There is provided methods of arthroplasty on a knee joint comprising obtaining a desired spacing of the femur (6) from the tibia (14) by inserting a spacer (28) into the knee joint between the tibia and the femur. The spacer is used as a reference for securing a guide jig in position about the knee joint for guiding resection of one or both of the femur and the tibia for fitting of tibial and/or femoral prostheses. Apparatus for use in the methods are also described.
