Analysis of risk factors of cage retropulsion after posterior lumbar interbody fusion

English Keywords:Posterior lumbar interbody fusion  Cage retropulsion  Risk factor

English Abstract:

  【Abstract】 Objectives: To investigate the risk factors of cage retropulsion(CR) after posterior lumbar interbody fusion(PLIF). Methods: Retrospective analysis was made on 17 patients(13 males and 4 females, with an average age of 63.7±9.9 years) who underwent revision surgery due to CR after PLIF in our hospital from September 2017 to September 2021. And the patients were included into the CR group. Another 34 patients without CR were matched in a ratio of 2∶1 according to the same fusion and fixation segments, time of initial surgery(±1 year), gender, and age(±2 years), including 26 males and 8 females, with an average age of 65.2±10.2 years. They were included in the control group. In the CR group, the average number of fixed segments was 1.8±0.8, and the average number of fused segments was 1.5±0.6; The time of CR was 7(0.75-132) months after the first operation; 15 patients had single segmental CR and 2 patients had two segmental CR. The lumbar lordosis(LL), pelvic tilt(PT), sacral slope(SS), and pelvic incidence(PI) were measured on full-spine X-ray before operation of the two groups of patients, the disc height(DH) of the diseased segment was measured on lateral lumbar X-ray, and the intervertebral range of motion(ROM) was measured on flexion-extension X-ray. The CT value of lumbar vertebrae was measured in CT examination before operation; The shape of disc was defined through MRI examination. The cage position was measured on X-ray immediately after operation(The ratio of the distance between the marker line of the posterior margin of the cage and the posterior upper margin of the lower vertebral body to the length of the upper endplate of the lower vertebra). The paired sample t-test was used for single factor analysis to analyze the data of the two groups, after which, the parameters with statistical significance were analyzed with logistic regression to determine the independent risk factors of CR. Results: The mean vertebral CT value in the CR group was lower than that in the control group(124.8±39.7 vs 147.7±38.2, P=0.011); The cage position in the CR group was more posterior than that in the control group(0.15±0.09 vs 0.31±0.07, P<0.001). There was no significant difference between the two groups in LL(40.8°±12.9° vs 42.4°±7.5°, P=0.717), PT(19.6°±7.1° vs 17.1°±6.7°, P=0.356), SS(27.7°±6.5° vs 31.0°±4.3°, P=0.144), PI(44.3°±13.8° vs 44.7°±13.9°, P=0.926), DH(10.1±2.4mm vs 8.8±1.4mm, P=0.066), ROM(4.3°±2.8° vs 4.4°±2.2°, P=0.950), and Pear-shaped intervertebral discs(33.3% vs 21.4%, P=0.40). Logistic regression analysis showed that low vertebral CT value(osteoporosis)(OR=0.975, P=0.043) and cage position(OR=28.393, P=0.003) were the independent risk factors. Conclusions: Osteoporosis and posterior placement of cage are the risk factors for CR after PLIF.