The effect of inturning of the foot on knee kinematics and kinetics in children with treated idiopathic clubfoot

Objective. To assess the effect of internal foot progression angle (inturning) on knee dynamics in children with treated clubfeet. Design. Prospective study dividing a population of clubfeet according to the factor inturning. Background. Excessive internal or external foot progression angle increases knee flexion by a backward shift of the ground reaction force to the knee joint in children with cerebral palsy. Similarly, inturning in clubfeet was hypothesized to shift the ground reaction force backwards with reference to the knee joint, increasing the external knee flexion moment and the maximal knee flexion at stance. Methods. Three-dimensional gait analysis was performed on 20 children with surgically treated clubfeet (n=28) to assess alterations of knee dynamics related to inturning (>7°) and on 13 normal children. Results. Inturning occurred in 46% of the clubfeet and was associated during stance, at maximal knee flexion, to an increase in maximal knee flexion (+7°), external knee flexion moment (+60%) and related lever arm to the knee (+100%) and at minimal knee flexion, to a reduction in external knee extension moment (−62%) and related lever arm (−58%). Inturning was associated with a more frequent prolongation of internal knee extension moment and of rectus femoris activity exceeding 50% of stance. Conclusion. Inturning in clubfeet is associated with knee dynamics alteration, which might contribute to the long-term development of knee osteoarthritis.