INTRODUCTION International guidelines of groin hernia treatment strongly recommends to fixate the mesh in case of large M3 medial defects during laparoendoscopic approach (TAPP / TEP). Main purpose of fixation is to decrease recurrence rate which is alarmingly high in case of those defects. Recommendation was based on analysis of large German database (Herniamed). However, deeper look into those findings shows that most of TAPP and TEP procedures were performed with the use of lightweight, flat, macroporous meshes. In 2022 multidisciplinary team consisting of hernia surgeons and scientists from universities of technology conducted an experimental study with the use of 3d groin model to confirm or deny the hypothesis that fixation is not necessary in above cases. Study was conducted with the use of all 3-D anatomical meshes available on Polish market, as well as with flat, macroporous implants. Experiment showed that large, rigid and anatomically shaped meshes are able to maintain its position in groin without need of fixation. To confirm experimental results we decided to conduct large, multicentre, clinical study to evaluate necessity of mesh fixation of large, spatial, standard polypropylene implants.

STUDY HYPOTHESIS Non-fixation of spatial, standard polypropylene meshes is non-inferior as compared to fixation of flat, polypropylene lightweight meshes during TAPP / TEP procedures.

MATERIALS AND METHODS 11 large surgery centres in Poland having proficiency in laparoendoscopic groin hernia repairs (performing at least 80 TAPP/TEP a year) were recruited for this study. Before recruiting patients a two day "bootcamp" meeting was planned. Each centre designated one surgeon responsible for conducing the trial in its hospital and sent him/her to meeting. Recurrence rate in 12-month follow-up was set as a primary endpoint. Pain sensation (assessed with VAS scale) was made a secondary endpoint. Statistical analysis was performed by experts to adjust the sample sizes. The trial was planned as non-inferiority study with test power = 80%, p-value = 0,05 and threshold for clinical significance = 8%. Percentage loss was assumed at 10%. Recurrence rate was assumed 4% based on literature. Based on those assumptions minimal sample size in both arms was calculated at 83-102. Inclusion criteria: elective groin hernia repair, age \> 18 years, male and female patients can participate, M3 or M3+L1-3 (EHS classification) groin hernia confirmed during surgery, eligibility to laparoendoscopic repair, written informed consent. Exclusion criteria: age \<18 years, emergency surgery (incarcerated hernia), contaminated surgical field, extremely large scrotal hernia with the need of other forms of prevention of ACS (preoperative botox injection, bowel resection etc.) First arm (control group) will consist of patients repaired with the use of flat, macroporous, lightweight mesh fixated with histoacryl glue. Second arm will consist of patients repaired with the use of anatomically shaped, large, standard, polypropylene mesh (Dextile Anatomical Mesh - MEDTRONIC or 3D Max Mesh - BD) without the use of fixation material.

As M3 hernias are difficult to diagnose before the surgery, all patients planned for laparoendscopic repairs will be asked to participate in trial. During the surgery, when the defect size is measured, patient will be fully included in the study. After dissection of preperitoneal space (and establishing crucial checkpoints), surgeon will open envelope and find out the technique he will have to perform. Patients won't be aware of the method used during surgery. Unblinding will take place at the end of the trial. Pain will be measured during the hospital stay and then 7-days, 3-months and 12-months after surgery (VAS Scale). Follow up will be performed by Medical Assistant via phone call (also blinded to the method used). If any doubts occur, patient will be asked to come to ambulatory visit.

PREDICTED OUTCOMES Based on experimental study published in Surgical Endoscopy (Zamkowski et al., 2022) and own experience, we believe that recurrence rate in both arms will be on the same level. Those outcomes will be a strong argument for amending the guidelines in terms of mesh fixation. It would show that mesh fixation is not necessary if the proper, spatial mesh is used.