Female pelvis

This topic includes difference between female and male pelvis, various pelvis types, general description of pelvis bones, division of pelvis, landmarks of pelvis, plane, axis, sacral angle, diameters of inlet, cavity and outlet.

1. FEMALE PELVIS BY, MS. PRIYANKA GOHIL MSc (N) OBG PhD SCHOLAR

2. FEMALE PELVIS V/S MALE PELVIS

3. GENERAL DESCRIPTION OF BONES From the obstetrical standpoint, it is useful to consider the bony pelvis as a whole rather than separately. For descriptive purpose, an articulated pelvis is composed of four bones : two innominate bones sacrum coccyx. These are united together by four joints —two sacroiliac joints, sacrococcygeal joint and the symphysis pubis.

4. DIVISION OF PELVIS The pelvis is anatomically divided into : A false pelvis A true pelvis T he boundary line being the brim of the pelvis.

5. The bony landmarks on the brim of the pelvis from anterior to posterior on each side are : U pper border of symphysis pubis P ubic crest P ubic tubercle P ectineal line I liopubic eminence I liopectineal line S acroiliac articulation A nterior border of the ala of sacrum S acral promontory

6. FALSE PELVIS The false pelvis is formed by the iliac portions of the innominate bones and is limited above by the iliac crests . It has got little obstetric significance except that its measurements can to a certain extent, predict the size and configuration of the true pelvis. Its only obstetric function is to support the enlarged uterus during pregnancy. Its boundaries are : posteriorly—lumbar vertebrae, laterally—iliac fossa and anteriorly—anterior abdominal wall.

7. TRUE PELVIS This part of the pelvis is chiefly of concern to the obstetricians, as it forms the canal through which the fetus has to pass . It is shallow in front, formed by symphysis pubis and measures 4 cm (1 ½") and deep posteriorly, formed by the sacrum and coccyx and measures 11.5 cm (4 ½"). For descriptive purpose, it is divided into : I nlet C avity O utlet.

8. INLET As the inlet is the brim of the pelvis, the circumference of the inlet is formed by the bony landmarks . Shape : It is almost round (gynecoid) with the anteroposterior diameter being the shortest. Other different shapes of the inlet are anthropoid, android and platypelloid.

9. Plane : It is an imaginary flat surface bounded by the bony points mentioned as those of the brim. It is not strictly a mathematical plane and is, therefore, often referred to as superior strait.

10. Inclination : In the erect posture, the pelvis is tilted forward. As such, the plane of the inlet makes an angle of about 55° with the horizontal and is called angle of inclination. Another way of measuring the inclination radiographically is to take the angle between the plane of the inlet and the front of the body of the fifth lumbar vertebra. The angle is normally about 135°.

11. When the angle of inclination is increased due to sacralization of fifth lumbar vertebra, it is called high inclination. High inclination has got obstetric significances : There is delay in engagement because the uterine axis fails to coincide with that of inlet It favors occipitoposterior position There is difficulty in descent of the head due to long birth canal and flat sacrum interfering with internal rotation.

12. The angle of inclination may be lessened in case of lumbarization of first piece of sacral vertebra and is called low inclination. It has got no obstetric significance. It actually facilitates early engagement.

13. Sacral angle : It is the angle formed by the true conjugate with the first two pieces of the sacrum. Normally, it is greater than 90°. A sacral angle of lesser degree suggests funnelling of the pelvis.

14. Axis : It is a mid-perpendicular line drawn to the plane of the inlet. Its direction is downward and backward. When extended, the line passes through the umbilicus to coccyx. It is important that the uterine axis should coincide with the axis of the inlet so that the force of the uterine contractions will be spread in the right direction, to force the fetus to pass through the brim.

15. Diameters : The measurements of the diameters are all approximate and minor variation is the rule rather than the exception. Anteroposterior (Syn: true conjugate, anatomical conjugate, conjugate vera) Obstetric conjugate Diagonal conjugate Transverse diameter Oblique diameters

16. Anteroposterior (Syn: true conjugate, anatomical conjugate, conjugate vera) : It is the distance between the midpoint of the sacral promontory to the inner margin of the upper border of symphysis pubis. It measures 11 cm (4 ¼"). It is not the shortest diameter of the inlet in the anteroposterior plane. In practice, the true conjugate cannot be estimated directly.

17. However, its measurement is inferred by subtracting 1.2 cm (½") from the diagonal conjugate thus allowing for the inclination, thickness and height of the symphysis pubis.

18. Obstetric conjugate : It is the distance between the midpoint of the sacral promontory to prominent bony projection in the midline on the inner surface of the symphysis pubis. The point is somewhat below its upper border. It is the shortest anteroposterior diameter in the anteroposterior plane of the inlet. It measures 10 cm (4"). It cannot be clinically estimated but is to be inferred from the diagonal conjugate—1.5–2 cm (¾") to be deducted or by lateral radiopelvimetry.

19. Diagonal conjugate : It is the distance between the lower border of symphysis pubis to the midpoint on the sacral promontory. It measures 12 cm (4 ¾"). It is measured clinically during pelvic assessment in late pregnancy or in labor. Obstetric conjugate is computed by subtracting 1.5–2 cm from the diagonal conjugate depending upon the height, thickness and inclination of the symphysis pubis.

