Clubfoot pathoanatomy—biomechanics of deformity correction: a narrative review

Clubfoot is a common and complex, multi-segmental, 3-dimensional, congenital foot deformity. The segmental deformities have been recognized for millennia. They are cavus of the forefoot/midfoot, adductus of the midfoot, varus of the hindfoot, and equinus of the ankle, often referred to by the acronym CAVE. However, description of the deformities and their correction have varied over time with changes in consensus terminology for foot deformities and the understanding of foot biomechanics. In this narrative review, the most current terminology for foot deformities and understanding of foot biomechanics are applied to the clubfoot. The concept of the calcaneopedal unit (CPU) is applied to the in-depth discussion and understanding of clubfoot for perhaps the first time in the English language literature. Of the 4 basic clubfoot deformities, cavus and adductus are static structural deformities within the CPU, i.e., all bones of the foot except the talus. Varus is a restricted dynamic deformity between the CPU and the talus. Equinus is a restricted dynamic deformity in the ankle joint between the talus and the tibia. Understanding the CPU concept improves ones understanding of clubfoot deformities and the rationale for treatment techniques. Consensual agreement on the terms used to define interosseous relationships and motions in the foot improves communication. Finally, this narrative review highlights the histologic and biologic changes that occur in collagen and cartilage during clubfoot deformity correction to provide further understanding and rationale for treatment.