WHAT IS CEREBRAL PALSY? NEW DEFINITION AND CLASSIFICATION

Cerebral palsy (CP) constitutes one of the most common causes of chronic childhood disability, with rates estimated between 2 and 2.5 per 1000 live births.¹ This chapter discusses the evidence for interventions for ambulant children with CP. Any discussion about the effectiveness of interventions in CP must first consider what CP and its associated pathophysiology are, and take into account the heterogeneity and natural history of CP to put definitions of “effectiveness” into perspective.

An international multidisciplinary collaborative effort to arrive at a consensus definition and classification system for CP was begun in 2004.² This culminated in the Report on the Definition and Classification of Cerebral Palsy, which states that the term “CP 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 are often accompanied by disturbances of sensation, perception, cognition, communication and behaviour, by epilepsy, and by secondary musculoskeletal problems.”³ The robustness (reliability and validity) of this definition is yet to be established, and it is not the only one in current use, but this report based on collective expert opinion, represents the best effort to date to standardize the definition, inclusion/exclusion criteria, and the characteristics used currently for describing children with CP.

In this report, the international group also proposed a new classification system³ because the traditional classifications of CP based on the movement disorder (spastic, ataxic, or dyskinetic) and/or topographic distribution (hemiplegia, diplegia, and quadriplegia) alone were not reproducible, not reliably prognostic, or adequately descriptive of the heterogeneous population of children with CP. The new classification is based on 4 dimensions:

The new classification was developed by international expert opinion, and its overall reliability and validity is yet to be established.

PATHOPHYSIOLOGY

The hallmark of CP is abnormal muscle tone, of which spasticity is the most common type, accompanied by loss of selective motor control, muscle weakness, and impaired balance.⁷ Muscles grow in response to the stimulus of stretch derived from normal physical activity. Hypertonia and limited use of muscles because of developmental delay result in dynamic (velocity-dependent) muscle contractures, which become static joint contractures over time as the tight muscles fail to grow proportionately with their skeletal attachments (Level V evidence from animal studies).⁸ These abnormal forces on the growing skeleton lead to secondary bony deformities and joint instability, and related lever arm dysfunction.⁹ In children with ambulatory potential, the interaction of joint contractures, muscle weakness, bony deformities, and joint instability at multiple levels affect the quality and efficiency of gait and other aspects of their physical function. This understanding of the pathophysiology of CP is based on Level IV and V evidence.

IMPLICATIONS OF NATURAL HISTORY OF CEREBRAL PALSY ON OUTCOMES EVALUATION

Based on a prospective longitudinal cohort study of 657 children, Level I evidence has been reported that shows that gross motor function improves in children up to the age of 6 or 7 years, albeit with different trajectories for each GMFCS level, but it remains stable after motor development is complete.⁶ “Improvements” after any interventions in younger children must therefore be placed in the context of expected improvements in gross motor function before the age of 7 years. In contrast, although the primary central nervous system pathology is static, the secondary musculoskeletal pathology and its consequences are known to deteriorate over time in older children. Bell and colleagues¹⁰ report deterioration in passive range of motion, and spatiotemporal and kinematic parameters on gait analyses an average of 4.5 years apart in a group of 28 ambulatory children with CP who had not undergone any surgery during this interval.¹⁰ Johnson and coworkers¹¹ found similar rates of deterioration in gait over a 32-month period in 18 ambulatory children (4–18 years old) regardless of age or history of prior surgery. Despite their small sample sizes, both these longitudinal case series (Level IV evidence) suggest that effectiveness of surgical interventions for this population must be interpreted in the context of natural deterioration of gait with growth. Consequently, preintervention versus postintervention comparisons in uncontrolled case series may underestimate the outcomes of these interventions in the short term.¹² However, short-term outcomes are also less meaningful because the growing child is at risk for recurrent deformity and gradual loss of mobility over the long term, because the primary central nervous system pathology remains unaffected by the intervention. Mobility in adulthood may also deteriorate over time (Level IV evidence).^13–15 These issues have implications both on the optimal age at which the surgical interventions should be performed and the timing of outcome assessments.

