An adolescent inter-condylar fracture of the distal femur was treated with percutaneous cancellous screws and an above-knee plaster. The subsequent fixed flexion deformity of the knee was initially considered to be due to soft tissue capsular scarring and adhesions but arthroscopic assessment of the joint identified an "Inverted Cyclops" lesion. This consisted of excess callus and fibrous tissue arising from the femoral notch. Arthroscopic excision of this tissue cured the deformity.