Duncan Wood

Spasticity: Clinical perceptions, neurological realities and meaningful measurement

The aim of this paper is to review briefly our understanding of the phenomenon of spasticity based in current evidence.

Biomechanical approaches applied to the lower and upper limb for the measurement of spasticity: a systematic review of the literature.

Purpose: To review and characterise biomechanical approaches for the measurement of spasticity as one component of the upper motor neurone syndrome. Method: Systematic literature searches based on defined constructs and a four-step review process of approaches used or described to measure spasticity, its association with function or associated phenomena. Most approaches were limited to individual joints and therefore, to reflect this trend, references were grouped according to which body joint(s) were investigated or whether it addressed a functional activity. For each joint, references were further sub-divided into the types of measurement method described. Results: A database of 335 references was established for the review process. The knee, ankle and elbow joints were the most popular, perhaps reflecting the assumption that they are mono-planar in movement and therefore simpler to assess. Seven measurement methods were identified: five involving passive movement (manual, controlled displacement, controlled torque, gravitational and tendon tap) and two involving active movement (voluntary and functional). Generally, the equipment described was in an experimental stage and there was a lack of information on system properties, such as accuracy or reliability. Patient testing was either by cohort or case studies. The review also conveyed the myriad of interpretations of the concept of spasticity. Conclusions: Though biomechanical approaches provide quantitative data, the review highlighted several limitations that have prevented them being established as an appropriate method for clinical application to measure spasticity.

Indices to describe different muscle activation patterns, identified during treadmill walking, in people with spastic drop-foot

This study was concerned with individuals who were unable to effectively dorsiflex their ankle when walking, as a result of a lesion of the central nervous system (CNS). Indices that categorise and quantify different patterns of calf and anterior tibial muscle activation patterns during treadmill walking have been derived from a sample of fifteen individuals with established hemiplegia following stroke and twelve age-matched individuals without impairment. As subjects walked on a treadmill, force sensitive foot-switches under the heel and first metatarsal head allowed EMG signals from the calf and anterior tibial muscles to be related to phases of the gait cycle. Normal activation periods for each muscle group were identified as percentiles of the gait cycle and indices for muscle activation periods were derived using ratios of integrated EMG during selected periods. Indices were derived that identified statistically significant differences, between normal and hemiplegic subjects, in calf activation during both push-off phase (P<0.001) and early stance phase (P<001), but not activation of tibialis anterior during swing (P=0.325) Observation suggested that integrated tibialis anterior activity during swing phase in hemiplegic subjects was not dissimilar to normal subjects, but the profile in hemiplegic subjects tended to lack the normal second peak of activity at initial foot contact. The reasons for drop-foot were shown to be varied and complex. The indices defined may be useful for directing therapy and measuring outcome.

New results in feedback control of unsupported standing in paraplegia

The aim of this study was to implement a new approach to feedback control of unsupported standing and to evaluate it in tests with an intact and a paraplegic subject. In our setup, all joints above the ankles are braced and stabilizing torque at the ankle is generated by electrical stimulation of the plantarflexor muscles. A previous study showed that short periods of unsupported standing with a paraplegic subject could be achieved. In order to improve consistency and reliability and to prolong the duration of standing, we have implemented several modifications to the control strategy. These include a simplified control structure and a different controller design method. While the reliability of standing is mainly limited by the muscle characteristics such as reduced strength and progressive fatigue, the results presented here show that the new strategy allows much longer periods (up to several minutes) of unsupported standing in paraplegia.

FES cycling may promote recovery of leg function after incomplete spinal cord injury.

Study design: Single subject pilot.Objectives: (i) To see whether strength and endurance for recreational cycling by functional electrical stimulation (FES) are possible following spinal cord injury (SCI). (ii) To develop the equipment for FES-cycling.Setting: England.Methods: Near-isometric or cycling exercise was performed by the incomplete SCI subject at home.Results: After training for an average of 21 min per day for 16 months, the stimulated muscles increased in size and the subject was able to cycle for 12 km on the level. Surprisingly, there was a substantial increase in the measured voluntary strength of the knee extensors and the subject reports improved leg function.Conclusion: FES-cycling may promote recovery after incomplete spinal cord injury. If so, it offers the possibility of being a convenient method for widespread use.Sponsorship: Spinal Injuries Unit, Royal National Orthopaedic Hospital, Stanmore.

Control of leg-powered paraplegic cycling using stimulation of the lumbo-sacral anterior spinal nerve roots

We investigated leg-powered cycling in a recumbent tricycle for a paraplegic using functional electrical stimulation (FES) with the lumbo-sacral anterior root stimulator implant (LARSI). A female complete T9 paraplegic had a stimulator for the anterior L2 to S2 spinal roots (bilaterally) implanted in 1994. She was provided with equipment for daily FES cycling exercise at home. The cycling controller applies a pattern of stimulation in each of 16 crank angle phases. A 7-bit shaft encoder measures the crank angle with adequate precision. Each pattern was originally chosen to give the greatest propulsive force in that position when there was no motion. However, dynamically, some reduction in co-contraction is needed; also the patterns are applied with a preset advance time. Maximal power is obtained with an advance of 250 ms, which compensates for muscle response delay and accommodates changes in cadence (from about 25 to 85 rpm). With this system, she has cycled 1.2 km at a time on gently undulating road. We found that spinal root stimulation gives sufficient control over the muscles in the legs to produce a fluid cycling gait. We propose that root stimulation for leg cycling exercise may be a practicable and valuable function for paraplegics following spinal cord injury.

