Page 76 - Clinical Anatomy

ECA2 7/18/06 6:42 PM Page 61

The fasciae and muscles of the abdominal wall 61

Note also that the external oblique has its posterior border free but the
deeper two muscles both arise posteriorly from the lumbar fascia.

The anatomy of abdominal incisions
Incisions to expose the intraperitoneal structures represent a compromise
on the part of the operator. On the one hand he requires maximum access;
on the other hand he wishes to leave a scar which lies, if possible, in an
unobtrusive crease, and which will have done minimal damage to the
muscles of the abdominal wall and to their nerve supply.
The nerve supply to the lateral abdominal muscles forms a richly com-
municating network so that cuts across the lines of fibres of these muscles,
with division of one or two nerves, produce no clinical ill-effects. The seg-
mental nerve supply to the rectus, however, has little cross-communication
and damage to these nerves must, if possible, be avoided.
The copious anastomoses between the blood vessels supplying the
abdominal muscles make damage to these by operative incisions of no
practical importance.

Midline incision
The midline incision is made through the linea alba. Superiorly, this is a rel-
atively wide fibrous structure, but below the umbilicus it becomes almost
hair-line and the surgeon may experience difficulty in finding the exact
point of cleavage between the recti at this level. Being made of fibrous
tissue only, it provides an almost bloodless line along which the abdomen
can be opened rapidly and, if necessary, from Dan in the North to Beersheba
in the South!

Paramedian incision

The paramedian incision is placed 1in (2.5cm) to 1.5in (4cm) lateral, and
parallel, to the midline; the anterior rectus sheath is opened, the rectus dis-
placed laterally and the posterior sheath, together with peritoneum, then
incised. This incision has the advantage that, on suturing the peritoneum,
the rectus slips back into place to cover and protect the peritoneal scar.
The adherence of the anterior sheath to the rectus muscle at its tendi-
nous intersections means that the sheath must be dissected off the muscle at
each of these sites, and at each of these a segmental vessel requires division.
Having done this, the rectus is easily slid laterally from the posterior sheath
from which it is quite free. The posterior sheath and the peritoneum form a
tough membrane down to half-way between pubis and umbilicus, but it is
much thinner and more fatty below this where, as we have seen, it loses its
aponeurotic component and is made up of only transversalis fascia and
peritoneum. The inferior epigastric vessels are seen passing under the
arcuate line of Douglas in the posterior sheath and usually require division
in a low paramedian incision.