WEEK 1: PELVIC ANATOMY

Question 1

What is the pelvic girdle?

Answer 1

The pelvic girdle is a ring-like bony structure, located in the lower part of the trunk. It connects the axial skeleton to the lower limbs.

Question 2

What is the pelvis?

Answer 2

It is the space within the pelvic girdle.

Question 3

State the 3 bones that make up the pelvic girdle.

Answer 3

The bony pelvis consists of the two hip bones (also known as innominate or pelvic bones), the sacrum and the coccyx.

Question 4

Describe the orientation of the pelvic girdle.

Answer 4

It is tilted slightly anteriorly in the anatomical position.

Question 5

State the 4 articulations within the pelvic girdle.

Answer 5

There are four articulations within the pelvis:

*Sacroiliac joints (x2) – between the ilium of the hip bones, and the sacrum

*Sacrococcygeal symphysis – between the sacrum and the coccyx.

*Pubic symphysis – between the pubis bodies of the two hip bones

Question 6

State the 6 functions of the Pelvis.

Answer 6

*Weight bearing wen sitting and standing

*Provides attachment for:
-Muscles of locomotion: posture, pelvic floor
-Abdominal muscles
-Erectile bodies of the external genitalia

*Contains and protects the abdominopelvic and pelvic viscera

*Used in forensics to differentiate between male and female skeletons

*Used in anthropology:
-Paleoanthropology: Is a multidisciplinary field of science that studies the evolutionary history of the human species and our ancient ancestors.

*Used in OB/ GYN as it is essential in childbirth.

Question 7

The osteology of the pelvic girdle allows the pelvic region to be divided into two:

*The greater pelvis
*The lesser pelvis

Which is a true pelvis and a false pelvis between the two?

Answer 7

*The greater pelvis: False pelvis
*The lesser pelvis: True pelvis

Question 8

State the contents of the true pelvis in males and females.

Answer 8

BOTH
*Rectum, urinary bladder

MALES
*Prostate gland

FEMALES
*Vagina, cervix

Question 9

State the contents of the false pelvis in males and females and those found in both?

Answer 9

BOTH
*Urinary bladder when full AND lower intestines

FEMALE
*Uterus, ovaries and uterine tubes

Question 10

What is the junction between the greater and lesser pelvis is known as?

Whatare the outer bony edges of this structure called?

Answer 10

The junction between the greater and lesser pelvis is known as the pelvic inlet.

The outer bony edges of the pelvic inlet are called the pelvic brim.

Question 11

Describe the borders of the pelvic inlet.

Answer 11

The borders of the pelvic inlet:

*Posterior – sacral promontory (the superior portion of the sacrum) and sacral wings (ala).

*Lateral – arcuate line on the inner surface of the ilium, and the pectineal line on the superior pubic ramus.

*Anterior – pubic symphysis

Question 12

The pelvic inlet determines the size and shape of the birth canal, with the prominent ridges a key site for attachment of muscle and ligaments.

Some alternative descriptive terminology can be used in describing the pelvic inlet:

*Linea terminalis
*Iliopectineal line

Answer 12

*Linea terminalis – the combined pectineal line, arcuate line and sacral promontory.

*Iliopectineal line – the combined arcuate and pectineal lines. This represents the lateral border of the pelvic inlet.

Question 13

Where is the pelvic outlet located?

Describe its borders.

What is the angle beneath the pubic arch known as that is of a greater size in women?

Answer 13

Pelvic Outlet
The pelvic outlet is located at the end of the lesser pelvis, and the beginning of the pelvic wall.

Its borders are:
-Posterior: The tip of the coccyx

-Lateral: The ischial tuberosities and the inferior margin of the sacrotuberous ligament

-Anterior: The pubic arch (the inferior border of the ischiopubic rami).

The angle beneath the pubic arch is known as the sub-pubic angle and is of a greater size in women.

Question 14

What are the female pelvis and male pelvis called?

State the 5 differences between the male and female pelvis which creates a greater pelvic outlet, adapted to aid the process of childbirth.

