A cage assembly for implanting between and securing together two portions of bone in a tibial tuberosity advancement, the cage assembly comprising: an elongated cage body having a first end , a second end , opposing sides , a top and a bottom , the cage body for placement between said two portions of bone such that each side contacts one of said portions of bone so as to maintain a space between the portions of bone; and a securing member configured to interlock with the cage body and for securing to said portions of bone; wherein the cage body comprises a box portion having a top wall , a bottom wall , a first end wall at the first end of the cage body and a second end wall towards the second end of the cage body; characterised in that : each of the top wall and bottom wall of the box portion is a single continuous rectangle; the cage body is made of a bio-absorbable polymer that will be absorbed into an animal body over time when implanted within the animal body; and the box portion comprises a support member extending from the corner formed between the bottom wall and the second end wall to the corner formed between the top wall and the first end wall ; and/or wherein the box portion comprises a support member extending from the corner formed between the bottom wall and the first end wall to the corner formed between the top wall and the second end wall . an elongated cage body having a first end , a second end , opposing sides , a top and a bottom , the cage body for placement between said two portions of bone such that each side contacts one of said portions of bone so as to maintain a space between the portions of bone; and a securing member configured to interlock with the cage body and for securing to said portions of bone; wherein the cage body comprises a box portion having a top wall , a bottom wall , a first end wall at the first end of the cage body and a second end wall towards the second end of the cage body; characterised in that : each of the top wall and bottom wall of the box portion is a single continuous rectangle; the cage body is made of a bio-absorbable polymer that will be absorbed into an animal body over time when implanted within the animal body; and the box portion comprises a support member extending from the corner formed between the bottom wall and the second end wall to the corner formed between the top wall and the first end wall ; and/or wherein the box portion comprises a support member extending from the corner formed between the bottom wall and the first end wall to the corner formed between the top wall and the second end wall . each of the top wall and bottom wall of the box portion is a single continuous rectangle; the cage body is made of a bio-absorbable polymer that will be absorbed into an animal body over time when implanted within the animal body; and the box portion comprises a support member extending from the corner formed between the bottom wall and the second end wall to the corner formed between the top wall and the first end wall ; and/or wherein the box portion comprises a support member extending from the corner formed between the bottom wall and the first end wall to the corner formed between the top wall and the second end wall . <EOS>