D efinir Oportunidades
3.12.3. Revisión de los Proyectos Six Sigma
CONTENTS 1.0 Introduction 2.0 Objectives 3.0 Main Content
3.1 The Female Bony Pelvis
3.2 Bones, ligaments joints, diameters and variations.
3.3 The Pelvic Floor Muscles 4.0 Conclusion
5.0 Summary
6.0 Self-Assessment Exercise 7.0 References/Further Reading
1.0 INTRODUCTION
Having a basic understanding of the female bony pelvis is essential preparation for your practical skills training. In this unit, you will learn to the different types of female pelvis and how they affect the birth process.
2.0 OBJECTIVES
At the end of this unit, you should be able to:
• describe the female bony pelvis
• explain the pelvic floor muscles.
• give an overview of bones, ligaments joints, diameters and variations of the pelvis.
3.0 MAIN CONTENT
3.1 The Female Bony Pelvis
The pelvis is a hard ring of bone (see Figure 10 below), which supports and protects the pelvic organs and the contents of the abdominal cavity.
The muscles of the legs, back and abdomen are attached to the pelvis, and their strength and power keep the body upright and enable it to bend and twist at the waist, and to walk and run. The bony pelvis form the bony canal through which the fetus must pass during the normal birth process. If the canal is of the normal shape, and size, the baby of the normal size will negotiate it without difficulties but, because pelvis vary in size and shape it is important that the midwife recognizes the normal pelvis so as to be able to detect deviation from the normal. One of the
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ways of estimating the progress of labor is by assessing the relationship of the fetus to certain pelvic landmarks.
Figure 10: The bones of the female pelvis. Thresyamma C.P. (2002) The woman’s pelvis is adapted for child bearing, and is a wider and flatter shape than the male pelvis. The pelvis is composed of pairs of bones, which are fused together so tightly that the joints are difficult to see. We will describe each of the bones in turn, and their major landmarks.
Functions
· It connects the spine to the lower limbs
· It protects the female reproductive organs, bladder, the urethra ,colon, rectum and anal canal
· It allows movement of the body especially walking and running
· It permits sitting and kneeling
· It forms a bony passage for the fetus during labor
· It transmits the weight of the trunk to the legs and holds the two femurs
· Protects the pelvic organs and to a lesser extent the abdominal contents
· The Sacrum transmits cauda equina and distributes nerves to various parts of the pelvis
3.2 Bones, Ligaments, Joints, Diameters and Variation
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Pelvic bones: There are four bones in the pelvis
• Two innominate bones (hip bones),
• One sacrum and
• One coccyx
A. Innominate Bones: each innominate bone is composed of three parts - the ilium, ischium and the pubis
Ilium: The major portion of the pelvis is composed of two bones, each called the ilium — one on either side of the backbone (or spinal column) and curving towards the front of the body. When you place your hand on either hip, your hand rests on the iliac crest, which is the upper border of the ilium on that side. At the front of the iliac crest, you can feel the bony protuberance called the anterior superior iliac spine (a
‘protuberance’ is something that sticks out, like a little hill or knob).
Ischium: The ischium is the thick lower part of the pelvis, formed from two fused bones — one on either side. When a woman is in labour, the descent of the fetal head as it moves down the birth canal is estimated in relation to the ischial spines, which are inward projections of the ischium on each side. The ischial spines are smaller and rounder in shape in the woman’s pelvis than in that of the man.
Pubic bones and the symphysis pubis: The pubic bones on either side form the front part of the pelvis. The two pubic bones meet in the middle at the pubic symphysis. (A symphysis is a very strong bony joint.) The pubic symphysis is immediately below the hair-covered pubic mound that protects the woman’s external genitalia.
B. Sacrum
The sacrum is a tapered, wedge-shaped bone at the back of the pelvis, consisting of five fused vertebrae (the small bones that make up the spinal column or backbone). At the bottom of the sacrum is a tail-like bony projection called the coccyx. The upper border of the first vertebra in the sacrum sticks out, and points towards the front of the body; this protuberance is the sacral promontory — an important landmark for labour and delivery.
