Literature DB >> 33771204

Foot characteristics and mechanics in individuals with knee osteoarthritis: systematic review and meta-analysis.

Rania N Almeheyawi1,2, Alessio Bricca3,4, Jody L Riskowski5, Ruth Barn5,6, Martijn Steultjens5.   

Abstract

BACKGROUND: Foot characteristics and mechanics are hypothesized to affect aetiology of several lower extremity musculoskeletal conditions, including knee osteoarthritis (KOA). The purpose of this systematic review was to identify the foot characteristics and mechanics of individuals with KOA.
METHODS: Five databases were searched to identify relevant studies on foot characteristics and mechanics in people with KOA. Meta-analyses were performed where common measures were found across included studies. Included studies were evaluated for data reporting quality using the STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) checklist.
RESULTS: Thirty-nine studies were included in this systematic review. Two studies reported participants with KOA had statistically significantly (P < 0.05) more pronated foot postures than those without. Meta-analyses for foot progression angle (FPA) and peak rearfoot eversion angle found no difference between those with and without KOA (FPA mean difference:-1.50 [95% confidence interval - 4.20-1.21]; peak rearfoot eversion mean difference: 0.71 [1.55-2.97]).
CONCLUSION: A more pronated foot posture was noticed in those with KOA. However, it was not possible to establish a relationship between other foot characteristics or mechanics in people with KOA due to heterogeneity between the included study and limited number of studies with similar measurements. There is need for identifying common measurement techniques and reporting metrics when studying the foot in those with KOA.

Entities:  

Keywords:  Foot characteristics; Foot mechanics; Foot posture; Knee osteoarthritis

Year:  2021        PMID： 33771204      PMCID： PMC8004391          DOI： 10.1186/s13047-021-00462-y

Source DB:  PubMed          Journal:  J Foot Ankle Res        ISSN： 1757-1146            Impact factor:   2.303


Background

Knee osteoarthritis (KOA) is a degenerative progressive joint disease characterized by chronic joint pain and stiffness, leading to the limitation of daily living activities and physical function [1-3]. KOA is estimated to affect 18% of adults over 45 years of age [4] and is a leading cause of functional disability [5]. Aetiology of KOA includes traumatic injury [6], genetics [7], obesity [8], and poor joint biomechanics, with poor biomechanics a likely cause of primary progressive KOA [9]. Given the important role of the foot in receiving and distributing forces during walking, foot characteristics and mechanics, including static foot posture and dynamic foot function, may significantly contribute to musculoskeletal conditions of the lower limb [10]. However, the specific associations between foot characteristics and mechanics and KOA [11] have not yet been investigated. Therefore, the primary purpose of this systematic review is to evaluate foot characteristics and mechanics in individuals with KOA and compare them to people without KOA. There were two aims of the study: 1) to provide an overview of the foot characteristics and mechanics that have been evaluated in the extant literature in people with KOA, and 2) to investigate whether foot characteristics and mechanics vary between people with and without KOA.

Methods

This systematic review was submitted and approved through the PROSPERO registry of systematic reviews (CRD42015023946), and it followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [12].

Search strategy and study selection

Five electronic databases were searched: MEDLINE, Web of Science, Current Nursing and Allied Health literature (CINAHL), Physical Education Index, and Physiotherapy Evidence Database (PEDro). The searches were conducted in May 2020, with no restrictions by language, year of publication or study design. The Medical Subject Headings (MeSH) search terms adopted were “foot” and “knee osteoarthritis” using the Boolean operator AND. Studies were evaluated for relevance by applying specific inclusion and exclusion criteria (see Table 1). At the title stage, one reviewer (RA) eliminated publications, with a second reviewer (JLR) verifying the results. At the abstract stage, two reviewers (RA and JLR) independently reviewed abstracts for inclusion, and reference lists of prior KOA review articles were searched to include relevant studies. For manuscripts included following the abstract stage, full-text articles were obtained and independently reviewed for inclusion by reviewers (RA and JLR).
Table 1

Study inclusion criteria

CriteriaDescription
Study designStudies with cross-sectional data or intervention data if the baseline data were available.
Study participantsStudies were included if they recruited participants with KOA; where a control group was included, they had to be otherwise healthy and free from KOA.
Study outcome domainsStudies had to include objective measures of foot mechanics or foot characteristics to be eligible. Objective measures of foot mechanics or characteristics included, but were not limited to, foot progression angle, rearfoot eversion, Foot Posture Index and muscle activity. Further data could be obtained from participants in a barefoot or shod condition, provided the shod condition was without any foot orthoses.
Study resultsResults had to provide quantitative data presented as mean and standard deviation or median and interquartile range clearly indicating if it was collected in a barefoot or shod condition.
Study inclusion criteria

Data extraction

Data from the included manuscripts were extracted (RA) and checked (JLR). For each manuscript, the data extracted was as follows: the country, year of study, sample size, age, gender, body mass index (BMI), diagnostic and inclusion criteria for participants, footwear condition (i.e., barefoot, shod), foot-related outcome measures, and foot-related outcome data. For intervention studies, the baseline data were extracted for analysis. The level of agreement was determined using weighted kappa statistics for inclusion/exclusion.

Assessment of study quality

Study quality of the information reported in the included manuscripts were based on the STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) checklist criteria [13], which is a reliable quality rating tool for observational studies [14]. Each criterion was scored “Yes”, “No”, or not applicable (NA). A criterion received a “Yes” if it was applicable and met in the study, “No” if it was applicable but not met, and “NA” if it was not relevant to the study. The number of “Yes” criterion divided by the number of applicable criterions per manuscript yielded a percentage of the applicable STROBE criteria. Articles were dichotomized by their rating scores, with ≥65% regarded as high-quality studies, and < 65% deemed low-quality. The 65% cut-off point is similar to work conducted by Andrews et al. [15] in dichotomizing high and low quality studies. The 65% cut-off point is lower than the recommended cut-off point of 80% [16] as the reported foot characteristics and mechanics were often not the study’s primary outcome measure.

Data analysis

Meta-analyses were performed to estimate the differences between the foot characteristics of participants, with and without KOA, for foot progression angle and peak rearfoot eversion angle. Mean differences (MD) with 95% confidence intervals (95% CI) were calculated. The standard deviation (SD) was extracted or estimated from the standard error of the mean, the 95% CI, P value, or other methods as recommended by the Cochrane Collaboration [17]. Meta-analyses were performed in STATA (16.1) using the ‘meta’ command. The effect sizes of the meta-analyses are reported in degrees.

