Tibial Tuberosity-Trochlear Groove Ratio Adjusts for Sex Differences and Improves Accuracy in Assessing Patellofemoral Instability.

BACKGROUND

Tibial tuberosity-trochlear groove (TT-TG) distance has typically been used to determine the need for a tibial tuberosity medialization. However, because it is an absolute value, TT-TG distance does not consider the patient's size and, therefore, has the potential to over- or underestimate the need for a medialization of the tibial tuberosity.

PURPOSE/HYPOTHESIS: The aim of the study was to propose a ratio combining the TT-TG distance and the posterior bicondylar width (PBCW) of the femur as a representation of patient size. It was hypothesized that this ratio would provide a more accurate assessment of patellofemoral instability than the TT-TG distance.

STUDY DESIGN

Cohort study (diagnosis); Level of evidence, 3.

METHODS

A consecutive series of patients with recurrent patellofemoral instability between 2020 and 2022 was reviewed and compared with a consecutive cohort of patients with isolated meniscal tears. The TT-TG distance and PBCW were assessed using magnetic resonance imaging, and the ratio created using both measurements (TT-TG ratio was calculated by expressing the TT-TG distance as a percentage of the PBCW) was compared to the TT-TG distance alone to evaluate differences in diagnostic accuracy and differences based on femoral size and sex.

RESULTS

In total, 129 patients with objective patellofemoral instability (OPI) and 105 controls were included in this study. The mean TT-TG distance was 15 ± 5.2 mm in the OPI group and 8.6 ± 3.6 mm in the control group ( < .001), with a cutoff value of 11.15 mm for distinguishing between the 2 groups. The TT-TG ratio was 22.3% ± 3% in the OPI group and 11.7% ± 4.6% in the control group ( < .001), with a cutoff value of 16%. The TT-TG distance had an area under the curve of 0.848, whereas the TT-TG ratio had an area under the curve of 0.892. Subgroup analysis indicated that the TT-TG distance ( = .02) and PBCW ( < .001) were significantly different based on sex in the OPI group; however, the TT-TG ratio did not show significant differences ( = .84).

CONCLUSION

The TT-TG ratio provides an enhanced discriminant value compared with the TT-TG distance in distinguishing patients with patellofemoral instability from controls. This ratio accounts for inherent sex- and size-based differences associated with the TT-TG distance, offering a more individualized assessment when considering the need for tibial tuberosity osteotomy and the extent of medialization required.

CLINICAL RELEVANCE

This study highlights the importance of the TT-TG ratio in the analysis of patients with patellofemoral instability, providing improved diagnostic accuracy while accounting for sex and size-based differences. This allows for a more personalized treatment approach and can lead to better decision making regarding tibial tuberosity osteotomy.