Cerebral Palsy Outcome Measures
An Outcome Measure is the result of a test that is used to objectively determine the baseline function of a patient at the beginning of treatment. Once treatment has commenced, the same instrument can be used to determine progress and treatment efficacy. With the move towards Evidence Based Practice (EBP) in the health sciences, objective measures of outcome are important to provide credible and reliable justification for treatment. The instrument should also be convenient to apply for the therapist and comfortable for the patient. An integral part of evaluating clinical practice is to objectively assess the intervention and measure it against a set of outcomes to determine its efficacy. Prior to determining any orthotic intervention, the careful choice of treatment goals and aims is essential in children with complex neuromuscular disability in order to identify and determine appropriate outcome measures.
This means the therapist can ensure they are providing the most appropriate intervention that meets the treatment goals and expectations of the child, parent/caregiver and the clinical team. Change is inevitable in growing and developing children with Cerebral Palsy and the change that occurs is nonlinear and variable by subset of Cerebral Palsy. The outcomes of interventions should be based on the expectations for children with Cerebral Palsy of the same age and gross motor function, rather than the established norms for children without developmental delays.
Reliability, Validity, Specificity and Responsiveness
Selecting the appropriate outcome measures can be used to establish more efficient and effective methods of intervention for children with varying presentations of Cerebral Palsy. The elements that constitute effective outcome measures include:
1. Reliability: measures are constant over time and when used by different raters.  
2. Validity: appropriate to assess what the clinician or researcher wants to assess in a manner that makes intrinsic sense.  
3. Specificity: the ability to distinguish between the presence or absence of a certain condition in people.  
4. Responsiveness: the ability to detect minimal, but clinically relevant changes.  
The International Classification of Function, Disability and Health (ICF) is the World Health Organization's framework for measuring health and disability at both individual and population levels. The ICF has shifted the focus of the impairments in children with Cerebral Palsy from restriction in joint ROM or abnormal muscle tone to the evaluation of functions by assessing the quantitative and qualitative aspects of a child’s Activities of Daily Living (ADL).  It states that the focus of rehabilitation should be shifted from identifying a person’s disability to focusing on enhancing a person’s function, ability and performance quality for each individual in a contextual manner. The ICF identified domains that should be evaluated in children with Cerebral Palsy to include body function and structure, activity and participation. A consensus-based survey of clinicians, parents and youth with Cerebral Palsy supported these domains as relevant to the evaluation of all health care interventions in children with Cerebral Palsy. 
The primary goal of orthotic treatment of ambulant children with Cerebral Palsy (GMFCS I-III) is to optimise their gait. This is with the expectation that it will preserve or improve their physical function and provide them with the ability to increase their participation in physical activities, recreation and sport.  Evaluating orthotic intervention requires the use of outcome measures that will not only assess the function and quality of walking, but also the health related quality of life. Quality of life is frequently used as a ‘catch all’ expression for any self-reported measure, even when the instrument is capturing information objectively verifiable as functional ability, activities or participation. 
Clinician Reported Outcome Measures (CROMs) used in the literature to evaluate the efficacy of orthoses and specifically AFOs for children with Cerebral Palsy include the Timed Up and Go test (TUG), the 88 and 66 item Gross Motor Function Measure (GMFM-88 and GMFM-66 respectively), Gross Motor Performance Measure (GMPM), Clinical Gait Assessment Score (CGAS), Pediatric Balance Scale (PBS) and the Standardised Walking Obstacle Course (SWOC). All of these outcome measures have been proven to be valid and reliable to evaluate motor function and performance in children with Cerebral Palsy.      
The TUG is a basic test of functional mobility that evaluates an individual's ability to manoeuvre his or her body capably and independently to accomplish everyday tasks. The standard TUG test requires a child to rise from a seat with assistance of their arms and where the knees are flexed at 90°, stand momentarily, walk 3m, turn, return to the same seat, and sit down. Statistically significant differences in TUG scores have been observed in children across the GMFCS levels I-III, meaning it can act as a predictor of gross motor function.   The TUG has displayed excellent reliability, validity and repeatability in children aged 3-18 years who can understand instructions and do not have cognitive deficits.  It is an outcome measure that can quickly and easily evaluate the common orthotic treatment goal of improving the efficiency of gait and also has the potential to monitor change over time. It is also possible to employ the TUG in the child’s own environment, closely aligning with values of the ICF domains.
