Classification of ossification of posterior longitudinal ligament in thoracic spine and its clinical meaning

English Keywords:Thoracic  Ossification of posterior longitudinal ligament  Thoracic spinal stenosis  Classification  Strategy

English Abstract:

  【Abstract】 Objectives: To investigate a new compositive classification of thoracic posterior longitudinal ligament(TOPLL) based on the imaging features of CT, MRI and the position and range of pathological changes and its role in clinical practice. Methods: 49 patients, including 8 males and 41 females, diagnosed as TOPLL from May 2007 to June 2013 were collected in this series. The mean age was 51.8±8.7 years(36-71 years), and the average duration of disease was 15.2±21.9 months(1-120 months). According to pre-operative information on both sagittal and axial planes of CT and MRI, 4 types of TOPLL were classified in practice: Ⅰ, regional compression(1-2 segments) in proximal thoracic spine(T1-T4); Ⅱ, regional compression(1-2 segments) in middle and distal thoracic(T5-T12); ⅡA, without ossification of ligamentum flavum(OLF) at the same segment; ⅡB, with OLF at the same segment; Ⅲ, continuous ventral compressions(≥3 segments); Ⅳ, discontinuous type of TOPLL; ⅣA, discontinuous type of TOPLL(interval≥3 segments); ⅣB, discontinuous type of TOPLL(interval<3 segments). This classification was applied into clinical practice, the types of TOPLL, operative data, JOA scores at pre- and post-operation and recovery rates and Frankel classification were recorded. Results: A total of 49 patients was recruited in this study, 6 cases were classified as type Ⅰ, and the treatment strategy was 360° circumferential decompression(PCD), named "cave in" technique; 2 as ⅡA, and the treatment strategy was anterior decompression(AD); 3 as ⅡB, the treatment strategy was circumferential decompression(PD); 30 as Ⅲ, among them, 13 received PD and 17 received PCD; 8 as Ⅳ, among them, 7 ⅣA received PCD and 1 ⅣB received PD. One patient died from brainstem hemorrhage 26 months after surgery. The remaining 48 cases were followed up for 12-85 months with an average of 47±24 months. Pre-operative JOA scores of these 48 patients were 4.6±1.8(0-9), while 8.8±2.1(4-11) at final follow-up, with an average recovery rate of (69±28)%(14%-100%). According to the Hirabayashi grading for recovery rate, 23 patients were ranked as excellent, 9 as good, 16 as middle, none as unchange or worse. 1 patient with Frankel A pre-operatively improved to B at final follow-up. Among 22 cases with Frankel B, 17 improved to C, and 2 Frankel C improved to D at final follow-up. 11 cases(22%) were complicated with cerebrospinal fluid leakage, including 1 case of PD and 10 cases of PCD. The interventions included removal of drainage, stressful dressing and delayed off bed 2 days later. At final follow-up, only 1 case(T8-T12 PD combined with T8/9 PCD) was still found presence of cerebrospinal fluid at T8/9 on MRI, and in other 10 cases, the CSF completely disappeared. None developed injury of spinal cord or infection. Conculsions: This article proposes a novel classification of TOPLL, which takes the sites, distribution and sources of compression into account, and also proposes surgical strategies respectively. Primary application of this classification in clinical practice suggests its value.