Results

Following the implementation of the outlined search strategy, MeSH search yielded 12,736 articles, of which 1837 were duplicate publications (Fig. 1), leaving 10,899 articles for the title stage. Screening at the title stage excluded 10,696 of these articles, leaving 203 articles eligible for the abstract stage. At the abstract stage, 43 titles were added from reference lists and other sources, making a total of 246 articles eligible for the abstract stage, and 136 articles were excluded. A total of 110 articles were then reviewed at the full-text stage and 72 articles were excluded, while one article matching the eligibility criteria was added in the full-text stage from other sources, leaving 39 articles found to have evaluated foot characteristics and/or mechanics in individuals with KOA. Kappa agreement values between the reviewers were 0.79, 0.79, and 0.73 for the title, abstract, and full-text stage, respectively.
Fig. 1

PRISMA flow chart diagram of the systematic review process

PRISMA flow chart diagram of the systematic review process

Study characteristics

The included studies were published between 2006 and 2020 (Table 2). There were 25 observational studies [18–22, 25, 27, 29, 32, 33, 37–41, 43, 45–52, 56] and 14 intervention studies [23, 24, 26, 28, 30, 31, 34–36, 42, 44, 53–55]. The 39 studies included a total of 2260 participants. In the KOA groups, the sample sizes ranged from eight [37] to 123 [42] participants, with a mean study sample size of 57 participants. Twenty-two studies included a control population [18–22, 25, 27, 29, 31, 37–41, 45–47, 49–51, 54, 56], with sample sizes ranging from ten [37] to 80 [18] participants, and a mean control sample size of 17 participants. Thirty-two studies included both genders [18, 19, 21–24, 26–30, 33–35, 37–53, 55], while four studies were limited to women [20, 32, 54, 56]. Three studies failed to report gender characteristics [25, 31, 36].
Table 2

Study and participants’ characteristics (data reported as mean ± standard deviation)

No.AuthorYear publishedCountrySubjects subgroupsNo. of subjects (Men/ Women)Age (years)BMI (kg/m2)
1Abourazzak et al. [18]2014MoroccoKOA100 (21/79)59.68 ± 7.6430.89 ± 4.94
Healthy control80 (20/60)48.66 ± 9.3028.00 ± 3.81
2Al-Zahrani and Bakheit [19]2002UKKOA58 (14/44)71 ± 8.40NR
Healthy control25 (10/15)69 ± 7.29NR
3Anan et al. [20]2015JapanKOA20 (0/20)69 ± 4.424.4 ± 2.8
Healthy control17 (0/17)69.8 ± 4.321.3 ± 2.7
4Arnold et al. [21]2014AustraliaKOA15 (7/8)67.0 ± 8.930.7 ± 6.2
Healthy control15 (7/8)68.2 ± 9.725.5 ± 5.3
5Bechard et al. [22]2012CanadaKOA20 (8/12)55 ± 828.9 ± 3.0
Healthy control20 (12/8)51 ± 825.9 ± 3.2
6Booij et al. [23]2020NetherlandsMedial KOA only30 (14/16)62.7 ± 5.925.5 ± 2.7
7Butler et al. [24]2009USAKOA only30 (13/17)63.1 ± 6.833.8 ± 6.9
8Butler et al. [25]2011USAMedial KOA15 (NR/NR)66.2 ± 7.832.2 ± 7.9
Lateral KOA15 (NR/NR)65.3 ± 6.430.4 ± 7.5
Healthy control15 (NR/NR)56.3 ± 10.727.8 ± 5.7
9Chapman et al. [26]2015UKKOA only70 (43/27)60.3 ± 9.630.5 ± ± 4.9
10Chang et al. [27]2007USAKOA only56 (23/33)66.6 ± 8.629.0 ± 4.2
11Charlton et al. [28]2018CanadaMedial KOA only16 (6/10)67.4 ± 9.324.6 ± 15.1
12Elbaz et al. [29]2017IsraelKOA63 (22/41)64.2 ± 8.1NR
Healthy control30 (21/9)67.9 ± 8.9NR
13Erhart-Hledik et al. [30]2017CanadaMedial KOA only10 (9/1)65.3 ± 9.827.8 ± 3.0
14Gardner et al. [31]2015USAKOA13 (NR/NR)56.8 ± 5.226.6 ± 3.6
Healthy control11 (NR/NR)50.0 ± 9.725.9 ± 5.4
15Guler et al. [32]2009TurkeyKOA only115 (0/115)62.11 ± 8.7232.91 ± 4.14
16Guo et al. [33]2007USAKOA only10 (6/4)64 ± 829.0 ± 5.6
17Hinman et al. [34]2012AustraliaKOA only73 (28/45)63.3 ± 8.427.7 ± 3.6
18Hinman et al., [35]2016AustraliaKOA only81 (39/42)63.3 ± 7.929.7 ± 3.7
19Khan et al. [36]2019MalaysiaKOA only20 (NR)61.5 ± 8.63NR
20Krackow et al. [37]2011USAKOA8 (4/4)59 ± 11.3433.84 ± 6.90
Healthy control10 (5/5)62.50 ± 4.1728.44 ± 4.23
21Levinger et al. [38]2010AustraliaKOA32 (16/16)65.84 ± 7.5729.97 ± 5.26
Healthy control28 (13/15)65.22 ± 11.4125.56 ± 3.95
22Levinger et al. [39]2012aAustraliaKOA50 (27/23)66.4 ± 7.629.6 ± 5.1
Healthy control28 (13/15)65.1 ± 11.225.7 ± 3.9
23Levinger et al. [40]2012bAustraliaKOA32 (16/16)65.8 ± 7.529.9 ± 5.2
Healthy control28 (13/15)65.2 ± 11.425.5 ± 3.9
24Lidtke et al. [41]2010USAKOA25 (6/19)60.2 ± 10.629.2 ± 4.6
Healthy control25 (12/13)58.5 ± 9.126.6 ± 3.3
25Nigg et al. [42]2006CanadaKOA only123 (56/67)57.4 ± 2.229.5 ± 1.6
26Ohi et al. [43]2017JapanKOA only88 (30/58)74.8 ± 7.5824.3 ± 3.54
27Paquette et al. [44]2015USAKOA13 (6/7)62.5 ± 928.3 ± 6.5
Healthy control13 (5/8)58.9 ± 8.323.9 ± 2.6
28Park et al. [45]2016CanadaKOA24 (7/17)54 ± 7.326.1 ± 3.4
Healthy control24 (8/16)52.4 ± 10.624.7 ± 3.2
29Reilly et al. [46]2006UKKOA60 (25/35)67.80 ± 8.09NR
Healthy control60 (28/32)64.92 ± 12.18NR
30Reilly et al. [47]2009UKMedial KOA20 (9/11)63 ± 8.7NR
Healthy control20 (4/16)56 ± 7.3NR
31Rutherford et al. [48]2008CanadaKOA asymptomatic50 (32/18)53 ± 1026 ± 4
KOA mild to moderate46 (20/26)60 ± 931 ± 5
KOA severe44 (20/24)67 ± 832 ± 5
32Rutherford et al. [49]2010CanadaKOA17 (10/7)56 ± 8.829.8 ± 6.5
Healthy control20 (7/13)46.5 ± 7.025.9 ± 4.8
33Saito et al. [50]2013JapanKOA50 (10/40)75NR
Elderly control44 (8/36)74NR
34Shakoor et al. [51]2008USAKOA27 (5/22)54 ± 1237.8 ± 8.6
Healthy control14 (5/9)47 ± 1429.8 ± 5.6
35Simic et al. [52]2013AustraliaKOA only22 (9/13)69.7 ± 9.028.4 ± 4.8
36Tan et al. [53]2020AustraliaKOA only21 (7/14)58 ± 827.0 ± 4.8
37Trombini-Souza et al. [54]2011BrazilKOA21 (0/21)6 5 ± 5NR
Healthy control24 (0/24)65 ± 4NR
38Van Tunen et al. [55]2018AustraliaMedial KOA only21 (9/12)63.4 ± 7.029.8 ± 3.6
39Zhang et al. [56]2017ChinaKOA23 (0/23)64.2 ± 6.623.3 ± 1.9
Healthy control23 (0/23)62.1 ± 2.422.6 ± 1.8

Abbreviations: KOA knee osteoarthritis, BMI Body Mass Index, NR not reported

Study and participants’ characteristics (data reported as mean ± standard deviation) Abbreviations: KOA knee osteoarthritis, BMI Body Mass Index, NR not reported

Participant characteristics

Participant age

The mean age of the study participants was 61.5 years, ranging from 47 years [51] to 74 years [50] in the control groups, and 53 years [48] to 75 years [50] in KOA groups (Table 2).