Answer 14

The majority of women have a gynaecoid pelvis, as opposed to the male android pelvis.

When comparing the two, the gynaecoid pelvis has:

*Oval obturator foramen in females and round obturator foramen in males

*A wider and broader structure yet it is lighter in weight

*An oval-shaped inlet compared with the heart-shaped android pelvis.

*Wider pelvic outlet compared to the narrower pelvic outlet in males.

*Less prominent ischial spines, allowing for a greater bispinous diameter

*A greater angled sub-pubic arch, more than 80-90 degrees.

*A sacrum which is shorter, more curved and with a less pronounced sacral promontory.

Question 15

State the 3 articulations of the hip bone.

Answer 15

The hip bones have three main articulations:

*Sacroiliac joint – articulation with the sacrum. Synovial joint’
*Pubic symphysis – articulation between the left and right hip bones. Cartilaginous joint.
*Hip joint – articulation with the head of femur and acetabulum of the hip bone. Ball and socket synovial joint.

Question 16

Composition of the Hip Bone

State the 3 parts that comprises the hip bone.

Together, the ilium, pubis and ischium form a cup-shaped socket known as the _______.

Answer 16

The hip bone is comprised of the three parts;
*The ilium,
*Pubis and
*Ischium.

Together, the ilium, pubis and ischium form a cup-shaped socket known as the acetabulum (literal meaning in Latin is ‘vinegar cup ‘). The head of the femur articulates with the acetabulum to form the hip joint.

Question 17

Name the structure that separate the ischium, pubis and ileum which its fusion begins at the age of 15-17.

Answer 17

Prior to puberty, the triradiate cartilage separates these parts – and fusion only begins at the age of 15-17.

Question 18

The wing of the ilium has two surfaces:

Describe the 2 surfaces.

The superior margin of the wing is thickened, forming the _______.

It extends from the anterior superior iliac spine (ASIS) to the posterior superior iliac spine (PSIS).

On the posterior aspect of the ilium there is an indentation known as the ___________.

Answer 18

The wing of the ilium has two surfaces:

*Inner surface – has a concave shape, which produces the iliac fossa (site of origin of the iliacus muscle).

*External surface (gluteal surface) – has a convex shape and provides attachments to the gluteal muscles.

The superior margin of the wing is thickened, forming the iliac crest.

It extends from the anterior superior iliac spine (ASIS) to the posterior superior iliac spine (PSIS).

On the posterior aspect of the ilium there is an indentation known as the greater sciatic notch.

Question 19

What is the clinical relevance for the ASIS?

Answer 19

Clinical Relevance: Anterior Superior Iliac Spine

The anterior superior iliac spine (ASIS) is an important anatomical landmark:

*Mid-inguinal point – halfway between the ASIS and the center of the pubic symphysis. The femoral artery can be palpated here.

*Mid-point of the inguinal ligament – halfway between the ASIS and the pubic tubercle.

In clinical practice, a patient’s “true” leg length is measured from the ASIS to the medial malleolus at the ankle joint.

This is distinct from “apparent” leg length, which is measured from the umbilicus to the medial malleolus.

True leg length discrepancy is a feature of various hip disorders, as well as being a potential complication of hip joint replacement (arthroplasty).

Question 20

It is the widest and largest of the three parts of the hip bone and is located superiorly.

The body forms the superior part of the acetabulum (acetabular roof).

Immediately above the acetabulum, it expands to form the wing (or ala).

Name the bone of the hip bone described above.

Answer 20

The ilium

Question 21

It is the most anterior portion of the hip bone.

It consists of a body, superior ramus and inferior ramus (ramus = branch).

Name the bone described above.

Answer 21

The pubis

Question 22

What is the clinical revelance of the pubis?

Answer 22

Clinical Relevance - Pubic Rami Fractures

Pubic rami fractures can sometimes be observed on x-rays in elderly patients who are investigated after simple low energy falls from standing height.

