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

Abstract

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 (P < .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 (P < .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 (P = .02) and PBCW (P < .001) were significantly different based on sex in the OPI group; however, the TT-TG ratio did not show significant differences (P = .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.