Can abdominal aortic calcification detected on lateral lumbar radiography predict instrument-related complications in patients undergoing posterior lumbar fusion?
Article information
Abstract
Objective
Abdominal aortic calcification (AAC) is well known as a useful and simple clinical indicator of the risk of fracture and cardiovascular disease. However, no studies have directly compared the postoperative implications of AAC in spinal surgery. The purpose of this study was thus to examine whether extended AAC (scores ≥5) negatively affected clinical outcomes after posterior lumbar fusion with instrumentation for degenerative lumbar stenosis or degenerative spondylolisthesis.
Methods
The subjects comprised 101 consecutive patients with spinal stenosis or degenerative spondylolisthesis who underwent posterior lumbar fusion and instrumentation between January 2016 and January 2019 and were followed for over 2 years. Propensity score matching was employed to assemble patient groups with similar baseline characteristics. Postoperative complications and radiologic outcomes were compared between the groups (33 patients in each) divided by extended AAC score.
Results
The incidence rates of junctional failure (6.1% vs. 30.3%, P=0.008) and screw-related complications (12.1% vs. 36.4%, P=0.019) were higher in the extended AAC group than in the mild AAC group. However, the rates of adjacent segment disease (24.2% vs. 36.4%, P=0.283) and revision (6.1% vs. 9.1%, P=0.642) were not significantly different between the 2 groups. In terms of postoperative medical complications, cardiovascular and cerebrovascular diseases were significantly more common in the extended AAC group than in the mild AAC group (0% vs. 15.2%, P=0.020).
Conclusion
Extended AAC indicates increased risk for postoperative junctional failure and screw-related complications, regardless of age, osteoporosis, and comorbidities.
Introduction
Bone metabolism involves a continual cycle of bone growth and resorption orchestrated by the dynamic relationship between osteoclasts, osteoblasts, and an array of hormonal and regulatory factors [1,2]. Several studies demonstrate an impact of bone turnover on the development of arterial calcification, and there is some evidence of reduced progression of vascular calcification (VC) with improvements in bone status [3].
VC can be the most dramatic consequence of chronic kidney disease. In the past, VC was thought to be a passive process of crystallization caused by an increase in calcium and phosphorus and their deposition on blood vessel walls. However, in the last 10 years, considerable progress has been made in identifying the mechanisms of VC. VC is an actively regulated process caused by a decrease in various calcification inhibitors, such as fetuin-A, pyrophosphate, matrix glycoprotein, BMP-7, genetic polymorphisms in these factors [4,5], old age, dialysis, and mineral bone metabolism abnormalities [6]. The process of VC is associated with increased arterial stiffness [7,8] and is a risk factor for cardiovascular events such as increased cardiac afterload and congestive heart failure.
Calcium and phosphorus concentrations significantly correlated with arterial calcification, and a non-significant association between bone mineral density (BMD) and arterial calcification has been reported [9]. In contrast, markers of bone turnover, such as P1NP, in patients on hemodialysis negatively correlate with calcification scores. Low markers of bone turnover can mediate impaired bone metabolism and exacerbate the body’s inflammatory response, leading to VC and increasing the risk of hemodialysis-related VC [10].
Previous studies have shown that osteoporosis is associated with proximal junction failure after spinal surgery [11]. Additionally, low BMD is an important risk factor for proximal junctional failure (PJF), and surgeons should consider prophylactic treatment when correcting adult spinal deformity (ASD) in patients with low BMD [12]. Regarding the association between arterial calcification observed on radiography and complications after spinal surgery in patients with osteoporosis, we have investigated this association.
Previous studies have revealed an association between abdominal aortic calcification (AAC) and complications after spinal surgery. For example, one study reported that calcification of the abdominal aorta can predict poor prognosis in patients who have undergone posterior decompression surgery [13]. Another study reported that AAC had a significant negative effect on the incidence of ASD after lumbar fusion. This finding reveals impaired blood flow due to atherosclerosis can exacerbate degenerative changes in adjacent segments [14].