In this context and provided they are the only injury a patient has sustained; these fractures are usually treated without surgery.

Healing can be expected within 6-8 weeks and patients are encouraged to fully weight bear straightaway.

Question 23

It forms the posteroinferior part of the hip bone.

It is composed of a body, an inferior ramus and superior ramus.

Name the bone described above.

Answer 23

The ischium

Question 24

The inferior ischial ramus combines with the inferior pubic ramus forming the______, which encloses part of the obturator foramen.

Answer 24

The inferior ischial ramus combines with the inferior pubic ramus forming the ischiopubic ramus, which encloses part of the obturator foramen.

The posteroinferior aspect of the ischium forms the ischial tuberosities and when sitting, it is these tuberosities on which our body weight falls.

Near the junction of the superior ramus and body is a posteromedial projection of bone, the ischial spine.

Question 25

State the 2 important ligaments that attach to the ischium.

Answer 25

Two important ligaments attach to the ischium:

*Sacrospinous ligament – runs from the ischial spine to the sacrum, thus creating the greater sciatic foramen through which lower limb neurovasculature (including the sciatic nerve) transcends.

*Sacrotuberous ligament – runs from the sacrum to the ischial tuberosity, forming the lesser sciatic foramen.

Question 26

Describe the 2 broad groups of pelvic fractures.

Answer 26

There are two broad groups of pelvic fractures:

1. Low energy injuries:
   For example, a simple fall from standing height in an osteoporotic patient resulting in pubic rami fracture.
   These are usually ‘stable’ injuries, not requiring surgery.
2. High energy injuries with direct or transmitted trauma:
   For example, after a high-speed road traffic accident.

These result in more extensive fractures which may include the acetabulum and sacroiliac joint.
These can be ‘unstable’ injuries and may require urgent surgery.

Higher energy injuries can be associated with soft tissue and vascular injury. In particular, the bladder and urethra are at high risk of damage.
Vascular injury can result in life threatening hemorrhage.

In the context of a high energy major trauma patient, the pelvis can be a major source of bleeding due to fracture. As a result, major trauma patients are assumed to have a pelvic fracture until proven otherwise and a ‘pelvic binder’ is used to stabilize the pelvis and minimize further bleeding.

Circumferential pressure is applied by the binder at the level of the greater trochanters – an important anatomical landmark.

Question 27

The sacroiliac joint is an articulation between the ilium of the pelvis and the sacrum of the vertebral column.

The articular surfaces are irregular in shape and interlock to produce a stable joint. They are lined with hyaline cartilage.

In later life, the sacroiliac joints may become completely fused, resulting in a loss of the joint cavity.

What type of a joint is the sacroiliac joint?

Answer 27

Joint Capsule
The sacroiliac joint is a synovial joint.

It is encompassed by a fibrous joint capsule, which is lined by a synovial membrane.

Question 28

The ligaments of the sacroiliac joint reinforce the synovial capsule. There are three main ligaments.

State the 3 ligaments of the sacroiliac joint.

Answer 28

Ligaments
1. Interosseous sacroiliac ligament – located posteriorly and superiorly to the joint, spanning between the ilium and sacrum. It is the strongest of the ligaments.

2. Posterior sacroiliac ligament – also located posteriorly to the joint, covering the interosseous ligament.
3. Anterior sacroiliac ligament – thickening of the anterior component of the joint capsule. It is relatively thin and weak.

Question 29

What is the primary function of the sacroiliac joint?

There is a small degree of gliding and rotational movement that can occur between the interlocking articular surfaces.

During pregnancy, the ligaments of the sacroiliac joint become slightly lax – this encourages movement within the joint in childbirth.

Answer 29

The primary function of the sacroiliac joint is to transmit forces from the lower limb to the vertebral column.

Question 30

Name the arterial supply to the sacroiliac joint.

Answer 30

Arterial supply to the sacroiliac joint is via the iliolumbar artery and the medial and lateral sacral arteries.

Question 31

Describe the venous drainage of the sacroiliac joint.

