Tibiofemoral rotation after isolated MPFL reconstruction in recurrent patellar dislocation with elevated TT–TG distance

Background This study aimed to retrospectively present the radiologic outcomes in a cohort with recurrent patella dislocation (RPD) who have an elevated tibial tubercle–trochlear groove (TT-TG) distance (> 20 mm) following isolated medial patellofemoral ligament reconstruction (i-MPFL-R), and to exhibit the tibiofemoral rotation in RPD patients. Methods RPD patients with a TT-TG distance exceeding 20 mm and tibial tubercle-posterior cruciate ligament (TT-PCL) distance within 24 mm who underwent i-MPFL-R between 2018 and 2022 in our department were included. Clinical outcomes and remeasurement of TT-TG distance and other radiological measurements were analysed postoperatively. Data from the contralateral knee of each patient were analysed for contral. Results A total of 51 knees with a median follow-up time of 36 months were included. TT-TG distance has significantly decreased after i-MPFL-R in those patients (pre 24.30[22.25,25.85]mm vs post 20.20[18.25,22.65]mm,P < 0.001) compared with contralateral knee (pre 21.95 ± 3.20mm, 95%CI: 21.04–22.85 vs post 20.30[19.15,23.45]mm, P = 0.471). No significant changes were observed in the TT-PCL distance. Additionally, there was a synchronous decrease in tibiofemoral rotation (TFR) and patellar tilt angle (PTA) after i-MPFL-R in these patients (pre 9.83 ± 3.57°, 95%CI: 8.83–10.84 vs post 6.96 ± 3.13°, 95%CI: 6.08–7.84, P < 0.001) and (pre 28.51[24.26,33.76]° vs post 12.13[6.53,18.48]°, P < 0.001), compared with contralateral knee (pre 8.51 ± 3.37°, 95%CI: 7.57–9.46 vs post 8.46 ± 3.52°, 95%CI: 7.47–9.45, P = 0.889) and (pre 23.01 ± 7.57°, 95%CI: 20.88–25.13 vs post 26.60[15.70,30.65]°, P = 0.848), respectively. Conclusion The elevated TT–TG distance caused by excessive tibiofemoral rotation decreased following i-MPFL-R, which may be attributed to the tibiofemoral rotation effect during patellar reduction. The tibiofemoral rotation makes TT-TG, TFR, and PTA collectively form a triad of radiological measurements to be considered in patellar instability.