Body mass index

In KOA groups, four studies reported a BMI mean of 18.5–24.9 kg/m2 (normal weight) [20, 28, 43, 56]; 19 studies reported participants’ mean BMI of 25–29.9 kg/m2 (overweight) [22, 23, 27, 30, 31, 33–35, 38–42, 44, 45, 49, 52, 53, 55]; eight studies reported the mean BMI of 30–34.9 kg/m2 (grade I obese) [18, 21, 24–26, 32, 37, 48]; and one study reported a mean BMI ≥35 kg/m2 [51] (grade II obese). Seven studies did not report the mean BMI of their participants [19, 29, 36, 46, 47, 50, 54]. In control groups, four studies reported a BMI mean of 18.5–24.9 kg/m2 (normal weight) [20, 44, 45, 56]; 12 studies reported participants’ mean BMI of 25–29.9 kg/m2 (overweight) [18, 21, 22, 25, 31, 37–41, 48, 51] and six studies did not report the mean BMI of their control participants [19, 29, 46, 47, 50, 54].

Participant eligibility criteria

The included studies evaluated foot characteristics and mechanics in those with KOA, yet four studies did not report the KOA diagnostic method used [19, 46, 47, 53]. Thirty-five studies diagnosed KOA severity using the Kellgren-Lawrence (KL) scoring system [18, 20–45, 48–52, 54–56]. Included studies were assessed for their reporting quality using the STROBE checklist criteria (Table 3). The percentages of STROBE criterion met ranged from 42% [19] to 84% [43]. Ten studies were categorized as high-quality studies [21, 25, 27, 35, 42–44, 47, 53, 55], while 29 studies scored less than 65% in relation to the applicable criteria on the STROBE checklist, and were therefore classified as low-quality studies [18–20, 22–24, 26, 28–34, 36–41, 45, 46, 48, 49, 51, 52, 54, 56].
Table 3

Assessment of study quality using the STROBE checklist

Item NumberRecommendationsAbourazzak et al., 2014 [18]Al-zahrani amd Bakheit, 2002 [19]Anan et al., 2015 [20]Arnold et al., 2014 [21]Bechard et al., 2012 [22]Booij et al., 2020 [23]Butler et al., 2009 [24]Butler et al., 2011 [25]Charlton et al. 2018 [28]Chang et al., 2007 [27]Chapman et al., 2015 [26]Elbaz et al., 2017 [29]Erhart-Hledik et al., 2017 [30]Gardner et al., 2015 [31]Guler et al., 2009 [32]Guo et al., 2007 [33]Hinman et al., 2012 [34]Hinman et al., 2016 [35]Khan et al., 2019 [36]Krackow et al., 2011 [37]
1aAbstract: study’s design in the title or the abstractNoNoNoYesNoNoNoYesNoNoNoNoNoNoNoNoNoYesYesNo
1bAbstract: balanced summaryYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
2Introduction: background and rationaleYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
3Introduction: objectives, including hypothesesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
4Methods: study design early in the paperYesNoNoYesNoYesNoYesNoNoNoYesYesNoNoNoNoYesYesNo
5Methods: setting, locations, and relevant dates, recruitment, data collectionNoYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
6aMethods: cohort eligibility criteria, follow-upNANANANANANANANANAYesNANANANANANANANANANA
6aMethods: case-control: eligibility criteria of cases and controlsYesYesYesNANANANANANANANANANANANANANANANANA
6aMethods: cross-sectional: eligibility criteria and methods of participants’ selectionNANAYesYesYesYesYesYesYesNAYesYesYesYesYesYesYesYesYesYes
6bMethods: cohort: number of exposed and unexposedNANANANANANANANANANANANANANANANANAYesNANA
6bMethods: case-control: matching criteriaYesYesYesNAYesNANANANANANAYesNAYesNANANANANANA
7Methods: define outcomes, exposures, diagnostic criteriaYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
8Methods: sources of data, methods of assessment (measurement)YesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
9Methods: how bias addressedNoNoNoNoNoNoNoNoNoYesYesNoNoNoNoNoNoYesYesNo
10Methods: power analysisNoNoNoNoYesNoYesYesNoNoNoNoYesNoNoNoNoNoYesNo
11Methods: quantitative variables addressedYesNoYesYesYesYesNoYesYesYesYesYesYesYesYesYesYesYesYesYes
12aMethods: statistical methodsYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
12bMethods: statistical subgroups and interactionsYesYesYesYesYesYesNAYesYesYesYesYesYesYesNoYesNAYesYesYes
12cMethods: how missing data addressedNANoNANoNoNoNANoNoNoNoNoNoNoNoNoNoYesNoNo
12dMethods: cohort: how loss to follow-up addressedNANANANANANANANANANANANANANANANANANANANA
12dMethods: case-control: how matching of cases and controls addressedNoNoNoNANANANANANANANANANANANANANAYesNANA
12dMethods: cross-sectional: sampling strategyNANANAYesNoNoYesYesNoNAYesYesNoNoNoYesNoNANoNo
12eMethods: sensitivity analysesNoNoNoYesNoYesNoYesNoNoNoNoNoNoNoNoNoYesNoNo
13aResults: numbers of individuals at each stageYesNoYesYesYesNoYesYesNoYesYesYesYesYesYesYesYesYesNoYes
13bResults: reasons for non-participation at each stageNoNoNoNoNoNoNoNoNoNoNoNoNoNoNoNoNoYesNoNo
13cResults: use of a flow diagramNoNoNoNoNoNoNoNoNoNoNoNoNoNoNoNoNoYesNoNo
14aResults: characteristics of study participantsYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
14bResults: number with missing dataNoNoNoNoNoNoNoNoNoNoNoNoNoNoNoNoNoYesNoNo
14cResults: cohort: follow-up timeNANANANANANANANANAYesNANANANANANANANANANA
15Results: cohort: summary measures over timeNANANANANANANANANAYesNANANANANANANANANANA
15Results: case-control: summary measures of exposureYesYesYesNANANANANANANANANoNANANANANAYesNANA
15Results: cross-sectional: numbers of events or measuresNANANAYesYesYesYesYesYesNAYesYesYesYesYesYesYesNAYesYes
16aResults: unadjusted estimatesYesNoYesYesYesNoYesYesNoYesNoYesYesYesYesNoYesNoNoYes
16bResults: category boundariesYesNoNoNoNoNoNoNoNoYesYesNoNoNoNoNoNoNANoNo
16cResults: translating relative risk into absolute riskNANoNoYesNoNANoNoNoNoNoNANoNANANoNoNANoNo
17Results: other analyses (subgroups and interactions, and sensitivity)YesNoNoNoNoNoNoNoNoYesNoYesNoYesNoNoYesYesNoYes
18Discussion: summarise key results with reference to study objectivesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
19Discussion: limitationsNoNoYesYesNoYesNoYesYesNoYesYesNoYesNoNoYesYesYesYes
20Discussion: overall interpretation of results considering other relevant evidenceYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
21Discussion: generalisability of resultsNoNoNoYesNoNoNoNoNoNoNoNoNoNoNoYesYesYesNoNo
22Funding: source of fundingNoNoNoNoYesYesNoYesYesYesYesNoYesYesNoNoYesYesYesNo
%Total percentage of successfully reported criteria in each study6142587258585372506663645963485361946156
Item NumberRecommendationsLevinger et al., 2010 [38]Levinger et al., 2012a [39]Levinger et al., 2012 [40]Lidtke et al., 2010 [41]Nigg et al., 2006 [42]Ohi et al., 2017 [43]Paquette et al., 2015 [44]Park et al., 2016 [45]Reilly et al., 2006 [46]Reilly et al., 2009 [47]Rutherford et al., 2008 [48]Rutherford et al., 2010 [49]Saito et al., 2013 [50]Shakoor et al., 2008 [51]Simic et al., 2013 [52]Tan et al., 2020 [53]Trombini-Souza et al., 2011 [54]Van Tunen et al., 2018 [55]Zhang et al., 2017 [56]
1aAbstract: study’s design in the title or the abstractNoNoNoNoYesNoNoNoNoYesYesNoNoNoNoNoNoYesNo
1bAbstract: balanced summaryYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
2Introduction: background and rationaleYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
3Introduction: objectives, including hypothesesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
4Methods: study design early in the paperNoNoNoNoYesYesNoNoYesYesYesNoNoYesNoYesNoYesNo
5Methods: setting, locations, and relevant dates, recruitment, data collectionYesYesYesYesYesYesYesNoYesYesYesYesYesYesYesYesYesYesYes
6aMethods: cohort eligibility criteria, follow-upNANANANANANANANANANANANANANANANANANANA
6aMethods: case-control: eligibility criteria of cases and controlsNAYesYesYesNANANANAYesNANANANANANANANANAYes
6aMethods: cross-sectional: eligibility criteria and methods of participants’ selectionYesYesYesYesYesYesYesYesNAYesYesYesYesYesYesYesYesYesNA
6bMethods: cohort: number of exposed and unexposedNANANANANANANANANANANANANANANANANANANA
6bMethods: case-control: matching criteriaYesYesYesYesNANAYesYesYesNANAYesYesNANANANANAYes
7Methods: define outcomes, exposures, diagnostic criteriaYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesNoYesYes
8Methods: sources of data, methods of assessment (measurement)YesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
9Methods: how bias addressedNoNoNoNoNoYesNoNoNoYesNoNoNoNoNoNoNoNoNo
10Methods: power analysisNoNoNoNoYesNoYesNoYesYesNoNoNoNoYesYesYesNoNo
11Methods: quantitative variables addressedYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesNo
12aMethods: statistical methodsYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
12bMethods: statistical subgroups and interactionsYesYesYesYesYesYesYesYesYesYesYesYesYesYesNAYesYesYesYes
12cMethods: how missing data addressedNoNoNoNoYesNoNoNoNoNoNoNoNoNoNoNoNoNoNo
12dMethods: cohort: how loss to follow-up addressedNANANANAYesNANANANANANANANANANANANANANA
12dMethods: case-control: how matching of cases and controls addressedNANoNoNoNANANoNoNoNANANoNoNANANANANANo
12dMethods: cross-sectional: sampling strategyYesYesYesYesYesNoYesNANAYesNoNANANoNAYesNoNoNA
12eMethods: sensitivity analysesNoNoNoNoNoYesYesNoYesYesNoNoNoNoNoYesNoYesNo
13aResults: numbers of individuals at each stageYesYesYesYesYesYesYesYesNoNoYesYesYesYesYesYesYesNoNo
13bResults: reasons for non-participation at each stageNoNoNoNoYesYesNoNoNoNoNoNoNoNoNoNoNoNoNo
13cResults: use of a flow diagramNoNoNoNoYesYesNoNoNoNoNoNoNoNoNoNoNoNoNo
14aResults: characteristics of study participantsYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYesYes
14bResults: number with missing dataNoNoNoNoYesYesNoNoNoNoNoNoNoNoNoNoNoNoNo
14cResults: cohort: follow-up timeNANANANAYesNANANANANANANANANANANANANANA
15Results: cohort: summary measures over timeNANANANAYesNANANANANANANANANANANANANANA
15Results: case-control: summary measures of exposureNANANANANANANoYesYesNANANANANANANANANAYes
15Results: cross-sectional: numbers of events or measuresYesYesYesYesYesYesYesYesNAYesYesYesYesYesYesYesYesYesNA
16aResults: unadjusted estimatesYesYesYesYesNoYesYesYesNoYesYesYesNoYesYesYesNoYesNo
16bResults: category boundariesNoNoYesNoYesNoYesNoNoYesNoNoNoNoNoNoNoNoNo
16cResults: translating relative risk into absolute riskNANoNoNANoNANoNANoNoNoNoNoNoNoNoNoNoNo
17Results: other analyses (subgroups and interactions, and sensitivity)NoNoNoNoYesYesNoNoYesYesYesNANoYesNoNoNoYesNo
18Discussion: summarise key results with reference to study objectivesYesYesYesYesYesYesYesYesNoYesYesYesYesYesYesYesYesYesYes
19Discussion: limitationsNoYesYesYesNoYesYesYesNoYesYesYesYesNoYesYesNoYesNo
20Discussion: overall interpretation of results considering other relevant evidenceYesYesYesYesNoYesYesYesYesYesYesYesYesYesYesYesYesYesYes
21Discussion: generalisability of resultsNoNoNoNoYesYesYesNoYesYesNoNoNoNoNoNoNoYesYes
22Funding: source of fundingNoYesYesYesYesYesYesYesYesYesNoYesNoYesYesYesYesYesYes
%Total percentage of successfully reported criteria in each study56606362838469586181636352636069506948

