Three-dimensional Magnetic Resonance Imaging Improved Diagnostic Accuracy Of Posterior Ligamentous Complex Disruption In A Goat Spine Injury Model

Background and Objective:The posterior ligamentous complex(PLC),which is composed of supraspinous ligament(SSL),interspinous ligament(ISL),ligamentum flavum(LF),and the facet joint capsules(FC),protects the spine from excessive translation,rotation,flexion,and distraction.PLC injuries are major causes of spinal instability.According to the recently-established Thoracolumbar Injury Classification and Severity Score(TLICS),PLC integrity is an important consideration for surgical candidacy and may influence the surgical approach.Therefore,it is necessary to accurately evaluate PLC injuries before surgery in clinical settings.Methods for clinically assessing the PLC include physical examination,ultrasonography(US),plain radiography,computed tomography(CT),and magnetic resonance imaging(MRI).Palpation is the most unreliable and inaccurate method.US is operator-dependent.Plain radiography and CT only provide indirect evidence of ligamentous injuries,though they can allow visualization of osseous anatomy.MRI can directly detect soft-tissue injuries,and is the preferred means of diagnosing ligamentous injuries.However,some studies reported that MRI was highly sensitive,but had a poor positive predictive value especially when severe hemorrhage exists around PLC,suggesting an unacceptable false positive rate.Normally,ligaments show low signal intensity on all MRI sequences and loss of ligamentous continuity,or fluid that crosses the location of the ligament on T2-weighted sequences,are specific signs of ligamentous tears.Remarkably,this was the exact criteria used for diagnosing SSL and LF disruption in most published articles.In these studies,ISL injuries were diagnosed by observation of increased signal(hyperintensity),and FC injuries were indicated by either articular liquid or diastasis of the facet joint.However,liquid in the facet joint is not uncommon in non-traumatic patients clinically.And hyperintensity on fluid-sensitive sequences suggests edema,hemorrhage,or inflammation.These findings are associated with ligamentous disruption or bone fractures but do not necessarily indicate the presence of a ligamentous tear.Using this sign as a standard for diagnosing ligamentous disruption inevitably lowers diagnostic specificity.Some authors have even questioned the role of MRI for assessing PLC integrity.These issues highlight the need for further development of consensus-based criteria to define MRI-features of PLC(ISL,FC)disruption or integrity.Three-dimensional MRI allows thinner slice imaging,with no interslice gaps,and enables multiplanar reconstructed images to be viewed in any plane.Therefore,the purpose of this study was to investigate whether three-dimensional MRI could improve diagnostic accuracy for suspected PLC(ISL,FC)disruption.Materials and Methods: This study was approved by the Animal Care Committee of our institution.We used 20 freshly-harvested goat spine samples with 60 segments,with intact surrounding soft tissue.The animals were 1—1.5-years-old,8 males and 12 females,and sexually mature,but not in full weight.Initially,all segments underwent sagittal followed by coronal T2-weighted short inversion time inversion recovery(STIR)scans.Following these scans,3D proton density-weighted spectrally selective inversion recovery(3D-PDW-SPIR)scanning was performed in the coronal plane,and later images were reconstructed in the sagittal plane.All the images were acquired using 1.5T MR.Then,we created a paraspinal contusion model by injecting 10 ml saline percutaneously to each side of the ISL but not around the FC,because FC was not clearly depicted on either 2D STIR or 3D-PDW-SPIR images.Afterward,some ISLs were cut percutaneously under fluoroscopic control using a metal crochet hook and the segments were re-scanned,as before.After the final MR scanning,each specimen was subjected to a meticulous anatomic dissection by an operator who was blind to the cutting procedure and MR images,and ISL status was confirmed by direct visualization.Two radiologists with subspecialty in musculoskeletal radiology independently assessed the images in a blinded fashion to determine tear of ISL on sagittal STIR,coronal STIR,sagittal 3D-PDW-SPIR,and coronal 3D-PDW-SPIR images,separately.The imaging interpretations were compared with the findings in the anatomic dissection to determine diagnostic accuracy,sensitivity,and specificity.The reliability of ISL tear interpretation between the two observers was assessed using the Kappa coefficient.The k values were defined as slight(0–0.20),fair(0.21–0.40),moderate(0.41–0.60),substantial(0.61–0.80),and almost perfect(0.81–1.00).The chi-square test was used to compare diagnostic accuracy among images obtained via different MR techniques.A p value < 0.05 was considered significant.Results: Forty out of 60 ISL segments were successfully harvested,as confirmed by the anatomic dissection.Only the soft tissues adjacent to the ISL were cut with intact ISLs in the remaining 20 segments.For reader A,regarding the ISL injury diagnosed with sagittal STIR,coronal STIR,coronal 3D-PDW-SPIR and sagittal 3D-PDW-SPIR,the values of sensitivity,specificity,and diagnostic accuracy were 42.5%,70.0%,and 60.8%;55.0%,90.0%,and 78.3%;100%,96.3%,and 97.5%;100%,75.0%,and 83.3%,respectively.The false positive rate of sagittal STIR,coronal STIR,coronal 3D-PDW-SPIR and sagittal 3D-PDW-SPIR for identifying ISL tear was 30.0%,10.0%,3.8%,and 25.0%,respectively.For reader B,regarding the ISL injury diagnosed with sagittal STIR,coronal STIR,coronal 3D-PDW-SPIR and sagittal 3D-PDW-SPIR,the values of sensitivity,specificity,and diagnostic accuracy were 47.5%,71.3%,and 63.3%;60.0%,92.5%,and 81.7%;100%?97.5%,and 98.3%;100%?77.5%,and 85.3%,respectively.The false positive rate of sagittal STIR,coronal STIR,coronal 3D-PDW-SPIR and sagittal 3D-PDW-SPIR for diagnosing ISL tear was 28.8%,7.5%,2.5%,and 22.5%,respectively.The interobserver reliability for detecting ISL disruption with sagittal STIR,coronal STIR,coronal 3D-PDW-SPIR,and sagittal 3D-PDW-SPIR images was high to almost perfect(k = 0.776–0.949).The sensitivity,specificity,and diagnostic accuracy of coronal 3D-PDW-SPIR for detection of ISL tears were significantly higher than those of sagittal STIR(p=0.000),coronal STIR(p=0.000),and sagittal 3D-PDW-SPIR(p=0.001).Conclusion: This investigation clarified a much higher diagnostic accuracy of coronal 3D-PDW-SPIR for ISL disruption than that of sagittal 3D-PDW-SPIR,sagittal STIR or coronal STIR.In a clinical setting,additional coronal 3D-PDW-SPIR to a routine MR protocol is critical for identifying PLC disruption if there is extensive edema or hemorrhage around the structure.Clinical Relevance/Application: Posterior Ligamentous Complex(PLC)injuries are related to fracture severity and neurological damage in patients with acute thoracic and lumbar burst fractures.Its status affects the patient's management.Magnetic resonance imaging(MRI)is considered the optimal means of diagnosing PLC injuries,however,being blamed for its high false positive rate in cases with extensive edema or hemorrhage around the ligaments.Additional coronal three-dimensional proton density-weighted spectrally-selective inversion recovery(3D-PDW-SPIR)to a routine MR protocol can improve diagnostic accuracy of PLC(ISL)disruption even if severe contusion exists around PLC.