Breaking down tibial tuberosity to trochlear groove distance into two components to enable patient-specific treatment...

Tibial tuberosity to trochlear groove (TT-TG) distance serves as one of the main metrics for patellofemoral instability (PFI) surgical decision-making. The purpose of this study is to split TT-TG into translational (caused by bony morphology) and rotational (external tibiofemoral rotation) components, elucidate how those two components relate to each other, and determine how the components differ between recurrent PFI patients and controls.

Computed tomography (CT) scans of PFI patients with at least two reported dislocation events, seen by our institution's orthopedic department, were retrospectively acquired. Control CT scans were acquired from the Multicenter Osteoarthritis Study (MOST). Three-dimensional (3D) landmarks were placed on the distal femora and the proximal tibias. TT-TG, its rotational and translational components, and tibiofemoral rotation were algorithmically calculated from these landmarks. The two cohorts' means were compared using Mann-Whitney U-tests. Pearson coefficients were used to evaluate the correlation between the TT-TG components. The reliability of the measurements was evaluated with intraclass correlation coefficients (ICCs). The minimal sample size for a power level of 0.80 was calculated with an a priori sample size calculation.

A total of 26 PFI (sex parity; age: 24.6 ​± ​10.0 years) and 294 control knees (sex parity; age: 52.6 ​± ​7.0 years) were analyzed. Statistically significant differences for TT-TG (18.7 ​± ​4.8 vs. 12.0 ​± ​3.4 ​mm, p ​< ​0.001), rotational (5.3 ​± ​2.5 vs. 1.0 ​± ​2.5 ​mm, p ​< ​0.001) and translational (13.4 ​± ​3.7 vs. 11.0 ​± ​3.1 ​mm, p ​= ​0.002) components of TT-TG, and tibiofemoral rotation (10.7 ​± ​4.7 vs. 1.9 ​± ​4.7°, p ​< ​0.001) were found. No significant correlation between the components of TT-TG was found (p ​= ​0.14, r² ​= ​0.29). Predictive ICCs for the four measurements ranged from 0.82 to 0.99.

TT-TG can be split into (1) a translational component, primarily dependent on bony morphology, and (2) a rotational component, caused by external tibiofemoral rotation, both of which can lead to an elevated TT-TG measurement independently of each other. The rotational component is the primary factor for differences observed between PFI patients and controls but might vary between consequential patient scans. Our findings emphasize the importance of personalized treatment strategies tailored to individual patient profiles in treating patellar instability and will aid in more accurately targeted selection of surgical methods addressing either or both translational or rotational components of TT-TG.

III Case-Control study.