Implicit Central Hand Representation in Children With Neonatal Brachial Plexus Palsy: Interrater and Intrarater Reliability of the HandUZ Device - A Validation Study
Conditions: Neonatal Brachial Plexus Palsy
Sponsor: University Hospital, Ghent

Study Protocol 
 
 
 
 
 
 
 
Validation Study of a Digital Measurement Device for 
Central Hand Representation in Children with Neonatal 
Brachial Plexus Palsy (NBPP) 
 
NCT Number 
NCT06950879 
 
Researchers: 
L. Vanhoorebeeck, N. Vermassen, E. Staelens, Prof. Dr. R. Van Der Looven 
Date: November 19, 2024 
Version: 1.2 
 
 

1. Introduction 
Hand function is one of the most complex sensorimotor skills, requiring both motor output and 
multisensory input. The brain forms a complex representation of the hand using visual, 
proprioceptive, and anthropometric information. 
This study focuses on implicit hand representation, which is influenced by non-visual afferent 
signals. In children with Neonatal Brachial Plexus Palsy (NBPP), this implicit hand representation 
appears to be disrupted, leading to altered hand function. 
Previous research by Van Der Looven et al. showed that the reproducibility of existing test 
methods is good but that the procedures are cumbersome. This led to the development of the 
HANDUZ prototype, a digitized device that can automatically capture and process hand 
representation. 
This validation study aims to evaluate the reproducibility of this prototype in children with 
NBPP. Reproducibility is measured both intra-observer and inter-observer. 
 
2. Study Design 
Type of study: 
Validation study with reproducibility analysis 
Design: 
This is a single-center, observational reliability study involving children with a confirmed 
diagnosis of NBPP. Each participant completes six localization trials per hand using the HandUZ 
device. Two trained raters alternate administration to assess interrater and intrarater reliability. 
The study is conducted at the Child Rehabilitation Centre of Ghent University Hospital. 
Population: 
Participants: 18 children aged 8–18 years diagnosed with NBPP. 
 
Inclusion and Exclusion Criteria: 
• 
Inclusion: Children with a confirmed diagnosis of NBPP 
• 
Exclusion: Children with other neurological, psychiatric, or physical disorders that could 
affect hand function 
Measurement method: 
Participants are seated comfortably in front of a custom-built HandUZ setup, which consists of a 
three-layered vertical structure: a bottom plate with a measuring mat for hand positioning, a 
middle plate for visual occlusion, and a top plate holding an overhead webcam. The camera 
captures an image of the participant’s hand for landmark annotation. The tested hand is placed 
palm-down on the measuring mat, and vision is occluded using the middle plate during the 
perceptual task. 
Each hand is assessed six times in an alternating sequence by two trained raters, following a 
standardized protocol. The examiner verbally names specific anatomical landmarks—including 
the centers of the metacarpophalangeal (MCP) joints, fingertips, and wrist styloid processes—
and the child uses the index finger of the contralateral (non-tested) hand to localize the 

corresponding point on the occluded test hand. The examiner then digitally records the judged 
location on the computer interface. 
The estimated finger length (FL) is calculated using the Euclidean distance between each 
fingertip and the corresponding MCP joint, as identified during the perceptual task. These values 
are averaged across two trials to obtain a representative estimated FL for each finger. 
Separately, the actual FL is calculated from the image of the participant’s hand (taken before the 
task), using the same anatomical landmarks. For each finger, the percentage overestimation 
(OE) is calculated using the following formula: 
OE (%) = 100 × [(Estimated FL – Actual FL) / Actual FL] 
Negative values indicate underestimation while positive values indicate overestimation. 
To account for potential learning effects, non-consecutive trials are averaged (e.g., trials 1 and 5; 
2 and 6). These averaged values are then used for reliability analyses. 
 
3. Statistical methods 
A detailed SAP is included in a separate section and outlines the statistical procedures for 
assessing reliability, learning effects, and assumption checks. All analyses were conducted 
using IBM SPSS Statistics (Version 29.0.2.0). A significance level of α = 0.05 was applied. 
ICC(3,1) was used for reliability analysis, and repeated-measures ANOVA assessed learning 
effects. Assumption checks included Shapiro-Wilk tests and Mauchly’s test for sphericity. 
 
4. Reporting of Results 
• 
Tables: ICC values for intra- and inter-observer reproducibility with 95% confidence 
intervals 
• 
Graphs: Bland-Altman plots to visualize measurement differences and detect 
systematic bias 
• 
Conclusions: Whether the HANDUZ system provides reproducible measurements for 
clinical use. High reproducibility would support its further clinical implementation. 
 
5. Ethical Considerations 
The study protocol was approved by the Ethics Committee of Ghent University Hospital 
(reference B6702024000525) and conducted in accordance with the Declaration of Helsinki. All 
participants and/or their legal guardians provided written informed consent.  
 
6. Potential Limitations 
• 
Small sample size (17 children) may limit generalizability 
• 
Accuracy of reference point indication by participants may vary, introducing minor 
measurement errors 

 
7. Study Timeline 
• 
Participant recruitment: 2 months 
• 
Data collection: 2 months 
• 
Data analysis and reporting: 1 month 
• 
Total study duration: ~5 months