Nomenclature regarding abdominal wall defects remains vague. Is this patient due to have an incisional hernia repair or a complex abdominal wall reconstruction?
Recent attempts have been made to create more holistic classifications of abdominal wall herniae. The Ventral Hernia Working Group (VHWG) developed a classification that uses an intuitive blend of patient and hernia characteristics to provide four categories  (Fig. 38.1). Simple and easy to use, it has gained popularity in reports of large case series, particularly those originating from North America. This simplicity, although appealing, may be a significant limitation, with marked intragroup variability. Only one study has assessed prospectively the validity of the classification system, and it recommended modifications . Slater et al.  attempted to define “complex abdominal wall hernia” on the basis of 22 patient- and hernia-related variables and also proposed three categories of patient severity. Although comprehensive, its use is complex and widespread adoption has not yet occurred.
Incisional hernia after laparotomy is common and may affect up to 20 % of unselected patients and up to 50 % of high-risk patients . The rate of incisional hernia development reported in the literature varies widely, in part because of the differences in the duration of follow-up and also because of the techniques used to detect herniae [10–12]. The longer the duration of follow-up, the higher the incisional hernia rate; long-term follow-up of randomized studies suggests that the rate of incisional hernia increased from 12.6 % at 1 year to 22.4 % after 3 years . Axial computed tomography has a sensitivity for hernia detection far higher than clinical examination, particularly in obese patients and in those who have had previous hernia repairs [14, 15]. Increased use of cross-sectional imaging as part of colorectal cancer follow-up programs will inevitably lead to a higher rate of hernia detection compared with clinical examination, but it does not necessarily inform which of the herniae found incidentally will ultimately require surgical intervention. This represents the rate of incisional hernia following laparotomy and the variation relates to time from surgery . Nevertheless, laparotomy remains a common procedure, with an estimated 4–5 million being performed annually in the United States, resulting in an estimated 500,000 incisional herniae, of which between 15 % and 47 % may be classified as “large” and in need of abdominal wall reconstruction .
Traditional wisdom held that incisional herniae resulted from technical failure during the surgical closure of the abdominal wall. The situation is far more complicated, however, with a myriad of factors pertaining to the patient, the surgeon, and the postoperative course all playing a role – namely, to have an adverse effect on wound healing. The quality of the data underpinning this wider appreciation of hernia development has largely been derived from retrospective series, and the relative importance of each factor has been incompletely characterized.
38.4.1 Patient Factors
Factors that predispose a patient to incisional hernia formation may be broadly categorized as congenital or acquired. Both, however, are related in that the underlying pathology relates to connective tissue abnormalities resulting from altered synthesis, maturation, or degradation of collagen . This manifests as a decreased Type I : Type III collagen ratio and altered matrix metalloproteinase activity. Congenital syndromes such as Marfan, Loeys-Dietz, and Ehlers-Danlos are well recognized, but in these cases it has become increasingly accepted that herniae may be a reflection of a wider systemic disease process that has been termed herniosis [19, 20]. This represents an as-yet poorly defined nonspecific connective tissue disorder that may encompass conditions as diverse as abdominal wall herniae, aortic aneurysms, diverticulosis, and pelvic organ prolapse .
The relationship between herniosis, genetics, and epigenetic factors is not clearly understood. Mutations in certain genes have been implicated in the development of some abdominal wall herniae [22, 23], but this does not explain the formation of a hernia in the majority of those afflicted by the condition . It is more likely that differential gene expression (i.e. epigenetics) plays a part and may be related to collagen synthesis, deposition, maturation, and turnover regulated by matrix metalloproteinases and their endogenous inhibitors (tissue inhibitors of metalloproteinases) [18, 25]. As a systemic disease, the changes in collagen are noted in both the skin and abdominal wall fascia [25, 26].
