Dr. Muneoka’s remarkable article ( https://www.nature.com/articles/s41467-018-08278-4 ) provides the first direct evidence of postnatal joint regeneration in mice and provides an important proof-of-principle that joint regeneration is indeed feasible. The observations are transformative in the bone field as for more than 30 years, the regeneration of an intact, articulating joint was considered impossible! These critical research efforts have developed a method to stimulate joint regeneration following injury in mice using a combination of growth factors, including BMP-9. BMP-9 stimulates the formation of joint structures including a synovial cavity and a skeletal element lined with articular cartilage. This process also appears to require cells to express the Prg4 gene to initiate the formation of the synovial cavity. Please enjoy the attached article and congratulations to the entire Muneoka lab!