Muscles

1. Longitudinally orientated, centrally placed muscles:
   
   
   
   • Rectus abdominis (RA)
     
   • Pyramidalis.
   
   
2. Flat, laterally placed muscles:
   
   
   
   • External oblique (EO)
     
   • Internal oblique (IO)
     
   • Transversus abdominis (TA).

• Aponeuroses of EO, IO and TA fuse lateral to the lateral edge of RA to form the linea semilunaris.
  
• They divide into anterior and posterior laminae to enclose RA in a fascial sheath—the rectus sheath—before fusing again in the midline as the linea alba.
  
• The posterior lamina is deficient below the level of the ASIS; its free edge is the arcuate line.
  
  
  
  • The arcuate line is approximately ⅓ the distance from umbilicus to pubic symphysis.
  
  
• Superior to the arcuate line, the anterior rectus sheath comprises the aponeurosis of EO and the anterior leaf of IO aponeurosis.
  
• The posterior rectus sheath comprises the posterior leaf of IO and TA aponeurosis.
  
• Inferior to the arcuate line, all three of these muscles’ aponeuroses pass anterior to RA.
  
  
  
  • The posterior surface of RA therefore lies directly on transversalis fascia.
  
  
• Muscles have segmental nerve supply, usually T6/T7–T12.
  
  
  
  • EO is also supplied by the iliohypogastric nerve (T12, L1).
    
  • IO is also supplied by the iliohypogastric and ilioinguinal (L1) nerves.
  
  
• All nerves run in the neurovascular plane between IO and TA.

Arterial supply

• Segmental intercostal and lumbar vessels
  
• Superior epigastric arteries
  
• Superficial and deep inferior epigastric arteries
  
• Superficial and deep circumflex iliac arteries
  
• Superficial external pudendal arteries.

Temporary abdominal closure

• Purpose of temporary closure:
  
  
  
  • Protect intestines
    
  • Maintain a sterile (or at least clean) environment
    
  • Avoid fluid and temperature loss.
  
  
• Methods of temporary abdominal closure:
  
  
  
  • Skin-only closure using towel clips
    
  • Silo technique, using non-adherent plastic sheets to wrap around intestines
    
  • Temporary mesh
    
  • Intraperitoneal packing
    
  • Negative pressure wound therapy
    
  • Various proprietary devices.

Patient optimisation

• Patients are often critically ill.
  
• Optimisation maximises chances of successful reconstruction.
  
• Summarised by the ‘SNAP’ principle:
  
  
  
  • Sepsis control—both intra-abdominal infection and systemic inflammatory response.
    
  • Nutrition—usually requires supplemental enteral or parenteral feeding.
    
  • Anatomy—defining the defect by pre-operative imaging.
    
  • Planning—determining the type and extent of reconstruction required.

Definitive closure

• Small wounds may be amenable to delayed primary closure or healing by secondary intention.
  
• May be necessary to skin graft directly on to bowel or granulation tissue to minimise protein losses.
  
• Delayed reconstruction of the myofascial layer may be required months later.
  
• Patients unfit for reconstructive surgery are managed with an abdominal binder.

Reconstruction of the myofascial layer

1. Prosthetic
   
2. Bioprosthetic
   
3. Autologous.

Prosthetic reconstruction

• Materials may be meshed or non-meshed; absorbable or non-absorbable.
  
• Meshed materials allow continued drainage of the abdominal cavity.
  
• Granulation can grow through the mesh to permit delayed skin grafting.
  
• Alternatively, mesh can be covered with omentum and skin grafted.
  
  
  
  • Necessitates leaving a small abdominal defect for the omentum pedicle.
  
  
• Absorbable meshes are associated with higher rates of fistula and late hernia compared to polypropylene meshes, e.g. Marlex^®.

Bioprosthetic reconstruction

• Acellular dermal matrix (ADM) is popular for abdominal hernia repair.
  
• Tends to form fewer adhesions with bowel compared to prosthetic materials.
  
• Certain ADMs incorporate by regeneration and are replaced by native tissue.
  
  
  
  • They can therefore be used in infected wounds with relative impunity.
  
  
• ADMs generally lose integrity when used as ‘bridge grafts’ for ventral hernias, with high recurrence rates.

Autologous reconstruction

• Fascia lata, used as a graft or pedicled tensor fasciae latae flap.
  
  
  
  • Can also be transferred as part of an anterolateral thigh (ALT) flap.
  
  
• Muscle flaps from local or distant sources:
  
  
  
  • RA, either as a transposition or turnover flap.
    
  • EO, for upper abdominal defects.
    
  • IO, for lower abdominal defects.
    
  • Latissimus dorsi, rectus femoris, vastus lateralis and gracilis may also be used, either pedicled or free.
  
  
• Components separation
  
  
  
  • A technique described by Ramirez that allows greater advancement of myofascial layers towards the midline for direct closure.
    
  • Releasing incisions are made at pre-determined points in the deep fasciae:
    
    
    
    1. EO aponeurosis is divided from the rectus sheath just lateral to the linea semilunaris.
       
    2. RA is separated from the posterior rectus sheath by incising the medial edge of the sheath and freeing the muscle.
    
    
  • Allows bilateral advancement of rectus muscles and anterior rectus sheath:
    
    
    
    • 5 cm in the epigastrium
      
    • 20 cm at the umbilicus
      
    • 6 cm in the suprapubic region.

Source: Ramirez et al. (1990). Reproduced with permission of Elsevier.

• Tissue expansion
  
  
  
  • Adjacent myofascial tissue can be expanded prior to advancement.
    
  • Expander placement has been described between EO and IO and between IO and TA.

Post-operative complications

• Relatively common:
  
  
  
  • Wound dehiscence
    
  • Enterocutaneous fistula
    
  • Hernia
    
  • Infected prosthetic mesh—usually requires removal
    
  • Seroma.