Pelvic Joints - there are four pelvic joints
• One symphysis pubis – formed at the joint of two pubic bones, united by a pad of cartilage known as the symphysis pubis
• Two (right and left) sacroiliac joints – is the strongest joint in the body articulates sacrum to ilium. Normally there are little or no
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movements in these joints, but during pregnancy especially towards the end there is a certain degree of movement due to the relaxation of the ligaments of the joints. This may give rise to difficulties in walking and backache, especially the multiparous women. There is little widening during labour , commonly referred to as “give” of the pelvis.
• One sacrococcygeal joint – join the base of the coccyx to the tip of the sacrum
Pelvic Ligaments: ligaments bind the joints
• Inter pubic ligaments at the symphysis pubis
• Sacroiliac ligaments.
• Sacrotuberous ligament
• Sacrococcygeal ligaments.
• Inguinal ligament
Figure 11: Posterior view of the pelvis. Thresyamma C.P. (2002) Division of the Pelvis
The pelvis is divided into two parts, the true and the false pelvis. The false is the part above the brim. It as little importance in obstetrics.
The true pelvis is the bony canal through which fetus must pass during birth. It consists of brim, cavity and outlet. Brim is round except where sacral promontory projects into it. Commencing posteriorly the pelvic brim includes the following important landmarks.
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1. Sacral promontory 2. Sacral ala or wing 3. Sacroiliac joints 4. Iliopectineal line 5. Iliopectineal eminence
6. Superior ramus of the pubic bone
7. Upper inner border of the body of the pubic bone 8. Upper inner border of the symphysis pubis Diameters of the pelvis
Diameters of the brim
• Antero-posterior diameter – from sacral promontory to upper most border of symphysis pubis 12cm. A measurement to the posterior border of the upper surface to a point 1.25cm lower is called the obstetrical conjugate, 11cm. It is the available space for the passage of the fetus hence it is called the true conjugate
• Diagonal conjugate is anteroposterior diameter from the lower border of the symphysis pubis to the centre of the sacral promontory measured vaginally for pelvic assessment 12-13 cm
• Oblique diameter – from sacroiliac joint to the iliopectineal eminence on the opposite side (right and left). It measures 12cm
• Transverse diameter – it is between the points furthest apart on iliopectineal lines and measures 13cm. The fetal head commonly enters in transverse diameter of the pelvic brim
• Sacrocotyloid diameter – from sacral promontory to the iliopectineal eminence on each side, measures 9 – 9.5 cm
• The pelvic cavity extends from the pelvic brim above to the outlet below. Anterior wall is formed by pubic bones and symphysis pubis - depth is 4cm. The cavity is circular in shape and is considered to be 12cm all round.
Diameter of the outlet:
There are two Pelvic outlets: described as
• Anatomical Outlet and Obstetrical Outlet. The anteroposterior diameter of outlet – from the lower border of the symphysis pubis to the sacrococcygeal joints 13cm
• The oblique diameter of outlet - from the oburator foramen to the sacrospinous ligament 12cm
• The transverse diameter of outlet - is taken between two ischial spines 10 -11 cm which is the narrowest diameter of the pelvis
• Pelvic inclination there is difference in the inclination of the pelvis when the woman is standing, sitting and recumbent position. The inclination of the outlet is 11O, cavity 30O, brim 60O, almost 90O in Negro woman
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• Pelvic planes these are imaginary flat surfaces at the brim, cavity and outlet of the pelvic canal. The fetus will enter at right angle to the plane according to the inclination.
• Axis of the pelvic canal a line drawn exactly half way between anterior wall and posterior wall of the pelvic canal to the plan of the outlet, cavity and the brim the curve it makes is known as the curve of Carus, the path which the fetus takes as it travels trough the birth canal.
