Osteoarthritis (OA) is a degenerative joint disease also known as osteoarthrosis. It is caused by mechanical abnormalities arising due to degeneration of joints, which eventually affects the articular cartilage and subchondral bone [1]. Knee joint is the most often affected by OA [2]. It is associated with significant restrictions in mobility and a substantial financial burden [3]. According to the Global Burden of Disease study, Knee OA is one of the major health issues and ranked globally as the second leading cause in terms of disability [4]. 

Treatment of Knee OA is aimed at pain relief, reduction of disability [5,6] and improvement of muscle strength (7) and balance (8). The primary choice of treatment for Knee OA is conventional therapy which primarily includes  electrotherapeutic modalities and thermal agents for pain control [9], manual therapy [6] including mobilization, manipulation and myofascial release, exercises, and regular walk as recommended by Osteoarthritis Research Society International  [10].

Retro walking (6) is a fairly new type of treatment strategy for of the Knee OA. It encompasses reverse limb movement thus causing a backward propulsion and demonstrates different patterns of muscle activation as compared to forward walking [11]. The gait cycle of retro walking is the similar to forward walking, and goes through two phases ie stance phase (60%) and swing phase (40%). Retro walking initiates with toe strike and Knee in extension which further proceeds to flexion and again extension [1]. A study concluded that retro walking increases the rate of cadence, reduces stride length, and increases support time, hence enhancing functional range of motion at the knee [11].

Previous studies have examined the impact of retro walking along with conventional therapy among patients with Knee OA. Few studies compared retro walking with forward walking [12,13] whereas some compared it to balance training [14,15] in Knee OA patients. Studies examined the impact of RETROWALKING along with CT on hamstring flexibility and kinesiophobia among Knee OA population [16]. Another study evaluated the RETROWALKING effect when compared to quadriceps strengthening in Patello femoral pain syndrome population (kumar et al. 2020). But due to lack of complete availability of evidence on RETROWALKING with conventional therapy in Knee OA patients, one cannot comment on the results of individual studies, which leads to the knowledge gap in RETROWALKING adjunct with conventional therapy among Knee OA population.

Previous literature had examined the effects of retro walking and compared it clinically with forward walking in different conditions but did not conclude the beneficial effects over forward walking in Knee OA. This study aims to compare the beneficial effect of retro walking in addition to CT to conventional therapy alone in managing Knee OA symptoms. Up to the best of our knowledge, no meta-analysis had been conducted on retro walking and its beneficial effects in treating Knee OA. With the help of this meta-analysis, we can better understand the effectiveness of retro walking in unilateral Knee OA or bilateral Knee OA and will also be able to comment on the impact of duration, intensity, and frequency of retro walking on various outcomes.

Literature Research

A computer aided search was undertaken for articles published till October 2021 by two authors assessing: PubMed, PEDro, Scopus, Web of Science, Cochrane Library Central Register of Control Trails (CENTRAL). Standard search strategy as suggested by the Cochrane Collaboration Back Review Group [17] was used to identify Knee OA Randomised control trials (RCTs), followed by the search for the Retro walking, Backward walking, Osteoarthritic Knee, Degenerative joint disease, Reverse gait locomotion, Osteoarthrosis Knee, and OA Knee with (AND, OR and NOT) as text words and Medical Subject Headings (MeSH) terms.  The detailed search strategy is given in Appendix 1. A manual screening of titles, abstracts and full texts for eligibility was conducted by two independent reviewers. Any disagreement was sorted out by discussion.  Zotero was used as a reference manager software.

Eligibility Criteria

Type of Studies

 RCTs were included only if they were published as full papers in English language peer- reviewed, journal.

Population

RCTs that examined adults (>40 years), of either gender with unilateral or bilateral Knee OA, for more than 6 weeks were included in the study. Participants with any major co-morbidities (cardiovascular disease, cancer, neurological disorders, cognitive impairment, pregnancy, etc.) with Knee Osteoarthritis and Patellofemoral pain syndrome (PFPS) were excluded from this review.

Intervention

RCTs were included if they investigated retro walking along with conventional therapy only.

Comparison

Studies were included  if they compared  retro walking with conventional treatment to control group which  involves  treatment like pulsed SWD, hot fermentation, active SLR, strengthening exercises for Knee, hip abductors, and extensors, forward walking group or balance training.