The Gross Motor Functional Measure (GMFM) is a criterion-referenced measure expressly constructed for the purpose of assessing capacity to perform specific functions and evaluate change in the gross motor function of children with CP.  The GMFM-88 and 66 item tools were especially developed to assess the gross motor function in children with CP and are among the few outcome measures that have displayed sensitivity to change when evaluating orthotic intervention. There have also been strong correlations established between a child’s GMFCS level and the scores attained in the GMFM sections D and E.  A large study with 257 participants conducted by Russell et al. , described the ‘D’ dimension of standing and ‘E’ dimension of walking, running and jumping of the GMFM to be sensitive to functional change in children with CP when using AFOs.
The 88 and 66 item GMFM cover the five dimensions of lying and rolling, sitting, crawling and kneeling, standing, and walking running and jumping. Administering the full five dimensions of the GMFM 88 or 66 item scales is a time consuming process, often taking in excess of 45 minutes, which means clinical utility is often low. The particular dimensions ‘D’ and ‘E’ of the GMFM may be assessed separately when evaluating a specific area of function in order to save time, while still retaining reliability, validity and sensitivity of the full measure. However, after 5 years of age, changes in a child’s motor abilities are more related to developing and refining motor functions in specific environments, rather than the development of basic gross motor skills.  Ceiling effects have been identified in older or more able children assessed with the GMFM.  This may explain why some studies described larger improvements in gross motor function in children younger than 5 years of age when compared with older children.
While CROMs are very good at assessing the ICF domain of body function and structure, they do not necessarily correlate with the components of function in the ICF domains of activity and participation. An important feature of outcome measures is the extent to which they reflect a person’s activity in everyday life. Environmental factors influence health conditions such as Cerebral Palsy and these factors can have an impact on the performance of activities.  A Patient Reported Outcome Measure (PROM) such as the Pediatric Outcomes Data Collection Instrument (PODCI), the Pediatric Evaluation of Disability Inventory (PEDI) or Gillette Functional Assessment Questionnaire (FAQ), permits the child and family to provide information from their own everyday environment that relates not only to the function of the child’s gait but also to quality of life issues. It is not always possible for healthcare professionals to observe children in their own environment, which makes the PROM a powerful and valuable evaluation tool.
The PODCI is a parent-reported outcome measure that assesses the mobility, physical function, comfort, happiness and expectations of the healthcare interventions in children with musculoskeletal health issues.  In accordance with the ICF values, it not only focuses on assessing function and performance following healthcare interventions, but also evaluates quality of life issues. The PODCI has good reliability and validity when evaluating quality of life issues and walking function in children with Cerebral PalsyP, but does have floor and ceiling effects in the transfer and mobility scales.   It demonstrates only a modest sensitivity to detect changes of walking function in children with CP following orthopaedic surgery as the scoring system is considered too expansive to detect subtle changes.   Lee et al.  found statistically significant improvements in PODCI scores following orthopaedic surgery, but only minimal clinically relevant results. This may mean the PODCI may not be sensitive enough to evaluate the effects of orthotic intervention on mobility and provide results that are clinically relevant.
The PEDI is a parent reported outcome measure administered by a clinician that has shown to be reliable, repeatable and valid in children and adolescents with CP from ages 2-18 to evaluate motor function, self-care and participation.   Its clinical relevance is further supported by evidence that motor skills are not necessarily representative of overall functional improvements following healthcare interventions as it assesses not only capability but also quality of performance.  The mobility scales in the PEDI have less detail than the GMFM scales. As a result, the PEDI demonstrates only moderate responsiveness to change in motor skills and should not be used in isolation to evaluate the ICF domain of body function and structure.  However, unlike the GMFM, it does have the advantage of being able to assess a child’s gross motor function in their everyday environment and is therefore more reflective of community function. Despite the PEDI being a patient-reported outcome measure, it still requires a trained healthcare professional to administer the evaluation. The PEDI covers the broad range of motor function, self-care and participation and is very thorough. It can take more than 30 minutes to complete, which may take up already valuable clinical time.