Answer 31

Venous drainage is by accompanying veins into the internal iliac vein.

Question 32

Describe the innervation to the sacroiliac joint.

Answer 32

The sacroiliac joint is innervated by branches of the sacral spinal nerves.

Question 33

What is sacroiliitis?

What is the most common type of inflammatory arthropathy which affects the joint?

What does it cause?

State the typical symptoms.

Answer 33

Sacroiliitis refers to inflammation of the sacroiliac joint.

Ankylosing spondylitis (AS) is the most common type of inflammatory arthropathy which affects the joint.

It causes both spondylitis (inflammation of the vertebral joint) and sacroiliitis.

Classically, patients complain of early morning lower back pain and stiffness which improves with exercise and movement.

A plain X-ray typically demonstrates sacroiliitis (blurring of the joint margins, subchondral erosions, sclerosis, and changes in joint space). Furthermore, the vertebrae can demonstrate squaring of lumbar vertebrae, bamboo spine (late and uncommon) and syndesmophytes.

Question 34

In order to allow for urination and defecation, there are a few gaps in the pelvic floor. There are two ‘holes’ that have significance.

Outline them and their functions.

Answer 34

1. Urogenital hiatus – an anteriorly situated gap, which allows passage of the urethra (and the vagina in females).
2. Rectal hiatus – a centrally positioned gap, which allows passage of the anal canal.

Question 35

State the 3 functions of the pelvic floor.

Answer 35

1. Support of abdominopelvic viscera – through their tonic contraction.
2. Resistance to increases in intra-pelvic/abdominal pressure – during activities such as coughing or lifting heavy objects.
3. Urinary and fecal continence – the muscle fibers have a sphincter action on the rectum and urethra. They relax to allow urination and defecation.

Question 36

State the 3 separate paired muscles that make up the levator ani muscle of the pelvic floor.

Answer 36

The levator ani is a broad sheet of muscle.

It is composed of three separate paired muscles.
*Pubococcygeus
*Puborectalis
*Iliococcygeus

Question 37

Attachments: Originates from the posterior surface of the pubis. It forms a U-shaped sling around the anal canal and attaches to the pubis on the contralateral side.

Actions: Tonic contraction bends the anal canal anteriorly. This creates the anorectal angle which contributes to fecal continence. It is voluntarily inhibited during defecation.

Innervation: Nerve to levator ani and pudendal nerve.

Name the muscle described above.

Answer 37

Puborectalis

Question 38

It is located between the puborectalis and iliococcygeus within the pelvic floor.

Attachments: Originates from the posterior surface of the pubis. It blends with the contralateral muscle in the midline of the pelvic floor.

Actions: Stability and support of abdominal and pelvic organs.

Innervation: Nerve to levator ani and branches of the pudendal nerve.

Name the muscle described above.

Answer 38

Pubococcygeus

Question 39

It is a thin muscle which forms the posterolateral part of the levator ani muscle group.

Attachments: Originates from the ischial spines and the posterior tendinous arch of the internal obturator fascia. It inserts onto the coccyx, perineal body and anococcygeal ligament. It also blends with the fibers of the contralateral muscle in the midline of the pelvic floor.

Actions: Elevates the pelvic floor and anorectal canal.

Innervation: Nerve to levator ani and branches of the pudendal nerve.

Name the muscle described above.

Answer 39

The iliococcygeus

Question 40

It is a small triangular muscle located posterior to the levator ani muscle group.

Attachments: Originates from the ischial spines and inserts onto the inferior end of the sacrum and coccyx.

Actions: Supports the pelvic viscera and flexes the coccyx.

Innervation: Anterior rami of S4 and S5.

Blood supply: Inferior vesical, inferior gluteal and pudendal arteries.

Name the muscle described above.

Answer 40

Coccygeus

Question 41

State the 5 pelvic floor dysfunctions.

Answer 41

The weakening of these muscles can result in a loss of structural support to these organs – presenting as:

*Urinary incontinence
*Fecal incontinence
*Genitourinary prolapse
*Pelvic pain
*Sexual dysfunction

Question 42

Outline some CAUSES of the pelvic floor dysfunction.

