Vertebral body spread in thoracolumbar burst fractures can predict posterior construct failure

Background context The Load Sharing Classification (LSC) laid foundations for a scoring system able to indicate which thoracolumbar fractures, after short-segment posterior-only fixations, would need for longer instrumentations or additional anterior supports. Purpose We analyzed surgically treated thoracolumbar fractures, quantifying the vertebral body's fragments displacement with the aim of identifying a new parameter which could predict the posterior-only construct failure. Study Design Retrospective cohort/single institution. Patient sample One hundred twenty-one consecutive patients surgically treated for thoracolumbar burst fractures. Outcome measures Grade of Kyphosis Correction (GKC) expressed radiological outcome; Oswestry Disability Index and Visual Analogue Scale (VAS) were considered. Methods One hundred twenty-one consecutive patients who underwent posterior fixation for unstable thoracolumbar burst fractures were retrospectively evaluated clinically and radiologically. Supplementary anterior fixations were performed in thirty-four cases with posterior instrumentation failure, determined on clinic-radiological evidences or symptomatic loss of kyphosis correction. Segmental kyphosis angle and GKC were calculated according to the Cobb method. The displacement of fracture fragments was obtained from the mean of the adjacent endplates areas subtracted to the area enclosed by the maximum contour of vertebral fragmentation. The “spread”, derived from the ratio between this subtraction and the mean of the adjacent endplates areas. ANOVA, Mann-Whitney and ROC were performed for statistical analysis. The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. No funds or grants have been received for this study. Results The spread revealed to be a helpful quantitative measurement of vertebral body fragments displacement, easily reproducible with the current CT imaging technologies. There were no failures of posterior fixations with preoperative spreads 62.7% required supplementary anterior supports whenever LOC>10° were recorded. Most of the patients in a “grey zone”, with spreads between 42% and 62.7%, needed additional anterior supports because of clinical-radiological evidences of impending mechanical failures which developed independently from the GKC. Preoperative kyphosis (p<.001), LSS (p=.002) and spread (p<.001) significantly affected the final surgical treatment (posterior or circumferential). Conclusions Twenty-two years after the LSC both improvements in spinal stabilization systems and software imaging innovations have modified surgical concepts and approach regarding spinal trauma care. Spread was found to be an additional tool which could help in predicting the posterior construct failure, providing an objective preoperative indicator, easily reproducible with the modern viewers for CT images.