Approaching the Complex Abdominal Wall Hernia: General Principles of Component Separation Techniques

Abstract

Abdominal wall hernias represent a clinical spectrum ranging from a small defect in the abdominal wall causing minimal interruption to patients up to massive defects with severe impairment in abdominal wall function and physiology. Principles of successful hernia repair rely on re-approximation of fascial defect edges to achieve primary closure in a tension free manner and subsequent reenforcement of the repair with a mesh. In the case of large defects, especially in the incisional hernia scenario, advanced fascial release techniques with separation of components is often required to recreate normal anatomy. Relevant techniques are anterior component separation with or without sparing of periumbilical vascular perforators and posterior component separation with transverse abdominis release, representing an expansion of the retrorectus Rives-Stoppa repair. With regards to surgical planning, preoperative imaging, standardization of techniques according to patient and hernia defect characteristics as well as prehabilitation of the abdominal wall with botulinum toxin (“chemical component separation”) represent significant weapons in the armamentarium of the complex abdominal wall reconstruction surgeon. The scope of this chapter is to attempt to unify pathophysiologic concepts of hernias with anatomic-based advanced repairs.

1. Introduction

The definition of complex abdominal wall hernia comprises a hernia in the abdominal wall that requires advanced techniques for its repair. The vast majority of complex hernias develop in the area of a postoperative scar and are thus a subgroup of incisional hernias, according to the most recent European Hernia Society Classification of Hernias [1]. Complex hernias, although not defined per se, represent a constellation of unfavorable factors preventing simple repair of the defect, both patient- and disease-related. A recent consensus used as criteria for complex hernias size and location, contamination and soft tissue condition, patient history and risk factors as well as clinical scenario [2]. Surgical treatment of this subgroup of patients requires a detailed understanding not only of the techniques involved in advanced abdominal wall reconstruction, but also of the underlying pathophysiologic processes in this disease entity, in order for surgery to have a role of restoring normal anatomy as means to restore normal function [3].

2. General principles of component separation techniques

2.1 Pathophysiology of hernias

Abdominal wall hernias occur with loss of architecture in the load-bearing areas of muscle, fascial and tendinous tissues. Focusing on our task to enlighten the pathophysiological processes in the complex abdominal wall hernia setting, it seems prudent to attempt to establish a correlation between the macroscopic and the microscopic level of abdominal wall healing in the postoperative setting, as the majority of complex hernias are incisional in nature. Abnormal collagen metabolism with either a genetic basis, namely genetically acquired collagen disorders, or acquired, secondary to nutrition or smoking, seems to be one critical precipitating factor, leading to both primary and incisional hernias [4]. More importantly, however, and of probably greater interest for the cause of the present review, is fascial pathology secondary to acute laparotomy wound failure. Early laparotomy wound failure, as demonstrated in an animal model, seems to be a key event driving the subsequent development of incisional hernias [5]. Using radiopaque metal clips, the authors in the aforementioned paper followed laparotomy wound failure sequentially in time and showed that early laparotomy wound failure resulted in the formation of an incisional hernia, with authors assuming in their critical discussion part of the paper that early laparotomy wound failure resulted in distortion of normal wound healing architecture, thus creating a selecting process for abnormal population of wound repair fibroblasts deposing abnormal collagen [6, 7, 8]. It is this loss of normal healing architecture that creates an alteration in load forces that produces effects at the wound fibroblast and extracellular matrix level through mechanisms of mechanotransmission, in accordance with previous studies to play a significant role in tissue remodeling and repair. Apart from genetic factors in wound healing key mediators, wound ischemia of any cause also impairs normal processes [9]. Early wound laparotomy failure, unfortunately, is a clinical senescent process initially, and its incidence is, therefore, significantly underestimated before manifesting as a clinically evident incisional hernia at a later time [10]. Although useful for the purposes of academic research, dichotomising the pathophysiologic processes into mechanical and molecular in nature, these should be viewed as interweaving and overlapping.

