Week 5: Lecture 1 - Osteology and Ligaments of Coccygeal Region

Question 1

What Forms the Sacrum and what’s its general shape?

Answer 1

The sacrum is formed by the fusion of 5 sacral vertebrae, creating a triangular or wedged shaped structure

Question 2

What are the key structural features of the sacrum?

Answer 2

Base at an oblique angle forms lumbosacral angle (30° ±10°).

Lumbosacral articular facets face posteriorly; articulate with L5.

Apex (S5) articulates with coccyx.

Alar (wings) articulate with ilium

Sacral tuberosities articulate with iliac tuberosity

Question 3

What features are found on the anterior surface of the sacrum?

Answer 3

Transverse ridges: (4)
Middle portion has 4 transverse ridges - corresponds to 5 sacral bodies

Anterior Sacral Foramina: (4 pairs)
Anterior sacral foramina 4 on each side
First 4 sacral nerves exit here, arteries
enter here

Question 4

What are the key characteristics of the posterior sacral surface?

Answer 4

Convex
Narrower
highly irregular

Sacral canal
- runs down the center of the sacrum and represents the end of the vertebral canal.

Posterior sacral foramina (4 pairs)
- sacral nerve fibres exit from the sacral canal to these foramina

Sacral Crest (median, intermediate, lateral)

Sacral Hiatus (due to absent lamina/SP of S5. Used for anesthesia)

Sacral Cornua

Question 5

Sacral Crest?

Answer 5

Median sacral crest

Intermediate sacral crest

Lateral sacral crest

Question 6

What forms the median sacral crest and where is it located

Answer 6

Formed by the fusion of spinous processes of S1 to S3.

Located at the midline of the posterior sacrum

Appears as a prominent vertical ridge.

Question 7

How is the intermediate sacral crest formed and where is it found?

Answer 7

Formed by the fusion of articular processes of L5 to S4.

Located medial to the sacral foramina, on either side of the median crest.

Question 8

What forms the lateral sacral crest and what is its position?

Answer 8

Formed by the fusion of transverse processes of sacral vertebrae.

Found lateral to the posterior sacral foramina.

Question 9

What is the sacral hiatus and how is it formed?

Answer 9

The sacral hiatus is an opening at the caudal end of the sacral canal, created because the spinous process and lamina of the S5 vertebra fail to form, leaving a natural defect or hole in the posterior sacrum.

Question 10

What is the Sacral Cornua

Answer 10

remnants of the inferior articular process, lie on each side of the sacral hiatus

Question 11

The terminal point of the vertebral column is known as??

Answer 11

Tailbone

Question 12

What are the structural and functional features of the coccyx?

Answer 12

Terminal part of vertebral column.

Usually consists of 4 fused coccygeal vertebrae.

Forms part of the true pelvis wall.

Articulates with sacrum via sacrococcygeal symphysis.

Movement: minor flexion/extension during defecation/labor.

Question 13

Bony Landmarks of the coccyx

Answer 13

• Base (oval)
• Apex (rounded)
• Anterior surface
• Posterior surface
• Lateral surface

Question 14

What are the features of the posterior surface of the coccyx?

Answer 14

The posterior surface is convex.

It shows 4 rows of tubercles, which are rudimentary spinous processes from the fused coccygeal vertebrae.

Question 15

What are the coccygeal cornua and what do they articulate with?

Answer 15

The cornua of the first coccygeal vertebra (Co1) project upward.

They articulate with the sacral cornua, helping form the posterolateral boundary of the sacral hiatus.

Question 16

Describe the anterior surface of the coccyx.

Answer 16

Also known as the pelvic surface.

It is concave in shape and faces forward into the pelvis.

Question 17

What are the features of the lateral sides of the coccyx?

Answer 17

The lateral edges are thin and represent the remnants of transverse processes (TVPs) of the coccygeal vertebrae.

These are more distinct in Co1 and may be absent in the more distal segments.

