Protocol for the AFTERHERNIA Project: patient-reported outcomes of groin and ventral hernia repair
- Open Access
- 01.12.2025
- Original Article
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Abstract
Introduction
Hernia surgery accounts for a substantial proportion of all surgical procedures performed globally, affecting quality of life, and imposing substantial costs on healthcare systems worldwide [1]. In Denmark, around 10,000 groin hernia repairs and 5,000 ventral hernia repairs are performed annually [2] incurring considerable expenses for the Danish healthcare system. Postoperative outcomes for Danish patients undergoing hernia repair have previously been investigated extensively on a nationwide basis through the Danish Hernia Database, which has been instrumental in facilitating extensive, population-level research on postoperative outcomes such as reoperation for recurrence and readmission rates. These nationwide studies, along with similar large-scale studies from international registries, have continuously improved the quality of hernia surgery in recent years, both in Denmark and internationally [3, 4]. However, most nationwide studies related to hernia surgery have primarily relied on clinical outcomes rather than patient-reported outcomes. Above all, the outcome of interest in these nationwide studies has been the rate of reoperation for recurrence, which to some extent has guided clinical guidelines and surgical decision-making in the last couple of decades [5, 6]. Considering that the main objective of hernia surgery is to alleviate symptoms and improve quality of life, patient-reported outcomes may represent a more nuanced, conceptually appropriate, and patient-centered outcome of interest for the future [7, 8]. Currently, however, Danish population-level, hernia-related, patient-reported outcome data do not exist.
The AFTERHERNIA Project aims to bridge this evidence gap through its portfolio of studies, each with a distinct focus but unified in their aim to investigate which surgical approaches for groin and ventral hernia repairs yield the best patient-reported outcomes.
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Methods
The AFTERHERNIA Project is a nationwide study including register-based data and surveys among patients in Denmark who have received a groin or ventral hernia repair. The project consists of a portfolio of studies, and the general study design and data flow are illustrated in Fig. 1.
Fig. 1
Study design and data flow. REDCap: Research Electronic Data Capture
Participants
Potential participants will be identified based on surgical procedure codes in the Danish National Patient Registry (Tables 1 and 2). Eligible participants will be recruited through Digital Post, which is an online, personal communication service that is provided to all residents in Denmark and is used by approximately 95% of Danish residents ≥ 15 years of age [9]. Eligibility criteria for participation differ between the various studies in the project portfolio, but, in general, patients are eligible if they received a groin or ventral hernia repair in Denmark between 1 January 2014 and 31 March 2024, and if they were ≥ 18 years old at the time of hernia repair. Patients will be excluded if they are deceased, have emigrated, or are exempt from using Digital Post. Patients will also be excluded if they have insufficient knowledge of Danish, or if they are unable to complete the questionnaire due to cognitive or physical impairment, including comorbidities or concurrent surgery that prevent the distinction of symptoms specific to hernias or hernia repair. Patients with non-disclosure of street address will also be excluded as they are protected from contact without prior consent.
