Reliability of a Photo-Based Modified Foot Posture Index (MFPI) in Quantifying Severity of Foot Deformity in Children With Cerebral Palsy

Abstract

Introduction: Children with cerebral palsy (CP) have high rates of foot deformity. Accurate assessment of foot morphology is crucial for therapeutic planning and outcome evaluation. This study aims to evaluate the reliability of a novel photo-based Modified Foot Posture Index (MFPI) in the evaluation of foot deformity in children with CP. Methods: Thirteen orthopaedic surgeons with neuromuscular clinical focus from 12 institutions evaluated standardized standing foot photographs of 20 children with CP, scoring foot morphology using the MFPI. Raters scored the standardized photographs based on five standard parameters. Two parameters assessed the hindfoot: curvature above and below the malleoli and calcaneal inversion/eversion. Three parameters assessed the midfoot and forefoot: talonavicular congruence, medial arch height, and forefoot abduction/adduction. Summary MFPI scores range from −10 to +10, where positive numbers connote planovalgus, whereas negative numbers connote a tendency toward cavovarus. Intra- and interrater reliability were calculated using a 2-way mixed model of the intraclass correlation coefficient (ICC) set to absolute agreement. Results: Feet spanned the spectrum of potential pathology assessable by the MFPI, including no deformity, mild, moderate, and severe planovalgus or cavovarus deformities. All scored variables showed high intrarater reliability with ICCs from 0.891 to 1. ICCs for interrater reliability ranged from 0.965 to 0.984. Hindfoot total score had an ICC of 0.979, with a 95% CI, 0.968-0.988 (P<0.001). The forefoot total score had an ICC of 0.984 (95% CI, 0.976-0.991, P<0.001). Mean total score by the MFPI was 3.67 with an ICC of 0.982 (95% CI, 0.972-0.990, P<0.001). Conclusions: The photo-based MFPI demonstrates high intra- and interrater reliability in assessing foot deformities in children with CP. Its noninvasive nature and ease of use make it a promising tool for both clinical and research settings. MFPI should be considered as part of standard outcomes scores in studies regarding the treatment of CP-associated foot deformities. Level of Evidence: Level V.