MR Measurement And Evaluation Of Acute Patellar Dislocation

BackgroundAcute patellar dislocation(APD)used to appear mostly in sport-related injury in young people,accounting for 2%-3%[1]of all knee diseases,with the incidence of 7/100000[2].The APD is divided into 3 stages:dislocation period,reduction and post-reduction period.Patiens of APD were often diagnosis in the post-reduction period in admission cause the dislocated patellar could spontaneously instantly reset.Moreover,some patients do not provide medical history,physical examination by clinicians only sometimes missed.There had been less research about measurement and evaluation of APD on MR images,which may facilitate to understand the risk factors,recognize the existence of APD in the diagnosis and treatment of the accurate formulation.purposeto evaluate compare the relative measurement of APD on MR images in both of patients and healthy volunteers,to analyze the high-risk factors of APD,to improve the diagnostic rate of APD,and to guide the formulation of treatment programs.Materials and Methods It is a retrospective analysis on MRI data consisted of 48 APD patients knee joint and 31 healthy volunteers knee joint,by two senior radiologists,agree after consultations.1.Both respectively measured the height of patella(IS index),the proportion of lateral femoral trochlear groove angle and trochlear depth,pulley and tibia tubercle trochlear groove(TT-TG)distance,and the femoral trochlear DEJOUR type(type A:fairly shallow trochlea;type B:flat or convex trochlea;type C:asymmetry of trochlear facets with a hypoplastic medial condyle;type D andtype C are similar,asymmetry of trochlear facets plus vertical join or cliff pattern);48 cases of APD patients with knee or medial patellofemoral ligament(MPFL)injury and the extent of injury,and whether there is medial posterior and lateral femoral condyle cartilage and bone contusion,position,vastus medialis and distal injury degree,joint effusion(blood)were analyzed.Chi square test and independent sample T test were used for statistical analysis.2 MR Imaging was performed with a GE 1.5 T MR unit,application of 8 channel package surface coil,supine position and the knee natural unbend,approximately in 10°?15° of flexion,both sides of the knee joint is fixed on with the sandbags.Sagittal SE sequence T1WI were acquired using,TR 320ms,TE 10ms,FOV of 200mm X 200mm,Matrix of 352 X 256;axial fat suppressed proton density weighted imaging(PDWI)were acquired using,TR were 3060ms,TE 50ms,FOV of 180mm X 180mm,Matrix of 256 X 192;sagittal fat suppressed proton density weighted imaging(PDWI)were acquired using,TR 2120ms,TE 65ms,FOV of 200mm X 200mm,Matrix of 352 × 256;coronal fat suppressed proton density weighted imaging(PDWI),TR 2240ms,TE 65ms,FOV of 180mm × 180mm,Matrix of 288× 256;Slice thickness of 3?4mm,the layer spacing is 0.3?0.4mm.Results1:For 48 cases of APD,the knee joint patellar height,femoral trochlear angle,trochlear groove depth,trochlear internal and external side ratio and TT-TG distance were(1.17 ±0.17)cm,150 0±9.7 °,(0.43 ± 0.15)cm,0.50 ± 0.16,(16.0 ±2.30)mm while those of 31 cases of healthy voluteers,those were(1.08 ±0.15)cm,140.0 ±18.1 °,0.54 ± 0.15cm,0.67 ± 0.10,(14.4± 1.32)mm respectively;the APD group and the control group were in the height of patella and trochlear angle,trochlear groove depth,internal and external side of symmetry,TT-TG distance difference was significant,(P<0.05).Furthermore,the patellar height,trochlear sulcus angle and TTTG distance of the study group were significantly higher than those of the control group,while the depth of the groove,the symmetry of the lateral and the lateral surface were significantly lower than those of the control group.The A type of Trochlear DEJOUR type accounted for 33.3%in the APD group,the type B 18.7%,type C 8.3%,type D 4.2%,normal trochlear accounting for 37.5%;For the normal control group the type A 16.1%,type B 3.2%,type C and type D was 0,normal trochlear was 80.6%;The A,B,C and D type of trochlea DEJOUR type in the APD group compare with the normal control group had a statistically significant difference.the APD group was significantly higher than the control group.and the P values were less than 0.05.For 48 cases of APD,45 cases of MPFL injury included the fracture in 38 cases,7 cases of complete rupture of patella in 22 cases at(49%),located in the proximal femur in 7 cases(15%),located in the body in 3 cases(7%),located in the combined injury of patella femoral end and 13 cases(29%);47 cases of patella in posterior,lateral femoral condyle bone contusion;28 cases of cartilage injury,patella cartilage accounted for 16 cases(57%),4 cases of femoral cartilage(14%),patella and femoral cartilage injury and 8 cases(29%);20 cases of distal vastus medialis injury;48 cases of knee joint effusion and hematocele.Conclusion:1.patella alta,trochlear dysplasia,and TT-TG distances were more likely to occur in APD,suggesting that these factors were the relative high risk factors for APD.2.Moreover,APD has certain characteristics,based on the MPFL and distal medial vastus muscle injury,cartilage injury,medial posterior and lateral condyle of femur bone contusion,knee joint effusion or hematocele signs make accurate diagnosis of APD.