Numerous acquired factors have been postulated as predisposing to incisional hernia; these are summarized in Table 38.1. The deleterious effects of smoking  and obesity  on hernia formation have been known for some time and are likely to be mediated via epigenetic influences on several aspects of collagen metabolism. From a specifically colorectal perspective, the influence of neoadjuvant therapies such as radiotherapy and/or chemotherapy on rates of hernia formation has not been studied, although their detrimental effect on tissue healing is generally well known. Whether the innate or acquired aspects of abnormal collagen metabolism are more important in the development of incisional herniae is unclear, but a deeper understanding of the molecular, genetic, and epigenetic bases of the disease is likely to offer new avenues for therapeutic interventions.
Acquired factors postulated to predispose patients to incisional hernia development
High intra-abdominal pressure (chronic obstructive pulmonary disease, benign prostatic hyperplasia, ascites)
38.4.2 Surgeon Factors
Midline incisions remain the most common source of incisional hernia, in part because of the popularity of this method of surgical access to the abdominal cavity. Transverse incisions have been advocated by some surgeons because of a claimed lower incisional hernia rate. This was supported by a recent update of a Cochrane systematic review (odds ratio 0.49; 95 % confidence interval 0.26–1.72), although the methodological and clinical diversity, and the potential for bias in the studies included in the meta-analysis, invoked caution from the authors . This is understandable given that incisions away from the midline, such as those used for a temporary stoma, remain a common site of incisional herniae .
The type of suture material used and the technique used to close the wound have been subject to increased scrutiny. A systematic review and meta-analysis of randomized controlled trials (RCTs) suggests that slowly absorbable sutures result in lower incisional hernia rates than the use of rapidly absorbable or nonabsorbable suture material, and that continuous suturing techniques are superior to interrupted . The basis of abdominal closure as described by Jenkins  regarding the size of the pieces of tissue has been promulgated for decades as 1 cm “bites” 1 cm apart, but his has been challenged by both animal models and human evidence from RCTs [32, 33]. Multicenter RCTs are ongoing, and the adoption of the “small bite” technique is not yet widespread .
38.4.3 Postoperative Factors
Postoperative wound infection carries a significant risk of hernia development and is probably the single most important factor, although all complications that increase intra-abdominal pressure may also have deleterious effects on wound healing and rate of incisional hernia occurrence .
38.5 Preoperative Planning
Many very skilful operators are not good surgeons. William J. Mayo, cofounder of the Mayo Clinic, Rochester, MN.
The traditional aphorisms that abound in surgery regarding the appropriate investigation, planning, and selection of patients are pertinent to abdominal wall reconstruction. Performing the wrong operation on the wrong patient at the wrong time is a recipe for disaster for both the surgeon and patient. Every effort should be made to avoid getting into trouble in the first instance, and meticulous planning combined with multidisciplinary teamwork is essential. Optimizing the patient to minimize risk and maximize success should be the team’s endeavour before embarking on operative intervention.
38.5.1 Deciding Whom to Operate on
Not all patients who have an incisional hernia require surgery. Some undoubtedly present as an emergency with symptoms of strangulation or obstruction, but more common is the elective patient who has symptoms either of pain or relating to impairment of abdominal wall function and a subjective diminished quality of life. The patient must therefore be counseled in depth before embarking on an operation that carries not insignificant risk in many circumstances. This may necessitate a staged approach over time as all investigations are completed and (peri-)operative risk is accurately assessed. Asymptomatic patients may come to less harm if left alone, but if their hernia enlarges and causes problems, reassessment is advisable.
38.5.2 Computed Tomography
Cross-sectional imaging with computed tomography allows accurate assessment of the hernia defect, the quality of abdominal wall tissue, the contents of the hernia sac itself, and of the rest of the abdominal cavity. For patients who have had previous colorectal or other intra-abdominal cancer surgery, exclusion of recurrent or metachronous malignancy is mandatory (Fig. 38.2). Computed tomography allows the surgical approach to be planned preoperatively and may be used to calculate the risk of development of postoperative abdominal compartment syndrome  (Fig. 38.3).
