The invention relates to a femoral jig (1) for use in surgery, said jig comprising a component (2) shaped to represent the overall profile of a femoral prosthetic component of a specific side and size, and having extending therefrom an anterior reference arm (3)； said arm having a cutting guide (4) located thereon. It also relates to a tibial replacement thickness spacer (50) comprising a set of leaves and a tibial jig (20) for use in knee surgery, said jig comprising a component having tibial plate (21) and tibial posts (22) extending downwardly from said tibial plate and an anterior reference arm (23)； said arm having a cutting guide (24) located thereon. Kits comprising components are also described.
