Neurophysiological mechanisms of hypertonia and hypotonia in children with spastic cerebral palsy: surgical implications
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Neurophysiological mechanisms of hypertonia and hypotonia in children with spastic cerebral palsy: surgical implications M. Sindou 1,2 & A. Joud 2,3 & G. Georgoulis 4 Received: 3 June 2020 / Accepted: 5 June 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Mechanism of hypertonia in cerebral palsy children is dual: a neural component due to spasticity (velocity dependent) and a biomechanical component linked to soft tissue changes. Their differentiation—which might be clinically difficult—is however crucial, as only the first component will respond to anti-spastic treatments, the second to physiotherapy. Furthermore, spasticity is frequently associated with dystonia, which is a sustained hypertonic state induced by attempts at voluntary motion. Spasticity and dystonia have to be carefully distinguished as dorsal rhizotomy will not significantly influence the dystonic component. Spasticity, which by definition opposes to muscle stretching and lengthening, has two important consequences. First, the muscles tend to remain in a shortened position, which in turn results in soft tissue changes and contracture. The second is that movements are restricted. Thus, both hypertonia and lack of mobilization create a vicious circle leading to severe locomotor disability linked to irreducible musculotendinous retraction and joint ankylosis/bone deformities. These evolving consequences should be highly considered during the child’s assessment for decision-making. The hypotonic effects of lumbosacral dorsal rhizotomy, which are not only segmental on the lower limbs but also supra-segmental through the reticular formation, are finally discussed. Keywords Cerebral palsy . Dorsal rhizotomy . Hypertonia . Monitoring . Neurophysiological mechanism . Spasticity
Hypertonia is a frequent clinical condition in children affected with cerebral palsy (CP) that may be caused by several mechanisms, among which spasticity is predominant. The physiological definition of spasticity, given by Lance in 1980, remains the most widely accepted: “Spasticity is a motor disorder characterized by a velocity-dependent increase in tonic * G. Georgoulis [email protected] M. Sindou [email protected] A. Joud [email protected] 1
University of Lyon, 138 Avenue Lacassagne, 69003 Lyon, France
2
IRR Flavigny. UGECAM Nord-Est, 46 Rue du Doyen Parisot, 54630 Flavigny-sur-Moselle, France
3
Pediatric Neurosurgery Service, Department of Neurosurgery, CHRU Nancy, 29 Avenue Maréchal de Lattre de Tassigny, 54180 Nancy, France
4
Neurosurgeon, Department of Neurosurgery, General Hospital of Athens “G. Gennimatas”, Medical School, University of Athens, Athens, Greece
stretch reflexes with exaggerated tendon jerk, resulting from hyperexcitability of the stretch reflex, as one of the components of the upper motor neuron syndrome” [12]. Spasticity may be either useful—by compensating a decrease in motor strength—or harmful—by limiting both passive and active motion and at the extreme leading to irreducible contractures
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