Missing Midline Metatarsals Conform to Plantar Arterial Arch Dysgenesis.

Midline metatarsal ray deficiencies, which occur in approximately half of congenital short limbs with fibular deficiency, provide the most distal and compelling manifestation of a fluid spectrum of human lower-extremity congenital long bone reductions; this spectrum syndromically affects the long bone triad of the proximal femur, fibula, and midline metatarsals. The bony deficiencies correspond to sites of rapid embryonic arterial transitioning. Long bones first begin to ossify because of vascular invasions of their respective mesenchymal/cartilage anlagen, proceeding in a proximal-to-distal sequence along the forming embryonic limb. A single-axis artery forms initially in the embryonic lower limb by means of vasculogenesis. Additional arteries evolve in overlapping transitional waves, in proximity to the various anlagen, during the sixth and seventh weeks after fertilization. An adult pattern of vessels presents by the eighth week. Arterial alterations, in the form of retained primitive embryonic vessels and/or reduced absent adult vessels, have been observed clinically at the aforementioned locations where skeletal reductions occur. Persistence of primitive vessels in association with the triad of long bone reductions allows a heuristic estimation of the time, place, and nature of such coupled vascular and bony dysgeneses. Arterial dysgenesis is postulated to have occurred when the developing arterial and skeletal structures were concurrently vulnerable to teratogenic insults because of embryonic arterial instability, a risk factor during arterial transition. It is herein hypothesized that flawed arterial transitions subject the prefigured long bone cartilage models of the rapidly growing limb to the risk of teratogenesis at one or more of the then most rapidly growing sites. Midline metatarsal deficiency forms the keystone of this developmental concept of an error of limb development, which occurs as a consequence of failed completion of the medial portion of the plantar arch. Therefore, the historical nomenclature of congenital long bone deficiencies will benefit from modification from a current reliance on empirical physical taxonomies to a developmental foundation.