GOALS OF TREATMENT AND OUTCOMES TO CONSIDER

The goals of treatment of ambulatory children with CP are to preserve or improve present and future gait efficiency and physical function, and secondarily to improve the appearance of gait.¹⁶ The treatment principles to accomplish these goals are: (1) prevention of joint contractures and skeletal deformities by muscle stretching, spasticity reduction, and muscle strengthening; and (2) correction of significant contractures and bony deformities when these have already occurred. Evaluating the effectiveness of interventions to achieve these goals requires defining the outcomes of interest and the longevity of these outcomes.^17,18

The American Academy for Cerebral Palsy and Developmental Medicine (AACPDM) advocates the use of a two-part conceptual framework to evaluate the effectiveness of interventions.^19,20 The framework analyzes and categorizes treatment outcomes according to the components of the International Classification of Functioning, Disability and Health (ICF),²¹ and judges the strength of the evidence according to the study design and rigor in the conduct of the study. The ICF model has two parts, each with two components (Table 34-1).

TABLE 34-1 International Classification of Functioning, Disability, and Health Model

A common, but often untested assumption is that treatment at one level (e.g., body structure and function: knee flexion contracture) may positively affect another level (e.g., activity and participation: by permitting independent walking over longer distances). Similarly, interventions do not always have simple effects on a single dimension. For example, powered mobility may increase activities by providing an alternative means of efficient locomotion, which may also increase participation by allowing a student to be independent and move around the school faster and with less effort, but may have negative effects in the body structure and function such as increased knee flexion contractures.²² A multicenter cross-sectional study found at best a fair correlation between measures of spasticity or range of motion (body structure and function) and measures of gross motor function or physical function.²³

INTERVENTION STRATEGIES FOR AMBULATORY CEREBRAL PALSY

A number of complementary strategies are used sequentially or in combination, including physical therapy, orthotics (braces), and serial casting to simulate the stretch that would normally be derived from usual physical activity, to stimulate muscle growth. These strategies are often accompanied by measures to reduce muscle tone by pharmacologic (botulinum toxin type A [BTX-A], phenol) or neurosurgical methods (selective dorsal rhizotomy [SDR], intrathecal baclofen). These are believed to facilitate the stretch from therapy and serial casting, and to improve tolerance of brace wear, which, in turn, may prevent or delay the onset of static contractures and bony deformities.^24,25 The musculoskeletal changes, collectively referred to as “lever arm disease” are best addressed with orthopedic surgery.⁹

The remainder of this chapter reviews the evidence for the effectiveness of these strategies in the management of ambulant children with CP.

EVIDENCE FOR EFFECTIVENESS OF SPASTICITY REDUCTION METHODS

EVIDENCE FOR MULTILEVEL ORTHOPEDIC SURGERY

Established musculoskeletal problems are thought to be best addressed with simultaneous (single-event) multilevel orthopedic surgery (SEMLS) including tendon lengthening or transfers and corrective osteotomies based on small uncontrolled case series^50,51 and expert opinion (Level IV and V evidence). Addressing all deformities simultaneously avoids the “birthday syndrome” of staged isolated procedures¹⁶ and limits the interventions to one hospitalization and one period of rehabilitation (Level V evidence). However, to date, no comparative studies have tested the superiority of this approach, leaving room for some debate. Some surgeons recommend (Level V evidence) early surgical interventions during childhood development with the expectation that this will enhance function and allow further improvement of motor skills, with further surgery as needed when the child is older. ⁵² This approach also uses multilevel procedures as needed and has been referred to as Staged Multilevel Interventions in the Lower Extremity (SMILE). There is some weak Level IV evidence from small case series that children with spastic diplegia who underwent staged orthopedic procedures had unpredictable results.⁵³ In contrast, there is little evidence that the single-event multilevel surgery performed at the optimal (older) age eliminates the need for additional surgery in the future.