Risk factors analysis of proximal junctional kyphosis following posterior long instrumented spinal fusion for degenerative lumbar scoliosis

English Keywords:Proximal junctional kyphosis  Risk factor  Incidence  Degenerative lumbar scoliosis

English Abstract:

  【Abstract】 Objectives: To investigate the risk factors of proximal junctional kyphosis(PJK) following posterior long instrumented spinal fusion in degenerative lumbar scoliosis(DLS) patients. Methods: This retrospective review included 60 DLS patients who underwent one stage posterior long instrumented spinal fusion in our spinal center from April 2009 to May 2014. The inclusion criteria included: (1) age not less than 45 years; (2) at least five fusion vertebrae; (3) at least 2-year follow-up. All patients followed up 40.3±11.1 months(24-59 months). According to the occurrence of PJK at final follow-up, patients were divided into two groups: PJK group and control group. The differences of patient data, surgical data and radiographic parameters between the two groups were analyzed by univariate analysis and the potential risk factors were identified. Logistic regression analysis was used to find the independent risk factors. Patient data included preoperative data of sex, age, body mass index(BMI), bone mineral density(BMD) and T-score. Surgical data included the number of instrumented and fused vertebrae, upper instumented vertebra(UIV) level, lowest instumented vertebra(LIV) level, osteotomy and interbody fusion. Radiographic parameters included scoliosis Cobb angle, thoracic kyphosis (TK), thoracolumbar kyphosis(TLK), lumbar lordosis(LL), pelvic incidence(PI), pelvic tilt(PT), sacral slope(SS), global sagittal alignment(GSA), sagittal vertical axis(SVA) and proximal junctional angle(PJA1, the angle between the end plate of UIV+1 and the end plate of the UIV; PJA2, the angle between the end plate of UIV+2 and the end plate of the UIV). Results: The 60 DLS patients(45-74, 63.2±6.4 years) showed an average preoperative Cobb angle of 28.51°±10.94°(10.7°-55.1°), the mean number of instrumented levels was 6.7±1.3(5-9). PJK was developed in 11 of 60 patients(18.3%) until final follow-up, who were enrolled as the PJK group, and 49 patients without PJK at final follow-up were enrolled as the control group. There were statistically significant differences between the two groups in number of cases with BMD<0.850g/cm2(100.0% in the PJK group and 36.1% in the control group, P=0.005), number of UIV at T11-L1 patients(100.0% in the PJK group and 69.4% in the control group, P=0.030), number of preoperative PJA1>9° patients(45.5% in the PJK group and 10.2% in the control group, P=0.013), number of preoperative TLK≥15° patients(63.6% in the PJK group and 22.4% in the control group, P=0.012), number of preoperative SS＜25° patients(90.9% in the PJK group and 46.9% in the control group, P=0.016), number of immediate postoperative PJA2≥5° patients(100.0% in the PJK group and 46.9% in the control group, P=0.001) and number of immediate postoperative PJA2 increase ≥3° patients(90.9% in the PJK group and 46.9% in the control group, P=0.016). When included in a multivariate logistic regression model, preoperative PJA1>9°(OR=19.432, P=0.017), preoperative SS＜25°(OR=23.131, P=0.022) and immediate postoperative PJA2 increase≥3°(OR=22.382, P=0.025) were independent risk factors for PJK. Conclusions: Preoperative PJA1>9°, preoperative SS＜25° and immediate postoperative PJA2 increase ≥3° are identified as independent risk factors for PJK. BMD<0.850g/cm2, UIV at T11-L1, preoperative TLK≥15° and immediate postoperative PJA2≥5° are potential risk factors for PJK.