Outcome Measures

Primary outcome measures were pain as assessed by (Visual Analogue scale (VAS), Numeric Pain Rating Scale (NPRS), the intermittent and constant osteoarthritis pain (ICAOP), and functional disability assessed by (WOMAC), the ibadan knee/ hip osteoarthritis outcome measure (IKHOAM), secondary measures were muscle strength assessed by (Dynamometer) and balance assessed by time up and go (TUG) test at baseline and as well at follow-ups.

Study Protocol

This review follows the guidelines for the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and was  registered in PROSPERO (CRD42021265940) [18,19].

Risk of Bias Assessment

 The studies were assessed for the quality appraisal by going through their methodology via Cochrane risk of bias (ROB) tool 1 (Higgins et al. 2011). This tool constitute of six components which were  named  as selection bias, performance bias, detection bias, attrition bias, reporting bias and other bias. For conducting the analysis, all six components marked each element as ‘Low’, ‘Unclear’ and ‘High’ risk of bias by ROB tool one performed by RevMan 5.4 software.

Data Extraction

Retrieved data was screened by two independent reviewers using a standardised form, based on study design, participants’ characteristics, intervention (type of activity, intensity, duration, frequency per week), outcomes, control group and follow-ups for evaluation.

Data Analysis

Data retrieved from pain intensity, functional disability, muscle strength and balance was further analysed by considering the studies mean score, standard deviation and sample size of both the groups at post intervention. The pooling of data for various outcomes was conducted by making the forest plots for each measure. Then standard mean difference (SMD) was measured when confidence interval was fixed at 95% (95% CI) and then a random effect model was opted with inverse variance for continuous variables for examining the presence of heterogeneity (I2). Lately pooled value of SMD was used to infer its clinical relevance. As per the Cochrane guidelines the term effect sizes is usually used to refer to versions of the standardised mean difference. SMD <0.2 is inferred as small effect, 0.5 moderate effect and > 0.8 large effect (Maher et al. 2013).

Quality of Evidence

The quality analysis was conducted by two independent reviewers. The evaluation of the study bias was done by using the PEDro scale (Physiotherapy Evidence-Based Database). PEDro scale has 11 questions on the trails methodology in which 10 are used for assessing quality. Each criteria is rated as either yes (score= 1) or no (score=0) to decrease the uncertainty in each response. Trials with a rating of at least 9 or 10 on the PEDro scale were rated as excellent quality, 8-6 were marked as good quality, 5-4 rated as fair and <4   considered poor quality.

Search Results

This review was conducted according to the PRISMA guidelines. The detailed process of searching is shown in (Figure 1). A total of 336 studies were screened for eligibility. After duplication removal, 200 studies were further removed due to their titles and abstracts, which led to 13 potentially eligible studies for full text reading according to the eligibility criteria. Studies were excluded because of these reasons: (a) one study was not in English; (b) two articles were not fulfilling the criteria for the control group; (c) two studies were not accessible; and (d) the results of two studies were not available. Finally, six studies were included in this systematic review, i.e., qualitative analysis. One article was further excluded from the meta-analysis due to a lack of data availability for comparisons, and hence, five studies were finally included in the qualitative analysis, i.e., the meta-analysis.

Figure1: Prisma Flowchart (2009).

Study Characteristics

After due evaluation six studies were finally included in the systematic review. This had a recruitment of 280 participants aged more than 40 years.  Five studies has recruited participants with unilateral Knee involvement whereas one had participants with bilateral Knee involvement (Table 1).

Table 1: Study and Participants characteristics.

M-Male, F-Female, MCRG-Medical Research Council grading, ROM- Range of motion.

CT- Conventional Therapy, RW- Retro Walking, BW- Backward Walking, BT- Balance Training, FW- Forward Walking.

Control Interventions

The studies which were included in this systematic review recorded largely similar content in the control groups [11,13-15,20] [Joshi]. Participants of these studies underwent conventional therapy which included treatment strategy like moist hot pack, short wave diathermy, electrical stimulation, strengthening exercises for lower extremities and stretching exercises of lower limbs.  

Quality of Evidence

This systematic review included six studies, three being considered of good quality, two of fair quality and  one of excellent quality as reported by PEDro quality assessment (Table 2). Five studies included in this meta-analysis and were of good quality.

Table 2: Quality Assessment (PEDro).

