Fetal development of ligaments around the tarsal bones with special reference to contribution of muscles.

Through a histological examination of eight mid-term human fetuses (10-15 weeks) and seven late-stage fetuses (30-34 weeks), we attempted to determine how and when fetal ligaments around the tarsal bones form the regular arrangement seen in adults. Ligaments along the dorsal aspect of the tarsal bones developed early as an elongation of the perichondrium, in contrast to the late development of the plantar-sided ligaments. In contrast, a distal elongation of the tibialis posterior tendon was a limited plantar ligament in the early stage; finally, it extended from the navicular, ran obliquely to cross the dorsal side of the fibularis longus tendon, and inserted to the lateral cuneiform and fourth metatarsal. In the late stage, the adductor hallucis muscle origin provided multiple ligamentous structures along the cuneiforms and metatarsals. The tarsal sinus contained multiple fibrous bundles (possibly, the putative interosseous talocalcanean ligaments) that were derived from (1) insertion tendons of the extensor digitorus brevis muscle and (2) the fibrous sheath of the extensor digitorus longus tendon. The aponeurotic origin of the quadratus plantae muscle seemed to contribute to formation of the long plantar ligament. Therefore, tarsal ligaments appeared likely to develop from the long tendons, their fibrous sheaths and aponeuroses and intramuscular tendons of the proper foot muscles. Under in utero conditions with little or no stress from the plantar side of the foot, the muscle-associated connective tissue seems to play a crucial role in providing a regular arrangement of the ligaments in accordance with tensile stress from muscle contraction.