Incisional hernia is one of the most frequent long-term complications after abdominal surgery, with an incidence of 5–20% in the general patient population. However, in high-risk patients, the incidence of incisional hernia can increase to more than 30%.1, 2, 3 Obese individuals (ie, those with a body-mass index [BMI] ≥30 kg/m2) and people with abdominal aortic aneurysm are especially high-risk groups. Patients with abdominal aortic aneurysm are at risk because of an underlying connective tissue disorder, caused partly by dysregulation of collagen type 1 and 3; this impairment probably has an important role in the pathogenesis of distension of the aorta and in formation of incisional hernia in patients after median laparotomy.4 Individuals with obesity or a BMI equal to or higher than 27 kg/m2 have a more than 30% chance of developing incisional hernia after median laparotomy.5 This group of patients are believed to have a higher intra-abdominal pressure, which can cause higher tension on abdominal wall sutures. However, this pressure might not be the only contributing factor: obesity is also associated with wound-healing complications due to decreased vascularity of adipose tissue, leading to local hypoxia. In hypoxic wounds, the synthesis of mature collagen is impaired, resulting in weaker tissue and a deficiency in the overall healing process. In wound healing, other known risk factors play an important part—eg, malignant disease, parastomal hernia, wound infection, and smoking.6, 7, 8, 9, 10
Incisional hernia can cause morbidity (eg, pain) and can have a negative effect on patients' quality of life and body image.11, 12, 13 Furthermore, there is a risk of obstruction and strangulation of the bowel with perforation and possible mortality as a result. For these reasons, repair of incisional hernia is a surgical procedure that is done frequently. However, even though repair with mesh reinforcement has lower risk of recurrence compared with primary suture, the cumulative 10-year incidence is 32%, which is still too high.14, 15 Use of laparoscopic techniques has not yielded better results with respect to recurrence of incisional hernia.16, 17, 18 Incisional hernia not only has a large effect in medicine but also has a great socioeconomic effect. Therefore, prevention of incisional hernia is of paramount importance: it will lead to reduction of disease and is, thus, cost-effective.
Research in context
Evidence before this study
The European Hernia Society has developed guidelines on closure of abdominal wall incisions. Although prophylactic mesh reinforcement is suggested for an elective midline laparotomy in high-risk patients (ie, those with an aneurysm of the abdominal aorta or who are obese [body-mass index ≥30 kg/m2), to reduce incisional hernias, evidence for this approach is weak. The Guidelines Development Group has suggested larger trials are needed to make a strong recommendation for this strategy. However, it is unclear which mesh position (onlay or sublay) leads to a lower occurrence of incisional hernias. We did a systematic literature search up to July, 2016, with the keywords “incisional hernia”, “prophylactic”, “prevention”, “onlay”, “sublay”, and “mesh”. We did not restrict our search by language. Three researchers reviewed all records independently. We included prospective randomised controlled trials that enrolled patients aged 18 years or older undergoing midline laparotomy for all indications, with any type of mesh and mesh position. We evaluated 12 randomised controlled trials, with high heterogeneity among studies. Incisional hernia arose less frequently when a prophylactic mesh was placed during midline laparotomy. Occurrence of seromas was highest in patients who underwent mesh reinforcement. Individuals in whom a mesh was placed during laparotomy seemed to have a higher risk of developing a surgical-site infection compared with those without a mesh.
Added value of this study
Compared with previous studies, the PRIMA randomised controlled trial had three arms to compare onlay mesh reinforcement, sublay mesh reinforcement, and primary suture. Onlay mesh reinforcement had a stronger and more significant effect on prevention of incisional hernia than did sublay mesh reinforcement. Moreover, the frequency of surgical-site infections was not increased with onlay mesh reinforcement.
Implications of all the available evidence
The PRIMA trial provides strong evidence in favour of onlay mesh reinforcement for prevention of incisional hernia in high-risk patients undergoing midline laparotomy. This finding is important because onlay placement of a mesh is an easier surgical technique than is sublay mesh reinforcement. Therefore, this approach could be adapted readily, not only by surgeons but also by urologists and gynaecologists, who also perform midline laparotomies. Closure of laparotomy with onlay mesh reinforcement has the potential to become the standard treatment in high-risk groups.
Many studies have evaluated different types of incision, suture materials, and closure techniques to reduce the incidence of incisional hernia.19, 20, 21 Horizontal incisions and laparoscopy, or endovascular aneurysm repair (EVAR), in patients with abdominal aortic aneurysm are well-known surgical techniques that minimise the risk of incisional hernia. In each patient undergoing surgery, the best available technique should be considered. However, for several individuals, conventional laparotomy is unavoidable. Until now, no adequate method or gold standard to prevent incisional hernia has been reported for people undergoing midline laparotomy. Patients at particular high risk of incisional hernia, including those with abdominal aortic aneurysm and high BMI, might benefit most from prevention.22, 23, 24, 25 In 1995, Pans and colleagues26 did a prospective study to compare patients undergoing surgery for morbid obesity with or without intraperitoneal polyglactin mesh. No difference in incidence of incisional hernia was noted between the two groups.26 Several randomised and non-randomised prospective studies have been done to investigate how incisional hernia can be prevented. Currently, no level 1 evidence is available. The quality of published randomised studies is low and there is no consensus about the mesh position in the abdominal wall that should be used.27, 28
We initiated the PRIMA trial (PRImary Mesh closure of Abdominal midline wounds) in 2009 with the aim to investigate prophylactic mesh reinforcement in high-risk groups (ie, patients with abdominal aortic aneurysm or a BMI ≥27 kg/m2).29, 30 We also aimed to assess which mesh position in the abdominal wall should be used to prevent incisional hernia. The primary aim of the PRIMA trial was to study the effectiveness of prophylactic mesh reinforcement to prevent incisional hernia.