A cage assembly for implanting between and securing together two portions of bone in a tibial tuberosity advancement includes an elongated cage body having a first end and a second end, and a securing member. The first end of the cage body and the securing member are engagable with each other so as to interlock in a manner that prevents the securing member from moving longitudinally away from the cage body. The securing member is arrangable, when interlocked with the cage body, such that it has a portion which extends laterally outwards beyond each opposing side of the cage body for use in attaching the securing member to the portions of bone. Different sizes of securing member may be engaged with the cage body. The cage assembly therefore provides a convenient and flexible approach to tibial tuberosity advancement procedures.