Contents of Management

Conventional Therapy Characteristics

Included studies had performed conventional therapy in both groups i.e. the interventional group as well as the control group (Table.1). The conventional therapy included but not limited to exercise like static quadriceps exercises, static hamstrings exercises, strengthening of the hip abductors and extensors, straight leg raises, terminal knee extension exercises, dynamic quadriceps exercises, ultrasound,  forward walking, pulsed shortwave for 20 min., short wave diathermy, hot packs, retrowalking (inclined).   

Performance of Retro Walking

Participants of the studies included in this systematic review (Table 1) performed retrowalks on flat surfaces in three studies, ground-level treadmills in one, and inclined treadmills and ground-level treadmills in one [15]. Two studies had a session for 3 days per week for 6 weeks for 10 minutes (13) and Joshi et al. (2014), one study each had a session for 3 days per week for 2 weeks for 10 minutes (14), 3 times per day for 3 weeks for 10 minutes, two weeks, and 10 minutes for 6 weeks [11, 20].

Outcome Analysis

Qualitative Analysis

All six studies had reported the mean ± standard deviation which was further used to calculate Cohen’s d effect size by the formula [Cohen’s d = (M2-M1)/SDpooled; SDpooled= √((SD12 + SD22) ⁄ 2)].Four studies reported large effect size of retro-walking with CT on pain among patients with Knee OA  were as (1.09, 0.93, 1.18, 2.27) two reported moderate effect size (0.42, 0.33). For disability five studies reported large effect size for retrowalking with CT in knee OA patients (0.99, 1.62, 1.19, 2.10, 2.06) and one reported moderate effect size (0.69). Quadriceps muscle strength and balance was assessed by two studies out of six and reported larger effect size with (0.90, 1.57) and (0.97, 1.21) respectively.

Quantitative Analysis

For performing a meta-analysis all outcome variables must be assessed by same parameter. Pain was assessed -two studies by NPRS, three studies by VAS and one study by ICAOP. Pain assessed by ICAOP was excluded at this level and pooling of data was conducted on NPRS and VAS which involves five studies. Functional disability was assessed by WOMAC in all five studies. Quadriceps muscle strength and balance was evaluated by only two studies and was assessed by dynamometer and TUG test respectively. So, pooling of data was performed according to the assessed parameter.

Effect on Pain 

Forest plots of two studies on the effect of retro walking reported significant improvements with  larger effects on pain intensity as assessed by  NPRS scale [SMD = - 0.97, 95%, CI (- 1.41, - 0.52), I2 = 0%, p < 0.0001]  (figure 2a) and three studies reported non-significant results although had larger effects on pain intensity as assessed by VAS scale [SMD = - 0.97, 95%, CI (- 2.09, 0.16), I2 = 88%, p= 0.09] (figure 2b).

                                                 (2a)Pain on NPRS scale.

                                        (2b) Pain on VAS scale.

Figure 2: Forest plot of pain intensity on (a) NPRS and (b)VAS.

Effect on Functional Disability

Forest plot of five studies (fig. 3) on retro walking reported significant findings which were largely effective on functional disability assessed by WOMAC scale [SMD = -1.54, 95%, CI (-2.03, -1.05), I2 = 58%, p < 0.00001].

Figure 3: Forest plot of functional disability on WOMAC scale.

Effect on Muscle strength

Forest plot of two studies (fig. 4) evaluated the effect of retro walking on muscle strength assessed by dynamometer  reported significant improvement in the control group and had no effect on Knee OA patients [SMD = 1.04, 95% CI (0.52, 1.55), I2 = 13%, p < 0.0001].

 Figure 4: Forest plot of muscle strength on dynamometer.

Effect on Balance

Effect on balance was also assessed by forest plot of two studies (fig. 5) which improved significantly with larger effect size [SMD = - 1.05, 95%, CI (- 1.45, - 0.65), I2 = 0%, p < 0.00001].

Figure 5: Forest plot of balance on TUG test.

Risk of bias

The risk of bias of eligible studies was illustrated by risk of bias graph (figure 6a). It was found that only one study documented the low risk of bias in total. One study documented higher bias in three components and reported as high risk of bias. One study documented higher bias in two components, lower bias in three components and reported as low risk of bias. Three studies documented unclear bias in one, three and five components for each study respectively and reported as unclear risk of bias. The most documented component among the all were selection bias, detection bias and performance bias in four studies. The unclear bias was reported in all studies under the component of other bias.

Figure 6: Risk of bias of included studies (a) risk of bias graph and (b) risk of bias summary.

