Pelvis as a whole

Question 1

Linea terminalis

Answer 1

• A line extending from the pectineal line of the pubis to the pubic crest and then to the arcuate line (of the ilium) and to the sacral promontory

Question 2

Superior pelvic aperture

Answer 2

• Also know as the pelvic inlet
• Lies at 50-60 degrees to the horizontal plane in the anatomical position
• Defines the boundary between the pelvic cavity and the abdominal cavity (or between two parts of the pelvic cavity, called lesser pelvis and greater pelvis)

Question 3

Inferior pelvic aperture

Answer 3

• Also know as the pelvic outlet
• Anteriorly: the pubic arch
• Laterally: the ischial tuberosities
• Posterolaterally: the inferior margin of the sacrotuberous ligament
• Posteriorly: the tip of the coccyx

Question 4

Minor/true pelvis

Answer 4

• Contains the pelvic part of the colon, rectum, bladder and some sex organs
• Pelvic splanchnic nerves arising at S2-S4 are found here

Question 5

Major/false pelvis

Answer 5

• A space enclosed by the pelvic girdle from above and in front of the pelvic brim
• Laterally bound by the ilium on both sides
• Frontally incomplete
• Supports the ileum and sigmoid colon
• The femoral nerve from L2-L4 is in the greater pelvis, but not in the lesser pelvis

Question 6

Significant planes of female pelvis

Answer 6

• There are 4 significant planes
• Plane of the pelvic inlet - bordered by the linea terminalis and has an ovoid shape, longitudinal axis is oriented transversally
• Amplitudo pelvis plane - demarcated by a line linking the interface between S2 and S3 and the centre of the acetabular basis and the centre of the symphysis, and has a circular shape
• Angustia pelvis plane - bordered by a line linking margo inferior symphysis, spina ischiadica and apex ossis sacri, and has an ovoid shape, longer axis is oriented sagitally
• Plane of the pelvic outlet - demarcated by a line linking margo inferior symphysis, tuber ischiadicum and apex coccygis, and has a rhomboidal shape

Question 7

Dimensions of the plane of the pelvic inlet

Answer 7

• Diameter recta (conjugata anatomica) - links the promontorium and upper margin of the symphysis - 11cm
• Diameter transversa (largest d.) - biggest transverse distance between the lineae terminales - 13cm
• Diameter obliqua - between the sacroiliac join and the eminentia iliopubica - left or right - 12cm
• Diameter obstetrica - shortest distance between the dorsal side of the symphysis and the anterior margin of the sacral promontorium - 10.5cm
• Conjugata diagonalis - only one that can be performed directly, per vaginum - between margo inferior symphysis and margo anterior symphysis - 1.5 to 2cm greater than diameter obstetrica - 12.5 to 13 cm

Question 8

Dimensions of the amplitudo pelvis plane

Answer 8

• Diameter recta - from the S2/S3 interface to the centre of the dorsal side of the symphysis - 12.5cm
• Diameter transversa - line connecting the bases of the centres of the two acetabular fossas - 12.5cm

Question 9

Dimensions of the angustio pelvis plane

Answer 9

• Diameter recta - from margo inferior symphysis to the apex ossis sacri - 11.5cm
• Diameter transvera - line between the spina ischiadica (interspinous diameter) - 10cm

Question 10

Dimensions of the plane of the pelvic outlet

Answer 10

• Diameter recta - between inferior margin of the symphysis and the apex of the coccyx - 11cm
• Diameter transvera - between ischial tuberosities - 9cm, but during labour can reach 11-11.5cm

Question 11

External pelvis dimensions

Answer 11

• Measured with a pelvimeter
• Distantia bispinalis - between both anterior superior iliac spines - 26cm
• Distantia bicristalis - between most lateral parts of critae iliace - 29cm
• Distantia bitrochanterica - between major trochanters of both femurs - 31cm
• Distancia bituberalis - between apices of both ischial tuberosities - 12cm - gives information about the spaciousness of the pelvic outlet
• Conjugata externa - between the spinous process of L5 and the superior margin of the symphysis - 20cm (min. 18cm)

Question 12

Gender differences of the pelvis

Answer 12

1. Ala ossis ilii - Sagital in men, frontal in women and so cristae iliacae in women protrude more onto the body surface
2. Ischial tuberosities (bituberal distance) - greater in women than in men, and so the bitrochanteric distance is also larger and so the trochanters in women are more prominent
3. Pubic symphysis - In men lies higher, pubic bones below the symphysis create the angulus pubis, in women it lies much lower and so the pubic bones below the symphysis create the arcus pubis
4. Pelvic outlet - heart-shaped in men, promontorium is very prominent, in women the promontorium is less prominent and so the pelvic outlet is of an ovoid shape
5. Os sacrum - in women it is lower and wider than in men
6. Incisura ischiadica major - in women it is more spacious and wider, in men it is narrow and deep
7. Superior pubic ramus - Longer in women, and so their mons pubis protrudes more onto the body surface
8. Obturator foramen - triangular in women, ovoid in men