A 70-year-old male underwent elective total knee replacement for osteoarthritis. At initial review six weeks after surgery the prosthesis was functioning well and he was asymptomatic. He reattended clinic four months postoperatively having developed worsening pain on the lateral aspect of the knee but without any loss of function or stiffness of the joint. He subsequently underwent arthroscopy where synovial folds in the lateral gutter were debrided and entirely alleviated his symptoms. This is an unusual cause of pain following total knee replacement which has not been previously reported.