Knee osteoarthritis is a chronic joint disorder that causes considerable pain, immobility, and disability. The medial compartment of the knee is more likely to be affected because it supports 60% to 80% of total loads during the stance phase of gait.1,2 In the treatment of medial knee osteoarthritis, lateral wedge insoles (LWIs) are used to decrease the knee-ground reaction force lever arm during the stance phase.3 This decrease leads to a reduction in the knee adduction moment (KAM),4,5 which is positively correlated with medial knee loading.3,6 Sharma et al.7 demonstrated that first KAM peak is strongly associated with disease severity, whereas Walter et al.8 showed that second KAM peak is correlated with knee medial contact forces. In recent years, LWIs have tended to be replaced by customized foot orthoses (FO) with an integrated lateral wedge to improve patients' comfort and reduce the excessive eversion angle produced by LWIs.9
The degree of correction induced by LWIs or lateral FO depends on the amount of wedging.4 However, Kakihana et al.10 observed that the use of a fixed LWI height is not appropriate for up to 18% of medial knee osteoarthritis patients. Given that a fixed LWI height does not appear to be an effective solution for all patients, Reeves et al.11 suggested individualizing the elevation of the FO's inclination to improve comfort and optimize the effect of the lateral wedge. Individualization would make it possible to adjust the inclination height to each person's anthropometric and functional characteristics, thereby optimizing its ability to enhance comfort and provide the anticipated biomechanical effects. To date, no standardized and validated technique exists to individualize the amount of wedging. Some orthotists use several one-piece lateral FO (each with a different inclination height) for each patient, whereas others use two-piece lateral FO, that is, FO plus a set of LWIs of different heights. The inclination height (of the one-piece FO or the flat lateral wedge of the two-piece FO) is determined by trial and error following the orthotist's criteria, which are generally based on patient's pain and comfort ratings during the follow-up. However, we do not know whether these two ways of creating a given inclination height have equivalent biomechanical effects, in particular with regard to the reduction of external loading of the knee joint. Making a pair of laterally wedged customized FO is expensive, so making several such orthoses is not optimal for either orthotists or patients; thus, the use of two-piece FO could be a way of limit the cost. A two-piece FO has advantages related not only to costs but also to operations: it is possible to test several heights and identify the best fit.
The purpose of this technical note was to evaluate the difference in comfort and KAM between customized FO with integrated lateral wedge and customized neutral FO combined with LWIs. We hypothesized that no difference would be observed between one- and two-piece lateral customized FO with regard to comfort and KAM.
Nine men and eight women with isolated medial knee osteoarthritis (Kellgren and Lawrence grades II to III) according to the clinical and radiological criteria of the American College of Rheumatology12 participated in this study. The 17 patients had a mean (SD) age of 54.5 (8.9) years, mean (SD) body mass index of 29.2 (3.8) kg/m2, and mean (SD) knee varus alignment of 4.5° (2.9°). Inclusion criteria were symptomatic medial knee osteoarthritis (Kellgren-Lawrence grade II or III),12 knee pain greater than 31 of 100 (Western Ontario and McMaster Universities Arthritis Index), moderate activity level, varus knee alignment equal or superior to 2° and a minimum of 2 mm of joint space narrowing on standing radiographs. Exclusion criteria were mild or severe knee osteoarthritis (Kellgren-Lawrence grades I and IV), rheumatoid arthritis or other inflammatory arthritis, avascular necrosis, a history of periarticular fracture or septic arthritis, bone metabolic disease, pigmented villonodular synovitis, cartilaginous disease, neuropathic arthropathy, synovial osteochondromatosis, total or partial knee arthroplasty, flexion contracture of ipsilateral or contralateral knee greater than 15°, hip or ankle joint damage with mobility limitation, obesity (body mass index ≥40 kg/m2), intra-articular corticosteroid injection in the affected knee during the two previous months, and reduced mobility (Charnley C). Ethical approval was obtained from the Université Laval Institutional Ethics Committee, and written informed consent was obtained from all participants.
The kinematic and kinetic data were acquired at 100 and 1000 Hz, respectively, with an optoelectronic motion analysis system (FLEX:V100R2; NaturalPoint Inc, Corvallis, OR, USA), capture software (Acquire 3D™; C-Motion Inc, Germantown, MD, USA), and two force plates (Model BP400600NC; Advanced Mechanical Technology Inc, Watertown, MA, USA). For motion capture, 26 reflective markers were attached to anatomical landmarks (iliac crest, anterior superior iliac spine, posterior superior iliac spine, greater trochanter, medial and lateral femoral epicondyle, fibula apex of lateral and medial malleolus, heel, and forefoot of the shoe), and four rigid marker clusters made up of four markers each were affixed to the thigh and shank of both legs.13 Natural cadences were determined with a 3.5-m instrumented walkway (GAITRite; CIR Systems, Sparta, NJ, USA).
