Knee osteoarthritis (OA) has been shown to occur in 10% of individuals aged 55 years and older in the United Kingdom.1 The medial compartment is the most common location.2 Medial compartment knee OA is mainly associated with clinical symptoms and radiological changes, along with an increased knee varus, which consequently also increases the external knee adduction moment (EKAM) by shifting the knee joint center more laterally and the center of the load medially, especially during stance phase. This increases the load on the medial compartment, which has been associated with pain and progression of medial knee OA.3,4 Several conservative treatments have therefore been developed for reducing this excessive knee varus angulation, resulting increase in the EKAM.
One such treatment is the use of knee valgus braces, which are available as either custom-made or off-the-shelf (OTS) devices. Custom-made knee valgus braces have been shown to be more effective in reducing both the EKAM variables (first and second peak) and the knee varus angles than OTS devices,5 with reductions in EKAM between 5.5% and 33% being demonstrated,6,7 while other investigations have found no significant reductions in EKAM during walking8–10 or during stair climbing.10 One additional effect in one study has been a demonstrable reduction in knee flexion during swing phase.11
An alternative orthosis that could be useful in reducing the knee varus angle and the EKAM as well as potential compressive forces is a custom-made knee-ankle-foot orthosis (KAFO), which would take advantage of longer lever arms inherent in the design of the device. A cosmetic KAFO that is composed of a medial single upright with a single axis knee joint has the potential to keep the tibia and foot in a corrected position via an ankle-foot orthosis (AFO) section. This would encourage a reduction in knee varus deformity, prevent hyperextension, and potentially improve knee flexion by shifting the body's load anterior to the hip and posterior to the knee joint.12 However, to the authors' knowledge, no previous studies have investigated the effect of a KAFO on correcting a varus-aligned knee. The purpose of this study was therefore to examine the effect of a cosmetic KAFO on knee kinematics and kinetics in the sagittal and frontal planes and to compare these data with both a custom and OTS knee valgus brace and also without wearing an orthosis during walking and stair climbing activities.
CASE DESCRIPTION AND METHODS
One male individual with a 10° knee varus deformity (age, 45 years; mass, 85 kg; height, 1.68 m) participated in this study. Inclusion criteria were presence of a knee varus angle of more than 7° measured manually by a goniometer, no previous knee injury, no pain during ambulation, and being able to use stairs without any external assistance. Ethical approval was obtained from the local institution, and informed consent was provided before the enrollment.
The participant attended two sessions. In the first session, a cast was made by a certified orthotist with the affected knee in its maximal comfortable corrected position to allow fabrication of the KAFO. The individual was also measured for a custom-made and OTS knee valgus brace Ossur Unloader One (Össur UK, Manchester, UK) as per manufacturer's guidelines. The KAFO was a single upright design with an Ottobock knee joint (17lk1 = L/R1–5) from Germany, which tolerates up to 100 kg of loading, with 8 mm thickness and 23.6 mm width, and which incorporates a 5° knee flexion stop. The KAFO was also designed with a simple hinged ankle joint to allow free movement and manufactured in 4.5 mm copolymer polypropylene (Figure 1).
In the second session, the participant undertook a gait assessment in the following test conditions: wearing control shoes (Ecco-Zen), Ossur UnloaderOne custom, or OTS knee valgus braces, and a custom KAFO. The participant was asked to perform five trials with each condition during walking and stair climbing (ascending and descending) whereby the speed of the activity was controlled by a metronome. There was a 10-minute washout period between conditions. The CAST marker set technique13 was used whereby rigid clusters of four nonorthogonal markers were positioned over the lateral shank, lateral thigh, and sacrum to track the movements of the limbs. Retroreflective markers were glued securely to the control shoes with the foot modeled as a rigid segment (on the first, second, and fifth metatarsal heads, and calcaneal tubercle). Further markers were attached to medial and lateral malleolus, lateral and medial femoral epicondyle, greater trochanter, anterior superior iliac spine, posterior superior iliac spine, and iliac crest.
Three-dimensional gait analysis was performed using 16-infrared Qualisys OQUS cameras (Qualisys AB, Gothenburg, Sweden) at a sample rate of 100 Hz and two embedded AMTI force plates in a walkway (model-BP600400; AMTI, Advanced Mechanical Technology Incorporation, Watertown, MA, USA), which captured ground reaction force at a sample frequency of 1000 Hz. For the stair climbing, an interlaced (AMTI) stairway was used, which has three steps that are fixed over two force plates.14
Postprocessing calculation of the kinematics and kinetic data was conducted in Visual3D software (version-5; C-Motion Inc, Rockville, MD, USA). Motion and force plate data were filtered with a Butterworth fourth-order bidirectional low-pass filter with cutoff frequencies of 6 Hz and 25 Hz.11 All lower-limb segments were modeled as rigid bodies with anatomical frames defined by the landmarks surrounding the joints. Knee joint kinematics were calculated using an X-Y-Z Euler rotation sequence equivalent to the joint coordinate system.15 The net external knee moments were calculated using an inverse dynamic approach after normalization of the data according to the participant's mass (Nm/kg).
SPSS (version 20; IBM SPSS, Chicago, IL, USA) was used to perform a repeated measure analysis of variance (ANOVA) with a post hoc Bonferroni correction (corrected P = 0.05). Key outcome variables assessed included maximum sagittal plane knee angle at initial contact (IC) and mid swing, maximum frontal plane knee angle during stance phase, maximum frontal plane knee moment in early and late stance, the maximum and minimum sagittal plane knee moment, and knee adduction angular impulse (KAAI) values.3 Because the small sample size, all trials were assessed instead of the mean of all trials.
