Major Abdo Wall Hernia
DEFINITION

Abdominal wall keeps us waterproofed, leak proof, and assists with breathing, coughing, rotation and flexion of the trunk, posture, emesis, urination, and defecation.
Defects of the abdominal wall can compromise these functions, cause pain, or lead to herniation of the viscera.


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EPIDEMIOLOGY

See below

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AETIOLOGY

Various causes.

The components of the abdominal wall include the skin and subcutaneous fat layer, fascia, muscle, and peritoneum.
The loss of each component or combination of components requires specific techniques for reconstruction.


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BIOLOGICAL BEHAVIOUR

Skin / Subcut Fat
Defects relatively straightforward in that a split-skin graft will fix most problems.
- except cosmetically bad; plastics options exist for later improvements if desired

Fascia / Muscles
Usually lost together.
True defects are uncommon, e.g. when abdo wall tumours excised.
- fascia only defects usually inconsequential due to layered wall.
- repair if bulge of muscle through and cosmetic rationale
More common is separation at linea / incisional hernia
- lateral muscles of abdo wall retract recti further, shorten recti, pulling gape wider.
Arcuate line is 2cm above horizontal line across ASIS
- anterior rectus fascia defect below here will result in a hernia and should be fixed.

Peritoneum
Inconsequential biomechanically
But important protective lining over bowel relating to mesh placements
Polypropylene mesh contact is terrible with vigorous inflammatory response, dense, adhesion formation, mesh integration into bowel wall, perforation and fistulae.
- cf acellular dermal matrices; safely contact bowel and tend to resist adhesion formation

Composite Defects
Skin and myofascial layer
May be complicated when contaminated as precludes standard synthetic materials.

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MANIFESTATIONS

As per above

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INVESTIGATIONS

As per above
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MANAGEMENT

These lesions represent a major surgical challenge.

Composite Tissue Defects
Primary repair of fascia not recommended.
- unacceptable recurrence.
Use of standard synthetic materials may be precluded by inadequate skin cover or contamination.
--> further options include component separation, fascial grafts, flaps, tissue expanders, and biologic materials.

Component Separation
1. Divide adhesions vs abdominal wall / intra-abdominally
2. Undermining of the skin over fascia
- allows advancement but cost is seroma formation and risk of fat / skin necrosis
--> progress 1-2 cm beyond rectus and no more.
3. Incise EO fascia 1cm lateral to rectus margin
- may need to divide EO fibres at this level as well.
- carry over costal margin, do not violate inguinal ligament.
4. Advance rectus myofascial complex toward the midline;
- this degree of component separation usually buys 5cm on each side
5. If need more, can elevate EO off IO all the way to anterior axillary line.
- and can separate posterior rectus sheath off the back of the rectus if still not meeting.
Will achieve closure in up to 90%.
- if not acheived, meet using an underlay with 5cm overlap at least to fascia
6. Must secure repair with an over or under layer; else unacceptable recurrence rate.
- many advocate underlay with e.g. proceed mesh
- alternative is a broad onlay out to EO fascia
- in severe recurrent cases, can do a mesh sandwich; unproven benefit, however.

Acute situation with open abdomen and loss of domain
No role for acute component separation
Maintain domain with negative pressure therapy
Progressive primary fascial closure
- biologic to close any defect that cannot be closed within 2weeks and close the skin.
Component separation then becomes a valuable future option.

Implant Selection
Controversial and still evolving with evidence limited and in flux
Principles are simple:
1. Avoid synthetics in presence of infection, lack of skin coverage, bacterial contamination
- or if substantial comorbidities that are wound risk factors, e.g. obesity, smoking, radiation, immunosuppressed, COPD, malnutrition
2. Synthetic choice (e.g. for tumour excision) should be polypropylene.
- good incorporation, provided can be barrier off bowel, e.g. peritoneum.
3. Acellular dermal matrix barrier if no barrier and need to protect off bowel
New biologics have improved options; now no common role for fascial grafts.

Other options (Plastics)
Tissue expanders
- if extreme lack of fascia and skin.
Flaps
- pedicled, e.g. lat dorsi, rectus, tensor fascia lata,
- limited by arc of rotation.
- free flaps not commonly used as operative time, complexity and failure rate higher.
- donor site morbidity is significant.



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REFERENCES
Cameron 10th