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Bony pelvis and fetal skull Dr Manal Behery 2014

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Presentation on theme: "Bony pelvis and fetal skull Dr Manal Behery 2014"— Presentation transcript:

1 Bony pelvis and fetal skull Dr Manal Behery 2014

2 Objects Fetal head Pelvic anatomy Pelvic shapes

3 Passenger

4 Fetal head Landmarks Sutures Fontanelles Diameters

5 Fetal head From an obstetrical point of view it’s the most important part: largest least compressible part of the fetus. most frequent presenting part


7 Landmarks Head is divided into 3areas
(1) the sinciput or brow portion; (2) the vertex, or top of the head between the 2 fontanelles; (3) Base large, ossified, firmly united, and noncompressible

8 Sutures Membrane-occupied spaces between the cranial bones
1-Sagittal suture: - lies btw the parietal bones -extends in an AP direction btw the fontanelles -divides the head into right and left sides

9 2-lambdoid suture: extends from the posterior fontanelle laterally separate the occipital from the parietal bones.

10 3-coronal suture: extends from the anterior fontanelle laterally separate the parietal and frontal bones.

11 4- frontal suture: lies between the frontal bones extends from the anterior fontanelle to the glabella (the prominence between the eyebrows).

12 Clinical importance of sutures
Position of fontanelle & sagittal suture can identify attitude and position of vertex. By plapating the sagittal suture during labour, degree of internal rotation & molding of the head can be noticed. In deep transverse arrest, this sagittal suture lies transversely at the level of the ischial spines.


14 Moulding… Reshaping of the fetal skull:
Obliteration of the sutures. Overlapping of the bones of the vault: One parietal bone overlaps the other. Both overlap the occipital bone. It accounts for diminution of the biparietal diameter and suboccipitobregmatic diameters by cm. 0r even more.

15 A: Well flexed Head B: Partially Flexed Head C: Deflexed Head D: Face Presentation E: Brow presentation

16 The anterior fontanelle (bregma) :
diamond shaped area(2 × 3 cm) of unossified membrane formed by the junction of 4 suture.

17 The posterior fontanelle:
It is the triangular depressed area at the junction of 3 suture: closes at 6 to 8 weeks of life Y- or T-shaped





22 Bimastoid Suprapareital-subpareital

23 Transverse Diameters of the Fetal Skull
Biparietal Diameter 9.5 cm Between the 2 parietal eminences Bitemporal Diameter 8.5 cm. Bimastoid Diameter 7.5 cm. Between the 2 mastoid processes (Not reducible nor destroyable even by destructive procedures Supra-subparietal cm. Asynclitic head


25 presenting AP diameter when the head is deflexed >>> OP

26 presenting AP diameter in a brow presentation
longest AP diameter of the head

27 -4. Submentobregmatic (9.5 cm): presenting AP diameter in face presentations

28 6 Length Presentation 1-Suboccipito-bregmatic 9.5 cm. Flexed vertex
2-Suboccipito-frontal 10.5 cm. Partially deflexed vertex 3-Occipito-frontal 11.5 cm. Deflexed vertex 4-Mento-vertical cm. Brow 5-Submento-bregmatic Face 6-Submento-vertical Face Not fully extended


30 Engaging Diameters of Fetal Skull
Well Flexed Head Circle of 9.5 cm. The engaging Diameter is the Suboccipito-Bregmatic diameter A deflexed Head An oval The longer occipito-frontal diameter Of 11.5 cm. Is exposed. Greater Deflexion of the Head The longer mento vertical diameter of cm. is exposed Full Extension of the Head A circle of 9.5 cm. The engaging dimeter is the submento-vertical diameter

31 Female bony pelvis

32 False Pelvis bordered by: lumbar vertebrae posteriorly
iliac fossa bilaterally abdominal wall anteriorly. supports the abdominal contents after 1st trimester helps support the gravid uterus.

33 Inferior view with lig

34 Pelvic outlet

35 SP Ischial Spine Ischial Tuberosity



38 The Planes of the pelvis
Pelvic Planes: These are imaginary planes lie as follow: (1) Plane of pelvic inlet: passing with the boundaries of pelvic brim and making an angle of 55o with the horizon (angle of pelvic inclination). (2) Plane of mid cavity ( plane of greatest pelvic dimensions): - pass between the middle of the posterior surface of the symphysis pubis and the junction between 2nd and 3rd sacral vertebrae. Laterally, it passes to the centre of the acetabulum and the upper part of the greater sciatic notch. - It is a round plane with diameter of 12.5 cm. - Internal rotation of the head occurs when the biparietal diameter occupies this wide pelvic plane while the occiput is on the pelvic floor i.e. at the plane of the least pelvic dimensions. (3) Plane of obstetric outlet (plane of least pelvic dimensions): passes from the lower border of the symphysis pubis anteriorly, to the ischial spines laterally, to the tip of the sacrum posteriorly. (4) Plane of anatomical outlet: passes with the boundaries of anatomical outlet and consists of 2 triangular planes with one base which is the bituberous diameter. a- Anterior sagittal plane: its apex at the lower border of the symphysis pubis. b- Posterior sagittal plane: its apex at the tip of the coccyx. Anterior sagittal diameter: 6-7 cm from the lower border of the symphsis pubis to the centre of the bituberous diameter. Posterior sagittal diameter: cm from the tip of the sacrum to the centre of the bituberous diameter Plane of the pelvic inlet. Plane of the cavity: Plane of greatest Pelvic Dimensions Plane of the mid pelvis (plane of obstetric outlet) Plane of the Anatomical outlet

39 (Inlet (Pelvic brim) Bounded by passing with the boundaries of pelvic brim and making an angle of 55o with the horizon (angle of pelvic inclination).