As expected, no significant changes in walking speed (m/s) were found among the test conditions. The average speed was 0.97 ± 0.04, 0.4 ± 0.0, and 0.45 ± 0.0 m/s during walking, stair ascent, and descent, respectively, for all conditions.
KNEE KINETICS DURING WALKING AND STAIR CLIMBING
During walking, the KAFO significantly reduced the first peak value of EKAM compared with the shoe by 11.4% (P = 0.04). No significant difference was found compared with either the OTS or custom-made knee valgus braces, although reductions of 15% and 12.6%, respectively, were seen. The KAFO also reduced the second peak of the EKAM during walking by 12%, 12.3%, and 9.5% compared with the shoe, the custom, and the OTS knee valgus brace, respectively, but this was only significant compared with the custom valgus brace (P = 0.00).
During stair climbing, no significant changes were seen in the first or second EKAM peak during stair climbing between the conditions (Table 1, Figure 2). With regards to the sagittal plane, no significant changes were seen in knee kinetics when comparing the KAFO to any of the other test conditions during either test condition.
KNEE ADDUCTION ANGULAR IMPULSE
The KAAI was reduced when using the KAFO compared with the shoe during walking and stair ascent and descent, but this only reached significance during ascent (P = 0.00; Table 1). In addition, a significant difference was noted between the KAFO and OTS for this parameter (P = 0.03) during stair ascent. No significant differences in KAAI were found between the knee valgus braces for any task.
KNEE KINEMATICS DURING WALKING AND STAIRS CLIMBING
The knee adduction angle was significantly decreased when using the KAFO by 8.2° and 6° during walking and stair descent (P = 0.0 and 0.03, respectively) and insignificantly by 12° during stair ascent compared with the shoe. In addition, the KAFO significantly reduced the knee varus angle by 3°, 15°, and 6.8° compared with the custom knee valgus brace (P = 0.0 for all) and by 2.7°, 12.4°, and 3.5° compared with OTS knee valgus brace during walking, stair ascent, and descent, respectively (P = 0.04, 0.0, and 0.01, respectively; Table 2). The custom and OTS knee valgus braces significantly reduced the knee varus angle during walking compared with the shoe (P = 0.0 both), with the OTS significantly reducing the knee varus during descent (P = 0.03).
In the sagittal plane, the KAFO increased the knee flexion angle at IC significantly compared with the shoe and OTS during walking (mean difference, 8.6° and 4.1°, respectively). However, all the test conditions insignificantly reduced knee flexion at mid swing during walking (between 2° and 7°) compared with the shoe. Both of the knee valgus braces produced a significant increase in knee flexion at IC during walking compared with the shoe, with the OTS also increasing knee flexion at IC during stair descent.
This case study investigated the ability of a custom KAFO to reduce EKAM/KAAI and knee varus during walking and stair climbing to provide a potential new treatment option for individuals with a knee varus deformity and OA. The KAFO was more effective than both of the knee valgus braces in decreasing the knee varus during walking and stair climbing with decreases of up to 12°. The efficiency of a KAFO in reducing a knee varus angle is mainly related to the offset joint, which was used to correct knee deformity in the frontal plane (knee valgus/varus), with the length of the KAFO applying more force over a more extensive tissue area than knee valgus braces. This meant that it would theoretically be able to correct the deformity more effectively. Furthermore, the KAFO has a more intimate and extensive fit on the lower limb than that provided by an OTS device.
The KAFO reduced the first peak of EKAM by a greater margin than either of the knee valgus braces (11.4%, 15%, and 12.6% compared with the shoe, OTS, and custom knee valgus braces, respectively) during walking. No significant changes were seen during stair climbing, and this could be due to a high knee varus angle that was seen (up to 30°), and the interventions cannot reduce it efficiently. The mechanism for the difference is due to the KAFO design, which can apply four points of pressure over the thigh, knee, and shank to correct tibial alignment and keep the foot in a relatively neutral position. This design would shift the ground reaction force more laterally and the knee joint center more medially, thereby reducing the EKAM. Although the knee valgus braces also apply three points of pressure, the longer length of the KAFO compared with the knee valgus braces helped the KAFO to apply more force correction than the knee valgus braces due to longer lever arms.
In the current study, neither knee valgus brace produced any significant effect on EKAM during walking and stair climbing, which is similar to that demonstrated in previous studies.8–10 This could be due to the high varus angle of the participant (<7°) and due to the shorter length of the knee valgus braces, which could apply less force than KAFO to correct tibia and foot alignment. All The test conditions did show a reduced knee flexion at mid swing, but this was only significant for the OTS brace compared with the shoe during stair ascent. This could be due to the tight straps around the knee joint11 or axial rotation of the brace during movements.
There are obvious limitations in this case study. It examined the effect of the orthoses on one individual and was repeated on the same day. In addition, the washout time was short between conditions, which could have affected the results; however, orthoses generally make mechanical changes in the joint, and one would expect the effects to reduce back to baseline values directly after they removed each device.
In conclusion, using a custom KAFO produced a larger correction of the knee varus deformity and a reduction in EKAM by theoretically applying greater force over the thigh and shank. These results give preliminary indications that a KAFO could be a useful alternative orthosis for individuals with a high varus angle and medial knee OA. Further work will be needed to further evaluate the clinical and biomechanical benefits of a KAFO in a larger number of subjects with different severities of unicompartmental knee OA.
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