Autogenous bone graft is frequently obtained from the anterior
part of the ilium; however, many studies have shown that the harvesting
of autogenous iliac bone graft carries the risk of meralgia paresthetica2,4-6,8,9. Although the lateral femoral
cutaneous nerve usually emerges from the lateral border of the psoas
major muscle and crosses the ilium as it runs toward the anterior
superior iliac spine, its course can vary1,3,7.
We investigated the anatomy of the lateral femoral cutaneous nerve,
particularly as it relates to the harvesting of autogenous anterior
iliac bone graft.
The position of the lateral femoral cutaneous nerve was identified
on both sides of the pelvis in 108 formalin-embalmed cadavera from
Japanese individuals (sixty-four men and forty-four women) who had
been sixty to ninety-seven years old at the time of death. Eleven
of the 216 nerves could not be included because of tumor invasion,
leaving 205 nerves available for study. The lateral femoral cutaneous
nerve was identified after opening of the anterior abdominal wall and
evisceration of the abdomen. The psoas major muscle was removed,
and the second and third lumbar nerves were identified. The lateral femoral
cutaneous nerve was evaluated according to (1) the position of the
nerve in relation to the anterior superior iliac spine at the point where
the nerve crossed over the iliac crest or under the inguinal ligament,
and (2) the course of the nerve across the anterior surface of the
iliacus muscle. In cases in which two or more branches of the lateral
femoral cutaneous nerve were observed, the most lateral one was
measured.
The position of the nerve in relation to the anterior superior
iliac spine varied. We categorized each nerve as type A (crossing
over the iliac crest more than two centimeters posterior to the anterior
superior iliac spine), type B (crossing over the iliac crest within
two centimeters posterior to the anterior superior iliac spine),
type C (crossing at the anterior superior iliac spine), or type
D (crossing under the inguinal ligament and anterior to the anterior
superior iliac spine) (Fig. 1).
The course of the nerve also varied; some nerves ran straight
across the iliacus muscle, whereas others followed a convex or a
concave curve. We examined the lateral femoral cutaneous nerve at
a point five centimeters posterior to the anterior superior iliac
spine and categorized it as type 1 (crossing the iliacus muscle
within three centimeters of the iliac crest) or type 2 (crossing the
iliacus muscle more than three centimeters away from the iliac crest).
The results are summarized in Table I.
Many studies have shown that the harvesting of autogenous iliac
bone graft is associated with a risk of lateral femoral cutaneous
nerve injury, even if attention is paid to this danger2,4-6,8,9. Such an injury may occur
because of the variability of the anatomical course and the location of
the lateral femoral cutaneous nerve, as demonstrated in this study.
The variation of the course of the lateral femoral cutaneous
nerve suggests that some risk of injury is difficult to avoid during
an operative approach to the iliac crest. The findings of the present
study suggest that 9.9 percent of the nerves (including all of the
type-1 nerves as well as the type-2A nerves) may have been at risk
for injury if the patient had undergone harvesting of anterior iliac
bone. Therefore, all patients should be informed of the possibility
of lateral femoral cutaneous nerve injury before an iliac crest
bone graft is harvested.