Magnetic Resonance Imaging Features Of Posterior Oblique Ligament Injuries

Medial knee ligament injury is the most common knee ligament injury.With the development of anatomy and biology,the restrictive effect of posteromedial corner(PMC)in knee valgus and tibial rotation has been paid more and more attention.Among many PMC structures,the posterior oblique ligament(POL)is an important static and stable structure.In recent years,magnetic resonance(MR)has been widely used in knee ligament injury due to its good tissue resolution.MR can not only observe the ligament injury of knee joint,but also observe the meniscus injury,joint effusion or hematocele,bone injury and other associated injuries.This study investigated the MR anatomy of PMC structure and the MR signs of POL injury in knee joint,in order to accurately diagnose and evaluate the injury of medial knee ligament,and provide a reliable basis for clinical selection of appropriate treatment strategies.Part one:Anatomy of PMC of knee in MRPurpose:To explore the anatomic course and adjacent relationship of the major structures of the PMC of knee joint in MR.Methods:Thirty knee joints of 15 volunteers were scanned by MR.The GE Discovery MR 7503-Tesla MR imaging system was used for MR image acquisition.The 8-channel knee coil(foot first)was used for unilateral imaging.The MR involved the transverse,sagittal,coronal and oblique coronal positions of proton-phase scanning.Results:POL was divided into three branches including central branch,superficial branch and articular capsule branch.The central branch could be distinguished in all positions.The superficial branch was well showed in coronal and oblique coronal positions,and the cross-sectional display rate was 70%.The articular capsule branch fused with the posteromedial joint capsule,and could not be distinguished as an independent structure.The separated part of the articular capsule branch could not be distinguished in all series.Every branch of POL showed strip or linear low signal in all series.The direct arm,anterior arm,meniscal arm and distal tibial expansion of semimembranosus(Sm)tendon could be distinguished.The direct arm and anterior arm were the primary arms,and could be seen in all series.The direct arm was a structure consisting of multiple bundles of low signals,and was a direct extension of the distal Sm tendon.The anterior arm showed slightly high signal which was obviously higher than other ligaments and lower than muscles because of the magic angle artifact.The meniscal arm and distal tibial expansion showed strip or linear low signal connected to the meniscus and proximal tibia.The anterior arm was intimate to POL,but no structure was shown to connect them.OPL was connected with the distal Sm tendon and the direct arm,and it could be showed in axial and sagittal positions as low signal,but couldn't be distinguished in coronal or oblique coronal positions.Other branches of the distal Sm tendon could not be distinguished.Conclusions:(1)The central branch is the thickest and largest branch of the POL,which courses from femoral attachment in the medial condyle downward and slightly backward to the upper edge of meniscus.The superficial branch is located below the central arm and the capsular arm is located posterior to the central arm and merges with the posterior medial capsule mostly.(2)The direct arm,anterior arm,meniscal arm and distal tibial expansion of Sm tendon can be distinguished.OPL is connected with the straight arm and distal Sm tendon.Other arms cannot be distinguished.There are developmental variations in the size of anterior arm.Significance:This study has described the movement and adjacent relationship of POL and Sm distal tendon complex in MR.This can help us to recognize and distinguish these fine structures in MR,and lay a foundation for understanding and mastering the function and damage characteristics of these structures.Part two:MR features of POL injuryPurpose:To explore the MR features of POL in acute and chronic injuries and the associated ligament injury mode,so as to improve the accuracy of evaluating medial ligament injury of knee joint.Methods:Seventy-nine cases with POL injury confirmed by MR were enrolled.The GE Discovery MR 7503-Tesla and Signa HDe 1.5-Tesla MR imaging systems were used for image acquisition.The 8-channel knee coils or orthogonal coils(foot first)was used for unilateral imaging.The MR involved the transverse,sagittal,coronal and T1-weighted sagittal positions of proton-phase scanning.POL injury was divided into three regions including femoral origin,midsubstance and menisci insertion and three grades including grade I,grade II and grade III.The patients were divided into acute trauma group,acute sprain group and chronic injury group.In addition,the injuries of the superficial medial collateral ligament(sMCL),deep medial collateral ligament(dMCL),distal Sm tendon,medial patellofemoral ligament(MPFL),anterior cruciate ligamen(ACL),posterior cruciate ligament(PCL)and medial meniscus were evaluated.SPSS 17.0 software was used to carry out chi-square test in statistical analysis.Results:There were 10 cases of simple injury and 26 cases of complex injury in the acute trauma group,with 12 cases of simple injury and 9 cases of complex injury in the acute sprain group and 11 cases of simple injury and 11 cases of complex injury in the chronic injury group.There was no significance difference among three groups(P>0.05).The number of grade ?,?,and ? injury cases was 9,39 and 31,respectively.The number of grade ?,?,and ? injury cases was significantly different between acute trauma group and chronic injury group(P<0.05).There are 6 cases of simple POL injury,68 cases of accompanied sMCL injury,57 cases of accompanied dMCL injury,32 cases of accompanied ACL injury,10 cases of accompanied PCL injury,59 cases of accompanied meniscus injury and 16 cases of accompanied distal semimembranosus tendon injury,respectively.There were 52 cases of accompanied sMCL,POL and dMCL injuries,39 cases of accompanied sMCL,POL and MPFL injuries and 26 cases of accompanied sMCL,dMCL,POL,MPFL and VMO injuries.The distal tibial expension of the distal Sm tendon was the thickest branch of the distal Sm tendon in 7 cases.Conclusions:(1)There is no significant difference in the POL injury location among acute trauma,acute sprain and chronic injury groups.The degree of POL injury in acute trauma patients is higher than that in chronic injury patients.(2)The single POL injury usually occurs in non-contact injuries.The sMCL and dMCL injuries are the most frequently accompanied in POL injury.The MPFL and VMO locating in the anterior medial of knee can be injured accompanied by the sMCL,dMCL and POL.(3)There is variation in the size of distal tibial expansion of distal Sm tendon.The distal tibial expansion will become the largest branch substituting the direct arm in a certain proportion of population.Significance:POL is an important stable structure in the knee joint PMC.The surgical treatment is needed to restore the stability of knee joint when POL injury is accompanied by joint instability.It is of great significance to make a comprehensive and accurate assessment of the medial knee ligament injury for the selection of clinical treatment strategies.