Bailey & Love's Essential Clinical Anatomy PDF Chapter 9: The Pelvis

Bailey & Love · Essential Clinical Anatomy · Bailey & Love · Essential Clinical Anatomy 9 Essential Clinical Anatomy · Bailey & Love · Essential Clinical Anatomy · Bailey & Love BaileyChapter & Love · Essential Clinical Anatomy · Bailey & Love · Essential Clinical...

Bailey & Love · Essential Clinical Anatomy · Bailey & Love · Essential Clinical Anatomy 9 Essential Clinical Anatomy · Bailey & Love · Essential Clinical Anatomy · Bailey & Love BaileyChapter & Love · Essential Clinical Anatomy · Bailey & Love · Essential Clinical Anatomy The pelvis The hip (innominate) bone......................................... 136 Micturition......................................................................... 144 Joints and ligaments of the pelvic girdle.............. 138 The female internal genital organs.......................... 144 The articulated pelvis................................................... 139 The male internal genital organs............................. 147 Muscles and fasciae of the pelvis............................ 139 MCQs.................................................................................. 150 The pelvic floor............................................................... 140 SBA..................................................................................... 151 The rectum and anal canal......................................... 141 EMQs................................................................................... 151 Defecation........................................................................ 143 Applied questions.......................................................... 152 The bladder...................................................................... 143 The bony pelvis comprises two hip (innominate) bones, the curved and palpable iliac crest extends from the anterior to sacrum and the coccyx, which when articulated enclose the the posterior superior iliac spines. It is thick and gives attach- pelvic cavity. The hip bones articulate anteriorly with each ment to muscles of the lateral and posterior abdominal walls, other at the symphysis pubis and posteriorly with the sacrum tensor fascia lata anteriorly and gluteus maximus posteriorly. at the sacroiliac joints. The highest points of the two iliac crests (intercristal plane) are at the level of the 4th lumbar vertebra and mark the level of the preferred site for lumbar puncture (the L4–L5 THE HIP (INNOMINATE) BONE intervertebral space is wide and allows access to the subarach- This large irregularly shaped bone has three parts – the ilium noid space below the termination of the spinal cord). The above, the ischium below and the pubis in front. In the child iliac crest is a common site for bone biopsy (see Fig. 5.1, they join in a Y-shaped epiphyseal cartilage in the acetabu- p. 80 and Fig. 8.1, p. 123), using the posterior superior spine lum, a laterally placed cup-shaped fossa with which the femo- as a landmark (it lies under the skin dimple, the ‘dimple of ral head articulates. The epiphyses close by late puberty. The Venus’) to the medial side of the upper buttock. It is more ilium expands upwards as a fan-shaped bone and, below it, the prominent in females and lies at the level of S2. pubis and ischium join to enclose the obturator foramen and The ischium, an L-shaped bone, has a body and a ramus. form the anterolateral walls of the true pelvis (Figs. 9.1a,b). The body forms two-fifths of the acetabulum and expands infe- The ilium forms the upper two-fifths of the acetabulum riorly to form the ischial tuberosity, which gives attachment and expands superiorly into a flattened plate, the ala, which to the hamstring muscles and the sacrotuberous ligament. To has lateral (gluteal) and medial (pelvic) surfaces surmounted the femoral surface of the body is attached obturator externus. by the iliac crest and separated by anterior and posterior Above the tuberosity the body is crossed by the sciatic nerve, borders. The gluteal surface gives attachment to the glutei: lying above a conical ischial spine that separates the greater gluteus minimus, gluteus medius and gluteus maximus from sciatic notch (foramen) above from the lesser sciatic notch anterior to posterior. The medial surface is divided into a pos- (foramen) below. To the spine are attached levator ani and terior auricular surface, which articulates with the sacrum, the sacrospinous ligament, thus producing the lessor sciatic and an anterior iliac fossa from whose upper two-thirds arises foramen (Figs. 9.2a,b). The pelvic surface of the body gives the iliacus muscle. Posteriorly it bears the roughened iliac attachment to the obturator internus muscle, and levator ani tuberosity for the sacroiliac ligaments. The short anterior and coccygeus are attached to the medial surface of the spine. border bears two small projections, the subcutaneous ante- The pubis has a body and superior and inferior pubic rami, rior superior iliac spine to which the inguinal ligament is which join with the superior and inferior rami of the ischium attached, and the anterior inferior iliac spine, an origin of to enclose the obturator foramen. The outer surface of the rectus femoris. The posterior border gives attachment to the body gives attachment to adductor muscles, and