Effects of deep heating to treat osteoarthritis pain : systematic review

BACKGROUND AND OBJECTIVES: Osteoarthritis is an inflammatory and degenerative joint disease, causing pain, musculoskeletal disorders and impact on functionality, daily life activities and quality of life. The action of physical agents by means of deep heating seems to be an alternative to treat such disease. This study aimed at verifying the effects of deep heating on osteoarthritis patients. CONTENTS: A systematic review was carried out in Medline, Scielo and LILACS databases as from keywords “Osteoarthritis”, “Induced Hyperthermia”, “Physiotherapy” and “Ultrasound”, and other keywords such as “Deep heat”, “Microwaves” and Short-waves”, in Portuguese, English and Spanish, in the period from January 2005 to January 2016, and 986 articles were found. Initially, 16 potentially relevant articles were selected for the study and, after a judicious qualitative analysis, nine complete articles meeting inclusion criteria were selected. CONCLUSION: Physical deep heating physical agents (ultrasound, short-waves diathermy and microwaves) were beneficial to manage pain and other variables in individuals with osteoarthritis in different levels of severity, especially in the long term. However, these effects are better observed when applied simultaneously with kinesiotherapy.


INTRODUCTION
Osteoarthritis (OA) is a degenerative inflammatory joint disease resulting from chondrocytes and synoviocytes-mediated responses, in addition to presenting higher serum and synovial inflammatory cytokine levels as compared to individuals not affected by the disease [1][2][3] .OA is multifactorial and involves changes in osteoarticular alignment causing joint instability 4 .This is the most common form of arthritis, being considered one of the ten more disabling diseases in developed countries and one of the most prevalent rheumatic diseases among the elderly [5][6][7] .Although able to affect any body region, it preferably affects joints supporting major weight loads and requiring frequent use, such as the knees 3 .Clinical results show increased joint volume due to synovitis caused by synovial effusion or thickening, pain at rest, morning stiffness, deformities, instabilities, movements limitation, Rev Dor.São Paulo, 2017 jan-mar;18 (1):79-84 REVIEW ARTICLE DOI 10.5935/1806-0013.20170016incapacity and muscle weakness [8][9][10] .Pain intensity may vary from no pain to individuals' immobilization and physical incapacity 2 .In this sense, physiotherapy attempts to attenuate OAinduced injuries and adverse effects of drugs 11 .In addition to kinesiotherapy, some physical resources, such as deep heating involving tools such as ultrasound (US), short-waves diathermia (SWD) and microwaves (MW), have been used with analgesic and anti-inflammatory action 12,13 , and have shown good results with regard to pain and functionality of OA patients 13 .This study aimed at reviewing in the literature sources documenting the effects of deep heating on pain management of OA individuals.

CONTENTS
A systematic search was carried out looking for articles published in journals indexed in Medline, Scielo and LILACS databases.Descriptors used for search were according to Health Science Descriptors, as from the primary descriptor "osteoarthritis" crossed with secondary descriptors such as "induced hyperthermia", "physiotherapy" and "ultrasound".In addition, the following keywords were used: "deep heating", "microwaves" and "short waves".A search was also carried out with variations of these words in Portuguese and Spanish.Included in the study were randomized clinical trials; studies carried out exclusively with humans; studies with pain evaluation as outcome, being or not followed by other variables, such as mobility, joint movement amplitude, muscle strength, gait velocity, functionality, incapacity and/or quality of life; studies found in full and available for free; studies in Portuguese, English or Spanish; studies published between January 2005 and December 2015.
Exclusion criteria were unfinished studies, studies involving individuals submitted to some surgical procedures due to OA or those not complying with mentioned criteria.Initially, titles and abstracts were identified and independently evaluated by a reviewer, to select those meeting eligibility criteria.Potentially relevant studies were kept for further analysis of the full text.Table 1 shows the strategy for studies search and selection.Among selected studies, four involved the use of SWD, four the use of US (continuous or pulsed) and one involved MW.Sample size of included studies has varied from 25 to 203 OA individuals, being that 100% had knee joint affected.Most samples were predominantly females and elderly.All studies had comparison between at least two groups.Table 2 shows sample characterization of included studies.Table 3 shows used evaluative tools and intervention protocols, as well as outcomes found in included studies.Selected studies suggest a limitation of the subject proposed by this review, since in a period of tem years, just nine studies have contemplated the effects of deep heating on pain management of OA patients, according to required criteria.It is possible to observe that scientific interest on the subject seems to be recent, because seven studies were carried out in the last five years.However, included studies have shown that heating tools are beneficial for pain management of OA patients.Although they do not stand out with regard to conventional kinesiotherapy, they may complement treatment when used simultaneously with physical exercises.Such measures were of major interest for managing OA-induced impacts and complications, especially with regard to pain.

