The kinematic coupling during Ponseti correction in idiopathic clubfoot: A quantitative analysis.

Background: The study aimed to quantify and correlate kinematic coupling linkage of foot abduction (correction of adduction) and inversion, heel varus and ankle equinus for clubfeet corrected by Ponseti technique.

Methods: Measurements of foot abduction (derotation of carpopedal block), heel varus and ankle equinus were available from Dimeglio scores in 25 feet. Radiological angles were considered for foot inversion-eversion. Values of above parameters were obtained at the start of treatment (T1), pre tenotomy (T2) and after tenotomy (T3). The values of T2-T1 corresponded to the manipulative phase of Ponseti technique while T3-T2 corresponded to the Achilles tenotomy.

Results: During the manipulative phase, coupling rhythm between foot abduction to correction of equinus, heel varus and inversion was calculated to be 1:0.3, 1:1.1 and 1:0.5 respectively. Post tenotomy, coupling rhythm between ankle dorsiflexion to changes in foot abduction, heel varus and inversion was calculated to be 1:0.5, 1:0.1 and 1:0.4 respectively. A moderate significant correlation was obtained on comparison of T3-T2 values between clinical equinus and foot abduction (r = 0.54, p = 0.05).

Conclusion: The foot inversion, heel varus and ankle equinus corrected at 1.1, 0.5 and 0.3 times respectively of foot abduction in the manipulative phase. The phenomenon of kinematic coupling between various foot movements was however inconsistent during Ponseti treatment of clubfoot. More significant associations were obvious towards late phase of deformity correction when foot alignments were much improved. Larger prospective studies are needed to delineate the precise linkage between foot movements in a pathological condition such as clubfoot.Level of evidence - II.