Figure 12: Diameter of the Pelvis Thresyamma C.P. (2002) Types of Pelvis
• Gynaecoid pelvis – ideal pelvis for child bearing
• Android pelvis – resembles a male pelvis
• Anthropoid pelvis – has long oval brim in which anteroposterior diameter is longer than transverse diameters. Labor does not present any difficulties but favors occipitoanterior or occipitoposterior positions
• Platypelloid pelvis - flat with kidney shaped brim
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Figure 13: Types of Pelvis Thresyamma C.P. (2002)
2.2.2.3 THE PELVIC FLOOR MUSCLES
The pelvic floor is formed by the soft tissues that fill the outlet of the pelvis. It forms a strong diaphragm of muscle sling from the walls of the pelvis. The pelvic floor is made up of:
1. The Skin
2. Subcutaneous Fat 3. Superficial Muscles 4. Deep Muscles 5. Pelvic Fascia 6. Peritoneum
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Figure 14: Pelvic Floors (Anterior and Posterior View) Thresyamma C.P. (2002)
Functions:
• Supports the weight of the abdominal and pelvic organs
• Responsible for the function of the menstruation and defecation and plays an important part in sexual intercourse
• Influence passive movement of the fetus during childbirth
Muscle Layers
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Superficial Layers consists of five muscles:
1. The external and sphincter muscle 2. The transverse perineal muscle 3. The bulbocavernous muscle 4. The ichiocavernous muscle
5. The membrane sphincter of urethra
The Deep Layer is composed of three parts of muscle which together are known as the Levator Ani Muscles (left and right):
1. Pubococcygeal muscle 2. Iliococcygeal muscle 3. Ischiococcygeal muscle
Perineal body is a pyramid of muscles and fibrous tissue between vagina and rectum. Perineal body measures 4cm in each direction
Injury to the pelvic floor
• Overstretching of the muscles
• Laceration –1st 2nd &3rd degree tears
Figure 15:The pelvic canal seen from the side, with the body facing to the left. Thresyamma C.P. (2002)
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Figure 16: Diameters of the pelvic inlet, viewed from above Thresyamma C.P. (2002)
Figure 17: Diameters of the pelvic outlet, viewed from below.
Thresyamma C.P. (2002)
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SELF-ASSESSMENT EXERCISE
i. The female bony pelvis is broader and flatter than the male pelvis.
ii. The pelvic inlet is narrower than the pelvic outlet.
iii. List four possible features of the maternal bony pelvis and/or the fetal skull that may result in a difficult labour and delivery.
4.0 CONCLUSION
The pelvis is divided into two parts, the true and the false pelvis. The pelvic floor is formed by the soft tissues that fill the outlet of the pelvis.
It forms a strong diaphragm of muscle sling from the walls of the pelvis.
5.0 SUMMARY
The pelvis is a hard ring of bone (see Figure 10 below), which supports and protects the pelvic organs and the contents of the abdominal cavity.
The muscles of the legs, back and abdomen are attached to the pelvis, and their strength and power keep the body upright and enable it to bend and twist at the waist, and to walk and run.
6.0 TUTOR-MARKED ASSIGNMENT
7.0 REFERENCES/FURTHER READING
Adele Pillitteri (2010) Maternal and Child Health Nursing : Care of the Child Bearing and Child Rearing Family. Lippincot Williams &
Wilkins, New York.
Fraser D.M. Cooper M.A. and Nolte A.G.W. (2006) Myles Textbook for Midwives African Edition.
Thresyamma C.P. (2002) A Guide to Midwifery Students. Jaypee Brothers Medical Publisher (P) Ltd. New Delhi.
Ojo O.A. and Briggs E.B. (2006) A Textbook for Midwives in the Tropics. 2nd ed. Jaypee Brothers Ltd. New Delhi.
DiDona N.A. and Marks M.G. (1996) Introductory Maternal Newborn Nursing Lippincott.
Ministry of Health. 2007. Malawi national reproductive health service delivery guidelines. Lilongwe, Malawi: Ministry of Health.
Marieb, Elaine N. 2000. Essentials of human anatomy and physiology.
6th ed. San Francisco, CA: Benjamin/Cummings.
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