ANNALS OF ANATOMY The different growth zones of the fetal foot Hannes Gruber, Erich Brenner, Oliver Schmitt*, and Helga Fritsch Institut ftir Anatomie und Histologie, Miillerstral3e 59, A-6010 Innsbruck, Austria, and *Institut ftir Anatomie, Medizinische Universit~it Liibeck, Ratzeburger Allee 160, D-23538 Ltibeck, Germany Summary. Previous publications revealed no reliable data or models concerning the three-dimensional ontogenesis of the lower extremity. Using the method of plastination- histology in combination with 3D-computer-reconstruc- tions we were able to produce exact, virtual 3D-speci- mens of 19 healthy fetal feet. The fetuses were aged between 9 to 38 weeks of gestation and age-dependently related to four defined age-groups. We compared these feet with the help of a new geometrical method. Thus, we obtained a kind of "slow-motion-picture" of the undis- turbed three-dimensional development of the fetal foot. Our results show that the human fetal foot has a desul- tory mode of growth and that growth priorities within the foot-skeleton change dependent upon age and region. Though the growth of the fetal foot-skeleton is desultory, it is not disconnected. The result of this peculiar mode of growth is to create the foot arches and thus seems to be functionally-oriented toward the human loot's specific purposes. Key words: Human fetal foot - Foot-arch formation - Growth mode - Geometry - Three-dimensional computer reconstruction Introduction Knowledge of the normal formation of the foot is essen- tial for the understanding of possible disorders and their treatment. Developmental processes of the locomotor system do not happen as successively as one would ex- pect. The formation of the lower extremities starts with bud-like formations of the lower lateral rump-wall in late embryonic stages (Streeter 1945, 1948; Gardner et al. Correspondence to: H. Fritsch E-mail: helga.ffitsch@uibk.ac.at 1957). Shortly after forming plate-like endings these limb- precursors undergo a so-called "inner formation", creat- ing the basis for the different parts of the locomotor sys- tem of the developing foot (His 1880; Collins 1995). In the early footplate all anlagen of the future bones are po- sitioned in one plane oriented more or less sagittally. At the end of the embryonic period a "positioning work" within the foot takes place moving it out of the so-called "praying position" (Streeter 1951), so that a "miniature adult" foot results from an outer aspect (Hasselwander and Schwalbe 1903; Whillis 1940; Kaback and Boizow 1987; Uhthoff 1990). Nevertheless the arrangements of the "end-embryonic" foot and its skeletal size-relations have not yet reached an adult situation (Gardner and O'Rahilly 1975). The fetal period is characterised not only by the growth of the loot's preformed cartilaginous bone-anlagen but also by their definite arrangement. There is no doubt that the post-embryonic positioning of the cartilaginous anla- gen is based on slight but tangled movements (Pisani 1998). The few studies dealing with the fetal cartilaginous anlagen are only partially concerned with their size and unaltered position (Gardner et al. 1959; O'Rahilly 1972; McKee and Bagnal11987). Most authors studying this prob- lem have focussed on descriptions of the alteration of the developing loot's outer appearance (Bardeen and Lewis 1901/1902; Blechschmidt 1961; Christ 1990; Pisani 1998; Tillmann and T6ndury 1998). Even excellent attempts at measuring and qualifying single fetal foot-skeleton ele- ments concerning their age-dependent mode of growth have not been able to answer the question of how these in- teractive proceedings occur (Lippert 1963; Martin 1957). All previous theories about growth and positioning are either based on incomplete observations of the fetuses' outer appearance or solely on histological sections through the foot. There is no reliable data on growth and position of the skeletal foot-elements as a single undis- turbed entity during certain periods of development Ann Anat (2001) 183:267-273 © Urban & Fischer Verlag http://www.urbanfischer.de/jou rnals/annanat 0940-9602/01/183/3-267 $15.00/0