Risk factors of kyphosis recurrence after implant removal in the treatment of thoracolumbar burst fractures with posterior short-segment fixation

SUN Xiang-yao; ZHANG Xi-nuo; HAI Yong

doi:10.3969/j.issn.2095-252X.2017.09.013

Abstract：Objective To evaluate the curative effects of short-segment pedicle instrumentation with screw insertion in the fracture level and find risk factors predicting kyphosis recurrence in thoracolumbar burst fractures. Methods Patients with thoracolumbar burst fractures who underwent short-segment posterior pedicle screw instrumentation in the department of orthopedics, Beijing Chao Yang Hospital from January 2006 to January 2013 were carefully reviewed. Cobb's angle of the fractured segment, RA ( regional angle ), UIVA ( upper intervertebral angle ), LIVA ( lower intervertebral angle ), VWA ( vertebral wedge angle ), AVH％ ( the anterior vertebra height ratio ), PVH％ ( the posterior vertebra height ratio ), the number of patient with AVH％ < 50％, the number of patients with upper end plate injury, LSC ( load-sharing classification ), VAS ( visual analogue scale ), BMI ( body mass index ) were collected. The patients were divided into two groups according to if kyphosis occurred or not. Results Age ( P < 0.001 ), number of females ( P < 0.001 ), BMI ( P < 0.001 ), preoperative UIVA ( P = 0.002 ) in the group with kyphosis occurrence was larger than the group without kyphosis occurrence. Preoperative A / P ratio ( P = 0.038 ), preoperative AVH％ ( P = 0.003 ) in the group with kyphosis occurrence was less than the group without kyphosis occurrence. No between-group differences were found in other parameters. Results of logistic regression analysis showed female ( R2 = 0.324, B = 2.618, P < 0.001), age ( R2 = 0.509, B = 0.728, P < 0.001 ), BMI ( R2 =0.509, B = 0.728, P < 0.001 ), preoperative UIVA ( R2 = 0.160, B = 0.282, P = 0.004 ) were all risk factors of kyphosis recurrence. However, preoperative A / P ratio ( R2 = 0.072, B = -0.049, P = 0.043 ), preoperative AVH％ ( R2 = 0.143, B = -0.066, P = 0.006 ) were protective factors. Results of ROC curve analysis showed the cut-off values of age, BMI, preoperative UIVA were 49 years old ( area under the curve = 0.816 ), 25 ( area under the curve = 0.871 ), -4.5 ( area under the curve = 0.667 ). However, preoperative AVH％ ( area under the curve = 0.317 ) and preoperative A / P ratio ( area under the curve = 0.386 ) were of less guiding significance ( area under the curve < 0.5 ). Conclusions Age, female, BMI, preoperative AVH％, preoperative UIVA, preoperative A / P ratio are impact factors of the kyphosis recurrence after the instrumentation removal. However, BMI seems to be better than other impact factors. Age >49 years old, BMI > 25, preoperative UIVA < -4.5° are optimal predictive factors of the kyphosis recurrence after the instrumentation removal.