The influence of a bespoke unloader knee brace on gait in medial compartment osteoarthritis: A pilot study

Abstract

Background:

Patients suffering from mild-to-moderate medial compartment knee osteoarthritis may be treated with an unloader knee orthosis. However, compliance has been shown to be an issue with such devices.

Objectives:

The aim of this study was to identify the effects of a new design of knee unloader orthosis on specific gait parameters in patients with mild-to-moderate medial knee osteoarthritis.

Methods:

The gait of seven patients was assessed in two conditions: without an orthosis and when wearing a new design of unloader knee orthosis. Gait analysis was performed to determine alterations to the adduction moment, speed of walking, step length, cadence and knee sagittal plane range of motion during ambulation for the two test conditions.

Results:

The knee adduction moment was significantly reduced (p = 0.001), and the speed of walking significantly increased (p < 0.001) when wearing the orthosis. However, a reduction in knee range of motion (p = 0.002) and an increase in step length (p < 0.001) were observed with the orthosis donned. Cadence was not significantly altered (p = 0.504).

Conclusion:

The use of a new design of unloader knee orthosis as a conservative treatment approach for patients with mild-to-moderate medial compartment osteoarthritis appears warranted.

Clinical relevance

Various conservative modalities have been used to reduce pain and improve function in medial compartment osteoarthritis. A new design of an unloader knee orthosis has been developed and is shown to have immediate benefits in patients with mild medial knee osteoarthritis.

Keywords

Knee osteoarthritis conservative treatment knee unloader orthoses walking gait parameters

Introduction

Knee osteoarthritis (OA) is the most commonly seen type of arthritis, especially in the elderly population.^1,2 Pain and reduced activity in OA causes functional deficits, disability and a reduction in the quality of life.^3,4 Long-term disability may lead to decreased mobility and reduced independence of the individual, plus difficulty in performing both daily living activities and recreational and sports activities.³

The prevalence of medial compartment OA is almost five times that of the lateral compartment.⁵ A common reason cited for this increase is that 62% of the loading passes through the medial compartment during walking.⁶ Initially, there is a tendency towards a varus deformity, followed by an increase in the adduction moment in the knee during gait as well as a reduced joint space in the medial compartment.^7,8 The incidence of this complication in US population was reported in 2003 to involve approximately 20 million people and was predicted to reach 40 million in 2020.⁹ The potential consequence of medial compartment knee OA is therefore a considerable burden for individuals and society because of the costs of the related interventions and treatments.¹⁰ Conservative treatment in the form of orthotic intervention should therefore aim to open up the medial joint space of the knee to reduce loading in the medial compartment and hence theoretically reduce pain levels at the knee while not causing discomfort due to the application of excessive corrective forces proximal or distal to the knee joint.

The overall goals of conservative treatment in OA are to reduce pain, improve function and reduce disease progression rates.¹¹ From an orthosis perspective, these approaches aim to reduce the externally applied knee adduction moment acting on the medial aspect of the knee.

Cross-over studies have previously demonstrated that unloader (valgus) braces improve confidence and function during gait¹² and that custom-made patient-adjustable knee braces improve function, stiffness and varus angulation and reduce medial compartment loading of knee.¹³ One study suggested that valgus braces immediately improved the function of the patient with unicompartmental OA of the knee.¹⁴ A randomised clinical trial by Kirkley et al.⁷ also showed that unloader knee orthoses were effective in improving the quality of life and function in patients with knee OA. In comparison with other types of knee orthoses, knee unloader orthoses may theoretically offer a more beneficial effect.^13,15,16 However, they have been shown to reduce overall sagittal plane knee range of motion (ROM) by increasing maximal knee flexion during stance phase and also reducing knee extension during swing phase.^8,17

Nevertheless, brace compliance has been reported as the main problem in using this type of orthosis. Due to the uncomfortable superstructure and non-user-friendly designs of knee orthoses, these devices are not being used for extended periods of time by patients with knee OA compared to foot orthoses.¹⁸ Current knee OA orthoses have mostly been obtained from designs, technology and materials previously used for orthoses designed to protect anterior cruciate-deficient knees. Existing corrective knee orthoses provide corrective forces via straps, adjustable superstructures on either the lateral or the medial superstructure, which translate and rotate the proximal and distal segments of the knee towards corrective alignment. The clinical effect of wearing these braces over long periods may cause skin irritation.^7,12 As indicated in a previous study,¹⁹ there appears to be a clear need for a new design of bespoke orthosis to be developed that is based on providing both comfort and an adequate valgus/varus correction to reduce medial knee loading.

