Background: A detailed study of the biomechanical changes before and after abdominal wall reconstruction (AWR) has not been performed. Changes in abdominal wall tension and intra-abdominal pressure have physiological consequences on respiratory and cardiology function. AWR surgeons currently do not know if they are applying too much tension when re-aligning the abdominal wall muscles during AWR. Too much tension is likely to cause respiratory and cardiac post-operative complications. The investigators propose to study the perioperative changes in abdominal biomechanics and cardiorespiratory physiology after AWR. In addition, investigators will also analyze the pre-operative patient CT scan to see if there any CT predictors of post-operative cardiorespiratory complications and hernia recurrence. The researchers hypothesize that there is a threshold value or force at which ventral hernias are repaired 'too tight' subjecting the patient to the increased risk of recurrence and cardiorespiratory complications.

Method: An in depth biomechanical and physiological study of 18-22 participants with midline ventral hernias will be carried out. Ventral hernias at least 5cm in width and only those in which primary fascial closure have been achieved will be included. Any operative technique used to achieve primary fascial closure will be included. Biomechanical and physiological measurements will be taken at five separate stages during the course of the patients' abdominal wall reconstruction. The final lung function tests, taken six weeks post op, will be compared to the patients' pre-operative tests. Meticulous attention will be paid to the study protocol making sure that in each patient the measurements are all taken at the same time and under the same conditions.

Discussion: This full biomechanical and physiological work up will enable AWR surgeons to assess when an AWR patient is subjected to too much biomechanical and physiological stress. The abdominal wall tension and strain will be measured to see if this predicts post complications and hernia recurrence.

Inclusion Criteria:

• Patients with midline hernia defects. Only patients with one or more midline defect will be included. For our study, we will define a midline hernia as herniation through the linea alba and with the rectus muscles falling either side of the hernia. The pre-operative CT scan will be used to study the hernia morphology and to see whether the patient fulfills these criteria.
• Patients undergoing primary or incisional ventral hernia repair, without formation of or closure of a stoma.
• Patients with either a maximal ventral hernia axial width of greater than 5cm or a loss of domain of greater then 20%, as measured on their pre-operative CT or MRI scan. The loss of domain will be measured using the patients' preoperative CT or MRI scan following the method of Tanaka et al.
• Patients aged ≥ 18 years old.
• Midline hernias closed in the midline with primary fascial closure with or without mesh augmentation. Any reconstruction technique can be used (e.g. anterior or posterior component separation) as long as primary fascial closure is achieved. The mesh may be placed in either the retro-rectus position (with or without a transverse abdominis release) or the onlay position.
• Participants who have a synthetic or bio-synthetic mesh implanted.
• Midline ventral hernias of VHWG grade 2 or 3. Clean and or Clean-contaminated wound classification.
• The participant is legally competent, has been informed of the nature, the scope and the relevance of the study, voluntarily agrees to take part and has duly signed the consent form.

Exclusion Criteria:

• Emergency/Redo surgery.
• Defects not in the midline. Patients with one or more defect not through the linea alba on the pre-operative CT scan.
• AWR for abdominal wall sarcoma, invasive intra-abdominal carcinoma or other malignant disease.
• Contaminated VHWG grade 4 hernias. Or Contaminated or Dirty wound according to the CDC wound classification system.
• Concomitant procedures such as bowel resection.
• The hernia requires a bridged repair.
• Individuals with co-morbid respiratory disease requiring oral corticosteroids or home oxygen therapy.
• Individuals who require the mesh to be placed in the intra-abdominal position.
• A patient with active peritonitis or an active mesh or subcutaneous infection.
• Individuals with a diagnosis of Crohn's disease.
• Individuals of American Society of Anesthesiology grade 4 or 5.
• Complete removal of an existing synthetic mesh (or biosynthetic mesh if not absorb) from a prior hernia repair in the same location is not possible.
• Participants with human immunodeficiency virus (HIV), known liver cirrhosis or alcohol abuse with a known relapse within 12 months.

Designated members of the research team will be responsible for data entry at different steps of the patient pathway. All researchers will be responsible for the accuracy of the documentation and must ensure that all entries can be verified by the source data. An explanation will be given for all missing data. All the study documents and proformas containing the participant data will be kept on site in the General Surgery department at our hospital. At no point, will these documents be removed from the department. Study data will be pseudo-anonymised for data analysis. The file containing the pseudo-anonymised data will be password protected. Only the pseudo-anonymised data will leave the hospital department, it will be transferred using the secure UCLH.nhs.uk and NHS.net email systems. Only the primary researcher, SGP, will have access to the pseudo-anonymised data outside our hospital department, where the password protected data file will be keep on his secure personal laptop.