Table 1
Surgical procedure codes for groin hernia repair
Code | Description | Mesh | Open/Lap | |
|---|---|---|---|---|
Inguinal hernia | ||||
KJAB00 | Inguinal hernia operation | - | Open | |
KJAB10 | Operation for inguinal hernia with plasty | - | Open | |
KJAB11 | Laparoscopic inguinal hernia operation | + | Lap | |
KJAB20 | Inguinal hernia operation with fascia repair | - | Open | |
KJAB30 | Inguinal hernia operation with synthetic material | + | Open | |
KJAB40 | Inguinal hernia operation with abdominal wall plasty through laparotomy | - | Open | |
KJAB96 | Other inguinal hernia operation | ? | Open | |
KJAB97 | Other laparoscopic inguinal hernia operation | + | Lap | |
Femoral hernia | ||||
KJAC10 | Femoral hernia operation | - | Open | |
KJAC11 | Laparoscopic femoral hernia operation | + | Lap | |
KJAC30 | Femoral hernia operation with synthetic material | + | Open | |
KJAC40 | Femoral hernia operation with abdominal wall plasty through laparotomy | - | Open | |
KJAC96 | Other femoral hernia operation | ? | Open | |
KJAC97 | Other laparoscopic femoral hernia operation | + | Lap | |
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Table 2
Surgical procedure codes for ventral hernia repair
Code | Description | Mesh | Open/Lap | |
|---|---|---|---|---|
Umbilical hernia | ||||
KJAF10 | Operation for umbilical hernia | - | Open | |
KJAF11 | Laparoscopic operation for umbilical hernia | + | Lap | |
KJAF14 | Endoscopic retromuscular operation for umbilical hernia | + | Lap | |
KJAF14A | Endoscopic retromuscular eTEP operation for umbilical hernia | + | Lap | |
KJAF14B | Endoscopic retromuscular eMILOS operation for umbilical hernia | + | Lap | |
KJAF20 | Operation for umbilical hernia with fascial transplantation | - | Open | |
KJAF30 | Operation for umbilical hernia with implantation of foreign material | + | Open | |
KJAF33 | MILOS operation for umbilical hernia | + | Lap | |
KJAF96 | Other operation for umbilical hernia | ? | Open | |
KJAF97 | Other laparoscopic operation for umbilical hernia | ? | Lap | |
Epigastric hernia | ||||
KJAE10 | Operation for epigastric hernia | - | Open | |
KJAE11 | Laparoscopic operation for epigastric hernia | + | Lap | |
KJAE14 | Endoscopic retromuscular operation for epigastric hernia | + | Lap | |
KJAE14A | Endoscopic retromuscular eTEP operation for epigastric hernia | + | Lap | |
KJAE14B | Endoscopic retromuscular eMILOS operation for epigastric hernia | + | Lap | |
KJAE30 | Operation for epigastric hernia with implantation of foreign material | + | Open | |
KJAE33 | Minimally invasive retromuscular operation for epigastric hernia (MILOS) | + | Lap | |
Incisional hernia | ||||
KJAD10 | Operation for incisional hernia | - | Open | |
KJAD11 | Laparoscopic operation for incisional hernia | + | Lap | |
KJAD14 | Endoscopic retromuscular operation for incisional hernia | + | Lap | |
KJAD14A | Endoscopic retromuscular eTEP operation for incisional hernia | + | Lap | |
KJAD14B | Endoscopic retromuscular eMILOS operation for incisional hernia | + | Lap | |
KJAD20 | Operation for incisional hernia with fascial transplantation | - | Open | |
KJAD30 | Operation for incisional hernia with implantation of foreign material | + | Open | |
KJAD33 | MILOS operation for incisional hernia | + | Lap | |
KJAD96 | Other operation for incisional hernia | ? | ? | |
Other unspecified hernia | ||||
KJAG00 | Operation for other hernia | ? | Open | |
KJAG01 | Laparoscopic operation for other hernia | ? | Lap | |
KJAG30 | Abdominal wall reconstruction with graft | ? | Open | |
KJAG60 | Abdominal wall reconstruction with implantation of foreign material | ? | Open | |
Questionnaire
The AFTERHERNIA Project will use the questionnaire Abdominal Hernia-Q (AHQ), which was developed in the United States in 2020 [10]. The AHQ is intended for the assessment of patient-reported outcomes in patients undergoing ventral hernia repair. It features both a pre- and a postoperative form including a total of 24 items with responses scored on 4-point Likert scales. The AHQ covers seven different content domains: expectations, self and others, surgeon and surgical team, sensation, function, appearance, and overall satisfaction [11]. The instrument’s development included extensive patient input and psychometric validation [10‐12], and it is likely to be the most thoroughly validated questionnaire for this purpose [13].
