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The use of lateral foot wedging in the management of medial knee osteoarthritis is under scrutiny. Interestingly, there have been minimal efforts to evaluate biomechanical effectiveness with long-term use. Therefore, we aimed to evaluate dynamic knee loading (assessed using the knee adduction moment) and other secondary gait parameters in patients with medial knee osteoarthritis wearing lateral foot wedging at a baseline visit and after 1 year of wear. Three-dimensional gait data were captured in an intervention group of 19 patients with symptomatic medial knee osteoarthritis wearing their prescribed laterally wedged foot orthoses at 0 and 12 months. Wedge amounts were prescribed based on symptom response to a step-down test. A control group of 19 patients wearing prescribed neutral orthoses were also captured at 0 and 12 months. The gait of the intervention group wearing neutral orthoses was additionally captured. Walking speed and shoes were controlled. Analyses of variance were conducted to examine for group-by-time (between the groups in their prescribed orthoses) and condition-by-time (within the intervention group) interactions, main effects, and simple effects. We observed increased knee adduction moments and frontal plane motion over time in the control group but not the intervention group. Further, within the intervention group, the mechanical effectiveness of the lateral wedging did not decrease. In patients with medial knee osteoarthritis, the effects of lateral foot wedging on pathomechanics associated with medial knee osteoarthritis were favorable and sustained over time. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 659–664, 2013
Knee osteoarthritis (OA) is a progressive and disabling disease that is common in older adults. Approximately 12.1% of the general population in the United States aged over 45 years is diagnosed with knee OA.1 The medial tibiofemoral compartment, which bears more than 60% of the medial–lateral load in a normal knee, is most commonly affected.2 The knee external adduction moment (KEAM) is the most often used surrogate measure for medial–lateral loading at the knee. This moment has been correlated to in vivo medial knee loading in an instrumented knee,3 and has been found to be elevated in individuals with medial knee OA,4, 5 as well as in asymptomatic varus knees.6 Consistent with these cross-sectional findings, prospective studies have found that the KEAM may be a modifiable risk factor for the development and progression of medial knee OA.7–9
A number of interventions are aimed at laterally redistributing tibiofemoral loads for those with medial knee OA. The most invasive of these interventions are osteotomies.10 However, conservative management strategies are more appropriate for most individuals with medial knee OA. For example, use of knee braces has been recommended for individuals with varus gonarthrosis.11 Unfortunately long-term compliance with bracing has been problematic.12 Another approach is the use of laterally wedged foot orthoses.13–37 These devices indirectly alter frontal plane knee mechanics by directly influencing foot, ankle, and tibial mechanics.13, 34
The immediate effect of laterally wedged devices on the KEAM has been examined in both healthy and patient populations. In healthy subjects, Crenshaw et al.19 observed a 7% reduction in the KEAM when using a 5° full-length insole. In contrast, a later study on 15 healthy subjects found no significant reductions using a 10° lateral wedge.22 In patients, KEAM reductions between 5% and 12% have been noted with the use of full-length devices.20, 24, 30, 32 However, a 5° lateral heel wedge resulted in no significant decreases in peak KEAM.21 Accordingly, a later comparative study found heel wedges to be less effective than full-length insoles.33
Laterally wedged orthoses do not appear to discernibly alter knee kinematics. No reductions in peak knee adduction angle, a measure of dynamic knee alignment, have been reported with lateral wedging.19, 22, 24, 30 While an immediate reduction in knee adduction angle excursion from heel strike to peak knee adduction angle, sometimes termed varus thrust, has been observed, the implications of this reduction in frontal plane knee motion remain unclear.30
To the best of our knowledge, only one biomechanical study to date has evaluated the effects of laterally wedged orthoses on the KEAM in a test–retest design. Hinman et al.36 found that a 5° laterally wedged insole significantly reduced the KEAM similarly at both baseline and at a 1-month follow-up, suggesting that the mechanical effects were not diminished after a month of wear. These reductions were observed for both the first and second peaks of the moment waveform, as well as the knee adduction angular impulse (KAAI). However, their study lacked a longer-term follow-up, did not report kinematic results, and did not incorporate a control group.
Therefore, the primary aim of this study was to compare the knee mechanics of individuals with medial knee OA wearing laterally wedged orthoses (treatment group) to those of a control group wearing a neutral orthoses over the course of 1 year. We expected mean peak KEAM, KAAI, peak knee adduction angle, and knee adduction angle excursion to increase in both groups over time, but increase to a greater extent in the control group. As a secondary aim, we tested the effects of wearing laterally wedged orthoses within the treatment group at baseline and after 1 year to explore the potential for diminishing mechanical effectiveness.
