The column principle divides the acetabulum into an anterior
and posterior column which becomes important when considering acetabular
fractures and their management. The anterior column is composed of the anterior
ilium, the anterior wall and dome of the acetabulum and the superior pubic
ramus. The posterior column extends from the obturator foramen through the
posterior aspect of the weight bearing dome of the acetabulum and then
obliquely through the greater sciatic notch. The ischiopubic ramus is a complex
structure that consists of the inferior pubic ramus and the inferior ramus of
the ischium. It forms the inferior border of the obturator foramen. The pelvis
is oriented to form an inverted “Y” shape. The obturator artery is a branch of
the anterior division of the internal iliac artery. It arises in the pelvis and
it enters the obturator canal. The obturator artery the divides into two
branches: the anterior and posterior branches of the obturator artery form a
vascular circle around the outer surface of the obturator membrane. An
acetabular branch reaches the hip joint and joins the ligamentum teres to
supply the head of the femur. It usually supplies a small portion of the head
of the femur. Corona mortis is a connection between the internal iliac branch
(obturator) and the external iliac or its branch, the inferior epigastric.
Corona mortis is predominantly a venus connection and the arterial connection
is much less. Its location on the superior pubic ramus is variable. It is about
3-7 cm from the symphysis pubis. It is located behind and on top of the
superior pubic ramus and one must be careful with lateral dissection of the
superior pubic ramus. The Corona Mortis is susceptible to injury in pelvic
trauma and in pelvic surgery especially during the ilioinguinal approach. Be aware that the sciatic nerve
can be split, and this can be a normal variant. Keep the knee flexed and the
hip extended during posterior approach to the acetabulum. This will protect the
sciatic nerve. The sciatic nerve is posterior to the obturator internus muscle
and anterior to the piriformis muscle. When using the sciatic nerve retractor
in the lesser sciatic notch, the muscle and tendon of the obturator internus
protects the sciatic nerve. It acts as a buffer layer between the retractor and
the nerve, because the nerve is posterior to the muscle. Sliding trochanteric
osteotomy allows exposure of the dome and the superior aspect of the
acetabulum. This type of osteotomy keeps the muscles intact and this will
balance its pulling forces. There will be less of a chance of displacement of
the greater trochanter this way. The superior gluteal nerve is close to the
superior gluteal artery at the greater sciatic notch. The superior gluteal
nerve can be injured from approaches that involve more than 5 cm above the
acetabulum. Excessive traction or attempt to control the bleeding from the
superior gluteal artery at the greater sciatic notch, may injure the nerve by a
suture or by a vascular clip that may entangle the nerve. Injury to this nerve
may affect the gluteus minimus. Injury to this nerve affects the abductors of
the hip joint and the patient may end up with Trendelenburg Gait. The inferior
gluteal nerve may also be injured. It innervates the gluteus maximus muscle.
The Lateral Femoral Cutaneous Nerve can become injured during the ilioinguinal
approach for acetabular fixation. The Lateral Femoral Cutaneous Nerve usually
passes under the ilioinguinal medial to the anterior superior iliac spine
(ASIS).
