Prosthetics and Orthotics International http://poi.sagepub.com/ Effect of an ankle−foot orthosis on knee joint mechanics: A novel conservative treatment for knee osteoarthritis Cynthia H Fantini Pagani, Steffen Willwacher, Rita Benker and Gert-Peter Brüggemann Prosthet Orthot Int published online 10 December 2013 DOI: 10.1177/0309364613513297 The online version of this article can be found at: http://poi.sagepub.com/content/early/2013/12/10/0309364613513297
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POI0010.1177/0309364613513297Prosthetics and Orthotics InternationalFantini Pagani et al.
INTERNATIONAL SOCIETY FOR PROSTHETICS AND ORTHOTICS
Original Research Report
Effect of an ankle–foot orthosis on knee joint mechanics: A novel conservative treatment for knee osteoarthritis
Prosthetics and Orthotics International 0(0) 1–11 © The International Society for Prosthetics and Orthotics 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0309364613513297 poi.sagepub.com
Cynthia H Fantini Pagani, Steffen Willwacher, Rita Benker, and Gert-Peter Brüggemann
Abstract Background: Several conservative treatments for medial knee osteoarthritis such as knee orthosis and laterally wedged insoles have been shown to reduce the load in the medial knee compartment. However, those treatments also present limitations such as patient compliance and inconsistent results regarding the treatment success. Objective: To analyze the effect of an ankle–foot orthosis on the knee adduction moment and knee joint alignment in the frontal plane in subjects with knee varus alignment. Study design: Controlled laboratory study, repeated measurements. Methods: In total, 14 healthy subjects with knee varus alignment were analyzed in five different conditions: without orthotic, with laterally wedged insoles, and with an ankle–foot orthosis in three different adjustments. Three-dimensional kinetic and kinematic data were collected during gait analysis. Results: Significant decreases in knee adduction moment, knee lever arm, and joint alignment in the frontal plane were observed with the ankle–foot orthosis in all three different adjustments. No significant differences could be found in any parameter while using the laterally wedged insoles. Conclusion: The ankle–foot orthosis was effective in reducing the knee adduction moment. The decreases in this parameter seem to be achieved by changing the knee joint alignment and thereby reducing the knee lever arm in the frontal plane. Clinical relevance This study presents a novel approach for reducing the load in the medial knee compartment, which could be developed as a new treatment option for patients with medial knee osteoarthritis. Keywords Knee osteoarthritis, knee varus alignment, orthotics, joint mechanics Date received: 14 May 2013; accepted: 18 October 2013
Background Osteoarthritis (OA) is one of the most frequent causes of disability in the elderly population.1 Painful knee OA associated with mild-to-moderate disability affects up to 10% of adults over 55 years of age.2 The causes of this degenerative disease are based on a combination of various systemic and biomechanical risk factors.3–5 It has been suggested that mechanical load plays an important role for the disease progression.6,7 Medial knee OA progression was reported in patients with higher knee adduction moment (KAM),8 which is an indicator of load distribution between medial and lateral knee compartments.9 The use of orthotic devices as conservative therapy for knee OA is supported by the concept that reducing the mechanical load in the affected knee compartment could
decelerate disease progression. Valgus knee braces and lateral wedged insoles have been shown to be effective in reducing the KAM to different extents.10–18 The reduction of this parameter with the use of different orthotic devices can be achieved by different mechanisms. A direct application of an abduction moment at the knee joint by a valgus brace was reported in previous studies as a mechanical Institute of Biomechanics and Orthopedics, German Sport University Cologne, Cologne, Germany Corresponding Author: Cynthia H Fantini Pagani, German Sport University Cologne, Am Sportpark Müngersdorf 6, 50933 Cologne, Germany. Email: [email protected]
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strategy for reducing the knee varus moment.17,19 In addition, changes in the knee lever arm in the frontal plane due to changes in the ground reaction force (GRF) components and joint alignment are also probable mechanisms described in the literature for the reduction of the KAM with the use of knee braces and wedged insoles.11,12 A recent study reported that the reduced lever arm in the knee joint observed with lateral wedged insoles resulted primarily from changes in the frontal plane orientation and location of the GRF vector relative to the knee center, rather than changes in the location of the knee center relative to the GRF due to changes in joint alignment.12
An important aspect for the effectiveness of lateral wedged insoles or wedged shoes on the reduction of knee joint loading is the stabilization of the ankle joint by using an ankle orthosis or strapping of the subtalar joint.20–23 The combination of wedged soles/insoles and ankle stabilization produced higher decreases in the KAM and medial knee joint force compared to the use of wedged soles/ insoles alone. According to the above-cited literature, ankle stabilization could contribute to avoid potential compensating coronal plane movements in foot and/or ankle joint, thereby increasing the effect of wedged insoles in knee joint unloading. Although the effectiveness of different knee braces has been shown in the literature, high cost and compliance are the factors which could compromise treatment success. Lateral wedged insoles present the advantages of low cost and high compliance; however, the decreases in the KAM are relatively small compared to that observed with knee braces. Additionally, some inconsistencies in the literature regarding the effectiveness of this intervention are reported.24–28 An alternative for decreasing the KAM could be achieved by increasing the ankle joint stabilization using an ankle–foot orthosis (AFO), which should reduce the lateral rotation of the tibia in the frontal plane, thereby reducing the knee varus deformity. This altered tibia position would lead to a more medial location of the knee joint center, reducing the knee lever arm in the frontal plane and therefore causing a decrease in the KAM. The purpose of this study was to analyze the effect of an AFO in different adjustments on knee joint kinetics and kinematics. We hypothesize that using an ankle orthosis in an adjustment, which should provide a medial shift of the knee joint center, will cause a decrease in the KAM. Therefore, the main outcome analyzed was the KAM. The second aim of this study was to analyze the mechanisms by which the KAM is altered with use of the AFO. Although alteration in the knee lever arm was found in previous studies with use of wedged insoles and knee braces, this alteration can be a result of a combination of various factors such as changes in knee joint position or alignment, changes in the center of pressure (COP)
position, or inclination of the GRF vector. Therefore, this study also aimed to analyze changes in those biomechanical parameters, such as secondary outcomes, which could contribute to the reduction of the KAM. In addition, possible kinematic changes in the ankle joint were also investigated because the AFO could possibly restrict ankle joint motion in the frontal and transversal planes.
Methods Participants In total, 14 healthy male subjects (age: 24 ± 4.8 years, height: 178.8 ± 5.7 cm, mass: 73.7 ± 8.0 kg) participated in this study. Inclusion criteria were varus knee alignment and the absence of pain or previous injuries of the lower extremity. Varus alignment was assessed using the intercondylar distance. Subjects presenting at least 50 mm intercondylar distance measured with a caliper were recruited for participating in the study. Because this pilot study was conducted with healthy subjects, a radiographic assessment of knee alignment was not performed for ethical reasons. High correlation (r = 0.89) between mechanical axis obtained using full radiographs and the intercondylar distance was recently reported.29 Ethics approval was obtained from the local institution, and all participants provided written informed consent before enrollment. Each subject attended the laboratory only once.
Data collection The test was conducted in the gait analysis laboratory at the Institute of Biomechanics and Orthopedics of the German Sport University Cologne. By using a study design with repeated measurements, each subject performed walking trials in each of the following conditions: without any kind of orthosis (baseline), with laterally wedged insoles (4° inclination), and AFO in neutral adjustment, in 4° valgus adjustment, and in 4° varus adjustment. Detailed information about the different AFO adjustments is provided in section “AFO” below. The different test conditions were applied at random order and participants were blinded to the different orthosis adjustments. Using a routine written in MATLAB 7.0 (The Math Works Inc., Natick, USA), 14 different sequences were created using random numbers, which represented the different conditions applied to the subjects. Before testing, subjects were asked to walk five times across a 13-m gait laboratory walkway to determine the mean (±5%) of their selfselected walking speed used for the data collection during the different test conditions. Overall, six trials were collected for each of the randomized conditions. The subjects used standardized neutral shoes manufactured by Victoria (Model: Victoria Sneaker marron; Calzados Nuevo
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Figure 1. Marker set used for the collection of kinematic data.
Milenio S.L., Calahorra, La Rioja, Spain) and provided with three holes for the positioning of screwable markers on the heel.
Gait analysis Participants underwent three-dimensional (3D) gait analysis using a 10-infrared camera system (Vicon Motion Systems, Oxford, UK) at 200 Hz. Two force plates (Kistler Instruments, Winterthur, Switzerland) embedded in the walkway captured GRF data at 1000 Hz. The moments acting about each joint were calculated by an inverse dynamic model and expressed as external moments. A custom-made model30,31 adjusted for the purpose of this study was used. The lower extremity was modeled as a linkage of three rigid bodies representing the foot, shank, and thigh. Infrared cameras were used to measure the 3D positions of retro-reflective markers, which were attached to each subject’s skin over the following bony landmarks: anterior superior iliac spines; posterior superior iliac spines; greater trochanter; medial and lateral femoral epicondyles; medial and lateral tibial condyles; tibia; medial and lateral malleoli; medial, lateral, and posterior aspects of the calcaneus; distal heads of the first and the fifth metatarsals; and hallux. The marker set used is represented in
Figure 1. The marker set was not changed throughout all test conditions. During the reference trial for the definition of joint centers, markers were placed on medial and lateral malleoli. Using this reference trial, ankle joint center could be defined in relation to the other three markers placed on the shank. Once the ankle joint center was defined, malleoli markers were removed for orthosis fitting, and ankle joint center could be calculated for the dynamic trials using the remaining shank markers.
