Bony Pelvis and Pelvic Floor

Male Bony Pelvis:

Bony pelvis Male General structure Thick and heavy Greater pelvis Deep Lesser pelvis Narrow and deep Pelvic inlet Heart-shaped Pelvic outlet Small Pubic arch and subpubic angle Narrow (<70°) Obturator foramen Round Acetabulum Large

Female Bony Pelvis:

General structure Thin and light Greater pelvis Shallow Lesser pelvis Wide and shallow Pelvic inlet Oval or rounded Pelvic outlet Large Pubic arch and subpubic angle Wide (>80°) Obturator foramen Oval Acetabulum Small

The bony pelvis serves several functions:

Protects the contents of the pelvic cavity. Provides attachment points for muscles and ligaments (both fibrous and peritoneal). Provides passage for childbirth. Transmits weight from the spine to the femurs. Allows for alternating movement and weight bearing of the lower extremities for locomotion.

The hip bones are formed from the fusion of three bones: the ilium, the ischium, and the pubis Slide 8. All three contribute to the ____________ which is the depression that articulates with the head of the femur.

acetabulum

Pelvis: The pelvis refers to either the part of the trunk between the abdomen and the thighs or the part of the skeleton within it (bony pelvis). The pelvic region consists of the bony pelvis, the pelvic cavity and its contents, the pelvic floor (below the pelvic cavity), and the perineum (the region below the pelvic floor). The pelvic cavity is enclosed by the bony pelvis. It contains the reproductive organs, the urinary bladder, and the rectum. The bony pelvis or pelvic girdle is formed by the two hip bones, the sacrum, and the .

coccyx

The ____ consists of 4 fused vertebrae that articulate with the base of the sacrum. The vertebrae of the coccyx are rudimentary in that they do not have fully developed pedicles and transverse processes.

coccyx

The _____ conjugate extends from the sacral promontory to the inferior margin of the pubic symphysis. It is the most easily determined and is used to calculate the obstetrical conjugate. The obstetrical conjugate is determined by subtracting 1.5 to 2.0 cm from the diagonal conjugate. The maximum transverse diameter and the distance between the ischial spines can also be measured.

diagonal

Pelvic fractures: Hip fractures are common in the elderly that have osteoporosis (systemic bone loss). They generally do not occur in the hip bones but rather in the ____ ____ Slide 21. Fractures of the pelvic bone do not occur in isolation. That is, if there is one fracture there will be others Slides 22,23. The pelvic girdle forms a ring. You cannot break a pretzel in one place!

femoral neck

The ____ ____ is superior to the pelvic inlet and is bounded by part of the anterior abdominal wall, the alae of the ilium bones, and the L5 and S1 vertebrae Slides 2,3. It is considered part of the abdominal cavity which is why it is called the false pelvis. It supports the ileum and sigmoid colon.

greater pelvis

The blood supply to the pelvis and perineum is mainly from branches of the ___ ____ _______ Slide 33,34. The internal iliac artery branches into the anterior and posterior trunks and further into multiple important arteries such as the uterine artery, the umbilical artery, the superior gluteal artery, and others that supply the pelvic organs.

internal iliac artery

The ischium Slide 11 is the posterior part of the hip bone and is found below the ilium and behind the pubis. It is a thick and strong bone. The ____ ____ forms the lower part of the obturator foramen. The ischial tuberosity is posterior and bears body weight on sitting.

ischial ramus

The ____ _____ are formed by the hip bones including the obturator foramena. These are closed by the obturator membranes and the obturator internus muscles Slides 25,26. The medial surface of the obturator internus muscles are covered by the obturator fascia.

lateral walls

The _____ _____ lies between the pelvic inlet and the pelvic outlet. It is the location of the pelvic organs. It is bounded by the hip bones, the sacrum, the coccyx, and the levator ani muscles.

lesser pelvis (pelvic cavity)

The pelvic floor or pelvic diaphragm consists of the ____ and ___muscles Slide 27. The levator ani are a group of three muscles that are difficult to separate with dissection; the puborectalis Slide 28, the pubococcygeus Slide 29 and the Iliococcygeus Slide 30 muscles. The puborectalis is a sling that passes posterior to the anorectal junction and plays a role in maintaining fecal continence. The coccygeus is posterior to the levator ani muscles Slide 31.

levator ani and coccygeus muscles Together, the muscles of the pelvic floor relax to allow urination and defecation. Contraction can resist intraabdominal pressure that would otherwise force urine, gas, or stool through the pelvic outlet. This occurs reflexively with coughing, sneezing, or vomiting. The pelvic floor plays a key role in and is subject to injury during childbirth.

The weight bearing capacity of the pelvis is reinforced by many thick powerful ligaments Slides 16,17,18. The weight of the spine at the sacral promontory causes rotational force on the sacrum that would move it posteriorly. This is counterbalanced by the strong sacrotuberous and sacrospinous ________ that bind the inferior sacrum to the ischium. The sacrotuberous ligament attaches the sacrum to the ischial tuberosity. The sacrospinous ligament attaches the sacrum to the ischial spine.

ligaments

The _____ ___ unite the L5 and S1 vertebrae anteriorly at the intervertebral disc and posteriorly at the facet joints.

lumbosacral joints

Measurements of the female pelvis: The anteroposterior diameter extends from the sacral promontory to the upper inner border of the symphysis pubis and measures approximately 11 cms Slide 19. This is the shortest conjugate and is called the ______ conjugate. The anatomical (true) conjugate is measured from the promontory of the sacrum to the center of the upper surface of the symphysis pubis and measures approximately 12 cm. Although it is slightly longer than the obstetric conjugate, the extra space is not available for the passage of the fetus.

