Search

Previous research showed that an Inertial Measurement Unit (IMU) on the anterior side of the shank can accurately measure the Shank-to-Vertical Angle (SVA), which is a clinically-used parameter to guide tuning of ankle-foot orthoses (AFOs). However, in this context it is specifically important that differences in the SVA are detected during the tuning process, i.e., when adjusting heel height. This study investigated the validity of the SVA as measured by an IMU and its responsiveness to changes in AFO-footwear combination (AFO-FC) heel height in persons with incomplete spinal cord injury (iSCI). Additionally, the effect of heel height on knee flexion-extension angle and internal moment was evaluated. Twelve persons with an iSCI walked with their own AFO-FC in three different conditions: (1) without a heel wedge (refHH), (2) with 5 mm heel wedge (lowHH) and (3) with 10 mm heel wedge (highHH). Walking was recorded by a single IMU on the anterior side of the shank and a 3D gait analysis (3DGA) simultaneously. To estimate validity, a paired t-test and intraclass correlation coefficient (ICC) between the SVAIMU and SVA3DGA were calculated for the refHH. A repeated measures ANOVA was performed to evaluate the differences between the heel heights. A good validity with a mean difference smaller than 1 and an ICC above 0.9 was found for the SVA during midstance phase and at midstance. Significant differences between the heel heights were found for changes in SVAIMU (p = 0.036) and knee moment (p = 0.020) during the midstance phase and in SVAIMU (p = 0.042) and SVA3DGA (p = 0.006) at midstance. Post-hoc analysis revealed a significant difference between the ref and high heel height condition for the SVAIMU (p = 0.005) and knee moment (p = 0.006) during the midstance phase and for the SVAIMU (p = 0.010) and SVA3DGA (p = 0.006) at the instant of midstance. The SVA measured with an IMU is valid and responsive to changing heel heights and equivalent to the gold standard 3DGA. The knee joint angle and knee joint moment showed concomitant changes compared to SVA as a result of changing heel height.

Introduction and aim: In patients with post polio syndrome (PPS), gait is frequently hampered by excessive and/or abrupt ankle dorsiflexion, caused by weakness of the plantar flexors. This can lead to instability and fatigue due to a reduced walking efficiency [1]. To provide stability and increase walking efficiency, patients with plantar flexor weakness can be prescribed with a spring-like dorsiflexion stopped ankle-foot orthosis (DS-AFO). In patients with stroke and MS presenting spastic leg paresis, it has been shown that walking with such an AFO can optimize walking efficiency by choosing the correct ankle stiffness [2]. A similar principal might also apply to patientswith flaccid paresis. The aimof this studywas to evaluate the effect of different degrees of DS-AFO ankle stiffness on walking efficiency and gait biomechanics in patients with PPS and plantar flexor weakness. Patients/materials and methods: One male patient with PPS and mild plantar flexor weakness participated (age: 67 years, MRC score plantar flexors: 4+, gait pattern: excessive ankle range of motion combined with persistent knee flexion during stance). For this patient a custommade foot partwith calf casingwas fabricated, in which five interchangeable carbon leaf springs with a different degree of stiffness (k) could be placed (range: k1: 0.8Nm/deg to k5: 7.3Nm/deg, as measured with the BRUCE device [3]). The patient was first assessed for gait biomechanics (Vicon MX, AMTI force plates) at comfortable speed while walking with the DS-AFO (5 springs, tested in random order). Each measurement started after the patient indicated to be customized to the new spring. After each condition, satisfaction was rated with a visual analogue scale. Subsequently, walking efficiency was assessed (Cosmed) during a 6-min walk test for the most satisfying DS-AFO spring, the stiffest and themost compliant spring. Gait biomechanics andwalking efficiency were also assessed for the patients’ own DS-AFO and for walking with shoes alone. Results: The patient rated DS-AFO-k3 (2.5Nm/deg) asmost satisfying: ‘It supported, butdidnot constrain toomuch’.Walkingwith this DS-AFO resulted in the highest comfortable gait speed (10% higher compared to shoes alone) and it increasedwalking efficiency with 2.5% compared to walking with shoes alone and to walking with his ownDS-AFO (Fig. 1). However,most efficient gaitwas seen with the stiffest spring (k5 =7.3Nm/deg): +4.1% compared to walking with shoes alone. Regarding gait biomechanics, ankle range of motion (range: k1: 33◦ to k5: 19◦) and ankle power during push-off (range: k1: 2.1W/kg to k5: 1.2W/kg) reduced with increasing stiffness. Only the three stiffest springs resulted in a decreased knee flexion during terminal stance (all about −4.8◦), compared to the two most compliant springs. Discussion and conclusions: The results of this case study indicate that for this patient with PPS and plantar flexor weakness optimizing DS-AFO ankle stiffness was useful for improving gait with respect to walking efficiency. Walking with the stiffest DSAFO (k5 =7.3) resulted in the most efficient gait, and, although the improvements were small, gait efficiency and reduction of knee flexion seemed to be related. However, the most efficient DS-AFO wasnot considered themost satisfyingDS-AFO. Sinceplantar flexor weakness from themeasuredpatientwas onlymild, a high stiffness may not be optimal. This is the first result from an ongoing project; we expect that a broader range in plantar flexorweaknesswill yield more precise relations onhowDS-AFOmechanics andpatient characteristics interact towards gait performance. Ultimately, this will serve DS-AFO stiffness selection in patients with PPS.

