Objective: There are variabilities in the distance between the tibial tuberosity and the trochlear groove. The knee angle needs to be considered when talking about patellofemoral instability.
Methods: This retrospective study analyses the MRI images of knee angles from 0 and 30 degrees in the patella dislocation group (20 cases) and in the control group (20 cases) from Dec 2017 to Dec 2019. Two experienced orthopedic physicians separately measure the study with a blind experiment method.
Results: The TT-TG data of the patella dislocation group and control group are 17.88 ± 3.40 mm and 13.31 ± 3.01 mm when the knee angle is 0, which indicates a difference with statistical significance (P < 0.01). The TT-TG data of the patella dislocation group and control group are 11.51 ± 3.60 mm and 7.40 ± 1.93 mm when the knee angle is at 30 degrees, indicating a statistically significant difference (P < 0.01). Also, the TT-TG data of both the patella dislocation group and control group have statistically significant differences within different knee angles of the same group (P < 0.01). The differences of TT-TG are 6.36 ± 2.43 mm and 5.92 ± 1.65 mm when the knee angle changes from 0 to 30, which shows no statistically significant difference (P > 0.01).
Conclusion: This research initially obtained the relevant MRI data of the TT-TG distance from different knee angles between the Chinese patella dislocation patient group and control group. The study received a new criterion to evaluate the TT-TG of patients with patella dislocations when the knee angle is below 30 degrees. The knee flexion angles need to be considered to measure the TT-TG distance when comprehensively evaluating patellofemoral instability. The TT-TG distance gradually increases when the knee changes from flexion to extension. The difference of the TT-TG distances shows no statistically significant difference.
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