Instrumentation for gauging the size, position and/or rotational orientation of one or more resections of a proximal tibia for receipt of a tibial implant, comprising: a cutting guide instrument configured for resection of the proximal tibia at an intended level of resection, including: a mounting base adapted for coupling to the proximal tibia; a cutting guide extending in a medial-lateral direction along a cutting plane, the cutting guide configured to guide a cutting device generally along the cutting plane to facilitate formation of a resection cut in the proximal tibia at the intended level of resection; and a tibia gauge (700, 750) for referencing one or more peripheral aspects of the proximal tibia at the intended level of resection, including: a reference plate; and at least one reference arm (720, 730) defining a distal end surface configured for engagement with a peripheral aspect of the proximal tibia; characterised in that the reference plate is adapted to be engaged with the cutting guide with the at least one reference arm positioned along the cutting plane and with the distal end surface dimensioned for engagement with a peripheral aspect of the proximal tibia at the intended level of resection. a cutting guide instrument configured for resection of the proximal tibia at an intended level of resection, including: a mounting base adapted for coupling to the proximal tibia; a cutting guide extending in a medial-lateral direction along a cutting plane, the cutting guide configured to guide a cutting device generally along the cutting plane to facilitate formation of a resection cut in the proximal tibia at the intended level of resection; and a tibia gauge (700, 750) for referencing one or more peripheral aspects of the proximal tibia at the intended level of resection, including: a reference plate; and at least one reference arm (720, 730) defining a distal end surface configured for engagement with a peripheral aspect of the proximal tibia; characterised in that the reference plate is adapted to be engaged with the cutting guide with the at least one reference arm positioned along the cutting plane and with the distal end surface dimensioned for engagement with a peripheral aspect of the proximal tibia at the intended level of resection. a mounting base adapted for coupling to the proximal tibia; a cutting guide extending in a medial-lateral direction along a cutting plane, the cutting guide configured to guide a cutting device generally along the cutting plane to facilitate formation of a resection cut in the proximal tibia at the intended level of resection; and a tibia gauge (700, 750) for referencing one or more peripheral aspects of the proximal tibia at the intended level of resection, including: a reference plate; and at least one reference arm (720, 730) defining a distal end surface configured for engagement with a peripheral aspect of the proximal tibia; characterised in that the reference plate is adapted to be engaged with the cutting guide with the at least one reference arm positioned along the cutting plane and with the distal end surface dimensioned for engagement with a peripheral aspect of the proximal tibia at the intended level of resection. a reference plate; and at least one reference arm (720, 730) defining a distal end surface configured for engagement with a peripheral aspect of the proximal tibia; characterised in that the reference plate is adapted to be engaged with the cutting guide with the at least one reference arm positioned along the cutting plane and with the distal end surface dimensioned for engagement with a peripheral aspect of the proximal tibia at the intended level of resection.