Introduction: For children with cerebral palsy (CP) whose gait pattern is characterized by excessive knee flexion in midstance, a Floor Reaction Orthosis (FRO) is commonly prescribed. FROs are very stiff andaimto counteract excessivekneeflexion inmidstance, by shifting the ground reaction force anteriorly. Although an FRO is effective in this respect [1], it impedes plantar flexion in preswing, therebyobstructingpush-off power. A spring-like FROcouldpotentially be more beneficial, since it can store energy at the beginning of the stance phase, being returned in preswing, thereby creating ankle push-off power. Literature shows that energy cost of walking with a typical spring-like Ankle-Foot Orthosis can be minimized by selecting an optimal stiffness [2]. Recently, a new type of hinge with adjustable springswas designed, which can be integrated into an FRO. However, exact knowledge of themechanical properties of the hinge is lacking. This study aims to quantify the mechanical properties of this new hinge build within an FRO. Patients/materials and methods: One test FRO with an integrated 14mm Neuro Swing® ankle joint (Fior & Gentz, Germany) was constructed.Weusedfive springswithin thehinge,withdifferent stiffnesses. The spring’s mechanical properties were measured with BRUCE [3]. Each spring was fully compressed and released slowly (i.e. a few seconds for the whole range of motion (ROM)) three times, while the hinge angle and the exerted net moment were continuously measured [3]. ROM (deg) (i.e. elastic range), stiffness (Nm/deg) (i.e. slope of the linear fit of the relation between angle and net joint moment in the ROM), threshold (Nm) (i.e. exerted moment at the start of ROM), and hysteresis [%ESTOR] (i.e. storage (ESTOR) minus release (ERLS) of energy) were averaged for each spring. ESTOR was defined as the surface underneath the compression phase (upper line) and ERLS as the surface underneath the release phase (lower line). Results Discussion and conclusions: Our results indicate that the five springs seem to be useful in optimizing orthoses with respect to energy cost of walking in children with CP. Hysteresis, probably mainly caused by friction of the spring in the shaft of the hinge, is present in all springs, resulting in a loss of energy that potentially could be used for ankle push-off. Nevertheless, FROs with integrated springs might still be more beneficial compared to conventional FROs, in which no energy can be stored at all. However, it remains unknown whether the stiffness of the springs is sufficient to counteract knee flexion in stance. This will be subject of further research to investigate the effects of the mechanical properties of the springs on gait in CP.