AFO A prototype of an AFO, which was developed to induce changes in the tibia position in the frontal plane and stabilize the ankle joint, was used in this study. Ankle joint stabilization should be achieved by avoiding a lateral rotation of the proximal aspect of the tibia in the frontal plane. This prototype comprised a sole, which was inserted in the shoe, and a unilateral tubular frame, which passed laterally upward along the shank and was connected to the subject’s leg via a fastening device with straps. The orthosis joint could be adjusted in several varus/valgus angulations, which should lead to changes in the tibia position in the frontal plane. The orthosis’ joint allowed for unrestricted plantar and dorsal flexion; however, movements in the
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Figure 2. Subject with foot–ankle orthosis in (a) sagittal view and (b) frontal view. (c) Apparatus for adjusting the foot–ankle orthosis. The figure shows the orthosis in the neutral position. Black lines indicate the 4° valgus and varus adjustments.
frontal and transversal planes were restricted. The structure of the orthosis was complemented by a soft padding on the inside of the splint to ensure a comfortable wearing of the orthosis. To define the neutral position, the sole was inserted in the shoe, and the orthosis was positioned on the ankle and fixed to the subject’s leg, with the subject sitting on a chair. For adjusting the tubular frame to the shank contour, two adjusting screws localized at the orthosis’ joint axis and two screws localized at the tubular frame (proximal aspect of the shank) were loosened (Figure 2(a)). The subjects were asked to walk several steps with the orthosis before the screws were retightened so that the tubular frames of the orthosis could be adjusted to the subject’s leg contour. This orthosis adjustment was defined as “neutral” adjustment. By retightening the screws and adjusting the straps, a firm tension was produced to avoid orthosis’ slipping, without soft tissue binding. Once the orthosis was adjusted and fixed at the subject’s shank, the strap tension was kept constant by maintaining the same strap length for the other conditions (4° valgus, 4° varus). After setting the neutral adjustment by fitting the orthosis to the subject’s leg, the orthosis was positioned on an apparatus for setting varus/valgus adjustments from this individual neutral position (Figure 2(c)). A pole adjustable in height included three holes, in which a perpendicular reference bar could be positioned. Before loosening the screws for allowing changes in the AFO adjustment, only the position of the adjustable pole with the reference bar was
changed to fit to the individual neutral position of the orthosis. For this purpose, the reference bar was placed in the middle hole, and the pole was lifted up until the bar was in contact with the tubular frame. For each subject, the initial height of the pole was maintained at this position, and for the two other conditions (4° valgus and 4° varus), only the reference bar was repositioned. The 4° valgus adjustment was achieved by placing the reference bar in the lowest hole and loosening the screws to permit adjustments of the tubular frame, changing the AFO adjustment. The frame was set down until they had contact with the reference bar and the screws were then retightened in this position. For the 4° varus adjustment, a similar procedure was applied using the upper hole of the pole. The distance between each hole corresponded to changes of 4°. In this study, the “valgus adjustment” was defined as the adjustment which would induce a more valgus alignment at the knee by avoiding a lateral rotation of the proximal aspect of the tibia in the frontal plane. Then, this definition of “valgus adjustment” refers to kinematic changes at the knee and not at the ankle joint.
Data analysis Joint moment calculations were based on the mass and inertial characteristics of the limb, the derived linear and angular velocities, and accelerations of each lower extremity segment, as well as GRF and estimated joint center position. Marker trajectories were filtered using
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Fantini Pagani et al. Table 1. Mean and SD of the KAM (first and second peaks) and knee adduction angular impulse during different test conditions. For the intervention conditions (wedged insoles and AFO), mean differences with 95% CI and effect sizes related to the baseline condition are also presented.
Baseline Mean (SD) Wedged insoles Mean (SD) Mean difference (95% CI) Effect size AFO varus Mean (SD) Mean difference (95% CI) Effect size AFO neutral Mean (SD) Mean difference (95% CI) Effect size AFO valgus Mean (SD) Mean difference (95% CI) Effect size
KAM—first peak (N m/kg)
KAM—second peak (N m/kg)
Knee adduction angular impulse (N m s/kg)
0.658 (0.151)
0.579 (0.149)
0.245 (0.055)
0.656 (0.146) 0.002 (−0.025/0.029) 0.013
0.567 (0.158) 0.012 (−0.012/0.036) 0.078
0.241 (0.055) 0.004 (−0.003/0.011) 0.073
0.605 (0.149)*† 0.053 (0.014/0.091) 0.353
0.583 (0.150) −0.004 (−0.024/0.015) 0.027
0.237 (0.058)*‡ 0.008 (0.0001/0.016) 0.142
0.586 (0.123)*† 0.072 (0.030/0.115) 0.523
0.576 (0.142) 0.003 (−0.016/0.022) 0.021
0.232 (0.053)* 0.013 (0.003/0.024) 0.241
0.580 (0.137)*† 0.078 (0.038/0.118) 0.541
0.574 (0.147) 0.005 (−0.022/0.031) 0.034
0.227 (0.055)*† 0.018 (0.012/0.025) 0.327
KAM: knee adduction moment (positive: adduction); SD: standard deviation; AFO: ankle–foot orthosis; CI: confidence interval. Knee adduction angular impulse: positive area under the KAM curve (positive: adduction impulse). Effect size = (MeanBaseline − MeanCondition)/SDPooled, where SDPooled = sqrt[((nBaseline −1)SDBaseline 2 +(nCondition −1)SDCondition2 ) / (nBaseline +nCondition − 2)] . *Significant
differences compared to the condition “Baseline”; SPSS Bonferroni-adjusted p < 0.05. †Significant differences compared to the condition “Wedges”; SPSS Bonferroni-adjusted p < 0.05. ‡Significant differences compared to the condition “Valgus”; SPSS Bonferroni-adjusted p < 0.05.
a fourth-order recursive Butterworth filter with a cutoff frequency of 10 Hz. All kinetic parameters were normalized to body mass. A custom algorithm written in MATLAB 7.0 was used for the calculations. Variables of interest were KAM, knee lever arm and position of knee joint center in the frontal plane, knee angles in the frontal and transversal planes, position of COP, and inclination and magnitude of the GRF vector in the frontal plane. Additionally, ankle angles in the frontal and transversal planes were also investigated because the orthosis’ joint restricted movements in those planes. For the KAM, first and second peaks during stance were analyzed as well as the knee adduction angular impulse. As the secondary purpose of this study was to analyze the mechanisms for possible changes in the KAM, all other parameters were analyzed at the instant of the first peak KAM or second peak KAM if significant changes were observed for those peaks.
Statistics After testing for normal distribution of the data, comparisons between conditions were performed with analysis of variance with repeated measures since all conditions for using parametric tests were attended. Bonferroni corrections
were applied in the post hoc pairwise comparisons, when a significant overall main effect was detected, so that corrected p values were used for the pairwise comparisons between all test conditions at a level of significance of 0.05. Statistical analyses were performed using IBM SPSS Version 20 (IBM Corporation, New York, USA).
Results Subjects walked with a mean gait velocity of 1.44 m/s (baseline: 1.45 (0.17), wedged insoles: 1.44 (0.18), AFO neutral: 1.44 (0.17), AFO varus: 1.44 (0.18); and AFO valgus: 1.45 (0.17)). Significant differences in the first peak KAM and in the knee adduction angular impulse were observed for the conditions with AFO in the three different adjustments (Table 1). Decreases of 8.1%, 10.9%, and 11.9% in the first peak KAM were observed for the varus, neutral, and valgus adjustments, respectively, compared with the baseline condition. For the parameter knee adduction angular impulse, decreases of 3.3%, 5.3%, and 7.3% were found for the varus, neutral, and valgus adjustments, respectively, compared with the baseline condition. No significant differences were observed between baseline and laterally wedged insoles. GRF data are presented in Table 2. No significant differences were observed among test conditions.
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Table 2. Mean and SD of the GRF in the frontal plane during different test conditions. Presented GRF data correspond to the instant of first peak knee adduction moment. For the intervention conditions (wedged insoles and AFO), mean differences with 95% CI and effect sizes related to the baseline condition are also presented.
