Reliability and validity of motion analysis in children treated for congenital clubfoot according to the Clubfoot Assessment Protocol (CAP) using inexperienced assessors

BACKGROUND: The Clubfoot Assessment Protocol (CAP) was developed for follow-up of children treated for clubfoot. The objective of this study was to analyze reliability and validity of the six items used in the domain CAPMotion Quality using inexperienced assessors. FINDINGS: Four raters (two paediatric orthopaedic surgeons, two senior physiotherapists) used the CAP scores to analyze, on two different occasions, 11 videotapes containing standardized recordings of motion activity according to the domain CAPMotion Quality These results were compared to a criterion (two raters, well experienced CAP assessors) for validity and for checking for learning effect. Weighted kappa statistics, exact percentage observer agreement (Po), percentage observer agreement including one level difference (Po-1) and amount of scoring scales defined how reliability was to be interpreted. Inter- and intra rater differences were calculated using median and inter quartile ranges (IQR) on item level and mean and limits of agreement on domain level. Inter-rater reliability varied between fair and moderate (kappa) and had a mean agreement of 48/88% (Po/Po-1). Intra -rater reliability varied between moderate to good with a mean agreement of 63/96%. The intra- and inter-rater differences in the present study were generally small both on item (0.00) and domain level (-1.10). There was exact agreement of 51% and Po-1 of 91% of the six items with the criterion. No learning effect was found. CONCLUSION: The CAPMotion quality can be used by inexperienced assessors with sufficient reliability in daily clinical practice and showed acceptable accuracy compared to the criterion.