Overview of component separation

INTRODUCTION — More than 350,000 ventral hernias are repaired annually in the United States [1,2]. All repair techniques have limitations to their durability, leading to some inevitable recurrences that beget further complexity [3,4]. In the 21^st century, component separation techniques have emerged as an important tool in the surgeon's armamentarium for large or complex hernias [5].

Ramirez first defined the term "components separation" in 1990 as a way "large abdominal wall defects can be reconstructed with functional transfer of abdominal-wall components," rather than relying on remote muscle flaps or bridging prosthetics [6]. Since then, strategic, serial division of the rectus and lateral abdominal wall musculofascial layers has been explored to address undue tension when closing large midline defects.

In this overview topic, we will discuss the relevant abdominal wall anatomy, purposes and techniques of component separation, patient selection criteria, preoperative adjuncts that could potentially assist with fascial or soft tissue closure, and complications of component separation.

Technical details of various component separation techniques can be found elsewhere. (See "Open anterior component separation techniques" and "Open posterior component separation techniques" and "Robotic component separation techniques".)

Basic ventral hernia repair techniques that do not involve component separation are discussed in other topics. (See "Management of ventral hernias" and "Laparoscopic ventral hernia repair" and "Robotic ventral hernia repair" and "Lateral abdominal wall hernia repair".)

ANATOMY OF ANTERIOR ABDOMINAL WALL

Muscles — Three muscles constitute the lateral abdominal wall. From superficial to deep, they are the external oblique (EO), internal oblique (IO), and transversus abdominis (TA) muscles, followed by layers of transversalis fascia and peritoneum (figure 1 and figure 2). (See "Anatomy of the abdominal wall", section on 'Muscles'.)

Linea semilunaris — The three lateral abdominal wall muscle layers do not fuse at a single point. Rather, fibers of the IO aponeurosis branch into anterior and posterior lamellae at the linea semilunaris (figure 3). More medially (1 to 3 cm), fibers of the EO aponeurosis fuse with fibers of the anterior lamella of the IO to form the anterior rectus sheath, while fibers of the posterior lamella of the IO fuse with the TA to form the posterior rectus sheath. The semilunar line marks the lateral extent of the rectus space and is a key anatomical concept for understanding component separation techniques.

Linea alba — The anterior and posterior rectus sheaths encase the rectus muscle, then fuse medially to form the linea alba. Depending on the width of the linea alba, associated diastasis, or midline hernia, the distance of the rectus muscles from the midline can be somewhat variable. (See "Rectus abdominis diastasis".)

Posterior rectus sheath — The cross-sectional composition of the posterior rectus sheath varies by its anatomical location (figure 3):

●In the superior one-third of the abdomen, there is a prominent TA muscle belly beneath the posterior lamella of the IO before each aponeurosis fuses medially to form the posterior rectus sheath (image 1).

●In the middle third of the abdomen, the TA is aponeurotic beneath the posterior lamella of the IO before these layers fuse medially to form the posterior rectus sheath. Above the arcuate line, the peritoneum and transversalis fascia are densely adherent to the posterior rectus sheath.

●In the lower third of the abdomen, the posterior rectus sheath ends abruptly at the arcuate line and becomes contiguous with peritoneum and transversalis fascia (figure 3). All lateral muscle layers travel anterior to the rectus muscles below the arcuate line.

Finally, the superior third of the TA begins to interdigitate with the diaphragm along the costal margin, and the two can be difficult to distinguish.

Blood vessels and nerves

Retrorectus space — The medial retrorectus space is relatively avascular. As the lateral retrorectus space is developed, the inferior epigastric vessels are encountered just medial to the linea semilunaris in the lower third of the abdominal wall. As the inferior epigastric vessels course superiorly, they bury themselves in the belly of the rectus muscle. Only at the most cephalad aspect of the rectus muscles do the superior epigastric vessels become visible before they too become invested in rectus muscle (figure 4).

