David Ewins

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.

Limb blood flow, cardiac output and quadriceps muscle bulk following spinal cord injury and the effect of training for the Odstock functional electrical stimulation standing system

As part of the assessment of the Odstock functional electrical stimulation (FES) standing system for mid to low thoracic lesion spinal cord injured (SCI) subjects, cardiac output, thigh blood flow and quadriceps muscle thickness were measured before and following an electrical stimulation muscle retraining programme. The same parameters were also measured in a group of uninjured subjects and in SCI subjects. It was found that there was no difference in cardiac output between the groups. However thigh blood flow was found to be around 65% of normal values in the spinally injured group. This returned to normal values following the retraining programme. The quadriceps muscle wasted to approximately 50% of its original thickness in the first 3 weeks following spinal cord injury. The retraining programme increased the muscle thickness to near normal values.

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.

Silicon-based microelectrodes for neurophysiology, micromachined from silicon-on-insulator wafers

A process is described for the fabrication of silicon-based microelectrodes for neurophysiology using bonded and etched-back silicon-on-insulator (BESOI) wafers. The probe shapes are defined without high levels of boron doping in the silicon; this is considered as a step towards producing probes with active electronics integrated directly beneath the electrodes. Gold electrodes, of 4μm by 4μm to 50μm by 50μm are fabricated on shanks (cantilever beams) 6μm thick and which taper to an area approximately 100μm wide and 200μm long, which are inserted into the tissue under investigation. The passive probes fabricated have been successfully employed to make acute recordings from locust peripheral nerve.

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.

Silicon-based microelectrodes for neurophysiology fabricated using a gold metallization/nitride passivation system

The multimicroelectrode probe (microprobe) is a device used in neurophysiology to record signals from nerve cells. Microprobes typically have a number of gold recording sites supported on a narrow cantilever beam which is inserted into the tissue. Conducting tracks connect the recording sites to bonding pads on the body of the device. The metallization is insulated, except at the recording sites and bonding pads, by a passivation layer. Boron etch stop techniques can be used to produce narrow cantilever beams upon which recording sites are situated. Previously, polysilicon interconnects were used on microprobes fabricated using boron etch stop techniques, with gold inlaid onto the recording sites using a lift-off technique. This meant that mechanical jigging was required before the final shaping of the probes in potassium hydroxide (or other etch) to prevent the etch from attacking the polysilicon conductors beneath the inlaid gold. The process reported here incorporates a gold metallization layer, in conjunction with a plasma-enhanced chemical vapor deposition (PECVD) nitride passivation layer. Since both these materials etch very slowly in potassium hydroxide, no mechanical jigging, or other steps, need to be taken to protect the front of the wafer during the shaping stage. This simplifies the fabrication of these devices.

The Emotiv EPOC neuroheadset: an inexpensive method of controlling assistive technologies using facial expressions and thoughts?

Purpose – The EPOC neuroheadset is a commercially available device that allows game players to control a computer using their facial expressions or their thoughts. This paper aims to examine whether it has the potential to be used as an input for assistive technology (AT) devices.Design/methodology/approach – Two experiments were conducted. In the first, 12 non‐impaired subjects used the neuroheadset to control a computer with their facial expressions. They also used a simple system of two head switches for comparison. In the second experiment, three non‐impaired subjects were trained to use the neuroheadset to control a computer with their thoughts.Findings – In the first experiment, the neuroheadset was slower and less accurate than the head switches (p<0.05), and was also harder to use. It is unlikely to be preferred to existing methods of accessing AT for those that retain a small amount of head movement. In the second experiment, by the end of the week, all three subjects achieved accuracy rates grea...

Neuromuscular electrical stimulation for children with cerebral palsy: a review

The aim of this review paper is to consider the application of neuromuscular electrical stimulation (NMES) to improve gait or upper limb function in children with cerebral palsy (CP). Although most NMES research has been directed at adults with neurological conditions, there is a growing body of evidence supporting its use in children with CP. In line with a recent meta-analysis, the use of electrical stimulation to minimise impairment and activity limitations during gait is cautiously advocated. A detailed commentary on one of the most common lower limb NMES applications, tibialis anterior stimulation (either with or without gastrocnemius stimulation) is given. Although there is a lack of randomised controlled trials and a predominance of mainly small studies, this review further concludes that the balance of available evidence is in favour of upper limb exercise NMES offering benefits such as increased muscle strength, range of motion and function in children with CP. The use of dynamic splinting with NMES has been shown to be more effective than either treatment on its own in improving function and posture. There is at present little published work to support the application of botulinum toxin type A to temporarily reduce muscle tone as an adjunct intervention to NMES in this population, although the presence of parallel applications to manage similar symptoms in other muscular disorders is noted.

Comparative analysis of power-line interference between two- or three-electrode biopotential amplifiers

Differential input amplifiers are commonly used in the measurement of biopotential signals. This is because of their ability to reject common-mode signals, for example power-line interference. Rejection is further enhanced by referencing the subject to the instrumentation system. One such referencing technique uses a third subject electrode connected either to circuit common or to ground. However, these techniques are rarely explained or quantified in the literature. Four recording configurations are examined, isolated and non-isolated amplifiers with two and with three electrodes, and existing models are extended. From a brief assessment of power-line interference sources, it is concluded that only displacement currents induced into the leads and the body need be considered. The effect of these on the four configurations is analysed using SPICE. Results show that interference from displacement currents induced into the leads and into the body is dependent upon the recording configuration used and is significantly lower in three-electrode than in two-electrode amplifiers. Isolation also reduces levels of interference. It is concluded that the choice of referencing may affect interference levels on the biopotential signal significantly. Experimental and further analytical work is planned to confirm this.

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.