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Null hypothesis 1, There will be no significant reduction in the external knee adduction moment in the group using the lateral wedged insole compared to the comparator group. The null hypothesis was rejected as the LWI group reduced the first peak of the EKAM at both one and six weeks compared to the comparator group and also compared to the baseline. However, participants in weeks one and six demonstrated faster walking speed in LWI group compared to baseline and this could increase loads at the knee joint, the EKAM significantly reduced after wearing LWI due to the effect of the LWI on the knee joint. LWI are designed to reduce the loading on the medial compartment of knee joint by alter the position of the centre of pressure under the foot and thereby displace the GRF laterally with respect to the knee joint (Yasuda and Sasaki, 1987; Hinman et al., 2013). One of the primary mechanisms in the external knee adduction moment is the vertical GRF. The vertical GRF did not change significantly between groups and visits although, the vertical ground reaction forces increased by 3% and 4% after wearing the LWI for one and six weeks, respectively, compared to the baseline. This is explained by the strong correlation between high ground reaction forces and faster acceleration (Winter, 1984; Shelburne et al., 2006) where walking speeds increased in LWI group, so one would expect that the EKAM have a corresponding increase, which was not found. With no significant change in vertical ground reaction forces in the LWI group, the EKAM would have been reduced by another mechanism. This mechanism is determined the reduction in the length (distance) of the moment arm when wearing the LWI. The LWI acts to displace the line of the GRF more laterally to the centre of the knee joint by altering the calcaneus (rearfoot) into valgus position (Pollo, 1998). The maximum effect of the LWI happens during the early stance period of stance phase (first peak of the EKAM) because of the structure of the LWI where the inclination of the insole was greater (5˚) at the heel and gradually decreased to 0˚ at the 5th metatarsal head. The first peak of the EKAM significantly reduced after wearing the LWI for one and six weeks by 15% and 16.8%, respectively, compared to the baseline. Therefore, the knee load reduced and disease progression may be delayed (Miyazaki et al., 2002).

Whereas, the second peak of the EKAM significantly reduced after wearing LWI for one and six weeks by 14.2% and 10%, respectively, compared to the baseline. The wedged gradually decreases under the mid and forefoot, therefore the 0˚ of inclination of the LWI at the 5th metatarsal head may be the reason of no significant difference between groups was found in term of the second peak of the EKAM (late stance peak).

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The KAAI was reduced significantly after wearing LWI at both one and six weeks compared to the baseline but no change was recorded in comparator group compared to baseline. After wearing LWI for six weeks, there was a significant reduction in the KAAI compared to comparator group. The results of the current study are in the agreement with the majority of the studies (Kerrigan et al., 2002; Hinman et al., 2008, 2009 & 2012; Barrios et al., 2013; Jones et al., 2013a, 2013b, 2014 & 2015). In the current study, the EKAM and KAAI reduced by 12% and 11.6%, 15% and 17.8%, and 16.8% and 22% after immediately, one week, six weeks, respectively, of wearing LWI compared to baseline. These results of the current study are in agreement with a crossover randomized study (Jones et al., 2013a) where the EKAM and KAAI reduced by 12% and 7%, respectively, after wearing LWI for two weeks compared to baseline.

Hinman et al., (2012) found that the EKAM and KAAI significantly reduced by 5.8% and 6.3% as an immediately effect of wearing LWI. The participants in Hinman et al., (2012) study wore LWI without a medial support whereas LWI with medial support were worn in the current study. Kerrigan et al (2002) investigated the immediately effect of LWI without support and they found that the EKAM significantly reduced by 6% compared to the baseline (no insole). The reduction in the EKAM was diminished when using LWI without medial support and the difference was 1.08% for LWI with medial support; however, there was no significant difference between to kind of insole in term of EKAM reduction (Jones et al., 2014). Therefore, the structure of the LWI, for example that used in Hinman et al., (2012) study, may be the reason of that lower reduction in the EKAM in Hinman et al., (2012) study compared to the current study. In addition, the material of the LWI particularly the densities of the insole may be the reason of variability in the EKAM reduction. Hinman et al., (2012) tested LWI with a durometer score 57.5 and Kerrigan et al., (2002) used LWI with durometer score of 55, while the density of the LWI in the current study was 70 which stiffer insoles were recommended (Radzimski et al., 2012) and used (Jones et al., 2014) to treat medial knee OA.