Also housed in the retrorectus space are laterally perforating neurovascular bundles that originate from T6 to L1 and travel between the TA and IO until they pierce the posterior lamella of the IO to enter the retrorectus space [7]. Their presence, just medial to the linea semilunaris, serves as a valuable landmark. Along with the musculophrenic and lumbar arteries, these lateral perforators supply the lateral (flank) abdominal wall (figure 5).

The suprapubic abdominal wall at and below the anterior superior iliac spines is also supplied by the inferior epigastric arcade, along with help from the superficial external pudendal, superficial, and deep circumflex iliac arteries.

Just below the arcuate line, there is consistently an unnamed vessel that branches medially off the epigastric vessels coursing toward the midline. Also, while most laterally perforating neurovascular bundles appear just medial to the semilunar line, there is typically a single large perforator in the superior third of the abdomen that is much more medial than the rest.

Subcutaneous space — Anterior perforators off the deep epigastric vessels pierce the anterior rectus sheath to supply the subcutaneous tissue above the rectus muscles, and for this reason the rectus muscle is more closely bound to its anterior fascial envelope [8]. The surgeon should remain mindful of the blood supply to the anterior abdominal wall, particularly when a patient has had several abdominal incisions that could compromise blood flow and lead to tissue necrosis in "watershed" areas (picture 1).

PURPOSES OF COMPONENT SEPARATION — In contemporary hernia surgery, component separation serves two purposes.

Relieve tension on midline fascial closure — The traditional aim of a component separation is to strategically divide myofascial layers of the abdominal wall to alleviate tension on fascial approximation, typically in the midline.

The benefits of reestablishing the midline during any hernia repair are to improve core muscle function by aligning the rectus muscles in the vector of their proper usage and to give lateral abdominal muscles a firm insertion point. The functional benefits in strength, stability, respiratory function, and quality of life warrant "sacrifice" of one of the lateral muscles [9-12]. Cross-sectional imaging has even suggested that division of one lateral abdominal wall muscle to achieve midline closure results in compensatory hypertrophy of the other two remaining muscles [13].

Surgical technique to relieve tension on midline fascial closure has been pursued as early as 1916 [14,15], but earlier techniques of relaxing incisions on the medial rectus sheaths were insufficient for closing larger midline defects [16,17]. Bridging synthetic mesh is not a good option, given the high rates of infection, excision, fistulization, and hernia recurrence [18-20]. Meanwhile, autologous tissue transfers such as the free or pedicled tensor fascia lata flaps are also associated with high recurrence rates in addition to donor site morbidities [21,22].

Oscar Ramirez first described a localized dissection of the lateral abdominal wall that would provide additional fascial medialization beyond that which can be accomplished with dissections limited to the rectus fascial envelope [6]. Since then, strategic, serial division of the rectus and lateral abdominal wall musculofascial layers has been explored to address undue tension when closing large midline defects. (See 'Techniques of component separation' below.)

The size of a fascial defect that justifies usage of a component separation is not well defined, and this ambiguity exists for several reasons:

●The compliance of each patient's abdominal wall is variable. One patient with a large defect but more compliant abdominal wall may achieve fascial closure more easily than other patients with smaller defects but more rigid abdominal walls.

●The length and width of a fascial defect alone are often not reflective of the rest of the hernia, as small fascial defects can be associated with voluminous hernia sacs and loss of domain.

●There are advantages to a component separation other than midline fascial approximation. This point is critical to understanding the evolution of component separation utilization and its wide adoption during the past 10 years and is further discussed below. (See 'Facilitate retromuscular mesh placement' below.)

