Introduction

Lumbar spinal stenosis (LSS) is a pathology where there is a narrowing of the spinal canal, that may compress nerve roots. Clinically expressed with lumbar pain radiating to the lower limbs and/or neurogenic claudication.  LSS diagnosis has been increasing thanks to the use of Magnetic Resonance Imaging (MRI) and Computed Axial Tomography (CT scan). Degenerative lumbar stenosis (DLS) is the most common cause of spine surgery in patients over 55 years of age [1].

From an anatomical point of view, lumbar stenosis can be classified according to the location where the narrowing occurs: central, lateral recess, or foramina [2]. The most frequent cause is degenerative, affecting the facet joints and intervertebral discs, occasionally associated with pathologies such as scoliosis or spondylolisthesis [3].

There is currently no precise data on the prevalence of this condition. However, a meta-analysis published in the European Spine Journal in 2020 found that clinical diagnoses were present in 11% of the general population, while diagnosis through radiological imaging was present in 38%Most studies on the topic were conducted in North America, Japan, and Europe, which means they may not apply to the Chilean population. Additionally, 68% of the articles studied had a representativeness bias, indicating that the available information is limited. This suggests that more research is needed to fully understand the situation in Chile. [4].

Regarding treatment, the first preference should be conservative treatment. This includes the use of analgesics, NSAIDs or opioids, physiotherapy, and even infiltration of the spine with epidural steroid injections, and facet joint blocks. Surgery should be considered in severe cases where medical treatment has proven ineffective, and the patient is experiencing severe pain, neurological deterioration, and a decrease in their overall quality of life [5].

When surgery is decided, there are two options: surgery with decompression alone and surgery with decompression and spinal fusion (arthrodesis). It is important to note that Lumbar Fusion surgery typically involves the use of spinal instrumentation. Decompression surgery with or without fusion aims to relieve radicular pain, reduce low back pain, and improve quality of life.

Currently, there are no clinical or epidemiological data available in Chile to predict the appropriate surgical technique, although numerous factors influence the decision-making process regarding which technique to use [6].

In 1982, a system called “diagnosis-related groups” or DRGs was created at Yale University by Dr. Robert B. Fetter and his team. It was developed to bring standardization to the healthcare industry, particularly regarding managing funds. The DRG system uses classification algorithms that categorize patients into groups with similar clinical and resource consumption characteristics, using ICD-9 and ICD-10 coding. This system helps hospitals quantify, standardize, and compare processes, generate indicators for benchmarking, and optimize health management systems. It’s considered to be the most accurate funding mechanism because it can assess the complexity of each hospital. Since 1982, DRGs have been used as a payment tool and have become widespread and diversified. They expanded worldwide in the 1990s and became the primary method of financing in Europe and Oceania. In Asia and Latin America, DRGs were introduced as a mixed method.

Chile is recognized as one of the most advanced countries in Latin America in the use of the DRGs system. In 2010, they implemented the “International-Refined DRG” (IR-DGR) system, which has been incorporated into the national financing policy through the budget law. FONASA, Fondo Nacional de Salud (it means National Health Fund), has included this system since 2020. Currently, GRDs have been implemented in 86 healthcare centers in the public network[10].

The following study aims to utilize the data available in the DRG system of Chile to identify the clinical and epidemiological variables of patients who undergo surgery for degenerative lumbar stenosis. This study aims to determine the factors that could influence the choice of using arthrodesis as a complement to decompression.

Material and Method

A retrospective observational study was conducted on patients with a diagnosis of lumbar or lumbosacral stenosis, obtained from the national database of diagnosis-related groups (DRGs), requested by the Transparency Law from the Chilean Ministry of Health.

The database includes information from 31 public hospitals in Chile, covering patients discharged between 2020 and 2022. The study variables were obtained from MBDS (Minimum Basic Data Set), which uses ICD-10-WHO (2013) nomenclature for diagnoses and ICD-9-MC 32.0 (2014) for procedures. The current classification system is IR-DRG, version 3.0.

The inclusion and exclusion criteria are described below:

The study aimed to identify variables predicting the need for fusion in patients with degenerative lumbar spinal stenosis, discussing their epidemiological and clinical features. The study considered the following factors: age, gender, presence of other spinal pathologies (such as scoliosis, spondylolisthesis, herniated disc, and degenerative osteoarthritis/arthrosis), and the specialty of the attending physician.

Statistical Analysis

For the descriptive analysis of qualitative variables, frequencies and percentages with 95% confidence intervals (CI) were used. The “difference of proportion hypothesis test” was used to assess significant differences between the two groups.

The study used the median and interquartile range to describe quantitative variables and the Mann-Whitney U test to compare groups.

The study used both univariate and multivariate logistic regression analysis to estimate Odds Ratios with a 95% CI. The stepwise method was used for the multivariate model, with a significance level of 0.05 and 0.1 for including and eliminating variables in the final model, respectively. The Hosmer-Lemeshow test was used to evaluate the goodness-of-fit of the model, and the area under the ROC curve was used to assess the discriminant capacity.

For all tests, a statistical significance of less than 0.05 was considered. Data were analyzed in STATA version 15.1 software.

Results

A total of 1024 patients were analyzed with lumbar spinal stenosis, out of which 54.6% (CI: 51.5-57.6%) were female and

45.4% (CI: 42.4-48.5%) were male (p= 0.0034). Among them, 39.1% were aged between 40 and 59 years, 57.4% were between 60 and 79 years, and 3.5% were 80 years or older (p=0.0000). The majority (51.1%) of patients with degenerative spinal stenosis underwent surgery in the metropolitan region, Santiago de Chile, and 48.9% in regional hospitals (p=0.5960). According to a study, 64.5% of patients who underwent surgery in Chile for degenerative lumbar spinal stenosis were operated on by neurosurgeons, while 35.5% were operated on by orthopedic surgeons (p=0.0000). This difference is mainly because, in regional hospitals, 86% of patients were operated on by neurosurgeons. In Santiago, 44% of patients were treated by this specialty (p=0.000).