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A total of 38 subjects participated in the study. Nineteen subjects were assigned to each group (Table 2). The average degree of wedging in the treatment group was 8.7 ± 3.3°, and generally increased with disease severity. The baseline characteristics of the groups were not significantly different for age (p = 0.608), BMI (p = 0.190) and radiographic disease severity (p = 0.400) (Table 3). No differences in walking speed were observed between groups, conditions or visits (p > 0.05).
Table 2. Baseline Characteristics of the 38 Subjects
| ||Neutral orthoses (control)||Wedged orthoses (treatment)|
|Age (mean years ± SD)||61.2 ± 9.4||62.6 ± 7.4|
|BMI (mean kg/m2 ± SD)||30.4 ± 7.1||33.6 ± 7.6|
| II (# of subjects)||9||8|
| III (# of subjects)||8||6|
| IV (# of subjects)||2||5|
Table 3. Mean and Standard Deviations for the Four Variables of Interest at the Knee (NW Is the Non-Wedged Condition, W Is the Wedged Condition), and Interaction and Main Effect p-Values for the Analyses of Variance Conducted
| ||Control group||Treatment group|| || || || || || |
|Baseline||1 year||Baseline||1 year||Interaction, p-values||Group (Aim 1) or condition (Aim 2) main effect, p-values||Visit main effect, p-values|
|NW||W||NW||W||NW||W||NW||W||Aim 1||Aim 2||Aim 1||Aim 2||Aim 1||Aim 2|
|Peak KEAM Nm/(kg m)||0.376 (0.118)||—||0.408 (0.108)||—||0.369 (0.142)||0.342 (0.131)||0.358 (0.127)||0.330 (0.115)||0.052||0.482||0.139||<0.001||0.379||0.474|
|KAAI (Nm s)/(kg m)||0.169 (0.068)||—||0.185 (0.059)||—||0.158 (0.078)||0.157 (0.078)||0.155 (0.076)||0.148 (0.066)||0.086||0.837||0.245||0.009||0.570||0.561|
|Peak adduction (°)||3.0 (3.7)||—||4.1 (4.2)||—||2.3 (5.5)||1.9 (4.8)||0.8 (5.3)||0.9 (5.7)||0.076||0.389||0.142||0.512||0.933||0.128|
|Adduction excursion (°)||5.2 (1.9)||—||6.9 (1.8)||—||7.0 (2.6)||6.5 (2.7)||6.2 (2.6)||6.1 (2.6)||0.003||0.309||0.729||0.286||0.082||0.177|
For the first aim, we compared the control group (in their neutral orthoses) with the treatment group (in their wedged orthoses) at baseline and 1 year. Results revealed no baseline group differences. In addition no significant interactions or main effects were noted for knee adduction angle or KAAI. However, a group-by-time interaction was observed for knee adduction angle excursion (p = 0.003), and nearly for first peak KEAM (p = 0.052). Simple effect analysis revealed that the interactions were primarily a consequence of increases in knee adduction angle excursion (p = 0.001) and peak KEAM (p = 0.047) in the control group, and reductions in peak KEAM (p = 0.039) in the treatment group.
For the secondary aim, within the treatment group only, we compared the wedged and neutral conditions at both visits. There were no significant interactions, so main effects were assessed. We found that first peak KEAM (p < 0.001) and KAAI (p = 0.009) were lower in the laterally wedged versus neutral condition when pooled across visits, suggesting mechanical effectiveness of the devices across the year.
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The purpose of this prospective biomechanical study was to evaluate frontal plane knee mechanics in individuals with medial knee OA who wore laterally wedged orthoses over a 1-year period. Increasing magnitudes in these mechanics are thought to be deleterious. The results suggest that these mechanics remained largely stable in the group that received lateral wedging. However, these same mechanics demonstrated a tendency to increase over the course of the year in the control group wearing the neutral orthoses. Additionally, we found that the mechanical effectiveness of the wedged orthoses on knee mechanics in the treatment group were largely maintained across the year of wear.
