The greatest limitation of the commonly used classification systems for thoracolumbar fractures, including AO and Denis staging, is that they treat injuries to bony structures of the spine and injuries to soft tissue structures such as ligaments and nerves as two separate systems. In addition, the commonly used classification systems often assess only the type of injury without providing appropriate treatment recommendations. With the development of the assessment system for thoracolumbar injuries, in 2005 Vaccaro [3] proposed the Thoracolumbar Spinal Cord Injury Classification and Severity Score (TLICS).The TLICS system considers the assessment of thoracolumbar injuries based on three main points. Fracture morphology, PLC status, and neurological status, but also the integrity of the PLC as an important basis for stability evaluation and treatment modality selection. I. PLC and spinal stability Currently, the choice of treatment for thoracolumbar spine injuries is based primarily on the stability of the spine. Most of the stable thoracolumbar spine injuries are selected for conservative treatment [4], and unstable ones are selected for surgical treatment to prevent the deterioration of neurological function and the occurrence of secondary spinal deformities. However, in practice it is still difficult to judge the stability of the spine or it is still very controversial and there is no uniform standard. the role of PLC as an independent reference index in the assessment of stability of thoracolumbar segment injuries has been increasingly appreciated. Shaffrey CI et al [5] reported that a posterior spinal column ligamentous structure or bony structure disruption is an unstable fracture. nagel et al [6] considered an anterior or middle column injury as unstable as long as it is accompanied by a posterior column fracture or PLC injury. mcAfee [7] et al. analyzed the CT findings of 100 patients with thoracolumbar fractures and found that the fracture was unstable due to the possibility of progressive kyphosis and further worsening of neurological symptoms, and classified thoracolumbar fractures with posterior column injuries as unstable fractures. Biomechanical studies have also confirmed the role of PLC on spinal stability.James [8] et al. found in a study of spinal fracture models that anterior and middle column fractures but with intact posterior structures in thoracolumbar fractures were stable fractures and could be treated satisfactorily.The injury to the posterior column was found to play a more important role in the evaluation of burst fracture stability than the injury to the middle column. Panjabi et al [9] showed that the supraspinous, interspinous, and ligamentum flavum ligaments stabilize the spine in flexion and referred to the PLC as an “endogenous ligamentous stabilization system.” Asano et al [10] demonstrated that the supraspinous and interspinous ligaments have a significant role in tension loading and tension strength coefficients, and that the PLC plays an important role in maintaining the stability of the spine. stability has an important role. The diagnosis of PLC injury is based on clinical examination, X-ray, CT reconstruction, MRI, etc. The typical manifestations of PLC injury are widened spine spacing and subluxation and subluxation of the articular processes. 1, physical examination: from the clinical examination can be palpated whether there is a gap between the spinous processes, whether there is a sense of step, whether there is pressure pain, etc. to assist in the diagnosis, but clinically due to the injury of the thoracolumbar segment resulting in bleeding and swelling of the posterior muscle ligaments or posterior bony structures, resulting in unsatisfactory local palpation, interspinous palpation can cause pain at the fracture site, thus it is impossible to determine whether the pain originates from the interspinous ligaments. Therefore, imaging is often required clinically to determine this [11]. 2, X-ray X-rays can indirectly determine the presence of ligamentous injury through the morphology of the fracture and the relationship between the vertebrae. For example, fracture dislocation, widening of the spinous process gap, separation of small joints, and increased posterior convexity angle (lesser damage to bony structures) [12]. In the orthogonal position, it is possible to measure whether there is widening of the spinous process spacing and determine whether there is rotational injury based on the relationship between the spinous process, the pedicle and the articular tuberosity joint; in the lateral position, it is possible to observe whether there is dislocation, widening of the spinous process gap, separation of the articular tuberosity joint, and to measure the posterior convexity angle. Some scholars use the posterior convexity angle to evaluate the PLC status, and Vaccaro AR, et al [13] considered that a posterior convexity angle greater than 300 indicates a rupture of the posterior ligament and used it as one of the indications for surgical treatment of thoracolumbar spine injuries. However, because there are many methods of measuring the posterior convexity angle and no uniform standard has been formed, the change in the posterior convexity angle can only be used as a hint of PLC injury, but not a definitive diagnostic method. 