale
(VAS) measured in centimeters. Overall, the application of US
resulted in decreased pain [SMD (CI) ¼ 0.49 (0.79, 0.18),
P ¼ 0.002] [Fig. 2(A)]. However, high heterogeneity was found
(c2 ¼ 10.26, P ¼ 0.07, I2 ¼ 51%), therefore predefined subgroup
analyses were conducted. Ultrasound mode, intensity, and therapeutic dose completely explained the inconsistency between the
groups [Fig. 2(B)]. In all subgroups, effect estimates favored US
therapy; however, the differences were statistically significant only
in the low intensity/pulsed US and US dose < 150 J/cm2 subgroups
[SMD (CI) ¼ 0.85 (1.16, 0.54)]. Overall, trials17,20 that reported
VAS at 12 months (10 months after completing the interventions)
favored US [SMD (CI) ¼ 0.77 (1.15, 0.39), P < 0.001] [Fig. 2(C)].
No studies were identified which reported an outcome related
to patient-perception of disease severity.
Effect of US on cartilage repair
Only one study18 reported an outcome related to knee joint
structure. The authors measured 99mTechnetium uptake on bone
scans in order to determine an ‘index of arthritis severity’,
99m
Technetium uptake in the knee divided by the 99mTechnetium uptake in the middle third of the ipsilateral femur. The
authors validated this outcome measure on animal models of
cartilage injury45. The results of this study showed a significant
decrease in the ‘index of arthritis severity’ measured after an 8
week US intervention for patients in the lowest and middle
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A. Loyola-Sánchez et al. / Osteoarthritis and Cartilage 18 (2010) 1117e1126
Fig. 2. Meta-analyses of ultrasound effect on pain (cm-VAS). A: SMDs at the end of the intervention. B: Mode/intensity and dose subgroup analysis. C: SMDs at 12 months
(10 months after completing US).
tertile for baseline measures of ‘index of arthritis severity’ [MD
(CI) ¼ 0.8 (0.32, 1.28), P < 0.001 and 1.8 (0.85, 2.75), P < 0.001,
respectively] but not for those in the highest tertile at baseline
[MD (CI) ¼ 0.10 (1.06, 1.26), P ¼ 0.87]. We considered this
outcome an indirect measurement of cartilage status/repair. Our
search did not yield any trial reporting a direct measurement of
cartilage repair.
Adverse events
One study42 described the intention to monitor the incidence of
adverse events related to the application of US and reported the
absence of major complications. Another study43 reported that no
adverse events occurred either during or after the interventions.
Since the number of adverse events reported in these two trials was
A. Loyola-Sánchez et al. / Osteoarthritis and Cartilage 18 (2010) 1117e1126
1123
Fig. 3. Meta-analyses of ultrasound effect on self-reported physical function (LSI scores and WOMAC physical function subscale scores). A: SMDs at the end of the intervention. B:
SMDs of LSI scores at 12 months (10 months after completing US).
zero, and adverse events were not reported in the rest of the
included trials, an estimate of US safety could not be calculated.
Discussion
This systematic review provides a meta-analysis of the efficacy
of US for decreasing pain and improving physical function in people
with knee OA. New evidence was found (Table I) which shows that
US can reduce pain by 21%, compared to a control group (Appendix
B). The clinical importance of this finding can be appreciated in
terms of the number of patients it is necessary to treat in order to
observe improvement in pain in one patient. To calculate the
number needed to treat (NNT), we used the formula proposed by
Chinn et al.46. The SMD was transformed to an odds ratio and the
proportion of subjects in the control group that will experience
improvement in pain (29%) was determined from a prospective
study involving a comparable patient sample47. Using this
approach, the NNT is 7. It also seems that US applied using low
intensity (<1 W/cm2), pulsed mode, and a therapeutic dose < 150 J/
cm2 could be more effective at reducing pain than US applied using
high intensity (1 W/cm2), continuous mode and a therapeutic
dose > 150 J/cm2. In general, a non-significant positive effect
(19.68% lower Lequesne Severity Index (LSI) score than the control
group) was observed on physical function with the use of US
(Appendix B). Based on the findings from two trials by one research
group17,20, beneficial effects may last for 10 months after the US
treatment is completed [Figs. 2(C), 3(B) and 4(B)].
