A tibial tuberosity implant system (ATT) configured to maintain an advanced tuberosity (30) of a quadruped in an advanced position with respect to a tibial body (23), where the advanced position is cranially separated from a first position when the Tuberosity is part of the tibial body. The ATT implant system comprises: an implant body (82) that includes: a distal end (86) that extends a longitudinal axis (L)； the distal end defines several bone anchor holes (90) and each bone anchor hole is configured to receive a bone anchor so as to fix the distal end to the tibial body； a proximal end (84) configured to receive a bone anchor such that it joins the proximal end with the advanced tuberosity； the proximal end is accommodated with respect to the distal end in a cranio-caudal direction； an intermediate portion (88) extending between the proximal and distal ends, along a central axis defining an angle α, with the longitudinal axis, where the intermediate portion is formed to separate the proximal end cranially with respect to the end distal in the cranio-caudal direction enough to maintain the advanced tuberosity in the advanced position, when the implant body is attached to the tibial body and the advanced tuberosity； and an expandable spacer (96) that is separated and not directly adhered to the implant body, the expandable spacer is configured to deposit in the space (40) defined between the advanced tuberosity and the tibial body, to resist the movement of the advanced tuberosity Towards the first position. The spacer comprises: a first spacer body (98a) and a second spacer body (98b) separated from the first spacer body and expandable with respect to the first spacer body in the cranio-caudal direction when the expandable spacer is deposited in space, the first spacer body defines a first surface facing the bone (104a) configured to engage with the advanced tuberosity, and the second spacer body defines a second surface facing the bone (104b) configured to engage
