In recent years, with the advancement of medical technology, most patients with spinal disorders can be treated by surgery, which significantly improves their quality of life. However, due to the large surgical trauma, long operation time, and the need to implant exogenous fixation, the risk of postoperative infections in patients is relatively high (1). Some studies have shown that the high incidence of postoperative infections in spinal surgery patients not only prolongs the hospitalisation time of the patients, which is not conducive to wound healing, but may also lead to secondary surgery, which increases the difficulty of treatment and prognosis of rehabilitation, and has a serious impact on the patients' physical health and quality of life (2, 3). Neutrophils to lymphocytes ratio (NLR) can reflect the balance between inflammation-activated neutrophils and regulatory lymphocytes, and is one of the common indicators for diagnosing infectious diseases (4). Studies have shown that NLR demonstrates significant clinical value in the diagnosis of early infection in fracture patients undergoing surgery (5). In addition, CRP/ALB ratio, two proteins synthesised by liver cells, have different physiological functions. Specifically, CRP levels increase significantly when the body is exposed to microbial attack or tissue damage, while ALB, the most abundant protein in the serum, is mainly used to assess the nutritional status of patients. However, recent studies have also found an association between ALB and the inflammatory response triggered by infection. Therefore, the ratio of CRP/ALB ratio can be regarded as an indicator of inflammatory status in the body (6). Currently, the application of NLR and CRP/ALB ratio in predicting early infection after open fracture and bone arthroplasty has been investigated, however, they have been relatively less studied in the prediction of postoperative infections in patients with spinal disorders (7–9). In this study, we retrospectively analysed the clinical data of patients with osteoporotic vertebral compression fractures from January 2020 to December 2023, and used logistic regression to analyse the predictive risk factors for postoperative infection after spinal surgery, in order to provide effective preventive and therapeutic measures to prevent postoperative infections and improve surgical outcomes.

In recent years, with the aging of society, the incidence of spinal diseases has continued to climb, prompting more and more patients to prefer surgery as a means of treatment (10). However, factors such as prolonged operation time, the placement of internal fixation, and the decline in patients' physical fitness have all become high-risk factors for postoperative infection (11). Postoperative spinal infections not only significantly elevate the risk of patient mortality rates but also substantially increase healthcare expenditures for both patients' families and society as a whole (12). Therefore, the prevention of postoperative spinal infections has increasingly received widespread attention from all sectors of society. Laboratory indicators play a pivotal role in the diagnosis of postoperative orthopedic infections. Although bacterial cultures of incisional secretions and deep puncture fluids can provide important diagnostic clues, their longer detection period, lower positive rate, and possible contamination during specimen collection may affect the accuracy of diagnostic results (13). Meanwhile, peripheral blood leukocytes and CRP, as inflammatory markers, though they have reference value, face limitations in application due to susceptibility to factors such as immune status and inflammatory responses. In recent years, serum CD64, VEGF, SDF-1, NLR, and the CRP/ALB ratio have been increasingly recognized for their potential in early infection diagnosis. The aim of this study was to explore the application value of these indicators in predicting postoperative infections in patients with spinal disorders, thereby providing a scientific basis for clinicians to implement timely and effective interventions (14).

Neutrophils, lymphocytes, and thrombocytosis are important manifestations of systemic inflammation, and NLR and PLR calculated from the above indicators can more accurately reflect the severity of systemic inflammation, therefore, NLR and PLR have been gradually used in the diagnosis of postoperative spinal infections and their complications (15). NLR is the ratio of neutrophils to lymphocytes, which is a readily available indicator. It can exclude the effects of excessive body fluids, dehydration, and specimen handling (16). NLR is also a reliable indicator for the assessment of conditions such as infections, chronic obstructive pulmonary disease, and cancer (17). In our case, NLR levels were significantly higher in the infected group compared to the non-infected group. The multifactorial lo gistic regression model corrected for confounders still suggested an association between NLR level showed an independent association with postoperative infection. Therefore NLR can be used as a predictor of postoperative spinal infection. The mechanisms may be 1. neutrophils, as an important participant in the immune response to infection, arrive at the site of inflammation under the action of chemokines to phagocytose and kill pathogenic bacteria (18); and 2. lymphocyte apoptosis is increased in the state of immuno inflammation. The NLR can reflect changes in both neutrophil and lymphocyte levels, and thus its changes are more effective in reflecting the presence of infection than a single indicator (19).

