Biomechanics of the Pelvis and Sacrum

Question 1

3-joint complex, with much the same function as the typical vertebral functional unit.

Answer 1

Pelvic joints: 2 SI joints + Pubic symphysis

Question 2

What is the least understood and most controversial function of any area in the musculoskeletal system?

Answer 2

Pelvic joints: 2 SI joints + Pubic symphysis

Question 3

Provide support for the trunk, guide movement, and help to absorb the compressive forces associated with locomotion and weight-bearing.

Answer 3

SI joint

Question 4

What is unique about the shape and configuration of the SI joints?

Answer 4

surface contours develop into interlocking elevations and depressions producing a KEYSTONE EFFECT of the sacrum, effectively distributing axial compressive forces through the pelvic mechanism.

Question 5

How are forces of the lower extremity distributed to the pelvic joints?

Answer 5

head upward toward the spine and anteriorly toward the pubic symphysis, and downward forces of gravity on the spine split to both sides

Question 6

The sacrum is __________ in shape and serves as a keystone in the arch b/w the two columns formed by the LE.

Answer 6

triangular

Question 7

Describe the SI joints at birth.

Answer 7

underdeveloped, smooth, and flat

Question 8

Describe the SI joints after ambulation.

Answer 8

begin to take on their adult characteristics

Question 9

Describe the SI joints in teen years.

Answer 9

joint surfaces begin to roughen and develop their characteristic grooves and ridges

Question 10

Describe the SI joints in later years.

Answer 10

high % of (male) patients will have interarticular adhesions across the SI joints and will have lost SI joint motion

Question 11

What are the 2 most common pelvic types?

Answer 11

Gynecoid and Android

Question 12

Describe the : 
Inlet-
Sacrosiciatic Notch -
Sacrum-
Subpbic Arch -

of a Gynecoid pelvis

Answer 12

inlet: round
Scrosciati N: Average size
Sacrum: Avg
Subpubic Arch: inclination well curved

Question 13

Describe the : 
Inlet-
Sacrosiciatic Notch -
Sacrum-
Subpbic Arch -

of an Android pelvis

Answer 13

inlet: triangular
Scrosciati N: Narrow
Sacrum: Forward
Subpubic Arch: inclination straight

Question 14

What are the ligaments of stability in the pelvis?

Answer 14

1. Posterior Sacroiliac lig
2. Sacrotuberous big
3. Anterior sacroiliac lig
4. Sacrospinous lig

Question 15

The SI joint os most active during what?

Answer 15

locomotion

Question 16

Describe the SI joint motion during locomotion.

Answer 16

The SI joints flex/extend in unison with the corresponding hip joint. Movements of flex/exten in one point are mirrored by the opposite movement at the other joint

Question 17

As the left innominate moves PI (post, infer), how does the left sacral base move?

Answer 17

AI (ant, infer) (nutation)

Question 18

As the right innominate moves AS (ant, sup), who does the right sacral base move?

Answer 18

PS (post, sup) (counternutation)

Question 19

The proposed axes of motion in the SI articulation allow a “_________” movement.

Answer 19

gyroscopic

Question 20

What muscles cross the SI joint?

Answer 20

None, silly! It provides stability, not mobility.

Question 21

What are the possible Pelvic sublations?

Answer 21

Ant
Superior 
Post 
Inferior 
External 
Internal

Question 22

What are the possible Sacral subluxations?

Answer 22

Apex (SAL, SAR)
Base Posterior (BP
(Apex posterior?)
Left/Right Posteriority (P-L, P-R)

Question 23

Sacral øz rotation: Apex Left

Answer 23

(+)øz

Question 24

Sacral øz rotation: Apex Right

Answer 24

(-)øz

Question 25

Sacral øx Rotation

Answer 25

AKA: Flexion malposition (nutation)
AKA: Extension malposition (counternutation)
* can also have neutral