3, CT CT images, especially 3D reconstructed CT images, can clearly show the morphology of the fracture and the relative relationship of bony structures, thus indirectly responding to the state of the ligamentous structures, so the posterior ligament can be indirectly judged by the type of fracture. For example, CT can well show the articular synovial joint separation and changes in the spinous process gap, which can suggest PLC injury. In addition, CT can show whether there is rotation, dislocation, and angulation of the fracture. for X-ray shows that the compression of vertebral body > 50%, and CT sees no fracture of the posterior wall of vertebral body, the injury of posterior structure especially PLC should be considered. 3D reconstruction of CT and lateral X-ray can determine whether there is avulsion fracture on the upper and lower sides of the spinous process attached to PLC, so as to judge the injury of PLC. 4, MRI The value of MRI for the assessment of soft tissue injury is superior to CT, and it has been reported in the literature [14] that the specificity and sensitivity of MRI for the diagnosis of PLC rupture in patients with thoracolumbar spine fractures is higher. Ligamentous structures are shown to be low-signal, nearly black signal in both T1 and T2 image MRI, and because of the poor contrast between T1 image and other tissues, PLC is often observed in T2 median sagittal position, and PLC rupture can be diagnosed if there is an interruption of PLC signal. However, because various injuries of PLC can lead to local hemorrhagic edema, which causes increased signal at the injury site and needs to be distinguished from the high signal area of surrounding adipose tissue, the T2 lipid suppression image can reduce the interference of surrounding adipose tissue and improve the accuracy of diagnosis. According to the TLICS system, incomplete injury can be defined when there is a lack of signs of complete PLC fracture (such as increased sphenoid gaps, fracture dislocation, and articular synovial joint separation on palpation and imaging), but there are signs of injury such as abnormal PLC signal on MRI. Moreover, MRI can observe changes such as damage to nerve and disc structures while showing PLC, which can help in the selection of treatment modality. Although MRI has a high accuracy in evaluating ligament injuries, there are false-positive and false-negative rates. False positives may be due to severe hematomas on both sides of the spinous process and subcutaneous hematomas or secondary hematomas caused by fractures of the vertebral plate, spinous process, and articular eminence, which may result in T2-weighted PLC signal changes. False negatives can also occur after more than 72 hours of trauma [14]. These situations need to be ruled out and noted by the clinician in the judgment process. 5, ultrasound Ultrasound is noninvasive, rapid, convenient, economical, and repeatable in a short period of time, making it possible to utilize it in the evaluation of PLC injuries. With its application in the diagnosis of ligament injuries in other parts of the body, ultrasound is gradually being applied to the evaluation of PLC in the thoracolumbar spine. Ligament injuries can manifest in ultrasound as abnormal morphology, echogenic inhomogeneity, and interrupted echogenic continuity, which often predicts ligament rupture [15]. von Scotti F’s prospective study [16] analyzed the diagnostic value of ultrasonography for PLC injuries, using ultrasound to determine the status of the PLC and comparing it with the status of the PLC intraoperatively, and found that ultrasonography made a correct determination in 91% of patients, with a sensitivity of 83.3% and specificity of 93.8% as a diagnostic method.Similar results were obtained in a study by Vordemvenne T [17], who acknowledged the unique superiority of MRI in the diagnosis of PLC injury, but for the presence of relative contraindications to MRI, such as hyperthermia, non-titanium implants in the body, claustrophobia phobia, etc., is a good choice. In addition, in patients with severe multiple injuries, the risk of examination can be reduced and a rapid diagnosis can be made. Ultrasonography is a valuable test for the evaluation of PLC injuries. In 2006, Vaccaro AR, [13] reviewed 14 clinical signs or imaging manifestations mentioned in previous literature reports that could determine PLC injury, ranked them in order of