Where Surgeons Place Hernia Mesh May Shape the Risks of Every Future Abdominal Operation

Ventral hernia repair is one of the most frequently performed operations in the world, and almost every modern repair relies on a synthetic or biologic mesh to reinforce the weakened abdominal wall. Yet a deceptively simple question continues to divide surgeons: where exactly should that mesh sit? A new international study called ORION, described in the Journal of Abdominal Wall Surgery, is launching a systematic attempt to answer it by following patients who return to the operating room years after their original hernia repair. Its central premise is that the anatomical plane chosen for the mesh—inside the peritoneal cavity or outside it—may quietly determine how dangerous, difficult, and painful any subsequent minimally invasive abdominal surgery will be.

The technical distinction at the heart of the study is more consequential than it might first appear. In minimally invasive ventral hernia repair, the mesh can be placed in several anatomical planes: intraperitoneal, where the prosthesis lies directly against the bowel within the peritoneal cavity; preperitoneal, tucked between the peritoneum and the abdominal wall; retro-muscular, positioned behind the rectus muscles; or onlay, placed superficial to the fascia. Techniques that keep the mesh outside the peritoneal cavity have been gaining popularity, largely because intraperitoneal placement carries well-documented short-term drawbacks, including increased postoperative pain driven by fixation tackers and early recurrences linked to mesh migration. Still, the most appropriate mesh position remains genuinely controversial, and the long-term consequences of each choice have never been rigorously compared.

The concern driving ORION is adhesion formation. When mesh sits intraperitoneally, it is in permanent contact with viscera, and animal studies have shown that even composite meshes designed to resist adhesion provoke fibrous bands in that space. Imaging studies and surgical revisions in these patients frequently reveal adhesions between bowel and mesh, and the clinical consequences can be serious: bowel entrapment, chronic pain, obstruction, and, most acutely, visceral injury during later operations. Surgeons performing adhesiolysis—the careful division of scar tissue—in a patient with prior intraperitoneal mesh face a landscape where loops of intestine may be densely fused to the prosthesis itself. Most existing research has focused on hernia-related outcomes such as recurrence and infection, potentially underreporting the downstream morbidity that adhesions generate over years.

The ORION investigators, a collaborative group led by researchers at the University of Milan and IRCCS Istituto Auxologico Italiano and endorsed by the European Hernia Society, have formulated a clear primary hypothesis: that prior intraperitoneal mesh placement is associated with a higher risk of intraoperative visceral injury during adhesiolysis at subsequent minimally invasive abdominal surgery than prior extraperitoneal placement. Their secondary hypotheses extend the comparison further, predicting that intraperitoneal placement brings a greater burden of adhesion-related complications, longer adhesiolysis time, higher conversion rates from minimally invasive to open surgery, and—among patients reoperated for recurrence—higher rates of chronic post-surgical pain and neuropathic features at ninety days.

The study design is deliberately pragmatic. ORION is a prospective, multicentre, observational study recruiting surgical centres across Europe, with data collection running from 1 March 2026 to 28 February 2027. Any European hospital performing elective or emergency minimally invasive abdominal surgery can participate, and there is no minimum patient quota per centre. Eligible patients are adults who previously underwent minimally invasive mesh-based ventral hernia repair—whether primary, recurrent, or incisional—with either intraperitoneal or extraperitoneal mesh, and who now require further minimally invasive abdominal surgery for any reason, from cholecystectomy to colorectal resection to gynecologic procedures. This broad capture is intentional: it reflects the real-world risk of adhesiolysis-related visceral injury across the full spectrum of abdominal operations, not just hernia redo surgery.

Participants are divided into two pre-specified cohorts. Cohort A comprises patients undergoing minimally invasive surgery for indications other than recurrent hernia repair, and these patients are assessed only up to discharge, with in-hospital outcomes recorded. Cohort B comprises patients undergoing minimally invasive repair of a recurrent ventral or incisional hernia, and this group receives scheduled follow-up at thirty and ninety days. The investigators restricted post-discharge follow-up to the recurrence cohort to prevent indication-driven heterogeneity in outcome ascertainment, a design choice that preserves internal validity for early morbidity analyses while maintaining external validity for the primary intraoperative endpoint, which is captured across all procedures performed after prior mesh placement.