Facilitate retromuscular mesh placement — A posterior component separation, specifically transversus abdominis release (TAR), has allowed for additional benefits other than midline fascial advancement, including [23]:

●Relief of tension on the posterior rectus sheath/peritoneal closure

●A large retromuscular pocket for mesh reinforcement with wide overlap

●A well-vascularized plane for optimal mesh ingrowth

●Mesh placement that is not in contact with the viscera and is separated by muscle from the superficial wound

●Allows for the use of uncoated monofilament polypropylene (both inexpensive and resilient to infection)

Because of these benefits offered by retromuscular mesh placement, contemporary surgeons now have an additional motivation to utilize a TAR other than just anterior rectus approximation. (See 'Patient selection' below.)

TECHNIQUES OF COMPONENT SEPARATION — Depending on the lateral abdominal wall muscle(s) divided, techniques of component separation can be broadly categorized into anterior and posterior. Both anterior and posterior component separations allow for a maximum bilateral rectus advancement of approximately 20 cm. Uniquely, transversus abdominis release (TAR) also allows for significant posterior fascial advancement >20 cm to create a large visceral sac and retromuscular pocket.

It should be emphasized that anterior and posterior component separations should not be performed concomitantly, or else the anterior abdominal wall may be destabilized.

Open anterior component separation — The original Ramirez component separation involved two myofascial divisions on each side of the abdominal wall. First, medial division of the posterior rectus sheath and its separation from the overlying rectus muscle allows for each rectus muscle and its associated anterior fascia to be advanced medially 3, 5, and 3 cm in the upper, middle, and lower third of the abdominal wall, respectively (6, 10, and 6 cm bilaterally).

If this is insufficient to alleviate midline tension, the external oblique muscle can be longitudinally divided 1 to 2 cm lateral to the semilunar line and separated from the underlying internal oblique muscle in a relatively avascular plane. When combined with posterior rectus sheath division, this allows for 5, 10, and 3 cm of advancement, again respectively in each third of the abdominal wall, totaling 10, 20, and 6 cm of bilateral advancement (table 1) [6].

While this operation was initially referred to as a "components separation" without ambiguity, when newer techniques of separating the posterior rectus sheath and contiguous transversus abdominis (TA) from the anterior internal oblique (IO)/external oblique (EO)/rectus muscle bodies were termed a "posterior component separation," Ramirez's division of the anterior EO inherited the designation "anterior component separation" retroactively.

Open anterior component separation techniques are discussed separately. (See "Open anterior component separation techniques".)

Open posterior component separation — Following medial division of the posterior rectus sheath, the retrorectus space is entered and can be dissected as lateral as the linea semilunaris; this retrorectus dissection is usually referred to as the "Rives-Stoppa" repair [24]. If further myofascial release is required for midline fascial approximation or posterior rectus sheath closure, the posterior lamella of the IO and TA can both be divided to continue the retromuscular dissection in the preperitoneal space (TAR). The space between the IO and TA is not usually developed, as it would require division of laterally perforating neurovascular bundles. (See 'Retrorectus space' above.)

In order to assess the relative effectiveness of a posterior component separation in regards to fascial advancement, cadaveric dissections were performed [25]. Each of these operative steps offers consistent medial advancement of the anterior and posterior layers. Unilateral maximum anterior advancement is 7.6 cm after a retrorectus dissection, 8.0 cm after division of the posterior lamella of the IO, 8.6 cm after TA division, and 9.9 cm after completion of the retromuscular dissection. Respective posterior sheath advancement is 7.5, 8.3, 9.5, and 11.2 cm after each corresponding step. These results are comparable to Ramirez's findings (table 1).

Open posterior component separation techniques are discussed separately. (See "Open posterior component separation techniques".)

Robotic posterior component separation — The robotic platform has allowed for minimally invasive adaptations of these retromuscular hernia repairs that, for most surgeons, could not be done using traditional laparoscopy. There are both transabdominal and totally extraperitoneal iterations of the Rives-Stoppa retrorectus repair for hernias <7 cm wide [26]. For hernias >7 cm wide, a robotic transversus abdominis release is also a potential option [27]. (See "Robotic component separation techniques".)

