Anatomy of the female pelvis (Question-Answers )


Where is mid cavity ? It is between the inlet above and outlet below.Which part of the pelvis has no role in labour ? False pelvis. What are the three parts of female pelvis ? The brim or inlet , mid cavity and the outlet. Tell me what are the boundaries of the brim ? Lateral–sacroiliac joint , ileopectineal line , upper borders of pubic bonesPosterior—sacral promontory , and ala of sacrum.Anteriorly—Superior border of symphysis pubis. What are the boundaries of mid cavity ? Posterior–sacrum and coccyxLateral—sacrospinous ligaments and ischium.Anterior–posterior surface of pubic symphysis. What is the length of anterior and posterior walls of mid-cavity ? Posterior–4-5 inches.Anterior–2 inches. What are the boundaries of anatomical outlet ? Behind–tip of coccyx.Lateral–sacrospinous ligaments, ischial spine and ischial tuberosity.Anterior–inferior pubic ramus, lower border of symphysis pubis. How does an obstetric outlet differs from anatomical outlet ? It’s boundaries are–Posterior–tip of sacrumLateral–ischial spines and inner surface of ischial tuberosities.Anterior–inferior pubic ramus and lower border of symphysis pubis. What is the importance of the curve of birth canal ? It is responsible for downward and forward passage of the fetus and because of this curve , foetus passes easily through obstetric outlet and not through anatomical outlet. How you are going to have a rough estimate of obstetric outlet ? By measuring the transverse diameter of anatomical outlet which is the distance between inner aspect of ischial tuberosities. What are the types of female pelvis ? Gynecoid, android, anthropoid and platypelloid. Which one is the ideal female pelvis ? Gynecoid which is 41 % What is gynecoid pelvis ? It has round brim so the head easily engages, round sacro-sciatic notches , rounded subpubic arch >90 degrees , tendency to eversion of ischial spines.Everything is round. What is android pelvis ? It is male type of pelvis,incidence is 33% .It is funnel shaped , having triangular inlet , angular sacroiliac notches , staright sacrum, inverted ischial spines and acute sub-pubic arch.Everything is angular. What is anthropoid pelvis ? It is ape shaped, incidence is 23%, has an oval brim and reduced transverse diameter of the mid cavity.If head engages as LOA or ROA it does not have any difficulty. But if it engages as ROP or LOP, then it becomes persistent occipito-posterior leading to C-section. What is platypelloid pelvis ? It has an oval brim , short antero-posterior diameter, elongated transverse diameter.It causes late engagement of the foetal head.But there is no difficulty in rotation of the head and descent once it is engaged. What are the diameters of pelvic brim ? Antero-posterior–true conjugateRight and left obliqueTransverse diameter What is true conjugate ? Distance between the centre of sacral promontory and superior border of posterior surface of symphysis pubis.It is 4.5 inches. How will you measure the right and left oblique diameter of the brim ? From right and left sacroiliac joints to the iliopectineal eminence on the superior rami of pubic bones on apposite side. It is 4.75 inches.It is more likely that head enters in transverse diameter in the brim.Previously it was thought that it enters in one of the oblique diameters. What is the transverse diameter of the inlet ? It is between the farthest points of the lateral pelvic wall at brim level.It is 5.25 inches. What is the extent of mid cavity ? It extends between pelvic brim above and pelvic outlet below.It has only one diameter of 4.75 inches. Describe diameters of pelvic outlet ? They are antero-posterior and transverse.Antero-posterior extends between the posterior surface of the inferior border of symphysis pubis and the tip of sacrum and measures 5.25 inches.Transverse is between the tips of ischial spines.It is 4.25 inches. At what level the head is arrested in persistent occipito-posterior position ? At the pelvic outlet. What is the difference between an obstetric outlet and anatomical outlet ? The diameter between two ischial spines is obstetric outlet and diameter between two ischial tuberosities is anatomical outlet.Fetal head passes through ischial spines shortly before birth, not between the ischial tuberosities. What is zero station of fetal head ? At the level of ischial spines. What is crowned head ? It is 4 cms below ischial spines. How do you assess the pelvis ? By bimanual examination. If middle finger touches the sacral promontary what do you mean by that ? Possibility of contracted pelvis. What do you palpate during bimanual examination ? Sacral promontary–ideally it should not be palpable.Ischial spines are felt to see inversion or eversion.Front of sacrum and its curve and tip of sacrum.Subpubic arch with knuckles of closed fist and subpubic angle. How is the diagonal conjugate measured ? With woman in prone position , the index and middle finger are passed to feel the sacral promontory.The point at which subpubic angle bites the index finger is noted and finger is withdrawn.The distance between the biting point on index finger and tip of the middle finger is diagonal conjugateIt gives the fair assessment of the A-P diameter of the brim. If you subtract half an inch from diagonal conjugate what is obtained ? True conjugate ( half an inch is the depth of pubic symphysis ). What are the parts of fetal skull ? The vault, the face and the base. Which bones do not take part in the moulding ? The base and face bones. What is moulding ? Overriding of the bones so as to reduce the diameters of skull is called moulding. What is the danger of excessive moulding ? Hypoxia of the brain. When it is insufficient ? In post maturity. What are the bones in the vault of skull ? Frontal, parietal , occipital , upper part of temporal. What are longitudinal sutures ? Frontal–lies in midline and divides two frontal bones.Sagittal–between anterior and posterior fontanelle.Occipital–rarely felt in mature fetus. What is the main guide in determining the position ofhead. Sagittal suture. What is the most important landmark on the foetal skull ? It is posterior fontanelle , which is felt when the head is fully flexed. Where it lies ? It is between posterior end of sagittal suture and medial ends of lambdoid suture.It is felt in mature fetus as a triangular depression at the back of foetal skull.In premature fetus it is soft and may get confused with anterior fontanelle. What is bregma or anterior fontenelle ? It is lozenge shaped.Larger than posterior fontenelle.It has membranous floor where as posterior one is hard to feel.It lies anteriorly.When head is fully flexed , it is not felt. When is the bregma felt ? If head is deflexed in LOA and ROA.ROP and LOPDeep transverse arrest.Persistent occipito-posterior positions. When is the bregma felt posteriorly ? In deflexed head in LOA and ROA positions. When is the bregma felt anteriorly ? In ROP, LOP and persistent occipito-posterior positions. When is the bregma felt on one or the other side ? If head is arrested in ROL and LOL positions. What is the importance of anterior fontanelle in new born ? In intracranial injuries it is tense.In dehydrated babies it is depressed. Which diameter of skull is very important ? The biparietal diameter.This is the widest diameter and measures 3.75 inches. What are the diameters of the head ? Suboccipitobregmatic (flexed vertex )Occipito frontal (Extended vertex )Mento vertical (brow presentation )Submento bregmatic ( face presentation )What are the true anatomical diameters of the skull ? Biparietal (3.75 inches–9.525 cms)Bitemporal (3.5 inches) What is suggested by engaged head ? That maximum diameter -biparietal has passed through pelvic inlet.There is no cephalo-pelvic disproportion. When the head engages in multigravida ? Shortly before or just after the onset of labour