Limited evidence found in this review prevents conclusive
statements regarding dose effects and the effectiveness of US on
cartilage repair. Our findings which suggest a threshold US dosage
for pain reduction in persons with knee OA are consistent with
previous findings that higher US doses are less effective for tissue
repair in humans48 and even harmful for the growth plate of
rabbits49. Only one small trial with unclear risk of bias assessed the
cartilage repair process. This study used an indirect measurement
of cartilage status in people with knee OA and reported that low
intensity pulsed US may help to enhance the cartilage repair
process on this population. These findings together with animal
studies which permit direct measurement of cartilage tissue
response to US7,8,9 are consistent with the “mechanotransduction
theory”. This theory proposes that mechanical stimuli increase the
chondrocyte production of proteoglycans and anti-inflammatory
Fig. 4. Meta-analyses of ultrasound effect on walking performance (time to walk 50 m in minutes and walking speed in m/min). A: SMDs at the end of the intervention. B: SMDs of
walking speed (m/min) at 12 months (10 months after completing US).
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proteins50. Further studies are warranted to determine if low dose
pulsed US is optimal for pain relief and stimulation of cartilage
repair.
Our findings suggest that US delivered using a pulsed mode and
at low intensities have a pronounced effect on pain reduction. In
theory, the thermal effect of US is proposed to reduce pain6. The
thermal effect is achieved by applying high intensity US in
a continuous mode to heat the nerve fibers which attenuates nociception5. However, our findings suggest a non-thermal mechanism
for pain reduction which may be related to a threshold dose effect, as
stated previously, or attenuation of the nociceptive signals via
mechanical stimuli. Nevertheless, the limited number and quality of
the trials included in the subgroup analyses limit further inferences.
None of the subgroup analyses that we conducted explained the
heterogeneity observed for physical function and walking performance outcomes. Heterogeneity was reduced for self-reported
physical function (I2 reduced from 86% to 30%) and walking
performance (I2 reduced from 94% to 0%) when groups with
a similar severity of knee OA were compared and the US group was
favoured. However, these subgroups were comprised of subjects
with mild disease severity (Altman II), so it is unclear if these
observations are related to the comparison of homogeneous groups
or to the mild disease severity. Thus, consideration of disease status
may be important when assessing the effects of US in the knee OA
population.
The main results of this review support the findings of
a recently updated Cochrane review51. However some differences
warrant comment. The authors of the Cochrane review assumed
that the US provided in the study by Falconer et al.42 was pulsed.
For the current review, however, the authors confirmed that it
was continuous. Our search yielded one unpublished trial18
related to our objective to evaluate the effectiveness of US on
cartilage repair. This trial was not considered in the updated
Cochrane review. Finally, we decided to analyze the data from
two trials17,20 that reported outcomes at 12 months (10 months
after the interventions were completed) to explore the longer
term US effects. These long-term effects were not considered in
the updated Cochrane review. Despite these differences, our
results are compatible.
A limitation of our review is that the findings are based on
evidence which has a high risk of bias and low quality. When we
synthesized only the trials that adequately blinded the participants42,43 the effect size decreased considerably and was no longer
statistically significant [SMD (CI) ¼ 0.24 (0.63, 0.14)]. This
suggests that the effect sizes for pain found in this review could be
partly inflated by the methodological limitations of the included
studies.
A further limitation is the decision to pool the results of the
studies that compared US and placebo with studies that included
co-interventions. We assume that no interaction between US and
the isokinetic exercises occurred, however we cannot test this
assumption. It is well known that exercise is beneficial in relieving
pain and improving physical function for people with knee OA52.
Therefore, a positive interaction between US and exercise cannot be
ruled out. Finally, because of the limited number of small trials
identified, the risk of publication bias could not be determined.
Hence, the possibility exists that only positive trials were published
while negative trials were not. Overall, the methodological limitations described reduce the confidence in the effect estimates
observed in the present meta-analyses.
Implications for practice
US (10e24 sessions) appears to be efficacious for decreasing
pain, and may improve physical function in patients with knee OA.
It is possible that the mode, intensity, and dose of US all influence
the effect on pain. It is also possible that pain reduction may be
sustained for 10 months after US is discontinued. However, these
results are currently supported by low quality evidence and
definitive trials are needed.
Implications for research
Trials that are methodologically rigorous and adequately
powered are needed to confirm the effectiveness of US to reduce
pain, and improve physical function in people with knee OA.
Outcome measures in trials should include cartilage repair and
patient-perception of knee OA severity to provide insight into
potential synergistic action mechanisms. Careful consideration of
ultrasound prescription and disease stage is required to assess the
optimal therapeutic parameters and the subgroup(s) of people
who will benefit most. Long-term effects of the US intervention
should be assessed as well. Finally, the mechanism by which
therapeutic ultrasound reduces pain in knee OA needs to be
explored further.