Basic requirements for robotic repairs include the ability to achieve minimally invasive access to the peritoneal cavity and safely clear the anterior abdominal wall of visceral adhesions, including safe reduction of the hernia contents. While the surgeon can often avoid a laparotomy using these techniques, any residual scar from a previous laparotomy would be left behind, and this can sometimes impact a patient's preference.

In line with the evolution of other techniques from open to a minimally invasive approach, evidence has begun to accrue demonstrating shorter length of stay and decreased wound morbidity for these robotic retromuscular hernia repairs [28,29].

Robotic component separation techniques are discussed separately. (See "Robotic component separation techniques".)

Mesh reinforcement — Although component separation was portrayed as a method to alleviate tension on midline hernia repairs without any prosthetic reinforcement, subsequent reports have revealed early recurrence rates (within one year) as high as 53 percent [30]. Given our modern understanding that mesh is critical to the durability of any hernia repair, contemporary descriptions of any component separation include some prosthetic reinforcement.

Mesh reinforcement is suboptimal with anterior component separation techniques for several reasons. Large defects will not allow for retrorectus mesh placement, because the posterior rectus sheaths will be under too much tension for closure, and a concomitant posterior component separation to aid posterior sheath closure cannot be combined with any anterior component separation. While raising large skin flaps allows for large onlay meshes, it is also more likely to undermine the blood supply of the subcutaneous tissue and predispose patients to wound morbidities. Conversely, minimizing skin flaps curtails mesh overlap, which makes an onlay technique impractical. Ultimately, intraperitoneal mesh is commonly utilized, and these barrier-coated synthetics or bio-prosthetics incur additional cost.

Taking all this into consideration, it becomes obvious that the reason the posterior component separation technique TAR has gained such wide popularity is not just because TA division offers superior fascial medialization compared with EO division. Rather, it is also because TAR, in addition to allowing for equivalent myofascial relaxation to approximate the midline, creates a reproducible, well-vascularized, retromuscular pocket for mesh placement, all through a midline incision without the need for skin flaps [31]. Release of the posterior rectus sheaths allows for creation of a large visceral sac to isolate the viscera. With rare exception, this consistently allows for use of uncoated monofilament polypropylene, which is inexpensive and resilient to infection. (See 'Facilitate retromuscular mesh placement' above.)

PATIENT SELECTION — The decision to pursue a component separation is first guided by hernia width that can be determined preoperatively by physical exam or cross-sectional imaging (algorithm 1). The further choice among multiple options within each hernia width category is usually dictated by surgeon experience and preference.

●Typically, hernias <7 cm do not require a component separation and can often be repaired with either an open, laparoscopic, or robotic approach with intraperitoneal mesh or an open or robotic approach with retrorectus mesh as described by Rives and Stoppa. There are both transabdominal and totally extraperitoneal iterations of the robotic Rives-Stoppa retrorectus repair for hernias <7 cm wide [26]. Such hernias can also be repaired with onlay mesh using open techniques.

●Hernias 7 to 10 cm typically will not require a component separation for midline fascial approximation and can be repaired laparoscopically with a large piece of intraperitoneal mesh or repaired in an open retromuscular approach. An open or robotic TAR can be added to achieve posterior rectus sheath closure if necessary. A rectus width to hernia width ratio >2 reliably predicts the ability to close the fascia with a Rives-Stoppa repair alone and no further myofascial release in almost 90 percent of cases [32].

●Hernias >10 cm, depending on abdominal wall compliance, may require either an anterior or posterior component separation for both rectus approximation (midline closure) and posterior fascial approximation. This can be accomplished with either open anterior component separation or open or robotic TAR.

We reserve component separation for nonemergency hernia repairs. Use of these techniques to achieve fascial closure in an open abdomen situation after an abdominal catastrophe is feasible but will negate future abdominal wall reconstruction options. During emergency operations, we prefer to attempt primary closure with interrupted figure-of-eight sutures or bridge the fascial defect with a nonpermanent prosthetic.