the inner sacrotuberous ligament and also has two projections, the surface is related to the bladder and gives attachment to leva- posterior superior and posterior inferior iliac spines. The tor ani. The oval symphyseal surface is covered by hyaline  PART 2 | THE ABDOMEN 137 Iliac crest Iliolumbar Sacrum 5th lumbar ligament Iliac bone vertebra Posterior Anterior superior superior Sacrum iliac spine iliac spine Superior Short dorsal Posterior inferior pubic Anterior sacroiliac iliac spine ramus inferior ligaments Sacrospinous Pubic iliac spine ligament tubercle Sacrotuberous Acetabulum ligament Sacrococcygeal ligament Obturator Symphysis Ischial foramen pubis Ischial (a) tuberosity Inferior pubic ramus tuberosity (a) Articular 9 facets 4 for L5 Lower end of 1 erector spinae 5 attachments Median sacral crest Foramen for dorsal roots Gluteus 8 maximus 2 (b) Sacral hiatus 12 3 7 6 11 8 2 10 3 1 7 (b) 7 10 2 2 1 6 3 3 5 11 14 9 12 4 (c) 4 4 13 (c) Figure 9.1 (a) Articulated pelvis, anterior view. (b) Dissection of pelvic bones and ligaments, anterior view: 1, iliac bone (thin); 2, anterior Figure 9.2 (a) Posterior aspect of the sacrum showing the ligaments superior iliac spine; 3, inguinal ligament; 4, iliac crest; 5, sacral of the pelvis. (b) Muscle attachments. (c) Dissection of posterior view promontory; 6, sacrotuberous ligament; 7, sacrospinous ligament; of the pelvic bones and ligaments: 1, iliac bone; 2, posterior superior 8, anterior sacral foramina; 9, iliolumbar ligaments; 10, obturator iliac spine; 3, sacroiliac joint; 4, ischial tuberosity; 5, sacrotuberous foramen covered by membrane; 11, lesser sciatic notch (foramen); ligament; 6, sacrospinous ligament; 7, posterior sacral foramina; 12, greater sciatic notch (foramen). (c) X-ray view: 1, sacrum; 8, iliolumbar ligaments; 9, obturator foramen covered by membrane; 2, sacroiliac joints; 3, arcuate line; 4, pectineal line. The pelvic inlet or 10, greater sciatic notch (foramen); 11, posterior hip joint capsule; brim, through which the fetal head must pass down into the true pelvis 12, greater trochanter of femur; 13, lesser trochanter of femur, (dashed line), is bounded by these four structures above and the pubic 14, pubic symphysis symphysis anteriorly  PART 2 | THE ABDOMEN 138 CHAPTER 9 The pelvis cartilage and joined to its fellow by a fibrocartilaginous disc face for articulation with the ilium and, posteriorly, a pitted and ligaments. Its superior border, the pubic crest, is palpa- area for attachment of the strong interosseous ligaments. ble and gives attachment to rectus abdominis, the conjoint The coccyx is small and triangular and is formed by the tendon and the external oblique aponeurosis. The palpable fusion of four coccygeal vertebrae. It articulates with the apex pubic tubercle, at the lateral end of the crest, gives attach- of the sacrum and is the remnant of a human tail. ment to the inguinal ligament. The superior ramus bears a ridge diverging from the pubic tubercle; the pectineal line gives attachment to part of the inguinal ligament. In the mid- JOINTS AND LIGAMENTS OF line the pubic bones articulate to form the pubic arch. The sacrum is formed of five fused sacral vertebrae (Figs. THE PELVIC GIRDLE 9.2b and 9.3a). Triangular in shape, it possesses a base supe- riorly, an apex inferiorly and a dorsal, a pelvic and two lateral Sacroiliac joint surfaces. It is divided by four paired rows of sacral foramina The sacroiliac joint is a plane synovial joint between the into a median portion, corresponding to the fused vertebral irregular auricular surfaces of the sacrum and ilium; in older bodies, and a pair of lateral masses, formed of the transverse people it may become partly fibrous and may even fuse. processes. The pelvic and dorsal sacral foramina commu- nicate with the central sacral canal and convey the sacral Ligaments segmental nerves. The base faces upwards and forwards; its projecting ante- Capsular – attached to the articular margins with capsular rior margin is known as the promontory. It bears an articular thickenings – the very strong ventral and dorsal sacroiliac facet for the 5th lumbar vertebra anterior to the opening of ligaments. the sacral canal, on each side of which are two projecting Extracapsular – the interosseous sacroiliac ligament is superior articular processes. The apex articulates with the also very strong and unites the auricular surfaces of the coccyx. The pelvic surface is concave; the alae give attach- two bones. ment to piriformis. The upper part of the surface is in contact Accessory ligaments – (i) the sacrotuberous ligament – a with peritoneum and the lower part with the rectum. The strong thick band from the ischial tuberosity to the coc- dorsal surface is convex and irregular, giving attachment to cyx, lateral crest of the sacrum and posterior iliac spines; erector spinae, the thoracolumbar fascia and gluteus maximus. (ii) the sacrospinous ligament – a triangular ligament In the midline it bears a median sacral crest. Inferiorly the that converges from the lateral margin of the sacrum and posterior wall of the sacral canal is deficient between paired coccyx to the ischial spine (Fig. 9.2a); (iii) the iliolumbar sacral cornua, forming the sacral hiatus, which is closed by ligament –which attaches the 5th lumbar transverse pro- fibrous tissue. The sacral