Classification Systems in Cerebral Palsy

Because of increasing interest in conducting large-scale, multicenter investigations into the epidemiology of cerebral palsy and its prevention and treatment, efforts have been made to establish a standard definition and classification systems for cerebral palsy. In recent years there has also been increased focus on measurement of functional status of patients and new classifications for gross and fine motor function have been developed. The purpose of this article is to update the orthopaedic community on the current classification systems for patients with cerebral palsy. This information will be of value to surgeons in determining patients’ suitability for certain treatments and will also assist them in reviewing current literature in cerebral palsy.

The past decade has seen significant progress made in the evaluation of cerebral palsy (CP) and treatments for its sequelae. Because of advances in neonatal care and increased survival rates for preterm and low birth weight infants, efforts are being made to document the incidence and prevalence of CP through registries in Europe and Australia. Advances in orthopaedic care for children with CP have also been significant. Computerized gait analysis has led to refinements of orthopedic surgeries performed in these patients. Single event, multilevel surgery is now considered the standard of care in areas where gait analysis testing is available. New treatments have emerged, such as botulinum toxin injection and intrathecal baclofen, to treat spasticity and other types of hypertonia directly.

Because of increasing interest in conducting large-scale, multicenter investigations into the epidemiology of CP and its prevention and treatment, efforts have been made to establish a standard definition and classification systems for CP. In recent years there has also been increased focus on measurement of functional status of patients, and new classifications for gross and fine motor function have been developed.

The purpose of this article is to update the orthopaedic community on the current classification systems for patients with CP. This information will be of value to surgeons in determining patients’ suitability for certain treatments and will also assist them in reviewing current literature in CP.

Definition of cerebral palsy

In 2007, the results of an International Workshop on Definition and Classification of CP were published. The group included experts in the field of CP and developmental disorders from around the world. The purpose of the workshop was to update the existing definition and classification of CP to incorporate current knowledge about the disorder, and to improve communication among clinicians, researchers and epidemiologists. The following definition of CP was agreed upon:

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 cerebral palsy are often accompanied by disturbances of sensation, perception, cognition, communication and behavior, by epilepsy, and by secondary musculoskeletal problems.

This definition improves upon previous ones by emphasizing that CP involves a variety of disorders caused by various factors acting at different points in fetal development, and also highlights the importance of comorbidities that accompany the orthopaedic and neurologic manifestations. The definition excludes neurodevelopmental disabilities in which movement and posture are unaffected, as well as progressive disorders of the brain. The definition does not specify an upper age limit for onset of disorders, but inclusion of the phrase “fetal or infant” implies that it refers to insults occurring before full development, before specific milestones, such as walking, would have been achieved.

There remains some disagreement about this definition, but it is generally accepted and being used. Current issues with it include the lack of definition of an upper limit for age at onset in postnatally acquired cases, the need for definition of a lower limit for severity of involvement for a case to be classified as CP, and the need for a decision regarding whether to categorize syndromes, genetic disorders, or brain abnormalities resulting in static encephalopathy as CP.

International classification of functioning, disability, and health

In 2001, the World Health Organization published the International Classification of Functioning, Disability, and Health (ICF) for member states to use to standardize health and disability data worldwide. The ICF is increasingly being incorporated into research in developmental disabilities. The ICF describes disability as dysfunction at 1 or more of 3 levels: impairment of body structures (organs or limbs) or functions (physiologic or psychological), limitations in activities (execution of tasks or actions by the individual), and restriction of participation (involvement in life situations). Researchers frequently design studies addressing these various domains of disability. Currently, classification schemes exist for CP at both the impairment and activity limitation levels, and these are the focus of this article. No classification systems exist to date for restriction of participation.

International classification of functioning, disability, and health

Classification of impairments

Motor Abnormalities

It has been estimated that about 80% of children with CP have some type of movement disorder. CP is most often classified as either spastic, dyskinetic, or ataxic. Although spasticity is often the dominant disorder, many children with CP have mixed spasticity and dystonia. When more than 1 type of movement disorder is present in patients, experts recommend classifying patients by the predominant disorder, for epidemiologic purposes, with listing of secondary disorders as well. Secondary movement disorders should be noted because this may impact treatment decisions. In particular, the results of soft-tissue surgeries are often less predictable in children with movement disorders.