We have identified several common health conditions among the patients. The data shows that 51.0% (CI: 47.9-54.0%) of patients have arterial hypertension, with an equal prevalence among men and women. Additionally, 20.1% (CI: 17.8-22.7%) of patients have non-insulin-dependent diabetes mellitus, with a slightly higher prevalence among women (18.1% men and 21.8% women; p=0.1414). Obesity of all types was found in 12.4% (CI:

10.5-14.6%) of patients, with a higher prevalence among women (9.0% men and 15.2% women; p=0.0027). Similarly, dyslipidemia was found in 11.4% (CI: 9.6-13.5%) of patients, with no significant difference in prevalence between men and women (10.3% men and 12.3% women; p=0.3159). Finally, hypothyroidism was found in 10.8% (CI: 9.1-12.9%) of patients, with a significantly higher prevalence among women (4.7% men and 15.9% women; p=0.0000).

The patients diagnosed with lumbar spinal stenosis frequently had other spinal pathologies associated with their condition. The most common among these were herniated discs, which affected 20.8% (CI: 18.4-23.4%) of patients, with a slightly higher prevalence in men (22.6%) than in women (19.3%) (p= 0.1952). Lumbar spondylolisthesis was found in 18.0% (CI: 15.720.4%) of patients, with a higher prevalence in women (22.9%) than in men (12.0%) (p=0.0000). Osteoarthritis and degenerative osteoarthrosis of the spine were found in 6.2% (CI: 4.8-7.8%) of patients, with similar prevalence in men (5.6%) and women (6.6%) (p=0.5071).

Regarding surgical treatment, 56.3% of the patients underwent decompression alone, while 43.7% underwent decompression and arthrodesis (p=0.0000).

We compared the baseline characteristics of the population and provided statistical comparisons between Decompression alone and Decompression with Fusion (Table 1).

Table 1: Baseline characteristics of the population, by type of surgery.

We analyzed the length of stay (LOS) of patients who underwent decompression alone versus those who had decompression with fusion. We found a significant difference in the LOS between these groups (p<0.0000). Patients operated on by neurosurgeons who underwent decompression with fusion had a longer LOS compared to patients operated on by orthopedic surgeons (Table 2).

Table 2: Days of hospitalization (length of stay) for patients with lumbar spinal stenosis based on surgery type and specialty

Univariate analysis was performed to assess the association between each predicting factor and the surgical option for decompression with fusion. The most significant predictors of the univariate model were the attending physician’s specialty in orthopedic surgery, female sex, and the presence of other spinal pathologies such as scoliosis, herniated disc, and spondylolisthesis (Table 3).

In our study, we found that 75% of orthopedic surgeons performed decompression plus arthrodesis on patients operated for lumbar stenosis, while neurosurgeons performed decompression alone in 73% of the cases when it did not consider other spine pathologies (such as spondylolisthesis or scoliosis).

The univariate analysis indicates that the probability of a patient with lumbar stenosis undergoing decompression plus arthrodesis increases 8.2 times if treated by an Orthopedic Surgeon compared to those treated by a Neurosurgeon.

Another variable that conditions the surgical decision in lumbar spinal stenosis is the presence of spondylolisthesis (in the absence of herniated disc and scoliosis), increasing 6.2 times decompression plus arthrodesis and 6.6 times in the presence of scoliosis (in the absence of spondylolisthesis and Herniated Disc).

Among patients diagnosed with both lumbar spinal stenosis and spondylolisthesis, 89.8% of those treated by an orthopedic surgeon and 71.8% of those treated by a neurosurgeon underwent decompression plus arthrodesis surgery (p=0.0089). On the other hand, in patients with spinal stenosis without spondylolisthesis, 64.6% of patients treated by an orthopedic surgeon and 35.4% of those treated by a neurosurgeon underwent decompression plus arthrodesis surgery. The difference was statistically significant (p=0.0000).

In patients with lumbar spinal stenosis and herniated disc, decompression is the predominant surgical decision by neurosurgeons, with a rate of 89.7%. However, for orthopedic surgeons, the rate reduces to 48.9% (p=0.0000).

Neurosurgeons tend to opt for decompression alone (75%) when treating patients with lumbar spinal stenosis plus spondylolisthesis with a herniated disc. On the other hand, orthopedic surgeons only choose this procedure 10% of the time (p=0.0000). This preference remains the same for spondylolisthesis without herniated disc cases treated by orthopedic surgeons. However, neurosurgeons tend to reverse their decision and opt for decompression plus instrumented arthrodesis (71.8%) in such cases.

Table 3: Univariate analysis of predictors for the surgical alternative of decompression plus fusion in patients with lumbar spinal stenosis.

The predictive utility of the multivariate model was found to be 0.82. The model takes into account the following variables to determine the surgical option for decompression plus arthrodesis: Orthopedic Surgeon, presence of scoliosis, presence of spondylolisthesis, absence of herniated disc, and age between 40 to 59 years (Table 4).

Table 4 shows the results of the multivariate analysis of predictors for the surgical alternative of decompression plus arthrodesis in patients with lumbar spinal stenosis. The constant value is 0.24 (CI of 0.18-0.31).

Discussion