Reliability and Reproducibility of the EOS 3D Imaging System in Measuring TT-TG Distance in Patients With Recurrent Patellar Dislocation.

Background: In clinical practice, preoperative radiographic assessment of the tibial tuberosity-trochlear groove (TT-TG) distance in patients with recurrent patellar dislocation (RPD) typically relies on conventional computed tomography (CT). A novel EOS imaging system may be a new option for measuring the TT-TG, which provides less radiation and costly time to perform.

Purpose: To determine the reliability and reproducibility of the EOS 3-dimensional (3D) imaging system to measure TT-TG values.

Study design: Cohort study (Diagnosis); Level of evidence, 2.

Methods: Data from 34 patients (36 knees) diagnosed with RPD in our sports medicine department were retrospectively analyzed. Two senior radiologists independently measured the alignment of the patients' lower limbs via EOS images. The TT-TG values measured by EOS 3D images and CT scans were compared. To evaluate intrareader reliability, measurements were repeated on 2 separate occasions ≥3 days apart and intraclass correlation coefficients (ICCs) and Bland-Altman plots were calculated.

Results: When lower-limb alignment was measured with EOS, there were no statistically significant differences in the femoral and tibial lengths (P = .87 and P = .78, respectively), femoral offset (P = .83), knee joint varus and valgus angles (P = .73), femoral and tibial mechanical angle (P = .70 and P = .83, respectively), and femorotibial torsion angles (P = .82) measured by the 2 radiologists. Excellent intraobserver ICC (>0.75) was observed. The TT-TG measurements using EOS 3D were 18.4 ± 4.2 mm (radiologist 1) and 18.4 ± 3.5 mm (radiologist 2), while the corresponding values from CT were 19.2 ± 4.0 mm and 18.5 ± 3.7 mm, respectively. The measurements between EOS and CT showed good intrarater consistency (ICC > 0.7). Bland-Altman analysis revealed mean differences of 0.743 mm and 0.081 mm between the 2 methods, with >91% of data points falling within ±1.96 SD, indicating strong agreement between the 2 measurement techniques.

Conclusion: Our study showed that the EOS 3D imaging system provides reliable and reproducible TT-TG measurements comparable with CT. This technology has the potential to serve as an alternative method for assessing lower-limb alignment and TT-TG values in patients with RPD.