The most current and comprehensive set of classifications for motor disorders has been published by the Task Force on Childhood Motor Disorders. The group is an interdisciplinary panel of experts in the field of movement disorders and cerebral palsy, including pediatric neurologists and neurosurgeons, orthopaedic surgeons, pediatricians, physical and occupational therapists, and other specialists. Their aims included establishment of definitions and classifications of motor disorders, with an ultimate goal of allowing improved communication among clinicians and researchers, and improving classification of patients for clinical and research purposes. To date, definitions have been established for hypertonic and hyperkinetic movement disorders, as well as negative motor signs in children.

Hypertonia

Hypertonia is defined as “abnormally increased resistance to externally imposed movement about a joint.” Hypertonicity can be caused by spasticity, dystonia, or rigidity (though rigidity is rare in children and not associated with cerebral palsy).

Spasticity

Spasticity is hypertonia in which resistance to passive movement increases with increasing velocity of movement (or exhibits a spastic catch), and “varies with direction of the movement, and/or rises rapidly above a threshold speed or joint angle.” Spasticity is often a component of upper motor neuron syndrome, along with hyperreflexia, clonus, reflex overflow, positive Babinski sign, and pyramidal distribution weakness (upper extremity extensors, lower extremity flexors). Spasticity is caused by a hyperactive stretch reflex mechanism and is amendable to treatments, such as botulinum toxin, baclofen, selective dorsal rhizotomy, and orthopaedic surgery, for resultant contractures or balancing of muscle/tendon forces about the joints.

Dystonia

Dystonia is defined as “a movement disorder in which involuntary sustained or intermittent muscle contractions cause twisting and repetitive movements, abnormal postures, or both.” When dystonic postures are such that they are present at rest and do not relax upon attempts at passive movement, they cause hypertonia. Dystonia can also be classified as hyperkinetic (see the following). Dystonic hypertonia is present in cases where the resistance to passive movement does not change with changes in speed of passive movement or joint angle (is present at low and high speeds with no spastic catch), may be associated with simultaneous agonist and antagonist contraction (equal resistance when the direction of passive movement is reversed), the limb tends to return to a fixed involuntary posture, and is triggered or worsened by voluntary movements at distant joints. Dystonia is not associated with hyperreflexia and often disappears when the child is asleep. Because myelination is needed for development of dystonia, it typically occurs later in life than spasticity (around 5–10 years of age).

It is postulated that a significant proportion of patients with cerebral palsy have a secondary component of dystonia, resulting in mixed hypertonia. Dystonia is associated with disruption of the basal ganglia and therefore is not improved by selective dorsal rhizotomy. In fact, what was previously considered recurrent spasticity after rhizotomy is now thought to be unrecognized dystonia. It is generally accepted that tendon lengthening and transfer procedures are contraindicated in cases of dystonia, because of the risk for recurrence of deformity or development of reverse deformities. Although this is the conventional wisdom, evidence in the literature is limited. Occasionally, surgery may be required despite optimal medical management of the dystonia. This outcome is most commonly seen with deformities of the foot and ankle, particularly varus deformities, which may make shoe wear and bracing problematic. In such cases, surgery with split tendon transfers may be considered to address the varus foot. Whole tendon transfers should be avoided in children with dystonia. Dystonic hypertonia is responsive to botulinum toxin as well as intrathecal baclofen, which generally weaken overactive muscles or muscle groups. For patients in whom the primary movement disorder is hypertonic dystonia (vs spasticity), evaluation by a specialist in movement disorders is recommended before considering orthopaedic surgery for tendon lengthening or transfers. However, bony deformities in these patients, such as femoral anteversion, tibial torsion or bony foot deformities, are appropriate and beneficial when indicated.

Hyperkinetic Movements

Hyperkinetic movements are defined as “any unwanted excess movement” that is performed voluntarily or involuntarily by the patient, and represent what have traditionally been referred to as extrapyramidal symptoms. The hyperkinetic movements most commonly seen in CP include dystonia, chorea, athetosis, and tremors.

Hyperkinetic dystonia is characterized by “abnormal postures that are superimposed upon or substitute for voluntary movements.” These are repeated postures that are unique to each patient, although some common patterns exist, such as foot inversion and wrist ulnar deviation. They can be of varying durations, and can be triggered by volitional movement. Chorea is defined as “an ongoing random-appearing sequence of one or more discrete involuntary movements or movement fragments.” It is similar to hyperkinetic dystonia except that it involves brief extraneous movements rather than postures, which imply maintenance for a length of time. Choreiform movements are also random, can appear continuous and jerky, and can be difficult for patients to relax. Athetosis is defined as “a slow, continuous, involuntary writhing movement that prevents maintenance of a stable posture,” where discrete, repetitive movements or postures cannot be identified. It usually involves the hands or feet, and perioral muscles. Athetosis is not common as an isolated movement disorder in CP and is most often found in combination with chorea. The taskforce recommends that the term dyskinetic CP is used instead of athetotic CP , because athetosis is rare as an isolated finding, and when present is not often the primary movement disorder.

