11.03 Bones and Joints of the Pelvis

Question 1

What bones form the pelvis?

What does pelvis roughly translate into?

Answer 1

The hip bone and the sacrum

Pelvis roughly translates into basin

Question 2

What are the two divisions of the pelvis?

What delinetaes them?

Answer 2

The upper part of the basin is called the false (greater pelvis) which holds some of the abdominal viscera.

The area below that is the true (lesser) pelvis which has walls anteriorly, laterally and posteriorly.

The Iliopectineal line (pelvic brim) is the line between them

Question 3

What makes up the walls that surround the lesser (false) pelvis

Answer 3

Anterolateral walls are formed by the hip bone and posterior wall by the sacrum.

Question 4

What are important structures arising from the walls of the lesser (false) pelvis?

Answer 4

Muscles arise from the sacrum and get out of the pelvis and muscles from the lateral wall of the pelvis which have an important role in relation to the pelvic floor.

Question 5

What is the ileopectal line?

Answer 5

(also called the pecten pubus)

A line/ridge from the ileum posteriorly to the pubis anteriorly. It demarcates false and true pelvis

The pectineal line forms part of the pelvic brim. Lying across it are fibers of the pectineal ligament and the proximal origin of the pectineus muscle.

Question 6

What is the general difference between the male and female pelvis?

Answer 6

Female pelvis is broad, wide and is shallower from above downwards (sacrum is broad and width equivalent to the length).

Male pelvis is narrower but is longer.

Question 7

The two hips joints home together at the midline in a typical midline joint arrangement. Describe this

Answer 7

Anteriorly the two pubic bones come together in a midline joint

(All midline joints in the body are symphiseal joints with a fibrocartilaginous discs).

Question 8

Describe the surfaces that make up the sacroileac joint

Answer 8

The second joint of the pelvis.

The ileum has an ear shaped surface covered by haline cartilage called the auricular surface.

The sacrum also has an auricular surface on it lined by hyaline

Question 9

Describe the sacrum

Answer 9

• It has a coccyx (variable structure)
• Anterior foramine which has nerves (ventral rami and sacral plexus) going through them.

Question 10

Structures other than the nerves pass through the ventral foraminae of the sacrum. What are these structures and what is the significance of this?

Answer 10

These foraminae are also roots for veins draining pelvic viscera (plexuses of veins).

Normally this drainage is back into the inferior vena cava; but if there is interference of flow then there is passage through anterior sacral veins into spinal canal itself (also common route of cancer spread)

Question 11

Describe the bones of the pelvis in terms of epiphyseal sites.

What is the importance of this?

Answer 11

There are many epiphyseal sites in the pelvis

Children: multiple sites of empiphysise: acetabulum, ishium, crest of the ileum

Question 12

What are the two parts of the main pelvic hole?

Answer 12

Pelvic inlet (doing down from above)

Pelvic outlet (coming out from above)

Question 13

What are the four main types of pelvic inlet shapes? What proportion of women have that particular shape?

Answer 13

1. Gynaecoid - 50%
2. Android - 30%
3. Anthropoid - 18%
4. Platepelloid - 2%

Question 14

Describe the gynaecoid pelvic inlet shape

Answer 14

The pelvic inlet is broad to accommodate the head of the baby as it passes through birth canal. The true pelvis the dimension of width is retained down the pelvis and the pelvic outlet is also broad (subpubic angle)

Question 15

Describe the android pelvic inlet shape \

Answer 15

Narrow inlet and narrow true pelvis and narrow outlet (not designed for transmission of the foetus).

The male pelvic inlet is heart shaped (is narrow).
The outlet is diamond shaped in both males and females but is more broader in females.

Question 16

Describe the anthropoid and platapelloid pelvis shapes

Answer 16

Anthropoid (narrow from side to side but enlongated in the AP direction).

The remainder are playpelloid which is wide from side to side and narrow in the AP direction.

Question 17

Describe the line of gravity through the pelvis

What is the net effect of this?

Answer 17

Lumbar lordosis provides flexibility in stance and locomotion.

The line of gravity passes through the vertebrae and passes anteriorly to the sacrum.

The net effect of gravity is to force the sacrum to tilt forwards and inferior in the inverse direction of the lumbar spine.

Question 18

Describe the alignment of the major anterior structures of the hip bone (ASIS and pubic tubercle) in normal stance

Answer 18

In normal orientation the ASIS is in line with the pubic tubercle (vertical alignment).