This study investigated whether AAC could affect complications such as ASD after lumbar fusion, along with complications related to screws and cages.
Purpose
AAC is a useful and simple clinical indicator of the risk of fractures and cardiovascular diseases [11,15,16]. However, no studies have directly compared AAC’s postoperative effects in spinal surgery. Thus, this study aimed to examine whether extended AAC (≥5 scores) negatively affects clinical outcomes after posterior lumbar fusion with instrumentation for degenerative lumbar stenosis or spondylolisthesis.
Material and Method
ASD is a broad term that encompasses many complications of spinal fusion, including listhesis, instability, herniated nucleus pulposus, stenosis, hypertrophic facet arthritis, scoliosis, and vertebral compression fractures [17]. In this study, patients with listhesis, instability, herniated nucleus pulposus, and stenosis observed on retrospective images were included as patients with ASD.
Proximal junctional kyphosis (PJK) and PJF are complications of long-instrumented posterior fusion for ASD surgery. PJK is a radiological phenomenon of adjacent segment pathology and involves ongoing adjacent segmental problems at the transition between the fused and mobile segments. PJK has a spectrum of disease severity, ranging from no clinical symptoms to clinical symptoms that may require revision surgery. PJF is a progressive process in the spectrum of PJK and involves structural failures, such as vertebral body fracture, posterior ligament complex, or both, and vertebral subluxation. Patients with PJF may present with higher morbidities, including pain, neurological deficits, and revision surgery [18]. In this study, patients with vertebral body fractures and posterior ligament complex injuries observed on retrospective imaging were included as patients with junctional failures.
The subjects of this study comprised 101 consecutive patients with spinal stenosis or degenerative spondylolisthesis who underwent posterior lumbar interbody fusion and instrumentation between January 2018 and January 2020 and were followed for ≥2 years. Propensity score matching was used to assemble patient groups with similar baseline characteristics. Postoperative complications and radiologic outcomes were compared between the groups (each 33 patients) and were further investigated for associations with extended AAC scores (≥5 scores). According to the scoring system of Kauppila et al. [19], the AAC score (a surrogate marker of systemic atherosclerosis) was assessed using preoperative lateral radiographs of the lumbar spine.
According to Abdellah’s study of the correlation between AAC and vertebral fracture in an elderly patient cohort, significant results were shown between patients with AAC scores of less than 5 and those with scores of 5 or more. Therefore, this study compared patient groups based on AAC scores above and below 5 (Fig. 1) [15].
This retrospective study was approved by the Institutional Review Board of Bundang Jaesaeng General Hospital (DMC 2024-02-007). Informed consent was obtained from all individual participants included in this study.
Results
Each of the 33 control groups that were selected through propensity score matching did not show significant differences in sex (15:18 vs. 20:13, P=0.217), mean age (75.24±4.77 vs. 76.82±7.41, P=0.308), body mass index (25.48±3.62 vs. 26.31±4.15, P=0.390), BMD (−1.63±1.02 vs. −2.06±0.95, P=0.087), osteoporosis (18.2% vs. 33.3%, P=0.157), operative time (312.81±98.91 vs. 329.09±123.80, P=0.561), and estimated blood loss (690.63±458.86 vs. 721.21±502.97, P=0.799) (Table 1).
The prevalence of junctional failure (6.1% vs. 30.3%, P=0.008) and screw-related complications (12.1% vs. 36.4%, P=0.019) were significantly higher in the extended AAC group than in the mild AAC group. The screw-related complications included screw pull-out, screw fractures, and screw halos. Furthermore, adjacent segment disease (24.2% vs. 36.4%, P=0.283) and revision (6.1% vs. 9.1%, P=0.642) rates did not differ between the 2 groups (Table 2).
In terms of postoperative medical complications, cardiovascular disease (0% vs. 6.1%, P=0.151), cardiovascular disease (0% vs. 9.1%, P=0.076), surgical site infection (3.0% vs. 3.0%, P=1.000), and renal failure (0% vs. 3.0%, P=0.314) showed no significant differences between patient cohorts. However, cardiovascular and cerebrovascular diseases were significantly more common in the extended AAC group than in the mild AAC group (0% vs. 15.2%, P=0.020) (Table 3).
