Pelvis - Obstetrical Significance

Human Pelvis anatomy is basic and fundamental and essential topic every obstetrician need to know and learn thoroughly and practice every day to become more perfect.

1. Pelvis Dr. Chaduvula Suresh Babu Professor Department of OBGYN GIMSR Visakhapatnam, AP, India

2. Pelvis – Its Bones It is made up of 4 bones 1. Os innominatum [2] 2. Sacrum 3. Coccyx Os innominatum is made up of 3 bones 1. Ilium 2. Ischium 3. Pubis

3. Pelvis – Its Joints Pelvis has 4 joints 1. Pubic symphysis – Fibrocartilagenous jt. It has 3 ligaments – superior and inferior pubic ligaments and arcuate ligament in between 2. Sacroiliac jt . Or synchondrosis [2] - synovial 3. Sacrococcygeal jt . – Synovial hinge

4. Pelvis and its Angles 1. Angle of inclination – 55-60 degrees [more the angle bad is outcome] 2. Sacral Angle – 90 degrees [ less is bad] 3. Subpubic angle – 85-90 degrees [ less is bad and it will increase waste space of Morris ]

5. Pelvis & its Essential Diameters Any decrease in diameter will alter mechanism of labour. They are 1. AP diameter of Inlet – 11cm 2. AP diameter of least pelvic dimension – 11.5 cm 3. ISD – 10.5 cm 4. AP diameter of outlet – 11.5 cm 5. ITD – 11 cm 6. Obstetrical conjugate – 10cm 7. Diagonal conjugate – 12.5 cm 8. True or Anatomical conjugate or conjugate vera -11cm

6. Pelvis & its Essential Diameters

7. Diagonal conjugate

8. Pelvis – its types There are 4 types – Caldwell Moloy classification 1. Gynaecoid type [50%] 2. Android type [25 %] 3. Anthropoid type [20%] 4. Platypelloid type [ 5%]

9. Pelvis Pelvis is divided into Pelvis Major or False Pelvis and Pelvis Minor or True Pelvis by Linea Terminalis . Linea Terminalis is formed by upper border of Sacral vertebra, arcuate line of the I lium and pectineal line of the Pubis. Pelvis above linea is Pelvis major. Pelvis below linea is Pelvis minor.

10. Structure of Pelvis True Pelvis is divided into Inlet, Cavity and Outlet. Inlet or Brim is formed by from anterior to posterior upper border of symphysis pubis, pubic crest, pubic tubercle, pectineal line iliopubic eminence, iliopectineal line, sacroiliac joint, anterior border of ala of sacrum and upper border of sacral promontory and same on the opposite side.

11. Cavity Described as a bent cylinder with deep posterior wall than the anterior. Extends from inlet above to the outlet below. In erect position, direction of cavity is downwards and backwards in the upper part and forwards and downwards in the lower part and this curve is called “ Curve of Carus ” which is J shaped.

12. Pelvis Length of anterior wall of pelvis is 5 cm and posterior is 10 cm. Boundaries of true pelvis is formed by, bones, ligaments, muscles and fascia around them. Bony boundaries are posteriorly anterir surface of sacrum, laterally ischial bones, sacrosciatic nothes and anteriorly pubic bones, ascending rami of pubis and obturator foramina. L igaments like sacrotuberous and sacrospinous ligaments and fascia surrounding them. Muscles are posteriorly by cocygeus , laterally pyriformis and obturator internus , inferiorly levator ani .

13. Pelvic Diaphragm Musculoaponeurotic part separating peritoneal cavity from vulva. It is made up of levator ani and coccygei muscles. It has 3 orifices. They are urethral meatus , vaginal introitus and anus.

14. Planes of Pelvis 1 . Plane of Inlet – corresponds to brim of pelvis – It has AP, transvers and oblique diameters – 11,13 and 12 cm and post sagital 4cm 2. Plane of greatest pelvic dimension – middle of posterior part of sym. Pubis to jt. Of 2 nd and 3 rd sacral vertebra and laterally no bony land marks. It has 2 diameters – AP – 12 and Trans. 12 cm

15. Planes of Pelvis 3 . Plane of least pelvic dimension – lower border of Symphysis Pubis to ischial spine upto tip of 5 th sacral vertebra or jt. of S4 and S5. It has AP 11.5 cm. ISD – 10cm and Post. Sagital – 4.5 cm 4 . Plane of outlet – lower border of sym. Pubis to ischail tuberosity to tip of coccyx formed anteriorly by urogenital triangle formed by ischiopubic rami and line joining ischial tuberosities & posteriorly by anal triangle formed by tip of coccyx and line joining ischial tuberosities . It has AP 11.5 , ITD 11cm and Post sagital 7.5 cm