Baseline Mean (SD) Wedged insoles Mean (SD) Mean difference (95% CI) Effect size AFO varus Mean (SD) Mean difference (95% CI) Effect size AFO neutral Mean (SD) Mean difference (95% CI) Effect size AFO valgus Mean (SD) Mean difference (95% CI) Effect size
GRF resultant frontal (N/kg)
GRF Z (N/kg)
GRF Y (N/kg)
11.43 (1.17)
11.42 (1.17)
11.55 (1.17) −0.12 (−0.47/0.24) 0.097
11.53 (1.17) −0.11 (−0.47/0.24) 0.099
0.52 (0.18) −0.01 (−0.12/0.11) 0.031
2.57 (0.74) 0.00 (−0.60/0.62) 0.006
11.49 (1.23) −0.06 (−0.40/0.28) 0.048
11.48 (1.23) −0.06 (−0.40/0.29) 0.049
0.51 (0.15) 0.00 (−0.13/0.13) 0.005
2.58 (0.70) −0.01 (−0.67/0.66) 0.003
11.30 (1.25) 0.13 (−0.23/0.49) 0.109
11.29 (1.25) 0.13 (−0.24/0.49) 0.107
0.49 (0.13) 0.03 (−0.12/0.18) 0.161
2.49 (0.60) 0.08 (−0.67/0.84) 0.107
11.41 (1.34) 0.02 (−0.54/0.58) 0.017
11.40 (1.34) 0.02 (−0.54/0.58) 0.0167
0.54 (0.15) −0.03 (−0.15/0.09) 0.163
2.75 (0.76) −0.18 (−0.82/0.46) 0.214
0.51 (0.21)
GRF angle (°)
2.57 (0.92)
SD: standard deviation; GRF: ground reaction force; AFO: ankle–foot orthosis; CI: confidence interval. GRF Z: vertical component of the ground reaction force (positive: up); GRF Y: mediolateral component of the ground reaction force (positive: medial); GRF angle: angle between the ground reaction force vector in the frontal plane and a vertical axis (positive: inclination in the medial direction). Effect size = (MeanBaseline − MeanCondition)/SDPooled, where . 2 2
SDPooled = sqrt[((nBaseline −1)SDBaseline +(nCondition −1)SDCondition ) / (nBaseline +nCondition − 2)]
Significant decreases in the knee lever arm in the frontal plane were found with the AFO orthosis in the three different adjustments compared to baseline condition (Table 3). This parameter also decreased significantly with the AFO in neutral and valgus adjustments compared with the laterally wedged insoles. No significant differences were observed among AFO adjustments. Decreases observed in relation to baseline were 6.7%, 8.8%, and 10.3% for the varus, neutral, and valgus adjustments, respectively. The knee angle in the frontal plane also decreased significantly, indicating a change from varus to a valgus position. Mean curves of KAM, knee lever arm, knee angle, and tibia rotation in the frontal plane for all subjects during the different test conditions are presented in Figure 3. At the instant of the first peak KAM, significant differences were observed for the angle of the ankle joint in the frontal plane between wedged insoles and all other test conditions, indicating a higher eversion of the calcaneus in relation to the tibia with laterally wedged insoles (baseline: 1.38° ± 2.55°; wedged insoles: 4.36° ± 3.03°; varus: 1.11° ± 4.64°; neutral: 0.33° ± 3.69°; and valgus: 0.03° ± 4.84°). In the transversal plane, no significant differences in the external rotation could be observed between conditions (baseline: 5.81° ± 3.26°; wedged insoles: 6.99° ± 3.18°; varus: 6.50° ± 2.87°; neutral: 6.45° ± 3.07°; and valgus: 6.40° ± 3.38°).
Discussion The primary aim of this pilot study was to investigate the effect of an AFO on the KAM in subjects with knee varus alignment. The AFO tested in this experiment was a prototype, which was designed to change the tibia orientation in the frontal plane and to stabilize the ankle joint. The valgus adjustments of this orthosis should contribute to keep the tibia in a more vertical position, avoiding a lateral rotation of the proximal aspect of the tibia in the frontal plane. This would cause a decrease in the knee lever arm in the frontal plane and thereby decreasing the KAM. The varus adjustment should cause an opposite effect increasing the knee varus malalignment and the KAM. Significant decreases in the KAM, knee lever arm, and knee varus angle in the frontal plane were observed with the AFO in all three adjustments, which contradicts our expectations. The neutral adjustment adopted in this study was defined as the orthosis configuration, which should fit to leg contour. From this position, valgus and varus adjustments corresponded to 4° changes in relation to the neutral adjustment in either direction. It is possible that changing the orthosis configuration by only 4° in each direction was not sufficient for producing different effects among the three adjustments. This limitation regarding the different orthosis adjustments should be investigated in future studies. It seems that the AFO, independent from the adjustment used, offers ankle stabilization
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Baseline
−17.90 (9.22) −17.84 (8.07) −0.06 (2.65/2.53) 0.001 −18.80 (9.02) 0.90 (−2.29/4.09) 0.099 −20.28 (8.88) 2.38 (−1.20/5.96) 0.263 −20.61 (8.49) 2.71 (−0.88/6.29) 0.306
59.37 (11.69) 58.26 (10.40) 1.11 (−0.87/3.09) 0.101 55.37 (10.98)* 4.00 (0.28/7.74) 0.353 54.15 (8.30)*† 5.22 (0.81/9.64) 0.515 53.26 (10.25)*† 6.11 (2.04/10.19) 0.556
COP (mm)
0.34 (2.29)*† 1.90 (1.04/2.77) 0.755
0.49 (2.34)*† 1.76 (0.86/2.65) 0.690
0.59 (2.74)*† 1.65 (0.91/2.39) 0.603
2.26 (2.61) −0.02 (−0.29/0.24) 0.009
2.24 (2.73)
Knee angle (°) (frontal plane)
−1.14 (1.01) 0.75 (−0.10/1.60) 0.769
−1.21 (0.98) 0.82 (−0.05/1.69) 0.854
−1.09 (1.00) 0.69 (−0.25/1.63) 0.717
−0.51 (1.06) 0.12 (−0.38/0.61) 0.116
−0.39 (0.94)
Knee angle (°) (transversal plane)
−41.75 (13.63)* −7.09 (−12.18/−2.00) 0.513
−45.25 (14.17) −3.58 (−7.49/0.32) 0.254
−44.04 (12.95)* −4.79 (−9.38/−0.20) 0.355
−45.85 (13.72) −2.98 (−7.21/1.24) 0.215
−48.83 (14.02)
Position of knee joint center (mm) (frontal plane)
*Significant
Pooled
Condition
Condition
Baseline
Condition
differences compared to the condition “Baseline”; SPSS Bonferroni-adjusted p < 0.05. †Significant differences compared to the condition “Wedges”; SPSS Bonferroni-adjusted p < 0.05.
Baseline
SD: standard deviation; COP: center of pressure; AFO: ankle–foot orthosis; CI: confidence interval. Knee lever arm: distance between knee joint center and ground reaction force vector in the frontal plane (positive: vector passes medially to knee joint center); COP: distance between point of force application and gait direction (positive: medial to the midline of the foot); knee angle: angle between femur and shank segments in the frontal plane (positive: varus) and transversal plane (positive: internal rotation); position of knee joint center in the frontal plane: with respect to the posterior heel marker at the instant of touchdown in the mediolateral direction (positive: medial). Effect size = (MeanBaseline − MeanCondition)/SDPooled, where 2 2 SD = sqrt[((n −1)SD +(n −1)SD ) / (n +n − 2)] .
Baseline Mean (SD) Wedged insoles Mean (SD) Mean difference (95% CI) Effect size AFO varus Mean (SD) Mean difference (95% CI) Effect size AFO neutral Mean (SD) Mean difference (95% CI) Effect size AFO valgus Mean (SD) Mean difference (95% CI) Effect size
Knee lever arm (mm)
Table 3. Mean and SD of knee lever arm in the frontal plane, COP, knee angle (frontal and transversal planes), and position of the knee joint center in the frontal plane during different test conditions. Presented data correspond to the instant of first peak knee adduction moment. For the intervention conditions (wedged insoles and AFO), mean differences with 95% CI and effect sizes related to the baseline condition are also presented.
