Clinical Efficiency Of MRI For The Diagnosis Of Infrapatellar Fat Pad Injury

BackgroundInfrapatellar fat pad(IFP)injury,also known as Hoffa disease or infrapatellar fat pad inflammation,is a common clinical condition induced anterior knee pain or functional limitation.To date,rare studies have been focused on the roles of IFP injury in the fields of radiology[1].Patients with IFP injury usually present IFP associated edema and/or thickening caused by abrasion,injury and inflammation.Besides,patients with IFP injury usually present compression or impact to the tibial and femoral joints,as well as the patellofemoral joints,which subsequently leads to knee joint pain.In clinical settings,more attention has been paid to the knee joint pain induced by meniscus and ligament injuries.Rare attention has been paid to the diagnosis of IFP injury.According to the previous study,many patients with IFP injury are misdiagnosed with meniscus syndrome[2]To date,rare studies have been focused on the roles of MR in the diagnosis of IFP injury.It is essential to understand the MR imaging features of IFP injury and evaluate the severity of IFP injury.This is of prime importance to the clinical diagnosis and treatment of IFP injury.ObjectiveThis study was designed to retrospectively analyze the features of IFP injury upon clinical diagnosis or follow-up.In addition,we investigated the typical MRI findings and the clinical efficiency,which may provide accurate imaging basis for the clinical treatment.MethodsSubjects and project In this retrospective analysis,we analyzed the MR images of the 111 cases diagnosed with IFP injury upon clinical analysis or follow-up in Jinan Jigang Hospital between April 2018 and April 2019.The MRI images were viewed by two sophisticated physicians(one chief physician and one attending physician).A deep communication was held between them in the presence of any disputes.Firstly,we determined the edema(or bleeding)signals of the IFP among the 111 patients.Meanwhile,mucous infrapatellar bursa hydrops was observed,together with the formation of extra-anatomical fissure and marginal fissure.Moreover,fibrosis or calcifications and the articular dropsy(e.g.hematocele)was evaluated.Secondly,the injury score was conducted based on the edema signals and morphological changes of the IFP injury,as well as the previous literatures[1,3]The IFP injury was classified into three grades(mild,moderate and severe).Based on the IFP injury severity and imaging grade,corresponding treatment was given to the regions near the fat pad.The patients were followed up for 4-8 weeks after termination of treatment.Visual analogue scales(VAS)were used to evaluate the treatment effect before and after treatment.Examination devices and parametersMR scan was performed using GE SIGNA HDe(1.5 T).Lap surface coils were utilized.The patients were in a supine position,with the legs straight.The toe showed an extorsion of 10°～15°.Complete fixation was given to the knee joints.Conventional scan was performed in the sagittal view and coronary view,respectively.If necessary,the transverse view was added.The scanning sequences were as follows:fast spin echo T1 weighted sequence(TR 550～650 ms,TE 16.5 ms);fat suppression fast spin echo T2 weighted sequence(TR 4400 ms,TE 76.5 ms);fat suppression fast spin echo proton density weighted sequence(TR 2900 ms,TE 22.5 ms);the slice thickness was 3.5 mm;the slice distance was 0.3 mm;the FOV was 20×20cm and the matrix was 288×224.ResultsAmong the 111 cases,126 knee joints were involved including left knee(57),right knee(39)and both knees(15).Among these 126 knee joints with IFP injury,117 showed edema(or bleeding)involving the posterior part(47,37.3%),upper part(29,23.0%),upper and posterior parts(15,11.9%),anteroinferior part(7,5.6%),diffused edema(19,15.1%),mucous bursa hydrops(75,59.5%),as well as anatomical fissure(50,39.7%).Marginal fissure was noticed in 29 fat pad(23.0%).Fibrosis or calcifications was noticed in 8 fat pad(6.3%).A total of 61(48.4%)showed knee joint dropsy and hematocele.Among the 126 knee joints with IFP injury,there were 54 with mild conditions featured by slight pain in the posterior part of the patellar tendon or external/internal hsiuen.In addition,43(34.1%)showed moderate injury featured by slightly severe pain together with knee joint edema.Furthermore,29(23.0%)showed severe injuries featured by severe pain in a long-term,and even rest pain.These patients received corresponding treatment to the fat pad region according to the imaging score of the IFP injury.The patients were followed up about 4-8 weeks after termination of therapy.VAS score was utilized to evaluate the index differences before and after treatment.Student’s t-test indicated that there was significant differences in the VAS score among the three groups after treatment compared with the baseline levels(P<0.001).Conclusion1 IFP injury patients showed typical MRI findings.Significant MRI signs included fat pad edema(or bleeding)signals,infrapatellar mucous bursa hydrops,anatomical fissure,marginal fissure near the fat pad,fibrosis or calcifications and articular hydrops.In clinical settings,the accurate diagnosis should be given to the IFP injury based on these findings.2 MRI could accurately evaluate the severity of IFP injury,which provides beneficial information for the imaging findings to the clinical treatment.