The Imaging Features Of The Meniscal Roots On 3D MRI And The Diagnostic Accuracy Of 3D MRI For The Detection Of Meniscal Root Tears

Part OneThe Imaging Features of the Meniscal Roots on 3D MRI in Young Asymptomatic VolunteersBackground:The meniscal roots of the knee play an important role in maintaining the normal positions and biomechanical functions of the menisci.Several biomechanical studies have reported that the effects of a meniscal root tear(MRT)were functionally equivalent to those of a total meniscectomy,and the proper placement of the meniscal root attachment is reportedly critical to restoring meniscal function.Therefore,tears of the meniscal roots have attracted more attention for radiologists and orthopedists.MRI has been widely used as a primary diagnostic tool for MRTs during preoperative planning,and is regarded as both reliable and accurate for detection.Understanding the normal imaging features of the meniscal roots was a prerequisite to diagnose MRTs.Only few studies had revealed the anatomy of the meniscal roots with MRI,and most studies used the routine 2D sequence with a section thickness>3 mm.Thick sections can lead to an average volume because the meniscal roots are small,affecting the accuracy of the observations.3D MRI offers several potential improvements on 2D MRI,including improved spatial resolution,and can facilitate interactive 3D visualization and multiplanar reconstructions in any imaging plane,which is advantageous when evaluating small and complex structures.The single-slab 3D sampling perfection with application-optimized contrasts using different flip angle evolutions(SPACE)was a relatively new sequence.In contrast to rapid 3D gradient echo techniques,3D SPACE sequence can produce T2-weighted imaging(T2WI)or intermediate-weighted imaging(IWI)contrast resolution,which is best suited for evaluating internal derangements and can clearly display the anatomical structures of the knee.The study objects in previous studies were patients,and the imaging features of the meniscal roots in young asymptomatic volunteers have not been studied,which may reduce selection bias from degenerative process or anatomical anomaly when relatively older people were included.Objective:This study aimed to describe clearly the normal imaging features of the meniscal roots on MRI with 3D IWI SPACE sequence at 3T.Methods:A total of 60 knees from 31 volunteers(2 volunteers underwent scanning of one side of the knee,13 males and 18 females,mean age was 22 years,age range was 20-23 years)were involved in the study.Only volunteers with no symptoms and no history of injury,infection,synovitis,or arthritis of the knee were included in the study.All examinations were performed with a 3.0-T MR scanner(Magnetom Skyra with TIM system,Siemens Healthcare,Erlangen,Germany)and a dedicated knee coil with an eight-channel receiver.The volunteers were examined in the supine position,with their knees in the knee coil in extension position.An isotropic fat-suppressed(FS)3D IWI SPACE sequence(TR/TE = 1200ms/60ms,section thickness/interslice gap = 0.6mm/0mm,NEX = 1,field of view,160 mm x 160 mm;matrix,256 × 256)was obtained from all volunteers.All MRI studies were reviewed by two radiologists(with 10 and 9 years of subspecialty expertise in musculoskeletal MRI)in consensus.Interobserver reliability was assessed by calculating ? coefficients.The ? value can be interpreted as poor(? = 0),slight(?=0.0-0.2),fair(? = 0.21-0.40),moderate(? × 0.41-0.60),substantial(? = 0.61-0.80),and almost perfect(? = 0.81-1.00).Image analysis was performed on a picture archiving and communication system workstation(GE RA 1000).A dynamic 3D interactive visualization model was used to evaluate the four meniscal roots.The insertion patterns,MRI signals of the meniscal roots,and the connection between the meniscal roots and between the meniscal roots and adjacent structures were reviewed in the combined axial,coronal,and sagittal planes.Results:Inter-observer agreement was excellent for all evaluated meniscal roots(k ranged from 0.84 to 0.93).The insertion patterns of the anterior root of the medial meniscus(ARMM),the anterior root of the lateral meniscus(ARLM),and the posterior root of the medial meniscus(PRMM)were relatively fixed,whereas the posterior root of the lateral meniscus(PRLM)had relatively more complex insertion patterns.The ARMM(96.7%),the ARLM(100%),and the PRMM(100%)usually had one insertion site,whereas 53.3%of the PRLM had on inserton site,and 46.7%of the PRLM can be divided into major and minor insertion sites.The meniscal root can consist of a single,two,or multiple(?3)fiber bundles.The ARLM(100%)and the PRMM(68.3%)usually consisted of multiple fiber bundles,whereas the ARMM(95%)and the major(100%)and minor(89.3%)PRLM often consisted of a single fiber bundle.The normal meniscal root can appear as hyperintense,hypointense,or mixed signals.The