40 Pelvic inclination: The plane of the pelvic inlet makes an angle of 55 degree with the horizon in the standing position"

41 The consequences of walking upright…
When a women stands erect: The pelvic inlet makes an angle of about 55° with the horizon. The pelvic outlet makes an angle of 15° with the horizon If the angle made by the inlet is greater than 55° this may make the descent of the fetal head in the pelvis difficult. Effect of the inclination of the pelvis on the engagement of the fetal head

42 Diameters of the pelvic inlet

43 The Diagonal Conjugate = 12 cm The Obstet. Conjugate = 10.5cm
The True Conjugate = 11 cm The ideal obstetric pelvis

44 (4) External conjugate:
From: The upper anterior margin of the symphysis pubis. To: The depression below the tip of the 5th lumbar spine (20 cm).

45 (5) Anatomical transverse diameter:
Between the farthest points on iliopectineal lines (= 13 cm). It lies 4 cm infornt of the sacral promontory, 7 cm behind the symphysis pubis. (6) Obstetric transverse diameter: It bisects the true conjugate (12.5 cm) TC ATD OTD

46 The right diameter ends in the right eminence & vice versa.
(7) The oblique diameters: (12 cm) The right extends from the right joint to the left eminence and vice versa. (8) Sacrocotyloid diameter: (9-9.5 cm) The right diameter ends in the right eminence & vice versa.

47 The pelvic Cavity Boundaries: Above: pelvic brim.
Below: plane of least pelvic dimensions. Anteriorly: syrnphysis pubis. Posteriorly: sacrum.

48 2- pelvic cavity The plane of greatest diameter:
bordered by: the posterior midpoint of the pubis anteriorly the upper part of the obturator foramina laterally the junction of the 2nd and 3rd sacral vertebrae posteriorly. The fetal head rotates to the anterior position in this plane

49 The pelvic Outlet Anatomical outlet: Lozenge -shaped, bounded by:
Lower border of symphysis pubis. Pubic arch. Ischial tuberosities Sacrotuberous & sacrospinous ligaments. Tip of the coccyx.

50 The Plane of the Outlet Anterior Sagittal Plane
Posterior Sagittal Plane

51 Diameters of the pelvic outlet
Anteroposterior Anatomical anteroposterior (11 cm) b Obstetric anteroposterior (13 cm)

52 Diameters of the pelvic outlet
(2) Transverse diameters Bituberous (11 cm), between the inner aspects of ischial tuberosities Bispinous (10.5 cm), between the tips of ischial spines.

53 Obstet. Ant. Post diam= 13 cm.
Interspinous diam. = 10.5 cm. outlet Anato. Ant. Post diam= 11 cm. Obstet. Ant. Post diam= 13 cm.

54 (4) Posterior sagittal diameter = 7-10 cm
Diameters of the pelvic outlet (3) Anterior sagittal diameter = 6-7 cm . (4) Posterior sagittal diameter = 7-10 cm

55 Diameters of the pelvic

56 The pelvic axis: Anatomical axis (Curve of Carus):

57 The Obstetric Pelvic Axis
This represents the path that the presenting part must follow for delivery to occur: The upper part moves downward approximately in a straight line till the level of the ischial spine. The trajectory then changes to become a curvilinear path directed forward and downward Anatomical axis (curve of Carus): - It is an imaginary line joining the centre points of the planes of the inlet, cavity and outlet. - It is C shaped with the concavity directed forwards. - It has no obstetric importance.

58 The Fetal Head Has Five Fifths…
fifth above the pelvic brim 0 : Head Not Palpable 1 : Sinciput felt – Occiput Not Felt 2 : Sinciput felt – Occiput Just Felt 3 : Sinciput easily felt – Occiput Felt 4 : Sinciput High – Occiput easily Felt 5 : Complete above pelvic brim -5 +5

59 Pelvic Shapes

60 Gynecoid Pelvis The classic female type.
Found in approximately 50% of women. Characteristics:

61 Android Pelvis The typical male type Found in less than 30% of women
Characteristics: Triangular inlet with a flat

62 Anthropoid Pelvis Resembles ape pelvis.
Found in approximately 20% of women Characteristics: ,

63 Platypelloid Pelvis Flattened gynecoid pelvis.
Found in only 3% of women



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