Cross-sectional imaging with computed tomography not only demonstrates the complex nature of the abdominal wall defect but also shows any pathology, such as a metachronous colonic carcinoma (arrow)
Computed tomography allows for the defect to be assessed in detail, operative techniques to be planned, and the risk of abdominal compartment syndrome to be assessed once the abdomen has been reconstructed
38.5.3 Smoking Cessation
Smoking is associated with a significant increase in the risk of hernia recurrence following surgery and predisposes patients to postoperative wound complications (Fig. 38.4). In addition, smoking cessation during the perioperative period reduces surgical site infections . The evidence for the benefits of smoking cessation before a wide variety of surgeries is now well established, and insistence on smoking cessation should be considered every bit as essential as the correction of other medical comorbidities such as hypertension, diabetes, and cardiac disease . Perioperative smoking cessation programs are effective in an elective setting, and patients should be referred as necessary.
Smoking predisposes patients to wound complications such as flap necrosis due to microvascular insufficiency
38.5.4 Obesity Management and Dietitian Assessment
Obesity is well recognized as a risk factor for the development of incisional hernia, and it is also associated with an increased risk of recurrence and postoperative complications [28, 38, 39]. Conclusive evidence that preoperative weight loss makes a positive difference is lacking because few studies have been performed, and those that have lack statistical power . The degree of weight loss required to effect a clinically significant reduction in either recurrence rates or postoperative complications is simply unknown. The complication rate and risk of hernia recurrence increase sharply with a body mass index >35 kg/m2. Therefore, in the elective setting, postponing surgery and referring the patient to an obesity management service seems prudent. If the patient loses weight, they should be encouraged to carry on. The optimal timing of surgery is probably when the patient’s BMI is <30 kg/m2 or when their weight stops decreasing.
Despite the prevalence of obesity among those with large incisional herniae, micronutrient imbalance is common, with tissue concentrations of copper and zinc being depleted [41, 42]. These trace elements have a well-described role in wound healing, and it is highly conceivable that their diminished concentrations have a negative effect on hernia recurrence rates. Correcting levels in either the tissue or plasma by supplementation alone may not be sufficient without addressing the complex interplay with inflammatory processes that initiated the imbalance. Although studies of micronutrient supplementation have been performed in conditions of superficial wound healing, burns, and pressure sores, there is an absence of data to support their use in patients with hernia.
38.5.5 Cardiopulmonary Exercise Testing
Cardiopulmonary exercise testing has recently come to the fore as the method of choice for assessing the cardiorespiratory fitness of any patient due to undergo high-risk surgery as well as high-risk patients (usually elderly [i.e. >70 years old]) due to undergo any surgery. The level of an anaerobic threshold “cut off” between those deemed fit and unfit varies in the literature between 10 and 11 mL/kg/min, but it seems to correlate with outcome across a range of abdominal operations, although data specific to abdominal wall reconstruction are absent. This correlation may be useful when counseling patients regarding complex surgery and when planning postoperative care pathways, such as elective admission to critical care units . The data may also be used as a baseline to monitor improvements in fitness with graduated exercise or “prehabilitation” programs.
38.5.6 Elderly Patients
Elderly patients warrant special consideration because of the relatively high prevalence of medical comorbidities. Perioperative care of older people having surgery services have been developed over the past decade or so, predominantly in orthopedic surgery, with considerable benefit and are now extending across many other areas of surgical practice . This positive development is to be welcomed; its benefits include better preoperative optimization, fewer postoperative medical complications, and better discharge planning for those with complex social care needs.
Anaemia is a common among the general population but particularly in the preoperative population, and patients with concomitant gastrointestinal diseases have a high prevalence . Several cohort studies of a wide range of surgical procedures consistently demonstrated that patients with preoperative anemia have poorer postoperative outcomes than nonanemic patients to the extent that many now regard anemia as a contraindication to elective surgery . Transfusion of packed red blood cells has long been considered the default option for correction of anemia, but it is increasingly recognized that it may be associated with adverse postoperative outcomes . Consequently, a multimodal approach to patient blood management is now advocated, and guidance exists on strategies for preoperative correction .
