Ratio of the tibial tuberosity-trochlear groove distance to the tibial maximal mediolateral axis: A more reliable and standardized way to measure the tibial tuberosity-trochlear groove distance

Background: Tibial tuberosity-trochlear groove distance(TT-TG) is a measurement to assist in the diagnosis and treatment of patellar instability, however it still has some limitations. Our study was to modify the accepted measurement method and seek a more reliable and standardized method. Methods: The data of 65 healthy controls and 49 patients with bilateral patellar instability from 2010 to 2016 were collected and analyzed by CT. The TT-TG, tibial maximal mediolateral axis (MML), and their ratio (i.e., the modified-TT-TG (M-TT-TG)] were compared between the two groups. Results: The MML (71.9 +/- 12.0 vs. 71.3 +/- 10.9) was not significantly different between the two groups (P > 0.05). However, the TT-TG(18.1 +/- 6.0 vs. 13.1 +/- 2.9) and M-TT-TG (0.25 +/- 0.08 vs. 0.19 +/- 0.04) were significantly different between the two groups (P < 0.05). A TT-TG of >15 mm was found in 24.5% of healthy controls and 71.5% of patients. The healthy controls with a TT-TG of >15 mm were compared with the patients; although no significant difference was found in the TT-TG (16.8 +/- 1.5 vs. 18.1 +/- 6.0), the healthy controls had a significantly larger MML (76.9 +/- 12.7 vs. 71.9 +/- 10.9) and significantly smaller M-TT -TG (0.22 +/- 0.04 vs. 025 +/- 0.08). A total of 53.1% of patients but only 6.9% of healthy controls had an M-TT-TG of >025. Conclusion: The M-TT-TG is a more reliable and standardized way to measure the effect of the TT-TG with the goal of reducing the false-positive rate associated with the standard measurement technique. The normal M-TT-TG ranges from 0.11 to 0.25, with an M-TT-TG of >0.25 being associated with patellofemoral malalignment. (C) 2017 Elsevier B.V. All rights reserved.