Two pairs of customized FO with medial arch support were made for each participant (Figure 1). One had a lateral wedge (one-piece), whereas the other did not (neutral). The customized FO were composed of two parts: an ethylene vinyl acetate base with a density of 75 to 80 durometers and an SPC® M.P. (Podiatech, France) cover with a density of 40 to 45 durometers. Medial arch support, lateral inclination, and size of the orthoses were adjusted to fit each participant so they could be inserted into their shoes. The mean (SD) heights of the medial arch support for all participants were 27.7 (3.4) mm. In addition, a pair of LWIs was made for each participant. The wedges were composed of ethylene vinyl acetate with a density of 75 to 80 durometers and the amount of wedging was constructed along the entire length of the foot. The lateral wedge magnitude of the LWIs and the one-piece FO was the same (mean [SD], range, 5.2 [1.5] mm, 2–7 mm). The wedge height was set according to the orthotist's experience, mainly based on patient's level of pain and four static measures taken from the frontal plane of the patient's lower limbs: shank angle in relation to the vertical, calcaneus angle in relation to the vertical, tibiocalcaneal angle, and bimalleolar angle in relation to the horizontal. The orthotist remained blind to the patient's grade of knee osteoarthritis and mechanical alignment.
Each patient walked on an 8-m walkway following the beat of a metronome, which was adjusted to their self-selected cadence, as measured previously on the instrumented walkway. Participants carried out five trials in three conditions: without orthosis, with one-piece lateral FO, and with the combination of neutral FO and LWIs (two-piece). A trial was considered successful when the cadence was correct and the participant hit each force plate, located in the middle of the walkway. FO and LWIs were worn bilaterally in participants' own shoes. The sequence of conditions was randomized between participants to avoid possible sequence effects of testing conditions. After each condition, participants were instructed to assess using a 20-cm visual analog scale (results expressed in percentage) how comfortable the orthoses were in their shoes, where lower scores indicate greater comfort.
Visual 3D software and modeling (Version 4.93; C-motion Inc) were used to process gait velocity, ankle eversion moment, and knee flexion and adduction moment. External joint moments were calculated using three-dimensional inverse dynamics in the proximal segment coordinate system and normalized to body mass and height (kg × m). A custom-written software program (Matlab 2007b; Mathworks Inc, Natick, MA, USA) was used to find maximum ankle eversion and knee flexion moments, and KAM peaks.
Statistical analyses were done with STATISTICA 8.0 (StatSoft, Inc, Tulsa, OK, USA). Data were initially analyzed by repeated measures one-way analyses of variance and, when necessary, Tukey honest significant difference for multiple comparisons was employed as a post hoc test. The level of significance was set at p < 0.05.
ONE- VERSUS TWO-PIECE CUSTOMIZED FOOT ORTHOSES
No difference in comfort, KAM, or any of the variables was observed between one-piece and two-piece customized FO (Table 1; Figure 2).
CUSTOMIZED FOOT ORTHOSES VERSUS WITHOUT ORTHOSIS
The first peak of KAM was similar for both the customized FO and the without-orthosis conditions (p = 0.41; power, 0.20; effect size, 0.05; Figure 2). On the other hand, the FO conditions led to a 7% decrease in second KAM peak compared with the without-orthosis condition (p < 0.001; power, 0.97; effect size, 0.40; Figure 2). Gait velocity, knee flexion moment, and comfort were no different compared with the without-orthosis condition (p values > 0.21; power, 0.17–0.32; effect size, 0.03–0.09; Table 1). Ankle eversion moment increased with customized FO (p < 0.01; power, 0.85; effect size, 0.27; Table 1).
The aim of this study was to investigate whether the use of two-piece lateral FO has the same impact on comfort and knee loading during gait as one-piece lateral FO does in the treatment of medial knee osteoarthritis. Our results indicate that both types of lateral FO lead to a similar decrease in knee loading and alteration in frontal plane ankle kinetics during the stance phase of gait. The second-peak KAM decrease of 7% with lateral FO was similar to results previously reported in studies using LWI or lateral FO.4,9
Outside the laboratory, a lateral wedge is always assigned arbitrarily, based on the orthotist's experience, and it is quite common for the inclination to be too high or too low. Butler et al.14 customized lateral wedge magnitude with several inclination heights to obtain immediate pain relief for patients. They observed that amount of wedging increases with disease severity, but they noted that the method needed to be improved.15 In particular, the anthropometric and functional characteristics of the lower limbs needed to be taken into consideration. Thus, the combination of FO without wedge and LWI could allow patients' treatment to be managed in accordance with the progression of the disease; the wedge magnitude can easily be modified if it is too low or too high. Moreover, this method can also be used while searching for the best inclination for individual patients, as in the study of Butler et al.14
The power observed in the comparison of one- and two-piece lateral customized FO suggests that the lack of difference between the two is a real one. The experimental protocol stipulated that foot markers were attached to the footwear, so we did not see any variation of the foot within the footwear. However, our study design compared participants within repeated conditions, so the statistical results should remain unchanged.
This study confirms that the use of a lateral customized FO made in two pieces effectively reduces knee loading and ensures comfort equivalent to a one-piece orthosis in patients with isolated medial knee osteoarthritis (Kellgren and Lawrence grades II to III). The results of this study will be valuable for professionals who prescribe and design plantar orthoses. The use of a two-piece FO is a practical and economical way of improving or adjusting treatment by changing the inclination of the FO for patients with medial knee osteoarthritis.
The authors thank Annie-Pier Fortin for her assistance with the data collection. We gratefully acknowledge the editing work and suggestions by Zofia Laubitz.
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Keywords:© 2016 by the American Academy of Orthotists and Prosthetists.
knee adduction moment; lateral wedge insoles; gait analysis; customized