PREOPERATIVE ADJUNCTS — Preoperative adjuncts (such as botulinum toxin injection or tissue expansion) have been used to facilitate fascial and/or abdominal wall closure when a hernia volume to peritoneal volume ratio is >20 to 25 percent. However, there is a lack of consensus regarding the routine use of preoperative adjuncts in abdominal wall reconstruction, especially progressive pneumoperitoneum with its associated severe complications [33].

Botulinum toxin — The use of botulinum neurotoxin type A (BoNT-A) to preoperatively relax the lateral abdominal wall muscles and reduce tension on midline abdominal wall closure has been termed a "chemical component separation" or "chemical component paralysis" [34].

There is no consensus on which patients would benefit from BoNT-A injections prior to ventral hernia repair, but many authors have cited hernia volume to peritoneal volume ratio >20 to 25 percent (as defined by Tanaka [35]) to warrant consideration of preoperative BoNT-A [36].

While BoNT-A injection is a safe procedure, evidence to support its use and the associated cost is limited. In small case series and a meta-analysis, the use of BoNT-A before ventral hernia repair decreased the width of the abdominal wall defect by approximately 5.8 cm, increased the length of the abdominal wall by approximately 3 to 4 cm, and increased the volume of the peritoneal cavity [34,37-40]. However, such radiographic changes have not translated into tangible clinical benefits such as reduced need for component separation [40,41]. A propensity-score matched study of 145 patients undergoing abdominal wall reconstruction found a higher percentage of fascial closure (92 versus 81 percent), but also a greater need for component separation with preoperative BoNT (61 versus 47 percent) [42].

BoNT-A is typically delivered as three to five injections per side of the abdominal wall [43].

●When possible, these injections should be given under conscious sedation to minimize patient discomfort.

●A total of 300 units of BoNT-A is reconstituted in 150 cc of injectable 0.9% sodium chloride solution (final concentration of 2 units/cc).

●Two syringes are labeled and loaded onto a three-way stopcock, one with the BoNT-A solution and the other with injectable saline. This stopcock is attached to an extension tubing secured to an 18 gauge spinal needle.

●The three muscle bellies of the lateral abdominal wall (external oblique [EO], internal oblique [IO], transversus abdominis [TA]) are identified by ultrasound at three sites on each side of the abdomen (subcostal, anterior axillary line, and lower quadrant).

●Under ultrasound guidance, the spinal needle is passed into the TA muscle belly first at each of the sites. Sterile saline is injected to confirm needle location, before 8.3 cc (16.6 u) of BoNT-A is injected into the TA muscle belly.

●Next, the needle is withdrawn into the IO and then the EO muscle and the sequence is repeated twice, injecting a total of 25 cc and 50 units of BoNT-A at each site.

●The same sequence is repeated at each of the six sites.

●This should be done at least two weeks before attempting the ventral hernia repair.

Tissue expanders — Tissue expansion involves placement of a silicone balloon under subcutaneous tissue or fascia followed by serial injections of saline to inflate the balloon to expand the local tissue in preparation for a local reconstruction [44,45].

Tissue expansion can be used for patients with very large fascial and soft tissue defects in the context of a large ventral hernia with loss of domain or tissue loss from traumatic injury, soft tissue infection, oncologic resections, or a prior open abdomen. Pediatric surgeons encounter these scenarios in the setting of gastroschisis and omphalocele.

Tissue expanders can be placed in two types of planes:

●Placement between the lateral abdominal wall muscle layers (IO/EO or IO/TA) results in bidirectional expansion, indirectly increasing intra-abdominal pressure. This results in a less effective expansion of the skin and subcutaneous tissue [46].

●Alternatively, expansion of the skin and subcutaneous tissue is more effective when the expansion devices are placed between the subcutaneous tissue and the abdominal wall muscles. In the context of an abdominal wall reconstruction where component separation is providing sufficient myofascial advancement in the vast majority of cases, we reserve the role of tissue expansion for assuring the patient has sufficient soft tissue at the end of a case.

