Abstract: Objective To discuss the feasibility of manual measurement of the tibial tuberosity-trochlear groove(TT-TG) distance in the patient with patellar instability by modified single image method.
Methods Thirty cases patients with patellar instability were selected. Senior surgeons A and B measured the TT-TG distance of patients with patellar instability by modified single-image method and compared with senior radiologist C who measured the TT-TG distance of patients with patellar instability by double-image method.The Cronbach′s alpha coefficient was used to evaluate the reliability of the results.The intraclass correlation coefficient was used to evaluate the repeatability of the results.The Bland-Altman analysis diagram was used to evaluate the consistency of the results.
Results Senior surgeons A and B who measured the TT-TG distance of patients with patellar instability by modified single-image method compared with senior radiologist C who measured the TT-TG distance of patients with patellar instability by double-image method: Cronbach′s alpha coefficients were 0.913 and 0.959, respectively.The intragroup correlation coefficients were 0.913 and 0.958, respectively. The Bland-Altman analysis diagrams showed that the mean of TT-TG distance D-value(mm) was -0.276(95% CI：-3.526-2.974) and 0.143 (95% CI：-3.110-3.397). Senior surgeons A and B used the modified method to measure TT-TG distance manually in patellar instability patients.The Cronbach′s alpha coefficient was 0.891. The intragroup correlation coefficient was 0.891. 〖JP2〗The Bland-Altman analysis showed that the mean of TT-TG distance difference(mm) was -0.276 (95% CI：〖JP〗-3.526-2.974).
Conclusion The modified single image method is simple to measure TT-TG distance manually in patients with patellar instability. It can accurately measure TT-TG distance in patients with patellar instability. This method and double image method can be used interchangeably.

Key words: patella, tibial tuberosity-trochlear groove distance, magnetic resonance imaging