The reason for the design of unloader knee orthoses described in this study was to potentially improve brace compliance by offering design features to obviate discomfort when wearing the brace. However, it was initially necessary to undertake a pilot study in a small patient group to ascertain its effect on gait parameters before embarking on a longitudinal study to determine its acceptability in a larger population. This new design of custom-made unloader knee orthosis was therefore developed with long thermoplastic collateral shells and internal padding and pneumatic translation to potentially re-distribute loads and interface pressures over a wider area. The aim of this study was to identify the effects of this new design of custom-moulded unloader knee orthosis on selected temporal–spatial parameters, kinematics and kinetics of walking in symptomatic individuals with medial compartment knee OA.

This was the first time the brace had been used in a trial. The hypothesis was that use of long lever arms in the orthosis would prove beneficial in reducing the adduction moment compared to when walking without the orthosis.

Methods

Subjects

Seven volunteer subjects (mean age = 62.40 years and body mass index = 27.47 kg/m²) participated in this study. Subjects were referred to the Orthotics & Prosthetics Clinic of University of Social Welfare and Rehabilitation Sciences. The sample selection was based on non-probability judgement sampling – where the researchers selected subjects to be sampled based on their knowledge and professional judgement.²⁰ The sampling method utilised the clinical experience of the team members in deciding to invite participants to the study who were perceived to be representative of typical cases seen in their clinical caseload.

Referred subjects were assigned to participate in this study according to the following inclusion and exclusion criteria. Inclusion criteria included the following: pain in one or both knees, with Grade 1 or 2 knee medial compartment OA according to the Kellgren–Lawrence (KL) scale, which ranges from a severity of 0–4, with 0 being the lowest rating.²¹ Subjects who had received any injury or invasive treatment including injection therapy for the knee during the past 6 months, neurological disease, a symptomatic spine, hip, ankle or foot disease, skin problems or any disease that made it difficult to apply a brace (e.g. due to arthritis in the hand or difficulty in bending) were excluded from the study. Subjects wore a knee orthoses on the affected side. The subjects with bilateral knee pain wore knee orthoses bilaterally. Subject characteristics are reported in Table 1. The ethical committee of University of Social Welfare and Rehabilitation sciences approved the performance of this study, and the subjects signed an informed consent form.

Table 1.

Volunteer participant characteristics.

	Age (years)	Gender	Mean body mass index (kg/m²)	Index knee
				Kellgren/Lawrence Grade(21)
Subject 1	64	Female	27.47	Bilateral: Right KL grade:1 Left KL grade:2
Subject 2	63	Male	29.35	Left KL grade:1
Subject 3	62	Female	26.63	Bilateral: Right KL grade:2 Left KL grade:1
Subject 4	60	Male	25.58	Left KL grade:2
Subject 5	60	Female	25.72	Right KL grade:1
Subject 6	62	Female	26.35	Bilateral: Right KL grade:2 Left KL grade:1
Subject 7	64	Female	27.49	Bilateral: Right KL grade:2 Left KL grade:1
Mean ± SD	62.14 ± 1.67	5 Females, 2 males	26.94 ± 1.30

SD: standard deviation.

Description of knee unloader orthoses

Subjects used a new design of bespoke knee unloader orthosis, which comprised a bilateral side bar design (Figure 1). The knee unloader orthoses were custom-moulded and individually constructed from a cast of each subject’s lower extremity. The cast was taken in the maximally corrected valgus position. Valgus correction was performed manually during the casting process by an experienced orthotist. The knee was corrected in the frontal plane to a less-varus position while the patient was sat down with the knee extended. It was corrected to the maximal corrected position which was still comfortable for the patient. This was performed manually while the plaster of Paris cast was set and following an initial assessment prior to casting.