Balloon implants come in a variety of shapes and sizes and can include remote or integrated ports. When possible, the implant should match the length of the wound. Placement should be through an incision that will either be incorporated into one margin of the eventual flap or placed perpendicular to the line of expansion to prevent dehiscence. Expansion of the device can begin at the time of implantation or one to three weeks later, providing sufficient tension for expansion without compromising perfusion or the integrity of the wound through which it was placed. Generally, the devices are injected weekly for 6 to 12 weeks to maximize expansion.

Tissue expansion requires multiple surgeries and careful management of the expansion in between. It should start at least 6 to 12 weeks prior to the hernia repair. Complications such as device infections or flap necrosis can occur in 15 percent of patients [47].

COMPLICATIONS

Wound morbidity — Open anterior component separation is associated with wound morbidities in as many as 50 percent of patients, about half of whom developed surgical site infections [48,49]. Alternatives to traditional open component separation are associated with much lower rates of wound complications ranging from 2 to 14 percent [50-52]. (See "Open anterior component separation techniques".)

The wound morbidity rates of anterior and posterior component separation techniques are generally comparable [53-55].

Risk factors for wound morbidity and mesh complications include patient factors (eg, body mass index, poorly controlled diabetes, history of a previous surgical site infection), hernia factors (size and wound class), and technical factors related to the surgical approach (open versus minimally invasive, mesh type and position) [56].

The Abdominal Core Health Quality Collaborative (ACHQC) app can use preoperative and intraoperative information to provide patient-specific risk-adjusted 30 day and one-year outcomes.

Pulmonary complications due to intra-abdominal hypertension — Another postoperative concern specifically for massive ventral hernia repairs with loss of domain is the potential development of postoperative abdominal compartment syndrome.

In our experience, abdominal compartment syndrome in the setting of elective myofascial release most commonly manifests as postoperative respiratory complications requiring reintubation and/or transfer to the intensive care unit (ICU). We found that changes in plateau pressure (PP) after ventral hernia repair directly correlated with postoperative respiratory complications (increase in PP ≥6 mmHg, odds ratio [OR] 8.67; increase in PP ≥9 mmHg, OR 11.5) [57].

Thus, for large abdominal wall reconstruction patients with a tight abdominal wall closure, we will have the anesthesia provider measure the PP before and after closure of the anterior abdominal wall fascia using the same tidal volume.

●Patients with a PP increase of <6 mmHg can be safely extubated.

●Young patients with no pulmonary disease or concern from anesthesia staff are extubated even with a PP increase of ≥6 mmHg but are still monitored in the ICU overnight.

●Those with a PP increase of ≥6 mmHg and any concern for pulmonary compromise (old age, history of obstructive sleep apnea or underlying lung disease) will typically remain intubated until they are reassessed by the ICU staff in the morning.

●Paralytics are only added if there is difficulty ventilating the patient or decreased urine output that is not due to hypovolemia. Such clinical signs are usually associated with a PP increase of ≥9 mmHg, although a PP increase of ≥9 mmHg per se is not an indication to paralyze the patient.

Elevations in intra-abdominal pressure after ventral hernia repair are unique in that they are usually transient and can be expected to resolve within 48 hours. This could be due to fluid shifts and increase in compliance of the abdominal wall as a result of component separation. However, such patients are still at risk of developing postoperative respiratory complications [58].

Twenty percent of patients in a historic series had an increase in PP by >6 mmHg [57]. By contrast, <5 percent of patients require postoperative intubation in contemporary practice as anesthesia providers are using lower tidal volumes and less crystalloid fluid. Of note, we no longer measure bladder pressure, as it does not provide additional information.

It should be recognized that patients undergoing elective hernia repair with a myofascial release are very different from the context in which abdominal compartment syndrome is traditionally encountered (typically acute abdominal catastrophes). As a result of these findings, the World Society of the Abdominal Compartment Syndrome has recognized intra-abdominal pressure changes in the elective setting as a separate and distinct phenomenon [59].