Answer 42

The causes of pelvic floor dysfunction are understood to be multifactorial and include:

*Obstetric trauma
*Increasing age
*Obesity
*Chronic straining

Question 43

From where in the hip bone does the gluteus Medius originate?

A. Iliac fossa

B. Anterior aspect of the iliac crest

C. Greater sciatic notch

D. External surface of the ileal wing

Answer 43

D

Question 44

What is the acetabulum?

Answer 44

The acetabulum also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.

Question 45

When considering the pelvic inlet, which of the landmarks demarcates its anterior border?

A. Sacral promontory

B. Arcuate line

C. Pubic symphysis

D. Superior pubic ramus

Answer 45

C

Question 46

Which of the following forms the posterior border of the pelvic outlet?

A. Ischial tuberosities

B. The pubic arch

C. The inferior margin of a sacrotuberous ligament

D. The tip of the coccyx

Answer 46

D

Question 47

What is a typical feature of a gynaecoid pelvis?

A. Heart-shaped pelvic inlet

B. Prominent ischial spines

C. Wide and broad shape

D. Narrow sub-pubic arch

Answer 47

C

Question 48

In order to determine the narrowest fixed distance that the fetus would have to negotiate, the minimum antero-posterior diameter of the pelvic inlet is measured.

This distance is between the sacral promontory and the midpoint of the pubic symphysis (where the pubic bone is thickest) and is known as the______________.

However, this measurement cannot be assessed clinically, due to the presence of the bladder.

Answer 48

Obstetric conjugate (or true conjugate).

Question 49

What is the diagonal conjugate?

(To do this you use the tip of your middle finger to measure the sacral promontory and then using the other hand to mark the level of the inferior margin of the pubic symphysis on the examining hand. You then use the distance between the index finger and the pubic symphysis to measure the diagonal conjugate, ideally 11cm or greater)

In addition to measuring the diagonal conjugate, a mid-pelvis check is carried out. Here, the clinician is testing for straight side walls and measuring the bispinous diameter which is narrowest part of the pelvic canal. The width of the subpubic angle at the pelvic outlet can be determined by the distance between the ischial tuberosities.

Answer 49

The diagonal conjugate is the alternative, measuring from the inferior border of the pubic symphysis to the sacral promontory and can be measured manually via the vagina.

Question 50

What passes through the obturator foramen?

Answer 50

The obturator foramen is a large opening in the pelvis formed by the ischium and pubis bones. It is not a passageway for specific structures like nerves or blood vessels; rather, it serves as a space for the passage of several important structures and is covered by a membrane. What passes through or is adjacent to the obturator foramen includes:

1. The obturator nerve: This nerve, which arises from the lumbar plexus (specifically, L2-L4), exits the pelvis through the obturator foramen. It supplies motor innervation to the muscles of the medial thigh, including the adductor muscles.
2. The obturator artery and vein: These blood vessels are branches of the internal iliac artery and vein, respectively. They pass through the obturator foramen to supply blood to the structures in the medial thigh and pelvis.

The obturator membrane: This is a fibrous membrane that covers the obturator foramen, except for a small opening called the obturator canal. The obturator membrane provides additional structural support and separates the pelvic cavity from the thigh.

Question 51

What is pelvimetry?

Answer 51

It is the measurement of the diameter of the female pelvis especially the birth canal.

Measure the size of the pelvic inlet and outlet.

Question 52

What can be used to measure pelvimetry?

Answer 52

*Ultrasound
*Physical examination

Question 53

Why is the measurement of the pelvic cavity in pregnant women important?

Answer 53

Foetus must pass through the narrow opening of the pelvis at birth.

Question 54

State the following diameters of the pelvis.
* Transverse
* Oblique
* Anterior- posterior

Answer 54

• Transverse: 13cm
• Oblique: 12.5cm
• Anterior- posterior: 11cm

Question 55

What is the pelvic axis?

