Lumbar fusion surgery is a standard procedure for treating degenerative lumbar disease. Despite advances in surgical technique and implants over the past two decades, the rate of unplanned reoperation did not decrease with the increase in lumbar fusion volume[2, 5, 9]. In the present study, we found that the cumulative incidence of unplanned reoperation was about 3.9% at three months,5.6% at 1 year, and 7.9% at 4 years. A wide range (3.4–14.4%) of reoperation rates following fusion surgery was reported in previous publications[6, 8, 10, 11]. The rate of unplanned reoperation in our patient cohort was broadly in line with these results. The changes in cumulative reoperation rate and reason for reoperation at different times were demonstrated in prior studies[6, 8]. The present study aimed to identify the indications and risk factors for early reoperation and late operation following fusion surgery.
There are differences in reasons for reoperation between the early reoperation group and the late reoperation group. The primary reasons for the early reoperation in the present study were SSI and hematoma, followed by early displacement of implant, residual stenosis and ASD. The results of our study were similar to previous studies. Liu et al. conducted a multicenter study and reported that the reasons for reoperations within 3 months after lumbar fusion surgery included wound infection (45.4%), screw misplacement (25.6%), cerebrospinal fluid leakage (13.0%), wound hematoma (8.7%) and neurologic deficit (7.2%). In another study, Durand et al. found that reasons for unplanned reoperation within one month after fusion surgery were mostly infection and hematoma. The present study’s most common indication for late reoperation was ASD, which was consistent with a previous study. A prospective cohort study by Irmola et al. also reported a high incidence of ASD and the reoperation for ASD was performed a mean of 2.3 years after fusion surgery. We also found that SSI and implant displacement were common reasons for readmission to reoperation 3 months or more after surgery. By analyzing the indication and timing of reoperation, this study demonstrated that the surgeon should be focused on different issues according to the length of time after fusion surgery.
Postoperative pain in the lower back or leg is a major complaint among patients receiving reoperation. We found that lumbar fusion surgery provided efficient pain relief in patients with degenerative lumbar disease, and most patients experienced a significant reduction in VAS scores after fusion surgery. However, some patients required a second procedure to achieve effective pain relief. We found that the VAS scores of these patients remained higher than those who did not undergo the second procedure at the final follow-up, which was consistent with the results of previous studies[6, 14]. In a retrospective study of 309 patients, Montenegro et al. found that up to 23% of patients had a declined functional status at the 6 months after reoperation. The underlying reason for this is unclear; however, more extended hospital stays and higher costs may lead to lower satisfaction and confidence in the operation[16, 17].
By multivariable analysis, we found that osteoporosis and diabetes were risk factors for early reoperation; however, the remaining variables did not affect the rate of early reoperation after lumbar fusion. Osteoporosis is characterized by a reduction of bone mineral density and is diagnosed based on X-ray, computed tomography, and dual-energy X-ray absorptiometry. Patients with osteoporosis are at higher risk of implant displacement including screw loosening, cage sinking and fractures[18, 19]. Khalid et al. reported that osteoporosis was independently associated with pseudoarthrosis and revision surgery in adult patients undergoing single-level lumbar fusion. Previous studies have also found that vertebral osteoporosis is a risk factor for adjacent vertebral fractures and for proximal junctional kyphosis after multilevel fusion [21, 22]. For patients diagnosed with osteoporosis, the reduced number of manipulations and the use of bone cement may reduce the incidence of screw loosening and adjacent vertebral fractures . Diabetes is associated with poor wound healing. Golinvaux et al. reported that patients with diabetes had a higher incidence of postoperative wound infection than other patients. Kim et al. performed a multivariate regression analysis and found that diabetes was an independent risk factor for unplanned reoperation after fusion surgery, which was consistent with our findings. Insufficient local blood supply, poor immunity and neurological damage increase the risk of surgical wound infection in patients with diabetes. Moreover, Rathmann et al. found that diabetes was associated with a higher rate of fractures. Early reoperation is usually performed for debridement and depression in patients with long-term wound infection and residual stenosis. We did not find any other remaining variables associated with early reoperation, including age, other comorbidities, and ASA score. In a retrospective study of 22151 patients, Durand et al.  found that obesity, ASA, disseminated cancer, weight loss and multilevel fusion were identified as significant risk factors for reoperation within 30 days following elective lumbar spinal fusion. Another study found that only ASA ≥ 3 was independently associated with a higher incidence of reoperation within 30 days. Differences in the study population may have a significant impact on the results of different study. In the present study, we only included patients who underwent open lumbar fusion surgery and excluded patients who underwent decompression alone and MIS-TLIF surgery.
We found that only the number of fused levels > 2 was an independent risk factor for late reoperation. This result is similar to that of Durand 's study, which reported that long-segment fusion was independently associated with reoperation during long-term follow-up. In long-segment fusions, surgical procedures destroy more paraspinal muscles and alter spinopelvic sagittal parameters. Compared with short-segment fusion, long-segment fusion has a higher risk of adjacent segment degeneration. Furthermore, previous studies have found that the number of fused levels >2 was an independent risk factor for revision surgery due to screw loosening and rod breakage. ASD and late displacement of implant mostly cause persistent lower back pain and can only be detected by imaging examination. Persistent lower back pain should be given more attention in patients undergoing long-segment fusion.
Few published studies have reported differences in risk factors between early and late reoperation to the best of our knowledge. In the present study, we compared characteristics, laboratory tests, primary diagnosis and surgery-related variables in the reoperation and non-reoperation groups in the same patient cohort and found that diabetes and osteoporosis were independently associated with early reoperation, whereas long-segment fusion was independently associated with late reoperation. Our study demonstrates the association between the risk factors of reoperation and the duration of follow-up. In future studies, follow-up time should be considered as an independent variable when evaluating outcomes of patients undergoing lumbar fusion surgery.
There are some limitations to this study. First, the differences in surgical indications and techniques among hospitals significantly impact on reoperation rates; nevertheless, we were unable to verify this due to the nature of single-center retrospective studies. Second, patients’ radiographic data such as sagittal parameters were not recorded; therefore, we could not compare the degree of lumbar spondylolisthesis and the grade of disk degeneration between groups. Third, although the same surgical team performed the surgery, each individual's specific surgical procedure, including decompression of the segment and lateral area, is challenging to analyze. Further prospective multicenter studies should include patient imaging data and expand the sample size to draw more reliable conclusions.