Cerebral Palsy (CP) is defined as a non-progressive clinical syndrome with movement and postural impairments due to brain damage before the age of 1 year and has an incidence of approximately 2.4 per 1000 live births[1]. The resulting movement impairments are frequently lateralized, usually with serious involvement of the upper extremity. In particular, fine motor control of the hand and fingers is compromised. The involved extremity may demonstrate disorders in muscle tone, dyskinetic and atactic motor disorders as well as a reduction in strength and sensibility. Consequently, the paretic extremity may be used below the level of individual capacity in a broad range of age-appropriate tasks. Indeed, several converging lines of evidence suggest that non-use of a deafferented limb in monkeys or of the paretic arm in patients with unilateral stroke or CP is a learning phenomenon leading to a conditioned suppression of movement on the affected side, which is referred to as 'learned non-use' in adults and 'developmental disregard' in children[2, 3]. Developmental disregard is not so much reflected in the individual capacity of the child to involve the affected limb in tasks that require bimanual performance, but rather in the overall duration of use and the frequencies of specific behaviours of the affected arm and hand during tasks that allow predominantly single-handed performance. Very often, children with unilateral CP will tend to limit the use of their affected hand to simple functions, for example as a 'stabilizer' for the non-affected hand[4]. In this perspective, many young children with an asymmetric upper limb function due to CP must be stimulated to improve their bimanual performance, especially in their pre-school and primary school age[5].

In previous research[6–8] the use of the paretic hand in children with CP has been assessed by videotaping bilateral manipulation. Yet, the applied procedures have not been described and tested in detail. As a result widespread replication and implementation of these methods would not be justified. More importantly, many available instruments focus on the individual capacity of arm and hand movements during tasks demanding optimal use, whereas the amount of spontaneous use of the affected limb (in terms of overall duration and frequency of specific behaviours) is not assessed. For example, the Melbourne Assessment of Unilateral Upper Limb Function (Melbourne)[9] comprises 16 different skills among which range of motion, target accuracy, and fluency of movement are scored, and the Quality of Upper Extremity Skills Test (QUEST)[10] scores grasping, weight-bearing and protective extension as important skills. Only the Assisting Hand Assessment (AHA)[11, 12] has been described and evaluated in detail. It consists of 22 items that focus on the effectiveness of use of the assisting hand during bimanual activities in a semi-structured play situation and summarizes all behaviours into one sum score. Yet, none of the existing tests specifically focuses on the amount of spontaneous use of the affected limb during 'natural' activities as the most important indicator of developmental disregard. Indeed, existing instruments do not quantify how often and for how long the affected limb is used, and which variety of behaviours is shown, during different types of tasks.

In 2003 new computer software, the VOAA (Video Observations Aarts and Aarts), was designed to score and evaluate two important aspects of spontaneous upper limb use, i.e. overall duration and frequency of specific behaviours during predetermined, age-appropriate activities[5]. The scoring system of the VOAA-software supports the raters with well standardized videos that can be accurately and reliably assessed using buttons for all pre-determined behaviours that are linked to an integrated timer function. Furthermore, the software allows fast descriptive and statistical analyses. The applied module, which consisted of three tasks (making a sandwich, building Lego blocks and taking off shoes), showed an excellent content validity index (0.93) and a good intrarater and interrater reliability (Cohen's kappa 0.62-0.85). However, in order to identify developmental disregard, it was necessary to develop a new module (VOAA-DDD) with two well designed tasks with greater subtask variety and a better contrast between the tasks in terms of the necessity to use the affected arm and hand: 1) 'stringing beads' demanding the use of both hands, and 2) 'decorating a muffin' stimulating the use of both hands. These tasks were standardized and adjusted for two age groups: 2.5-5 years and 5-8 years.

Because in the VOAA-DDD two new tasks are introduced with a specific diagnostic purpose, the goal of the present study was to provide insight into some important properties of the VOAA-DDD. In this perspective, the following research questions were posed:

1. What is the interrater, intrarater and test-retest reliability of the VOAA-DDD in children with spatic unilateral CP between 2.5 and 8 years of age?

2. Is the VOAA-DDD a discriminative instrument to distinguish children with spastic unilateral CP in the age of 2.5 and 8 years from healthy children of the same age groups?

The latter question was aimed to underscore the construct validity of the VOAA-DDD. It was hypothesized that in healthy children the overall duration and frequency of specific hand use would be equal for both hands and the same in either task (stringing beads or decorating muffin), whereas children with CP would be more inclined to disregard their affected arm and hand, particularly during the task that merely stimulated the use of the impaired limb (decorating a muffin). The duration of hand use was considered the most sensitive and primary outcome measure for identifying developmental disregard.