Author contributions
All authors made substantial contributions to the conceptualization, design, data collection, analysis, interpretation, drafting and
revisions; and approved the final version.
Conflict of interest
None of the authors has any financial and personal relationships
with other people or organizations that could potentially and
inappropriately influence this work and its conclusions.
Acknowledgement
Role of funding sources: AL was supported by the Consejo
Nacional de Ciencia y Tecnologia (CONACYT) of Mexico scholarship
(number 209621), and by a McMaster University School of
Graduate Studies International Excellence Award. These sponsors
had no involvement in the design, conduct or publication of this
study.
Appendix A. Medical Subject Headings and keyword search
strategy performed in Ovid MEDLINE (1950 to January week 4,
2009)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
22
Exp Osteoarthritis/
Osteoarthritis.mp.
Exp Arthritis, Experimental/
Exp Arthritis/
Arthritis experimental.mp.
Exp Wound Healing/
Ultrasonic Therapy/
Exp Ultrasonics/
Ultrasound therapy.mp.
Ultrasonic therapy.mp.
Exp Sonication/
Sonication.mp.
Low intensity pulsed ultrasound.mp.
Low intensity ultrasound.mp.
Exp Diathermy/
Cartilage, Articular/
Exp Cartilage/
Cartilage repair.mp.
6 or 1 or 18 or 3 or 16 or 17 or 2 or 5
11 or 7 or 9 or 12 or 15 or 14 or 8 or 10 or 13
20 and 19
A. Loyola-Sánchez et al. / Osteoarthritis and Cartilage 18 (2010) 1117e1126
1125
Appendix B. Summary of findings and quality of evidence assessment
Outcomes
Control group Ultrasound group mean with respect to
mean
the control group (CI)
Pain
3.95z
VAS from 0 (no pain) to 10
(intense pain)
Follow up: 2e8 weeks
Follow-up: 12 monthsx
3.95z
Physical function
LSI scale from 0 (better) to
26 (worst)
Follow-up: 2e8 weeks
Follow-up: 12 monthsx
LSI
Walking performance
Walking speed (m/min)
Follow-up: 2e8 weeks
Follow-up: 12 monthsx
Walking speed (m/min)
Cartilage repair
Follow-up: 8 weeks
Arthritis Severity Index
(smaller values mean
less severity)
5.65z
5.65z
82.47z
82.47z
4.9
Relative changek (CI)
Quality of
Comments
the evidence*,y
0.84 Lower (1.2e0.48 lower)
21% Lower
(30%, 12%)
Low
High risk of bias of the included
studies and considerable results’
heterogeneity.
1.22 Lower (1.62e0.82 lower)
30% Lower
(40%, 20%)
Low
Blinding issues and lack of
completeness in the follow-up
data (<85% of participants) detected.
High risk of bias of the included
studies and considerable results’
heterogeneity.
1.11{ Lower (2.45 lower to 0.24 higher) 19.68% Lower (89.32%
Mild severity (grade II) subgroup ¼
lower to 8% higher)
2.7{ lower (4.03e1.38 lower)
47% Lower
(71%, 24%)
2.07{ Lower (2.91e1.22 lower)
36% Lower
(51%, 21%)
4.64{ Higher (0.5 lower to 9.85 higher) 5% Higher (0.6% lower
Mild severity (grade II) subgroup ¼
to 12% higher)
11.17{ higher (14.32e8.07 higher)
13% Higher
(17%, 10%)
13% Higher
10.89{ Higher (7.07e14.71 higher)
(8%, 18%)
1.8 Lower (2.47e1.13 lower)
36% Lower
(50%, 23%)
Low
Low
Low
High risk of bias of the included
studies and considerable results’
heterogeneity.
Low
Low
High risk of bias and indirectness
of the outcome measure
(we consider bone scan as a
surrogate measurement of
cartilage repair).
We considered that the probability of having a “publication bias” in this review is low.
GRADE Working Group grades of evidence15. High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further
research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an
important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate.
z
The final score mean for the control groups was calculated by pooling the means and standard errors through a generic inverse-variance method.
x
All patients included inthese studies had
mild knee OA (Altman Grade II) and completed a home-exercise program after 2 months of treatment/sham US.
k
Mean difference
Relative change ð%Þ ¼ Final
100.
control mean
{
MD were calculated through a back transformation of the SMD using the SD reported in Villanueva et al.21 [Lequesne severity index ¼ 2.06] and Huang et al.22 [walking
speed 5.73].
*
y
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