Salim Ghoussayni

A six degrees-of-freedom marker set for gait analysis: Repeatability and comparison with a modified Helen Hayes set §

Kinematic gait analysis is limited by simplified marker sets and related models. The majority of sets in clinical use were developed with low resolution imaging systems so required various assumptions about body behaviour. Further major limitations include soft tissue artefact and ambiguity in landmark identification. An alternative is the use of sets based on six degrees-of-freedom (DOF) principles, primarily using marker clusters for tracking. This study evaluates performance of a 6DOF set, based largely on CAST/ISB recommendations, through comparison with a conventional set and assessment of repeatability. Ten healthy subjects were assessed in treadmill walking, with both sets applied simultaneously on two occasions. Data were analysed using repeatability coefficients, correlation of key features, and comparison of joint angle curves and difference curves with confidence bands. Apart from pelvic tilt all segment and joint angles from both sets showed high within and between session repeatability (CMC>0.80). Hip rotations showed clear differences between the two sets with indications in support of the 6DOF set. Knee coronal angles showed evidence of cross-talk in the conventional set, highlighting difficulties with anatomical identification despite control measures such as a foot alignment template. Knee transverse angles showed inconsistent patterns for both sets. At the ankle the conventional set only allowed true measurement in two planes so with high repeatability the 6DOF set is preferable. The 6DOF set showed comparable performance to the conventional set and overcomes a number of theoretical limitations, however further development is needed prior to clinical implementation.

Gait Event Detection on Level Ground and Incline Walking Using a Rate Gyroscope

Gyroscopes have been proposed as sensors for ambulatory gait analysis and functional electrical stimulation systems. Accurate determination of the Initial Contact of the foot with the floor (IC) and the final contact or Foot Off (FO) on different terrains is important. This paper describes the evaluation of a gyroscope placed on the shank for determination of IC and FO in subjects walking outdoors on level ground, and up and down an incline. Performance was compared with a reference pressure measurement system. The mean difference between the gyroscope and the reference was less than −25 ms for IC and less than 75 ms for FO for all terrains. Detection success was over 98%. These results provide preliminary evidence supporting the use of the gyroscope for gait event detection on inclines as well as level walking.

Detection of gait events using an F-Scan in-shoe pressure measurement system

A portable system capable of accurate detection of initial contact (IC) and foot off (FO) without adding encumbrance to the subject would be extremely useful in many gait analysis applications. Force platforms represent the gold standard method for determining these events and other methods including foot switches and kinematic data have also been proposed. These approaches, however, present limitations in terms of the number of steps that can be analysed per trial, the portability for outdoor measurements or the information needed beforehand. The purpose of this study was to evaluate the F-Scan((R)) Mobile pressure measurement system when detecting IC and FO. Two methods were used, one was the force detection (FD) in-built algorithm used by F-Scan software and a new area detection (AD) method using the loaded area during the gait cycle. Both methods were tested in ten healthy adults and compared with the detection provided by a kinetic detection (KT) algorithm. The absolute mean differences between KT and FD were (mean+/-standard deviation) 42+/-11 ms for IC and 37+/-11 ms for FO. The absolute mean differences between KT and AD were 22+/-9 ms for IC and 10+/-4 ms for FO. The AD method remained closer to KT detection for all subjects providing sufficiently accurate detection of both events and presenting advantages in terms of portability, number of steps analysed per trial and practicality as to make it a system of choice for gait event detection.

Gait event detection during stair walking using a rate gyroscope.

Gyroscopes have been proposed as sensors for ambulatory gait analysis and functional electrical stimulation systems. These applications often require detection of the initial contact (IC) of the foot with the floor and/or final contact or foot off (FO) from the floor during outdoor walking. Previous investigations have reported the use of a single gyroscope placed on the shank for detection of IC and FO on level ground and incline walking. This paper describes the evaluation of a gyroscope placed on the shank for determination of IC and FO in subjects ascending and descending a set of stairs. Performance was compared with a reference pressure measurement system. The absolute mean difference between the gyroscope and the reference was less than 45 ms for IC and better than 135 ms for FO for both activities. Detection success was over 93%. These results provide preliminary evidence supporting the use of a gyroscope for gait event detection when walking up and down stairs.

