2023 ISAKOS Biennial Congress ePoster
Tibial Tubercle-Trochlear Groove (TT-TG) Distance Is Less Predictive Of Patellofemoral Instability Risk Than Three-Dimensional (3D) Trochlear Groove Curvilinearity
Kristin Yu, MD, Rochester, MN UNITED STATES
Brian Beitler, BS, New Haven, CT UNITED STATES
John P. Fulkerson, MD, Litchfield, CT UNITED STATES
Yale School of Medicine, New Haven, CT, UNITED STATES
FDA Status Not Applicable
Summary
The entry point-transition point angle—a 3D measurement of trochlear groove curvilinearity—demonstrated superior discriminative accuracy between a cohort of patients with recurrent patella instability and age-matched controls over the absolute TT-TG distance and normalized TT-TG/TW ratio.
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Abstract
Background
The tibial tubercle-trochlear groove (TT-TG) distance is a common measurement employed in the evaluation of patella instability patients. The purpose of this study was to evaluate the diagnostic accuracy of the TT-TG distance in differentiating between subjects with recurrent patella dislocation and controls in comparison to a three-dimensional (3D) measurement of trochlear groove curvilinearity, the entry point (EP)-transition point (TP) angle.
Methods
3D prints were generated from patients with a history of recurrent patella dislocation treated by the senior author between January 2020 and November 2021. 24 recurrent patella dislocation patients (18 female, six male) were included. TT-TG distances and trochlear widths were measured on axial CT images. 3D prints were generated from 10 control subjects, all female, with no history of patella dislocation whose whole-body CT scans were included in the New Mexico Decedent Image Database. To evaluate 3D trochlear groove curvilinearity, the entry point (EP)-transition point (TP) angle was used. All EP-TP measurements were obtained with the models resting on their posterior femoral condyles. All statistical analyses were performed in Prism 9.0 using two-way, unpaired student’s t-tests and receiver operating characteristic curves. P-values of <0.05 were considered statistically significant.
Results
No significant differences were observed in TT-TG distance or TT-TG/TW between the recurrent dislocation and control cohorts. Conversely, a significant difference was observed in EP-TP angles between the control and instability cohorts, p<0.0001. More obtuse, larger EP-TP angles were observed in the control subjects. TT-TG and TT-TG/TW area under the curve (AUC) analyses failed to attain statistical significance. An AUC of 0.9250 was observed for EP-TP angle measurements, p<0.0001. The highest likelihood ratio was observed at an EP-TP angle cutoff <144.6 degrees, such that EP-TP angles <144.6 degrees were more 16 times more likely to be observed in control patients than recurrent patella instability patients. This threshold value demonstrated a sensitivity of 80% and specificity of 95% for recurrent patella instability.
Discussion
The EP-TP angle demonstrated superior discriminative accuracy between a cohort of patients with recurrent patella instability and age-matched controls over the absolute TT-TG distance and normalized TT-TG/TW ratio. This three-dimensional measurement of trochlear groove curvilinearity may be incorporated in clinical decision-making for patients with recurrent patella instability.