38.6 Operative Strategies
No single operative strategy is sufficient for every hernia, patient, or situation, and consequently those surgeons who perform abdominal wall hernia repair require a large armamentarium of techniques. The key principles of any hernia repair have been defined as closure of the defect without excess tension and excision or obliteration of the sac, which can be achieved by several approaches. The first dichotomy relates to an open or laparoscopic approach. Open surgery remains the method of choice for large hernia defects, patients who require concomitant bowel surgery, and patients in whom laparoscopy is not feasible because of intra-abdominal adhesions. Debate remains regarding what may be classed as a “large defect” with most advocating open surgery for hernia defects larger than 10 cm in diameter. While hernia defects with a diameter less than 5 cm may be most amenable to the laparoscopic approach, the optimal approach for defects with diameters between 5 and 10 cm remains a source of controversy.
38.6.1 Open Approaches
Open repair of complex abdominal wall defects has the potential to be one of the most technically challenging procedures in the field of abdominal surgery. It may be associated with a significant physical insult to the patent, and meticulous preoperative planning is essential, not least in terms of pain relief that the patient will require in the postoperative setting. Patients with large defects usually benefit from epidural analgesia, which offers superior analgesia compared with alternative strategies and results in fewer postoperative complications .
126.96.36.199 Primary Suture Repair
The challenge of obtaining good long-term results with fascial apposition using sutures alone has been recognized for some time. Although some surgeons have advocated specific suture techniques designed to allow progressive tensioning via what is essentially a pulley mechanism , high-quality long-term data demonstrating effectiveness are lacking. Simple suture repair alone often fails because the edges of the repair are under tension following closure. The superiority of mesh repair compared with suture repair is now well established , and suture repair is no longer advocated in the setting of planned, clean surgery. The role of suture repair is now confined to the contaminated and or infected setting, which often occurs in emergency surgery, where the operating surgeon feels the placement of mesh (of whatever type) is contraindicated, largely because suture repair has a significantly lower rate of infective complications. A definitive repair with mesh can be performed at a future date as a planned procedure should a hernia develop again.
188.8.131.52 Components Separation
A technical advance on simple suture repair is the separation of the components of the abdominal wall to allow medial displacement of the myofascial edge, thus reducing tension to physiological levels and consequently facilitating the repair. Although various descriptions of lateral relaxing incisions have appeared in the literature for nearly 100 years , their use in abdominal wall reconstruction was popularized by Ramirez et al  in 1990. In anterior component separation, the rectus abdominis, internal oblique, and transversus abdominis are separated from the external oblique by an incision of the external oblique aponeurosis just lateral to the linea semilunaris. This may allow the unilateral medial fascia to be advanced a maximum of 10 cm. Despite the ability to close large defects, evidence to support the superiority of anterior component separation over primary suture repair is lacking, and high recurrence rates have been reported . Consequently, many now describe its use in conjunction with reinforcing mesh repairs. The anterior component separation technique is also associated with significant tissue trauma, which may result in lipocutaneous flap necrosis, seroma, and wound infection. Minimally invasive variants of the anterior component separation technique have been described that seek to minimize such tissue trauma .
An alternative strategy to facilitate closure of large defects is posterior component separation, which releases the rectus abdominis and external and internal oblique muscles from the transversus abdominis. During a laparotomy, the retrorectus plane is developed laterally until the perforating neurovascular bundles are reached, just medial to the linea semilunaris. The posterior rectus sheath is incised to afford access to the plane between the internal oblique and transversus abdominis. The insertion of the transversus abdominis muscle into the posterior sheath can be divided and the muscle separated from the underlying transversalis fascia and peritoneum. This technique avoids the large lipocutaneous flaps of the anterior component separation technique and associated wound morbidity, but still allows a similar degree of myofascial medialization . Evidence of its effectiveness is limited to case series where it is usually combined with a retromuscular mesh repair.
