Investigations on prescription parameters of an ankle-foot orthosis for patients with chronic-stroke hemiplegia

Abstract

Stroke is one of the leading causes of gait disabilities, and ankle-foot orthoses (AFOs) have historically been supplied for their assistance. However, their prescriptions are predominantly dependent on individual experience of a clinician. An introduction of objectiveness would warrant a more evidence-based practice in AFO prescription. The purpose of this study was, therefore, to investigate objective parameters that were associated with AFO prescription, particularly clinical assessment, AFO flexibility and gait evaluation parameters, in patients with chronic-stroke hemiplegia. Clinical assessment parameters included ankle joint resistance quantified as torque (Nm) or stiffness (Nm/°) and lower limb joint muscle strength (Kg). AFO flexibility parameters were also quantified as torque (Nm) or stiffuess (Nm/°). Finally, gait evaluation parameters comprised temporal-spatial, kinematic, and centre of mass (COM) displacement data. Series of novel custom-made devices were applied to investigate these parameters. Firstly, ankle joint resistance was quantified using a manual device, while muscle strength was measured using a hand-held dynamometer. Their influence on gait was subsequently investigated. Secondly, an automated device was introduced to quantify AFO flexibility. Thirdly, an AFO prescription assistive device (APAD) that could quantify both ankle joint resistance and AFO flexibility was developed. Finally, a prescription assistive AFO (PAAFO), which could adjust its flexibility, was introduced. The results using the manual device to quantify ankle joint resistance in twelve patients with stroke and the automated AFO flexibility measurement device to measure a sample AFO and the PAAFO demonstrated their feasibility and potential advantages over other techniques. Furthermore, the measurement of the ankle joint resistance in another group of ten patients with stroke and the flexibility of six AFOs using the APAD also demonstrated its potential ability to facilitate AFO prescription. The results of gait analysis in patients with stroke suggested that increased ankle joint stiffness as a result of wearing an AFO with appropriate flexibility would not impede gait. AFOs were suggested to improve gait by positively influencing other factors. Knee extensor strength of the affected side was shown to be associated with gait ability. The influence of the flexibility of an AFO on gait evaluation parameters using data collected from the ten patients wearing the PAAFO with a nine degree of flexibility setting revealed that ankle joint kinematics was the most responsive gait evaluation parameter. It was also revealed that the effect of the flexibility of an AFO would vary with the individual, but gradually diminish toward proximal joints and trunk in general. The results of a correlational study among gait evaluation parameters suggested that hip joint kinematics would be the most significant kinematic parameter in gait capacity showing good correlations with gait velocity. It was also demonstrated that vertical excursions of COM were closely associated with hip joint kinematics and temporal-spatial parameters. Therefore, the potential efficacy of the new devices presented in this study to facilitate AFO prescription was suggested as a useful adjunct to existing clinical treatment pathways. Further research to investigate the benefit of these devices would be promising to facilitate more objective AFO prescription.