2025 ISAKOS Biennial Congress ePoster
Analyzing the Alignment Error in Tibial Tuberosity-Trochlear Groove Distance (TT-TG) in Clinical Scans Using 2D and 3D Methods
Johannes M. Sieberer, MSc, New Haven UNITED STATES
Nancy Park, BS, New Haven, CT UNITED STATES
Shelby T Desroches, MS, New Haven, CT UNITED STATES
Albert L Rancu, BS, New Haven, CT UNITED STATES
Curtis McDonald, MASc, New Haven, CT UNITED STATES
Armita Razieh Manafzadeh, PhD, New Haven, CT UNITED STATES
Steven Tommasini, PhD, New Haven, Connecticut UNITED STATES
Daniel Wiznia, MD
John P. Fulkerson, MD, Litchfield, CT UNITED STATES
Yale Schoold of Medicine, New Haven, CT, UNITED STATES
FDA Status Not Applicable
Summary
The correct measurement of TT-TG requires correct alignment of the patient legs in the scanner gantry, in this study we show this is not always achieved utilizing a 3D version of TT-TG.
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Abstract
Background
Tibial tuberosity to trochlear groove distance (TT-TG) is often used as a primary metric for surgical decision making in the treatment of patellofemoral instability (PFI), particularly when considering tibial tubercle transfer. While having high interrater reliability (IRR), it is prone to measurement differences caused by the alignment of the patient’s leg in a scanner gantry, potentially influencing surgical decision making. Quantification of this error within the clinical literature remains limited.
Purpose
The purpose of this study is to quantify and specify the error in TT-TG caused by leg-scanner alignment by using detailed topographical landmarks and 3D analysis of CT-scans of patients with PFI.
Study Design
Case Series. Level of evidence IV.
Methods
3D models of knees with PFI were created from CT scans and TT-TG landmarks identified. TT-TG was measured using the established 2D and a 3D methods. A model to estimate the differences between these two methods was created, and the orientations of the patients’ legs in relation to scanner longitudinal axis measured to validate this model via linear regression. IRR was calculated via interclass correlation coefficients (ICC).
Results
44 knees of patients with PFI were analyzed. Differences between the 2D and 3D methods ranged from -4.0 to 14.8 mm (mean±std: 2.7 ± 4.0) with a root mean squared difference (RMS) of 4.8mm. The TT-TG distance of the 2D method (patients: 19.8±7.2 mm) was significantly (p=0.045) longer than when using the 3D method (17.1±4.9 mm). The variance of the 2D method was significantly larger than that of the 3D method. 13 or 29.6% of the knees had a difference of more than 5 mm between 2D and 3D TT-TG. The estimation model had an adjusted r-squared value of 1.00 and a resulting RMS of 0.21mm. The interrater reliability ICC was good to excellent (0.94 (CI95%: 0.81-0.98)).
Conclusion
TT-TG in three dimensions (3D TT-TG) can correct scanner-leg alignment errors, some of which are substantial when using only 2D TT-TG measurements. The findings in this study suggest a need for caution and awareness of the potential effects of differences in alignment of the axes of the leg and scanner when using purely 2D TT-TG as a basis for surgical planning.
Key Terms
Patellofemoral instability, Tibial Tuberosity to Trochlear Groove distance (TT-TG), alignment error, three-dimensional (3D) analysis