Clubfoot pathology in fetus and pathogenesis. A new pathogenetic theory based on pathology, imaging findings and biomechanics-a narrative review.

Several studies have described the pathology of idiopathic congenital clubfoot (ICCF) in fetus. Numerous pathogenetic theories have been postulated on ICCF, but many of them lack any objective evidence. Pathologic studies in fetus together with MRI studies in patients with ICCF seem to favor the theory of a muscular imbalance of the foot activators during fetal growth as the main pathogenetic factor of ICCF. Our objectives were: (I) To support the theory of muscular imbalance as the primary pathogenetic factor of ICCF; (II) To clarify why atrophy and shortening affect the activator muscles of the foot unevenly, as reported by literature. A literature search based on MEDLINE and the COCHRANE database was performed to identify all published studies from 1929 to 2020 which report ICCF pathology in fetus, its etiopathogenesis, and imaging and biomechanical studies showing how the basic pathology may be addressed by Ponseti treatment. A manual search was also performed of the references cited in studies, reviews, and university libraries. Altered size, shape and articular relationships of the tarsal bones, and uneven atrophy and shortening of the leg muscles together with capsule and ligament abnormalities were the main pathologic findings reported in fetus with ICCF. Regarding ICCF pathogenesis, the main debate is between the advocators of a primitive blastemal defect of the tarsal bones leading to the skeletal abnormalities and those who hold that the latter are secondary to a deforming force generated by the soft tissues. Imaging studies have shown that the Ponseti method is able to address the skeletal abnormalities, the correction of which is maintained until adulthood, whereas leg muscle atrophy is not improved but tends to worsen with growth. Preliminary histochemical studies of the soleus-Achilles tendon junction have shown a decrease of the growth factors and the presence of myostatin, both down-regulators of muscle growth in patients with ICCF. The authors postulate that a defect of both the radial and the longitudinal growth unevenly affecting the leg muscles with a consequent imbalance of the foot activators might be the main pathogenetic factor of ICCF. Further studies are needed to confirm this theory.