The primary outcome is precisely defined: adhesiolysis-related visceral injury, meaning intraoperative damage to bowel, bladder, or solid organs during the division of adhesions. Injuries are categorized as serosal tears, full-thickness bowel injuries such as enterotomy or perforation, or other visceral injuries involving organs like the bladder, spleen, liver, or stomach. Notably, omental injury or division is considered inherent to adhesiolysis and is recorded separately rather than counted as a primary event. Secondary outcomes include the incidence of adhesion-related complications such as bowel obstruction, the duration of adhesiolysis in minutes, the rate and reasons for conversion to open surgery, and a detailed characterization of adhesions using the Peritoneal Adhesion Index, with the abdomen mapped into five regions and adhesion tenacity graded as flimsy, moderate, or dense.

For the recurrence cohort, the study digs into questions that have rarely been examined with such granularity. Investigators will document the anatomical or technical mechanism behind each hernia recurrence—central mesh failure, marginal recurrence, or mesh migration—and record how the recurrence was managed, including whether the same mesh type was reused, which anatomical plane was chosen, and which fixation methods were employed. Quality of life will be measured with the EuraHS-QoL scale at thirty and ninety days. Most distinctively, ORION incorporates validated neurological outcome measures: chronic post-surgical pain is defined as an increase of at least three points on the Visual Analogue Scale in the surgical area compared with the pre-operative baseline, new since surgery and unexplained by complications such as recurrence, infection, or obstruction. Suspected neuropathic features will be screened with the DN4 questionnaire, sensory changes around port sites will be recorded, and opioid use at day thirty will be tracked.

The statistical framework is built to detect clinically meaningful differences. A sample of 345 patients per group, 690 in total, provides ninety percent power to detect a ten percent absolute difference in adhesiolysis-related visceral injury rates, assuming an event rate of twenty-five percent in patients with prior intraperitoneal mesh and fifteen percent in those with prior extraperitoneal mesh. Relative risks will be calculated with log-binomial regression, adjusting for clinical and sociodemographic variables that differ between groups, while logistic regression models will assess associations between mesh position and chronic pain or opioid use. The investigators acknowledge the assumptions are pragmatic, drawn from available reoperation data after laparoscopic ventral hernia repair, because robust comparative estimates remain scarce.

The team is candid about the limitations inherent in an observational, non-randomized design. Because patients are identified at a subsequent operation rather than at the index repair, the study has no denominator of all originally treated patients and cannot estimate absolute risks per index procedure; the reported relative risks are conditional on reoperation and may be affected by selection bias, making the findings hypothesis-generating rather than definitive. Extraperitoneal repair is also a more recent technique, so intraperitoneal cases will tend to involve a longer interval since the original operation, and time and surgical era will be treated as covariates. Unblinded intraoperative assessment may introduce detection bias, and a twelve-month recruitment window cannot capture late complications such as adhesion-related bowel obstruction that may emerge years later. Even so, if ORION confirms that mesh position shapes the hazards of future surgery, its findings could reshape how surgeons weigh the long-term costs of intraperitoneal repair, inform the selection of mesh type and fixation strategy, and give renewed attention to the under-recognized neurological sequelae of abdominal wall reconstruction.

Subject of Research: Prospective multicentre observational study comparing long-term outcomes of intraperitoneal versus extraperitoneal mesh placement in ventral hernia repair

Article Title: The ORION study protocol: impact of prior intraperitoneal versus extraperitoneal mesh placement on subsequent minimally invasive abdominal reoperations

Article References: Pelfini, E., Lauricella, S., Nisi, A., Dionigi, G., & Brucchi, F. (2026). The ORION study protocol: impact of prior intraperitoneal versus extraperitoneal mesh placement on subsequent minimally invasive abdominal reoperations. Journal of Abdominal Wall Surgery, 5, Article 17325. https://doi.org/10.3389/jaws.2026.17325

Image Credits: AI Generated

DOI: 10.3389/jaws.2026.17325

Keywords: ventral hernia repair, mesh placement, intraperitoneal mesh, extraperitoneal mesh, adhesions, adhesiolysis, visceral injury, minimally invasive surgery, hernia recurrence, chronic post-surgical pain, European Hernia Society, observational study