Short-term rigid and flaccid paralyses diminish growth of embryonic chick limbs and abrogate joint cavity formation but differentially preserve pre-cavitated joints.

The influence of movement on joint space formation during limb development has been the subject of much interest. Our aim was to investigate the short-term influence of movement upon cavitation by immobilizing chick embryos in ovo, both in a rigid manner where dynamic stimulation is removed, and a flaccid manner where both dynamic and static stimulation are absent. Induction of rigid immobilization with decamethonium bromide (DMB) or the novel induction of flaccid immobilization with pancuronium bromide (PB) for 3 days, during the normal cavitation of joints resulted in the loss of cavity formation. Immobilization after the formation of an overt cavity demonstrated that static stimulation (during rigid paralysis) was able to maintain joint cavities and preserve some of the hyaluronan (HA) content of articular surfaces, whereas flaccid paralysis resulted in the loss of cavities and a marked depletion of HA content. Assessments of the growth and deposition of cartilage and bone in the limbs of embryos immobilised during cavitation showed that the length of limb elements was greatly reduced and that decreases in epiphyseal widths were most marked and more pronounced distally. The volume of bone in these elements remained unchanged whereas the cartilage volume decreased significantly, suggesting that chondrogenic but not osteogenic events in the embryo are particularly sensitive to mechanical stimulation. In addition to describing a novel method of inducing flaccid immobility in ovo, these data point towards the important role of both static and dynamic stimuli in the growth of embryonic limbs and the development of a functional joint space.