Figure 1.

Bladder positions (lateral side) in new orthosis.

All orthoses construction was performed by an experienced orthotist. The orthoses comprised thigh and calf polypropylene shells connected by free orthotic knee joints incorporating a hyperextension stop with two laterally placed pneumatically adjustable pads to apply correction, which extended proximally and distally to the knee so as to cover two-thirds of the femur and tibia length. This was done to provide suitably long lever arms for varus control within the orthoses in preference to off-the-shelf devices. At the beginning of the intervention, the brace adjustment was tailored for each subject according to his or her individual requirements by setting the brace valgus angle at a position that was both comfortable and acceptable for the patient.^22,23

Two inflatable bladders manufactured using nylon (240 mm long and 80 mm wide) were adhered to the lateral aspect of the proximal and distal sections of the orthosis. The bladders were designed to translate the thigh and leg segments against the medial superstructure, which was anatomically shaped in the comfortably corrected position. The bladders were designed to be inflated by the wearer using a detachable inflation bulb. The tube attached to the inflation bulb was permanently attached. The bladders could also be deflated so that a comfortable correction pressure could be reached (Figure 1).

Three-point pressure systems are conventionally used to provide corrective forces in unloader knee braces to knees with medial compartment OA. To apply a more even distribution of force application, a bespoke moulded superstructure offering a larger surface area for correction was thought to be advantageous, as well as lateral air bladders to again re-distribute the load applied to the lateral aspect. The force system in this new orthosis utilised a theoretical four-point force system (rather than three), by inflation of the adjustable pneumatic components. This four-point system is designed to ‘de-rotate’ the tibial and femoral segments of the lower limbs in the frontal plane, which effectively reduces the knee varus angle. The tibial segment would be rotated anti-clockwise and the femoral component clockwise for the left leg and vice versa for the right leg when viewed from the anterior aspect. The length of the brace was chosen to increase the lever arms while still being practically acceptable and appropriate while not being cumbersome. Figure 2 shows the new orthosis, which was used in this study.

Figure 2.

The custom-fitted knee unloader orthosis used in this study.

Gait analysis

Prior to gait analysis, the subjects were assessed to confirm an acceptable quality of orthosis fit and comfort. The gait of seven patients was assessed in two conditions and in a random order (i.e. with and without the orthosis in situ). Randomisation was performed by subjects picking either ‘A’ or ‘B’, which represented either the braced or unbraced condition as the first walking condition.

The subjects wore identically styled lightweight, comfortable footwear for each gait analysis session. The shoe was selected to reflect a typical heel height and pitch, which could be worn by subjects. Subjects were aware of the location of the force platforms and performed a number of trial walks for both test conditions until they had enough time to gain a self-selected walking speed and in the case of the orthosis test condition, to habituate fully to the orthosis before reaching force plates and were able to strike the force plates successfully. They eventually walked along the walkway of the gait laboratory at their comfortable self-selected speed in each test condition in order to collect five data sets. Kinematics and kinetics data were gathered by a Vicon digital motion capture system (Oxford Metrics Group, Oxford, UK), using six cameras (Infrared model number 460; Vicon) at a frequency of 100 Hz and two force platforms set apart and positioned to capture a left and right heel strike (Kistler 9286BA, Switzerland). The marker placements were based on those utilised in a previous article.²⁴ In total, 14 markers were put bilaterally over the position of the anterior superior illiac spine (ASIS), greater trochanter, lateral condyle of the femur, head and lateral malleolus of the fibula, the second metatarsal and calcaneus. Markers were placed at the centre of the orthotic knee joint, which, following current practice, was positioned 60% posterior to the external anteroposterior (A/P) width of the knee and 14 mm above the joint line in order to simulate the equivalent sagittal plane single-axis anatomical knee joint centre. When walking with the knee orthosis, the lateral condyle of the femur markers was placed on the uprights but as close as possible to the positions where they would be located on the subject’s skin during walking without orthosis. This placement caused the markers to be offset from the skin by the thickness of the uprights. These offsets imposed by the orthoses were factored into the calculations of the knee joint centres. The marker data (x-, y- and z-coordinates of the markers) were captured by the Vicon cameras at a frequency of 100 Hz. The foot markers were placed on the subject’s skin through the holes of the shoes in the second metatarsal and calcaneus portions. Sagittal plane knee ROM, maximum externally applied knee adduction moment, walking speed, cadence and step length were analysed in this study. The knee joint adduction moment was calculated using an inverse dynamics model and reported in the units of Nm/kg.²⁵