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Figure 3. Mean curves of (a) knee adduction moment, (b) knee lever arm, (c) knee angle, and (d) tibia rotation in the frontal plane normalized through the stance phase for all subjects during the different test conditions. The shaded area indicates ±SD of the baseline condition. SD: standard deviation; AFO: ankle–foot orthosis.
avoiding the external rotation of the shank in the frontal plane (Figure 4). By keeping the shank in a more vertical position, the knee lever arm (distance between GRF vector and knee joint center) is shorter. This altered position of the tibia in the frontal plane while wearing the AFO is illustrated in Figure 3(d). It is important to note that this graph shows the orientation of the shank segment in the global coordinate system and does not represent the angle of the ankle joint in the frontal plane. The angle of the ankle joint (angle between calcaneus and tibia) was not significantly altered by the AFO compared to baseline. Stabilization of the ankle joint was already pointed out in early studies as an important factor for the effectiveness of laterally wedged insoles.22,23 According to those authors, kinematic changes in the subtalar joint induced by laterally wedged soles could be better transferred to the tibia by strapping the ankle joint, avoiding compensating
movements of the talus. Although significant increase in the eversion angle between calcaneus and tibia was observed with wedged insoles in this study, this change was not transferred to the tibia and no changes in the knee angle in the frontal plane could be found. Kutzner et al.20 reported slightly higher unloading effect of the medial knee compartment using a combination of wedged insoles and a soft ankle orthosis. Also, better results regarding the KAM were observed by Schmalz et al.21 combining wedged soles and ankle orthosis. The above-cited studies used the ankle orthosis only as a stabilization element for the joint. This study analyzed the effect of changing the orthosis alignment in the frontal plane to induce kinematic and/or kinetic changes at the knee joint. The combination of wedged insoles and the AFO was not analyzed in this study. Changes in the KAM with laterally wedged insoles could not be observed in this sample of healthy
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Figure 4. Schematic representation of different mechanisms for changing the knee adduction moment. The AFO alters the tibia rotation in the frontal plane, reducing the knee varus malalignment, which causes a reduction in the lever arm in the frontal plane. AFO: ankle–foot orthosis; COP: center of pressure.
individuals. Small decreases (about 7%) in the second peak KAM were reported in our previous study with patients with medial knee OA using the same insoles as used in this study.11 Individual responses to laterally wedged insoles are widely reported in the literature, and it is known that some subjects present an opposite effect on the KAM than that expected while using such foot orthotics.12,13,24,26,27 The reasons for these individual responses are not clear. In our sample of 14 subjects, 5 individuals presented an increase in the first peak KAM and 3 individuals in the second peak KAM. It is interesting to note that the opposite response in the first and second peak KAM was not observed in the same subjects. Future studies should investigate the reasons for these findings. Possibly, treatment success with laterally wedged insoles could be related to ankle joint stiffness of each subject. Stiffness is defined by the relationship between the applied force and the resulting displacement. Since joint movement occurs mostly rotational and not translational, joint stiffness can be defined as the relationship between external joint moment and changes in the angle of the joint (resistance to movement). It is affected by the combination of different factors such as passive joint structures (tissue viscoelastic properties of joint capsule and ligaments) and neuromuscular aspects.32 Those factors determine how much movement can be achieved in a joint for a given external joint moment. Maybe subjects with higher joint stiffness in the frontal plane could have more benefit from wearing laterally wedged insoles than subjects with lower
joint stiffness, by allowing kinematic changes in the subtalar joint to be better transferred to the tibia. This speculation is based on previous studies, which reported better results of laterally wedged insoles using subtalar strapping or ankle stabilization.20–23 A secondary objective of this study was to investigate the reasons for possible changes in the KAM. Therefore, other biomechanical parameters besides KAM were also investigated. No significant changes in the COP and GRF magnitude or inclination at the time of the first peak KAM could be identified with the different orthotic devices. Those parameters were not analyzed for the second half of the stance phase because no significant changes were identified in the second peak KAM. A recent study by Hinman et al.12 used a regression analysis to identify the contribution of different biomechanical parameters to the reduction of the KAM observed with wedged insoles. This approach was not applied in this study due to the small sample size analyzed. Nevertheless, it seems that the underlying mechanisms for decreased KAM observed with the AFO are different from that observed with laterally wedged insoles reported by Hinman et al.12 Those authors identified a reduction of the knee lever arm in the frontal plane, which explained about 46% of the changes in the KAM. Although this was the only parameter, which significantly explained the changes in the KAM, Hinman et al.12 reported significant differences in the COP and GRF data. Additionally, changes in those parameters (COP and GRF) correlated significantly with the changes observed in the KAM. In
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this study, a reduction of the knee lever arm was also observed; however, we suppose that this change occurs due to the alteration in the knee angle in the frontal plane since no changes were observed in the COP or GRF (Figure 4). Future studies with a larger sample would elucidate the mechanisms for reduced KAMs with an AFO by using a regression analysis. Besides the small sample size, a further limitation of this study is the investigation of an orthotic device in healthy subjects. Although the sample was composed of individuals with knee varus alignment, a joint deformity, which is often observed in patients with medial knee OA and associated with higher joint loads in the medial knee compartment, the generalization of the results for an osteoarthritic population should be done with caution. Some gait strategies used by patients with knee OA, such as toe-out gait and lateral trunk sway, were reported in the literature as an attempt to reduce knee joint loading.33 Future studies should investigate whether patients still would use such strategies in combination with the orthotic device. Anyway, the tested AFO showed to be effective in reducing knee varus malalignment, which from a mechanical point of view would contribute to reduce the KAM also in patients with knee OA and varus alignment. Another important aspect, which should be investigated in future studies, is patient compliance achieved with the AFO. Compliance is a concern regarding almost all orthotic devices. However, when comparing this AFO to traditional knee braces for knee OA, some advantages of the former device regarding wearing comfort can be pointed out, which could contribute to better compliance. Most patients complain about the length, weight, and the difficulty of wearing knee braces under the cloths. Those aspects could be minimized using an AFO compared to knee braces. Wedged insoles show better acceptance; however, its effectiveness is questionable. Future studies with patients with knee OA should provide more insight into compliance of this new orthotic device.
Conclusion In summary, a significant decrease in the KAM could be observed in subjects with knee varus alignment while using an AFO in different adjustments (4° valgus, neutral, and 4° varus). The orthosis was effective in changing the knee joint alignment and the knee joint lever arm in the frontal plane. Long-term effects on the KAM, symptoms, joint function, and compliance in patients with medial knee OA should be investigated in future studies. The use of AFOs designed to change the tibia position and thereby the knee joint alignment in the frontal plane could represent an alternative for conservative treatment of knee OA. Conflict of interest None declared.
Funding This study was founded by the Institute of Biomechanics and Orthopedics of the German Sport University Cologne.
References 1. Guccione AA, Felson DT, Anderson JJ, et al. The effects of specific medical conditions on the functional limitations of elders in the Framingham Study. Am J Public Health 1994; 84(3): 351–358. 2. Peat G, McCarney R and Croft P. Knee pain and osteoarthritis in older adults: a review of community burden and current use of primary health care. Ann Rheum Dis 2001; 60(2): 91–97. 3. Felson DT, Goggins J, Niu J, et al. The effect of body weight on progression of knee osteoarthritis is dependent on alignment. Arthritis Rheum 2004; 50(12): 3904–3909. 4. Garstang SV and Stitik TP. Osteoarthritis: epidemiology, risk factors, and pathophysiology. Am J Phys Med Rehabil 2006; 85(Suppl. 11): S2–S11. 5. Suri P, Morgenroth DC and Hunter DJ. Epidemiology of osteoarthritis and associated comorbidities. PM R 2012; 4: 10–19. 6. Andriacchi TP, Mündermann A, Smith RL, et al. A framework for the in vivo pathomechanics of osteoarthritis at the knee. Ann Biomed Eng 2004; 32(3): 447–457. 7. Andriacchi TP, Koo S and Scanlan SF. Gait mechanics influence healthy cartilage morphology and osteoarthritis of the knee. J Bone Joint Surg Am 2009; 91(Suppl. 1): 95–101. 8. Miyazaki T, Wada M, Kawahara H, et al. Dynamic load at baseline can predict radiographic disease progression in medial compartment knee osteoarthritis. Ann Rheum Dis 2002; 61(7): 617–622. 9. Schipplein OD and Andriacchi TP. Interaction between active and passive knee stabilizers during level walking. J Orthop Res 2005; 9(1): 113–119. 10. Crenshaw SJ, Pollo FE and Calton EF. Effects of lateralwedged insoles on kinetics at the knee. Clin Orthop Relat Res 2000; 375: 185–192. 11. Fantini Pagani CH, Hinrichs M and Brüggemann GP. Kinetic and kinematic changes with the use of valgus knee brace and lateral wedge insoles in patients with medial knee osteoarthritis. J Orthop Res 2012; 30(7): 1125–1132. 12. Hinman RS, Bowles KA, Metcalf BB, et al. Lateral wedge insoles for medial knee osteoarthritis: effects on lower limb frontal plane biomechanics. Clin Biomech 2012; 27(1): 27–33. 13. Hinman RS, Payne C, Metcalf BR, et al. Lateral wedges in knee osteoarthritis: What are their immediate clinical and biomechanical effects and can these predict a three-month clinical outcome? Arthritis Rheum 2008; 59: 408–415. 14. Kerrigan DC, Lelas JL, Goggins J, et al. Effectiveness of a lateral-wedge insole on knee varus torque in patients with knee osteoarthritis. Arch Phys Med Rehabil 2002; 83(7): 889–893. 15. Lindenfeld TN, Hewett TE and Andriacchi TP. Joint loading with valgus bracing in patients with varus gonarthrosis. Clin Orthop Relat Res 1997; 344: 290–297. 16. Nakajima K, Kakihana W, Nakagawa T, et al. Addition of an arch support improves the biomechanical effect of a laterally wedged insole. Gait Posture 2009; 29(2): 208–213.
