Lots of big words and no pictures so I can't tell the differences. I know I needed an AFO that prevented ankle rolling so I don't know if helical does that.
Comparison between a novel helical and a posterior ankle–foot orthosis on gait in people with unilateral foot drop: a randomised crossover trial
Journal of NeuroEngineering and Rehabilitation volume 20, Article number: 63 (2023)
Abstract
Background
Neuromuscular disease and peripheral neuropathy may cause drop foot with or without evertor weakness. We developed a helical-shaped, non-articulated ankle–foot orthosis (AFO) to provide medial–lateral stability while allowing mobility, to improve gait capacity. Our aim was to evaluate the effect of the helical AFO (hAFO) on functional gait capacity (6-min walk test) in people with peripheral neuropathy or neuromuscular disease (NMD) causing unilateral drop foot and compare with a posterior leaf spring AFO (plsAFO). Secondary aims were to compare functional mobility, 3D kinematic and kinetic gait variables and satisfaction between the AFOs.
Methods
Single centre, randomised crossover trial from January to July 2017 in 20 individuals (14 with peripheral neuropathy and 6 with NMD, 12 females, mean age 55.6 years, SD 15.3); 10 wore the hAFO for the first week and 10 wore the plsAFO before switching for the second week. The 6-min walk test (6MWT), Timed Up and Go (TUG) test and 3D gait analysis were evaluated with the hAFO, the plsAFO and shoes only (noAFO) at inclusion and 1 week after wearing each orthosis. Satisfaction was evaluated with the Quebec user evaluation of satisfaction with assistive technology (QUEST).
Results
Median [interquartile range] 6MWT distance was greater with the hAFO (444 m [79]) than the plsAFO (389 m [135], P < 0.001, Hedge’s g = 0.6) and noAFO (337 m [91], P < 0.001, g = 0.88). TUG time was shorter with the hAFO (8.1 s [2.8]) than the plsAFO (9.5 s [2.6], P < 0.001, g = − 0.5) and noAFO (10.0 s [2.6]), P < 0.001, g = − 0.6). The plsAFO limited plantarflexion during the loading response (plsAFO − 7.5 deg [6.0] vs. noAFO -13.0 deg [10.0], P = 0.0007, g = − 1.0) but the hAFO did not (− 11.0 deg [5.1] vs. noAFO, P = 0.05, g = − 0.5). Quasi-stiffness was lower for the hAFO than plsAFO (P = 0.009, g = − 0.7). The dimensionless eversion moment was higher (though not significantly) with the hAFO than noAFO. Neither orthosis reduced ankle power (P = 0.34). Median total QUEST score was higher for the hAFO (4.7 [0.7]) than the plsAFO (3.6 [0.8]) (P < 0.001, g = 1.9).
Conclusions
The helical orthosis significantly and considerably improved functional gait performance, did not limit ankle mobility, increased lateral stability, though not significantly, and was associated with greater patient satisfaction than the posterior leaf spring orthosis.
Trial registration The trial began before registration was mandatory
Introduction
Diseases that affect the strength of the dorsiflexor muscles, such as stroke, peripheral neuropathy and neuromuscular disease (NMD), can result in foot drop. Foot drop restricts gait capacity and induces compensatory strategies, such as increased hip and knee flexion, to clear the foot and avoid tripping [1, 2]. Foot drop may be associated with evertor weakness, which reduces medial–lateral stability and may also only become apparent as the muscles fatigue.
Ankle–foot orthoses (AFOs) are commonly prescribed, conservative methods to reduce foot drop and improve gait capacity [3]. They are designed to compensate for the lack of active dorsiflexion by preventing plantar flexion during the swing phase of gait [3]. Although AFOs do not normalise the gait pattern, they reduce kinematic and kinetic anomalies [4, 5], the aim of which is to reduce compensatory strategies and risk of falls, and increase gait capacity, which may in turn facilitate participation [6]. The use of AFOs to improve gait capacity has been well studied in patients with stroke, however their use in people with NMD or peripheral neuropathy has been little evaluated.
Many types of AFOs have been designed and different materials have been used [7, 8], however, in France, posterior leaf spring AFOs made of thermoformable polypropylene are frequently used because they are reimbursed [9]. These orthoses effectively prevent foot drop and are compact and low cost, however they are not designed to provide stability in the frontal plane (they must be worn with high shoes), are not lightweight and are unable to restore energy to aid propulsion.
According to Alam et al. (2014), the ideal AFO must meet the following design specifications: be lightweight, compact, efficient, and untethered, prevent drop foot during swing while allowing normal ankle motion during other phases, and assist push off if necessary [8]. People with NMD or peripheral neuropathy often have associated weakness of the ankle evertor muscles, resulting in an unstable base of support during stance, therefore AFOs must also provide medial–lateral stability [10]. However, AFOs can only effectively improve gait capacity if they are actually worn [11,12,13]. Comfort and aesthetics are important criteria which contribute to compliance with AFOs [14] and must therefore be considered in the design.
Few commercialised orthoses currently meet all these criteria: carbon orthoses are lightweight and compact and may provide some push off assistance [15, 16], however, in our clinical practice we have found that if they provide lateral stability, this is often at the expense of mobility in the sagittal plane. Several attempts have been made to produce AFOs that specifically provide lateral stability. For example, Bishop et al. 2009 used an interesting design to prevent inversion during walking and running, however the AFO held the foot in maximal dorsiflexion, therefore altering the normal gait pattern [17]. Another group designed an ankle control strap to prevent unwanted eversion during gait [18], however it was worn on a bulky, inaesthetic AFO. Furthermore, AFOs may reduce propulsion forces, even in people who have sufficient plantarflexor strength to generate such forces [4, 16]. Since people with NMD often have plantarflexor weakness, a further requirement of an AFO is therefore to restore energy to assist push-off, or at least not reduce propulsive forces. Spiral orthoses have been proposed in the past to overcome these issues [19]. They are lightweight and can control motion in all planes. However, 3D gait kinematics have not been compared between spiral orthoses and AFOs that are typically prescribed today.
One of the authors of the present study (BC) designed and developed a new type of carbon fibre orthosis with a helical shape that would: (1) prevent foot drop in swing, (2) allow normal ankle range of motion, (3) not reduce propulsion and (4) provide medial–lateral stability of the ankle. It was also intended to be lightweight, and aesthetically acceptable. Such an orthosis could improve gait capacity.
The purpose of this study was first to determine if the orthosis improved gait capacity, which is the main aim of the wearer (activities level of the International Classification of Functioning, Disability and Health [6]), and second to determine if improvements in gait capacity with the orthosis could be related to improvements in the 4 criteria described above (body function and structures level of the International Classification of Functioning, Disability and Health).
The primary aim of this study was to evaluate the effect of this helical AFO (hAFO) on functional gait capacity (distance) in comparison with the effects of a posterior leaf spring AFO (plsAFO) or no AFO in patients with peripheral neuropathy or NMD causing drop foot with or without a concomitant loss of evertor strength. The secondary aims were to evaluate and compare functional mobility, 3D kinematic and kinetic gait variables and satisfaction between the two types of AFO.
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