An important landmark of the pelvis that determines the distance of the descent of the head is known as.. Ischial spines

An important landmark of the pelvis that determines the distance of the descent of the head is known as:

a- Linea terminalis
b- Sacrum
c- Ischial spines
d- Ischial tuberosities

Answer: C.
Ischial spines are the point of reference in determining the station (relationship of the fetal presenting part to the ischial spines).

When the fetal head is at the level of the ischial spines the station is zero. When it is 1 cm above the ischial spines it is -1 and if 1 cm below the ischial spines it is +1.
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The ischial or promontory tuberosity of the ischium is a bony bulge of the ischium, the lower part of the coxal bone.

The tuberosity of the ischium is located in the upper and posterior portion of the ischium branch and, together with the tip of the coccyx, forms the lower opening of the pelvis.

When an individual sits, body weight often falls on the ischial tuberosity.
This ischial promontory is palpable in the middle gluteal region, at the same height as the greater trochanter of the femur.

Divisions:
The ischial tuberosity is divided into two portions, a lower, rustic and somewhat triangular portion and an upper, smooth and quadrilateral portion.

+ The lower portion is subdivided by a longitudinal crest that crosses the lower half from the base to the apex of the rough triangle that forms this lower portion.

This crest divides this region into two:
- the outer half, the furthest from the midline of the body, provides the insertion point of the muscle Adductor major of the thigh;
- the inner half gives insertion to the greater or sacrotuberous sacrocytic ligament.

+ The upper portion is subdivided into two areas by an oblique crest that runs from top to bottom:
- the semimembranous muscle part of the upper and outer half;
- In the lower and inner half the long head of the crice and semitendinosus biceps is inserted.

Pathologies:
Ischial tuberosity is one of the pressure points in the prostrate patient that causes the appearance of pressure ulcers.

Violent trauma to the gluteal region can cause fracture of the ischial tuberosity.