Abbreviation: NA not applicable

Assessment of study quality using the STROBE checklist Abbreviation: NA not applicable Among the common criterion not met included methods for addressing potential bias, with six meeting this criterion [26, 27, 35, 36, 43, 47]; study generalizability and external validity, with 11 meeting this criterion [27, 33–35, 42–44, 46, 47, 55, 56]; and sample size calculations provided, with 12 meeting this criterion [22, 24, 25, 30, 36, 42, 44, 46, 47, 52–54].

Outcomes measures

Twenty-four studies included measures of participants taken while barefoot [18–21, 23, 27–29, 32, 36–41, 43, 44, 46–49, 51, 54, 55], while 14 were in shod conditions [22, 24–26, 30, 31, 33, 34, 42, 45, 50, 52, 53, 56] (Tables 4, 5 and 6). The majority of the studies (n = 24) used a three-dimensional (3D) motion analysis system and force platforms [19–28, 30, 31, 33, 34, 36, 37, 39, 40, 44, 48, 49, 52–54], whereas the rest (n = 14) used other measurement instruments including pressure plates [41], plantar pressure insoles [56], the Biodex system [42], static footprint [38], foot scanners [50], digital callipers [29], a dynamometer force system [45], a biothesiometer [51], and objective visual and manual measurements including foot posture index (FPI) [18, 47, 53, 55], goniometer [46], and lateral talometatarsal angle [32].
Table 4

Common foot variables in participants with KOA (data reported as mean ± standard deviation)