16. Significance of plane of least pelvic dimension 1. Station of the presenting part 2. Internal rotation occurs 3. Levator ani muscle exists 4. Pudendal block 5. Forward curvature of pelvis occurs 6. Narrowest plane It has 3 diameters – 1. Interspinous – 10cm 2. AP diameter- 11.5 cm 3. Post.sagital – 4.5 cm

17. Boundaries & Diameters of Inlet Inlet has 3 boundaries – Anteriorly – symphysis pubis and horizontal rami of pubis Laterally – linea terminalis Posteriorly – sacral promontory and alae of sacrum It has 3 diameters 1. AP dia.[3] - 2. Transverse - 13 cm – farthest pts. Of linea 3. Oblique dia - 12 cm – SI.jt to iliopectineal eminence

18. Diameters of Inlet Antero- postero diameter has 3 diameters . 1. Obstetrical conjugate – important – from sacral promontory to neaest point on the post. Surface of pubis – 10 cm 2. Diagonal conjugate – clinically detected – from sacral Promontory to lower border of SP or apex of pubic arch – 12cm [DC-1.5 to 2cm is obs.conj .] 3. Anatomical conjugate or conjugate vera or true conjugate – from sacral promontory to inner surface of upper part of sym. Pubis – 11cm

19. Transverse diameter of inlet transects diagonal conjugate 4 cm from sacral promontory.[ Post. Sagital ]

20. Depth of Pelvis It is the distance between lateral brim of the pelvis to ischial spines.

21. Boundaries & Diameters of Outlet Irregular in outline and formed by 2 triangles with intervening inter-tuberous line. Boundaries are- Posteriorly – tip of coccyx Laterally – ischial tuberosities Anteriorly - Pubic arch formed by rami of ischium and pubis

22. Diameters of Outlet 3 diameters 1. AP diameter – from lower border of SP to tip of coccyx - 9.5 to 11.5 cm 2. Transverse – Bituberous – 11 cm 3. Post.sagital diameter – tip of sacrum to transecting point of bitubrous diameter – 7.5 cm

23. Clinical Significance of Pelvic Joints 1. Relaxation of sacroiliac joints and SP occurs due to Relaxin in pregnancy 2. Upward gliding movement of SI jt. occurs 3. At the time of delivery in dorsal lithotomy position displacement of SIJ occurs by 1.5 to 2 cm 4. In shoulder dystocia while doing McRobert’s technique success occurs due to mobility of SIJ

24. Classification of Pelvic Shapes 1 . Gynecoid – Inlet is round or oval Mid pelvis – side walls parallel and iscial spines not prominent, ISD -10cm Outlet – Pubic arch is wide Sacrum – inclined neither anterior or posterior and sacro -sciatic notches are round

25. Classification of Pelvic Shapes 2. Android – Inlet – Heart or triangular shaped Cavity – side walls convergent, ischial spines prominent Oulet – Pubic arch narrowed Sacrum – Inclined anteriorly , straight sacrum without curve, Sacro -sciatic notch – narrow Importance – Occipitoposterior common, Deep transverse arrest,

26. Classification of Pelvic Shapes 3. Anthropoid Inlet is Oval antero-posteriorly Cavity – convergent , spines prominent Outlet – Arch- narrow Sacrum – 6 segments and sacrosciatic notch is large Importance - Persistent OccipitoPosterior Position

27. Classification of Pelvic Shapes 4. Platypelloid Inlet – Oval transversely Cavity – side walls straight, spines not prominent, ISD wide Outlet – Arch is wider, ITD wide Sacrum – Sacral inclination average, sacrosciatic notch – narrow Importance – Difficulty in engagement of Head

28. Abnormal Pelves 1. Rachtic Pelvis – A child with rickets no treated properly. 2. Naegele’s Pelvis – Absence of one ala of sacrum 3. Robert’s Pelvis – Absence of both ala 4. Pelvic deformity due to Spinal problems and lower limb problems. Ex.- pott’s spine, spinal injuries, fracture vertebra and femur, Poliomyelitis etc.,

29. Mixed type of Pelvis Most of the pelves are mixed varieties. It means it has combination of 2 types of pelves . Gynecoid pelvis with Android tendency – Here posterior segment denotes type and anterior segment signifies android tendency.

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