The effect of tibia inclination on gait pattern of stroke patients with genu recurvatum who wear an Ankle Foot Orthosis: A pilot study

1. Introduction

Stroke is one of the leading causes of adult disability in many countries including Thailand. In Indonesia, the prevalence of stroke is 0.0017% in rural Indonesia, 0.022% in urban Indonesia, 0.5% among urban Jakarta adults, and 0.8% overall [1]. In Vietnam, the prevalence of stroke is 415 out of every 100,000 people; in Sri Lanka, the prevalence of stroke is 9 per 1,000 people [2], and in Bangladesh the prevalence of stroke is 3 per 1,000 [3]. Meanwhile in Thailand the prevalence of stroke is estimated to be 1.88% among adults 45 years and older [4]. One of the negative effects of stroke is impaired mobility; only 50% of the stroke survivors regain limited levels of ambulation [4]. The effects of a stroke are determined by the extent and site of the brain injury. Around 40–60% of post stroke patients suffer from genu recurvatum and are treated with a rigid Ankle Foot Orthosis (AFO) [5].

The genu recuvatum gait is marked by a lack of tibial progression over the foot in stance which could be due to limited ankle range of motion (ROM) or insufficient hip extensor activity, allowing the pelvis to remain posterior to the hip during stance [6]. Ankle Foot Orthoses (AFO) are assistive devices commonly used to improve gait after stroke. This custom device improves gait and walking efficiency by manipulating the joint positions (through directing the ground reaction force), correcting abnormal ankle plantarflexion (ankle equinus) and knee hyper extension (genu recurvatum) during stance [7, 8, 9, 10].

In recent years many researchers have studied how to tune the AFO, with the intention of improving rehabilitation and orthotic management of post-stroke patients. Tuned AFOs can be occur by adding various heel heights under the AFO. This will alter the tibial inclination during stance phase and thus, change the knee flexion angle during mid stance.

This research focused on changing the anterior inclination of the tibia (AFO) to determine an optimum inclination to normalize lower extremity segment kinematics for individuals who had suffered hemiparesis secondary to stroke with genu recuvatum of 10 ∘ –30 ∘ .

The aims of this pilot study were to investigate the optimum inclination of the Rigid Tuned Ankle Foot Orthosis (RT-AFO) to normalize knee kinematics for stability in the sagittal plane with 10 ∘ –30 ∘ genu recurvatum of stroke patients in stance phase, and to compare the effects of RT-AFO with different inclination in spatio-temporal parameters.

The study protocol was reviewed and approved by the Institutional Review Board at Siriraj Hospital, Bangkok Thailand (Si 584/2015), and was supported by the SSPO Fund. Assessment of participants was performed as required for custom orthosis prescription. All participants were cast for a plastic rigid AFO with ankle foot alignment in neutral position. The rigid AFOs were fabricated from 5 mm polypropylene and reinforced at the ankle by adding 3 mm polypropylene.

Four hemiplegia post-stroke individuals who were able to ambulate within the community were recruited as participants in this study (see Table 1). The mean age was 51 years (SD = 15.2). Mean onset time of stroke was 10.7 years prior (SD = 3.5) and mean wear time of the AFO was 9.5 years (SD = 3.7). Mean of genu recurvatum from the initial evaluation was 11.7 (SD = 2.4). Custom made Rigid AFO were fabricated for each participant, additional wedges were prepared to tune the AFO, later called Rigid Tuned AFO (RT-AFO) in desired inclinations. Insoles were also prepared to compensate for any leg length discrepancies.

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Gait measurements were performed in the clinical gait lab at the Sirindhorn National Medical Rehabilitation Institute (SNMRI), Thailand. Each subject carried out one gait analysis session and walked in five conditions (Fig. 1): without RT-AFO (T1), with RT-AFO in 0 ∘ inclination (T2), with RT-AFO in 5 ∘ inclination (T3), with RT-AFO in 10 ∘ inclination (T4), and with RT-AFO in 15 ∘ inclination (T5). The genu recurvatum (GR) angle was measured by a lateral radiograph of participants angle between anatomical axis of the femur and tibia [11]. Normally, this angle must be 180 degrees. GR angle up to - 10 degrees can be accepted as physiological [12]. However in our study, we accepted tibiofemoral angles equal to 10 degrees or more as GR. All subjects were able to complete the required number of trials in the five conditions. Data were acquired until the subject completed a total of three clean force plate strikes with the affected limb, totaling approximately 15 gait cycles.

Gait was analyzed using a motion capture system with 8 Vicon MX-T40 cameras (Vicon, Oxford, UK); 2 piA1000-48gc cameras (Basler, Germany); and 3AMTI force plates (AMTI, MA, USA). The sampling rates for the cameras and the force plates were 100 Hz and 1000 Hz respectively. The trajectories of 38 markers placed on anatomical landmarks, using a Plug-in gait full body model were collected (Fig. 2).

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For statistical analysis, the nonparametric Kolmogorov-Smirnov test was used to assess normality and evaluate distribution of four participants. Paired t -test analysis was used to compare between T1 and four other conditions in both the kinematics of the knee flexion extension angle data and the spatio-temporal parameter data. The significance level considered was p ⩽ 0.05.

