Knee joint morphogenesis of the quail (Coturnix japonica) embryo.

Knee joint development and its morphogenetic events have been studied in human, chicken and other animal models and differences have been found in the pattern of the knee joint morphogenesis among the studied species. According to the small number of studies which have focused on the chronology of knee morphogenesis, a "morphogenetic timely pattern" is hard to suggest. Quail is an animal model for which there is no information about knee joint morphogenesis. This study was planned to define the time table of the knee joint structures formation in this bird. For this purpose embryonated Japanese quail eggs were incubated for 3 to 12 days. Embryos were removed from their eggs every twelve hours and staged according to Ainsworth et al. The hind limbs of the embryos at the stages 17 to 41 were dissected and 6 μm thick slides were prepared from their knee region. The time of appearance of menisci, ligaments, articular cavity and other knee joint components were identified in the quail embryo. During quail knee morphogenesis we observed the appearance of a three layered interzone, femorotibial cavitation and long bone ossification earlier than in chicken. A hypothesis is presented on the differential role of the flexor and extensor muscles of the knee joint on embryonic knee development in birds as compared with humans.