Question 19

Describe the horizontal alignment betwen the sacrum and the hip bone (pelvis)

Answer 19

The top of the pubic symphisis is in the same horizontal plane as the tip of the coccyx

Question 20

Compare the forward/inferior tilt in females with that in males

Answer 20

The tilt is eccentuated in females due to increased lumbar lordosis

Question 21

What does the pelvic outlet transmit?

Answer 21

Pelvic outlet is diamond shaped and it transmits tubular viscera to the exterior (as well as important muscles and ligaments)

Question 22

How is the pelvic outlet divided?

Answer 22

Divided into 2 triangles

1. Urogenital triangle (uretha and vagina in females and beginning of membranous urethra in males).
   
   1. Boundaries are boney structures
2. Anal triangle which contains the opening for the anal canal.
   
   1. Boundaries are mainly ligamentous: sacrotuberous ligament .

Question 23

Describe the anterior and posterior definitions of:

• Pelvic Inlet
• Pelvic Outlet

Answer 23

Pelvic Inlet:

• Top of pubic symphisis to the first sacral vertebrae.

Pelvic outlet:

• From the inferior pubic symphisis to tip of the cocyx

Question 24

Where and what is the narrow pelvic plane?

Answer 24

The narrow pelvic plane runs from inferior part of pubic symphis through the ischeal spine to S4.

It is the narrowest part of the pelvis that has to be negotiated by foetal head in childbirth.

Question 25

The narrow pelvic plane also corresponds to another plane of the pelvis.

Answer 25

**The pelvic pain line** (site from which pain is referred back to the CNS).

Question 26

What is the pelvic pain line?

Answer 26

* Any viscera located above the line (eg. body of bladder) refers pain to the lower thoracic/upper lumbar spinal cord with sympathetics. * Below the pain line, pain is through parasympathetic pain line S2,3,4 (to the skin)

Question 27

The pelvis forms an important interface to the surrounding structures. Elaborate on this

Answer 27

Pelvis provides interface between abdomen above, back behind and lower limb below.

Question 28

Draw and describe the apertures of the pelvis

Answer 28

1. Pelvic inlet – from abdomen 2. Anterior sacral foraminae – to back 3. Obturator canal – to lower limb 4. Greater sciatic foramen – to lower limb 5. Lesser sciatic foramen – to perineum & gluteal region

Question 29

Describe the forensic significance of the pelvis

Answer 29

pelvis is useful to identify sex of individual and age by looking at the shape of the body of the pubis. Male: body is narrow from front to back and the subpubic angulation is acute. Symphiseal surface may give a rough indication of age. Bottom picture has a smooth (eroded) surface from elderly individual. Younger have ridges and grooves.

Question 30

The bones of the pelvis forms 2 arches. What are these arches and what is their significance?

Answer 30

* Passes from acetabulum to top of sacrum and then to acetablum to other side (primary of the two arches) * The other arch is under the two pubic bones at the pubic symphisis. Line from inferior arch to greater arch shows **buttressing effect of bone** **for load bearing in sitting and standing** (superior ramus of the pubis transmitting considerable force)

Question 31

What is the major weight function of the pelvis?

Answer 31

Pubic bones transfer load & absorb force between trunk & limbs

Question 32

Where do the forces run down in the pelvis?

Answer 32

Forces depends on what we are doing: Standing: force is directed from junction where hip bone articulates to sacrum (from trunk along lines of boney trabeculae from pelvis to lower limb and reverse) Sitting: Bone is reinforced in the area of ischeal tuberosity and inferior ramus of the pubis. Together they transmit forces inferiorly and superiorly (in locomotion)

Question 33

What are the two joints of the pelvis?

Answer 33

1. Pubic symphysis 2. Ileosacral joint

Question 34

Describe the parts of the sacroileal joint

Answer 34

The anterior part of the joint tends to lie more lateral than the posterior (a little more medial). It is a **mixed joint:** * Part synovial (anterior)/ part fibrous (posterior) * There Fibrous part of the joint: bones held together by very powerful ligaments.

Question 35

What are the four ligaments critical for stabilising the sacroilieac joint?

Answer 35

1. Interosseoussacroiliac 2. Iliolumbar 3. Sacrotuberous 4. Sacrospinous

Question 36

Describe the sacral and ileal surfaces of the sacroileal joint

Answer 36

Has surfaces on the ileum and a mirror image of it on the sacrum. They are both called auricular surfaces.

Question 37

What lies within the space of the sacroileal joint?

