Haptic-visual evaluation of the J-Sign revealed a significant correlation with patella height, tibial tubercle – trochlear groove distance, trochlear bump height and the total number of risk factors for lateral patellar instability

J-sign assessment is considered a helpful clinical parameter in the treatment of lateral patellar instability (LPI). However, it is unclear whether there is a correlation between the degree of the J-sign and anatomic risk factors. The aim of this study was to investigate whether there is a correlation between the degree of the J-sign assessed by haptic-visual assessment and anatomic risk factors of LPI. J-sign grading was prospectively assessed by two experienced observers in 51 knee joints in 46 patients (male/female 19/32; age 25.1 ± 10 years; ≥ 1 patellar dislocation) according to the quadrant method of Zhang et al. Assessment was done with haptic-visual assessment, including palpation of the medial and lateral patellar facets with the thumb and index finger. The J-Sign grade was correlated with known anatomic risk factors for patellar instability, including the Caton‒Deschamps index, the Dejour type of trochlear dysplasia with additional measurements of trochlear bump height and lateral trochlear inclination angle, the tibial tuberosity–trochlear groove (TT–TG) distance, the tibial tuberosity–posterior cruciate ligament (TT–PCL) distance, the varus/valgus deformity and the total number of anatomic risk factors. There was a significant correlation between the J-sign and the Caton–Deschamps index (r1 = 0.51; p < 0.001 and r2 = 0.41; p = 0.005), the total number of anatomic risk factors (r1 = 0.34; p = 0.015 and r2 = 0.30; p = 0.032) and the trochlear bump height (r1 = 0.36; p = 0.021 and r2 = 0.35; p = 0.027) for both raters. Moreover, the results revealed a significant correlation between the J-sign grade assessed by one rater and the TT–TG distance (r1 = 0.31; p = 0.044). Haptic-visual assessment of the J-sign revealed a significant correlation with patella height, trochlear bump height, TT–TG distance and the total number of anatomic risk factors for patellar instability.