Influence of hamstring lengthening on muscle activation timing.

The purpose of this study was to describe the changes in muscle activation patterns using surface electromyography (sEMG) during walking in patients with cerebral palsy (CP), before and after hamstring lengthening. In the current clinical use of sEMG during walking in CP for pre-operative planning, various authors have observed that timing of muscle activation patterns hardly changes after surgical intervention. This observation is based on tendon transfer studies and visual interpretation of raw EMG signals. Little is known about the effect of muscle lengthening on muscle activation patterns of the lengthened muscles and their antagonists. Fifteen children with CP comprising a total of 23 hamstring lengthenings were included in this study. Surface EMG of semitendinosus and vastus lateralis was measured before and after surgery. Timing parameters of the sEMG patterns were quantified, using an objective burst detection algorithm and statistically evaluated. Results showed that hamstring lengthening causes statistically significant differences in timing of both the semitendinosus and vastus lateralis. It is concluded that timing parameters of operated muscles and their antagonists after surgery do change. The delayed off-time of the semitendinosus and the decreased burst duration of the antagonist (the vastus lateralis) after surgery were the most important changes.

A feasibility study of remote consultation to determine suitability for surgery in stroke rehabilitation.

We studied knowledge transfer for the determination of the suitability of stroke patients for a specialist surgical procedure (split anterior tibial tendon transfer). Gait analysis data from patients at a general hospital were discussed with an expert in another country using personal computers, an ISDN connection (128 kbit/s) and TCP/IP-based communication tools. The key issue was whether the staff in the general hospital became better able to determine suitability for surgery. Twelve patients were studied. In three of the first four cases the advice of the remote expert changed the plan for surgery. After that the treatment plans did not change after consultation. After eight cases the local clinicians did not need to ask for further advice. There was a rapid increase in skill in determining suitability for surgery. The experience and skills of the local clinicians were thought to increase more rapidly than would have been the case without the consultations with a remote expert.

Development of a teleconsultation system for communication between physiotherapists concerning children with complex movement and postural disorders.

We investigated whether a relatively low-cost, PC-based teleconsultation system could be used for interinstitutional communication about children with complex movement and postural disorders. Four paediatric physiotherapists in three different institutions participated. Both email and videoconferencing were tested. Videoconferencing was unsuccessful, as the low-bandwidth analogue lines, used by the majority of the therapists, made the quality of the realtime video-images very poor. However, email with attached video-recordings was successful and the therapists used the system to consult each other about 20 cases. The therapists regarded the system as effective in clinical practice. However, some improvements would be desirable, such as making the system quicker to use and reducing the number of technical errors. Nonetheless, structured communication between physicians about complex postural and movement disorders appears to be promising both for patient referral and for decisions concerning treatment.

[Clinical analysis of motion using multimedia technology]. / Klinische bewegingsanalyse met multimediatechnieken.

In disabling orthopaedic and neurological disorders, in addition to clinical and imaging examination, observation of the motion is an important method of examination. It serves as a starting point for the motion analysis using digital video. In this way, muscle functions can be measured with the aid of a kinesiological EMG. Load on the joints of the lower extremities can be deduced from a projection of the foot reaction vector on the body. Combination of a video film of the motion (the gait) with measurement of the kinesiological EMG provides a motion analysis based on multimedia techniques. With modern personal computers, interactive examination of these digital data is simple. Three examples of this functionality can be viewed at the Internet site of this journal (http:@appendix.niwi.knaw.nl): the normal walking cycle, the active stabilization of the knee after an injury of the anterior cruciate ligament and the gait of a woman with cerebral palsy before and after orthopaedic surgery. Motion analysis using multimedia techniques makes it possible to analyse relationships between muscular and articular functions on the one hand and impaired motion on the other in a way that is meaningful to the clinician.

Estimation uncertainty in ensemble averaged surface EMG profiles during gait.

This paper reports on a theoretical investigation into some of the properties of ensemble averaged electromyographic profiles (EAEPs) which are frequently applied in gait analysis. The study treats the quantification of the surface EMG signal by means of a linear envelope detector as an estimation problem. The surface EMG signal obtained in gait analysis is modelled as an amplitude modulated Gaussian random signal with a limited bandwidth, and the smoothed rectified EMG (SRE) signal at a given instant is interpreted as an estimate of the local standard deviation over a short time-averaging interval. An equivalent impulse response for the linear envelope detector's lowpass filter is introduced. This allows the prediction of the detector's response to the modulated EMG signal. The results show that stochastic estimation errors may contribute considerably to the observed variability in EAEPs. They also explain how these errors depend on the spectral characteristics of the EMG signal, the design of the lowpass filter in the linear envelope detector and on the time course of a muscle's myoelectric activity.

Effects of electromyographic processing methods on computer-averaged surface electromyographic profiles for the gluteus medius muscle.

The objective of this study was to demonstrate how two different linear envelope detectors, as used in the quantification of surface electromyographic (EMG) signals, can lead to differences in the properties of observed computer-averaged EMG profiles. Eight healthy male subjects, aged 24 to 32 years, participated in the study. Computer-averaged EMG profiles for the gluteus medius muscle were recorded at a free-walking cadence and at stepping frequencies of 78 and 120 steps/min, using detectors with 3- and 25-Hz cutoff frequencies simultaneously. The 3-Hz filtered EMG profiles proved to be smoother, to exhibit a significantly lower cycle-to-cycle variability, and to have a greater time lag with respect to the original unprocessed EMG signal than the 25-Hz filtered EMG profiles. The observed intersubject variability also was lower for the 3-Hz filtered EMG profiles than for the 25-Hz filtered EMG profiles. The results indicate that comparison of EMG profiles recorded with different detectors is difficult. A standard detector may solve this difficulty.

Simultaneous measurement of surface EMG and movements for clinical use.

A system for simultaneous measurement of surface EMG, joint movement and temporal parameters of gait has been developed for clinical use. Some design constraints, imposed by the clinical situation, are indicated. Multiple cycles of movement are recorded and averaged patterns of muscle activation and joint movements are determined. Data processing runs concurrently with data acquisition, so that the results are available for clinical interpretation immediately after the measurement. Instrumentation, signal processing and software are described and some examples of application of the system for evaluation of therapies and functional aids are presented. It is proposed that clinically relevant quantitative information can be obtained by comparison of different recordings of the individual patient rather than comparison with patterns found with normal subjects.