Foot variablesStudy, yearInstrument- Shod conditionResultsP-value
KOAControls
Foot Progression Angle or toe-out degree (0)Bechard et al., 20123D motion analysis system, force platform- Wearing lab shoes6.2 ± 6.19.4 ± 5.00.68
Booij et al., 20203D motion analysis system, force platform- Barefoot−40.12 ± 4.80No controlsNA
Chang et al., 20073D motion analysis system, force platform- Barefoot18.1 ± 8.4No controlsNA
Guo et al., 20073D motion analysis system, force platform- Wearing lab shoes2.0 ± 6.8No controlsNA
Hinman et al., 20123D motion analysis system, force platform- Wearing lab shoes−6.06 ± 5.56No controlsNA
Khan et al., 20193D motion analysis system, force platform- Barefoot9.6 ± 3.7No controlsNA
Krackow et al., 20113D motion analysis system, force platform- Barefoot8.58 ± 2.3715.36 ± 2.12NR
Paquette et al., 20153D motion analysis system, force platform- Barefoot13 ± 412.2 ± 3.50.82
Rutherford et al., 20083D motion analysis system, force platform- Barefoot7.5 ± 57.3 ± 5NA
Rutherford et al., 20103D motion analysis system, force platform- Barefoot6.6 ± 7.34.9 ± 4.70.625
Simic et al., 20133D motion analysis system- Wearing lab shoes−4.5 ± 1.5No controlsNA
Trombini-Souza et al., 20113D motion analysis system, force platform- Barefoot12.2 ± 6.7413.1 ± 7.900.71
Peak rearfoot eversion (0)Arnold et al., 20143D motion analysis system, force platform – Barefoot5.3 ± 4.24.5 ± 5.00.850
Butler et al., 20093D motion analysis system, force platform- Wearing lab shoes3.5 ± 4.3No controlsNA
Butler et al., 20113D motion analysis system, force platform- Wearing lab shoes6.2 ± 5.03.5 ± 2.70.01*
Chapman et al., 20153D motion analysis system, force platform- Wearing lab shoes3.51 ± 2.77No controlsNA
Erhart-Hledik et al., 20173D motion analysis system, force platform- Wearing lab shoes13.9 ± 5.4No controlsNA
Levinger et al., 20123D motion analysis system, force platform- Barefoot1.3 ± 5.22.3 ± 3.9NR
Nigg et al., 2006Biodex system- Wearing lab shoes41.9No controlsNA
Peak rearfoot inversion (0)Arnold et al., 20143D motion analysis system, force platform- Barefoot1.4 ± 4.41.1 ± 4.20.708
Levinger et al., 20123D motion analysis system, force platform- Barefoot11.6 ± 5.214.9 ± 5.0NR
Nigg et al., 2006Biodex system- Wearing lab shoes45.1No controlsNA
Pes planus prevalence (%)Abourazzak et al., 2014Visual observation (FPI)- Barefoot42220.03*
Guler et al., 2009Objective manual testing- Barefoot38.3No controlsNA
Foot pronation (difference in FPI)Abourazzak et al., 2014Visual observation (FPI)- Barefoot1.5 ± 2.680.72 ± 2.630.05*
Levinger et al., 2010Visual observation (FPI)- Barefoot2.46 ± 2.181.35 ± 1.430.022*

*Statistically significant p-value at 95% confidence interval

Abbreviations: 3D three dimensional, FPI foot posture index, KOA knee osteoarthritis, NA not applicable, NR not reported

Table 5

Static foot variables in participants with KOA (data reported as mean ± standard deviation)

Study, year of publishFoot variable (outcome)Instrument- Shod conditionResultsP-value
KOAControls
Abourazzak et al., 2014 [18]Prevalence of pes cavus (%)Visual observation (FPI)- Barefoot58770.004*
Elbaz et al., 2017 [29]Achilles tendon thickness (mm)Digital caliper- Barefoot17.1 ± 3.415.1 ± 3.10.009
Guler et al., 2009 [32]Hallux valgus deformity (%)Objective manual testing, radiography (x-ray)- Barefoot22.60No controlsNA
Hinman et al., 2016 [35]FPI (n, %)Visual observation (FPI)- Barefoot
Severely supinated1 (1)No controlsNA
Supinated0 (0)
Normal44 (54)
Pronated30 (37)
Severely pronated6 (7)
Levinger et al., 2010 [38]Vertical navicular heightObjective manual testing, static footprint- Barefoot0.23 ± 0.030.24 ± 0.030.542
Navicular drop0.02 ± 0.010.03 ± 0.010.019*
Arch index0.26 ± 0.040.22 ± 0.040.04*
Ohi et al., 2017 [43]Hallux valgus angle (°)3D footprint automatic (laser) measurement- Barefoot13.6 ± 7.22No controlsNA
Presence of hallux valgus (%)12.5
Navicular height (mm)30.1 ± 6.75
Calcaneus angle relative to floor (°)1.35 ± 5.09
Rear foot angle (°)6.01 ± 3.76
Reilly et al., 2006 [46]Navicular height in sitting (cm)Objective manual testing (goniometer)- Barefoot5.22 ± 0.945.28 ± 0.890.005*
Navicular height in standing (cm)4.69 ± 0.834.73 ± 0.980.003*
Reilly et al., 2009 [47]FPI**Visual observation (FPI)- Barefoot7.0 (−2 to 10)**1.0 (−4 to 8)**< 0.001*
Ankle dorsiflexion during sitting (°)**Objective manual testing using goniometer -Barefoot9.0 (0 to 32)**7.5 (0 to 15)**< 0.001*
Shakoor et al., 2008 [51]VPT (volts)Biothesiometer, AP radiography- Barefoot
First MTPJ15 ± 9.96.4 ± 3.3< 0.001*
Medial malleolus22 ± 11.712.3 ± 5.20.001*
Lateral malleolus22.3 ± 10.510.4 ± 3.2< 0.001*
Tan et al., 2020 [53]FPI

Visual observation (FPI)-

Midfoot and arch height mobility/arch indices- Barefoot

3 (1 to 7)No controlsNA
Arch height difference (mm)8.8 ± 5.2
Midfoot width difference (mm)8.9 ± 3.1
Foot mobility magnitude (mm)14.8 ± 7.9
Van Tunen et al., 2018 [55]FPI (n, %)

Visual observation (FPI)- Barefoot

Foot mobility magnitude calculation

Navicular drop test

Normal (scores 0 to + 5)9 (43)No controlsNA
Pronated (scores + 6 to + 9)11 (52)
Highly pronated (scores greater + 9)1 (5)
Foot mobility magnitude (mm)9.6 ± 3.8
Navicular drop (mm)7.6 ± 3.1

*Statistically significant p-value at 95% confidence interval

** Data reported as median (interquartile range)

Abbreviations: 3D three-dimensional, FPI foot posture index, KOA knee osteoarthritis, MTPJ metatarsophalangeal joint, NA not applicable, NR not reported, SAI Staheli arch index, VPT Vibratory perception threshold

Table 6

Dynamic foot variables in participants with KOA (data reported as mean ± standard deviation)

Study, year of publishFoot variable (outcome)Instrument- Shod conditionResultsP-value
KOAControls
Al-Zahrani and Bakheit 2002 [19]Ankle plantar flexion in stance (°)**3D motion analysis system, force platform- Barefoot19.01 (15.90 to 22.70)**30.88 (23.50 to 35.60)**< 0.12
Ankle plantar flexion in swing (°)**27.76 (17.70 to 26.40)**22.74 (15.90 to 22.70)**< 0.02*
Ankle moment (pre-swing) (Nm/kg)**0.57 (0.36 to 0.78)**0.79 (0.61 to 0.91)**< 0.002*
Ankle power (pre-swing) (Watt/k.)**1.46 (0.53 to 2.31)**3.86 (2.91 to 4.58)**< 0.000*
Anan et al., 2015 [20]Maximum ankle plantar flexion moment during STS (Nm/kg)

