Risk factors and new grading system of J sign in recurrent patellar dislocation patients / 中华骨科杂志

ABSTRACT

Objective To investigate the risk factors of J sign in patients with recurrent patellar dislocation, and to estab?lish a new grading system of J sign. Methods From January 2017 to August 2018, a consecutive case series of 111 recurrent pa?tellar 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 tuber?osity?trochlear groove (TT?TG) distance and rotational parameters of the lower extremity (including femoral anteversion angle, ex?ternal tibial torsion angle and knee rotation angle) were measured to compare the differences of these parameters between the inter?vention 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 patel?lar 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 high?er 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 pa?tellar 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.