The Effect of Common Peroneal Nerve Stimulation on Quadriceps Spasticity in Hemiplegia

Summary Contemporary physiotherapy for neurologically impaired patients puts emphasis on the management of spasticity. A randomised controlled trial of the Odstock dropped foot stimulator (ODFS), a common peroneal stimulator used to correct drop-foot during walking, showed a reduction in spasticity of the quadriceps muscles in a sample of 32 chronic hemiplegic subjects. Both treatment (FES) and control groups received a course of ten physiotherapy sessions during the first four weeks of the trial period. The treatment group used the stimulator as part of the physiotherapy sessions and independently each day as they found useful. Both groups received the same amount of therapy contact time. The treatment group continued to use the stimulator for the 12-week period. Assessments also included measurement of walking speed and effort of walking, gait analysis and mobility and quality of life questionnaires. Results of these tests are not presented in this paper but are referred to in relation to changes in spasticity. Spasticity of the quadriceps muscles was measured using the Wartenberg pendulum test. Results showed that during the first four-week period both groups had a reduction in spasticity which was statistically significant in the control group; measured by both the relaxation index (p = 0.005) and the area beneath the curve (p = 0.036) and in the FES group only as the area beneath the curve (p = 0.028) At 12 weeks, reduction in spasticity in the control group was no longer statistically significant in either of these parameters, whereas in the treatment group reduction measured as area beneath the curve was statistically significant (p = 0.001). There was no statistically significant difference between the two groups. These results are discussed in relation to the subject of measurement of spasticity, the effect of physiotherapy on spasticity and observations made on changes in speed and effort of walking.

Is the spinal cord the generator of 16-Hz orthostatic tremor?

Primary orthostatic tremor is characterized by 16-Hz motor activity that is coherent between muscles. It has been suggested that this tremor originates in the brain. This view is questioned by findings from a patient with complete paraplegia who experiences intermittent leg spasms at rest. The EMG activity within the spasms showed a 16-Hz component that was coherent between muscles unilaterally and bilaterally. This raises the possibility that the spinal cord could be the source of orthostatic tremor.

Spinally generated electromyographic oscillations and spasms in a low-thoracic complete paraplegic

We have measured some oscillatory properties of severe lower limb spasms experienced by a low‐thoracic complete paraplegic during assisted standing. Electromyograms (EMG) were recorded from the leg muscles while the patient stood passively in a standing frame. The patient also stood using functional electrical stimulation (FES) while ground and handle reaction force vectors were measured together with EMG activity. During passive standing, spasms appeared simultaneously in all leg muscle groups on one side. The interval between spasms varied between 3 and 30 seconds. Within the spasms, there was a tendency of repetitive grouped discharge of motor units as well as a strong 10‐Hz component in the EMG that was coherent across ipsilateral muscle groups. Thus, the spasms were inherently oscillatory. During FES‐assisted standing, clinically similar spasms were observed. However, the interspasm interval became relatively fixed at around 16 seconds, which may indicate entraining of the spasm cycle by FES. There are similarities between this patients spasms and the pathological motor activities seen in other movement disorders that may also be of spinal origin.

Recruitment by motor nerve root stimulators: significance for implant design

Three paraplegics have been implanted with stimulators of the lumbar anterior roots. Twelve roots were trapped in slots, each with three electrodes, a central cathode and two anodes, but the anodes in all the slots were connected together to reduce the number of wires. Cross-talk between roots was observed at lower levels than expected. Cross-talk was assessed from the ratio of the roots threshold to the threshold of the contralateral response (expected ratio: 72). Two hypothetical reasons for this low ratio were: that the cathode current was not equally shared by the anodes; or that the contralateral responses were reflex. Experiments showed that neither explanation was valid. The ratio of the contralateral to ipsilateral threshold for individual slots (K(1)) was sometimes low because the ipsilateral threshold was high. By taking the ratio of the lowest contralateral response to lowest ipsilateral response, for all roots in each subject (K(2)), the ratio should approach the theoretical value. However, for the two subjects with small slots, it was 7.9 and 15.3, much less than 72, suggesting that the original theory was incorrect. Approximate calculations of the activation function suggest that the reason may be that roots which run close to a slot, but not through it, may pass through a virtual anode region outside the ends of the slots, and that anodal break stimulation in those regions causes the cross-talk. Our estimate is that this cross-talk would be expected to occur at intensities above 5.3 times the cathodal threshold. If the roots are stimulated in pairs, below the levels of cross-talk, experimental results show that the moments obtained in response are additive to within 5%.