Embodiments of the present disclosure are directed to a systems, devices and methods for displacing bones of a living mammal. In some embodiments, a device is provided which includes at least two engagement elements positioned at a distance from each other for engagement with two separate bones Each of the engagement elements may be carried by a support part which in turn is supported in a support portion of a distance unit (5). The said support part and support portion form a support unit, where each engagement element extends at an angle (α) with respect to a straight line (L) between two support units. At least one of the support units includes an arrangement for altering the angle which includes an actuating unit maneuverable for adjustment of the angle (α). Some embodiments of the disclosure are directed to a system for engagement with vertebrae including such devices (noted above), as well as uses of the device and associated methods of treatment.