The longitudinal results of this study were surprising. We expected both groups to show progressive degradation of mechanics, with the control group degrading more. However, the wedged group's data essentially remained the same, suggesting a mitigating effect of the wedged devices. They appeared to prevent the progression of faulty mechanics. However, the control group demonstrated increases (either significant or trending) in all four frontal plane knee variables tested. Most notably, these results suggest a degradation of knee mechanics as both peak dynamic load and frontal plane knee motion increased over the course of the year in the unwedged individuals. This is important as increased peak KEAM has been shown to be predictive of the presence and progression of knee OA.7, 9
The increase in knee adduction angle excursion at heel strike to the instance of maximum knee adduction angle in the control group may be related to ligamentous laxity or neuromuscular insufficiencies that have been noted in those with medial knee OA.42 We should note that the method by which we calculated knee adduction angle excursion is similar to the method used to derive “varus thrust” in another study.43 Kuroyanagi and coworkers further describe “varus thrust” as an abnormal lateral motion of the knee seen in medial knee OA that is also a dynamic worsening of limb alignment that closely relates to progression of disease.
The mechanical effectiveness of the wedging appeared to remain consistent throughout the year-long intervention. Immediate improvements in frontal plane knee kinetics associated with lateral wedging from this trial have already been described by Butler and colleagues.30 These authors noted a 9% reduction in first peak KEAM compared to the neutral condition at baseline. Our 1-year data revealed that this relative reduction was maintained (8%). These results are in line with the 1 month results reported by Hinman et al.,36 however they observed slightly lower KEAM reductions (between 4% and 6%) at both baseline and after 1 month. Peak knee adduction angle was not significantly altered in the wedged condition either acutely30 or over the course of 1 year. These findings corroborate previous radiographic studies, where wedging had either a minimal or no measurable effect on knee alignment.13, 17, 21 Thus, our results strengthen the increasingly accepted notion that measures of knee alignment, whether static or dynamic, are not strongly influenced by laterally wedged orthoses.
Overall, we did not find KAAI useful in providing additional information regarding frontal plane knee mechanics and lateral wedging in this study. While peak KEAM has been identified as a risk factor for the progression of medial knee OA,7, 9 it represents a discrete instance during stance. In comparison, KAAI is a measure of loading over the entire stance period. Therefore, we felt the variable might provide additional insight into the effect of wedging on the quantity of overall knee loading. However, consistent with the results of Hinman et al.,36 we did not find this to be true. This null response may have been related to the fact that KAAI values are partly dependent on stance duration. Since we matched each subject's average walking speed at the 1 year collection to their walking speed at the baseline collection, stance time at the follow-up was similar to that at baseline. This matching procedure can constrain changes in KAAI magnitudes to some degree. Future studies might consider collecting a natural walking speed at follow-up in addition to a controlled speed, as natural walking speed may change over time. However, based on the available data, lateral wedging does not appear to influence KAAI.
Interestingly, the results of these longitudinal biomechanical data provide a contrast to the longitudinal clinical outcomes reported previously from this same trial.35 The clinical outcome measures included the WOMAC index, a 6-min walk test, and a stair negotiation task. Unlike the biomechanical measures that favored the wedged group, these functional outcome measures were similarly improved in both groups at 1 year. However, the degradation of knee mechanics over time in the control group suggests a disconnect between knee mechanics and function. Alternately, the neutral orthosis, with its arch support, may have somehow provided enough added support and shock absorption to improve function, but was not designed to affect improve frontal plane knee mechanics. In a well-executed randomized controlled trial, Bennell et al.37 also found no advantages to lateral foot wedging over neutral insoles in symptom or structure modification.
A possible limitation in longitudinal gait studies is the test–retest reliability of gait measurements. This study utilized a marker set with high between-day reliability for the peak KEAM.41 Other reliability studies have evaluated both healthy individuals and those with medial knee OA.44–46 These four studies suggest that test–retest reliability for the KEAM is adequate for intervention studies. A second consideration is the small sample. As many of our p-values were borderline significant at the 0.05 level, we would have been able to make more definitive inferences with a larger sample. Third, as mentioned previously, follow-up assessment for disease progression could have been useful in interpreting the findings. Finally, we acknowledge that our study design did not incorporate a more traditional pre-treatment data point, rather allowing for accommodation to the orthotic prior to the baseline testing. Further information may have been revealed had we collected a third data point capturing the pre-accommodation data.
In summary, this study is among the first to present long-term knee mechanics data in a knee OA population,47 and is the first long-term study of the effects of lateral wedging on frontal plane knee mechanics. Our results suggest that lateral wedging may aid in maintaining baseline frontal plane knee mechanics over a 12-month time period in patients with medial knee OA as compared to neutral devices. Further, our data suggest individuals can expect long-term biomechanical effectiveness from lateral foot wedging. From a purely biomechanical perspective, these findings support the continued consideration of using lateral wedging in the management of medial knee OA.