184.108.40.206 Mesh Repair
Mesh repairs of herniae have been used for over 100 years, but only with the advent of modern synthetic materials and the pioneering work of the American surgeon Francis Usher in the 1950s did any significant advance in outcome occur. Meshes work via two main mechanisms. Initially, they have their own tensile strength that imparts additional support to the repair. They subsequently induce (or support) tissue ingrowth and collagen deposition to form a scar that adds strength. Mesh may be placed in numerous positions within the abdominal wall.
In the onlay technique, the mesh sits superficial to the anterior rectus sheath and usually overlies the apposed fascial edges, with an overlap of 5–8 cm. The inlay technique essentially utilises the mesh as a bridge across the fascial edges of the hernia defect. This was a popular technique during the 1990s and borrowed the concept of “tension-free” repair from inguinal hernia surgery and applied it to abdominal wall hernias, although the biomechanics of the two areas are different. The mesh may overlap, either superficially or deep, beyond the margins of the defect to facilitate fixation.
“Sublay” is a term that results in some confusion because it has been used to refer to both the retromuscular and intraperitoneal positions. In retromuscular placement, the plane between the rectus abdominis muscle and the posterior rectus sheath is developed by incising the posterior rectus sheath approximately 0.5 cm from its medial edge. Dissection may be the initiated just above the level of the umbilicus and progressed laterally using diathermy until the linea semilunaris is reached. The perforating neurovascular bundles that enter the rectus sheath just medial to the linea semilunaris are preserved. Once both sides are mobilized, the posterior sheath is closed. If the posterior sheath is incomplete and cannot be approximated, either the hernia sac may be used to provide coverage of the abdominal contents, the falciform ligament, or bladder, or the omentum can be carefully placed over the bowel to prevent adhesions forming to the mesh. The mesh lies posterior to the rectus abdominis muscle but superficial to the posterior rectus sheath cranial to the arcuate line (Fig. 38.5). The mesh lies in the preperitoneal plane, caudal to the arcuate line. The anterior sheath is then reapproximated in the midline.
Retrorectus placement of a biologic mesh during an open repair
In the intraperitoneal placement technique, the mesh lies inside the abdominal cavity and is fixed to the abdominal wall. In open surgery, the midline defect is usually closed, whereas in the laparoscopic variant, the defect is not necessarily closed, with the mesh acting as a barrier to intra-abdominal organs entering the hernia sac (often known as intraperitoneal onlay mesh repair). The deep surface of the mesh may come into contact with intra-abdominal organs.
The relative merits of each of the mesh placement techniques have been debated for some time, with passionate advocates for each at some point over the past 50 years. The onlay technique is technically easy and versatile, as is the inlay technique (often referred to as “bridging”). The retromuscular and intraperitoneal positions are thought to have superior biomechanical advantages, with the meshes being held in the correct positions by intra-abdominal pressure. Ultimately, recurrence rate following hernia repair has been used as the measure for determining which technique offers the optimal outcome.
The inlay technique is now recognized to have an unacceptably high recurrence rate. The reasons for failure of the hernia repair are multifactorial and may be the result of shrinkage of the synthetic mesh, the complex biomechanical forces of the abdominal wall that cause the mesh itself to fail, the mesh–tissue interface, or undue stretching on the ingrowing tissue. Furthermore, many of the meshes originally used with the inlay technique were associated with complications such as erosion into the bowel and enterocutaneous fistulas. Consequently, the technique is no longer advocated. Systematic review of randomized trials failed to demonstrate any superiority of onlay versus sublay mesh placement techniques . Conversely, national registry data suggest that retromuscular repair results in a markedly lower recurrence rate compared with the other techniques . Many authors and the European Hernia Society now regard the retromuscular technique as the reference standard for open repair. It can be combined with posterior component separation to facilitate the closure of large defects.