DISCUSSION
OA is a disease causing more persistent musculoskeletal pain and may affect one out of five individuals, especially females and the elderly, causing chronic pain and incapacity especially on the knees 5,21 , which can be observed in selected studies, since in 100% of the reviewed content, samples had knee OA (levels from I to IV, with predominance of level III among studies), and in eight out of nine studies mean age was above 60 years, characterizing predominantly elderly samples.Interaction of factors such as disease worsening, pain, associated comorbidities, psychological and social factors, decreased aerobic work and lower limbs muscle weakness are determining factors for physical incapacity in OA individuals 15 .Functional impairment may negatively interfere with quality of life of these people, especially if they are old aged, females  and symptomatic.OA knee pain prevalence is high (32.2% for males and 58.0% for females) which increases in up to five times the risk of poorer lower limbs function 22,23 .
Lequesne and WOMAC indices are specific and reliable tools for OA evaluation 15 .It was observed that studies have used such protocols, being that five have used WOMAC index 10,13,[17][18][19] , three have used Lequesne index 15,17,20 and one has used the KOOS questionnaire, a scale of 11 questions to evaluate pain and functionality 16 .
In this sense, induced hyperthermia seems to be a strategy to manage OA pain since it is a conservative, low cost and noninvasive therapy 24 , which has led to the choice of this therapy as the target of our study.Four recruited studies 10,15,17,18 have used physical agents as aid or intervention to physical exercises (kinesiotherapy).It was observed that groups adopting deep heating as treatment strategy have improved pain and other evaluated variables, without the adverse effects of individuals submitted to intervention protocols.From these, one has compared the action of physical agents and their placebos and has observed improved pain and functionality, movement amplitude and functional independence, without statistically significant difference among groups 18 .However, intervention groups have presented lower drug ingestion, indicating higher impact on OA treatment.So, it is possible to observe the importance of conventional kinesiotherapy to decrease pain and improve other variables of knee OA individuals, being that physical agents may act as optimizers of the physiotherapeutic protocol.In addition, such resources decrease the use of drugs by OA patients and their possible adverse effects.
Studies suggest that US is beneficial to treat knee OA, because it is a safe strategy, decreases pain and improves physical functions, regardless of the mode (continuous or pulsed).Treatment duration should be adapted to specific needs of each individual 25 .Two studies 19,20 have compared the effects of deep heating (US) and conventional kinesiotherapy or even other nonthermal physical agents.Their results show benefits with regard to pain, functionality, movement amplitude, functional independence 19 and muscle strength 20 , without significant difference among approaches 19 .However, it is worth highlighting that such experiments were carried out just with US and in one of them US with kinesiotherapy has been superior in the distance travelled by the individual 19 .The other has shown just immediate US effects 20 , which is in disagreement with most authors, since they report deep heating as therapy with long term benefits.MW is a noninvasive method increasing in vivo temperature of internal tissues (±0.2°C), in a depth of 3 to 7cm 26 .Its properties are beneficial to treat OA, since joint heat stimulation increases chondrocytes metabolism and partially generates cartilaginous matrix 24 .
A study has compared MW therapy (deep heating) with the use of hot compresses (superficial heat) and has concluded that deep approach has significant effect on pain, stiffness, physical limitation and muscle strength in knee OA individuals 13 , in the long term, since such disease is chronic and generates severe pain.SWD aims at decreasing pain in the clinical practice 10 .SW therapy in low (power of 14.5W; duration 19 minutes; total energy 17kJ) or high doses (power of 14.5W; duration 38 minutes; total energy 33kJ) is beneficial for pain relief and increased muscle strength in the long term, especially in low doses 16 .It may decrease joint inflammatory process, being or not associated to drugs 14 .Two recruited studies 14,16 have evaluated the effects of deep heating exclusively with physical agents, observing positive effects on evaluated variables, such as those measured by WOMAC index, pain, joint movement amplitude or muscle strength.However, authors are not sure about its isolated efficacy.

CONCLUSION
Physical agents in the form of deep heating (US, SWD and MW) are beneficial to manage pain and other variables such as muscle strength, joint movement amplitude, functionality, stiffness, daily life activities and quality of life in individuals with different levels of OA, especially in the long term.However, it has to be highlighted that such effects are better observed when applied simultaneously with kinesiotherapy.

Table 1 .
Studies search and selectionStudies identified by electronic search in Medline (n=873), Scielo (n=98) and LILACS (n=15) databases Eligibility 16 complete evaluated articles 7 have not met inclusion criteria 3 had no outcome variables 2 were not available in full and for free 1 was unfinished 1 was a systematic review Inclusion 9 articles were included in the qualitative synthesis

Table 2 .
Sample characterization of recruited studies on deep heating effects for osteoarthritis pain management

Table 3 .
Evaluative tools, intervention protocols and outcomes of studies on the effect of deep heating on osteioarthritis pain management Continue...

Table 3 .
Evaluative tools, intervention protocols and outcomes of studies on the effect of deep heating on osteioarthritis pain manage-