Answer 37

**The interosseus sacroiliac ligament** (between bones). It is one of the most powerful ligaments of the body - **intrinsic ligaments**. It serves as a very powerful stabiliser of the sacroileac joint.

Question 38

Describe the sacrotuberous and sacrospinous ligaments

Answer 38

* Sacrotuberous ligament runs from the sacrum to the tuberosity of the ischium with fibres running vertical * Sacrospinous ligament with horizontal fibres that run from the ischial spine to lateral margins of the sacrum. They resist inferior part of sacrum from tilting backwards. Gluteal side (sacrospinous ligament) but pelvic side it is covered by muscle fibres that form part of the pelvic floor (coccygeous ligament).

Question 39

Describe the iliolumbar ligament in terms of location and function

Answer 39

Iliolumbar ligament from the tip of the transverse processes of the lumbar spine (L5 mainly and maybe L4) to the posterior part of the ileac crest. It helps hold the ileum in position.

Question 40

How does the sacrum tilt as a result of the line of gravity passing in front of it?

Answer 40

The sacrum wants to rotate with upper part tilting forward and lower part tilting backwards.

Question 41

Where is the axis of rotation for the sacrum tilt?

Answer 41

The second sacral vertebra

Question 42

The sacral tilt as a result of the line of gravity has a special type of movement. What is this movement called?

Answer 42

A "nodding" movement. This is called **nutation.**

Question 43

Describe the reverse keystone effect of the sacrum, the hipbones and their related ligaments

Answer 43

When standing, the sacrum sinks forwards & downwards into the pelvis between the ileac bones. The posterior ligaments tighten & draw iliac bones together. Stability is due to ligaments (particularly the interosseous sacroiliac ligaments) Bones tend to ‘open’ the joint up while the ligamentous fibres resulting in increased stability and tightness of the structures at the joint.

Question 44

Describe nutation and counternutation in terms of the range of movements and what happens to the hip bones in this movement

Answer 44

In nutation, the sacrum tilts forwards (about the axis of S2) and the hip bones tilt inwards (superior part tilts inwards). In counternutation, the sacrum tilts backwards and the hip bones tilt outwards. These movements primarily occur from the lying position to standing. The **range of movement is very small** (only about 2-8 degrees)

Question 45

Describe the clinical significance of the nutation/counternutation movement

Answer 45

These movements may increase during mid-late stages of pregnancy as the pelvis widens causing a laxity of the ligaments responsible for stability particularly of the last trimester under the influence of the hormone relaxin. Post-partum, the ligaments may tighten but not in the appropriate manner which may result in pain after.

Question 46

What is the nerve supply of the sacroileac joint and where does pain refer to?

Answer 46

Nerve supply is from the dorsal rami of L5-S3. Pain referred to medial & lower buttock

Question 47

There is an additional structure that helps to stablise the sacroileac joint. What is this structure?

Answer 47

A sling of muscle that criss-crosses the sacroileac joint. These massive muscles use the lumbar fascia as an interface causing a forced closure at the SIJ * Lower sling = gluteus maximus * Upper sling = Latissimus dorsi. The fibres of these large powerful muscles connect across the posterior aspect of the SIJ on the fascia. [Exercises that recruit these muscles can be sufficient to increase stability of the joint and overcome problems with laxity]

Question 48

Describe the pubic symphysis

Answer 48

A cartilaginous joint (hyaline cartilage on bones external to symphysis) Located anterior and inferiorly. And is a classical symphisis joint with a broad interarticular fibrocartilaginous disc

Question 49

Describe the stabilising ligaments of the pubic symphysis

Answer 49

The joint is reinforced by * *arching fibres above =* **Superior pubic ligament** and * *arcuate bundle below* = **inferior arcuate ligament** Together they maintain the proximity of bones holding them together resisting forces in all directions.

Question 50

Muscle fibres also add to the stability of the joint. Describe this

Answer 50

The **Adductor longus** muscle merges with the aponeurosis of i**nternal oblique and transversus abdominus** providing an **anterior sling** from trunk to opposite limb. [Clinically: Pain may not be associated with inflammation or degeneration at the joint itself and may be due to pull of attachments of these muscles]

Question 51

What makes the pelvis a common site for fractures?

Answer 51

Common site of avulsion fractures due to the multiple ephyseal sites (especially in children) The ring structure of bones means fracture at one site is associated with a fracture in a diagonal direction (the ring principle). (multiple fractures to the pelvic are often not compatible with life)