A prosthetic sternum device with a manubrium includes a plate and a device for attachment to ribs. Each of the devices for attachment to ribs includes an end for rigid connection to the plate and an end provided with a device for engaging with a rib. The plate further includes, in the upper region of same, two elements. Each element rigidly connects a pin and includes a polyaxial joint shaped to allow the multidirectional mobility of the pin.