Complications rate and risk factors in unplanned reoperation of degenerative lumbar spondylolisthesis in geriatric patients: a retrospective single-center cohort study of 33 patients

Background: The study aimed to investigate the complications rate and risk factors in unplanned reoperation among geriatric patients who underwent posterior lumbar fusion(PLF) for degenerative lumbar spondylolisthesis(DLS). Methods: 1100 DLS patients who were older than 60 years were reviewed from January 2006 to December 2016 and 33 patients underwent unplanned reoperations who were analyzed and divided to two groups(Group A: posteriolateral fusion, Group B: intervertebral fusion). Gender, body mass index (BMI), radiographic data and clinical outcomes data were analyzed to evaluate complications rate and the risk factors for unplanned reoperations. Results: 33 patients were performed by the unplanned reoperations(3%).The patients were followed up for an average of 4.20±2.25 years (Group A)and 4.32±2.54 years(Group B)without significant difference. The significant difference was found in mean age, levels involved levels, hospital stay, surgery time, blood loss between the groups. The causes of unplanned operation were: wound infection, screw misplacement, neurological deficit, nonunion, screw fracture which were significant except the wound infection between the groups. Higher BMI (obesity), diabetes mellitus(DM), more bleeding and gender(female) were the risk factors of the complications. The cases of the screw misplacement, neurological deficit, nonunion and screw fracture in group A were more significantly than in group B. Conclusion: The patients of higher BMI, DM, age, posteriolateral fusion, female predicted higher incidence of unplanned reoperations. The spine surgeons maybe need to pay more attention in their preoperative training and in improving

surgical technique which could reduce the reoperation rate.
background As the arrival of the aging population, the incidence of degenerative lumbar spondylolisthesis(DLS) and its surgical treatments also get more and more attention, because the rapid progress of anesthesiology and surgical instruments lead to active surgical management in geriatric patients [1]. However, preventing revision spinal surgery is still a matter of cardinal significance for the spine surgeons and their patients. Unplanned reoperation means an unexpected event, a status of persistent symptoms, deterioration of the previous potential diseases, or complications related to the primary operation [2][3]. A better understanding of the complications rate and risk factors of unplanned reoperation could help improve the surgical outcomes and prognosis. It was reported that the cumulative reoperation rate in lumbar degenerative diseases was 4.7% at 3 months, 6.1% at 1 year, 8.5% at 2 years, 15.2% at 3 years, 17.7% at 5 years and 23.3% (38/163 patients) at the final follow-up [4][5][6][7][8]. Reducing rate of lumbar surgery revision is also vital because of endings of DLS reoperation for may be worse than the the initial surgical management results.
Therefore, the study aimed to investigate the incidence of unplanned reoperation in geriatric patients performed surgically for DLS and to analysis the complications rate and risk factors. methods

Patient selection
The study was approved by the institutional review board of ourhospital. 1100 patients were restropectively reviewed and the unexpected reasons for the unplanned reoperation were recorded and assessed. Between January 2006 and December 2016, 33 reoperation patients with DLS, aged more than 60 years old were enrolled.
The inclusion criteria: one-level or two-level DLS requiring surgical treatment again.
All the surgeries were performed of posterior lumbar fusion including posterolateral fusion and intervertebral fusion. Unplanned surgery was defined as receiving the reoperation in operation room after the primary surgery. The primary and revision surgery were all performed by the same senior surgeons team. The exclusion criteria: the patients suffered the lumbar disc herniation, or lumbar spinal stenosis, or lumbar vertebral fractures, spondylitis and tumors.
Patients' demographic data, including the primary surgical procedure and revision surgery information were recorded in our study. The reasons for the unplanned surgery were assessed and the reoperation rates of DLS were calculated.

Statistical analysis
All statistic data were analyzed with SPSS version 22.0 statistical software(SPSS, Inc., Chicago,IL,USA). The data were analyzed by Student's t-test for continuous variables and Chi square test for categorical variables. Values of P<0.05 were regarded statistically significant. For all regression models, a p value less than 0.05 with a confidence interval (CI) of 95% was considered significant.  The wound infection were revised for debridement surgery without removing implants, who were treated with antibiotics sensitive to the bacterial. The pedicle screws displacement were detected on thepostoperative X-ray from those patients manifested leg pain or persistent sciatica after the primary surgery. All of the screws were corrected immediately and the leg pain improved after the reoperation and the recovered to normal at the final follow-up.

Risk factors analysis
Based on the previous documents, the potential factors were selected and assessed for analyzing risk factors, the following data: age, gender, body mass index(BMI), fusion methods of surgery fusion. Higher BMI, diabetes mellitus(DM), more bleeding and women predicted higher occurrence of wound infection (Table 2).
Different fusion methods, female predicted the development of nonunion and 6 screw fracture.  Several previous studies reported reoperation following an primary lumbar surgery for degenerative conditions and indicated that the revision rates were 14.0% in the 1997 to 2000 cohort and 12.4% in the 1990 to 1993 cohort [17]. Ghogawala demonstrated that the re-operation rate after only decompression for DLS at 1-year postoperatively was 15% [18]while Blumenthal reported 37.5% at a mean follow-up of 3.6 years [19]. The reoperation rate occurred in the present study nearly as the same as in the previous studies: the reoperation rate for only decompression at 1year follow-up was 10.8% and the rate increased to 29.7% at 5-year postoperatively and to 33.4% at the final follow-up [20][21]. Another report demonstrated the cumulative reoperation rate was 6.1% at 1 year, 8.5% at 2 years, 15.2% at 3 years, 17.7% at 5 years, and 23.3% at the final follow-up [22]. Different from the studies mentioned above, the reoperation rate of DLS was 3.0% in our study, which was lower than those previous studies. The reason for the lower reoperation rate in our study may be that we just reported the reoperation during patients of one-level or two-level DLS.
Elderly patients have commonly been considered to be at a higher risk of postoperative complications of DLS than younger patients. It was documented an approximate 80% of complications rate who were performed surgically for DLS [23][24][25][26][27]. In the study of Okuda, postoperative complications were found in 16% of elderly patients after PLIF with pedicle screw placement [28]. In our series, the major reasons for the reoperation were wound infection, screw misplacement, neurologic deficit, nonunion, screw fracture, which were similar to previous reports.
Therefore, the better understanding of the complications, risk factors and unplanned reoperations rate is helpful to improve the surgical outcomes.
In our study, higher BMI , DM, more bleeding and women predicted the occurrence   L4 and L5 DLS of a 75-year-old woman treated with L4/5 laminectomy and intervertebral inte