Perioperative AKI is a pathological condition that has attracted attention mainly in the field of cardiac surgery, where postoperative AKI is reported to be associated with a high rate of respiratory infections, gastrointestinal bleeding, sepsis and postoperative death [1, 2]. Even if AKI is mild and renal function recovers, the onset of AKI itself has been reported to be associated with poor prognosis [1, 2]. The incidence of AKI following cardiac surgery has been reported to range from 12.4–39% [10–12]. In the field of orthopedic surgery, including joint replacement procedures such as total hip, knee, and shoulder joint surgeries, the incidence of AKI ranges from 1.8–8.2% [4, 13]. For spinal surgeries, the reported incidence of AKI is between 1.6% and 3.9% [14–16], while in spinal surgeries for individuals aged 80 and above, it has been reported to be 0–2.7% [17, 18]. Factors associated with the onset of AKI include preoperative factors such as chronic renal dysfunction, diabetes, hypertension, anemia, liver dysfunction, and muscle injury. Intraoperative factors encompass surgical invasion, hypotension, renal ischemia, anesthetic agents, while postoperative factors include decreased circulating blood volume, decreased cardiac output, renal ischemia, medications such as NSAIDs and antibiotics, acute lung injury, and inflammatory reactions [3, 4, 15]. In this study, the extent to which the surgical invasiveness of MIS-PLIF/TLIF affects renal function was particularly investigated. According to previous reports, the surgical invasiveness associated with posterior lumbar single-level interbody fusion surgery, as assessed by postoperative CPK levels on the day after surgery, ranged from an average of 387 to 907 U/L in MIS-TLIF [19, 20]. In contrast, traditional open TLIF procedures showed CPK levels ranging from 739 to 1004 U/L [19, 21]. In this study, CPK levels in the 80 + group were 637 ± 334 U/L, and 725 ± 398 U/L in the 60–79 group. Rhabdomyolysis did not occur in patients over 80 + group, but did occur in two patients in the 60–79 group. The incidence of rhabdomyolysis after spinal surgery ranges from 1.6–22.4% [14, 22] and 10–30% of rhabdomyolysis cases are reported to develop AKI [23]. Risk factors for the development of rhabdomyolysis due to surgery include operating time lasting more than 4 hours and obesity [24]. The causes of rhabdomyolysis due to spinal surgery have been presumed to include the compression and displacement of paraspinal muscles due to surgical procedure and the compression of the psoas muscle associated with the supine position[25]. Severe outcomes of AKI due to rhabdomyolysis after spinal surgery were reported in two cases: a 60-year-old and a 63-year-old who underwent lateral lumbar interbody fusion (LIF) with fixation from Th10 to L4 and fixation from L1 to L4, respectively. Postoperatively, CPK levels rose to 24,704 U/L and 26,800 U/L, necessitating dialysis [14]. Additionally, a 29-year-old female who underwent posterior decompression and fusion surgery for thoracic ligament ossification developed postoperative rhabdomyolysis, with CPK levels reaching 49,735 U/L. This led to AKI progressing to multi-organ failure, and the patient succumbed on the 12th postoperative day [26]. These reports highlight extreme cases with markedly elevated CPK levels, and there are studies suggesting that AKI is unlikely to occur if CPK is below 5000 U/L [27]. On the other hand, there are reports suggesting a CPK cutoff value of 773 U/L for the onset of AKI due to rhabdomyolysis [28]. Therefore, careful postoperative monitoring based on CPK levels is deemed necessary. It has been pointed out that the mechanisms underlying the development of acute kidney injury (AKI) due to rhabdomyolysis involve the massive influx of muscle cell contents, specifically myoglobin and heme, into the circulating plasma. This influx leads to the excessive production of iron ions and reactive oxygen species, ultimately resulting in necrosis of renal tubular cells [29, 30].
In this study, two cases of rhabdomyolysis were observed in the 60–79 group, with four cases showing a one-grade deterioration in postoperative renal function compared to preoperative levels on the 7th day. However, in the 80 + group, neither rhabdomyolysis nor AKI was identified. Two cases of rhabdomyolysis were observed in the 60–79 group, which may reflect differences in muscle mass, as the 80 + group weighed significantly less than the 60–79 group.
These results suggest that single intervertebral MIS-PLIF/TLIF might be performed relatively safely even in patients over 80 years of age, including those with preoperative renal function of Grade 3b or lower.
The limitations of this study include the small number of cases in each group and the lack of consideration for comorbidities, fluid volume, and urine output. It is deemed important for future research to accumulate more cases and thoroughly investigate these factors for a comprehensive understanding.