obstetrical

The ____ ____ is the angle formed by the convergence of the inferior rami of the ischium and pubis Slide 7.

pelvic arch (angle)

The ___ ____ is bordered by the inferior margin of the pubic symphysis, the inferior ramus (ramus is an arm or branch of a bone) of the pubic bone, the ischial tuberosity, the sacrotuberous ligament, and the tip of the coccyx Slide 6.

pelvic outlet

The ____ _____ is a fibrous structure that is an important muscle attachment for some of the fibers of the levator ani muscles Slides 32. In the female, it is in the midline between the vagina and the anal canal. In the male, it is between the bulbs of the penis (extensions of the corpora cavernosa) and the anal canal. It is subject to injury during childbirth. It is subcutaneous and can be palpated.

perineal body

The main nerve of the perineum is the ____ ____. It provides sensation for the perineum of both males and females. In females, it can be blocked with local anesthetic to provide anesthesia during childbirth. Its use has diminished relative to epidural blocks. It has the disadvantage of requiring a high degree of skill and can lead to failure of anesthesia if the anesthetic is injected distant to the nerve. A pudendal nerve block provides anesthesia for the perineum but does not stop the pain of labor. The pudendal nerve (S2,3,4) enters the perineum through the obturator foramen in the pudendal canal (Alcock's canal, Benjamin Alcock 1801 - ?, Irish anatomist) which passes through the obturator fascia.

pudendal nerve

The pubis Slide 12 is the anterior part of the hip bone. It is divisible into a body of the pubis and the superiorand inferior pubic rami. The right and left pubic bones articulate at the pubic symphysis. The pubic tubercle is a projection on the superior surface of the superior pubic ramus. It is an attachment point for the inguinal ligament. The superior border of the superior pubic ramus between the pubic tubercle and the pubic symphysis is the pubic crest. It is an attachment point for the conjoint tendon, the rectus abdominis, the external abdominal oblique muscle, and the ___ ____.

pyramidalis muscle.

The pubic symphysis joins the pubic bones in the midline. It is lined by fibrocartilage. Under the influence of the hormone ____ the pubic symphysis and the sacroiliac joint become more flexible during pregnancy to allow a small amount of expansion for childbirth.

relaxin

The lamina of the 5th sacral vertebra fail to meet in the midline thereby forming the __ ___. The vertebral foramina of the sacrum form the sacral canal. The sacral canal contains the anterior and posterior nerve roots of the lumbar, sacral, and coccygeal spinal nerves. The anterior and posterior surfaces of the sacrum have four foramina on each side for the passage of the anterior and posterior rami of the upper 4 sacral nerves. The 5th spinal nerves exit the spine through the sacral hiatus.

sacral hiatus

The posterior pelvic wall is formed by the sacrum and coccyx, the sacroiliac joint and its associated ligaments, and the piriformis muscle. The piriformis muscle exits the pelvis through the greater sciatic foramen to attach to the femur. The posterior wall is also the site of the ___ ___. Piriformis syndrome is a neuromuscular condition associated with pain of the buttock region. It is believed to be the result of sciatic nerve compression by the muscle. Clinically, it can be confused with radiculopathy.

sacral plexus

The pelvic inlet (pelvic brim) is bordered by the superior margin of the pubic symphysis, the posterior border of the pubic crest, the arcuate line of the ilium, the anterior border of the ala of the sacrum, and the ___ ____ Slides 4,5.

sacral promontory

The ____ ____ is slightly moveable but it can become obliterated with age. It is a combined synovial and syndesmotic (fibrous) joint.

sacrococcygeal joint

Joints of the pelvis: The ___ ____ in a young person has limited movement. It is partially syndesmotic (bones joined together by fibrous connective tissue) and partially lined by cartilage. The articular surfaces of this joint are quite irregular Slide 24. In older people, it becomes progressively more fibrotic and can become ossified. Degenerative changes of the cartilaginous component of the joint can result in pain.

sacroiliac joint

The ilium is the largest bone of the pelvis and contributes the largest area of the acetabulum Slides 9,10. It can be described as having two parts; the ala (wing) and the body. The separation of these two parts is marked on the medial surface by the arcuate line. The iliac crest, and the anterior superior and posterior superior iliac spines are palpable subcutaneously. The ilial contribution of the _____ ___ is part of the body of the ilium. The auricular surface (shaped like an ear) of the ilium articulates with the sacrum to form the sacroiliac joint.

sacroiliac joint

The _____ Slides 13,14,15 consists of 5 fused vertebrae that form a single bone with a forward concavity. The upper border articulates with L5 and the lower border articulates with the coccyx. Laterally, the sacrum articulates with the two iliac bones at the sacroiliac joints. The anterior upper margin of the first sacral vertebra projects forward as the sacral promontory. The sacral promontory is the posterior margin of the pelvic inlet. It is an important obstetric landmark when measuring the size of the pelvis.

sacrum

During most normal deliveries the baby's head enters the pelvic brim with a _________ orientation Slide 20. This is called engagement. It is the entrance of the largest diameter of the fetal head into the smallest diameter of the pelvis. As it descends, the head undergoes internal rotation that brings the head into an anterior posterior position with the occipital region facing anteriorly. After delivery of the head, the baby rotates to a transverse position again (external rotation) bringing the shoulders into an anterior posterior position. Although the passage narrows below the pelvic brim, internal rotation of the head may also be related to the dimensions of the opening of the pelvic floor muscles.

transverse

Pelvic walls and floor: The antero-inferior wall is formed by the bodies and rami of the pubic bones and the pubic symphysis. It provides support for the ____ _____. The pubic bones are separated from the urinary bladder by the retropubic space or space of Retzius (Anders Retzius 1796 - 1860, Swedish anatomist). It normally contains fat and loose connective tissue.

urinary bladder