Sacrum, Coccyx (Exam 3)

What are the 5 surfaces of the sacrum?

- Base

- Apex

- Auricular (lateral)

- Anterior (pelvic)

- Posterior (dorsal)

What forms the base of the of the sacrum?

Body of S1

What are 4 features of the base of the sacrum?

- Sacral promontory

- Sacral ala

- Sacral canal

- Superior articular process

What forms the posterior portion of the pelvic girdle?

Sacrum

What are the 3 joints of the lumbosacral joint?

- 1 intervertebral

- 2 z-joints

What is the sacral canal?

Continuation of vertebral canal

What are the 4 contents of the sacral canal?

- Lower Cauda equina (spinal nerve roots of L2-C1)

- Filum terminale

- Spinal meninges/dural sac

- Extrabural fat

What are the 3 layers of the dural sac?

- Dura mater

- Arachnoid mater

- Pia mater (contacts nervous tissue)

What runs below the arachnoid mater?

Subarachnoid space: cerebrospinal fluid

What is the range of the dural sac?

Cranium to S2

What is the range/function of the internum Filum terminalis?

Conus medullaris to S2 in dural sac

Tethers spinal cord to coccyx

What is the range/function of the externum Filum terminalis?

S2 - coccyx out of dural sac

Tethers spinal cord to coccyx

What is the conus medullaris?

Tapered end of spinal cord (L1-L2)

What is the difference between the anterior and posterior sacral surface?

A: concave, smooth

P: convex, rough

What are the transverse ridges of the sacrum?

Fused IVDs

What are the anterior sacral foramina?

Opening in sacrum analogous to the IVF

What runs through the anterior sacral foramina?

Anterior rami of S1-S4

What can anterior rami of spinal nerves form?

Somatic plexuses

What is the median sacral crest?

Fusion of S1-S4 spinous processes

What is the articular/intermediate/medial sacral crest?

Fusion of articular processes

What is the lateral sacral crest?

Fusion of transverse processes

What is a plexus?

Intermingling of nerves and blood vessels

What is the inferior lateral angle?

Lower portion of sacrum that curve medially

What are the sacral grooves?

Grooves between sacral crests

What is the sacral hiatus?

- Inferior opening

- Absence of S5 lamina

- Natural "defect"

What are the contents of the sacral hiatus?

- Coccygeal nerve

- 5th sacral spinal nerve

- Filum terminale externum

- Fat

What are the 2 parts of the lateral sacrum?

- Auricular surface

- Sacral tuberosity

What is the articular surface of the sacrum?

- Forms the sacroiliac joint

- Lined with hyaline cartilage

What is the sacral tuberosity?

Rough posterior surface for muscle attachment

What portion of the sacral fuse first?

S2-S5

What are the 6 joints of the sacrum?

- 2 Sacroiliac

- 3 Lumbosacral joints

- 1 Sacrococcygeal joint (symphysis)

What type of cartilage is the SI joint?

- Sacrum: hyaline cartilage

- Iliac: fibrocartilage

What innervates the SI joint?

S1-S2 dorsal rami

What percent of back pain is caused by the SI joint?

50%

Who has a more flexible SI joint and why?

Females for birth

What does degeneration of the SI joint cause?

Bone growth / fusion

What is the pelvic girdle?

Ring formed by:

- Hip bones

- Sacrum

- Coccyx

What are the 3 function of the pelvic girdle?

- Transfers weight

- Attaches axial skeleton to lower limbs

- Attachment for muscles/ligaments

What are the 2 main functions of the SI joint?

- Eases locomotion

- Shock absorption

What are the main SI ligaments?

- Anterior SI

- Posterior SI

What are the 3 accessory SI ligaments?

- Sacrotuberous

- Sacrospinous

- Iliolumbar

What is the anterior SI ligament? What is its range?

- Thickening of anterior-inferior joint capsule

- Ala of ilium => anterior-lateral sacrum

What is the function of the posterior SI ligament?

Reinforces superior and posterior joint

What are the 3 bands of the posterior SI ligament from anterior to posterior?

- Interosseous

- Short posterior

- Long posterior

What is the interosseous SI ligament? What is its range?

- Deepest, strongest main SI ligament

- Iliac tuberosity => Sacral tuberosity

What is the short posterior SI ligament? What is its range?

- Fills gap between ilium and sacrum

- 1st and 2nd transverse tubercles of sacrum => iliac tuberosity

What is the long posterior SI ligament? What is its range?

- Most superficial

- Limits counternutation

- PSIS => 3rd and 4rd transverse tubercles of sacrum

What 2 ligaments prevent nutation?

- Sacrotuberous

- Sacrospinous

What is the sacrotuberous SI ligament? What is its range?

- Superficial to posterior SI ligaments

- PSIS =>

- Posterior sacrum => Ischial tuberosity

- Posterior coccyx =>

What is the Sacrospinous SI ligament? What is its range?

- Anterior to sacrotuberous

- Lower anterior sacrum/coccyx => ischial spine

What do the accessory ligaments form?

Greater/lesser sciatic foramen

What is nutation?

- Forward movement of sacral base

- Ilium comes together in back

- Lumbar lordosis increases

What muscle increases nutation?

Erector spinaes

What is counternutation?

- Posterior movement of sacral base

- Decrease lordosis

What muscles increase counter nutation?

Abdominal muscles

What is the difference in the sacrum between males and females?

Males:

- narrower/longer

- vertical

- less curve

- decreased lumbosacral angle

- <90 degree pubic angle

Female: opposite

What is the Q-angle?

Angle between the axis of the femur and the line between the patella and tibial tuberosity

What are the areas of the coccyx?

- Cornua

- Base

- Apex

How many fused segments make up the coccyx?

4