Discussion
Previous research has shown that blood calcium and phosphorus concentrations and various other factors affect AAC [9,20]. Therefore, extended AAC is associated with excessive bone resorption and bone weakening, which frequently leads to device-related complications [21]. In agreement with this correlation, the findings of this study revealed that certain complications, such as postoperative instrument dislocation, can be predicted through a simple lumbar radiography test.
The biggest problems after deformity or multilevel fusion surgery are instrument-related complications, ASD, and nonunion (fusion). Various methods exist to evaluate the risk of these postoperative complications [22], such as a global alignment proportion score [23,24], Scoliosis Research Society-Schwab classification [25], and Roussouly classification [26]. However, these evaluation methods are somewhat complicated, usually performed as a retrospective evaluation after surgery, and are not intuitive, making them difficult to apply in clinical practice. The results of this study can be used to intuitively screen for the possibility of complications after surgery through a simple preoperative plain lumbar radiograph. A similar study used preoperative computed tomography (CT)-based Hounsfield units (HU) in patients with ASD to identify those at high risk for bone PJK. This study showed a significant inverse relationship between the mean HU at the upper instrumented vertebra (UIV) and UIV+1 and the postoperative increase in the PJK angle [27]. Similar to the findings of this study, a previous study showed that the HU value of the UIV or L4 on CT could predict the risk of PJF in female patients with ASD undergoing lumbar interbody fusion [28]. Thus, our findings confirm that complications after posterior lumbar fusion surgery can be predicted with a simple X-ray test, compared to a relatively complex CT scan, and prevent excessive exposure to X-rays.
The findings of this study reveal that it is possible to predict future prognosis and decide whether to perform posterior fusion with a simple preoperative X-ray test. In particular, we confirmed a positive correlation between extended AAC and junctional failure and between extended AAC and screw-related complications. However, there was no significant correlation with medical conditions, such as cardiovascular disease, stroke, or renal failure.
Second, there have been no studies on AAC in spinal surgery, although several studies have shown that AAC is associated with bone metabolism [3,20]. The findings of several studies have demonstrated the impact of bone replacement on the development of arterial calcification, and there is evidence that improvement in bone condition may reduce the progression of VC [3]. This scale is considered a good tool for predicting device-related complications, such as postoperative fusion, screw loosening, and cage migration.
The association between AAC and various internal medical diseases has been partially revealed, with additional research ongoing. Although our study did not show a significant correlation between AAC and other medical conditions, many other studies have shown significant correlations. One study reported a positive correlation between AAC and factors such as old age, high blood pressure, and smoking. Furthermore, AAC is associated with an increased risk of death, coronary heart disease, and stroke. Aortic calcification predicts an increased incidence of cardiovascular events. However, the reason for this association requires further investigation [29]. In situations where AAC is emerging as an important factor that increases cardiovascular death and overall mortality beyond simple bone metabolism, using AAC before spinal surgery is thought to help predict the development of postoperative medical complications or the postoperative course of patients [29–31].
The first limitation of this study was that it was impossible to match underlying diseases and laboratory values between groups. For example, more patients in the extended AAC group had renal dysfunction, which can adversely affect postoperative complications independent of AAC. In addition, because the number of comparison groups was small, future studies should include more patients. Finally, this was a study on complications within 2 years of surgery. Thus, further research on complications over a longer period is required.
Conclusion
Extended AAC is an indicator of an increased risk of prevalent postoperative junctional failure and screw-related complications, regardless of age, osteoporosis, or comorbidities. In addition to lumbar fusion, prognosis can be easily predicted through AAC in all surgeries that use instruments, such as deformity surgery. AAC may be helpful in decision-making and preoperative counseling regarding the risks and benefits of surgery.
Notes
Conflict of Interest
No potential conflict of interest relevant to this article was reported.