Fetal development of the first metatarsophalangeal joint complex with special reference to the intersesamoidal ridge.

In most individuals, plantar to the first metatarsal head, a more or less well developed crest separates the two furrows for the medial and the lateral sesamoid bones. In some instances, the absence of this crest has been observed in a previous study. This observation may be related to a pathological and/or an ontogenetic development. For the present examination, we have assumed the ontogenetic hypothesis. Twenty-two feet were examined at different developmental stages from week 12 to 38. The feet were prepared for examination using methods of plastination-histology. Sesamoids have already developed from the joint capsule by the first stage (12th week). Attachment bundles of collagenous fibers have deeply penetrated the cartilage of the sesamoids on their capsular side. Only some inner fibers of the muscular tendons join the sesamoids on their plantar side. The intersesamoid ligament is blended into the synovial tendon sheath of the flexor hallucis longus. The plantar crest has already developed in the fetal cartilage of the first metatarsal head as a strong ridge. With further growth, the surfaces become inwardly tapered on both sides of the ridge through the sesamoid bones, so that in the end the ridge results in a more or less clear crest. If the tapering of the furrows for the sesamoid bones proceeds too briskly or too far, this can result in an absence of the plantar crest. If the absence of this crest stands in relation to the formation of a Hallux valgus, this result would be a first indication of an developmentally based cause for this wide-spread disease of the foot.