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Fantini Pagani et al. 17. Pollo FE, Otis JC, Backus SI, et al. Reduction of medial compartment loads with valgus bracing of the osteoarthritic knee. Am J Sports Med 2002; 30(3): 414–421. 18. Self BP, Greenwald RM and Pflaster DS. A biomechanical analysis of a medial unloading brace for osteoarthritis in the knee. Arthrit Care Res 2000; 13(4): 191–197. 19. Fantini Pagani CH, Potthast W and Brüggemann GP. The effect of valgus bracing on the knee adduction moment during gait and running in male subjects with varus alignment. Clin Biomech 2010; 25(1): 70–76. 20. Kutzner I, Damm P, Heinlein B, et al. The effect of laterally wedged shoes on the loading of the medial knee compartment-in vivo measurements with instrumented knee implants. J Orthop Res 2011; 29(12): 1910–1915. 21. Schmalz T, Blumentritt S, Drewitz H, et al. The influence of sole wedges on frontal plane knee kinetics, in isolation and in combination with representative rigid and semi-rigid ankle-foot-orthoses. Clin Biomech 2006; 21(6): 631–639. 22. Toda Y and Tsukimura N. A six-month followup of a randomized trial comparing the efficacy of a lateral-wedge insole with subtalar strapping and an in-shoe lateral-wedge insole in patients with varus deformity osteoarthritis of the knee. Arthritis Rheum 2004; 50(10): 3129–3136. 23. Toda Y, Tsukimura N and Kato A. The effects of different elevations of laterally wedged insoles with subtalar strapping on medial compartment osteoarthritis of the knee. Arch Phys Med Rehabil 2004; 85(4): 673–677. 24. Kakihana W, Akai M, Nakazawa K, et al. Effects of laterally wedged insoles on knee and subtalar joint moments. Arch Phys Med Rehabil 2005; 86(7): 1465–1471.
25. Maly MR, Culham EG and Costigan PA. Static and dynamic biomechanics of foot orthoses in people with medial compartment knee osteoarthritis. Clin Biomech 2002; 17(8): 603–610. 26. Butler RJ, Marchesi S, Royer T, et al. The effect of a subject-specific amount of lateral wedge on knee mechanics in patients with medial knee osteoarthritis. J Orthop Res 2007; 25: 1121–1127. 27. Kakihana W, Akai M, Nakazawa K, et al. Inconsistent knee varus moment reduction caused by a lateral wedge in knee osteoarthritis. Am J Phys Med Rehabil 2007; 86(6): 446–454. 28. Bennell KL, Bowles KA, Payne C, et al. Lateral wedge insoles for medial knee osteoarthritis: 12 month randomized controlled trial. BMJ 2011; 342: d2912. 29. Navali AM, Bahari LAS and Nazari B. A comparative assessment of alternatives to the full-leg radiograph for determining knee joint alignment. Sports Med Arthrosc Rehabil Ther Technol 2012; 4(1): 40. 30. Braunstein B, Arampatzis A, Eysel P, et al. Footwear affects the gearing at the ankle and knee joints during running. J Biomech 2010; 43(11): 2120–2125. 31. Cappozzo A, Della Croce U, Leardini A, et al. Human movement analysis using stereophotogrammetry. Part 1: theoretical background. Gait Posture 2005; 21(2): 186–196. 32. Butler RJ, Crowell HP III and Davis IM. Lower extremity stiffness: implications for performance and injury. Clin Biomech 2003; 18: 511–517. 33. Simic M, Hinman RS, Wrigley TV, et al. Gait modification strategies for altering medial knee load: a systematic review. Arthrit Care Res 2011; 63(3): 405–426.
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513297 research-article2013
POI0010.1177/0309364613513297Prosthetics and Orthotics InternationalFantini Pagani et al.
INTERNATIONAL SOCIETY FOR PROSTHETICS AND ORTHOTICS
Original Research Report
Effect of an ankle–foot orthosis on knee joint mechanics: A novel conservative treatment for knee osteoarthritis
Prosthetics and Orthotics International 0(0) 1–11 © The International Society for Prosthetics and Orthotics 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0309364613513297 poi.sagepub.com
Cynthia H Fantini Pagani, Steffen Willwacher, Rita Benker, and Gert-Peter Brüggemann
Abstract Background: Several conservative treatments for medial knee osteoarthritis such as knee orthosis and laterally wedged insoles have been shown to reduce the load in the medial knee compartment. However, those treatments also present limitations such as patient compliance and inconsistent results regarding the treatment success. Objective: To analyze the effect of an ankle–foot orthosis on the knee adduction moment and knee joint alignment in the frontal plane in subjects with knee varus alignment. Study design: Controlled laboratory study, repeated measurements. Methods: In total, 14 healthy subjects with knee varus alignment were analyzed in five different conditions: without orthotic, with laterally wedged insoles, and with an ankle–foot orthosis in three different adjustments. Three-dimensional kinetic and kinematic data were collected during gait analysis. Results: Significant decreases in knee adduction moment, knee lever arm, and joint alignment in the frontal plane were observed with the ankle–foot orthosis in all three different adjustments. No significant differences could be found in any parameter while using the laterally wedged insoles. Conclusion: The ankle–foot orthosis was effective in reducing the knee adduction moment. The decreases in this parameter seem to be achieved by changing the knee joint alignment and thereby reducing the knee lever arm in the frontal plane. Clinical relevance This study presents a novel approach for reducing the load in the medial knee compartment, which could be developed as a new treatment option for patients with medial knee osteoarthritis. Keywords Knee osteoarthritis, knee varus alignment, orthotics, joint mechanics Date received: 14 May 2013; accepted: 18 October 2013
Background Osteoarthritis (OA) is one of the most frequent causes of disability in the elderly population.1 Painful knee OA associated with mild-to-moderate disability affects up to 10% of adults over 55 years of age.2 The causes of this degenerative disease are based on a combination of various systemic and biomechanical risk factors.3–5 It has been suggested that mechanical load plays an important role for the disease progression.6,7 Medial knee OA progression was reported in patients with higher knee adduction moment (KAM),8 which is an indicator of load distribution between medial and lateral knee compartments.9 The use of orthotic devices as conservative therapy for knee OA is supported by the concept that reducing the mechanical load in the affected knee compartment could
decelerate disease progression. Valgus knee braces and lateral wedged insoles have been shown to be effective in reducing the KAM to different extents.10–18 The reduction of this parameter with the use of different orthotic devices can be achieved by different mechanisms. A direct application of an abduction moment at the knee joint by a valgus brace was reported in previous studies as a mechanical Institute of Biomechanics and Orthopedics, German Sport University Cologne, Cologne, Germany Corresponding Author: Cynthia H Fantini Pagani, German Sport University Cologne, Am Sportpark Müngersdorf 6, 50933 Cologne, Germany. Email: [email protected]
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strategy for reducing the knee varus moment.17,19 In addition, changes in the knee lever arm in the frontal plane due to changes in the ground reaction force (GRF) components and joint alignment are also probable mechanisms described in the literature for the reduction of the KAM with the use of knee braces and wedged insoles.11,12 A recent study reported that the reduced lever arm in the knee joint observed with lateral wedged insoles resulted primarily from changes in the frontal plane orientation and location of the GRF vector relative to the knee center, rather than changes in the location of the knee center relative to the GRF due to changes in joint alignment.12
An important aspect for the effectiveness of lateral wedged insoles or wedged shoes on the reduction of knee joint loading is the stabilization of the ankle joint by using an ankle orthosis or strapping of the subtalar joint.20–23 The combination of wedged soles/insoles and ankle stabilization produced higher decreases in the KAM and medial knee joint force compared to the use of wedged soles/ insoles alone. According to the above-cited literature, ankle stabilization could contribute to avoid potential compensating coronal plane movements in foot and/or ankle joint, thereby increasing the effect of wedged insoles in knee joint unloading. Although the effectiveness of different knee braces has been shown in the literature, high cost and compliance are the factors which could compromise treatment success. Lateral wedged insoles present the advantages of low cost and high compliance; however, the decreases in the KAM are relatively small compared to that observed with knee braces. Additionally, some inconsistencies in the literature regarding the effectiveness of this intervention are reported.24–28 An alternative for decreasing the KAM could be achieved by increasing the ankle joint stabilization using an ankle–foot orthosis (AFO), which should reduce the lateral rotation of the tibia in the frontal plane, thereby reducing the knee varus deformity. This altered tibia position would lead to a more medial location of the knee joint center, reducing the knee lever arm in the frontal plane and therefore causing a decrease in the KAM. The purpose of this study was to analyze the effect of an AFO in different adjustments on knee joint kinetics and kinematics. We hypothesize that using an ankle orthosis in an adjustment, which should provide a medial shift of the knee joint center, will cause a decrease in the KAM. Therefore, the main outcome analyzed was the KAM. The second aim of this study was to analyze the mechanisms by which the KAM is altered with use of the AFO. Although alteration in the knee lever arm was found in previous studies with use of wedged insoles and knee braces, this alteration can be a result of a combination of various factors such as changes in knee joint position or alignment, changes in the center of pressure (COP)
position, or inclination of the GRF vector. Therefore, this study also aimed to analyze changes in those biomechanical parameters, such as secondary outcomes, which could contribute to the reduction of the KAM. In addition, possible kinematic changes in the ankle joint were also investigated because the AFO could possibly restrict ankle joint motion in the frontal and transversal planes.
