Tibial prosthesis systems for implantation or use in a knee joint are disclosed. A tibial prosthesis system for implantation on a resected tibia can include a bearing component, a base component, and a shim component. The insertion of the shim component can provide spacing adjustment between the bearing and base components. The shim component can have a generally uniform height or thickness, or a variable height. A cut guide attachment, removably attachable to the prosthesis system, can be used to facilitate further resection of the tibia and create one or more additional resection surfaces on the tibia at an angle relative to the first resection surface. Multiple cut guide attachments can be available to the user to provide various resection angles. The cut guide attachment can include a modular design. The cut guide attachment can be configured to adjust the angle of the subsequent resection in at least one direction.