Orthopaedic surgery in cases of predominantly hyperkinetic movement disorders associated with cerebral palsy is most often limited to bony procedures, because fixed contractures are rare because of the often nearly continuous movements of the extremities and joints. Such patients should be referred to a movement disorders specialist for management, because this type of movement disorder may be best managed through medications.

As noted, bony surgery is more commonly performed in such patients than is tendon surgery. Tendon lengthening in patients with hyperkinetic movement disorders are unreliable and may result in a reverse deformity compared with that seen preoperatively (eg, a posterior tibial tendon lengthening may result in a previously varus foot being positioned in valgus postoperatively). If tendon transfer surgery is contemplated, it should be remembered that split tendon transfers are more successful in patients with dystonia than are whole tendon transfers. Isolated osseous surgery has more reliable results in these patients, but casting should be minimized when possible because these patients often do not tolerate casts well and their dystonia may be exacerbated following cast removal.

Hypertonia in CP is most often rated using the Modified Ashworth Scale (MAS). The Tardieu scale is preferred by some clinicians and researchers, because it assesses resistance to both fast and slow stretches, the angle at which resistance is felt initially (R1), as well as the end of passively available range of motion (R2). Neither test is able to distinguish spasticity from hypertonic dystonia (or contracture, in the case of the MAS). There are no pure measures of spasticity available. Dystonia in children with CP (hypertonic and hyperkinetic) is assessed using the Barry-Albright Dystonia scale, which was adapted for use in CP from the Fahn-Marsden Movement scale used in adults with primary dystonia. A new scale is being developed to quantify both spasticity and dystonia in the same patient, because this is a frequent occurrence, and determine the primary disorder (Hypertonia Assessment Tool-Discriminant).

Negative Signs

Hypertonicity and dyskinetic movements constitute positive motor signs of increased activity. Negative signs include characteristics that are decreased or insufficient and include weakness (insufficient muscle activation), poor selective motor control (inability to activate a specific pattern of muscles in an isolated fashion), ataxia (inability to activate the correct pattern of muscles during a movement), and apraxia/developmental dyspraxia (inability to activate the correct pattern of muscles to perform a specific task, either because of loss of ability or lack of acquisition of the skill). These problems often coexist with positive signs and can be more disabling than positive signs in some patients. Negative signs should be recognized because their presence may contribute to poor surgical outcomes. These problems are best addressed through physical and occupational therapy.

Topography or Limb Distribution

The traditional classifications of limb distribution for the hypertonic (primarily spastic) form of CP, hemiplegia, diplegia, and quadriplegia/tetraplegia (and occasionally triplegia), continue to be used clinically. However, these classifications have shown poor inter-rater reliability and have been the source of discrepancies in proportions of CP subtypes reported by registries in different countries. Inconsistencies arise because of lack of definition of how much upper extremity impairment is needed to classify patients as quadriplegic versus diplegic. In addition, children with hemiplegia often have some motor signs on the contralateral side, which could put them in a category of asymmetric diplegia, quadriplegia, or triplegia. Some experts recommend abandonment of these labels and advocate simplified classifications, such as unilateral or bilateral , with an indication of upper and lower extremity function (such as Gross Motor Function Classification System level, or Manual Ability Classification System level) as is done in the Surveillance of Cerebral Palsy in Europe registry. This change in classification is controversial, however, because there are suggestions in the literature of etiologic, radiological, and functional distinctions between diplegia and quadriplegia. If the traditional terms (diplegia, quadriplegia, hemiplegia) are used, complete description of the motor impairments in all body regions (including the trunk and oropharynx) is recommended. The term paraplegia is no longer used with respect to CP, because all children with diplegia have some level of impairment of fine motor upper extremity skills. If no upper extremity involvement is seen in a child with spasticity in the lower extremities there should be a suspicion of hereditary (familial) spastic paraparesis, tethered cord, or spinal cord tumor. Some experts suggest a limb-by-limb description of motor impairment and tonal abnormalities seen in each limb, such as that used in the Australian CP register. Their thought is that a description of the clinical presentation yields more valid and reliable information than placement of patients into categories, such as diplegia and quadriplegia.

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