Up to the best of our knowledge, this is the first systematic review to examine the effects of retro walking, specifically with conventional therapy, on pain, functional disability, quadriceps muscle strength, and balance in knee OA patients. This meta-analysis included five studies with 220 participants for primary outcomes on pain and disability, 88 participants for secondary outcomes on muscle strength, and 110 participants on balance. Primarily, this meta-analysis illustrated that retro-walking with conventional therapy is more effective in managing knee OA symptoms than conventional therapy alone.

Our meta-analysis featured different contents in the knee OA treatment programs. A variety of exercises can be used in clinical practices, with land-based closed-kinetic chain exercises including lower extremity strengthening exercises, aerobic exercises, and balance exercises recommended by various guidelines [21, 22]. Four studies directly compared the retro-walking effects of CT to those of CT alone [Joshi et al. 2019; 11, 14, 20]. One study compared retrowalking with CT and the other two groups, one with forward walking and one with CT alone [13]. One of the important factors of the exercise program is the ‘dosage’ of retrowalking, which includes duration and frequency, which varied significantly among the studies. Although the dosages administered were quite similar, uncertainty may still be present.

Previous studies reported that retro walking had a positive effect on the management of knee OA (Joshi et al. 2019) and low back pain [23]. Recently, a few studies reported immediate changes in pain and disability following walking in knee OA patients, but they were not sustained at follow-ups of six and 12 months [24]. Considerable heterogeneity was found to be high in pain, moderate in functional disability, and low in muscle strength. For the post-treatment effect of retrowalking in adjunct to CT on pain, function, quadriceps muscle strength, and balance, 3 of 5 studies (60%) were categorized as having a low risk of bias for selection bias, attrition bias, and reporting bias [13, 15, 20].

Our study reported that retrowalking in conjunction with CT is effective in reducing pain and disability, hence improving function in the retrowalking group. There was a significant improvement with a larger effect size in knee function and pain in the retrowalking group when performed with CT. It can be on account of multiple factors, like decreasing the patellofemoral joint compressive forces, thus reducing eccentric contraction of the quadriceps muscle and eventually lowering down the maximal vertical forces on the knee during retro walking [25,26]. A reduction in the adductor moment at the knee joint during the stance phase of gait is also reported, which leads to a decrease in the abnormal compressive forces on the medial side of the knee joint, hence improving the muscle activation pattern, which eventually leads to improved function [11,14].

Our study has further stated that retrowalking with CT leads to an improvement in muscle strength in patients with knee OA. Studies included in this meta-analysis demonstrate that retrowalking along with CT significantly improved quadriceps muscle strength and hip abductors and hip extensors strength [11,13,14]. Previous studies have shown that during retrowalking, the knee joint undergoes different loads from the initial toe strike to the heel strike compared with the initial heel strike of forward walking; there is activation of quadriceps muscle (primary power producers) with co-contraction of hamstring muscle, and ankle planter flexors act as shock absorbers (27, 28). This leads to... Another study by Swati et al. stated that retrowalking significantly improved quadriceps muscle strength by putting the shear forces anterior to the knee joint [29].

Retrowalking along with CT also demonstrated significant improvement in dynamic balance [13] (Joshi et al. 2019). It is stated that kinetic exercises facilitate other muscles as well, improve proprioception of the knee joint, and enhance joint stabilization, which helps in improving balance while performing weight-bearing activities [30]. A study by [31] demonstrated that retrowaling helps reduce peak planter pressure and enhance balance. Another study reported that patients with chronic KNEE OA showed improvement in function through increased concentric activity of quadriceps muscle and eccentric activity of hamstring muscle, which led to a reduction in extension lag and enhanced dynamic balance. [32].

A limited number of studies is one of the major limitations. This is because the research conducted on the topic is fairly limited, and our criteria of selection were also stringent to maintain homogeneity. The studies taken for quantitative analysis did not measure the ROM of the knee joint as an outcome measure, because of which we could not comment on it.

In this review, the effectiveness of retro-walking was systematically reviewed and quantified. The result of the study reported that retro walking is effective, along with CT, in managing patients with knee OA. The results were significant and had moderate evidence. It concluded that 10 minutes of retro walking three times a week for six weeks, along with CT, will be effective in reducing pain and disability, improving function and muscle strength, and enhancing balance. It further has other beneficial effects on the cardiopulmonary system.

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