**1. Introduction**

The International Executive Committee for Cerebral Palsy (CP) proposed the following definition: "*Cerebral palsy describes a group of permanent disorders of the development of movement and posture, causing activity limitation, that are attributed to non-progressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of CP are often accompanied by disturbances of sensation, perception, cognition, communication and behavior, by epilepsy, and by secondary musculoskeletal problems*" [1]. This definition is supplemented by an interpretation of the terms used in the definition. CP can be defined according to the anatomical location of the brain lesion (cerebral cortex, pyramidal tract, extrapyramidal system, or cerebellum); clinical signs and symptoms (spasticity, dyskinesia [dystonic and choreo-athetotic forms], or ataxia); topographical involvement of extremities (diplegia, hemiplegia, or quadriplegia); timing of presumed insult (prepartum, intrapartum, or postneonatal); and classification of degree of muscle tone (isotonic, hypotonic, or hypertonic) [2]. Hypertonia, which is characterized by abnormal resistance to joint movement, is common in CP [2]. Spasticity, dystonia, rigidity or mixed subtypes are particular forms of hypertonia. Spasticity is the most common form of hypertonia, which is characterized by increased resistance to motion above a threshold joint speed [2]. The efferent output of alpha motor neurons regulates the muscle tone [3]. Dystonia is involuntary muscle activation causing abnormal posturing. Rigidity is resistance to motion independent from velocity, caused by simultaneous contraction of agonists

and antagonist muscles. Treatment of CP targets the particular pathophysiology. In general, spasticity can be easier to manage than dystonia [4]. Studies on the management of spasticity are more abundant than those related to the management of dystonia in patients with CP.

There is an inverse relationship between the level of spasticity and voluntary motor control. In children with poor selective motor control, the spasticity can have functional importance (i.e. for standing). Treating this functional muscle tone may debilitate the child in everyday life [4]. Spasticity impairs selective motor control and treating it increases functionality.

The non-surgical treatment of CP includes enteral or intramuscular pharmacological agents, botulinum toxin injections, and physiotherapy [5]. When maximum tolerated dosage has been tried, neurosurgical alternatives such as intrathecal baclofen (ITB) therapy, selective dorsal rhizotomy (SDR), and deep brain stimulation (DBS) can be performed for the management of spasticity, muscle tone, and pain. The aim of neurosurgical interventions includes improvement in gross motor function, walking, muscle tone, health related quality of life, reduction of pain, and reducing the use of concurrent medication. In this chapter, we will review these procedures and provide up-to-date findings regarding neurosurgical alternatives in the management of hypertonia in CP.
