Tanaka MJ, et al. - Static CT images of 22 fully extended knees of persons with symptomatic patellar instability and images of 22 asymptomatic knees were reviewed in order to define a measurement to evaluate sagittal tibial tuberosity (TT)–trochlear groove (TG) distance and to contrast this between asymptomatic (control) persons and patients with symptomatic patellar instability. Mean TT–TG distances were 19.9 ± 4.4 mm (symptomatic) and 16.8 ± 5.5 mm (control) and mean anteroposterior TT–TG distances were 8.3 ± 7.8 mm (symptomatic) and −0.5 ± 4.6 mm (control). The symptomatic group had higher measurements of trochlear dysplasia, with lower lateral trochlear inclination, bigger sulcus angle, and lower trochlear depth. Anteroposterior TT–TG distance and trochlear depth were greatly negatively related. Thus, in asymptomatic individuals, the anteroposterior TT–TG distance was −0.5 mm, intimating that the TG and TT were approximately in the same coronal plane. In persons with symptomatic patellar instability, the TG was almost nine millimeters anterior, and this distance related to measurements of trochlear dysplasia.