A knee prosthesis includes a femoral component and a stem for implanting in a femur. A modular junction is provided for attaching the stem to the femoral component. The femoral component may include a boss having a slot for receiving the components of the modular junction. A portion of the modular junction may be placed within the slot and the modular junction may be tightened in place on the boss by threading the stem into engagement with a portion of the modular junction. Accordingly, the stem may be connected to the femoral component by a single threaded engagement and the position of the stem may be adjusted to any desired location along the anterior-posterior direction on the femoral component.