Methods Participants In total, 14 healthy male subjects (age: 24 ± 4.8 years, height: 178.8 ± 5.7 cm, mass: 73.7 ± 8.0 kg) participated in this study. Inclusion criteria were varus knee alignment and the absence of pain or previous injuries of the lower extremity. Varus alignment was assessed using the intercondylar distance. Subjects presenting at least 50 mm intercondylar distance measured with a caliper were recruited for participating in the study. Because this pilot study was conducted with healthy subjects, a radiographic assessment of knee alignment was not performed for ethical reasons. High correlation (r = 0.89) between mechanical axis obtained using full radiographs and the intercondylar distance was recently reported.29 Ethics approval was obtained from the local institution, and all participants provided written informed consent before enrollment. Each subject attended the laboratory only once.
Data collection The test was conducted in the gait analysis laboratory at the Institute of Biomechanics and Orthopedics of the German Sport University Cologne. By using a study design with repeated measurements, each subject performed walking trials in each of the following conditions: without any kind of orthosis (baseline), with laterally wedged insoles (4° inclination), and AFO in neutral adjustment, in 4° valgus adjustment, and in 4° varus adjustment. Detailed information about the different AFO adjustments is provided in section “AFO” below. The different test conditions were applied at random order and participants were blinded to the different orthosis adjustments. Using a routine written in MATLAB 7.0 (The Math Works Inc., Natick, USA), 14 different sequences were created using random numbers, which represented the different conditions applied to the subjects. Before testing, subjects were asked to walk five times across a 13-m gait laboratory walkway to determine the mean (±5%) of their selfselected walking speed used for the data collection during the different test conditions. Overall, six trials were collected for each of the randomized conditions. The subjects used standardized neutral shoes manufactured by Victoria (Model: Victoria Sneaker marron; Calzados Nuevo
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Figure 1. Marker set used for the collection of kinematic data.
Milenio S.L., Calahorra, La Rioja, Spain) and provided with three holes for the positioning of screwable markers on the heel.
Gait analysis Participants underwent three-dimensional (3D) gait analysis using a 10-infrared camera system (Vicon Motion Systems, Oxford, UK) at 200 Hz. Two force plates (Kistler Instruments, Winterthur, Switzerland) embedded in the walkway captured GRF data at 1000 Hz. The moments acting about each joint were calculated by an inverse dynamic model and expressed as external moments. A custom-made model30,31 adjusted for the purpose of this study was used. The lower extremity was modeled as a linkage of three rigid bodies representing the foot, shank, and thigh. Infrared cameras were used to measure the 3D positions of retro-reflective markers, which were attached to each subject’s skin over the following bony landmarks: anterior superior iliac spines; posterior superior iliac spines; greater trochanter; medial and lateral femoral epicondyles; medial and lateral tibial condyles; tibia; medial and lateral malleoli; medial, lateral, and posterior aspects of the calcaneus; distal heads of the first and the fifth metatarsals; and hallux. The marker set used is represented in
Figure 1. The marker set was not changed throughout all test conditions. During the reference trial for the definition of joint centers, markers were placed on medial and lateral malleoli. Using this reference trial, ankle joint center could be defined in relation to the other three markers placed on the shank. Once the ankle joint center was defined, malleoli markers were removed for orthosis fitting, and ankle joint center could be calculated for the dynamic trials using the remaining shank markers.
AFO A prototype of an AFO, which was developed to induce changes in the tibia position in the frontal plane and stabilize the ankle joint, was used in this study. Ankle joint stabilization should be achieved by avoiding a lateral rotation of the proximal aspect of the tibia in the frontal plane. This prototype comprised a sole, which was inserted in the shoe, and a unilateral tubular frame, which passed laterally upward along the shank and was connected to the subject’s leg via a fastening device with straps. The orthosis joint could be adjusted in several varus/valgus angulations, which should lead to changes in the tibia position in the frontal plane. The orthosis’ joint allowed for unrestricted plantar and dorsal flexion; however, movements in the
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Figure 2. Subject with foot–ankle orthosis in (a) sagittal view and (b) frontal view. (c) Apparatus for adjusting the foot–ankle orthosis. The figure shows the orthosis in the neutral position. Black lines indicate the 4° valgus and varus adjustments.
frontal and transversal planes were restricted. The structure of the orthosis was complemented by a soft padding on the inside of the splint to ensure a comfortable wearing of the orthosis. To define the neutral position, the sole was inserted in the shoe, and the orthosis was positioned on the ankle and fixed to the subject’s leg, with the subject sitting on a chair. For adjusting the tubular frame to the shank contour, two adjusting screws localized at the orthosis’ joint axis and two screws localized at the tubular frame (proximal aspect of the shank) were loosened (Figure 2(a)). The subjects were asked to walk several steps with the orthosis before the screws were retightened so that the tubular frames of the orthosis could be adjusted to the subject’s leg contour. This orthosis adjustment was defined as “neutral” adjustment. By retightening the screws and adjusting the straps, a firm tension was produced to avoid orthosis’ slipping, without soft tissue binding. Once the orthosis was adjusted and fixed at the subject’s shank, the strap tension was kept constant by maintaining the same strap length for the other conditions (4° valgus, 4° varus). After setting the neutral adjustment by fitting the orthosis to the subject’s leg, the orthosis was positioned on an apparatus for setting varus/valgus adjustments from this individual neutral position (Figure 2(c)). A pole adjustable in height included three holes, in which a perpendicular reference bar could be positioned. Before loosening the screws for allowing changes in the AFO adjustment, only the position of the adjustable pole with the reference bar was
changed to fit to the individual neutral position of the orthosis. For this purpose, the reference bar was placed in the middle hole, and the pole was lifted up until the bar was in contact with the tubular frame. For each subject, the initial height of the pole was maintained at this position, and for the two other conditions (4° valgus and 4° varus), only the reference bar was repositioned. The 4° valgus adjustment was achieved by placing the reference bar in the lowest hole and loosening the screws to permit adjustments of the tubular frame, changing the AFO adjustment. The frame was set down until they had contact with the reference bar and the screws were then retightened in this position. For the 4° varus adjustment, a similar procedure was applied using the upper hole of the pole. The distance between each hole corresponded to changes of 4°. In this study, the “valgus adjustment” was defined as the adjustment which would induce a more valgus alignment at the knee by avoiding a lateral rotation of the proximal aspect of the tibia in the frontal plane. Then, this definition of “valgus adjustment” refers to kinematic changes at the knee and not at the ankle joint.
Data analysis Joint moment calculations were based on the mass and inertial characteristics of the limb, the derived linear and angular velocities, and accelerations of each lower extremity segment, as well as GRF and estimated joint center position. Marker trajectories were filtered using
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Fantini Pagani et al. Table 1. Mean and SD of the KAM (first and second peaks) and knee adduction angular impulse during different test conditions. For the intervention conditions (wedged insoles and AFO), mean differences with 95% CI and effect sizes related to the baseline condition are also presented.
Baseline Mean (SD) Wedged insoles Mean (SD) Mean difference (95% CI) Effect size AFO varus Mean (SD) Mean difference (95% CI) Effect size AFO neutral Mean (SD) Mean difference (95% CI) Effect size AFO valgus Mean (SD) Mean difference (95% CI) Effect size
KAM—first peak (N m/kg)
KAM—second peak (N m/kg)
Knee adduction angular impulse (N m s/kg)
0.658 (0.151)
0.579 (0.149)
0.245 (0.055)
0.656 (0.146) 0.002 (−0.025/0.029) 0.013
0.567 (0.158) 0.012 (−0.012/0.036) 0.078
0.241 (0.055) 0.004 (−0.003/0.011) 0.073
0.605 (0.149)*† 0.053 (0.014/0.091) 0.353
0.583 (0.150) −0.004 (−0.024/0.015) 0.027
0.237 (0.058)*‡ 0.008 (0.0001/0.016) 0.142
0.586 (0.123)*† 0.072 (0.030/0.115) 0.523
0.576 (0.142) 0.003 (−0.016/0.022) 0.021
0.232 (0.053)* 0.013 (0.003/0.024) 0.241
0.580 (0.137)*† 0.078 (0.038/0.118) 0.541
0.574 (0.147) 0.005 (−0.022/0.031) 0.034
0.227 (0.055)*† 0.018 (0.012/0.025) 0.327
KAM: knee adduction moment (positive: adduction); SD: standard deviation; AFO: ankle–foot orthosis; CI: confidence interval. Knee adduction angular impulse: positive area under the KAM curve (positive: adduction impulse). Effect size = (MeanBaseline − MeanCondition)/SDPooled, where SDPooled = sqrt[((nBaseline −1)SDBaseline 2 +(nCondition −1)SDCondition2 ) / (nBaseline +nCondition − 2)] . *Significant
differences compared to the condition “Baseline”; SPSS Bonferroni-adjusted p < 0.05. †Significant differences compared to the condition “Wedges”; SPSS Bonferroni-adjusted p < 0.05. ‡Significant differences compared to the condition “Valgus”; SPSS Bonferroni-adjusted p < 0.05.
