A femur bone cutting guide system (100) for use in a knee replacement surgical procedure includes a positioning guide in the form of a moulding (132), a bone cutting guide assembly 18 comprising bone cuffing guide components (140, 142) and a guide mounting arrangement comprising a pair of mounting plates (144,1 and 144.2). The moulding (132) is constructed from anatomical data of the femur permitting it to be securely fifed to the lower extremity of the femur. Two attachment posts (154.1 and 154.2) which are connected to the moulding (132) provide for removable mounting of the components (140, 142) to the moulding. The components (140, 142) define guide formations for guiding a cutter for cutting prosthetic joint locating faces in the femur. The plates (144.1, 144.2) are removably mounted to the components (140, 142) and fixed to opposite sides of the femur. The components (140, 142) are then removed allowing removal of the moulding (132). Thereafter, the components are remounted to the plates (144.1, 144.2) to provide for cutting of the femur.
