BACKGROUND: In the knee joints of patients with recurrent patellar dislocation (RPD), an increased relative tibial external rotation (rTER) is often observed. However, the changes in this parameter pre- and postoperatively remain unclear. PURPOSE: The purpose of this study was to reveal preoperative and postoperative changes in rTER in patients with RPD. METHODS: A total of 48 cases with RPD in the knee joint were included in the study group, while 50 cases with normal knee joints were included in the control group. The measured parameters included tibial tubercle-trochlear groove distance (TT-TG) and rTER. Measurements were recorded for RPD patients both pre-and postoperatively. Analysis of variance was used to assess the intergroup differences in TT-TG and rTER, and a t-test was employed to evaluate differences among various surgical procedures. RESULTS: In the RPD group, rTER was significantly higher than in the control group (P＜0.001), with no statistically significant difference in postoperative rTER (P = 0.366). There was no significant difference in postoperative rTER between the RPD group and the control group (P = 0.057). The difference in TT-TG distance before and after operation in RPD patients was statistically significant (P <
0.001). Within the subgroups, there was a significant difference in rTER between pre - and post-operation in the tibial tuberosity osteotomy combined with medial patellofemoral ligament reconstruction (MPFLR) group (P = 0.043). Multivariate analysis showed that age and body mass index had no correlation with rTER. CONCLUSIONS: Compared with MPFLR alone, tibial tuberosity osteotomy combined with MPFLR can significantly reduce postoperative rTER and make rTER tend to be normal. For patients with elevated TT-TG and abnormal rTER, tibial tuberosity osteotomy combined with MPFLR may be a better choice.