Data analysis

Normality of data was approved by Kolmogorov–Smirnov test. A paired t-test was used for comparing the gait parameters for the two test conditions. SPSS version 16.0 (SPSS Inc., Chicago, IL, USA) was used to perform the data analysis. The level of significance was set at 0.05.

Results

Tables 2 and 3 show the overall results of use of the new unloader knee orthosis in this study. The external knee adduction moment was significantly reduced (p = 0.001) (Figure 3), and the speed of walking significantly increased (p < 0.001) when wearing the orthosis. A reduction in the knee ROM (p = 0.002) and an increase in step length (p = 0.001) were also observed with the orthosis donned. There was no significant difference between each of the conditions for cadence (p = 0.504) (Table 2).

Table 2.

Mean (SD) of variables in medial compartment OA subjects (n = 7).

	Without orthosis	With orthosis	p value
Knee ROM (°)	44 ± 1.86	39 ± 1.61	0.002
External knee adduction moment (Nm/kg)	0.55 ± 0.027	0.53 ± 0.021	0.001
Speed of walking (m/s)	0.90 ± 0.020	0.95 ± 0.022	0.001
Step length (m)	0.53 ± 0.038	0.56 ± 0.048	0.001
Cadence (steps/min)	102 ± 8	100 ± 7	0.504

SD: standard deviation; OA: osteoarthritis; ROM: range of motion.

Table 3.

Range of mean of variables for medial compartment knee OA subjects (n = 7).

	Knee ROM (°)		External knee adduction moment (Nm/kg)		Walking speed (m/s)		Step length (m)		Cadence (steps/min)
	A	B	A	B	A	B	A	B	A	B
Subject 1	42.00	36.00	0.55	0.52	0.90	0.96	0.55	0.58	98.00	99.00
Subject 2	45.00	37.00	0.53	0.51	0.87	0.95	0.58	0.63	90.00	90.00
Subject 3	47.00	38.00	0.58	.55	0.89	0.91	0.52	0.56	103.00	97.00
Subject 4	45.00	40.00	0.55	0.54	0.93	0.98	0.57	0.60	98.00	98.00
Subject 5	43.00	39.00	0.56	0.54	0.91	0.97	0.55	0.58	99.00	100.00
Subject 6	42.00	40.00	0.59	0.56	0.89	0.95	0.49	0.50	109.00	116.00
Subject 7	43.00	40.00	0.51	0.50	0.92	0.96	0.48	0.52	115.00	104.00

A: without orthosis; B: with orthosis; OA: osteoarthritis; ROM: range of motion.

Figure 3.

Mean external knee adduction moment for the patients with knee OA walking with and without the orthosis.

When comparing the means of knee angle over the trials while walking with the orthosis during stance phase (62% of the gait cycle), the knee joint flexed to a maximum similar value, but retained in a more flexed position during (approximately 2°) midstance and did not reach such an extended position without the brace donned. However, maximum knee flexion during swing phase was reduced to 39 (±1.61°) for the orthosis condition compared to 44 (±1.86°) when walking without the orthosis (Table 4). Decreased knee flexion during swing phase was therefore demonstrated when walking with the new unloader orthosis compared to the without-orthosis situation, and a relatively flexed position was also maintained during stance phase (Figure 4). There were significant differences between using and not using orthosis in knee joint ROM (p = 0.002).

Table 4.

Mean maximum knee flexion with and without the orthosis during the gait cycle plus gait cycle stance per cent of gait cycle.

