Table 1 The diagnostic criteria of ELPS

① All patients reported persistent pain and crepitus of anterior knee when going up and down stairs and squatting.

② The patellar medial shift [11] was less than 5 mm.

③ The anterior knee pain was induced by 30 degrees of knee flexion.

④ Patellar peripheral finger tenderness was touched on the surface of LR.

⑤ X-ray patella axial images showed obviously tilted outward patella, which was characterized by Wiberg type III or IV patellar [12].

⑥ The knee flexion 20 degree CT examination showed abnormalities of PTA and LPFA [13, 14].