a fourth-order recursive Butterworth filter with a cutoff frequency of 10 Hz. All kinetic parameters were normalized to body mass. A custom algorithm written in MATLAB 7.0 was used for the calculations. Variables of interest were KAM, knee lever arm and position of knee joint center in the frontal plane, knee angles in the frontal and transversal planes, position of COP, and inclination and magnitude of the GRF vector in the frontal plane. Additionally, ankle angles in the frontal and transversal planes were also investigated because the orthosis’ joint restricted movements in those planes. For the KAM, first and second peaks during stance were analyzed as well as the knee adduction angular impulse. As the secondary purpose of this study was to analyze the mechanisms for possible changes in the KAM, all other parameters were analyzed at the instant of the first peak KAM or second peak KAM if significant changes were observed for those peaks.
Statistics After testing for normal distribution of the data, comparisons between conditions were performed with analysis of variance with repeated measures since all conditions for using parametric tests were attended. Bonferroni corrections
were applied in the post hoc pairwise comparisons, when a significant overall main effect was detected, so that corrected p values were used for the pairwise comparisons between all test conditions at a level of significance of 0.05. Statistical analyses were performed using IBM SPSS Version 20 (IBM Corporation, New York, USA).
Results Subjects walked with a mean gait velocity of 1.44 m/s (baseline: 1.45 (0.17), wedged insoles: 1.44 (0.18), AFO neutral: 1.44 (0.17), AFO varus: 1.44 (0.18); and AFO valgus: 1.45 (0.17)). Significant differences in the first peak KAM and in the knee adduction angular impulse were observed for the conditions with AFO in the three different adjustments (Table 1). Decreases of 8.1%, 10.9%, and 11.9% in the first peak KAM were observed for the varus, neutral, and valgus adjustments, respectively, compared with the baseline condition. For the parameter knee adduction angular impulse, decreases of 3.3%, 5.3%, and 7.3% were found for the varus, neutral, and valgus adjustments, respectively, compared with the baseline condition. No significant differences were observed between baseline and laterally wedged insoles. GRF data are presented in Table 2. No significant differences were observed among test conditions.
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Table 2. Mean and SD of the GRF in the frontal plane during different test conditions. Presented GRF data correspond to the instant of first peak knee adduction moment. For the intervention conditions (wedged insoles and AFO), mean differences with 95% CI and effect sizes related to the baseline condition are also presented.
Baseline Mean (SD) Wedged insoles Mean (SD) Mean difference (95% CI) Effect size AFO varus Mean (SD) Mean difference (95% CI) Effect size AFO neutral Mean (SD) Mean difference (95% CI) Effect size AFO valgus Mean (SD) Mean difference (95% CI) Effect size
GRF resultant frontal (N/kg)
GRF Z (N/kg)
GRF Y (N/kg)
11.43 (1.17)
11.42 (1.17)
11.55 (1.17) −0.12 (−0.47/0.24) 0.097
11.53 (1.17) −0.11 (−0.47/0.24) 0.099
0.52 (0.18) −0.01 (−0.12/0.11) 0.031
2.57 (0.74) 0.00 (−0.60/0.62) 0.006
11.49 (1.23) −0.06 (−0.40/0.28) 0.048
11.48 (1.23) −0.06 (−0.40/0.29) 0.049
0.51 (0.15) 0.00 (−0.13/0.13) 0.005
2.58 (0.70) −0.01 (−0.67/0.66) 0.003
11.30 (1.25) 0.13 (−0.23/0.49) 0.109
11.29 (1.25) 0.13 (−0.24/0.49) 0.107
0.49 (0.13) 0.03 (−0.12/0.18) 0.161
2.49 (0.60) 0.08 (−0.67/0.84) 0.107
11.41 (1.34) 0.02 (−0.54/0.58) 0.017
11.40 (1.34) 0.02 (−0.54/0.58) 0.0167
0.54 (0.15) −0.03 (−0.15/0.09) 0.163
2.75 (0.76) −0.18 (−0.82/0.46) 0.214
0.51 (0.21)
GRF angle (°)
2.57 (0.92)
SD: standard deviation; GRF: ground reaction force; AFO: ankle–foot orthosis; CI: confidence interval. GRF Z: vertical component of the ground reaction force (positive: up); GRF Y: mediolateral component of the ground reaction force (positive: medial); GRF angle: angle between the ground reaction force vector in the frontal plane and a vertical axis (positive: inclination in the medial direction). Effect size = (MeanBaseline − MeanCondition)/SDPooled, where . 2 2
SDPooled = sqrt[((nBaseline −1)SDBaseline +(nCondition −1)SDCondition ) / (nBaseline +nCondition − 2)]
Significant decreases in the knee lever arm in the frontal plane were found with the AFO orthosis in the three different adjustments compared to baseline condition (Table 3). This parameter also decreased significantly with the AFO in neutral and valgus adjustments compared with the laterally wedged insoles. No significant differences were observed among AFO adjustments. Decreases observed in relation to baseline were 6.7%, 8.8%, and 10.3% for the varus, neutral, and valgus adjustments, respectively. The knee angle in the frontal plane also decreased significantly, indicating a change from varus to a valgus position. Mean curves of KAM, knee lever arm, knee angle, and tibia rotation in the frontal plane for all subjects during the different test conditions are presented in Figure 3. At the instant of the first peak KAM, significant differences were observed for the angle of the ankle joint in the frontal plane between wedged insoles and all other test conditions, indicating a higher eversion of the calcaneus in relation to the tibia with laterally wedged insoles (baseline: 1.38° ± 2.55°; wedged insoles: 4.36° ± 3.03°; varus: 1.11° ± 4.64°; neutral: 0.33° ± 3.69°; and valgus: 0.03° ± 4.84°). In the transversal plane, no significant differences in the external rotation could be observed between conditions (baseline: 5.81° ± 3.26°; wedged insoles: 6.99° ± 3.18°; varus: 6.50° ± 2.87°; neutral: 6.45° ± 3.07°; and valgus: 6.40° ± 3.38°).
Discussion The primary aim of this pilot study was to investigate the effect of an AFO on the KAM in subjects with knee varus alignment. The AFO tested in this experiment was a prototype, which was designed to change the tibia orientation in the frontal plane and to stabilize the ankle joint. The valgus adjustments of this orthosis should contribute to keep the tibia in a more vertical position, avoiding a lateral rotation of the proximal aspect of the tibia in the frontal plane. This would cause a decrease in the knee lever arm in the frontal plane and thereby decreasing the KAM. The varus adjustment should cause an opposite effect increasing the knee varus malalignment and the KAM. Significant decreases in the KAM, knee lever arm, and knee varus angle in the frontal plane were observed with the AFO in all three adjustments, which contradicts our expectations. The neutral adjustment adopted in this study was defined as the orthosis configuration, which should fit to leg contour. From this position, valgus and varus adjustments corresponded to 4° changes in relation to the neutral adjustment in either direction. It is possible that changing the orthosis configuration by only 4° in each direction was not sufficient for producing different effects among the three adjustments. This limitation regarding the different orthosis adjustments should be investigated in future studies. It seems that the AFO, independent from the adjustment used, offers ankle stabilization
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Baseline
−17.90 (9.22) −17.84 (8.07) −0.06 (2.65/2.53) 0.001 −18.80 (9.02) 0.90 (−2.29/4.09) 0.099 −20.28 (8.88) 2.38 (−1.20/5.96) 0.263 −20.61 (8.49) 2.71 (−0.88/6.29) 0.306
59.37 (11.69) 58.26 (10.40) 1.11 (−0.87/3.09) 0.101 55.37 (10.98)* 4.00 (0.28/7.74) 0.353 54.15 (8.30)*† 5.22 (0.81/9.64) 0.515 53.26 (10.25)*† 6.11 (2.04/10.19) 0.556
COP (mm)
0.34 (2.29)*† 1.90 (1.04/2.77) 0.755
0.49 (2.34)*† 1.76 (0.86/2.65) 0.690
0.59 (2.74)*† 1.65 (0.91/2.39) 0.603
2.26 (2.61) −0.02 (−0.29/0.24) 0.009
2.24 (2.73)
Knee angle (°) (frontal plane)
−1.14 (1.01) 0.75 (−0.10/1.60) 0.769
−1.21 (0.98) 0.82 (−0.05/1.69) 0.854
−1.09 (1.00) 0.69 (−0.25/1.63) 0.717
−0.51 (1.06) 0.12 (−0.38/0.61) 0.116
−0.39 (0.94)
Knee angle (°) (transversal plane)
−41.75 (13.63)* −7.09 (−12.18/−2.00) 0.513
−45.25 (14.17) −3.58 (−7.49/0.32) 0.254
−44.04 (12.95)* −4.79 (−9.38/−0.20) 0.355
−45.85 (13.72) −2.98 (−7.21/1.24) 0.215
−48.83 (14.02)
Position of knee joint center (mm) (frontal plane)
*Significant
Pooled
Condition
Condition
Baseline
Condition
differences compared to the condition “Baseline”; SPSS Bonferroni-adjusted p < 0.05. †Significant differences compared to the condition “Wedges”; SPSS Bonferroni-adjusted p < 0.05.