	With orthosis	Without orthosis
Maximum knee flexion during stance (° ± SD)	13.7° ± 1.84	13.5° ± 1.68
Maximum knee extension during stance (pre-swing)	6° ± 1.58	4° ± 1.82
Maximum knee flexion during swing	39° (±1.61°)	44° (±1.86°)
Stance percentage of gait cycle (%)	62.0 ± 3.6	63.5 ± 3.4
Swing percentage (%) of gait cycle	8.0 ± 2.2	36.5 ± 2.8

SD: standard deviation.

Figure 4.

Mean knee joint flexion and extension for the patients with knee OA walking with and without the orthosis.

Discussion

This study sought to investigate whether a new unloader orthosis would influence walking in patients with mild or moderate knee OA. The findings of this study showed significant decrease in the applied maximum external knee adduction moment and increased speed of walking as compared to without the orthosis when using the knee unloader orthosis.

The knee orthoses used in this study applied a corrective force to the knee joint and reduced the external knee adduction moment in these patients. Schmalz et al.²³ and Harrington²⁶ demonstrated that valgus-inducing knee brace can reduce approximately 10% of the produced external genu varus moment in the knee joint. This reduction in the external knee adduction moment is thought to be the main biomechanical mechanism in reducing knee pain, providing functional improvement and a more symmetrical gait pattern in patients with knee OA at early and middle stages of OA. Although the external knee adduction moment was significantly reduced in this study, the percentage reduction found in this study appears to be less (3%) compared to previous studies, and the reduction of 0.02 Nm/kg in this parameter may not be clinically relevant. The less (but significant) reduction in adduction moment may have been due to the volunteer subjects having KL1 and KL2 grade OA. Previous studies have involved subjects with these lower grades of OA classification.²⁷ A larger study is therefore planned to include all grades of OA severity.

The external knee adduction moment alone cannot reflect the true loading (i.e. the compression force on the joint surfaces of the knee), and the clinical benefit of this orthosis with regard to its effect on medial compartment loading needs to be confirmed in a future study. Previous studies^28–30 did not find a decrease in peak varus moment, although Pollo et al.²⁸ also observed a reduction in the load of the medial compartment of the knee (as estimated by an analytical model) in the ‘braced’ condition even though the external varus (adduction) moment was not reduced. Therefore, some studies that have found no significant reduction in adduction moment have simultaneously detected a reduction in medial knee compartment loading. Reduction in adduction moment was statistically significant in this study. The clinical benefit of this brace has to be proven in a longer term study and it is the intention to investigate this further in a longitudinal study. It was not the intention of this study to prove its medium- to long-term clinical benefit.

Enhanced proprioception that can occur when wearing a knee orthosis is another factor in the improvement of knee pain.³¹ Kirkley et al.⁷ reported that when comparing use of a knee unloader orthoses to a non-braced control group, the Western Ontario and McMaster Universities Arthritis Index (WOMAC) pain sub-scale score improved with an unloader knee brace. Due to immediate evaluation of this current design of knee orthosis, it was not possible to assess pain levels, but a longitudinal study is planned for longer term evaluation of this orthosis.

Using this new knee orthosis increased the immediate speed of walking in patients with medial compartment knee OA. Although the mean of this parameter was greater as compared to the without-orthosis condition, this mean is still low as compared to healthy subjects of similar age. An increase in step length linked with no significant difference in cadence when walking with the orthosis improved the speed of walking in these subjects. Factors such as an increased confidence in walking caused by a more stable knee joint when wearing an orthosis can cause this result. Ramsey et al.¹⁶ suggested that knee orthoses increased knee joint stability and improved function. Richards et al.¹² also reported that reducing the varus force using a knee unloader orthoses may have increased the knee joint space on the medial side and improved symptoms.