Comparison of kinematic and pressure measurement reference methods used in gait event detection

Purpose: A variety of methods have been proposed for detection of initial contact (IC) and foot off (FO) and some comparative analysis is reported in the literature. Pressure measurement insoles and kinematic systems are often part of footwear analysis. Although gait event detection algorithms using these systems have been proposed and evaluated against kinetic data (KN) from force platforms (typically used as a ‘gold standard’), they have not been compared directly. The objective of this work was to undertake this comparison using the same volunteer dataset and test conditions. Methods: Data from 10 healthy adults walking at self-selected normal speed were collected. Two kinematic algorithms (one using a fixed threshold, KM, and the other using high pass-filtering, HPA) and one algorithm using pressure measurement data from an insole (Contact Area Detection, AD) were tested and compared with the detection provided by KN. All data were synchronised and sampled at 200 Hz. Six basic spatio-temporal parameters were also calculated. Results: The absolute mean difference (AMD) in event detection between the three methods and KN was below 25 ms. However, the methods presented tendencies to detect events earlier or later than KN and this influenced the AMD between the methods, which increased to 47 ms for IC detection between HPA and AD. The spatio-temporal parameters showed no statistically significant differences between AD and KM, but differences reached statistical significance between AD and HPA. Conclusion: It is possible to compare gait events and basic spatio-temporal parameters detected using data from pressure measurement insoles and kinematic algorithms; however the kinematic algorithm used will influence the results. Hence the comparison of findings from alternative detection methods is an important issue for which information about the behaviour of the method used is required.

A pilot evaluation of the practicality of the Surrey virtual rehabilitation system: perspectives from end-users

The Surrey Virtual Rehabilitation System (SVRS) was developed for clinical use in physiotherapy for children with cerebral palsy (CP). The overall aim of this work was to evaluate the practicality of the SVRS for three simple lower extremity exercises. Two children with CP, two clinical engineering trainees, and a physiotherapist performed the tests whilst parents and a paediatric physiotherapist observed the exercise sessions. The feedback collected during an open-discussion and the descriptive analysis of responses to 15 closed-ended questions suggest that the participants were satisfied with the practicality of the SVRS. Outcome measures derived from data collected during the sessions indicate that the SVRS may provide clinically relevant feedback on the performance of patients for themselves and their treating clinicians. In conclusion, the SVRS appears practical for rehabilitation purposes and is worthy of further evaluation and development.

Effects of lighting illuminance levels on stair negotiation performance in individuals with visual impairment

BACKGROUND Stair-related falls of older people cause a substantial financial and social burden. Deterioration of the visual system amongst other factors put older people at a high risk of falling. Improved lighting is often recommended. The aim of this study was to investigate the effect of lighting illuminance on stair negotiation performance in older individuals with visual impairment. METHODS Eleven participants aged 60 or over with a vision of 6/18 or worse ascended and descended a staircase under: 50 lx, 100 lx, 200 lx, 300 lx and distributed 200 lx lighting. A motion capture system was used to measure movements of the lower limb. Clearance, clearance variability, temporal and spatial parameters and joint/segment kinematics were computed. FINDINGS There was no effect on clearance or clearance variability. Participants had lower speed, cadence, increased cycle time and stance time in the 50 lx compared to 300 lx and distributed 200 lx lighting in descent. The minimum hip angle in ascent was increased in the 200 lx lighting. Clearance was found to be moderately correlated with balance scores. INTERPRETATION Individuals with visual impairment adopt precautionary gait in dim lighting conditions. This does not always result in improvements in the parameters associated with risk of falling (e.g. clearance).

Virtual reality based lower extremity exercises for children with cerebral palsy: Preliminary work

The work outlined in this paper aimed to evaluate the practicality of the Surrey Virtual Rehabilitation System (SVRS) during simple hip and knee flexion-extension exercises. Two clinical engineering trainees, a physiotherapist and two children with CP performed two tests using the SVRS whilst parents and a paediatric physiotherapist observed the tests. Feedback collected using both questionnaires and an open-discussion suggests that the SVRS is practical for rehabilitation purposes during both physical exercises.