In addition, a significant reduction in the EKAM was found when the immediate effect of LWI has been investigated compared participant’s shoes in forty participants with medial knee OA (Hinman et al., 2008) which is slightly lower compared with the current study. The majority of the participants demonstrated a reduction in the first peak of the EKAM from 0.1% - 18.2% (Hinman et al., 2008) and 1.9%-27% in the current study. One of the potential reason the reduction of the first peak of the EKAM was greater is that a high density LWI (70) were worn bilaterally inside the participants’s own shoes in the current study which has an efficient effect compared to the medium density (57.5) that worn inside control shoes in Hinman et al., (2008). In addition, it is recommended that

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participant’s own shoes be used as control conditions to ensure they do no experience a large biomechanical change (Lewinson et al., 2016)

The results of the current study support Jones et al., (2013b) study who found as similar effect of LWI in 28 participants with medial knee OA. They found that the EKAM and KAAI reduced significantly by 10%, 14.2%, and 10% and 7.14% when wearing LWI with and without medial support, respectively, compared to control shod. Possible explanation for the reported greater reduction in the EKAM at early stance phase in the current study might be due to the participants in the current study wore their shoes as control insole and LWIs were inserted in their own shoes. Therefore, the nature of the shoes of the participants may play a role biomechanical changing (Lewinson et al., 2016). However, the same shoe that worn at baseline for each participant was worn at both visits. Other potential reason is that the LWI in the current study was designed with medial support to achieve a maximum effect regarding the studies (Jones et al., 2014).

The results of the current study are in agreement with one month results reported by Hinman et al., (2009) and one year results reported by Barrios et al., (2013). However, Hinman et al., (2009) observed lower EKAM reduction (between 4.2% and 7.4%) at both baseline and after one month, this may be because they used low density (57.5 shore) compared to the current study. Barrios et al., (2013) found the percentage of EKAM reduction after wearing LWI for one year was maintained at 8% as baseline result. In the current study, the EKAM reduction at baseline, week one and week six in the LWI group appeared to remain consistent or increased throughout the six weeks of intervention where reductions were 12%, 15% and 16.8%, respectively. The possible reason for reported grater reduction EKAM and KAAI in the current study might be due to the LWIs which used in the current study were with medial support that designs to offer greater reduction in the knee loading in healthy subjects by provide a better function foot by reduction ankle complex eversion angle (Jones et al., 2014). In addition, comfort score was not measured in Hinman et al., (2009) and Barrios et al., (2013) who used LWI without supported arch and thereby we assume the LWI without medial support may diminish the biomechanical effectiveness of LWI. The LWIs were found to be comfortable with the majority of the participants (75%) with high adherence (wearing time, average, 6.5-7.5 hours/day) in the current study. However, Hinman et al., (2009) concluded that the reduction of the EKAM did not decease over the time which is this result support by the current study. Moreover, the LWI with 70 shore density and medial support was used in the current study which offer greater reduction on the EKAM.

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Putting the reduction in first peak of EKAM into context, a large cohort study found that both peak EKAM and KAAI were associated with joint narrowing and cartilage loss over 12 months (Bennell et al., 2011a), 24 months (Chang et al., 2015) of follow-up and the risk of progression of knee OA increased 6.46 times when the EKAM increases by 1% on the 1st peak (Miyazaki et al., 2002). Therefore, reduced the EKAM in the current study by more than 12% when wearing LWI could delay the progression of knee OA.