The Special Application Of MR Imaging On Medial Plica Syndrome And Patellar Maltracking: A Preliminary Clinical And Basic Study

Patellofemoral pain syndrome is a common disease in the clinic with a high incidence of 25 percent in population, which usually affect the young with more activities or the old. It's hard to treat. It is often confused with patellar chondromalacia, patellofemoral syndrome, anterior knee pain, patellar subluxaion, patellar maltracking and patellofemoral pain. Because the therapeutic effect is not often satisfied, more and more studies are focused on it. The biomechanism of patellofemoral joint is very complex, multiple factors are related to its etiology and one kind of procedure may not solve the problem at all, which brings much more difficult for the treatment.For the high resolution and multiple direction scaning of Magnetic Resonance imaging, it has been thought of"golden standard"in the imaging of the joint diseases. With the popular use of it the diagnostic accuracy of diseases improved and more diseases such as medial plica syndrome and patellar maltracking are to know clearly. For medial plica syndrome the diagnostic accuracy before operation is low, because of the symptoms, physical signs and routine MR imaging are not typical. While for patellar maltracking, a common hypothesis was that the elevated cartilage stress improved the stress of subchondral bone which induced PFPS. For the technique reason determination of stress of cartilage is still a challenge and the hypothesis is lack of test now. The distribution of stress in vivo patellofemoral joint is not clear now.In our study we used MR imaging to try to solve above problems. It included:①Optimal concentration and MR sequence were discussed for the low field MR, when using Gd-DTPA solution as contrast media,②The diagnostic accuracy of MR arthrography were discussed by direct knee MRA for a group of PFP without definite reason,③A 3D entity model was constructed by MR imaging,④A three dimensional finite element model was constructed by MR imaging,⑤Stress distribution were calculated for normal patellar alignment, patellar laterally tilted and patellar laterally shifted to determine the realm value of stress concentration for patellar maltracking.The results were as followed:①Signal intensity enhancement of Gd-DTPA centralized on low concentration. For SET1, GET1 and GET2 signal intensity were above 1000 with concentration between 0.1 mmol/L and 5 mmol/L, while 0.1 mmol/L to 1 mmol/L for SET2. Signal intensity was higher of T1 than T2. Noise disturbance was clear for GE sequence.②9 patients(10 knees) were found with medial plica in routine MR vs. 80 patients (86 knees) were found with medial plica in the PFPS group (93 patients, 99 knees) without definite reason. Routine MR imaging showed 24.1% sensitivity, 100% specificity, 31.3% accuracy,100% PPV and 12% NPV in diagnosis of mediopatellar plica syndrome. The technique of MRA had high accuracy of 100% with 33.3% sensitivity, 93.8% specificity, 93.5% PPV and 100% NPV.③An entity model of patellofemoral joint was constructed using 51 2D-FS-FLASH MR imagings.④A 3D FEM of patellofemoral joint was constructed.⑤30°flexion and normal patellar location with 200N quadriceps force, inferior one third cartilage of patellar contacted with groove. The minimal contact pressure was 0.176MPa and the maximal was 2.112MPa. The average stress was 1.056MPa, homogeneously distributed on medial facet, middle facet and lateral facet.⑥Obvious stress concentration occurred when laterotorsion was more than 6°or lateral shift was more than 10mm.Main conclusions included:①2 mmol/L Gd-DTPA solution can show intraarticular structure clearly in SET1 sequence.②Medial plica syndrome is an important reason for PFPS.③Direct knee MRA can show medial plica clearly with high value in the diagnosis of PFPS caused by medial plica.④A 3D FEM of patellofemoral joint with corresponding material biomechanics propertyies can be constructed by MR imagings and it can compute patellofemoral stress exactly.⑤Patellar maltracking can change stress distribution markedly. Obvious stress concentration happens when laterotorsion is more than 6°or lateral shift is more than 10mm. The patellofemoral joint FEM based on MRI can be used in stress analysis and it can offer a new method to diagnose PFPS.