Previous studies have shown that loss of insertion of the lateral abdominal wall musculature into the linea alba, as is the case in an incisional hernia, causes distinct changes in abdominal wall physiology [11, 12], because the normal force across the composite myofascial structure ceases to exist, thus decreasing the loads transferred onto lateral muscles. Lateral abdominal wall muscles present with shortening and oblique muscles develop exempt a histopathologic pattern similar to disuse atrophy that chronically unloaded skeletal muscles develop. Stiffening of oblique muscles decreases abdominal wall compliance and increases the mechanical loads exerted on the midline, which per se could be a deleterious event for the “healing” midline in the early postoperative period, in which wound tensile strength grossly depends on sutures to withstand opposing mechanical forces, while allowing sufficient time for the normal healing processes to take place [13]. This process creates a perpetuating cycle of lateral muscle retraction away from the midline, thereby further enlarging the hernia defect [14]. These pathophysiologic processes seem to be reversed with hernia repair, though not up to the full tensile strength of the uninjured abdominal wall [15]. Interestingly, function of rectus abdomini muscle complex is preserved in the incisional hernia setting, implying that it is the reconstitution of the abdominal wall muscle complex as functional unit that should be the goal of abdominal wall reconstruction surgery [16]. Mesh repair of incisional hernias has been established as superior to suture only repair of incisional hernias even for small-sized hernia defects [17]. Augmentation of primary fascial closure with mesh seems to yield better results in terms of hernia recurrence rates and postoperative complications compared to bridging the fascial defect with mesh [18]. In an attempt to unify “reconstitution of anatomy” with restoration of physiology, it seems prudent to assume that the most effective strategy for repair of complex hernia defects would be achievement of primary fascial closure with sutures and reenforcement of a tension-free repair with mesh. Contrary to this rationale is a study including both a prospective cohort of patients in addition to a retrospective one, both undergoing laparoscopic repair in the primary hernia- and incisional hernia- setting [19]. In this study, closure of the defect did not result in fewer hernia recurrences, but rather increased postoperative complications.

2.2 Relevant surgical anatomy and techniques

In accordance with the pathophysiologically-oriented discussion in the previous section, that fascial approximation should be pursued for in incisional hernia repair. Complex hernias present in that sense unique challenges because they require advanced techniques and elaborate preoperative planning in order to mobilize fasciae in the correct planes and achieve the goal of tension-free midline reconstitution while minimizing morbidity. The idea to mobilize the fascial layers of rectus abdominis sheath, thus gaining increased fascial length to overlap a wide defect gave birth to anterior component separation techniques and to the Rives-Stoppa initially and posterior component separation with transverse abdominis release.

Anterior component separation [20] entails extensive separation of lipocutaneous flap over the rectus abdominis complex with lateral extension past linea semilunaris over the lateral abdominal wall muscles. A longitudinal incision of the external oblique aponeurosis along with some of its muscle fibers is performed 1–2 cm laterally to the linea semilunairis, extending from the coastal margins cranially to the ipsilateral inguinal ligament caudally. A potential plane is thus created between the external oblique muscle and the internal oblique muscle, which enables midline fascial approximation by 5 centimeters (cm) on each side at the level of the epigastrium, 10 cm around the umbilical area and 3 cm suprapubically. Midline tension-reconstitution is reinforced with mesh to achieve a wide overlap over the original hernia defect fascial edges [21]. Major morbidity of the anterior component separation technique [22] arises mainly from the disruption of the periumbilical perforators and the extensive mobilization of lipocutaneous flaps, thus dysruptic normal perfusion of suprafascial tissues and giving rise to hematomas and seromas. In an attempt to avoid creation of large lipocutaneous flaps, a perforator-sparing approach [23, 24] has been described, a tunnel is created longitudinally over the subsequent external oblique aponeurosis fasciotomy, while staying 4 cm laterally to the midline, which is the area corresponding to the vascular distribution of periumbilical perforators. Preservation of blood supply has been repeatedly shown to decrease perioperative complications [25]. Perforator-sparing anterior component separation techniques are increasingly performed using laparo-endoscopic techniques, resulting in decreased perioperative morbidity with equivalent rates of hernia recurrence compared to original component separation techniques [26, 27].

