RESUMEN
BACKGROUND: The Pirani scale is used for the assessment of Ponseti-managed clubfoot. Predicting outcomes using the total Pirani scale score has varied results, however, the prognostic value of midfoot and hindfoot components remains unknown. The purpose was to (1) determine the existence of subgroups of Ponseti-managed idiopathic clubfoot based on the trajectory of change in midfoot and hindfoot Pirani scale scores, (2) identify time points, at which subgroups can be distinguished, and (3) determine whether subgroups are associated with the number of casts required for correction and need for Achilles tenotomy. METHODS: Medical records of 226 children with 335 idiopathic clubfeet, over a 12-year period, were reviewed. Group-based trajectory modeling of the Pirani scale midfoot score and hindfoot score identified subgroups of clubfoot that followed statistically distinct patterns of change during initial Ponseti management. Generalized estimating equations determined the time point, at which subgroups could be distinguished. Comparisons between groups were determined using the Kruskal-Wallis test for the number of casts required for correction and binary logistic regression analysis for the need for tenotomy. RESULTS: Four subgroups were identified based on the rate of midfoot-hindfoot change: (1) fast-steady (61%), (2) steady-steady (19%), (3) fast-nil (7%), and (4) steady-nil (14%). The fast-steady subgroup can be distinguished at the removal of the second cast and all other subgroups can be distinguished at the removal of the fourth cast [ H (3) = 228.76, P < 0.001]. There was a significant statistical, not clinical, difference in the total number of casts required for correction across the 4 subgroups [median number of casts 5 to 6 in all groups, H (3) = 43.82, P < 0.001]. Need for tenotomy was significantly less in the fast-steady (51%) subgroup compared with the steady-steady (80%) subgroup [ H (1) = 16.23, P < 0.001]; tenotomy rates did not differ between the fast-nil (91%) and steady-nil (100%) subgroups [ H (1) = 4.13, P = 0.04]. CONCLUSIONS: Four distinct subgroups of idiopathic clubfoot were identified. Tenotomy rate differs between the subgroups highlighting the clinical benefit of subgrouping to predict outcomes in Ponseti-managed idiopathic clubfoot. LEVEL OF EVIDENCE: Level II, prognostic.