Question 18

Describe the Sacroiliac Joint (SI)

Answer 18

Between auricular surfaces of ilium and sacrum.

Synovial Joint

Synovial (anterior) and syndesmosis (posterior) components.

Iliac surface: fibrocartilage;

sacral surface: hyaline cartilage.

Question 19

What is the function of the Sacroiliac Joint (SI)

Answer 19

Distributes weight from upper body to legs.

Acts as a shock absorber.

Supports posture changes, movement.

In women: aids childbirth by increasing mobility.

Question 20

What movements occur at the SI joint?

Answer 20

Primarily movements are Anterior-posterior, also up and down

limited to 2mm-4mm/2-5degrees

Rotation around transverse axis
Nutation = anterior sacral tilt
Counter-Nutation = posterior sacral tilt

Question 21

Name the 3 main sacroiliac ligaments

Answer 21

• Anterior Sacro Iliac ligament
• Posterior Sacro iliac ligament
• Interosseus ligament

Question 22

What are the accessory SI ligaments and their roles?

Answer 22

• Sacrospinous ligament
• Sacrotuberous ligament

Question 23

What is the Anterior Sacroiliac Ligament ?

Answer 23

Blends with fibers of the capsule

Rich innervation of nociceptive fibers, it may be a significant source of pain

Fibers of this capsule blend with the joint’s capsule

Question 24

What is The Posterior Sacroiliac
Ligament:?

Answer 24

Overlies the interosseous sacroiliac ligament

Contribute most to SIJ mobility

This ligament undergoes tension during the transmission of forces from the legs to the upper body and vice versa

Question 25

What is The Interosseous Ligament:

Answer 25

Strongest ligament in the body Consists of short, strong bands, the fibers detach from the bone Blends with fibers of the capsule FUNCTION: Prevents forward and downward movement of the sacrum. Prevents excessive backward movement.

Question 26

What is the Sacrospinous accessory ligament?

Answer 26

From ischial spine to the sacrum Prevents excess posterior movement of the sacral apex Transforms the lesser sciatic notch into a foramen

Question 27

What is the Sacrotuberous accessory ligament?

Answer 27

Extends from the posterior ilium and lateral sacrum and coccyx to the ischial tuberosity Transforms the greater sciatic notch of the hip bone into a foramen Prevents posterior movement of the sacral apex Limits anterior movement of the sacral base

Question 28

What type of joint is the sacrococcygeal joint?

Answer 28

A symphysis, the two bones lined by Hayline cartilage and connected by fibrous disc Slight Flexion-extension during labor and defecation.

Question 29

List the ligaments of the sacrococcygeal joint.

Answer 29

*Anterior Sacrococcygeal Ligament *The lateral sacrococcygeal ligament *The superficial posterior sacrococcygeal ligament *The deep posterior sacrococcygeal ligament *The intercornual ligament

Question 30

What is the Anterior sacrococcygeal ligament

Answer 30

Extends from the anterior surface of the sacrum to the anterior surface of the apex of coccyx

Question 31

What is the lateral sacrococcygeal ligament

Answer 31

Attaches to the inferolateral angle of the sacrum and the transverse processes of the coccyx.

Question 32

What is the superficial posterior sacrococcygeal ligament

Answer 32

Arises from the margin of the sacral hiatus and attaches to the dorsal surface of the coccyx.

Question 33

What is the deep posterior sacrococcygeal ligament

Answer 33

Spans from the dorsal surface of the S5 to the dorsal surface of coccyx.

Question 34

What is the intercornual ligament

Answer 34

A band that connects the cornua of the sacrum and coccyx

Question 35

What are possible sources of pain in the SIJ region?

Answer 35

Non-SIJ related spinal pain (thoracic/lumbar). Hip diseases. Referred pain from pelvic organs. Muscular/myofascial pain: Pain due to neurological conditions Osteoporosis Inflammatory diseases, notably rheumatic diseases such as the spondyloarthropathies