3.1. Study selection
The initial search identified 13,441 studies. After duplicate removal, 5,362 studies remained. Following the screening of titles and abstracts, 43 full texts were further considered. Finally, 22 studies were eligible to be included in this systematic review with meta-analysis. Quantitative analyses were computed with all 22 articles. Fig 1 presents a PRISMA flow chart and illustrates the study selection process. Studies were then categorized according to the applied foot pronation assessment methods: (1) using the foot posture index (FPI-6) or clinical observation; (2) using the foot print arch index; (3) using the arch height index (including the navicular drop, the arch height index, the navicular height normalized to foot length [NNHT]); (4) the forefoot varus method; (5) the rearfoot eversion or rest calcaneal stance position method (RCSP).
Fig. 1. PRISMA flow diagram of studies included in this systematic review with meta-analysis
3.2. Study characteristics
Table 3 shows the characteristics of the included studies. The identified studies used different types of foot posture measurements (i.e., FPI-6, clinical observation, foot print arch index, navicular drop, arch height index, NNHT, forefoot varus, rearfoot eversion, RCSP) and different foot models for kinematic and kinetic analyses. For instance, six studies were identified with the FPI-6 or clinical observation 14, 30-34, three with the foot print arch index 35-37, six with the arch height index 3, 9, 15, 38, 39, four with the forefoot varus method 13, 16, 40, 41; two with the rearfoot eversion or RCSP method 42, 43.
Tang et al. 37 reported values for participants with and without pronated feet. For the purpose of this study, we only extracted data for the foot pronation group. If authors reported multiple values for peak or mean joint excursion in different phases, we only included the phase with the higher value 14, 34, 35, 42. Additionally, we reported numerical values for all types of foot orthotics used in the respective studies 13-16, 30-33, 38-42, 44. We extracted data from graphs out of five studies 15, 30, 31, 33, 43.
The outcome measures peak rearfoot eversion angle, peak ankle eversion and dorsiflexion angle, peak ankle eversion moment and knee adduction moment were reported in five or more than five studies. The remaining outcome measures with lower clinical relevance were included in the supplementary material (Supplementary File: Appendix 1-27).
Table 3 here
3.3. Quality assessment
The methodological quality of the included 22 studies amounted to 74% on the modified version of the Downs and Black checklist 25. This is indicative of moderate methodological quality (Table 4). Among the 22 included studies, 15 were rated high quality 3, 9, 14-16, 30, 32, 33, 35, 36, 39-42, 45, and seven moderate quality 13, 31, 34, 37, 38, 43, 44. Only two study 14, 31 involved assessors who were blinded for the experimental condition (FO or control) during testing. Authors from eleven studies 3, 9, 15, 16, 30, 35, 39, 41, 42, 45 reported the calculation of a priori power analysis to estimate the sample size.
Table 4 here
3.4. Effects of short-term FO application on lower limbs kinematics
3.4.1. Rearfoot
Nine studies reported the effects of short-term FO application on peak rearfoot eversion 3, 13, 14, 16, 37, 39, 40, 43, 44. Findings indicated moderate effects of short-term FO application. The analysis further revealed moderate level of heterogeneity (moderate SMDs=0.66, 95% CI 0.34 to 0.99, p<0.0001, I2=71%). More specifically, across the nine included studies, the peak rearfoot eversion was 1.72° (95% CI 1.01 to 2.44) lower in the FO condition compared to control (Fig 2). The subgroup analyses taking the methodological approach for the assessment of foot pronation into account showed no significant effect of short-term FO wearing for the studies that assessed foot posture using the arch height index 3, 39 (2 studies: SMDs=0.42, 95% CI -0.20 to 1.05, p=0.18) or the foot print arch index 37 (1 study SMDs=0.64, 95% CI -0.26 to 1.55, p=0.16). Yet, we observed significant effects of short-term FO application in studies that used the forefoot varus method 13, 16, 40 (3 studies: small SMDs=0.36, 95% CI 0.13 to 0.6, p=0.002), the FPI-6 or clinical observation 14, 44 (2 studies: large SMDs=1.42, 95% CI 0.20 to 2.63, p=0.02, I2=87) and the rearfoot eversion or RCSP methods 43 (1 study: large SMDs=1.28, 95% CI 0.39 to 2.17, p=0.005) for determination of foot pronation (Fig 2, Table 5).
Fig. 2. Forest plot illustrating the effects of short-term application of foot orthoses (intervention) versus control on peak rearfoot eversion during walking in individuals with pronated feet. The subtotal effect for each parameter and the total effect were calculated as standardized mean difference (95% CI). SD: Standard deviation; Std: Standardized; CI: Confidence interval.
