Idiopathic clubfeet follow four distinct trajectories during initial Ponseti management

Aim: To determine if subgroups of idiopathic clubfeet exist based on midfoot and hindfoot response to Ponseti management. Design: Retrospective chart audit of infants with clubfoot attending a tertiary clubfoot clinic (2008-2020). Methods: Group-based trajectory modelling (GBTM) of midfoot and hindfoot Pirani scores was used to identify groups of clubfeet that followed statistically distinct patterns of change during initial Ponseti treatment, to the point of correction. Chi-square analysis compared the percentage of tenotomies performed in each group. Results: Three hundred and thirty-five feet (226 infants, 70% male) commenced initial Ponseti management (mean age 20 days, SD 11.3), with an average 5 casts (SD 1.2) to achieve correction. Subgroups of feet were identified based on two hindfoot and two midfoot trajectories during casting, with 25% of feet in infants with bilateral clubfoot following different trajectories. The majority (57%) responded with steady hindfoot and fast midfoot improvement, with 50% achieving correction without tenotomy. A further 23% had similar hindfoot and midfoot improvement, with 78% requiring tenotomy. The remaining 20% of feet demonstrated no hindfoot and fast (6%) or steady (14%) midfoot improvement, with 97% requiring tenotomy. The need for achilles tenotomy was significantly different between groups (x2=26, p<0.001). Conclusion: The rate of improvement of midfoot and hindfoot deformity during initial Ponseti serial casting follows four distinct trajectories with differing needs for achilles tenotomy. Key practice points: Clinicians should document midfoot and hindfoot Pirani scores to help guide family expectations of treatment. Feet of infants with bilateral clubfoot may follow different trajectories.