confidence, and finally identified fracture dislocation as the first, sphenoid gap opening on radiographs as the second, and vertebral subtalar joint separation on CT as the third. It was also suggested that no vertebral injury had an increased angle of lordosis and anterior vertebral compression greater than 50%, but no vertebral posterior wall fracture on CT examination were suggestive of PLC injury, but an exact angle of lordosis was also not suggested. They also pointed out that radiographs are the most important indicator in determining whether PLC is fractured, and medical history and physical examination are the least significant. Third, the clinical significance of PLC in thoracolumbar segment injuries 1. Selection of surgical indications: With the development of assessment systems, more scholars have attempted to standardize the treatment of thoracolumbar segment fracture dislocations through standard quantitative assessment so that the selection of treatment methods can be followed [18]. The TLICS system, a scoring system for the extent of spinal cord injury in the thoracolumbar segment developed by the American Spinal Injury Study Group, is divided into three areas: fracture morphology, PLC status, and neurological function status, and the decision to operate is based on the total score after subscoring, with a total score ≤ 3 points Conservative treatment; total score = 4 points Conservative/surgical treatment; and total score ≥ 5 points Surgery [3]. Surgical treatment is mostly required for thoracolumbar segment injuries with combined PLC disruptions. The reasons for this are the following: (1) the PLC fracture destabilizes the spine; (2) the ligamentous structures are less capable of healing; (3) thoracolumbar segment injuries with combined PLC fractures are mostly associated with dislocation; (4) thoracolumbar segment injuries with combined PLC fractures are rated using the TLICS system with a score of at least 4 (3 points for PLC fractures and 1 point for fracture pattern compression; in fact, the fracture pattern in the case of PLC fractures should be distraction McCormack et al [19] proposed the Load Sharing Classification, which classifies and quantifies the severity of vertebral comminution and kyphosis based on the scoring system is based on plain films and CT and is divided into 3 parts: extent of fracture involvement, degree of fracture displacement, and the size of the kyphosis deformity to be corrected. When there is no dislocation of the thoracolumbar segment fracture, ≤6 points select the posterior approach; ≥7 points select the anterior approach; but ≤6 points select the posterior approach in the presence of dislocation; ≥7 points select the combined anterior and posterior approach. Judgment of whether to perform simple posterior reduction and fixation or simultaneous anterior reconstruction based on the score provides some basis for the selection of surgical access for thoracolumbar segment injuries. It is certainly better to be able to choose a standardized treatment based on quantitative assessment, but clinical patients are very different, and these assessment systems cannot be used mechanically, but must be combined with the actual situation of the patient’s injury and the surgeon’s proficiency in the approach [4]. For patients with thoracolumbar injuries with PLC rupture, the posterior approach is more suitable because PLC rupture is mostly caused by flexion-distraction violence, and the posterior approach can reverse the mechanism of injury to perform posterior column compression and anterior column bracing, and posterior surgical internal fixation can restore the tension band structure and length of the posterior spinal ligament. The posterior approach is convenient for repositioning, and the selection of fixed segments: there is no uniform standard for the number of fixed segments of thoracolumbar fractures. Long segment fixation increases the surgical trauma and sacrifices more motor segments, and short segment fixation also has the possibility of secondary fracture collapse and failure of internal fixation [20]. In contrast, combined thoracolumbar injuries with PLC rupture, some of which are patients with distraction injuries, type B1 in the AO staging, where the damage to the bony structures is not severe and the pedicle and bony inferior endplate are not involved, can be selected for posterior single-segment fixation in these cases by shortening the posterior column to brace the anterior column, thus allowing contact of the PLC ruptured end and restoring the posterior PLC tension band structure, thus reducing the fixation of too many motion segments [21]. In conclusion, the status of the PLC is of great clinical importance for the staging of thoracolumbar fractures, stability evaluation and treatment selection, and its assessment requires a combination of clinical and imaging methods.