RESUMO
Objective To investigate the radiographic characteristics of posterosuperior fracture fragment of the injured vertebral body and its effects on the results of surgical treatment in thoracolumbar burst fractures.Methods A total of 45 patients with acute thoracolumbar burst treated by either anterior or posterior surgery from January 2014 to December 2015 were analyzed by retrospective casecontrol study.There were 24 males and 21 females with a mean age of 33.6 years (range,23-52 years).Fractured segments included T12 in six cases,L1 in 15,L2 in 14,L3 in 5,and L4 in 5.Based on AO classification,there were ten cases of A3 fractures and 35 cases of Ag fractures,among which four cases of A4 were combined with B2 injuries.Eleven patients underwent anterior surgery and 34 patients posterior surgery.The operation time and intraoperative blood loss were recorded.The following parameters were also measured pre-and post-operatively,namely the displacement and inversion angle of posterosuperior fracture fragment,Cobb angle,anteroposterior diameter (APD) of spinal canal,and American spinal injury association (ASIA) neurological scale.Results All patients were followed up for 11-24 months (mean,17 months).There were no complications except for one case of implant loosening at three months after anterior surgery.The average operation time was 138.3 minutes and intraoperative blood loss was 293.7 ml in anterior surgery while the average operation time was 77.5 minutes and intraoperative blood loss was 54.7 ml in posterior surgery (P ＜ 0.05).Compared with postoperative situation,the canal APD was increased by 55.5％ in anterior surgery and the corresponding increase was 14.9％ in posterior surgery (P ＜ 0.01).There was no significant difference between two groups in Cobb angle correction.Compared with situation before surgery,the postoperative ASIA grading was improved in 73％ of the patients in anterior surgery and while it was enhanced in 24％ of the patients in posterior surgery (P ＜ 0.05).On the aspect of spinal canal decompression,anterior surgery had obvious decompression effects.The canal APD of anterior surgery was 94.4％,which was larger than 88.5％ in posterior surgery,although the difference was not significant.Notably,when the fragment displacement was ≤ 8 mm,posterior surgery could achieve 97.4％ APD which was comparable with that of anterior surgery.In contrast,when the fragment displacement was ＞ 8 mm,the APD was much smaller in posterior surgery with only 78.5％ (P ＜ 0.05).Similarly,when the fragment inversion was ≤25° or ＞ 25°,the APD was significantly different in anterior surgery and posterior surgery (95.4％ vs.80.8％) (P ＜ 0.05).Conclusions Although posterior surgery for thoracolumbar burst fractures is easy to perform and has short operation time and little intraoperative blood loss,it cannot always guarantee adequate decompression of spinal canal.When the posterosuperior fragment displacement is ＞ 8 mm or when its inversion is ＞ 25°,stand-alone posterior indirect reduction technique is likely to lead to inadequacy of canal restoration.In this case,anterior surgery should be considered in order to achieve more complete canal decompression.Therefore,this radiographic characteristic of the posterosuperior fragment could serve as an approach reference for thoracolumbar burst fractures.