Systems, methods, devices and instruments for adjusting the relative positioning of bones or bony tissues, such as two or more vertebrae, are provided. More particularly, in one form, an instrument includes first and second end members that are freely movable relative to one another in a first configuration of the instrument, while in a second configuration the first and second end members are only movable relative to one another upon rotation of a displacement member. In one aspect of this and/or other forms, the first and second end members include hook portions that are selectively rotatable relative to one another such that the instrument can be used for compression or distraction of the bones or bony tissues. In another form, techniques for adjusting the relative positioning of bones or bony tissues are provided.