MRI Quantitative Study Of Anatomical Risk Factors For Patellar Instability

Objective:1.To quantitatively analyze the anatomical differences of bone tissues and soft tissues of the knee joint between patients with patellar instability and healthy people by MRI,and to discuss the MRI imaging characteristics of patellar instability and anatomical risk factors.2.To explore the diagnostic value of each MRI measurement indicator corresponding to anatomical risk factors for patellar instability,and the application value of combined measurement index in the diagnosis of patellar instability,so as to provide imaging basis for the correct diagnosis and reasonable treatment of patellar instability.Materials and Methods:1.The MRI data of the affected side of the knee joint of 69 patients with patellar instability who were diagnosed and treated in Luoyang Orthopedic Hospital of Henan Province from October 2018 to October 2019 was retrospectively analyzed as patella instability group,the patients with peri-knee fractures,multiple ligament injuries,large amounts of joint effusion,rheumatoid arthritis and other knee diseases,as well as a history of knee surgery before the MRI examination were excluded.A total of 44healthy volunteers with no history of knee injuries,surgical history,rheumatoid arthritis or other knee diseases and no positive signs of patellar instability were collected as the control group and underwent knee MRI under the same conditions.2.The sulcus angle(SA),patellar tilt angle(PTA),tibial tuberosity-trochlear groove(TT-TG)distance,Insall-Salvati ratio(ISR),vastus medialis oblique(VMO)cross-sectional area and VMO muscle fiber angle on the MRI images of the two groups were independently measured by two imaging diagnostic physicians.Intraclass correlation coefficient(ICC)was used to evaluate the measurement consistency between the two physicians,and the mean value was used as the final statistical value.3.The independent sample t test or Mann-Whitney U test were used to compare the MRI measurement indicators between the two groups to explore the differences in bone structure and soft tissue structure of patellofemoral joint between patients with patellar instability and normal people.4.The binary Logistic regression was used to explore the anatomical risk factors of patellar instability,the receiver-operating characteristic curve(ROC)are used to observe the area under curve(AUC)of corresponding MRI measurement indicators in the diagnosis of patellar instability,and take the maximum Youden index as diagnostic threshold,calculate the corresponding sensitivity,specificity and accuracy.5.Establish a statistical prediction model,draw a ROC curve for the combined diagnosis of related MRI indicators,calculate the diagnostic value,sensitivity,specificity and accuracy of the model,and discuss the application value of the model in the diagnosis of patellar instability.Results:1.The ICC values of each MRI index(SA,PTA,TT-TG distance,ISR,VMO cross-sectional area and VMO muscle fiber angle)measured by the two physicians were:0.941,0.910,0.788,0.820,0.961,0.861(all P values<0.05),showing a good measurement consistency.2.The SA,PTA,TT-TG distance and ISR of the patient group and the normal group were(149.02±6.16)°,(23.76±5.00)°,(17.17±2.43)mm,(1.29±0.11)and(139.71±5.66)°,(13.46±3.60)°,(11.72±2.45)mm,(1.13±0.09),respectively,the differences were statistically significant(t=-8.087,t’=-12.725,t=-11.580,t’=-8.586,all P values<0.05).VMO cross-sectional area and VMO muscle fiber angle of the patient group and the normal group were(598.17±231.68)mm~2,(26.11±7.98)°and(664.91±311.69)mm~2,(23.67±5.75)°,respectively,there was no significant difference between the two groups(t’=1.221,t’=-1.889,all P values>0.05).3.Logistic regression analysis showed that SA,PTA and TT-TG distance were statistically related with patellar instability(all P values<0.05),OR value were 1.806,1.551,3.731.ISR was not statistically related with patellar instability(P>0.05).4.The AUC,diagnostic threshold,sensitivity,specificity and accuracy of SA were 0.869,>144.26°,85.5%,75.0%and 79.6%respectively;the AUC,diagnostic threshold,sensitivity,specificity and accuracy of PTA were 0.945,>17.22°,91.3%,88.6%and 89.4%,respectively;and the AUC,diagnostic threshold,sensitivity,specificity and accuracy of TT-TG distance were 0.938,>15.21mm,81.2%,95.5%and86.7%,respectively.5.Thestatisticalpredictionmodelwasestablishedas Y=1/[1+EXP(0.591·SA+0.439·PTA+1.317·TT-TG distance-110.967)],the ROC curve was drawn based on the prediction probability of patellar instability judged by the model,and the area under the curve was 0.995,the diagnostic threshold was 0.65,and the sensitivity,specificity and accuracy were 97.1%,97.7%and 96.5%,respectively.Conclusions:1.Compared with normal patients,patients with patellar instability mainly showed increased SA,increased PTA,increased TT-TG distance and increased ISR on MRI images.2.The increase of SA,PTA and TT-TG distance are all important pathogenic factors of patellar instability,among which the increase of TT-TG distance is the most important pathogenic factor.3.MRI measurements of SA,PTA and TT-TG distances are of high diagnostic value for patellar instability.4.The combined diagnosis of SA,PTA and TT-TG distance can improve the accuracy of the diagnosis in patellar instability,which is worthy of clinical promotion.