38.6.2 Laparoscopic Approaches
Laparoscopic approaches are ideally suited to patients who have amenable peritoneal cavities, smaller herniae, and require simpler procedures, usually without concomitant bowel resections or abdominoplasty. Adhesiolysis may be the most technically challenging aspect of the procedure, and avoiding energy devices is advisable; sharp dissection with scissors is preferable. Several reviews of randomized trials concluded that there is no difference in recurrence rates compared with open procedures, but that complications rates are lower, specifically wound infections [56, 57]. Recent data from national registries may suggest a lower crude recurrence rate with laparoscopy, but the data are not risk adjusted for selection bias regarding the surgical approach chosen, and interestingly, laparoscopy was associated with increased rates of the more serious complications .
220.127.116.11 Intraperitoneal Onlay of Mesh
The intraperitoneal position of mesh placement is synonymous with the laparoscopic approach. The most prevalent technique is to use the mesh as a bridge across the hernia defect. The optimal size of the mesh depends on the size of defect being repaired, but it needs to account for mesh shrinkage, which may be up to 94 % of the surface area . Consequently, the traditional advice of a 5-cm overlap may not be reliable as defects size increases and the mesh-to-defect ratio becomes smaller. Significant debate exists among surgeons as to the optimal method of fixation, positioning and tension in the mesh when placed during laparoscopic repair. If the mesh placement is not optimal, there is a risk of pseudo-recurrence (defined as a recurrent swelling at the site of the original hernia) as a result of the mesh bulging into the hernia sac or seroma, and which may occur much more frequently than initially thought, with rates of 19–31 % in incisional and ventral hernia repairs [59, 60]. Closure of the defect during laparoscopic repair may reduce the risk of these complications and of true hernia recurrence . Tacker mesh fixation may be associated with quicker surgery and less postoperative pain in the short term, but otherwise there is no difference from suture mesh fixation .
38.6.3 Intraoperative Anesthetic Considerations
Anesthetists often favor the use of an epidural anesthetic in conjunction with general anesthesia to facilitate abdominal wall relaxation and postoperative pain relief. As the abdominal wall is being closed, the anesthetist can monitor changes in respiratory physiology (such as airway pressure and tidal volume). If volume-controlled ventilation is being used, increases in airway pressure can be a surrogate for the likelihood of both postoperative respiratory complications and the risk of abdominal compartment syndrome. Communication between the anesthetist and surgeon can help identify at-risk patients, and, if necessary, additional surgical techniques can be used to relax the abdominal wall and reduce the intra-abdominal pressure.
38.6.4 Special Considerations
Some patients may have herniae of such complexity that the techniques described earlier are inadequate to close the abdominal wall. This may be particularly true in patients subject to penetrating trauma, necrotising fasciitis, laparostomy, or tumors invading into the abdominal wall. Furthermore, there may be complexity because of concomitant stoma problems or the effects of profound weight loss. In such circumstances, additional techniques may have to be considered.
18.104.22.168 Domain Loss
When significant amounts of tissue have been lost, techniques are available that may expand the amount of tissue within the abdominal wall. This has been achieved by the use of progressive preoperative pneumoperitoneum, tissue expanders, and botulinum toxin [63–65]. Preoperative pneumoperitoneum involves the induction of pneumoperitoneum using a Veress needle or endoperitoneal catheter that is maintained over a period of days or weeks . Pneumoperitoneum is sustained using regular insufflation of gases such as oxygen or nitrous oxide until sufficient abdominal wall expansion has been achieved or the hernia has reduced. Tissue expanders are placed in a specially created pocket between the external oblique and the superficial aspect of the internal oblique fascia. The expanders have remote ports that allow the injection of saline on a weekly or biweekly basis over a period of months, depending on the size of the defect, until there is adequate lengthening of the musculature to allow primary fascial closure . Botulinum toxin is a potent neurotoxin produced by the anaerobic gram-positive rod Clostridium botulinum. It blocks the release of acetylcholine at the presynaptic cholinergic nerve terminal and results in flaccid muscle paralysis . Injections of botulinum toxin into the lateral abdominal wall muscles essentially separate chemical components by allowing the muscles to achieve maximum relaxation, facilitating closure. When none of the adjuncts are sufficient, tissue transfer, via either free or pedicled flaps, is required .