Therapeutic modalities and postural balance of patients with knee osteoarthritis: systematic review

Objective: The objective of this review was to evaluate the evidence of the influence of therapeutic modalities on postural balance in patients with knee osteoarthritis (OA). Methods: A search for published papers on therapeutic modalities was conducted using the Pubmed, Medline, Lilacs and SciELO databases. The keywords “knee” and “balance” in combination with “osteoarthritis” were used as the search strategy. Randomized controlled clinical trials published in the last 10 years in either English or Portuguese were selected. The PEDro scale was applied to assess the quality of the selected clinical trials. Results: A total of 46 studies of patients with knee OA were found, of which seven were analyzed in full and 39 were excluded because they did not * AS: PhD, e-mail: silvadressa@gmail.com MTM: PhD, e-mail: tmello@demello.net.br SAGJ: specialist, e-mail: sagjr.fisio@gmail.com SSQ: PhD student, e-mail: sqsandra@terra.com.br ST: PhD, e-mail: sergio.tufik@unifesp.br SMM: PhD, e-mail: stela@ufscar.br


Introduction
The World Health Organization indicates that knee osteoarthritis (OA) is likely to become the leading cause of disability worldwide, and it is currently the fourth-highest cause in women and the eighth in men (1).Biochemical changes and biomechanical stress in the subchondral bone, articular cartilage and synovial membrane are important factors in the pathogenesis of OA (2).OA is characterized by pain, swelling, proprioceptive deficit, circulatory impairment, muscle stiffness and weakness (3), resulting in functional disability, reduced quality of life (4) and postural balance deficit, all indicators of functional impairment and the risk of falls (5)(6)(7).
Postural balance is a complex function that requires interaction between the visual, vestibular, somatosensory and neuromuscular systems (8).Proprioception is important for postural balance given the activation of reflex responses that protect and stabilize the knee's proprioceptive acuity.A proprioceptive deficit occurs in knee OA due to a significant decrease of mechanoreceptors in the ligaments, as well as in quadriceps muscle strength (9).
In the last 10 years there has been growing interest in the study of the most appropriate therapeutic modalities for the treatment of OA.The review by Roos and Juhl (10) showed that in 17 analyzed studies on non-pharmacological treatments for OA, physical exercise, education and weight loss were the most effective treatments.The systematic review by Silva et al. (11) showed that aerobic and resistance exercise improved postural balance in women with knee OA, and the studies that reported those findings were of high methodological quality and had strong scientific evidence.Physical exercise is a non-pharmacological intervention for knee OA recommended by the American College of Rheumatology (ACR) and the European League Against Rheumatism (12,13).This intervention aims to prevent muscle atrophy, increase muscle strength and resistance and maintain the range of motion of the knee joint to provide greater functional independence (14).However, other therapeutic resources (electrotherapy, hydrotherapy, manual therapy, massage) have also been applied for the treatment of patients with knee OA to reduce the risk of falls and pain and to improve physical function, functional capacity, the strength of knee extensors and hip abductors, range of motion, quality of life and postural balance (14)(15)(16)(17).
Given that postural balance is one of the factors responsible for falls and functional limitations in patients with OA, the objective of this review is to assess the clinical and scientific evidence of the influence of therapeutic modalities on postural balance in patients with knee OA.

Databases
Searches were conducted on the PubMed, Medline, Lilacs and SciELO electronic databases to identify publications on the therapeutic modalities proposed to improve postural balance in patients with knee OA.

Search strategy
The search strategy used the keywords "knee", "balance", "osteoarthritis" and "treatment".The bibliographic survey was restricted to publications of randomized controlled clinical trials in the last 10 years (May 2003-April 2013) in English and Portuguese.

Study selection
Only randomized controlled clinical trials that used therapeutic modalities as a form of non-pharmacological treatment in patients with knee OA to improve postural balance were considered.Studies were selected using the following inclusion criteria: patients with a clinical diagnosis of OA; study of the relationship between postural balance and OA; random sampling of patients; and comparison between intervention groups and/or between intervention and control groups for some physiotherapeutic treatment modality.Studies that used pharmacological treatments or surgery were excluded.
The articles were analyzed in their entirety using a structured approach.The following items were taken into account: author/year, sample, study design, evaluated outcomes, intervention, tools and effects found.

