Knee J-Sign in Recurrent Patella Dislocation: Incidence, Classification and Radiographic Characteristics / 中国运动医学杂志

Purpose To determine the incidence,degree and radiographic characteristics of knee Jsign in recurrent patella dislocation patients.Method It was a retrospective review of a consecutive series of 59 recurrent patella dislocation patients.The knee J-sign was classified into negative (-),positive one degree(mild,l+)and positive two degree(gross,2+)based on the severity of patellar lateral translation at the extreme extension of knees with quadriceps contracted actively.The computed tomography(CT)examination at 0° extension of the knee was performed to quantify the degree of patellar lateral translation and tilt,with three CT parameters measured and calculated in axial slices:patella bisect offset index (BOI),patella trochlear-groove (PTG) distance and patella lateral tilt (PLT) angle.Results In all the 59 patients,72.9％(43/59)showed positive J-sign,27.1％(16/59)of positive one degree(1+) and 45.8％(27/59)of positive two degree(2+).All the three CT parameters increased with the severity of Jsign(P＜0.05).Conclusion Among 59 recurrent patella dislocation patients,we have found 72.9％ of positive knee J-sign.The severity of J-sign has a positive correlation with the degree of patellar lateral translation and tilt.

Quantification of Patellar Maltracking Combined with J-Sign Using Computed Tomography / 中国运动医学杂志

Objective To quantify the patellar mal-tracking combined with J-sign using the computed tomography (CT).Method Fifty-three adult patients diagnosed as recurrent patellar dislocation (RPD) were chosen.According to their patellar tracking during knee active flexion and extension,they were divided into group A(with positive J-sign) and group B(with negative J-sign).The CT examinations were performed in all patients at 0°extension of the knee and the patella bisect offset index (BOI),patella troehlear-groove distance (PTG) and patella lateral tilt (PLT) were measured in the axial position and compared.The receiver operating characteristic analysis (ROC) curve was used to analyse the accuracy and stability of the three J-sign parameters.Results In all the 53 patients,thirty-seven(69.8％) knees were of positive J-sign,while the rest 16 were of negative J-sign.The mean values of CT parameters BOI,PTG and PLT in group A were significantly larger than those of group B.Moreover,the area under the curve for BOI,PTG and PLT were 0.906,0.883 and 0.833 respectively.The sensitivity and specificity of BOI were 83.3％ and 87.5％,while the predicting cut-off value was 97.5％.Conclusion In all the 53 recurrent patella instability patients,the morbidity of patella proximal mal-trackingis 69.8％.The CT parameter BOI can be used to quantify the J-Sign into positive and negative groups.