The AHQ has recently been translated into Danish and validated for use in a Danish-speaking population (manuscript in preparation). As part of the AFTERHERNIA Project, the AHQ will be adapted and re-validated for patients undergoing groin hernia repair: Groin Hernia-Q (GHQ). A detailed protocol for the questionnaire adaptation and re-validation for groin hernia patients will be published separately. Patients will receive the AHQ after ventral hernia repair and the GHQ after groin hernia repair.
Registries
The entirety of the AFTERHERNIA Project will be based on data from the Danish National Patient Registry, which offers a comprehensive, nationwide longitudinal record of detailed, routinely collected administrative and clinical data [14]. Since 1977, it has collected information on all public hospital contacts, and since 2003, also from private hospitals and clinics [14]. The Danish National Patient Registry serves as a valuable data source for identifying diseases, examinations, treatments, and surgical procedures [14]. Person-level data from the Danish National Patient Registry will be linked to the Danish Civil Registration System, which holds live electronic records of postal addresses, as well as information on patients who are deceased or have emigrated [15].
All residents in Denmark have a unique and mandatory personal identification number, which is used in all registries and in all contacts with both private and public hospitals, including private practices. The unique personal identification number is also linked to the electronic communication platform Digital Post, which enables survey distribution. All linkage between the included databases and Digital Post will be conducted with the unique personal identification number.
The project will also incorporate data from the Danish Hernia Database, which is a national, surgeon-reported clinical quality registry with mandatory registration of all hernia surgeries performed in Denmark. The Danish Hernia Database has collected data on Danish patients undergoing groin hernia repair since 1998, and on patients undergoing ventral hernia repair since 2007 [16, 17]. In 2022, the national registration rates in the Danish Hernia Database for groin and ventral hernia repairs were 92.8% and 88.5%, respectively [2].
Data collection and flow
The study population will be defined according to surgical procedure codes (Tables 1 and 2) in the Danish National Patient Registry. The study population will be established by the managing body of the Danish National Patient Registry. Subsequently, invitations to participate will be distributed to patients through Digital Post based on their unique personal identification number, and questionnaires will be completed using Research Electronic Data Capture (REDCap) [18]. Questionnaires will be distributed via unique links, ensuring that each participant receives a personal link to a questionnaire only designated for them, while also ensuring that each participant can only complete the questionnaire once. Participation consent will be obtained simultaneously through REDCap. Multiple reminders will be sent to participants, after which the remaining non-responders will be contacted by phone, if possible. Following informed consent and completion of questionnaires, responses will be integrated with clinical data from the Danish Hernia Database and the Danish National Patient Registry. This integration aims to augment the dataset with information necessary for most of the studies in the portfolio.
Project portfolio
The first studies in the AFTERHERNIA Project portfolio will focus on the adaptation, translation, and validation of the AHQ and GHQ questionnaires for use throughout the project. This will ensure a solid evidence base for the entirety of the project.
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Most subsequent studies will investigate the impact of various perioperative, patient-related, or surgeon-related characteristics on both clinical and patient-reported outcomes. These characteristics of interest include specific types of hernia repair, mesh characteristics, mesh placement, defect closure, specific methods and materials used to fixate these mesh implants, particular patient characteristics, surgeon characteristics, etc. Most studies will be comparative, intending to determine best practice, but a few studies will be descriptive and aim to determine the incidence of specific postoperative complications and their impact on patient-reported outcomes. We will investigate the influence of different mesh materials, mesh weights, mesh placements, mesh fixations, materials and methods for peritoneal closure, and more. Some studies will examine the influence of patient-related factors such as smoking, obesity, and age. Other studies will focus on surgeon-related characteristics, such as the impact of surgical volume and the potential difference in outcomes between surgeries performed by specialists vs. residents.
Lastly, a few studies will take a more meta-methodological approach. Some of these studies will focus on various ways to optimize response rates in large surveys such as this, and other studies will, for instance, investigate the reliability of patient-reported hernia recurrence.
A non-exhaustive list of planned studies in the AFTERHERNIA Project portfolio is available online [19].