canal contains, within the menin- cess to the posterior iliac crest. ges, the end of the cauda equina and cerebrospinal fluid, and, extradurally, the external vertebral venous plexus and spinal Functional aspects nerves. The lateral surface bears a roughened auricular sur- Movement is limited by the joint’s irregularities to slight glid- ing and rotation; stability is maintained entirely by ligaments. Body weight is transmitted through the vertebral column and Promontory tends to rotate the sacrum forwards, but this is resisted by the Iliacus Lateral mass sacrospinous and sacrotuberous ligaments. of sacrum The sacral hiatus is used to introduce anaesthetic solu- Anterior sacral tions into the sacral canal and block the sacral nerve roots foramen (caudal epidural block). Thus the birth canal, the pelvic Piriformis Site of fusion floor and perineum can be anaesthetized, with the lower limbs of 2nd and 3rd being spared. A pudendal nerve block is often used during sacral vertebrae labour to block the pain of an episiotomy. The hormones of Coccygeus late pregnancy allow stretching of these ligaments and a slight Facet for coccyx increase in movement of the joint, all of which contribute to (a) a 10 per cent increase in the transverse diameter of the female pelvis in late pregnancy, which in turn makes the passage of Spine the fetus much easier. Lamina Superior Sacral canal articular process Sacrococcygeal joint Body of 1st Lateral mass sacral vertebra The sacrococcygeal joint is a secondary cartilaginous joint Promontory whose stability is enhanced by a fibrocartilaginous interverte- (b) bral disc and a capsular ligament. In late pregnancy there is an Figure 9.3 Disarticulated sacrum: (a) anterior view showing muscle increase in laxity of the ligaments and an increased range of attachments; (b) superior view movement, which may result in trauma during delivery.  PART 2 | THE ABDOMEN Muscles and fasciae of the pelvis 139 Symphysis pubis In the female, the maximum diameter of the pelvic inlet is transverse and that of the outlet is anteroposterior. Thus The symphysis pubis (Fig. 9.1) is a secondary cartilaginous the larger diameter of the fetal head, the anteroposterior, nor- joint between the two pubic bones. Its articular surfaces are mally lies along the wider diameter of that part of the pelvis united by a fibrocartilaginous disc. containing it, and in normal labour the head undergoes par- Little movement occurs except for a little separation tial rotation during descent. of the pubic bones in late pregnancy. Splitting of this joint Sex differences are more evident in the pelvis than in (symphysiotomy) is sometimes performed to enlarge the birth other bones. The male pelvis is rougher, thicker and heavier; canal for delivery. its brim is heart-shaped rather than round/oval; its cavity is longer and the outlet narrower; its acetabulum is larger and the ischiopubic ramus is everted along the attachment of THE ARTICULATED PELVIS the crura of the penis; and the subpubic angle is less than 90 In the erect posture the pelvis lies obliquely, with the ante- degrees, often as acute as 60 degrees, whereas the female’s is rior superior iliac spines and pubic symphysis in the same ver- 90 degrees or more (Fig. 9.4). tical plane; it is divided into greater and lesser parts by the pelvic brim, which runs between the arcuate lines and the Pelvimetry promontory of the sacrum. The greater (false) pelvis is above the brim and bounds the lower abdominal cavity; the lesser Obstetricians require measurements of the pregnant women’s (true) pelvis lies below the brim and, because it forms the pelvis to assess whether problems may occur in childbirth. birth canal, is a space of much obstetric importance. It has an Previously done by X-ray, this is now achieved ultrasonically. inlet, a cavity and an outlet (Fig. 9.1c). Fractures of the pelvis are commonly caused by crush inju- The inlet is the pelvic brim; the male’s is heart-shaped ries and frequently result in injuries to related soft tissues; i.e. but the female’s is round or oval, with a transverse diam- bladder and urethral trauma is associated with fractures of the eter (13 cm) usually greater than its anteroposterior pubis and major vessel trauma (common and internal iliac) diameter (11 cm). The cavity is a short curved canal with sacroiliac fractures and dislocation. whose posterior wall is three times longer than its anterior wall. It is bounded by the true pelvic surfaces of the hip MUSCLES AND FASCIAE OF THE bones, the sacrum and the sacrospinous and sacrotuberous ligaments. The outlet is diamond-shaped, bounded by the PELVIS lower border of the pubic symphysis and ischiopubic rami, The muscles lining the walls of the pelvis – iliacus, obtura- the sacrotuberous ligaments and the coccyx. In the female tor internus and piriformis – are covered with pelvic fascia, the anterior diameter (conjugate) is larger than the trans- which, where it overlies the obturator internus, gives attach- verse diameter. ment to levator ani. Figure 9.4 Differences seen on X-ray between the female (a) and male (b) pelvis Note: 1. Female inlet is more circular, male more heart-shaped 2. Female subpubic angle is wide (90–120 degrees), male is narrower (60–90 degrees) 3. Female sacrum is wider and flatter 4. Female ischial spines are further apart (not shown)