The mean knee flexion-extension moments throughout the gait cycle for all the participants in all five test conditions are shown in Fig. 3. A significant reduction of GR angle was seen in all 4 conditions (T2, T3, T4 and T5) of RT-AFO with 0.05. The mean ± SD peak of GR at mid-stance in T1 was - 17.2 ∘ ± 7.4. It reduced up an average of - 5.9 ∘ ± 15.4 in T5 and became closest to normal ranges. Compared to the T1 condition (walk without AFO) walking with 15 ∘ tibial inclination in AFO T5 reduced the genu recurvatum by 11.3 degrees. Paired T -test comparisons of cadence, stride length, and walking speed when walking without AFO T1 to four other conditions (T2, T3, T4, and T5) are presented in Table 2. Across all conditions compared to T1, the only parameter that showed a significant difference was cadence. Statistically significant difference in cadence was p = 0.008 and this significant value was reported in T4 which represented a 10 degree tibial inclination (RT-AFO - 10 ∘ ). There was no statistically significant difference in stride length nor in walking speed between T1 and any of the other conditions with RT-AFO. Figure 1 shows the mean of knee-extension angle from all participants during gait captured by the Vicon system. In condition T1, where participants walked without AFO, the mean knee extension angle during mid stance was 17.2 ∘ (SD = 7.1), this is the value from the motion analysis system. Still, this vaule was different from the mean of knee extension angle data from our initial assessment which was 11.7 ∘ . In this study, we used the knee extension angle as assessed by the Vicon system.

4. Discussion

This study investigated varying tibia inclinations to obtain the optimum inclination of a rigid Ankle Foot Orthosis for post-stroke patients with 10 ∘ –30 ∘ genu recurvatum. The findings contribute to a better understanding of the functioning of AFO, which is turn helps to improve the treatment of post-stroke patients with GR. It was hypothesized that the subjects would exhibit a reduction of GR during mid-stance in gait when walking with larger tibia inclinations. The results demonstrate that the tall inclination conditions of the Rigid Tuned AFO (RT-AFO) can reduce the GR angle. Previous studies have reported the use of heel lifts to optimize the mid-stance orientation of the ground reaction force (GRF) in relation to the knee joint, reducing the knee extending moment arms in an adult with hemiplegia and knee hyperextension during stance in children with CP [12].

This study showed the highest genu recurvatum angle in mid stance when subjects were walking without RT-AFO (T1) with a mean value of 17.2 ∘ . There was a statistically significant reduction of genu recurvatum ( 0.05) in mid stance during walking trial with RT-AFO in different inclinations (T2, T3, T4 and T5). Thus, the greatest control over moment of genu recurvatum was achieved during walking with RT-AFO 15 ∘ (T5). During mid stance the shank and thigh segment moved from a reclined to an inclined position and ground reaction force (GRF) passed closer to the knee axis. In this study the maximum reduction angle of genu recurvatum was 11.3 ∘ and was achieved by wearing RT-AFO 15 ∘ .

The study results align with Jagadamma’s study which evidenced a reduction in the knee extension moment arm after using a tuned AFO Foot Combining (AFO-FC) in a patient with hemiplegic stroke [13]. The elimination of genu recurvatum in mid stance was achieved in which the SVA had been modified to 14 ∘ inclination using wedges, while in our study we found that the optimum inclination of the RT-AFO was 15 ∘ for a genu recurvatum angle of 10 ∘ –30 ∘ .

This study demonstrated that the RT-AFO was also responsive to changes in spatial-temporal gait parameters such as cadence, stride length and walking speed. Our study reported the highest cadence in T4 (RT-AFO - 10 ∘ ) ( - 7.24 ± 7.73 steps/min). This improvement is as a result of the RT-AFO allowing the tibia to progress forward easily with the assistance of the ground reaction force because of the inclination in the AFO. Manipulation of the shank segment kinematics, by the inclination of AFO, produced a near normal shank kinematics, which might be a key to a successful orthotics interventions. Normalization of shank kinematics helps facilitate normal thigh, pelvis and trunk kinematics and normal knee and hip kinematics and kinetics [14].

Results from T5 (RT-AFO - 15 ∘ ) evidencd a reduction in cadence, which was opposite to that observed with T4 (RT-AFO - 10 ∘ ). A study by Owen also concluded that the AFO with Shank Vertical Angle (SVA) of 10 ∘ –12 ∘ produces stability in stance phase for both for normal and pathological gait [15]. Moreover, this degree of inclination brings the center of the knee joint directly over the middle of the foot.

The reason for a significance reduction in cadence in the current study could be due to a sudden changing of tibial inclination angles as a result of the lifts provided. Our participants experienced all condition continuously in one day without any adaptation time. Jagadama mentions an adaptation time for new inclination of at least 3 months [16], Carmo et al. mentions three months of wear time in order to promote an increase of gait velocity, cadence, step and stride lengths for stroke patient [17].

This study reported no significant differences in stride lengths and walking speed with RT-AFO. Other studies reported the same results as ours on the effect of varying tibia inclination in children with cerebral palsy wearing an ankle foot orthosis [18]. Lewek et al., noted that improvement of the walking speed can be achieved through intense gait training using at least six weeks of combined treadmill-based gait training followed by over ground practice [18].

These aforementioned accomidations as well as our own study limitations must be considered, as we were limited in our sample size which reduces the power of this data. Therefore, studies with a larger sample and longer study periods are recommended. Only knee kinematics and kinetics of the affected side in the sagittal plane, specifically in mid stance, were examined. Further studies of the optimum inclination of RT-AFO should evaluate hip joint metrics, other points of the gait cycle and in other reference planes as well.

5. Conclusions

The results of this pilot study indicate that the optimum inclination of RT-AFO is 15 ∘ . The spatiotemporal results illustrate improvements in cadence with a RT-AFO of 10 ∘ . The present study evidences the potential clinical application of tuning the AFO in rehabilitation treatment of stroke patients.