Statistical methods
The statistical methods used will vary based on the specific aims of each study. Generally, analyses will begin with descriptive statistics, summarizing categorical variables (e.g., patient demographics, types of hernia surgery) using frequencies and proportions, and continuous variables (e.g., age, patient-reported outcome scores) using means, medians, standard deviations, or interquartile ranges. These summaries will be presented both for observed data and adjusted for non-response.
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To address missing data, including non-responses and incomplete answers, we will employ multiple imputation using chained equations (MICE), assuming data are missing at random (MAR). Sensitivity analyses will explore alternative assumptions, such as data missing not at random (MNAR), using methods like pattern-mixture or selection models. Weighting adjustments based on demographic and clinical characteristics will be used to correct for substantial non-response and ensure representativeness.
Multivariable regression models will assess associations between patient-reported outcomes and various factors. Linear regression will be used for continuous outcomes (e.g., quality of life scores), logistic regression for binary outcomes (e.g., presence of complications), and Cox proportional hazards models for time-to-event outcomes (e.g., time to hernia recurrence). All models will undergo diagnostic checks and be adjusted for non-response and missing data.
To control for type I errors given the exploratory nature of the project, statistical adjustments such as Bonferroni correction or false discovery rate (FDR) methods will be applied. All analyses will be conducted using R, with appropriate packages for imputation, regression modeling, and handling complex survey data.
Ethical considerations
Approval was obtained from the Capital Region of Denmark authorized under the Danish Data Protection Agency (p-2023-14805). Data will be supplied by the Danish Health Data Authority (FSEID-00006834). Ethical review board approval is neither possible nor required under Danish law. Informed consent will be obtained from all participants. The project poses no risk to participants and adheres to the Declaration of Helsinki [20]. To ensure confidentiality and to prevent any potential stigmatization of specific demographic groups, results will be anonymized, and no individual participants will be identifiable in any published reports.
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Discussion
The AFTERHERNIA Project represents a paradigm shift for population-level hernia research, focusing on patient-reported outcomes to measure surgical success on a national scale. While clinical outcomes have historically dominated, the exclusive focus on such metrics may overlook aspects critical to patients’ quality of life. We aim to close this evidence gap by capturing a broader spectrum of patient experiences.
Strengths and limitations
The AFTERHERNIA Project integrates detailed registry data from various sources with patient-reported outcome data, which allows for a robust longitudinal assessment of patient outcomes and offers insights into the long-term efficacy of different surgical approaches. The Danish Digital Post service guarantees that this project will reach a broad and representative sample of participants. All data collection will be conducted digitally, which ensures optimal data quality and coverage. The project is also strengthened by having a high external validity by covering all private and public hospitals in Denmark.
However, the project is not without its challenges, and in particular, inadequate response rates pose a risk of non-response bias. To mitigate this, the project plans rigorous follow-up strategies to maximize response rates, and the implementation of weighted analyses to ensure representativeness. Around 5% of Danish resident are exempt from using Digital Post. These are primarily individuals ≥ 75 years old and mostly residents in rural areas of Denmark [9], which presents an unavoidable source of selection bias for the planned studies.
Clinical implications
The AFTERHERNIA Project has the potential to directly influence clinical guidelines and improve patients’ lives. By providing a clearer picture of which factors lead to improved patient-reported outcomes, healthcare providers can better tailor surgical approaches to individual patient needs, ultimately enhancing patient satisfaction and outcomes.
Conclusion
The AFTERHERNIA Project will offer significant contributions to both hernia research and clinical practice, emphasizing the importance of patient-centered outcomes in surgical care. By shifting focus towards what truly matters to patients, the project aligns surgical interventions more closely with the goals of enhancing overall quality of life.
Declarations
Ethical approval
Approval was obtained from the Capital Region of Denmark authorized under the Danish Data Protection Agency (p-2023-14805). Ethical review board approval is neither possible nor required under Danish law.
Consent to participate
Informed consent will be obtained from all participants.
Consent for publication
Informed consent will be obtained from all participants.
Competing interests
All authors declare no competing interest.
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