G. Baardman

The influence of the reciprocal hip joint link in the Advanced Reciprocating Gait Orthosis on standing performance in paraplegia

The effect of reciprocally linking the hip hinges of a hip-knee-ankle-foot orthosis on standing performance was studied in a comparative trial of the Advanced Reciprocating Gait Orthosis (ARGO) and an ARGO in which the Bowden cable was removed (A_GO). Six male subjects with spinal cord injury (SCI) at T4 to T12 level participated in the study, which was conducted using a single case experimental design. Standing balance, the ability to handle balance disturbances (standing stability), and the performance of a functional hand task during standing were assessed in both orthosis configurations in the order A_GO-ARGO-A_GO-ARGO. No significant differences with respect to standing performance were found for the two orthosis configurations. However, the results indicate that the crutch force needed for maintaining balance during various tasks, especially for quiet standing with two crutches, may be much higher in the orthosis without Bowden cable. Therefore, it is very likely that the reciprocal hip joint link in the ARGO provides a substantial and clinically relevant reduction of upper body effort required for standing under functional conditions.

Comparative trials on hybrid walking systems for people with paraplegia: An analysis of study methodology

A new orthosis (SEPRIX) which combines user friendliness with low energy cost of walking has been developed and will be subject to a clinical comparison with conventional hip-knee-ankle-foot orthoses. In designing such comparative trials it was considered it may be worthwhile to use previous clinical studies as practical examples. A literature search was conducted in order to select all comparative trials which have studied two walking systems (hip-knee-ankle-foot orthoses) for patients with a complete thoracic lesion. Study population, intervention, study design, outcome measurement and statistical analyses were examined. Statistical power was calculated where possible. Of 12 selected studies, 7 were simple A-B comparisons, 2 A-B comparisons with a replication, 2 cross-over trials and 1 non-randomised parallel group design, the last of which was considered internally invalid due to severe confounding by indication. All A-B comparisons were considered internally invalid as well, since they have not taken into account that a comparison of two orthoses requires a control for aspecific effects (like test effects) which may cause a difference. Statistical power could only be examined in 4 studies and the highest statistical power achieved in one study was 47 %. It is concluded that statistical power was too low to be able to detect differences. Even analysis through interval estimation showed that the estimation of the difference was too imprecise to be useful. Since the majority of the surveyed papers have reported small studies (of only 4–6 patients), it is assumed that lack of statistical power is a more general problem. Three possibilities are discussed in order to enhance statistical power in comparative trials, i.e. multicentre studies, statistical pooling of results and improving the efficiency of study design by means of interrupted time series designs.

State detection during paraplegic gait as part of a finite state based controller

A finite-state model of paraplegic gait may serve as the basis for the design of an hierarchical control system for locomotion assisted by Functional Electrical Stimulation (FES). This approach compels the control system to detect the different states on-line during gait. Experimental results of two state detection strategies are presented. The preliminary results include various sensory feedback signals, such as hip gonio, footswitch and crutch force signals. Video recordings provided off-line comparison. State detection on the basis of footswitch and gonio data was problematic, probably due to time varying weight distribution in combination with a switch forcelevel and problems with robust attachment of the footswitches. Gonio together with crutch force data appeared to be more reliable for state detection.

Experimental on/off control of the swing phase of paraplegic gait induced by surface electrical stimulation

Abstmd Parameterized swing phase of paraplegic gait was obtained by stimulating the main hip flexors, hamstrings, and quadriceps using surface electrodes. The hipflexors were stimulated to generate a desired hip angle range. The hamstrings provided footclearance in the forward swing. The quadriceps were stimulated to acquire knee extension at the end of the swing phase. Stimulation patterns were optimized on the basis of an experimental sensitivity analysis. During open-loop stimulation with the optimized stimulation patterns, the hip angle range varied in time due to the effects of potentiation and muscle fatigue. This timedependent behaviour was succesfully compensated for using a cycle-tocyde PID controller, which computed the hip flexor stimulation pattern on the basis of the achieved hip angle range in previous cycles.

Speed dependence of crutch force and oxygen uptake : Implications for design of comparative trials on orthoses for people with paraplegia

OBJECTIVE To determine speed dependence of crutch force and oxygen uptake, and to discuss the implications of differences in self-selected walking speed between orthoses in a comparative trial. DESIGN Cross-sectional comparison. SETTING Treadmill experiments and gait laboratory experiments were performed at five and three different imposed walking speeds, respectively. PATIENTS Five paraplegic subjects with lesions between T9 and T12 were included. All subjects had experience with ambulation using the advanced reciprocating gait orthosis (ARGO) as well as walking on a treadmill. MAIN OUTCOME MEASURES Crutch force time integral (CFTI), crutch peak force on stance and swing side (CPFstance and CPFswing), oxygen uptake (VO2), oxygen cost (EO2). RESULTS VO2, EO2, and CFTI were strongly dependent on walking speed. CPFstance and CPFswing were less dependent. However, depending on the clinically relevant difference that should be detected in a comparative trial, the peak forces can still be confounded by walking speed. CONCLUSION CFTI, CPFswing, VO2, and EO2 should be adjusted for walking speed if differences in walking speed between orthoses are found, but this correction is relevant only if there is no effect modification. Such modification (different slopes between orthoses) cannot be excluded for the studied outcome measures. In addition, because determination of effect modification is difficult in small studies, standardization of walking speed, by means of a three-point design, is recommended.