Fig. 2

Typical intraoperative pictures of the lesions in PI, AF and GS. In patients with PI, the hypertrophied cyclops could be found at the backside of the quadriceps tendon which would contact with the distal edge of the trochlea, creating mechanical irritation. Signs of impingement could be seen (a). There were no hypertrophied synovium found in other areas of the joint (b). In patients with AF, hard scar tissue and fibrous bands could be found throughout the joint in the suprapatellar pouch (c), medial and lateral gutters and in the space between PE insert femoral prosthesis (d). All these scar tissue could prevent patients fully extend and flex their knees. In patients with GS, the hypertrophied and inflamed synovium could be detected throughout the whole joint in the medial and lateral gutters (e), suprapatellar pouch (f) and in the space between PE insert femoral prosthesis (e), which would lead to swelling of the knee joint. Signs of hyperemia in the synovium could be found, during extension and flexion, bleeding could occur due to entrapped synovium