Assessment of methodological quality
The PEDro scale (18) was used to evaluate the methodological quality of the included studies.This scale, based on the Delphi list (19) and translated into Portuguese in 2009 (18), consists of 11 items that evaluate the methodological quality of randomized clinical trials.Studies with a score greater than or equal to 5 (50%) were considered to have high methodological quality (20).The studies were independently analyzed by two reviewers.In cases where there were differences of opinion, discrepancies were reviewed and discussed with a third reviewer to reach a consensus on the score.A critical review of the contents was performed due to the small number of articles.

Evaluation of study quality
The seven articles were analyzed using the PEDro scale (18) (Table 1).Six of the articles were considered to be of high quality on the PEDro scale because they achieved a score greater than 5.Those  14) was considered to be of low methodological quality.

General data of the selected articles
We selected some information to represent the articles included in this review, summarizing them according to the following aspects: author/year, sample, evaluated outcomes, study design, interventions, tools and effects found (Table 2).Based on a critical analysis of the clinical trials selected, the therapeutic modalities used for the treatment of postural balance were hydrotherapy (15)(16)(17), massage (55), joint mobilization (55), land-based exercise (15,55), footwear (56), infrared, ultrasound and interferential current (14).However, laser therapy did not lead to any improvement in patients with knee OA (57).
The samples in the seven studies ranged from 39 to 140 individuals.In six studies the sample was composed of both genders (14,17,(55)(56)(57), whereas the treatment group of one study comprised only women.Most studies used the criteria proposed by ACR to perform the clinical diagnosis of OA.All studies were experimental, with pre and post-intervention evaluations.Long-term evaluation (follow-up) occurred in five studies (16,17,(55)(56)(57).Three studies found that interventions significantly improved balance (14,16,55).Note: *Since the score for the fi rst item is on external validity, it is not considered the in the fi nal score (Moseley et al. (20)).Question 1: The eligibility criteria were specifi ed; Question 2: The subjects were randomly distributed per group; Question 3: The distribution of the subjects was blind; Question 4: Initially, the groups were similar with respect to prognostic indicators more important; Question 5: All subjects participated in a blind fashion in study; Question 6: All physical therapists who administered the therapy did so in a blinded fashion; Question 7: All evaluators who measured at least one key outcome, they did it blindly; Question 8: Measurements of at least one key outcome was obtained by more than 85% of the subjects initially distributed by the groups; Question 9: All subjects from which they presented measurements of results received the treatment or the condition of control according to distribution or, became an analysis of the data for at least one of the key outcomes of "intention to treat"; Question 10: The results of statistical comparisons between groups were described for at least one key outcome; Question 11: The study presents both measures of accuracy as measures of variability for at least one key outcome.

