This study investigated 68 consecutive cases of fusion surgery for degenerative lumbar spine disease in patients over 80 years of age and demonstrated favorable outcomes in this patient population. The goal of minimally invasive surgery (MIS) is to limit tissue damage. This is particularly advantageous for elderly patients where intraoperative EBL, postoperative mobilization, and wound healing have profound implications [9].
MIDLF is an MIS fusion technique consisting of posterior lumbar interbody arthroplasty and posterior instrumentation using CBT screws [10]. Insertion with a divergent trajectory is advantageous for small cuts and tight screw fixation. First, CBT does not require an incision in the facet joint for insertion [10, 11]. Second, a biomechanical study was performed and reported a higher insertion torque of CBT screws than conventional pedicle screws [12]. This can be particularly important when performing lumbar fusion in elderly patients with low bone density. In addition, CBT requires less EBL than conventional pedicle screw insertion and requires only an interarticular incision without an enlarged incision of the mammary gland. Thus, the operating time is reduced.
Increased blood loss during lumbar spinal fusion correlates with increased muscle damage and dissection boundaries [13]. Another theoretical benefit of reducing blood loss is a reduced risk of blood transfusion and other complications in patients with comorbidities who are more sensitive to low postoperative hemoglobin levels. Since fusion may have a difference in operation time compared to decompression alone, we believe that side effects such as cerebral infarction and pulmonary complications are more likely to occur. Similarly, this study showed that lengthy surgery leads to a greater amount of blood loss, increasing the risk of postoperative complications and delaying functional pain relief.
The difference in EBL was still significant. This was expected since traditional PS implantation requires extensive exposure of the facet joints. We believe that the difference in the screw insertion method of fusion is the reason for the difference between the groups in the ODI and VAS scores of low back pain on the 7th day after fusion.
Complications were divided into postoperative complications and late complications, and there was a significant difference in late complications between the two groups. According to a study by Kobayashi et al., the risk factors for major complications (cerebral infarction, pulmonary embolism, coronary heart disease, and angina pectoris) after degenerative lumbar spine surgery were preoperative movement disorders, operation time, EBL, and instrument-assisted fusion in patients over 90 years of age [14]. In this study, postoperative pulmonary complications were found in the PLIF c PS group.
In addition, in the case of PLIF c PS, patients with cerebral infarction and postoperative hematoma required rehabilitation treatment due to motor weakness. Therefore, for elderly patients requiring fusion, selecting MIDLF, which has advantages in terms of EBL and operative time, would be a way to reduce major complications. Previous studies have also found that the amount of bleeding and operation time are related to the occurrence of complications [15].
In previous studies, the authors suggested performing decompression or fusion as needed without significant differences in complications [16, 17]. However, very old people over 80 years of age may have biological differences. Oldridge et al. reported an overall mortality rate of 0.5% in 34,418 Medicare patients who underwent lumbar spine surgery. For patients older than 80, the mortality rate of spinal fusion was greater than 10%. They concluded that the 80–85 years age group had the highest risk of a significant increase in morbidity and mortality for spinal fusion [18]. Therefore, MIDLF with less bleeding is advantageous when considering complications.
Average ASA and CCI values tended to increase with age, which was confirmed to increase the possibility of perioperative complications [19]. However, in this study, the MIDLF group had relatively few surgical scars, low blood loss, and short operation time, reducing the risk of complications and securing sufficient fixation. No statistically significant differences were observed in complications according to ASA and CCI values. We believe that a significant difference can be found if the number of cases is high.
The limitations of this study are: First, there are limitations in retrospective observation and analysis of a 10-year study conducted at a single institution. In addition, the indications for surgery in the two study groups were not exactly the same, and the preoperative status of patients differed between groups. Considering these limitations, we performed a statistical comparison of the basal conditions of the two groups before the operation and found no significant differences. Two spine surgeons participated in this study, and differences in surgical technique may have influenced the results. Additionally, due to the small number of cases, it is difficult to compare the results for each level, so the average of all levels of surgery was compared. The lack of long-term clinical follow-up is a final limitation, as the risk of recurrence is usually assessed over 5 years postoperatively in older patients [20]. In the case of octogenarians, from 80 to 85 years of age, natural death can occur. Considering these points, further studies may provide evidence that supports improved patient survival after MIDLF or PLIF c PS.