3D motion analysis system, force platform-

Barefoot

0.36 ± 0.070.34 ± 0.070.343
Mean ankle plantar flexion moment during STS (Nm/kg)0.23 ± 0.060.24 ± 0.080.685
Ankle planter flexion moment impulse during STS (Nms/kg)0.47 ± 0.160.38 ± 0.150.072
Arnold et al., 2014 [21]Hindfoot conronal plane ROM (o)3D motion analysis system, force platform- Barefoot10.9 ± 3.410.9 ± 4.30.562
Butler et al., 2009 [24]Rearfoot eversion excursion (o)3D motion analysis system, force platform- Wearing lab shoes10.1 ± 2.8No controlsNA
−0.030 ± 0.034
Peak rearfoot eversion moment (Nm/kg*m)
Butler et al., 2011 [25]Peak rearfoot inversion moment (Nm/kg*m)3D motion analysis system, force platform- Wearing lab shoes−0.050 ±− 0.062 ±0.38
Rearfoot eversion excursion (o)0.0450.030.96
10.6 ± 5.610.2 ± 3.7
Charlton et al. 2018 [28]Foot rotation angle during natural walking:3D motion analysis system- Barefoot
Ipsilateral foot (°)−7.8 ± 7.9No controlsNA
Contralateral foot (°)−8.4 ± 5.7
Gardner et al., 2007 [31]Planter flexion angle during cycling (o)3D motion analysis system, force platform- Wearing lab shoes−6.0 ± 8.5− 8.9 ± 10.70.834
Ankle eversion during cycling (o)−6.8 ± 8.5−13.2 ± 8.40.015*
Internal rotation angle (o)8.1 ± 7.19.2 ± 7.60.849
Guo et al., 2007 [33]FPA during stair ascent (o)3D motion analysis system, force platform- Wearing lab shoes2.5 ± 6.6No controlsNA
FPA during stair descent (o)11.3 ± 8.9
Hinman et al., 2012 [34]COP offset (mm)3D motion analysis system, force platform- Wearing lab shoes−5.6 ± 4.3No controlsNA
Levinger et al.,2012a [39]Ankle dorsiflexion (o)3D motion analysis system, force platform-Barefoot3.6 ± 3.32.4 ± 2.80.08
Ankle adduction (0)2.8 ± 1.94.2 ± 2.10.01*
Toe clearance sensitivity in ankle (mm/degrees)−0.1 ± 3.51.1 ± 4.50.05*
Levinger et al., 2012b [40]Rearfoot frontal plane ROM (o)3D motion analysis system, force platform- Barefoot10.2 ± 3.312.5 ± 3.1NR
Rearfoot transverse plane ROM (o)8.8 ± 4.710.0 ± 4.9NR
Internal rotation (o)11.7 ± 6.315.4 ± 7.9NR
External rotation (o)2.9 ± 5.85.4 ± 6.1NR
Lidtke et al., 2010 [41]COP indexPlantar pressure plate- Barefoot−5.87 ± 5.6−0.45 ± 3.45< 0.001*
Nigg et al., 2006 [42]Ankle plantar flexion (o)Biodex system- Wearing lab shoes50.6No controlsNA
Ankle dorsiflexion (o)22.2
Park et al., 2016 [45]MVIC of ankle inversion muscle group (N/kg)Force dynamometer- Wearing lab shoes0.62 ± 0.260.86 ± 0.310.007*
Reilly et al., 2006 [46]Ankle Plantar flexion in sitting (°)Objective manual testing (goniometer)- Barefoot50.72 ± 11.4952.13 ± 10.940.788
Ankle dorsiflexion in sitting (°)10.07 ± 4.298.4 ± 3.710.000*
Calcaneal angle in sitting (°)2.02 ± 2.04−0.25 ± 2.930.000*
Saito et al., 2013 [50]Partial foot pressure per body weight (%)Plantar pressure sensor insoles during walking- Wearing lab shoes
Heel27.1 ± 11.241.7 ± 8.5< 0.001*
Central33.1 ± 11.216.5 ± 13.8< 0.001*
Metatarsal12.4 ± 7.912.1 ± 6.7> 0.001
Hallux1.5 ± 2.23.5 ± 3.0< 0.001*
Lateral toes1.2 ± 1.72.5 ± 2.1> 0.001
Tan et al., 2020 [53]Peak dorsiflexion angle in stance (°) during walking3D motion analysis system, force platform-Wearing lab shoes14.9 ± 3.2No controlsNA
Peak dorsiflexion moment (Nm/kg) during walking0.15 ± 0.27
Peak dorsiflexion angle in stance (°) stair ascent / descent.9.7 ± 4.4
Peak dorsiflexion moment (Nm/kg) stair ascent / descent.1.08 ± 0.22
Weight bearing ankle joint dorsiflexion ROM (cm)Knee to wall test9.1 ± 3.2
Zhang et al., 2017 [56]Contact area (cm2)Plantar pressure sensor insoles during walking- Wearing lab shoes
Heel28.9 ± 2.928.6 ± 1.70.982
Midfoot41.5 ± 5.836.5 ± 7.30.043*
1st MTPJ13.8 ± 1.613.1 ± 1.30.875
2nd MTPJ13.6 ± 0.813.2 ± 1.30.922
3rd-5th MTPJ12.7 ± 0.612.8 ± 0.30.986
Hallux7.1 ± 1.76.6 ± 1.60.684
Lesser toes10.3 ± 1.110.8 ± 0.40.988
Maximum force (%BW)
Heel69.5 ± 15.267.1 ± 11.30.817
Midfoot30.3 ± 7.123.6 ± 7.40.43
1st MTPJ32.3 ± 7.126.5 ± 6.20.037*
2nd MTPJ35.2 ± 9.130.3 ± 5.10.041*
3rd-5th MTPJ17.7 ± 5.416.7 ± 4.90.843
Hallux14.3 ± 6.513.5 ± 5.60.901
Lesser toes12.0 ± 4.712.6 ± 3.20.973
Plantar pressure (kPa)
Heel252.9 ± 52.5243.7 ± 52.50.581
Midfoot132.8 ± 28.3116.5 ± 30.00.031*
1st MTPJ295.1 ± 100.4224.3 ± 62.40.024*
2nd MTPJ273.8 ± 103.9244.6 ± 56.10.183
3rd-5th MTPJ156.1 ± 43.1157.9 ± 49.30.981
Hallux231.9 ± 77.6219.6 ± 79.40.531
Lesser toes139.4 ± 49.4142.9 ± 44.90.801

*Statistically significant p-value at 95% confidence interval

** Data reported as median (interquartile range)

Abbreviations: 3D three-dimensional, %BW percent bodyweight, AP anteroposterior, COP centre of pressure, KOA knee osteoarthritis, NA not applicable, NR not reported, MVIC maximum voluntary isometric contraction, MTPJ metatarsophalangeal joint, ROM range of motion, STS sit-to-stand

Common foot variables in participants with KOA (data reported as mean ± standard deviation) *Statistically significant p-value at 95% confidence interval Abbreviations: 3D three dimensional, FPI foot posture index, KOA knee osteoarthritis, NA not applicable, NR not reported Static foot variables in participants with KOA (data reported as mean ± standard deviation) Visual observation (FPI)- Midfoot and arch height mobility/arch indices- Barefoot Visual observation (FPI)- Barefoot Foot mobility magnitude calculation Navicular drop test *Statistically significant p-value at 95% confidence interval ** Data reported as median (interquartile range) Abbreviations: 3D three-dimensional, FPI foot posture index, KOA knee osteoarthritis, MTPJ metatarsophalangeal joint, NA not applicable, NR not reported, SAI Staheli arch index, VPT Vibratory perception threshold Dynamic foot variables in participants with KOA (data reported as mean ± standard deviation) 3D motion analysis system, force platform- Barefoot *Statistically significant p-value at 95% confidence interval ** Data reported as median (interquartile range) Abbreviations: 3D three-dimensional, %BW percent bodyweight, AP anteroposterior, COP centre of pressure, KOA knee osteoarthritis, NA not applicable, NR not reported, MVIC maximum voluntary isometric contraction, MTPJ metatarsophalangeal joint, ROM range of motion, STS sit-to-stand A wide range of foot characteristics and mechanics were reported in the included studies. The most common foot-related outcomes investigated and reported were foot progression angle (FPA) or toe-out degree (n = 12) [22, 23, 27, 33, 34, 36, 37, 44, 48, 49, 52, 54], and peak rearfoot eversion angle (n = 7) [21, 24–26, 30, 40, 42]. Other outcome measures included the prevalence of pes planus among participants with KOA measured with reference to the medial arch index and the lateral talometatarsal angle [18, 32], and foot pronation measured by foot posture index (FPI) [18, 38]. One study measured partial foot pressure percentage by body weight [50], and another measured plantar load during walking [56].