20. How to measure ? The patient is placed in dorsal position. Two fingers are introduced into the vagina taking aseptic precautions. The fingers are to follow the anterior sacral curvature. In normal pelvis, it is difficult to feel the sacral promontory or at best can be felt with difficulty. However, in order to reach the promontory, the elbow and the wrist are to be depressed sufficiently while the fingers are mobilized in upward direction.

21. The point at which the bone recedes from the fingers is the sacral promontory. The fingers are then mobilized under the symphysis pubis and a marking is placed over the gloved index finger by the index finger of the left hand. The internal fingers are removed and the distance between the marking and the tip of the middle finger gives the measurement of diagonal conjugate. For practical purpose, if the middle finger fails to reach the promontory or touches it with difficulty, it is likely that the conjugate is adequate for an average size head to pass through.

22. Measurement of diagonal conjugate

23. Transverse diameter : It is the distance between the two farthest points on the pelvic brim over the iliopectineal lines. It measures 13 cm (5 ¼"). The diameter usually lies slightly closer to sacral promontory and divides the brim into anterior and posterior segment. The head negotiates the brim through a diameter, called available or obstetrical transverse. This is described as a diameter which bisects the anteroposterior diameter in the midpoint. Thus the obstetrical transverse is either equal or less than the anatomical transverse.

24. Oblique diameters : There are two oblique diameters—right and left. Each one extends from one sacroiliac joint to the opposite iliopubic eminence and measures 12 cm (4 ¾"). Right or left denotes the sacroiliac joint from which it starts. Sacrocotyloid—9.5 cm (3 ¾") : It is the distance between the midpoint of the sacral promontory to iliopubic eminence. It represents the space occupied by the biparietal diameter of the head while negotiating the brim in flat pelvis.

25. Sacrocotyloid—9.5 cm (3 ¾") : It is the distance between the midpoint of the sacral promontory to iliopubic eminence. It represents the space occupied by the biparietal diameter of the head while negotiating the brim in flat pelvis.

26. CAVITY Cavity is the segment of the pelvis bounded above by the inlet and below by plane of least pelvic dimensions. Shape : It is almost round. Plane : The plane extends from the midpoint of posterior surface of symphysis pubis to the junction of second and third sacral vertebrae. It is called plane of greatest pelvic dimensions. It is the most roomy plane of the pelvis and is almost round in shape.

27. Axis : It is the mid-perpendicular line drawn to the plane of the cavity. Its direction is almost downward. Diameters: Anteroposterior Transverse

28. Anteroposterior (12 cm or 4 ¾") : It measures from the midpoint on the posterior surface of the symphysis pubis to the junction of second and third sacral vertebrae. Transverse (12 cm or 4 ¾") : It cannot be precisely measured as the points lie over the soft tissues covering the sacrosciatic notches and obturator foramina.

29. OUTLET OBSTETRICAL OUTLET It is the segment of the pelvis bounded above by the plane of least pelvic dimensions and below by the anatomical outlet. Its anterior wall is deficient at the pubic arch; its lateral walls are formed by ischial bones and the posterior wall includes whole of the coccyx. Shape : It is anteroposteriorly oval.

30. Plane : The plane is otherwise known as plane of least pelvic dimensions or narrow pelvic plane. The plane extends from the lower border of the symphysis pubis to the tip of ischial spines and posteriorly to meet the tip of the fifth sacral vertebra.

31. Diameters : Transverse Anteroposterior Posterior sagittal

32. Transverse—Syn: Bispinous (10.5 cm or 4 1/5") : It is the distance between the tip of two ischial spines. Anteroposterior (11 cm or 4 ¼"): It extends from the inferior border of the symphysis pubis to the tip of the sacrum.

33. Posterior sagittal (5 cm or 2") : It is the distance between the tip of the sacrum and the midpoint of bispinous diameter. Axis : It is represented by a line joining the center of the plane with the sacral promontory. Its direction is almost vertical.

34. Composite measurements of the diameters of the inlet, cavity and outlet in centimeters

35. ANATOMICAL OUTLET It is otherwise known as bony outlet. It is bounded in front by the lower border of the symphysis pubis; laterally by the ischiopubic rami, ischial tuberosity and sacrotuberous ligament and posteriorly by the tip of coccyx. Thus, it consists of two triangular planes with a common base formed by a line joining the ischial tuberosities. The apex of the anterior triangle is formed by the inferior border of the pubic arch and that of the posterior triangle by the tip of the coccyx.

36. Shape: It is diamond-shaped. Plane : It is formed by a line joining the lower border of the symphysis pubis to the tip of the coccyx. It forms an angulation of 10° with the horizontal. Axis : It is a mid-perpendicular line drawn to the plane of the outlet. Its direction is downward and forward.

37. PELVIC JOINTS: 1. Symphysis pubis : It is a secondary fibrocartilaginous joint. It has got no capsule and no synovial cavity. The articular surfaces are covered with hyaline cartilage. Due to softening of the ligaments during pregnancy, there is considerable amount of gliding movement.

38. 2. Sacroiliac articulation : It is a synovial joint and is an articulation between the articular surface of the ilium and sacrum. The articulating surfaces are not alike. It has got a capsule and a synovial cavity. Engagement to diagnose, it is better to palpate gently with two hands facing down over the abdomen than to prod around with Pawlik’s grip, which in non-experienced hands is painful.

39. 3. Sacrococcygeal joint : Sacrococcygeal joint is a synovial hinge joint. It allows both flexion and extension. Extension increases the anteroposterior diameter of the outlet.

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