Discussion
The analysis of the selected studies showed that a variety of therapeutic modalities are used in physiotherapeutic clinical practice to improve postural balance in patients with knee OA.Of the seven studies evaluated, six studies had a PEDro score considered to represent high methodological quality, so their intervention methods can be used in clinical practice.These interventions are electrotherapy (14), hydrotherapy (15)(16)(17), massage (55), joint mobilization (55), physical exercise (16,55) and footwear (56).Three studies reported an improvement in balance in patients with knee OA: Tok et al. (14), Bennel et al. (55) and Lund et al. (16).
The methodological designs of the studies were appropriately described and developed, which enables clinical reproducibility.Moreover, the use of validated tools and the reliability of application increased the consistency of their results and the outcomes evaluated.In most of the studies, the diagnosis of OA was based on the ACR criteria, consisting of clinical and radiographic evaluation according to the K ellgren and Lawrence scale (16,55,57).
The representativeness of the sample can be considered adequate, with an average of 20 subjects per group, and only one study used 50 subjects per group.We selected studies that involved OA patients of both genders, but one study was conducted only with women (16).The percentage of women was higher in all studies, which is consistent with epidemiological data that show that OA is more prevalent in females due to hormonal effects (58).
The therapeutic modalities that stood out in the literature were land-based exercise and hydrotherapy, both aiming to strengthen the muscles of the lower limbs and improve balance (14,16,17,55).Improvement of hip abductor strength helps to stabilize the contralateral hip during gait due to the effect of the center of mass, which can reduce the adduction moment (compressive force), decrease pain and improve the muscle strength and physical function (59).Because knee extensor strength is related to anteroposterior oscillation, Pua et al. (60) designed different central nervous system (CNS) strategies to improve physical function by using the remaining receptors in patients with sensory and motor deficiencies.Furthermore, Slemenda et al. (61) and O'Reilly et al. (62) reported that strengthening the quadriceps and hip abductors leads to reduction in pain and stiffness and improves physical function, thereby contributing to improvement of postural oscillation, as highlighted by Hunt et al. (63).Those findings concur with Bennel et al. (55), who studied the risk of falls in elderly people with and without OA and found that decreased use of assistive walking devices led to reduced risk of falls in the elderly study group, in addition to a self-reported improvement in balance.
The results of the studies that used land-based exercises (16,55), hydrotherapy (15)(16)(17), electrotherapy (14), manual therapy (55) and footwear (56) showed positive effects on some evaluated outcomes, such as pain, stiffness, risk of falls and physical function.However, regarding the outcome of balance, Tok et al. ( 14) found a significant improvement, while Hinman et al. (15) found no difference in balance between groups.In contrast, Hale et al. (17) found a significant improvement in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, risk of falls, impact of illness and fear of falling and a subjective improvement in self-reported balance, in a study in which the experimental group performed strengthening exercises associated with balance for 4 weeks, once per week.These results demonstrate the effectiveness of strength and balance training in patients with knee OA.
The therapeutic approach used in most studies was hydrotherapy, which produced better results than land-based exercises, manual techniques, use of adapted footwear and electrotherapy.Lund et al. ( 16) compared water-based and land-based strength and balance exercises in patients with knee OA for 8 weeks, twice a week, and found differences in levels of pain, physical function and quality of life in both groups immediately after the exercise protocol.Nonetheless, the authors reported that hydrotherapy brought more benefits to patients with knee OA than those who performed the landbased protocol, which they attributed to the physical nature of hydrotherapy, which reduces overload on the joints and encourages greater participation compared with land-based exercise.
A recent study by Tok et al. (14), comparing a group who used electrotherapy combined with isometric exercises and a group using only electrotherapy for two weeks, three times a week, found improved balance, pain during activity and stiffness in both groups, but did not observe improvements in pain or function in either study group.Different results were found by Hsieh et al. (57), who did not observe any improvement in balance, pain, function, stiffness or functional capacity from electrotherapy.
Another therapeutic resource used for patients with knee OA is therapeutic footwear.Nigg et al. (56) found improvements in pain and static standing balance using such footwear, but no improvement was observed in these two parameters during walking.
It would appear that any conclusion as to the optimal duration and frequency of intervention, the tools used and the adverse effects would be unwarranted because the intervention period in these evaluated studies ranged from 2 weeks to 12 months, the frequency varied from 1 to 5 times a week and the tools used to assess pain and balance varied.
The present review found that various therapeutic modalities are used for the rehabilitation of patients with OA.Among other goals, those treatments aimed to improve balance.However, their results varied regarding the benefits of the therapeutic modalities, the treatment duration and the frequency of sessions.These inconsistencies are the main limiting factor of the studies analyzed.However, these treatment modalities are widely used in clinical practice by physiotherapists.Given that the studies included in this systematic review are of high methodological quality, it can be concluded that the therapeutic resources proposed and used in rehabilitation programs should be considered in clinical practice because of their positive effects on balance and the other benefits they offer for patients with knee OA.

Table 1 -
Methodological classification assessed by PEDro scale

Table 2 -
General data of the selected articles

Table 2 -
General data of the selected articles

Table 2 -
General data of the selected articles Note: ACR = American College of Rheumatology; IG = intervention group; CG = control group; US = ultrasound; WOMAC = Western Ontario and McMaster Universities Osteoarthritis Index; VAS = visual analogue scale; XR = X-ray; AQoL = Assessment of Quality of Life index; KOOS = Knee Injury and Osteoarthritis Outcome Score.