Imaging And Anatomical Studies On Posterior Ligamentous Complex Injury In Thoracolumbar Segments

ObjectivesIn the present study,we aimed to evaluate the indirect predictive value of X-ray and CT for the injury of posterior ligamentous complex（PLC）by analyzing the clinical imaging data of patients with thoracolumbar burst fracture（TLBF）.Moreover,we analyzed the value of X-ray and CT imaging parameters from an anatomical point of view based on the anatomical structures of the human spine thoracolumbar vertebral body and PLC.Collectively,our findings provided valuable insights into the clinical prediction of the PLC injury.Methods1.A total of 186 cases of TLBF were divided into the PLC-injured group（A group）and uninjured group（B group）based on MRI and surgical exploration.There were 105cases and 81 cases in the A group and B group,respectively.In the A group,there were 23cases of T₁₁fracture,31 cases of T₁₂fracture,34 cases of L₁fracture,and 17 cases of L₂fracture.In the B group,there were 17 cases of T₁₁fracture,23 cases of T₁₂fracture,21cases of L₁fracture,and 20 cases of L₂fracture.Local kyphosis（LK）,the anterior/posterior vertebral height ratio（A/P ratio）,vertebral body translation（VBT）,and increase of interspinous distance（IISD）were measured and calculated.All these X-ray and CT parameters were compared in different groups and different segments.2.A total of 12 formalin-preserved adult specimens were taken,and the T₉～L₃segments were dissected.The following aspects were assessed and measured:（1）the overall morphology of the thoracolumbar spine(T₁₁～L₂);（2）the morphology of the supraspinous ligament,interspinous ligament,facet joint capsule,and ligamentum flavum;（3）the length of the interspinous ligament between T₉～T₁₀(T₁₀segment),T₁₀～T₁₁(T₁₁segment),T₁₁～T₁₂(T₁₂segment),T₁₂～L₁（L₁segment）,L₁～L₂（L₂segment）,and L₂～L₃（L₃segment）,and the average length of the adjacent upper and lower interspinous ligaments of T₁₁～L₂segments was used as the standardized interspinous ligament length of the T₁₁～L₂segments;（4）the length of the ligamentum flavum between T₁₀～T₁₁(T₁₁segment),T₁₁～T₁₂(T₁₂segment),T₁₂～L₁（L₁segment）,and L₁～L₂（L₂segment）;（5）the heights of the anterior and posterior vertebral body of T₁₁～L₂and the ratio of the above-mentioned two.Besides,the differences of different segments were compared.Results1.（1）The LK and IISD of the A group were significantly higher compared with the B group（t=9.46,P=0.01;t=9.98,P=0.01）.The LK and IISD were independent risk factors for predicting the injury of PLC,and the OR（95%CI）values were 1.43（1.08～1.89）and 9.36（1.75～49.92）,respectively.The P values were all less than0.05.The LK of the A group was larger than 20°,among which the LK was>25°in the L₁segment.The IISD of the A group was larger than 4.00 mm.The LK of the B group was less than 20°.The IISD of the B group was less than 4.00 mm.（2）In the A group,there was a significant difference in LK in each segment,F=4.96,P=0.01<0.05.In the comparison of LK between segments of the A group,the average of the L₁segment was6.17°higher compared with the group T₁₁segment（95%CI:1.79-10.54,P=0.003）.There was no significant difference in IISD in each segment（P>0.05）.In the comparison between segments of the B group,there was no significant difference between LK and IISD in each segment.P values were all larger than 0.05.2.（1）Morphological assessment found that there was a physiological curvature from T₁₁to L₂.Among them,the thoracic spine was kyphotic,the lumbar spine was lordotic,and a single vertebral body was square in the sagittal position.The anterior longitudinal ligament was in front of the vertebral body,and the posterior longitudinal ligament was in the back.The posterior edge of the vertebral body and PLC were not directly connected.The vertebral body was filled with thicker intervertebral discs.The size of the vertebral body was gradually increased from the thoracic vertebra to the lumbar vertebrae.There was only a small difference in the height of the anterior and posterior edge of the vertebral body in the same segment.The supraspinous ligament was located behind the spine and run along the spinous process.It was closely connected to the fascia and tendons.The interspinous ligament was short and thin,which was located between the two adjacent spinous processes,the anterior was connected to the ligamentum flavum,and the posterior was connected to the supraspinal ligament.The ligamentum flavum was located behind the epidural space and run between the two adjacent laminas.It was divided into two rhomboid ligaments and merged at an acute angle at the midline into a longitudinal opening towards the ventral side.It was very thick and flexible.The vertebral facet joint capsules surrounded the facet joints,and the joint capsule fibers were clearly visible and closely connected with the surrounding tendons.（2）The length of the interspinous ligament at T₁₀～L₃was 3.17±0.77 mm,4.37±0.83 mm,6.79±1.36 mm,8.51±1.84 mm,9.09±1.78 mm,and 9.84±2.41 mm,respectively.The standardized interspinous ligament length of T₁₁～L₂was 4.98±1.03 mm,6.44±1.23 mm,7.94±1.56 mm,and 9.17±1.23 mm,respectively.The maximum difference between the anatomical measurements of the same segments was 3.30 mm,the minimum value was 0.00 mm,and the average was 0.77±0.71mm.The length of the ligamentum flavum at the T₁₁～L₂was 7.43±1.18 mm,9.52±1.96mm,12.15±1.50 mm,and 13.78±3.46 mm,respectively.The height of the anterior vertebral body of T₁₁～L₂was 21.44±1.07 mm,24.54±1.27 mm,26.37±0.87 mm,and27.76±1.70 mm,respectively.The height of the posterior vertebral body of T₁₁～L₂was23.35±1.83 mm,26.53±1.12 mm,28.47±1.34 mm,and 29.28±1.31 mm,respectively.The ratio of the two of T₁₁～L₂was 0.92±0.06 mm,0.93±0.05 mm,0.92±0.02 mm,and0.95±0.06 mm,respectively.There was a significant difference in the length of the interspinous ligament between different segments（Welch F=34.382,P<0.001）.There was a significant difference in the length of the ligamentum flavum between different segments（Welch F=29.267,P<0.001）.There was a significant difference in the height of the anterior and posterior vertebral bodies between different segments（P<0.001;P<0.001）.There was no significant difference between the anatomical measurements of the length of the interspinous ligament in T₁₁to L₂segments and the standardized interspinous ligament length in the same segments（P>0.05）.Conclusions1.In the diagnosis of the thoracolumbar PLC injury using X-ray and CT imaging parameters,when IISD>4.00 mm,and LK>20°at T11,T12 segments or LK>25°at L1,L2 segments,the injury of PLC should be highly suspected.2.When X-ray and CT were adopted to diagnose PLC injury,we should not overly rely on a single imaging parameter,and the diagnosis should be made based on the combination of multiple parameters.If possible,MRI or ultrasound should be added to carry out an adequate assessment of the injury.