INTRODUCTION
The incidence of proximal junctional kyphosis (PJK) after long-segment spinal fusion surgery in adult spinal deformity patients with concomitant osteoporosis was 27.6%. Accurate identification of PJK risk factors can help surgeons take preventive measures to reduce its occurrence.
METHODS
A retrospective study was performed on 76 adult spinal deformity patients with osteoporosis who underwent long-segment spinal fusion surgery at our hospital from June 2013 to December 2019. Based on whether PJK occurred during the 2-year follow-up after surgery, the patients were divided into PJK group (21 cases) and non-PJK group (55 cases). Baseline information, surgical details, preoperative and postoperative spinal-pelvic parameters, Hounsfield Units (HU) of the vertebral bodies, and paraspinal muscle morphology were compared between the two groups. Spinal-pelvic parameters included the main Cobb angle, lumbar lordosis (LL), lumbosacral lordosis (LSL), sagittal vertical axis (SVA), T1 pelvic angle (TPA), pelvic tilt (PT), sacral slope (SS), pelvic incidence (PI), and PI-LL mismatch. The HU values of the upper instrumented vertebra (UIV), UIV+1, and UIV+2 was measured in preoperative computed tomography (CT). The relative functional cross-sectional area (rFCSA) and functional muscle-fat index (FMFI) of the paraspinal muscle at the level of L3 lower endplate were measured in preoperative magnetic resonance imaging (MRI). The optimal cutoff values for HU values of the vertebral bodies and paraspinal muscle morphology were determined using ROC curve analysis. Multivariable logistic regression analysis was performed to identify independent risk factors for PJK, and odds ratios (OR) were calculated.
RESULTS
There were no significant differences in baseline information, surgical details, preoperative main Cobb angle, LL, LSL, SVA, TPA, SS, PI, and PI-LL mismatch between the groups (P > 0.05). However, preoperative PT (P = 0.007), postoperative LL (P = 0.043), LSL (P = 0.047), and SVA (P = 0.001) were significantly different between the groups. The HU values of UIV (113.62 ± 17.25 vs. 133.94 ± 16.61), UIV+1 (123.14 ± 16.03 vs. 138.27 ± 13.69), and UIV+2 (121.00 ± 15.91 vs. 134.47 ± 15.53) were significantly different between the groups (P < 0.05). The optimal cutoff values for the HU values of UIV, UIV+1, and UIV+2 was 120.72, 127.51, and 121.50, respectively. There were significant differences in rFCSA (156.87 ± 48.06 vs. 204.87 ± 50.16) and FMFI (0.31 ± 0.10 vs. 0.23 ± 0.09) between the groups (P < 0.05). The optimal cutoff values for rFCSA and FMFI were 175.43 and 0.24, respectively. Multivariable logistic regression analysis revealed that postoperative SVA (OR 1.332; 95% CI 1.128-1.592; P = 0.035), the HU values of UIV (OR 0.932; 95% CI 0.881-0.985; P = 0.013), and rFCSA of paraspinal muscle (OR 0.985; 95% CI 0.970-0.998; P = 0.045) were independent risk factors for PJK.
DISCUSSION
Decreased HU values of UIV, decreased rFCSA of the lumbar paraspinal muscle, and under corrected sagittal alignment were identified as independent risk factors for PJK in these patients. Spine surgeons might take appropriate measures to improve patients’ prognosis based on these risk factors.