ARMM(95%)and the PRLM(76.7%of the major root,and 63.2%of the minor root)usually appeared as hypointense,whereas the ARLM(100%)and the PRMM(91.7%)typically exhibited mixed signals.Some connections between the posterior medial and lateral meniscal roots,and between the meniscal roots and anterior and posterior cruciate ligaments were found.Conclusion:The meniscal roots can be complex and diverse,and certain characteristics of them were observed on 3D IWI SPACE sequence.The ARMM,the ARLM,and the PRMM usually had one insertion site,whereas the PRLM usually had two insertion sites.The ARLM and the PRMM usually consisted of multiple fiber bundles,whereas the ARMM and the PRLM often consisted of a single fiber bundle.The ARMM and the PRLM usually appeared as hypointense,whereas the ARLM and the PRMM typically exhibited mixed signals.Some connections between meniscal roots,and between meniscal roots and cruciate ligaments were found.Part TwoDiagnostic Accuracy of 3D MRI for the Detection of Posterior Meniscal Root TearsBackground:The meniscal roots of the knee play an important role in maintaining the normal positions and biomechanical functions of the menisci.Several biomechanical studies have reported that the effects of a meniscal root tear(MRT)were functionally equivalent to those of a total meniscectomy,and the proper placement of the meniscal root attachment is reportedly critical to restoring meniscal function.The diagnosis of MRTs can be challenging due to the absence of highly sensitive and specific history and physical examination findings.MRI has been widely used as a primary diagnostic tool for MRTs during preoperative planning,and is regarded as both reliable and accurate for detection.In some previous studies using conventional 2D sequences to diagnose posterior meniscal root tears(PMRTs),the sensitivity,specificity,and negative predictive value of MRI to detect PMRTs were relatively high;however,the positive predictive value was low.The low positive predictive value indicates that many PMRTs classified as torn via MRI were later determined to be intact on arthroscopic probing.The reasons for the low-positive predictive value may be related to average volume,and many meniscal roots appear as hyperintense may be another reason.To our knowledge,to date the diagnostic accuracy of 3D MRI for the detection of PMRTs has not been reported.The hypothesis in the current study was that some of the intact posterior meniscal roots appearing to exhibit PMRTs on conventional 2D sequences would be clearly displayed on 3D sequences.There have been some studies investigated the relationship of the PMRTs with meniscus extrusion and femorotibial osteoarthritis.However,few studies have directly compared the accompanying signs and clinical features between medial and lateral PMRTs groups.Objective:The purpose of the current study was to compare the diagnostic accuracy of 3D sequences for the detection of PMRTs.We also evaluated if there were differences in the accompanying signs and clinical features between medial and lateral PMRTs groups.Methods:For the enrollment of study subjects,we reviewed 520 consecutive patients who underwent MRI followed by arthroscopy at our institution from July 2014 through March 2017.Patients who had undergone previous knee joint surgery(n=33),and those with infectious or inflammatory arthritis of the knee(n = 16)were excluded.Twenty-six patients whose MR images(10 for 2D sequences and 16 for 3D sequences)were not of an acceptable diagnostic standard were also excluded from the study.The final subject pool included 445 patients(445 knees),202 male and 243 female,mean age 47 years,range 18-73 years.The time between MRI examination and knee arthroscopy was less than 90 days in all cases.All examinations were performed with a 3.0-T MR scanner(Magnetom Skyra with TIM system,Siemens Healthcare,Erlangen,Germany)and a dedicated knee coil with an eight-channel receiver.Patients were examined in the supine position,with their knees in the knee coil in an extended position.Standard routine 2D sequences and isotropic 3D SPACE sequence were obtained.The parameters of 3D SPACE sequence were the same as the part one.The parameters of conventional 2D sequences were as follows:Sagittal IWI+FS(TR/TE = 2400 ms/61 ms),Sagittal T2WI(TR/TE = 3600 ms/119 ms),Sagittal T1WI(TR/TE = 793 ms/11 ms),Coronal IWI+FS(TR/TE = 2660 ms/63 ms),Axial IWI+FS(TR/TE = 2780 ms/62 ms),the rest parameters were the same,including:section thickness/interslice gap:3 mm/0 mm,field of view:160 mm x 160 mm,matrix:256 x 256.MR image analysis was performed on a picture archiving and communication system workstation(GE RA 1000).All MR images were independently reviewed by two radiologists with 10 and 9 years of subspecialty expertise in musculoskeletal MRI.The 2D images were evaluated combined in all available image planes.The 3D images were evaluated on a