Poster 167: Anatomic Patellofemoral Factors that Affect the Sagittal Tibial Tubercle-Trochlea Groove Distance in Patella Instability Patients

Objectives: Sagittal tibial tubercle-trochlea groove (sTT-TG) distance is the sagittal plane distance between the cartilaginous nadir of the trochlear groove and the most anterior aspect of the tibial tubercle. sTT-TG is a potential surrogate indicator of patellofemoral (PF) sagittal overload and contact pressures and has been shown to be associated with the prevalence of PF chondral pathology and may also predict key lesion characteristics such as size. Despite increasing recognition of its clinical significance, the underlying anatomic factors that determine sTT-TG distance are yet to be clearly described in the literature. The purpose of this study was therefore to determine the anatomic drivers of sTT-TG distance. Methods: A retrospective review of patients evaluated for patella instability at a single institution between 2016 and 2021 was performed. All patients who had closed lateral patellar dislocation requiring manual reduction or history of a frank dislocation with spontaneous reduction and preoperative MRI and radiograph available for evaluation at the time of the study were included. sTT-TG and its anatomic relationship to patellofemoral measures, including dysplasia, femoral anteversion, tibial tubercle lateralization, knee rotation angle, and tibial torsion, sulcus angle, patella width, TT-TG, bump height, Caton-Deschamps Index (CDI) and trochlea depth were measured and subsequently quantified using univariate and multivariable analysis. Results: In total, 106 patients met inclusion criteria (74 female, 32 male; mean ± SD age, 21.84 ± 9.46 years). The mean sTT-TG distance was 6.64 ± 5.29 mm. Other baseline characteristics are presented in Table 1 . On univariate analysis, increasing CDI ( P < 0.01) and knee rotation angle ( P = 0.04) were significantly associated with increased sTT-TG. In contrast, increased patellar width and trochlear depth (LFC-Central) ( P < 0.01) demonstrated an inverse relationship with sTT-TG ( P < 0.01). Dejour A ( P = 0.17), C ( P = 0.23) or D ( P = 0.73) dysplasia patients did not demonstrate a significantly different sTT-TG compared to patients without trochlear dysplasia (4.79 ± 5.12 mm). However, patients with Dejour B dysplasia demonstrated a significantly increased sTT-TG (9.27 ± 4.09 mm) compared to non-dysplasia patients ( P = 0.02). On multivariable analysis, trochlear depth (LFC-central) ( P < 0.05), patellar width ( P < 0.01), and CDI ( P < 0.05) were significant determinants of sTT-TG distance. Notably, in accounting for these variables, knee rotation angle ( P = 0.64) and Dejour B ( P = 0.35) were no longer statistically significantly contributors in predicting sTT-TG distance. Conclusions: sTT-TG distance is most influenced by trochlear depth, patellar width, and CDI. Further studies are needed to confirm these findings and determine whether tibial torsion and femoral anteversion contribute significantly to sTT-TG.