Baseline
SD: standard deviation; COP: center of pressure; AFO: ankle–foot orthosis; CI: confidence interval. Knee lever arm: distance between knee joint center and ground reaction force vector in the frontal plane (positive: vector passes medially to knee joint center); COP: distance between point of force application and gait direction (positive: medial to the midline of the foot); knee angle: angle between femur and shank segments in the frontal plane (positive: varus) and transversal plane (positive: internal rotation); position of knee joint center in the frontal plane: with respect to the posterior heel marker at the instant of touchdown in the mediolateral direction (positive: medial). Effect size = (MeanBaseline − MeanCondition)/SDPooled, where 2 2 SD = sqrt[((n −1)SD +(n −1)SD ) / (n +n − 2)] .
Baseline Mean (SD) Wedged insoles Mean (SD) Mean difference (95% CI) Effect size AFO varus Mean (SD) Mean difference (95% CI) Effect size AFO neutral Mean (SD) Mean difference (95% CI) Effect size AFO valgus Mean (SD) Mean difference (95% CI) Effect size
Knee lever arm (mm)
Table 3. Mean and SD of knee lever arm in the frontal plane, COP, knee angle (frontal and transversal planes), and position of the knee joint center in the frontal plane during different test conditions. Presented data correspond to the instant of first peak knee adduction moment. For the intervention conditions (wedged insoles and AFO), mean differences with 95% CI and effect sizes related to the baseline condition are also presented.
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Figure 3. Mean curves of (a) knee adduction moment, (b) knee lever arm, (c) knee angle, and (d) tibia rotation in the frontal plane normalized through the stance phase for all subjects during the different test conditions. The shaded area indicates ±SD of the baseline condition. SD: standard deviation; AFO: ankle–foot orthosis.
avoiding the external rotation of the shank in the frontal plane (Figure 4). By keeping the shank in a more vertical position, the knee lever arm (distance between GRF vector and knee joint center) is shorter. This altered position of the tibia in the frontal plane while wearing the AFO is illustrated in Figure 3(d). It is important to note that this graph shows the orientation of the shank segment in the global coordinate system and does not represent the angle of the ankle joint in the frontal plane. The angle of the ankle joint (angle between calcaneus and tibia) was not significantly altered by the AFO compared to baseline. Stabilization of the ankle joint was already pointed out in early studies as an important factor for the effectiveness of laterally wedged insoles.22,23 According to those authors, kinematic changes in the subtalar joint induced by laterally wedged soles could be better transferred to the tibia by strapping the ankle joint, avoiding compensating
movements of the talus. Although significant increase in the eversion angle between calcaneus and tibia was observed with wedged insoles in this study, this change was not transferred to the tibia and no changes in the knee angle in the frontal plane could be found. Kutzner et al.20 reported slightly higher unloading effect of the medial knee compartment using a combination of wedged insoles and a soft ankle orthosis. Also, better results regarding the KAM were observed by Schmalz et al.21 combining wedged soles and ankle orthosis. The above-cited studies used the ankle orthosis only as a stabilization element for the joint. This study analyzed the effect of changing the orthosis alignment in the frontal plane to induce kinematic and/or kinetic changes at the knee joint. The combination of wedged insoles and the AFO was not analyzed in this study. Changes in the KAM with laterally wedged insoles could not be observed in this sample of healthy
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Figure 4. Schematic representation of different mechanisms for changing the knee adduction moment. The AFO alters the tibia rotation in the frontal plane, reducing the knee varus malalignment, which causes a reduction in the lever arm in the frontal plane. AFO: ankle–foot orthosis; COP: center of pressure.
individuals. Small decreases (about 7%) in the second peak KAM were reported in our previous study with patients with medial knee OA using the same insoles as used in this study.11 Individual responses to laterally wedged insoles are widely reported in the literature, and it is known that some subjects present an opposite effect on the KAM than that expected while using such foot orthotics.12,13,24,26,27 The reasons for these individual responses are not clear. In our sample of 14 subjects, 5 individuals presented an increase in the first peak KAM and 3 individuals in the second peak KAM. It is interesting to note that the opposite response in the first and second peak KAM was not observed in the same subjects. Future studies should investigate the reasons for these findings. Possibly, treatment success with laterally wedged insoles could be related to ankle joint stiffness of each subject. Stiffness is defined by the relationship between the applied force and the resulting displacement. Since joint movement occurs mostly rotational and not translational, joint stiffness can be defined as the relationship between external joint moment and changes in the angle of the joint (resistance to movement). It is affected by the combination of different factors such as passive joint structures (tissue viscoelastic properties of joint capsule and ligaments) and neuromuscular aspects.32 Those factors determine how much movement can be achieved in a joint for a given external joint moment. Maybe subjects with higher joint stiffness in the frontal plane could have more benefit from wearing laterally wedged insoles than subjects with lower
joint stiffness, by allowing kinematic changes in the subtalar joint to be better transferred to the tibia. This speculation is based on previous studies, which reported better results of laterally wedged insoles using subtalar strapping or ankle stabilization.20–23 A secondary objective of this study was to investigate the reasons for possible changes in the KAM. Therefore, other biomechanical parameters besides KAM were also investigated. No significant changes in the COP and GRF magnitude or inclination at the time of the first peak KAM could be identified with the different orthotic devices. Those parameters were not analyzed for the second half of the stance phase because no significant changes were identified in the second peak KAM. A recent study by Hinman et al.12 used a regression analysis to identify the contribution of different biomechanical parameters to the reduction of the KAM observed with wedged insoles. This approach was not applied in this study due to the small sample size analyzed. Nevertheless, it seems that the underlying mechanisms for decreased KAM observed with the AFO are different from that observed with laterally wedged insoles reported by Hinman et al.12 Those authors identified a reduction of the knee lever arm in the frontal plane, which explained about 46% of the changes in the KAM. Although this was the only parameter, which significantly explained the changes in the KAM, Hinman et al.12 reported significant differences in the COP and GRF data. Additionally, changes in those parameters (COP and GRF) correlated significantly with the changes observed in the KAM. In
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this study, a reduction of the knee lever arm was also observed; however, we suppose that this change occurs due to the alteration in the knee angle in the frontal plane since no changes were observed in the COP or GRF (Figure 4). Future studies with a larger sample would elucidate the mechanisms for reduced KAMs with an AFO by using a regression analysis. Besides the small sample size, a further limitation of this study is the investigation of an orthotic device in healthy subjects. Although the sample was composed of individuals with knee varus alignment, a joint deformity, which is often observed in patients with medial knee OA and associated with higher joint loads in the medial knee compartment, the generalization of the results for an osteoarthritic population should be done with caution. Some gait strategies used by patients with knee OA, such as toe-out gait and lateral trunk sway, were reported in the literature as an attempt to reduce knee joint loading.33 Future studies should investigate whether patients still would use such strategies in combination with the orthotic device. Anyway, the tested AFO showed to be effective in reducing knee varus malalignment, which from a mechanical point of view would contribute to reduce the KAM also in patients with knee OA and varus alignment. Another important aspect, which should be investigated in future studies, is patient compliance achieved with the AFO. Compliance is a concern regarding almost all orthotic devices. However, when comparing this AFO to traditional knee braces for knee OA, some advantages of the former device regarding wearing comfort can be pointed out, which could contribute to better compliance. Most patients complain about the length, weight, and the difficulty of wearing knee braces under the cloths. Those aspects could be minimized using an AFO compared to knee braces. Wedged insoles show better acceptance; however, its effectiveness is questionable. Future studies with patients with knee OA should provide more insight into compliance of this new orthotic device.
Conclusion In summary, a significant decrease in the KAM could be observed in subjects with knee varus alignment while using an AFO in different adjustments (4° valgus, neutral, and 4° varus). The orthosis was effective in changing the knee joint alignment and the knee joint lever arm in the frontal plane. Long-term effects on the KAM, symptoms, joint function, and compliance in patients with medial knee OA should be investigated in future studies. The use of AFOs designed to change the tibia position and thereby the knee joint alignment in the frontal plane could represent an alternative for conservative treatment of knee OA. Conflict of interest None declared.
Funding This study was founded by the Institute of Biomechanics and Orthopedics of the German Sport University Cologne.
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