3.4.2. Ankle
Peak ankle dorsiflexion was measured in five studies 9, 31, 32, 35, 42. Overall, our findings indicated small effects of short-term FO application (5 studies: small SMDs=-0.33, 95% CI -0.54 to -0.12, p=0.002, I2=0%). More specifically, the mean (five studies) peak ankle dorsiflexion was 0.61° (95% CI 1.05 to 2.75) lower in the FO compared to the control condition (Fig 3). The subgroup analyses showed no significant effects of short-term FO treatment in the studies that assessed foot posture using the arch height index 9 (1 study: SMDs=-0.19, 95% CI -1.03 to 0.65, p=0.18) or the foot print arch index 35 (1 study: SMDs=0.42, 95% CI -0.30 to 1.15, p=0.26). Significant effects of short-term FO application were found for the studies that used the FPI-6 or clinical observation 31, 32 (2 studies: small SMDs=-0.42, 95% CI -0.72 to -0.12, p=0.007, I2=0%) and rearfoot eversion or RCSP 42 (1 study: small SMDs=-0.42, 95% CI -0.78 to -0.06, p=0.02, I2=0%) to determine the foot posture (Fig 3, Table 5).
Fig. 3. Forest plot of the effects of short-term foot orthoses application (intervention) versus control on peak ankle dorsiflexion during walking in individuals with pronated feet. The subtotal effect for each parameter and the total effect were calculated as standardized mean difference (95% CI). SD: Standard deviation; Std: Standardized; CI: Confidence interval.
Peak ankle eversion was measured in seven studies 13, 30-33, 35, 40. Based on findings from the seven included studies, the analysis indicated significant moderate effects of short-term FO treatment (moderate SMDs=0.58, 95% CI 0.27 to 0.90, p=0.0003) (Fig 4) with a moderate level of study heterogeneity (I2=72%). More specifically, the mean (7 studies) peak ankle eversion was 1.10° (95% CI 0.58 to 1.62) lower in the FO condition compared to control. The subgroup analysis showed no significant effect of short-term FO application in the studies that assessed foot posture using the foot print arch index 35 (1 study: SMDs=0.55, 95% CI -0.18 to 1.28, p=0.14). Significant effects were observed for the studies that used the FPI-6 or clinical observation 30-33 (4 studies: moderate SMDs=0.68, 95% CI 0.13 to 1.23, p=0.01, I2=83%) and forefoot varus 13, 40 (2 studies: moderate SMDs=0.5, 95% CI 0.24 to 0.77, p=0.0002, I2=0%) to determine foot pronation (Fig 4, Table 5).
Fig. 4. Forest plot of the effects of short-term foot orthoses application (intervention) versus control on peak ankle eversion during walking in individuals with pronated feet. The subtotal effect for each parameter and the total effect were calculated as standardized mean difference (95% CI). SD: Standard deviation; Std: Standardized; CI: Confidence interval.
3.5. Effects of short-term FO application on lower limbs kinetics
3.5.1. Ankle
Five studies reported peak ankle eversion moment in Nm/kg. Overall, the analysis indicated no evidence of study heterogeneity (I2=0%) and yielded significant differences between short-term FO application and control (5 studies: small SMDs=0.38, 95% CI 0.17 to 0.59, p=0.0004) (Fig 5). The applied subgroup analysis showed a significant difference only for the one single study that used the arch height index 39 (Fig 5, Table 5). More specifically, the peak ankle eversion moment was 0.07 Nm/kg (95%CI 0.04 to 0.11) larger in the control condition.
Fig. 5. Forest plot illustrating the effects of short-term foot orthoses application (intervention) versus control on peak ankle eversion moment during walking in individuals with pronated feet. The subtotal effect for each parameter and the total effect were calculated as standardized mean difference (95% CI). SD: Standard deviation; Std: Standardized; CI: Confidence interval.
3.5.2. Knee
Six studies reported the effects of short-term FO application on peak knee adduction moments 9, 30-33, 45. For the FPI-6 and the clinical observation assessment of foot posture, the mean (4 studies) peak knee adduction moment was 0.04 Nm/kg (95% CI -0.07 to -0.02) greater in the FO compared to the control condition (Table 5). For the arch height index, findings did not reach the level of significance (2 studies) (Fig 6). Overall, there was a significant small effect of short-term FO application on the knee adduction moment (6 studies: SMDs=-0.30, 95% CI -0.50 to -0.10, p=0.004, I2=0%) (Fig 6, Table 5).
Fig. 6. Forest plot illustrating the effects of short-term foot orthoses application (intervention) versus control on peak knee adduction moment during walking in individuals with pronated feet. The subtotal effect for each parameter and the total effect were calculated as standardized mean difference (95% CI). SD: Standard deviation; Std: Standardized; CI: Confidence interval.
Table 5 contains a summary of the meta-analytical finding according to the applied methods that were used to assess foot pronation.
Table 5 here