The knee orthosis in this study induced a more flexed position during stance phase compared to the unbraced condition and also reduced maximum knee flexion during swing, meaning the overall knee sagittal plane ROM was reduced. This is in agreement with a previous study,¹⁷ where an OA knee orthosis was shown to reduce overall sagittal plane knee ROM by inducing a relatively flexed knee position and also reducing maximal knee extension during stance compared to an unbraced condition. This restriction in ROM can cause a decreased foot clearance. A similar result was also reported in the study by Richards et al.¹² One factor that may have produced this result in this study may have been the relatively long medial and lateral superstructures of the orthosis. The knee ROM was lower with the brace, but the step length was longer with the brace. Patients with knee OA have pain, instability of knee joint in stance and less ROM of hip joint^32,33 during walking. According to these points, we can expect that improvement of pain and stability of knee joint and increased ROM of hip joint during walking with orthosis may have affected increased step length, although the structure of orthosis may have influenced ROM of the knee joint in this study. The kinematics of hip and ankle joints was not analysed in this study, and further study will be beneficial in this field. However, similar results have been demonstrated when subjects with medial compartment OA walk with a substantive corrective OA knee orthosis with shorter lever arms. The long proximal and distal superstructures included in this current design were thought to be necessary for achieving long-term comfort. The knee orthoses used in this study were custom-made and extended two-third of the length of the upper and lower legs, giving an optimum fit and theoretically effective application of corrective forces using longer lever arms than most off-the-shelf devices.

The new orthosis was designed to decrease the interface limitations demonstrated when wearing previous orthoses evidenced in the literature by providing frontal plane correction via close-fitting custom-made shells, which would re-distribute load and interface pressures over a wider area, and inflatable bladders, which would not only add extra cushioning to the lateral aspect of the orthosis but also reduce friction effects and reduce leg motion relative to the orthosis during wear while maintaining the corrected lower leg position. While the reduction in knee adduction moments was statistically significant, they were still relatively small in value. The novel aspect of this brace was the use of long lever arms via a bespoke device to potentially maximise comfort and reduce interface pressures, particularly at the proximal and distal extremities of the superstructures. In addition, this technique could prove useful in areas where it is difficult to access commercially available products. The efficacy of the brace in unloading the medial compartment and therefore reducing pain levels is as yet not ascertained in a large population of people with medial compartment knee OA. This pilot study was designed to give initial findings, and therefore, the results cannot be generalised to a large population. However, the novel application of long lever arms and translation of the lateral lower leg structures along the majority of their length via extensive bladders rather than using tapered bladders plus the initial valgus angulation being decided by an appropriately qualified and experienced clinician makes this a novel device when compared to off-the-shelf variants.

The valgus/varus orientations of the uprights of the brace were positioned as dictated by the orthotist, and because this was the first clinical trial of the orthosis, caution was observed. It is the intention in a larger study to apply maximal corrective angulation via the brace in a larger study subject while still being comfortable for the participants.

There were some other limitations to this study. A limitation of this study was that only the immediate effects of ambulating with the knee orthosis were analysed and the effect on pain scores could not be assessed. In addition, this study did not have a placebo control group and the patients acted as their own controls. During the gait laboratory sessions, patients were allowed to acclimatise to wearing the orthosis prior to the formal testing. However, since the subjects walked over the force plates in the laboratory in one measurement session, this might not give a representative idea of the true loading of the knee joint after possible adjustments of the subjects’ walking pattern following longer term use. This is therefore needed in a future study. The small sample size, a mixture of patients with unilateral and bilateral knee OA and no account of amount of varus deformity of the knee were also limitations. Another limitation is the lack of subjects with KL3 and KL4 grades of OA included in this study, and the results demonstrated by the subjects in this study may not be replicated by subjects with more severe OA. The knee joint markers were placed directly onto the knee brace while subjects walked with orthosis. This approach would alter the magnitude of the knee joint moment which represents a further limitation of this study.

Conclusion

This pilot study demonstrated the potential of a new design of knee unloader orthosis as a conservative treatment approach for patients with mild medial compartment OA. Medial OA is a common complaint and various conservative modalities have been used to reduce pain and improve function. A new design of a unloader knee orthosis has been developed and is shown to have immediate benefits in patients with mild medial knee OA.

Footnotes

Declaration of conflicting interest

The authors report no conflict of interest.

Funding

This material was based on work supported by the Deputy of Research and Technology of the University of Social Welfare and Rehabilitation Science (grant number 92.801.1.12752).

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