Answer 55

It is a curved imaginary line which measures the route taken by the baby’s head to pass through the pelvis.

It is measured from the central point of the pelvic inlet to the central point of the pelvic outlet.

Question 56

The perineum is diamond shaped.
State the 2 triangles that make up this diamond shape.

Answer 56

*Urogenital triangle
*Anal triangle

Question 57

What is the perineal body?

Answer 57

It is the region where the perineal muscles insert.

Question 58

What is episiotomy?

Answer 58

An episiotomy is a surgical incision made in the perineum, which is the area between the vaginal opening and the anus.

It is a medical procedure performed during childbirth to widen the vaginal opening, allowing for easier delivery of the baby and reducing the risk of spontaneous tearing of the perineal tissues.

Question 59

Describe the functions of the 6 ligaments of the uterus.

Answer 59

1. Broad ligament: The broad ligament is a double-layered fold of peritoneum (a membrane that lines the abdominal cavity) that encloses and supports the uterus.

It consists of three parts:

*The mesometrium (the largest and most significant part, which supports the uterus),

*The mesosalpinx (which supports the uterine tube or fallopian tube)

*The mesovarium (which supports the ovary).

Round ligaments: The round ligaments of the uterus are a pair of ligaments that extend from the uterine horns (where the fallopian tubes enter) to the labia majora of the external genitalia.

*These ligaments play a role in supporting and anchoring the uterus in the pelvis.

*They also help maintain the anteverted position of the uterus (tilted forward).

Uterosacral ligaments: These ligaments extend from the posterior side of the cervix to the sacrum (a bone at the base of the spine).

*Uterosacral ligaments provide stability and support to the uterus, helping to prevent excessive movement or displacement of the uterus.

Cardinal ligaments: Cardinal ligaments, also known as transverse cervical ligaments, extend from the cervix and the lateral portion of the upper vagina to the sidewalls of the pelvis. They provide additional support to the uterus and play a role in maintaining its position within the pelvis.

Pub cervical and rectouterine ligaments: These ligaments help anchor the cervix to the anterior and posterior walls of the pelvis, respectively, and provide stability to the uterus.

Question 60

State the innervation of the female genital organs.

Answer 60

*Pudendal nerve: Perineal nerves (superficial branches of the pudendal nerve).
*Parasympathetic fibers
*Sympathetic fibers

Question 61

What is nerve block?

Answer 61

A nerve block is a medical procedure in which a local anesthetic is injected near a specific nerve or group of nerves to temporarily block the transmission of pain signals from that area to the brain.

The goal of a nerve block is to provide pain relief for a specific region of the body by interrupting the communication between the nerves and the brain.

Question 62

Where is the pelvic pain line?

Answer 62

Inferior limit of the peritoneum.

Question 63

Describe the following:
*Spinal anesthesia
*Caudal epidural block
*Pudendal nerve block

Answer 63

Describe the following:
*Spinal anesthesia:
-It is injected in the subarachnoid space at the L3-L4 vertebral level.
-Complete anesthesia including the lower limb.

*Caudal epidural block
-Anaesthetizes the entire birth canal, pelvic floor and most perineum
-The anesthetic is injected into the epidural space, which is located just outside the dura mater (the membrane surrounding the spinal cord) in the lower back, near the sacrum.

*Pudendal nerve block
-Peripheral nerve block
-Mother can still feel uterine contractions
-Most of perineum

-Used for pain relief during labor and childbirth, particularly for procedures such as the episiotomy (a surgical incision made during childbirth) or to relieve the pain of a perineal tear.

Question 64

Describe the anatomical landmark for identification of the pudendal nerve for pudendal nerve block.

Answer 64

Anatomical Landmarks:

*The pudendal nerve is located within the Alcock’s canal or pudendal canal, which is situated in the ischiorectal fossa.

*To locate the site for the pudendal nerve block, the provider will identify key anatomical landmarks, including the ischial spine, ischial tuberosity, and the anus.