A knee implant system includes a femoral adapter. The femoral adapter has a threaded bore so that a stem extension can be threaded onto the proximal end of the adapter. The same stem extension can be threaded onto the distal end of the tibial tray so that the number of stem extensions required in the system is reduced. The femoral adapter has a tapered exterior surface so that a metaphyseal sleeve can be frictionally connected to the femoral adapter. The metaphyseal sleeve has a threaded bore so that the same type of stem extension can be threaded onto the metaphyseal sleeve. The system can include a group of adapters to give the surgeon the option of selecting the appropriate valgus angle and anterior-posterior position of the stem extension.