The authors report three cases of unicompartmental knee arthroplasty (UKA), complicated with peri-operative periprosthetic fracture of the tibial plateau. The surgical technique was held responsible in all cases. The initial treatment was different in every case; all patients ultimately underwent revision total knee arthroplasty with a good functional outcome. The authors emphasise the importance of careful preparation of the tibial plateau during UKA, adequate sizing of the tibial component and caution when using a hammer during implantation of the tibial component. When a tibial plateau fracture occurs, the treatment of choice should be immediate revision total knee arthroplasty.