Focusing on the posterior lamella of the rectus sheath gave rise to innovative ideas in complex hernia repair initially with the Rives-Stoppa technique and its subsequent extension, namely the posterior component separation technique with tranverse abdominis release. Rationale for the Rives-Stoppa technique was to create a potential space in the retrorectus plane for mesh placement in a well vascularised position, protected from the underlying viscera, while intrabdominal pressures exert forces that aid in the process of mesh integration into the relevant anatomic planes [28]. An incision is made in the posterior sheath 0.5 cm laterally to the linea alba and the retrorectus plane is developed towards the linea semilunaris, while preserving the inferior epigastric vessels that run over the posterior sheath as well as the insertion of intercostal nerves as they enter into the rectus sheath approximately 1 cm medial to the linea semilunaris. The retrorectus plane is subsequently developed on the contralateral side finishing on the natural lateral extension of the Rives-Stoppa technique, that is the linea semilunaris. Dissection on each side extends until 5–8 cm past the superior and inferior edge of the hernia defect on each side to achieve wide overlap of it. The two respective dissection planes are joined by entering the suprapubic space of Retzius caudally and by releasing the posterior rectus sheath from its insertion in the xiphoid process. With regards to the pelvic dissection, due to the fact that below the arcuate line, the posterior rectus sheath is comprised only of peritoneum and transversalis fascia the dissection plane in essence extends into the preperitoneal space laterally all the way towards the pubic bone, Cooper ligament on each side as well as the medial edge of psoas muscle. The same applies for the subxiphoid dissection, where the original retrorectus plane continues essentially into the preperitoneal plane. With the aforementioned strategy, a new visceral sac is recreated achieving tension free reconstitution of the midline with primary repair and allowing placement of a mesh with wide overlap of the hernia defect. Intrinsic in the nature of Rives-Stoppa repair is the limit set by the linea semilunaris as the far most lateral border of dissection, resulting in maximum coverage of defects up to 10 cm wide [28, 29, 30]. Posterior component separation [31] technique aims to overcome the lateral limit of Rives-Stoppa dissection plane, thus enabling repair of hernias with widths greater than 10 cm or hernias in sites other than midline, such as flank hernias, lumbar hernias or complex hernias encompassing more than one areas and/or being huge in size. Advancing in lateral direction from the retrorectus plane past linea semilunaris can be accomplished by either switching towards the preperitoneal plane of dissection or by incising the muscle fibers of the transverse abdominis muscle, popularized as transversus abdominis release (TAR). It is important to notice at this point that transversus abdominis muscle fibers do not contribute to linea semilunaris, but rather reside medial to it and behind the rectus abdominis muscle in the upper 1/3 of the abdominal wall. Entering the TAR dissection plane is initiated approximately 0.5 cm medially to the linea semilunaris, where the muscle fibers are divided, thus opening an avascular plane behind the transverse abdominis muscle, that can be bluntly extended up to the costal margins, diaphragm, retropubic space, inguinal orifices and psoas muscles bilaterally. A new visceral sac is subsequently developed and a synthetic mesh is usually positioned in the sublay position. A key technical point is that the point of initiation of the TAR dissection is just medial to insertion of the neural bundles in the rectus sheath and therefore by traversing “one level’ below them as the plane is developed naturally, intercostal nerves are essentially protected, thus preventing denervation and subsequent atrophy of the rectus abdominus muscle complex. Of notice, intercostal nerves course below internal oblique and above transverse abdominis muscles and enter the rectus sheath medially to the linea semilunaris as noted above. As is the cause with Rives-Stoppa repair, retrorectus planes bilaterally are unified. In the subxiphoid area, if needed, the insertion of the posterior sheath into the xiphoid process can be divided, thus exposing the subxiphoid fatty triangle, and in extreme cases or in the case of subxiphoid hernias the dissection can be extended preperitoneally all the way to the tendinous portion of the diaphragm. Due to variable anatomic relation and overlap between the rectus abdominis sheath and transverse abdominis muscle at different anatomic levels [32], it is best to initiate TAR dissection plane above the umbilicus, in order to maintain the development of the correct plane. Of notice, advancing from the retrorectus plane towards division the transversus abdominus muscle fibers, by definition, involves, at an intermediate stage, division of the posterior lamella of the internal oblique, which has been shown to contribute crucially towards the subsequent medial advancement of the rectus myofascial complex [33]. Posterior component separation technique with transversus abdominis release and insertion of wide synthetic mesh in the sublay position has been established as an effective means of treating even wide hernia defects with minimal complications and excellent results in terms of hernia recurrence rates [34]. From the physiological standpoint, posterior component separation with TAR induces rectus abdominis muscle hypertrophy and is, furthermore, associated with hypertrophy of the lateral abdominal wall musculature, thus leading to restoration of function of the abdominal wall, in contrast to bridging the hernia defect with a synthetic mesh, which has no effects on abdominal wall muscles [35]. Posterior component separation has been shown to achieve significant medialization of the anterior and posterior lamella of the rectus sheath, thus enabling primary fascial closure in defects up to 20 cm wide [36].