Linea semilunaris disruption — Inappropriate anteromedial dissection during a TAR dissection or inappropriate posteromedial dissection during an anterior component separation can result in complete transection of the linea semilunaris, separating the medial rectus muscle from the lateral oblique muscles [60]. These patients can present with a lateral bulge as early as a few months after their operation. When bilateral bulges flank a "floating" rectus muscle, it gives the appearance of a "Mickey Mouse" hernia defect (image 2).

The incidence of these complications is currently unknown but could be increasing given the growing popularity of component separation techniques (especially robotic retromuscular adaptations) [61]. While this complication is typically only encountered by inexperienced surgeons during the "learning curves" of open or robotic TAR, those who are affected will likely never restore a "normal" or dynamic abdominal wall. Thus, surgeons who attempt component separations must have an appropriate respect for the complexity of the anatomy.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Ventral hernia".)

SUMMARY AND RECOMMENDATIONS

●Purposes of component separation – Component separation serves two purposes in modern hernia surgery: to alleviate tension on midline fascial approximation and to facilitate closure of the posterior rectus sheath and create a retromuscular pocket to accommodate mesh. (See 'Purposes of component separation' above.)

●Techniques of component separation – Component separation can be performed with either anterior or posterior techniques, both permitting maximum bilateral rectus advancement of approximately 20 cm. In addition, transversus abdominis release (TAR) also allows for significant posterior fascial advancement >20 cm to create a large visceral sac and retromuscular pocket. Specific techniques are discussed in other topics, but it should be emphasized that anterior and posterior component separations should not be performed concomitantly, or else the anterior abdominal wall may be destabilized. (See 'Techniques of component separation' above and "Open anterior component separation techniques" and "Open posterior component separation techniques".)

●Patient selection for component separation – The decision to pursue a component separation is typically guided by hernia width, which can be determined preoperatively by physical exam or cross-sectional imaging (algorithm 1) (see 'Patient selection' above):

•For patient with hernias <7 cm wide, hernias can typically be repaired without component separation.

•For patients with hernias 7 to 10 cm wide, the decision to use component separation is influenced by the width of the hernia versus the width of the rectus muscle. Although such hernias can be repaired without component separation, a TAR may be performed to achieve posterior rectus fascia closure if a retromuscular approach is undertaken.

•For patients with hernias >10 cm wide, we suggest repair with component separation rather than other techniques (Grade 2C). However, for patients with good abdominal wall compliance, hernia repair without component separation may be feasible.

●Preoperative adjuncts for component separation – Preoperative adjuncts (such as botulinum toxin injection or tissue expansion) have been used to facilitate fascial and/or abdominal wall closure when the hernia volume to peritoneal volume ratio is >20 to 25 percent. However, there is a lack of consensus regarding the routine use of preoperative adjuncts in abdominal wall reconstruction. (See 'Preoperative adjuncts' above.)

●Complications of component separation

•The wound complication rate of open anterior component separation is substantially higher than that of less invasive anterior alternatives, while the wound complication rates of comparable anterior and posterior component separation techniques are similar. (See 'Wound morbidity' above.)

•Postoperative respiratory failure requiring reintubation can be a manifestation of intra-abdominal compartment hypertension after large or complex ventral hernia repair. We use the increase in plateau pressure after fascial closure to decide whether to leave the patient intubated at the end of surgery. The increase in intra-abdominal pressure is usually transient for up to 48 hours. (See 'Pulmonary complications due to intra-abdominal hypertension' above.)

•Linea semilunar line disruption is a technical complication that causes separation of the medial rectus muscle from the lateral oblique muscles. The resulting deformity can be long-lasting or permanent. To avoid that, the surgeon should understand the relevant anatomy before pursuing these dissections. (See 'Linea semilunaris disruption' above.)