Tibial plateau fracture is a rare complication of unicompartmental knee arthroplasty. The fracture almost always occurs during surgery, and it is likely to be the result of a technical error, usually an unnecessarily deep vertical saw cut into the proximal tibia. However, anything that weakens or overloads the proximal tibia may contribute to fracture, such as damage to the posterior cortex, excess removal of bone particularly in small patients with osteopenic bones, inadequate preparation of the keel slot, or use of excessive force with a heavy hammer. This series of eight case reports presents our experience with this complication after medial Oxford unicompartmental knee arthroplasty and outlines a treatment protocol.