joint biomechanics

Question 1

3 curves of spine

Answer 1

• primary: anterior concavity in anterior portion
• secondary: anterior convexity in cervical, lumbar portions

Question 2

thoracic spine: motions

Answer 2

lateral bending, axial rotation

Question 3

lumbar spine: motions

Answer 3

flexion, extension, some axial rotation

Question 4

instantaneous axis of rotation

Answer 4

position of axis at single point along ROM
- in spine, its usually within IV disc
- abnormal changes create abnormal forces at vertebrae, discs

Question 5

creep

Answer 5

IV discs lose ability to return to original shape over time
- less affective in shock absorption; facets take on more stress

Question 6

coupling

Answer 6

consistent association of one motion about an axis w/ another motion about a different axis

*example: lateral flexion and transverse plane motion are always coupled

Question 7

motion segment

Answer 7

2 vertebrae and the soft tissue between them

Question 8

flexion and extension is highest at?

Answer 8

L5-S1

Question 9

sacroiliac joint in childhood

Answer 9

• synovial
• mobile, pliable joint capsule

Question 10

sacroiliac joint in young adulthood

Answer 10

• changes from diarthroidal to amphiarthroidal
• surface goes from smooth to rough

Question 11

sacroiliac joint in adulthood

Answer 11

multiple reciprocally contoured elevations, depressions

Question 12

1° ligaments of sacroiliac joint

Answer 12

• interosseous ligament
• short and long posterior sacroiliac ligaments
• anterior sacroiliac ligament

Question 13

2° ligaments of sacroiliac joint

Answer 13

sacrospinous and sacrotuberous ligaments

Question 14

sacroiliac joint motions

Answer 14

1° sagittal plane motion is small
- rotation: 0.2 - 2°
- translation: 1-2 mm

Question 15

nutation

Answer 15

anterior sacral tilt w/ posterior iliac tilt

Question 16

counter nutation

Answer 16

posterior sacral tilt w/ anterior iliac tilt

Question 17

sacral angle

Answer 17

angle of spuerior surface of sacrum to transverse plane

Question 18

hip: motions in each plane

Answer 18

hip is triaxial w/ 3° of freedom
- sagittal: flexion/extension
- frontal: abduction/adduction
- transverse: internal/external rotation

Question 19

circumduction

Answer 19

• circular motion/simultaneous motion in all 3 planes
• in gait, can indicate stroke

Question 20

hip joint 1° function

Answer 20

support weight of head, arms, trunk in static and dynamic weight bearing

Question 21

each hip bears how much body weight in static stance?

Answer 21

1/3 of body weight

Question 22

each hip bears how much body weight w/ muscle contraction?

Answer 22

• 3x body weight standing on 1 leg
• 6x body weight in stance phase of gait

Question 23

hip anatomy: infant

Answer 23

• high angle of anteversion
• acetabulum is anterior-facing while hip is 60° externally rotated (most of femoral head is uncovered when hip is extended)

Question 24

congenital hip dislocation

Answer 24

• common when swaddling in infants in hip-extended position
• most of femoral head is uncovered

Question 25

articulating surfaces within acetabulum

Answer 25

- only lunate surface has hyaline cartilage that contacts femur - space between femoral head and acetabular fossa helps provide shocks absorption

Question 26

closed packed/neutral position of hip

Answer 26

- hip extension

Question 27

hip neutral position is different from other joints because

Answer 27

- most joints: closed-packed is also point of maximum congruity - where capsule, ligaments are taut - in hip, it's not the same

Question 28

hip point of maximum congruity

Answer 28

90° flexed, abducted, externally rotated - capsular ligaments are uncoiled

Question 29

hip least stable position

Answer 29

hip flexed and adducted - decreased congruity, joint is loose-packed

Question 30

iliofemoral ligament in different positions

Answer 30

- extension: taut, resists hyperextension - adduction: superior fibers tensed - abduction: inferior fibers tensed

Question 31

pubofemoral ligament in different positions

Answer 31

- extension, abduction: taut limits extension, abduction, and external rotation

Question 32

ischiofemoral ligament in different positions

Answer 32

- extension: taut limits extension and internal rotation - flexion: loose

Question 33

trabeculae of pelvis and femur represent

Answer 33

weight-bearing forces passing through both - most lines pass through acetabulum

Question 34

hip joint: area of increased subchondral bone density

Answer 34

- superior acetabulum - corresponds to area of greatest weight-bearing within acetabulum

Question 35

hip joint: zone of weakness

Answer 35

- femoral neck, due to less trabecular reinforcement - most likely area of fracture

Question 36

pelvic tilt: CKC

Answer 36

- tilts anteriorly for hip flexion, posteriorly for hip extension - tilts laterally for abduction and adduction - lumbar spine compensates

Question 37

pelvic tilt: OKC

Answer 37

- lumbar-pelvic rhythm (hip, pelvis, lumbar spine work together to provide increased ROM) - falsely increases hip ROM when doing measurements

Question 38

standard values of hip ROM: frontal plane

Answer 38

45° of abduction and adduction - 5° is required for normal gait - 20° abduction is required for normal activities

Question 39

standard values of hip ROM: sagittal plane

Answer 39

- flexion w/ knee extended: 70-90° (limited by hamstrings) - flexion w/ knee flexed: >120° (limited by bony architecture or abdominal girth)