Foot progression angle (toe-out degree)

Twelve studies measured and reported FPA [22, 23, 27, 33, 34, 36, 37, 44, 48, 49, 52, 54]. Six studies recruited both KOA and control groups and compared the findings between them [22, 37, 44, 48, 49, 54]. The FPA meta-analysis showed no difference between participants with and without KOA (MD: -1.50, 95% CI − 4.20 to 1.21) (Fig. 2). Six other studies recruited KOA participants without a control group [23, 27, 33, 34, 36, 52], and three of these reported negative values for FPA [23, 34, 52], meaning that KOA participants walked with in-toeing gait, while the other three studies reported positive values of FPA [27, 33, 36] [27, 33, 36], meaning that KOA participants tended to walked with a toe-out gait.
Fig. 2

Forest plot for the differenuihjhjce in FPA during walking between KOA people and healthy controls. 95% CI = 95% Confidence Interval, SD = standard deviation

Forest plot for the differenuihjhjce in FPA during walking between KOA people and healthy controls. 95% CI = 95% Confidence Interval, SD = standard deviation

Peak rearfoot eversion angle

Seven studies measured peak rearfoot eversion angle in individuals with KOA [21, 24–26, 30, 40, 42] using 3D motion analysis systems (in weight bearing position during walking) [21, 24–26, 30, 40], and Biodex (non-weight bearing, in sitting position) [42]. Four studies recruited a KOA group only [24, 26, 30, 42], while three studies compared data to those without KOA [21, 25, 40] (Table 4). A meta-analysis of these studies showed no significant difference in peak rearfoot eversion angle during walking between groups (MD: 0.71, 95%CI − 1.55 to 2.97) (Fig. 3).
Fig. 3

Forest plot for the difference in peak rearfoot eversion angle during walking between KOA people and healthy controls. 95% CI = 95% Confidence Interval, SD = standard deviation

Forest plot for the difference in peak rearfoot eversion angle during walking between KOA people and healthy controls. 95% CI = 95% Confidence Interval, SD = standard deviation

Foot posture

FPI was reported in six studies [18, 35, 38, 47, 53, 55]. However, the study outcomes were not presented comparably between these studies, limiting the possibilities of meta-analysis. Two studies measured differences in foot posture using FPI in KOA and non-KOA populations [18, 38]. Both of them noted that participants with KOA had statistically significant (P < 0.05) highly pronated foot postures, with a difference of 0.78 [18] and 0.61 [38] between the groups (Table 4). Four additional studies measured FPI in individuals with KOA [35, 47, 53, 55], with the results reported here in Table 5 as they were measured differently, with two reporting results as median and interquartile ranges [47, 53] and two categorising and reporting the prevalence of individuals into categories. The first study categorised individuals into three categories: normal, pronated, or highly (severely) pronated [55], while the other study added two categories: supinated, and severely supinated [35]. The highest prevalence in both studies was in the pronated foot posture category, with 52% of participants (N = 11) in one study [55] and 37% (N = 30) in the other [35] (Table 5).

Pes planus

Two studies reported on the prevalence of pes planus in individuals with KOA. Pes planus was measured with reference to the medial arch index in one study, and it showed a statistically significant greater prevalence of pes planus in participants with KOA (42% vs. 22%) [18]. Another study measured pes planus by the lateral talometatarsal angle, where it was defined as an angle > 4°, and reported that 38.3% of participants with KOA had pes planus [32].

Other outcomes

Other foot characteristics and mechanics measured in individuals with KOA were divided into two categories and reported in two different tables: static foot variables (Table 5) and dynamic foot variables (Table 6). The medial arch of the foot was assessed and reported in four studies using different methods (vertical navicular height, navicular drop, and arch index), with different tools (arch index, static footprint, goniometer, and navicular drop test). Of those four studies, two studies compared the results of the KOA group to a control group [38, 46]. When participants with KOA were compared to those without, they were found to have a more significant navicular drop (0.03 ± 0.01 vs 0.02 ± 0.01), a significantly greater arch index (0.26 ± 0.04 vs 0.22 ± 0.04) [38], and significantly lower navicular height in sitting (5.22 ± 0.94 cm vs 5.28 ± 0.89 cm) [46] and standing (4.69 ± 0.83 cm vs. 4.73 ± 0.98 cm) [46]. Plantar pressure was measured during walking while wearing plantar pressure sensor insoles embedded inside lab shoes in two studies [50, 56]. One study [50] assessed and reported the percentage of partial foot pressure per body part, and reported that plantar pressure was statistically lower in participants with KOA compared to those without KOA in the heel (27.1 ± 11.2% vs. 41.7 ± 8.5%), and hallux (1.5 ± 2.2% vs. 3.5 ± 3.0%), and statistically greater at the midfoot (central) (33.1 ± 11.2% vs. 16.5 ± 13.8%) [50]. In the other study [56], a significantly greater plantar pressure was reported in the midfoot (132.8 ± 28.3 kPa vs. 116.5 ± 30.0 kPa), and the first metatarsophalangeal joint (295.1 ± 100.4 kPa vs. 224.3 ± 62.4 kPa) when compared to a control population [56]. One study [51] investigated the vibratory perception threshold (VPT) in specific foot areas and reported significant deficits in vibratory sensation in participants with KOA. Compared to participants without KOA, those with KOA demonstrated significantly greater VPT in the first metatarsophalangeal joint (15 ± 9.9 V vs. 6.4 ± 3.3 V), medial malleolus (22 ± 11.7 V vs. 12.3 ± 5.2 V), and lateral malleolus (22.3 ± 10.5 V vs. 10.4 ± 3.2 V) [51]. Another study which explored Achilles tendon thickness reported significantly thicker tendons in the KOA group compared to the control [29] (17.1 mm vs. 15.1 mm), with thickness associated positively with KOA severity.