CRP is an acute temporal response protein synthesised by the liver, which is an important component of the immune system and enhances phagocytosis by some CRP-expressing receptor macrophages (20). Studies have shown (21) that CRP is significantly associated with postoperative infections and complications. Wei Kewei et al. (22) found in a retrospective study of primary total knee replacement patients that a CRP level of 35 mg/L was the best diagnostic for periprosthetic infection, which could be used as a diagnostic basis for postoperative infection. In a study of postoperative complications in patients with Crohn's disease, Xu Xin et al. (23) showed that serum CRP levels have a predictive value for the occurrence of postoperative infectious complications in the abdominal cavity. In this study, serum CRP was significantly higher in the postoperative complication group than in the uncomplicated group of orthopaedic patients, suggesting that serum CRP levels may be intrinsically related to the occurrence of postoperative complications. CRP/ALB ratio levels are a good reflection of microvascular permeability, and there is a certain correlation between the levels and the degree of capillary leakage, which is one of the pathological features of organic infection (24). However, when a patient develops an infection, the liver synthesises stress response proteins such as CRP, which in turn reduces the amount of ALB synthesis, leading to an increase in CRP/ALB ratio levels (25). Therefore, elevated CRP/ALB ratio level was significantly associated with postoperative spinal infection.

The results of this study show that, based on the sensitivity analysis, Post-CRP/ALB ratio has the strongest predictive power (AUC = 0.878,95% CI: 0.845–0.909), indicating that the combined indicator of inflammation and nutritional status is significantly valuable for predicting outcomes; Age and Post-NLR have AUCs of 0.770 and 0.791, respectively, suggesting moderate predictive power for age and postoperative inflammatory response; Blood transfusion has the lowest AUC (0.577, 95% CI: 0.549–0.637), with its confidence interval approaching the random guess level (0.5), indicating limited predictive value of a single transfusion indicator. Overall, the results suggest that postoperative inflammatory-related indicators (such as Post-CRP/ALB ratio, Post-NLR) and age are core predictive factors, and their application potential needs to be further validated in clinical context. The results of multifactorial logistic regression analysis showed that older age, longer duration of surgery, intraoperative blood transfusion, use of internal fixation, and elevated postoperative NLR and CRP/ALB ratio suggested an increased risk of postoperative infection and the need for timely measures to prevent infection.

This study innovatively demonstrates the synergistic value of the neutrophil-to-lymphocyte ratio (NLR) and C-reactive protein/albumin ratio (CRP/ALB) in predicting postoperative spinal infections, addressing a critical evidence gap in biomarker applications for this field. Distinct from prior orthopedic research, this work is the first to systematically validate the superior predictive efficacy of postoperative CRP/ALB (AUC = 0.878, sensitivity 97.5%, specificity 80.7%) and NLR (AUC = 0.791) in a large-scale spinal surgery cohort (n = 380), establishing spine-specific optimal cutoff thresholds of CRP/ALB > 2.67 and NLR > 6.2. Crucially, multivariate regression reveals a unique high-risk architecture inherent to spinal surgery: internal fixation implantation emerged as the strongest independent risk factor (OR = 8.022, P < 0.001), which—together with operative duration and intraoperative blood transfusion—constitutes core procedural variables for spinal infection. Meanwhile, postoperative markers of inflammation-nutrition imbalance (CRP/ALB) and immune stress (NLR) are intrinsically linked to the pathophysiological processes triggered by deep-tissue trauma and implant placement. This model not only provides a highly sensitive tool for early infection detection but also establishes a dedicated risk assessment framework integrating surgical interventions and host response, thereby facilitating the development of individualized clinical prevention strategies.

However, this study also had the following limitations: i. it was a retrospective case study, which may have a selective bias of its own, in addition to the fact that it was not possible to radiologically screen all patients undergoing spinal surgery, which may have affected the results; ii. the sample for this study came from only one hospital database, which may have affected the generalisability of the results, and subsequent multi-centre, large-sample studies are still needed; iii. it was only internally validated, with the Lack of external datasets for further validation of the predictive ability of column line plots; iv. Future studies can explore the integration of Post-NLR and Post-CRP/ALB ratio indicators into a composite prediction model to further improve the discrimination ability; and v. In future clinical trials and cohort studies, gender must be analyzed as a key stratification or covariate to avoid masking true efficacy or risk or drawing biased conclusions due to the omission of gender factors. This will help obtain more reliable and generalizable results.

The results of this study suggest that the risk factors for postoperative spinal infection are multifactorial, including (age, surgery time, blood transfusion, internal fixation, postoperative NLR and postoperative CRP/ALB ratio, which may serve as potential predictors of postoperative spinal infection.