Published on March 20, 2014
Bony pelvis and fetal skull Dr Manal Behery 2014
Objects Fetal head Pelvic anatomy Pelvic shapes
Fetal head Landmarks Sutures Fontanelles Diameters
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
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
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
2-lambdoid suture: extends from the posterior fontanelle laterally separate the occipital from the parietal bones.
3-coronal suture: extends from the anterior fontanelle laterally separate the parietal and frontal bones.
4- frontal suture: lies between the frontal bones extends from the anterior fontanelle to the glabella (the prominence between the eyebrows).
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.
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 0.5-1 cm. 0r even more.
A: Well flexed Head B: Partially Flexed Head C: Deflexed Head D: Face Presentation E: Brow presentation
The anterior fontanelle (bregma) : diamond shaped area(2 × 3 cm) of unossified membrane formed by the junction of 4 suture.
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
LOP RO P LOP
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 8.25 - 9 cm. Asynclitic head
presenting AP diameter when the head is deflexed >>> OP
-presenting AP diameter in a brow presentation -longest AP diameter of the head
-4. Submentobregmatic (9.5 cm): presenting AP diameter in face presentations
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 13.75-14 cm. Brow 5-Submento-bregmatic 9.5 cm. Face 6
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 An oval The longer mento vertical diameter of 13.75-14 cm. is exposed Full Extension of the Head A circle of 9.5 cm. The engaging dimeter is the submento-vertical diameter
Female bonyFemale bony pelvispelvis
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.
Ischial Tuberosity Ischial Spine SP
The Planes of the pelvis 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
(Inlet (Pelvic brim) passing with the boundaries of pelvic brim and making an angle of 55o with the horizon (angle of pelvic inclination).
Pelvic inclination: The plane of the pelvic inlet makes an angle of 55 degree with the horizon in the standing position"
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.
Diameters of the pelvic inlet
The True Conjugate = 11 cm The Obstet. Conjugate = 10.5cm The Diagonal Conjugate = 12 cm
(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).
(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) ATD OTD TC
(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.
The pelvic Cavity Boundaries: Above: pelvic brim. Below: plane of least pelvic dimensions. Anteriorly: syrnphysis pubis. Posteriorly: sacrum.
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 2- pelvic cavity The plane of greatest diameter:
The pelvic Outlet (A)Anatomical outlet: Lozenge -shaped, bounded by: Lower border of symphysis pubis. Pubic arch. Ischial tuberosities Sacrotuberous & sacrospinous ligaments. Tip of the coccyx.
The Plane of the Outlet Anterior Sagittal Plane Posterior Sagittal Plane
Diameters of the pelvic outlet (1)Anteroposterior Anatomical anteroposterior (11 cm) b Obstetric anteroposterior (13 cm)
(2) Transverse diameters Bituberous (11 cm), between the inner aspects of ischial tuberosities Bispinous (10.5 cm), between the tips of ischial spines. Diameters of the pelvic outlet
Interspinous diam. = 10.5 cm. Obstet. Ant. Post diam= 13 cm. Anato. Ant. Post diam= 11 cm.
(3) Anterior sagittal diameter = 6-7 cm . (4) Posterior sagittal diameter = 7-10 cm Diameters of the pelvic outlet
Diameter Inlet Cavity outlet Anteroposterior diameter 11 12.5 13 Transverse diameter 13 12.5 11 Diameters of the pelvic
The pelvic axis: Anatomical axis (Curve of Carus):
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
The Fetal Head Has Five Fifths… 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 fifthabove -5 0 +5
Gynecoid Pelvis The classic female type. Found in approximately 50% of women. Characteristics:
Android Pelvis The typical male type Found in less than 30% of women Characteristics: 1. Triangular inlet with a flat
Anthropoid Pelvis Resembles ape pelvis. Found in approximately 20% of women Characteristics: ,
Platypelloid Pelvis Flattened gynecoid pelvis. Found in only 3% of women
1.Bony pelvis and fetal skull Dr Manal Behery 2014 . 2. Objects Fetal head Pelvic anatomy Pelvic shapes . 3. Fetal head Landmarks Sutures Fontanelles Diameters
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