Discussion

The purpose of this review was to evaluate foot characteristics and mechanics in individuals with KOA and compare them to people without KOA where possible. Variations in foot characteristics and mechanics in people with KOA were found in the included studies. These variations included differences in FPA, peak rearfoot eversion angle, pronated foot posture, and incidence of pes planus in people with KOA. Several studies compared foot characteristics and mechanics in individuals with KOA to those without KOA; however measurement techniques and outcome measures were not homogenous across studies. Therefore, meta-analyses were conducted on two foot variables only, FPA and peak rearfoot eversion angle. However, these revealed no statistical difference in FPA or peak rearfoot eversion angle. The results across the included studies were inconsistent, a situation which can be attributed to three main reasons: 1) several studies had no control group without KOA, limiting the ability to report between group differences; 2) studies employed different measurement techniques or methods of reporting, limiting the ability to combine data in meta-analyses; and 3) foot characteristics or mechanics were reported by only one study (e.g., VPT, prevalence of hallux valgus deformity, Achilles tendon thickness), making it impossible to draw robust conclusions. Therefore, further work is needed to fully understand the differences in foot characteristics and mechanics in individuals with KOA. Results of the present work suggest that the prevalence of pes planus and pronated foot posture is higher among participants with KOA. Zhang et al. (2017) reported significantly greater plantar pressure in the midfoot in those with KOA compared to those without. The increase of midfoot and central plantar pressure aligns with the increased incidence of pes planus [18, 32] and greater foot pronation [18, 38] associated with KOA. Further, the positive association noted between pes planus and lower vertical navicular height [38] may explain the high pressure in the midfoot area and the absence of a medial longitudinal arch in the foot [50]. The greater peak rearfoot eversion angles evident in individuals with KOA [21, 25, 31] also align with the reported FPA differences between those with and without KOA [22, 34, 37, 52, 54], as these measurements are hypothesised to influence each other biomechanically. As the included studies measured foot characteristics and mechanics in those with KOA at a single time point, it is unclear if foot posture or incidence of pes planus is a cause or effect of KOA. Nonetheless, the presence of the biomechanical foot differences (pronated foot posture, greater peak rearfoot eversion angle, and incidence of pes planus) associated with KOA highlight the importance of the kinetic chain and biomechanical influence of one joint on another, which may indicate that foot characteristics may be related to KOA progression. However, further longitudinal studies are required to confirm this. As foot posture and foot function have previously been associated with knee joint loading [38, 57], a cause of primary progressive KOA [9], it is possible that changing the foot posture or function may be an appropriate intervention for KOA. Conservative interventions targeting a biomechanical change to address KOA have included foot-related interventions [58, 59]. The most common foot-related interventions used to manage KOA are gait modifications and lateral wedge insoles [58]. Toe-out gait has been widely deployed as a conservative intervention in order to reduce knee adduction moment (KAM) and symptoms in people with KOA [59]. Walking with a greater toe-out angle as a mechanical intervention changes the knee joint load in individuals with KOA, shifting the KAM into a flexion moment and reducing knee pain [60]. Furthermore, a greater toe-out degree during walking has been associated with a reduced likelihood of disease progression in participants with KOA for over 18 months [27]. Therefore, this intervention can be limited to targeting people with KOA who walk with a toe-in gait pattern. However, the findings of this systematic review also revealed a diversity in walking patterns among people with KOA (toe-in vs. toe-out gait); thus, this intervention cannot be applied widely in people with KOA. Lateral wedge orthoses are another common foot-related intervention for KOA [58]. A recent systematic review and meta-analysis demonstrated a reduction in knee joint load, reported as a significant small reduction in first peak of external KAM (standardized mean difference [SMD]: − 0.19; 95% confidence interval [95% CI] -0.23, − 0.15) and second peak external KAM (SMD -0.25; 95% CI -0.32, − 0.19) with a low level of heterogeneity (I2 = 5 and 30%, respectively) and small but favourable reduction in knee adduction angular impulse during walking in people with KOA (SMD = − 0.14; 95% CI -0.21, − 0.07, I2 = 31%) [58]. However, the biomechanical changes reported as resulting from lateral wedge orthoses were considered minimal, thus limiting the efficacy of this intervention [58]. Furthermore, the impact of this intervention is still unknown for people with KOA who have pronated foot posture as lateral wedge orthoses were reported to significantly increase subtalar joint valgus moment [61]. Therefore, defining foot characteristics and mechanics in individuals with KOA is extremely important, as doing so can play an essential role in selecting the most appropriate foot-related interventions to fit the individual’s own foot characteristics and mechanics. This systematic review has identified several gaps and areas where future research is needed. Intrinsic foot muscle strength, which affects gait and balance [62], remains an unknown characteristic in the KOA population. Future work evaluating the association between foot muscle strength and KOA may prove beneficial in determining if foot strength or its improvement may be an effective KOA intervention. Further, only one study [51] to date has investigated and reported a loss of vibratory sensation in the foot and ankle with KOA, a measure also affecting gait [63]. Understanding if there is a loss in vibratory sense loss or proprioception as well as how it affects those with KOA may also inform the type of rehabilitation deemed appropriate for this population. It has been suggested that poor neuromuscular control affects injury risk and prevention [64], and neuromuscular control has been associated with KOA severity [65]. Therefore, improving foot neuromuscular control may potentially lessen the risk of knee injury and decrease the impact of KOA.

Strengths and limitations

As with any study, the systematic review and meta-analyses presented here should be evaluated with respect to their strengths and limitations. This review set out a wide range of foot characteristics and mechanics in people with KOA. However, most of the measures were only reported in one or two studies with a small sample of participants, which may limit their generalisability to the wider KOA population. Further, this study has evaluated foot characteristics and mechanics in individuals with KOA and suggested a potential relationship between some of the foot measures and KOA. However, the potential cause and effect relationship of foot characteristics and mechanics outcome measures to KOA is still unknown, as this work has reported foot- related data collected at one time point from observational studies, or data at baseline from intervention studies. Future researchers are advised to investigate the relationship between KOA and foot characteristics and mechanics in more depth via longitudinal studies. One strength of this study is its robust design, which allowed for the breadth of foot characteristics published to be included in the systematic review and meta-analysis, providing a strong background for researchers to develop longitudinal and intervention studies. However, the wide variety of techniques used to measure similar outcomes prevented the possibility of conducting multiple meta-analyses. Therefore, future studies are advised to develop and follow standardized techniques with which to measure foot characteristics and mechanics in order to facilitate further meta-analyses. The foot characteristics and mechanics reported in this systematic review were assessed and measured using a range of specific measurements. These could be divided into two categories: 1) laboratory-based measurement (e.g., 3D motion capture, static footprint, force platform, and Biodex); and 2) visual observation and objective manual measurements (e.g., navicular drop test, knee to wall test, FPI, Staheli arch index, and digital caliper). Many of the included studies omitted to provide sufficient details on how the measurements were taken. Moreover, due to the heterogeneity in measurement methods used to investigate foot characteristics and mechanics between the included studies, the process of pooling results for comparison was limited. One of the limitations identified during this review was the lack of quality in the included studies, as only ten studies attained 65% on the STROBE checklist and could thus be considered high-quality studies. A lower cut-off point of 65% was utilized during the assessment of study quality because foot characteristics and mechanics were not generally the primary outcome measure in the included studies; thus, a cut-off point higher than 65% would not have been achievable by the included studies.

Conclusion

In conclusion, despite the large body of prior research investigating foot characteristics and mechanics in individuals with KOA, many studies lacked a comparison group without KOA. Five foot characteristics and mechanics measures were commonly reported in the included studies (FPA, rearfoot peak eversion angle, peak rearfoot inversion angle, foot posture, and prevalence of pes planus). A more pronated foot posture was noticed in the presence of KOA. Further, of these five common foot characteristics and mechanics, two were of similar design, enabling a meta-analysis to be conducted - FPA and peak rearfoot eversion angle. Meta-analysis of these two variables demonstrated no significant differences between participants with and without KOA. Thus, the implications of the present work suggest a need to adopt and adhere to unified measurement techniques of common foot characteristics and mechanics to make meta-analyses more viable. Lastly, longitudinal studies are needed to identify the potential causal relationship between foot characteristics and mechanics and KOA in people with KOA.
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