Comparing anterior and posterior component separation techniques, both yield equivalent and excellent results regarding hernia recurrence, while the latter is associated with fewer wound complications. It is of notice, that both component separation techniques with primary fascial closure and use of mesh have better safety profiles in terms of surgical site occurrences when compared with bridged repair (spanning the hernia defect with a mesh) [37].

2.3 Outcomes

When comparing medial advancement achieved with Rives-Stoppa, anterior component separation and posterior component separation, it is noted that the anterior lamella of the rectus sheath is advanced by 1.2, 2.6 and 1.9 cm on each side for each respective technique, while the posterior lamella advancement reached 2.2, 3.0 and 5.2 cm respectively, favoring on the whole posterior component separation technique with regards to the ability to reconstitute large defects [38]. Both myofascial release techniques yield equivalent results in terms of hernia recurrence rates, while anterior component separation techniques comparatively have more surgical site occurrences with no long term sequelae of those, however [39]. An exhaustive review comparing anterior and posterior component separation is outside the scope of the current chapter, while clear-cut comparisons between posterior component separation with TAR, anterior component separation and/or perforator-sparing anterior component separation are lacking in the existing literature [36]. What is more clear, however, at the current time, is that abdominal wall reconstruction is associated with improvement in physiology and function of truncal muscles, yielding improved quality of life for patients [26, 40, 41]. A combination of anterior and posterior component separation techniques for extreme cases has been reported, although it is a strategy associated with increased morbidity mainly due to respiratory complications and issues of truncal stability due to the associated sacrifice of key core muscle stabilizers [42, 43], and is therefore a strategy that should be viewed with caution. From the anatomic standpoint, anterior component separation causes significant lateral displacement of the external oblique muscle, while transversus abdominis muscle is shifts very little after posterior component separation [44]. Anatomy and physiology of abdominal wall muscles are preserved by the muscles’ overlapping function and their ability to undergo compensatory trophism after reconstitution of midline, which results in reloading of the aforementioned muscles due to redistribution of mechanical loads. Anterior component separation creates, therefore, an autologous flap that moves across the abdomen to cover a hernia defect on the contralateral side. Different to that, is the presumed mechanism of action of posterior component separation. TAR essentially unloads tensions off neo-midline creation by means of disruption of a continuous hoop tension system spanning over the entire thoracoabdominal fascia. It is exactly this differential mechanism of action of the two myofascial release techniques, as well as the preservation of overlap of abdominal wall muscles that allows for rationalization and careful presurgical planning with potential combination of the two operative strategies [44].