The results of this study show an excellent interrater, intrarater and test-retest reliability for the various outcomes of the VOAA-DDD in children with spastic unilateral cerebral palsy between 2.5 and 8 years of age. Possible factors that might have contributed to this result are the use of standardized videotapes, a computer-supported scoring system and the thorough training of the raters. Indeed, the VOAA-DDD is primarily meant to be used by pediatric occupational therapists working with children with CP. As with other occupational assessment instruments, adequate training is a prerequisite for reliable clinical application. Until now, no reliable assessment of duration and frequency of spontaneous use of the affected arm and hand was available for these children. To assess children with CP comprehensively, a range of tools is required, some of which are better suited for clinical use and others for research[14]. The selection of tools should be tailored to the clinical setting, the children involved, and the purpose of measurement.

With the VOAA-DDD two aspects of use of the affected arm and hand are scored. The results of this study indicate that both the duration of spontaneous use and the frequency scores regarding basic behaviours of the affected arm and hand can be used to determine developmental disregard, by comparing a task that merely stimulates the use of both hands with a task that demands bimanual activity. In combination with other tests like the Melbourne, the AHA and the passive and active range of motion, the VOAA-DDD gives a good overview of individual capacity and actual performance of the affected arm and hand in children with CP. Such an overview can provide indications for individually tailored rehabilitation. For instance, when a child has full active range of motion in the affected wrist and, at the same time, a low A-score on the beads task of the VOAA-DDD, it should be trained to use its capacity of wrist extension in play and daily life activities. When a child with active wrist extension would only show affected hand use during the beads but not during the muffin task of the VOAA-DDD, it should be trained to overcome its developmental disregard, e.g. by means of constraint induced movement therapy. Although one could argue that the VOAA-DDD in its present form (using a standardized situation) is not truly a test of individual performance in a 'natural' environment according to ICF definitions (ICF, WHO 2009), we believe that its task design and focus on spontaneous behaviour uniquely contribute to currently available assessment tools that mainly focus on a child's capacity.

The validity of a new assessment tool is usually determined by criterion-referenced validity and by construct validity[15]. Because there is no criterion standard for the observed duration and frequency measures available in the literature, construct validity was determined by comparing children with CP to healthy children of the same age. It was hypothesized that, in healthy children, the duration of use of both hands would be the same while stringing beads as while decorating a muffin, whereas CP children would be inclined to use their affected arm and hand significantly less during the muffin task. Because the results of this study confirmed this hypothesis, they indicate a good construct validity of the VOAA for determining developmental disregard. When using the extreme values of the healthy children as cut-off values, 90% of the CP children aged 2.5-5 years and 50% of the CP children aged 5-8 years could be identified as suffering from developmental disregard. The number of healthy children included in this study is, however, too low to determine definitive cut-off values for developmental disregard for the various age groups.

We found that it was easy to obtain adequate cooperation of the preschoolers in our study, even though preschool age is a notoriously difficult age to assess children[16]. Apparently, the VOAA-DDD tasks are child friendly and playful. The time taken to administer the VOAA-DDD in this study varied from 20 to 40 minutes, which ensures its feasibility in clinical practice. The execution of the VOAA-DDD requires knowledge of the manual, handling of two equipment boxes, and attending a 3-hours training course for learning to use the software. Some additional practice in rating videotapes to improve one's intrarater reliability is recommended. The software is available in several versions, for instance, with and without the option to simultaneously observe from two different viewing angles.

A limitation of this study is the still moderate number of children with CP that were included and the subsequent stratification in only two age groups. Nevertheless, the included children showed a nice variation of Melbourne scores indicating sufficient variability in their affected arm and hand capacity. As already mentioned, the VOAA-DDD requires a standardized test situation, whereas one would preferably assess spontaneous use of the affected arm and hand in a completely natural environment. This latter option would, however, make it much more difficult to accurately and reliably compare the execution of two specific tasks to identify developmental disregard. Further investigation is necessary to assess the responsiveness of the VOAA-DDD in therapeutic trials targeting developmental disregard as well as to determine its clinimetric properties in children older than 8 years of age.

The VOAA-DDD is a reliable and valid instrument to assess spontaneous use of the affected arm and hand and to determine developmental disregard in children with spastic unilateral CP.