The Female Pelvis

Female pelvis:

The female pelvis (gynaecoid pelvis) is well adapted for childbearing by nature. The gynaecoid pelvis has the characteristics giving rise to no difficulties in childbirth with a normal size baby. The size and shape of the female pelvis is the most important factor during childbearing and childbirth. Fetal head makes certain movements during its descent through pelvis so that the smallest diameter of the fetal head is easily brought to the largest diameter of the bony pelvis.

Pelvic bones:

Pelvic is made up of four bones

1. Two innominate (nameless) bones or hipbones.

2. One sacrum.

3. One coccyx.

I. Two Innominate bones are made up of three

1. Ilium

• the large flared out part.
• Iliac crest as upper border
• Concave border is iliac fossa
• Anterior superior iliac spine
• Anterior inferior iliac spine
• Posterior superior iliac spine
• Posterior inferior iliac spine

2. Ischium

• the thick lower part.
• Acetabulum
• Ischial tuberosity
• Ischial spine: location in relation to fetal head, ie., above (-), below (+) or at (zero station)
• Greater sciatic Notch: extends from sacro iliac joint to ischial spine
• Lesser Sciatic Notch: extends from ischial spine to ischial tuberosity
• Obturator foramen: passage of pelvic nerve fibres

3. Pubic bone

• forms the anterior part.
• Inferior rami of Pubic bone (a)
• Superior rami of pubic bone (b)
• Symphysis pubis (a+b): It is formed at the junction of two pubic bones.
• Sub pubic angle: angle between the inferioir rami of the pubic bone.

II. Sacrum

• It is a wedge shaped bone consists of five fused vertebrae.
• Sacral promontory: projects inwards
• Sacro iliac joint
• Wings of Sacrum or Ala of Sacrum
• Hollow of the Sacrum: concave

III. Coccyx

• It is a vestigial tail consists of four fused vertebrae forming a small triangular bone.
• It is articulated with the sacrum
• Coccyx moves backward during childbirth

Pelvic Joints

• Symphysis Pubis
• Sacroiliac joint
• Sacro coccxygial joint

Pelvic Ligaments

• Interpubic ligament
• Sacroiliac ligament
• Sacro coccxygial ligament
• Sacrospinous ligament
• Sacrotuberous ligament
• Interspinous ligament
• Intertuberous ligament

Landmarks of the Pelvis

The true pelvis is the bony canal through which fetus must pass during birth. It consists of:

1.      Brim

2.      Cavity

3.      Outlet

I. Brim

• Anterior border: Pubic bone
• Posterior border: Sacral promontory and ala of the sacrum
• Lateral border: Iliac bones
• Brim of the pelvis consisits of:
• Sacral promontory
• Ala of the sacrum
• Sacro iliac joint
• Ileopectineal line
• Ileopubic eminence
• Pectineal line
• Pubic tubercle
• Pubic Crest
• Symphysis pubis

Diameters of the Brim

1. Anterior posterior diameter
• Anatomical/ True conjugate (11cm) : extends from the sacral promontory to symphysis pubis
• Obstetrical conjugate (10cm) : extends from sacral promontory to 1.25cm below the symphysis pubis
• Diagnal conjugate (12cm) : extends from sacral promontory to inferior border of symphysis pubis

2. Oblique diameter

·         Right Oblique diameter (12cm) : extends from Rt. Sacroiliac joint to Lt. sacroiliac joint.

·         Left Oblique diameter (12cm) : extends from Rt. Sacroiliac joint to Lt. sacroiliac joint.

3. Transverse diameter
• Farthest points in the ileopectineal lines (13cm).
• Longest diameter

II. Cavity

• Anterior border: Symphysis pubis
• Posterior border: Sacral hollow
• Lateral border: Soft tissues
• As it is round in shape, all diameters measure 12cms.

III. Outlet

1. Anatomical Outlet

·         It consisits of the lower border of all bones and sacro tuberous ligament.

·         (Anatomical outlet) – (pelvic strait) = Obstetrical outlet

·         Pelvic strait consists of lower border of symphysis  pubis, sacro coccxygial joint and sacro ischial spine.

2. Obstetrical Outlet
1. Antero posterior diameter (13cm): Extends from inferior border of the symphysis pubis to the sacro coccyxgial joint.
2. Oblique diameter

                                                              i.      Right Oblique diameter (12cm) : extends from Rt. Sacro spinous ligament to Obturator foramen

                                                            ii.      Left Oblique diameter (12cm) : extends from Lt. Sacro spinous ligament to Obturator foramen

                                                          iii.      Transverse diameter (11cm) : between the ischial spines.

Types of Pelvis

1. Gynaecoid pelvis

·         Most suitable for childbirth

·         Wider brim

·         Ischial spines are blunt

·         Sub pubic angle is 90º

2. Anthropoid pelvis

·         Oval in shape

·         Transverse diameter is shorter

·         Seen in tall women wuth narrow shoulders

·         Sub pubic angle more than 90º

3. Android pelvis

·         Heart shaped brim

·         Anterior posterior diameter is shorter

·         Transverse diameter is wider

·         Childbirth is difficult

4. Platypelloid pelvis

·         Kidney shaped

·         Anterior posterior diameter is smaller

·         Transverse diameter is wider

Muscles of the pelvic floor

• Superficial muscles
• Corpus cavernosa
• Ischiocavernosa
• Bulbocavernosa
• Transverse perineal
• External sphinter ani
• Deep Muscles
• Ischiocoxygeous muscle
• Ileocoxygeous muscle
• Pubocoxygeous