The Neurological Hand Deformity Classification: Construct validity, test-retest, and inter-rater reliability

Simon Garbellini, Melinda Randall, Michael Steele, Catherine Elliott, Christine Imms

Abstract

Background: The Neurological Hand Deformity Classification (NHDC) is an impairment-based tool that classifies hand deformity into one of two ordinal scales: flexion or extension deformities. Classification is made from live observation or from recorded video footage. Differentiation between the levels is determined by wrist position and wrist and finger movement.

Purpose: To examine aspects of validity and reliability of the NHDC.

Study design: A measurement study design.

Methods: Data from a convenience sample of 127 children with cerebral palsy, 66 males: 61 females, ranging in age from 8 months to 15 years, across all Manual Ability Classification System levels I to V, were analyzed. Construct validity was assessed by testing predetermined hypotheses of relationships between the NHDC and measures of body function and activity measures with observed performance using the Chi Squared Test of Independence and Spearman Correlation Coefficient. Test-retest and inter-rater reliability were assessed by calculating agreement between repeated measures and paired raters using weighted kappa and Cohen's kappa with 95% confidence intervals.

Results: Predicted hypotheses for the NHDC were met in nine of 10 Spearman's rho correlations with body structure measures and in 2 of 7 correlations with activity measures. Test-retest for flexion deformities: κw = 0.84; 95% CI 0.70-0.98; and extension deformities: κ = 1.0; 95% CI 1.0-1.0 was good to excellent; inter-rater reliability for flexion deformities: κw = 0.76; 95% CI 0.67-0.85; and extension deformities κ = 0.75; 95% CI 0.43-1.0 was moderate to excellent.

Conclusion: Expected relationships between the NHDC and other measures, stability between repeated measures and acceptable between-rater agreement supports confidence classifying hand deformity in children with cerebral palsy with the NHDC.