dynamic 3D interactive visualization model.The diagnostic criteria used by the readers to diagnose PMRTs were the presence of an abnormal morphologic structure with partial or complete root discontinuity or hyperintensity extending to the surface.Meniscal extrusion was designated present with the criterion that the meniscal body extended greater than 3 mm peripherally from the tibial plateau on the coronal plane,and we also measured the exact extent of the distance.Cruciate ligament tear was designated when discontinuity or focal or diffuse high signal intensity was present in the ligament.Radiographic assessment of knee osteoarthritis was carried out using Kellgren-Lawrence(K-L)grade.The clinical features including age and a history of trauma.Interobserver reliability was assessed by calculating ? coefficients.The ? value can be interpreted as poor(? = 0),slight(? = 0.0-0.2),fair(? = 0.21-0.40),moderate(? = 0.41-0.60),substantial(? = 0.61-0.80),and almost perfect(? = 0.81-1.00).Diagnostic accuracy parameters including sensitivity,specificity,and positive and negative predictive values were calculated with regard to the ability of 3T MRI to detect PMRTs,using the arthroscopy findings as the standard of reference.Differences in sensitivity,specificity,positive and negative predictive values for interpretations between 2D and 3D sequences,and differences in meniscal extrusion,cruciate ligament tear,and history of trauma between medial and lateral PMRTs groups were tested for significance with the Chi-square test.Differences in K-L grade between medial and lateral PMRTs groups were tested for significance with rank-sum test.Differences in age between medial and lateral PMRTs groups were tested for significance with independent-sample t test.A statistically significant difference was deemed to be present if P<0.05.Results:Arthroscopy revealed that PMRTs occurred in 9.5%(44/445)of knees,6.1%(27/445)for medial and 4.1%(18/445)for lateral root tears(one patient had both).The interobserver reliability of the readers for detecting PMRTs,meniscal extrusion,cruciate ligament tear and K-L grade was excellent(0.823 ???1).The sensitivity,specificity,positive and negative predictive values for 2D and 3D sequences to detect posterior medial meniscal root tears(PMMRTs)were 0.926,0.950,0.543,0.995(for 2D sequence);0.963,0.993,0.897,0.998(for 3D sequence);The sensitivity,specificity,positive and negative predictive values for 2D and 3D sequences to detect posterior lateral meniscal root tears(PLMRTs)were 0.833,0.951,0.417,0.993(for 2D sequence);0.944,0.993,0.850,0.998(for 3D sequence).For both posterior medial and lateral meniscal root,there were no significant differences in sensitivity or negative predictive value between 2D and 3D sequences in either of the readers(P>0.05).The specificity and positive predictive value were significantly higher for 3D sequences than for 2D sequences(P<0.05).Among the PMMRTs group(n=27)and PLMRTs group(n=18):22 patients had meniscal extrusion in PMMRTs group and the mean extrusion distance was 4.4mm(range,0.6 to 7.6),while 1 patient had meniscal extrusion in PLMRTs group and the mean extrusion distance was 0,9mm(range,-1.4 to 3.3).Meniscal extrusion was more common in PMMRTs group than in PLMRTs group(P<0.05);4 patients had anterior cruciate ligament tear in PMMRTs group,while 17 patients had anterior cruciate ligament tear in PLMRTs group.Anterior cruciate ligament tear was more common in PLMRTs group than in PMMRTs group(P<0.05);6 patients had a history of trauma in PMMRTs group,while 16 patients had a history of trauma in PLMRTs group.A history of trauma was more common in PLMRTs group than in PMMRTs group(P<0.05);The mean age was 53 years(range 28 to 70)in PMMRTs group,while the mean age was 31 years(range 18 to 64)in PLMRTs group.The mean age of PLMRTs group was significantly younger than PMMRTs group(P<0.05);23 patients had knee osteoarthritis(5 patients showed K-L grade 2,and 16 patients showed K-L grade 3,and 2 patients showed K-L grade 4)in PMMRTs group,while 5 patients had knee osteoarthritis(4 patients showed K-L grade 2,and 1 patients showed K-L grade 3)in PLMRTs group.The K-L grade was significantly larger in PMMRTs group than in PLMRTs group(P<0.05).Conclusion:The sensitivity,specificity,and negative predictive value of 2D and 3D sequences for detecting PMRTs were high;however,the positive predictive value of 2D sequences was low,and that of 3D sequence was significantly higher than that of 2D sequences.When PMRT is suspected based on 2D sequences,additional 3D sequence is necessary.The clinical features and other the accompanying signs were different between medial and lateral PMRTs groups.Meniscal extrusion and knee osteoarthritis was more common in PMMRTs group than in PLMRTs group,while anterior cruciate ligament tear and a history of trauma was more common in PLMRTs group than in PMMRTs group.