Abstract
Objective To investigate the risk factors of J sign in patients with recurrent patellar dislocation, and to establish a new grading system of J sign. Methods From January 2017 to August 2018, a consecutive case series of 111 recurrent patellar dislocation patients were included in the present study. Among these patients, a total of 68 patients had positive J sign (J sign (+) group), and the remaining 43 patients had negative J sign (J sign (-) group). Caton index, Dejour classification, tibial tuberosity- trochlear groove (TT-TG) distance and rotational parameters of the lower extremity (including femoral anteversion angle, external tibial torsion angle and knee rotation angle) were measured to compare the differences of these parameters between the intervention group and control group. Furthermore, the risk factors of J sign were analyzed in detail. Meanwhile, a new grading system of J sign was introduced based on the extent and form of lateral patellar shift. Results The prevalence of J sign in recurrent patellar dislocation was 61.3% (68/111). Univariate analysis showed that femoral anteversion angle (t=3.376, P=0.001), knee rotation angle (t=4.886, P=0.001), TT-TG distance (t=3.177, P=0.002) and prevalence of patellar alta (χ2=9.809, P=0.002) were much higher in the J sign (+) group, and the differences were statistically significant when compared with the J sign (-) group. Multivariate Logistic regressions demonstrated that increased femoral anteversion angle (OR=1.118, P=0.012), enlarged knee rotation angle (OR=1.178, P=0.016) and patella alta (OR=3.229, P=0.040) were independent risk factors of J sign in patients with recurrent patellar dislocation. Conclusion Increased femoral anteversion angle, enlarged knee rotation angle, and patellar alta were strongly associated with J sign. These factors may be independent risk factors of J sign in patients with recurrent patellar dislocation. Key words: Patellar dislocation; Joint instability; Risk factors
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