The main complication after midline laparotomy is incisional hernia (IH), with an prevalence of 12.8% at 23.8 months of follow-up [1, 2], although values of up to 69% have been reported in high-risk groups [3]. This prevalence is related to the study population evaluated, the type of incision made, and the methods of follow-up and with which the hernia is diagnosed [3–5].

IH not only results in morbidity associated with chronic pain, functional limitations and deterioration in quality of life but is also associated with a substantial economic burden related to the need for reinterventions [6]. In the United States, the cost of care for this complication is 4 billion dollars per year; a cost reduction of 32 million dollars has been estimated for every 1% decrease in the prevalence of IH [7]. Taken together, these data justify efforts to prevent the occurrence of this complication [2].

There is no single determining risk factor for the occurrence of IH, and the effects of each of the factors are cumulative; hence, not all patients have the same risk of developing an IH [2, 8]. Although preventative efforts have focused on optimizing the surgical technique used to close the incision or the use of prophylactic meshes [3], IH nevertheless occurs more frequently in patients with predisposing factors such as obesity [9], surgical site infection [10], malnutrition, the use of immunosuppressants and chronic diseases such as liver disease. More concerningly, several of these factors are unmodifiable, at least in emergency surgery settings [11].

Despite the multiple studies that have addressed factors associated with the development of IH and developed predictive scores, the results have been heterogeneous and sometimes contradictory. This inconsistency refers to the variation in reported clinical significance for the same factor. For instance, regarding male gender, Ganesh et al. [12] report finding no association, whereas Rios-Diaz et al. [13] report male gender as a statistically significant risk factor. Similarly, for Body Mass Index (BMI), Ganesh et al. [12] identify a significant risk for BMI >25 kg/m², whereas Tecce et al. [14] report significance only for BMI >30 kg/m², finding no association for BMI <30 kg/m². Some predictive models have shown clinical utility, but their applicability is limited by the lack of external validation, the inclusion of postoperative variables that are unavailable at the time of surgical decision-making, and the lack of stratification by type of patient or procedure [15].

The evidence on IH risk arises from heterogeneous study populations that combine different surgical approaches. Given the fundamental anatomical and pathophysiological differences between a full-length midline fascial incision and minimal-access port sites (which involve distinct risk profiles, prevention strategies, and even clinical guidelines), a synthesis focused specifically on open midline laparotomy is warranted. This approach ensures methodological homogeneity and provides clinically actionable evidence for the high-risk patient population that requires this specific surgical access, often in settings of emergency, complexity, or contraindication to minimally invasive techniques.

The objective of this study was to quantitatively evaluate the relative impact of relevant risk factors on the prevalence of IH after midline laparotomy through a meta-analysis of cohort studies to identify the specific magnitude of the effect of each factor. This analysis will establish a hierarchy of risk factors, providing solid evidence to guide clinical decision-making while also identifying the actual prevalence of IH associated with midline laparotomy.

The rationale for establishing this hierarchy is to move beyond a mere list of associations and create a clear, actionable framework for clinical practice. By stratifying risk, the findings can directly guide the intensity of preventive strategies: from mandating advanced measures like prophylactic mesh for high-risk patients to optimizing standard care for others. This approach personalizes management, prevents intervention fatigue, and focuses resources where they offer the greatest benefit.

A meta-analysis was conducted and reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines [16]. The study was registered with the hospital research and research ethics committees of the hospital, with registration numbers CEI/HRAEB/002/2025 and CEI-001-2025 and in the International Registry for Prospective Systematic Evaluations in PROSPERO (registration number: CRD420251107739) [17].

The European Hernia Society (EHS) guidelines for abdominal wall closure, published in 2015 and updated in 2022, report an prevalence of IH of 12.8% [2, 3] on the basis of the results of a meta-analysis by Bosanquet et al. (2015) [1]. However, that study presents several methodological biases that must be considered. First, 48% of the studies included were clinical trials, a design that is not ideal for estimating prevalence, since it is limited by the population defined by the inclusion criteria (for example, patients with obesity or aortic aneurysm, which does not represent the general population) [34, 35].

Second, 44% of the clinical trials included involved use of a laparoscopic approach. Pooling data from both open and laparoscopic procedures introduces substantial clinical heterogeneity and potential confounding, since the prevalence of IH differs substantially between these approaches, a fact recognized by the EHS guidelines, which state that laparoscopy reduces IH risk. Therefore, the aggregated prevalence reported by Bosanquet et al. may not accurately reflect the risk specific to open surgery. In contrast, by design, our meta-analysis focused exclusively on open midline laparotomy, and by excluding studies involving laparoscopic approaches, our pooled prevalence estimate is specific to the open midline laparotomy population. Consequently, our pooled prevalence estimate (10.1%) provides a more precise and directly applicable measure of risk for the specific patient population undergoing open abdominal surgery.

Finally, 38% of the included studies were conducted in the 1980s and 1990s, when both the imaging methods and the surgical techniques used substantially differed from those currently in use, which could have led to overestimations of the reported prevalence.

In this study, we reported an prevalence of IH of 10.1% at 39.6 months of follow-up. Only data from cohort and cross-sectional studies were analyzed; clinical trials and studies involving laparoscopic approaches were excluded. Consequently, our estimate specifically reflects the risk in patients undergoing open surgery. However, two important factors should be noted in the evaluation of this result: 1. Among the included studies, some involved diagnoses obtained from the patients’ files, while in others, patients who underwent IH repair were identified during the study period. Consequently, one potential bias is related to the fact that 16%–44% of patients with IH are usually asymptomatic [24, 36]; additionally, it has been reported that among patients with hernia, only 6.6%–20% end up undergoing surgical repair [26, 32, 37]. 2. Analyses of retrospective and prospective studies yielded incidence values of 9.5% vs. 15.2%, respectively; in the prospective studies, if physical examinations or imaging studies were performed to corroborate the presence of IH, performing imaging studies increased the number of patients identified with IH by up to 40% [24, 38].

