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Spasticity, time–frequency analysis in cerebral palsy: pre- and post-neurotomy

Cerebral palsy that corresponds to a motor control disorder in relation to lesions in the immature brain is currently associated with spasticity. Spasticity is in relation to hyperexcitability of stretch reflexes (Sinkjaer 1996), with additional muscular fibre contraction or different activations. Spasticity induces contractures and bone deformity. Thus, reducing this disorder is an important goal for medical staff. It is possible to evaluate spasticity during medical examination with the modified Ashworth’s scale (MAS), for instance. These semi-quantitative scales depend on the experience of the examiner (Hsin-Min et al. 2008). Therefore, it may be interesting to evaluate spasticity during gait in order to evaluate treatment. Surface electromyography (SEMG) is currently recorded with cerebral palsy in order to determine differences in muscle onset and offset timing during the gait cycle (Bouisset and Maton 1995; Sutherland 2001). SEMG processing needs normalisation in order to allow comparison between two patients, two exams, two examiners, etc. Several types of normalisation are currently referenced, such as the works by Sutherland (2001), Kleissen et al. (1998) and Bouisset and Maton (1995). Typically, maximum voluntary contraction (MVC) is used as such a reference. However, this value depends on motivation and the level of sincerity of the subject (Bouisset and Maton 1995; Sutherland 2001). This difficulty may be important in patients who sometimes present cognitive problems. Hence, normalisation may be possible with an SEMG record during no movement capture. Spasticity induces modification of SEMG: pattern and muscle fatigue (Nsenga et al. 2010). However, the SEMG pattern may be modified for different reasons. Hence, spasticity analysis with time–frequency approaches (wavelet (Lauer et al. 2005; Lauer et al. 2007)/spectrogram) may be interesting. The aim of this study is to compare EMG data (record on spastic muscles of cerebral palsy) according to the time–frequency analysis before/after treatment (selective neurotomy) in order to determine a tool that describes spasticity from SEMG during the gait cycle.