2.4 Preoperative planning - Abdominal wall prehabilitation

Careful preoperative planning is required for successful treatment of complex hernias. Complex hernias can be large in size and a large proportion of abdominal viscera can be contained in the hernia sac relative to the viscera remained in the native abdominal cavity, thus predicting traumatic reduction of hernia contents and increased postoperative complications such as abdominal compartment syndrome [45]. This disease entity is often termed “loss of domain hernia”, although established diagnostic criteria are currently lacking [46]. What appears to closely describe loss of domain hernias, is the ratio of hernia sac volume/total abdominal contents, or the ratio of hernia sac volume/native abdominal cavity volume [47, 48]. Using these defect quantification strategies, preoperative use of cross-sectional imaging usually with computed tomography (CT) can be employed to study relevant anatomy in complex hernias and predict the need for utilization of advanced myofascial release techniques [49]. Advanced imaging interpretation algorithms aiding in detailed complex hernia characterization and preoperative planning [50] can be employed, thus underlying the need for standardized terminology in complex hernias and multidisciplinary planning and treatment [51].

A new strategy for abdominal wall prehabilitation is use of botulinum toxin in the preoperative setting to achieve chemical paralysis of lateral abdominal wall musculature, often termed as “chemical component separation” [52]. Botulinum toxin can be injected in a standardized manner at points of insertion of lateral abdominal wall muscles into the rectus sheath, thus causing an elongation of the aforementioned muscles [53] which not only unloads tension off the future reconstituted midline at the early postoperative period. Relieving tension off the future neo-midline postoperatively by negating lateral abdominal muscle pulling forces, essentially, allows for wound healing and remodeling for a predicted time frame (corresponding to the duration of action of botulinum toxin), which is in line with the principles of successful abdominal wall reconstruction. Chemical component separation has been consistently shown to augment gain of length of medialisation of the lateral myofascial complexes, thus enabling primary fascial approximation even for large hernia defects, especially when combined with the aforementioned myofascial release techniques [54, 55]. Additionally, a hernia defect initially presumed to require complex repair techniques for achievement of primary fascial closure, may after chemical components separation be downgraded to a more simple repair [56]. Progressive preoperative pneumoperitoneum to augment hernia sac volume and native abdominal cavity volume can be added to chemical component separation, thus further enhancing the ability to tackle complex hernias [57]. Of notice, chemical component separation, which induces temporary paralysis of abdominal wall muscles only, can have a differential effect on hernia sac versus the native abdominal cavity, thus creating a selective effect of progressive preoperative pneumoperitoneum on abdominal wall prehabilitation, essentially, canceling its otherwise non-selective nature of action on both the hernia sac volume and native abdominal cavity volume, which theoretically leaves the aforementioned ratio of them unaltered [58].

3. Conclusions

Complex hernias comprise a disease entity, which requires a firm grasp of the related anatomy and pathophysiology before embarking on reconstitutional surgery. The goal of surgery should be reconstruction of anatomy to achieve reconstruction of function of the abdominal wall, translating into better outcomes for patients both in terms of quality of life as well as immediate postoperative complications and hernia recurrence rates. We have tried to create a unifying pathophysiologically- oriented approach to this complex problem and we have purposefully attempted to position new techniques, such as preoperative planning, chemical component separation with or without preoperative progressive pneumoperitoneum, into this frame. In order not to deviate from this strategy, we have not discussed topics such as component separation in the setting of contaminated fields or in the setting of open abdomen, both being a dynamic field of application of these strategies.

Complex hernias should be planned and dealt with in multidisciplinary and individualized fashion. Further studies with more strict diagnostic and patient selection criteria shall, in our opinion, be of great clinical benefit, along with generation of good quality data comparing the different reconstruction techniques. Standardization of procedures and creation of robust therapeutic algorithms for an ever-changing landscape of clinical problems, shall both aid in spreading knowledge of advanced abdominal wall reconstruction techniques among the surgical community.

Acknowledgments

None to be declared by the authors.

Conflict of interest statement

The authors report no conflict of interest.