One of the main objectives of this study was to rank the risk factors associated with the development of IH on the basis of not only their statistical significance but also their real clinical impact. In this sense, although the associations for multiple variables reached statistical significance (p < 0.05), the magnitude of the effect, measured with the HR, allowed us to determine the differences in the clinical impact of these factors. The factors with the highest risk (HR >2.0) included reoperation during hospitalization (HR = 4.09) and surgical site infection (HR = 2.96). Factors that imparted moderate–high risk (HR 1.5–2.0) included liver disease (HR = 1.76), diabetes (HR = 1.63), emergency surgery (HR = 1.60), surgical site complications (HR = 1.57), colon surgery (HR = 1.55), stoma creation (HR = 1.53) and a history of previous surgery (HR = 1.52). Factors that imparted moderate–low risk (HR 1.2–1.5) included smoking (HR = 1.40), chronic lung disease (HR = 1.30), kidney failure (HR = 1.20) and age ≥65 years (HR = 1.28). Finally, there was no significant association between sex, BMI ≥30 kg/m², hypertension (HR = 1.18), chronic heart failure (HR = 1.06), anemia (HR = 1.00) or cancer (HR = 1.38) and IH development.

The literature mentions that an HR >1.5 is usually considered the threshold of clinical relevance, since it represents a substantial increase in risk that justifies intervention. In contrast, an HR between 1.1 and 1.2, although potentially statistically significant, implies only a 10%–20% increase in risk, which rarely merits changes in clinical practice. In this study, factors such as age ≥65 years (HR = 1.28) and kidney failure (HR = 1.20) fell into this category and thus had limited clinical significance. In contrast, a hazard ratio (HR) >1.5 (and especially >2.0), such as that for reoperation and surgical infection, identified the variable as a priority target around which preventive strategies could be developed. This distinction is crucial to avoid over intervention based on marginal associations and focus resources on factors that truly impact the risk of IH [39, 40].

The impact of surgical site infection on the occurrence of IH is significant. Infections can compromise the integrity of the surgical wound and weaken the tissue and fascia at the incision site, which can lead to poor healing. In addition, surgical site infections can prolong hospitalization time, increase the need for additional surgical interventions to treat hernia and infection, and increase healthcare costs [41, 42]. This association is highly relevant, yet it has been underutilized in risk prediction. Few existing scales for predicting IH incorporate SSI as a predictor, and those that do often treat it simply as a dichotomous variable. Given that SSI emerged as the strongest risk factor in our analysis and considering that validated scales already exist to predict SSI, integrating these SSI prediction tools into existing or novel IH risk scores could significantly improve their predictive performance [43].

This meta-analysis presents several relevant strengths. The inclusion of studies from different regions and a cumulative sample of almost 800,000 patients (including more than 32,000 cases of incisional hernia), allows the estimation of the prevalence of IH in patients undergoing midline laparotomy with high precision. Only observational studies (multiple cohort and one cross-sectional study) were analyzed, none of which mixed experimental designs or different surgical approaches, which improves the clinical applicability of the results. In addition, the sensitivity analysis demonstrated the robustness of the estimates, and the protocol was registered in PROSPERO according to the PRISMA guidelines.

This review has limitations inherent to its design and the included studies. First, the assessment using the ROBINS-I tool indicated that potential selection bias (D2) was present across studies, as illustrated in Supplementary Appendix 3, which may affect the generalizability of our pooled estimates. Second, our evaluation of publication bias using Egger’s test yielded a statistically significant result (p = 0.002), and the accompanying funnel plot (Supplementary Figure SB) showed asymmetry, suggesting a potential underrepresentation of smaller studies with null or negative findings. Although we employed a comprehensive search strategy, this asymmetry indicates that the overall effect size should be interpreted with caution, as the meta-analytic estimate might lead to an overestimation of the true effect.

This study also has several limitations. One of these is the high heterogeneity among studies, which can be attributed to differences in definitions, diagnostic methods, and designs. Another important limitation is the relatively short mean follow-up of 39.6 months across the included studies, as IH can develop later than this period. Only ten of the twenty included studies contributed data for the risk factor analysis, which restricted the number of evaluable variables. Among the 76 initially identified factors, only 20 could be analyzed in an aggregate manner. Most of the studies were retrospective in nature, which is associated with a high risk of bias, and publication bias was evident. Some clinically relevant factors could not be included because of a lack of consistent data between studies. A major and modifiable limitation is the absence of data on fascial closure technique (e.g., suture-to-wound length ratio, stitch size), a critical peri-operative variable known to profoundly influence IH risk, which was not reported in the observational studies we synthesized.

These limitations reinforce the need for multinational prospective studies, with standardized protocols that validate the identified factors and allow exploration of other factors that have not yet been analyzed in sufficient depth.

This study revealed that IH after midline laparotomy is a frequent complication, with an estimated prevalence of 10.1%. Perioperative factors, especially in-hospital reoperation and surgical site infection, showed the greatest clinical relevance, surpassing even multiple comorbidities in terms of the imposed risk. The ranking of these factors according to their clinical impact could allow a more precise development of prevention strategies. The findings of this study underscore the need for standardized prospective studies that validate and complement this evidence to improve decision-making in abdominal surgery.