The Gillette Functional Ability Questionnaire (FAQ) is a reliable, repeatable and valid condition-specific functional scale that was developed especially for children with Cerebral Palsy.  (TABLE 4) Similar to the PEDI, it assesses a child’s walking ability across different domains. However it only focuses on the ability to achieve a particular level and not the capability. No training or equipment is necessary to administer the 10-level, parent-reported questionnaire and it is quick and easy to apply. It has shown sensitivity to change in children with Cerebral Palsy who have undergone orthopaedic surgery, but it is unclear as to whether it would be sensitive and responsive to change following orthotic intervention.  
TABLE 4: Description of each of the ten levels of the Gillette Functional Assessment Questionnaire, developed specifically for children with Cerebral Palsy. 
Given the heterogeneous nature of the Cerebral Palsy population, the goals of rehabilitation are often widely distributed across the ICF domains. This may result in problems interpreting the outcome when using standardised outcome measures alone.   Items in a standardised outcome measure may not match the individual treatment goals and even if they do, the outcome may not necessarily represent goal attainment. To breach this gap and complement standardised outcome measures, Goal Attainment Scales (GAS) have been successfully used to measure the extent to which individual goals are attained for ambulant children with Cerebral Palsy.  
The use of GAS measures allows the orthotist to not only perform the clinical evaluation of the orthotic intervention, but also ensure that patient and family satisfaction is measured. The clinician, parents and child are able to identify specific areas for evaluation, quickly perform the assessment and provide a score from a predetermined ordinal scale. In heterogeneous populations, GAS measures have exhibited increased responsiveness to the ICF domain of activity and participation than those of traditional standardised outcome measures.   
- Debuse D, Brace H. Outcome measures of activity for children with cerebral palsy: a systematic review. Pediatr Phys Ther. 2011 Fall;23(3):221-31
- Rosenbaum PL, Walter SD, Hanna SE, Palisano RJ, Russell DJ, Raina P, et al. Prognosis for gross motor function in cerebral palsy: creation of motor development curves. Jama. [Multicenter Study Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, P.H.S.]. 2002 Sep 18;288(11):1357-63
- Palisano RJ, Hanna SE, Rosenbaum PL, Russell DJ, Walter SD, Wood EP, et al. Validation of a model of gross motor function for children with cerebral palsy. Phys Ther. [Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, P.H.S. Validation Studies]. 2000 Oct;80(10):974-85
- Stanger M, Oresic S. Rehabilitation approaches for children with cerebral palsy: overview. J Child Neurol. [Review]. 2003 Sep;18 Suppl 1:S79-88
- Jerosch-Herold C. An evidence-based approach to choosing outcome measures: a checklist for the critical appraisal of validity, reliability and responsiveness studies. British Journal of Occupational Therapy. 2005;68(8):347-53
- World Health Organisation. International Classifiaction of Functioning, Disability and Health (ICF). Geneva, Switzerland: World Health Organization 2001
- Vargus-Adams JN, Martin LK. Measuring what matters in cerebral palsy: a breadth of important domains and outcome measures. Arch Phys Med Rehabil. [Research Support, N.I.H., Extramural]. 2009 Dec;90(12):2089-95
- Narayanan UG. Management of children with ambulatory cerebral palsy: an evidence-based review. J Pediatr Orthop. [Review]. 2012 Sep;32 Suppl 2:S172-81
- Morris C, Kurinczuk JJ, Fitzpatrick R. Child or family assessed measures of activity performance and participation for children with cerebral palsy: a structured review. Child Care Health Dev. [Evaluation Studies]. 2005 Jul;31(4):397-407
- Yi SH, Hwang JH, Kim SJ, Kwon JY. Validity of pediatric balance scales in children with spastic cerebral palsy. Neuropediatrics. 2012 Dec;43(6):307-13