arthritis 11 lecture (pathophysiology)

Question 1

describe effect of exercise when young on bone growth, and Heuter-Volkmann principle

Answer 1

growth plates at either end affected by amount of exercise (Heuter-Volkmann principle: if compressed, growth stops; if pulled, growth increases - used in practice e.g. 8-plate)

Question 2

weight bearing axis of varus (bow-legged) and valgus

Answer 2

varus: weight-bearing axis passes disproportionately medially, so weight on medial side of knee; valgus: weight-bearing axis passes disproportionately laterally, so weight on lateral side of knee

Question 3

ratio for weight-bearing axis

Answer 3

IC (inter-condylar): IM (inter-malleolar)

Question 4

effect of sport on weight-bearing axis

Answer 4

more exaggerated vagus due to compression of inside of knee (Heuter-Volkmann principle)

Question 5

effect of pelvis width on weight-bearing axis

Answer 5

as women typically have larger pelvises, affects gait and causes some valgus

Question 6

effect of weight-bearing axis on intitial presentation of arthritis

Answer 6

typically on one half initially due to disproportionate weight distribution (arthritis - erosion of cartilage - on medial knee in varus, lateral knee in valgus) - as affected by childhood exercise, vary sport when young

Question 7

what is diagnosis of arthritis based on in practice

Answer 7

imaging and clinical symptoms

Question 8

osteotomy as a way of potentially delaying, or even preventing, arthritis

Answer 8

cut bone to hinge it and change shape of leg, re-alligning weight-bearing axis

Question 9

describe Wolff’s law

Answer 9

bone responds to stresses put on it (more load e.g. exercise, it will lay down more bone and be made stronger; less load, trabeculae thin out)

Question 10

who is affected by developmental dysplasia of hip

Answer 10

affects foetus in utero, as if hip has slipped out of femur, acetabulum capsule doesn’t strengthen (Wolff’s law)

Question 11

risk factors for developmental dysplasia of hip

Answer 11

female (oestrogen means ligaments become more lax, so hip can slip out), if foetus is breached (hip pushed into abnormal position)

Question 12

treatment for developmental dysplasia of hip

Answer 12

put in harness so that hip joint is in acetabular socket (flex and abduct), so bone responds to form capsule (Wolff’s law)

Question 13

why does risk of arthritis increase in developmental dysplasia of hip

Answer 13

head of femur rubs against hip acetabulum, wearing out more quickly

Question 14

describe CAM impingement of hips

Answer 14

instead of slender neck, due to exercise femoral neck stresses are large, so more bone laid down (Wolff’s law), forming bump on outside

Question 15

describe PINCER impingement of hips

Answer 15

very deep socket even though femoral head and neck normal

Question 16

3 groups predisposed to arthritis

Answer 16

elderly (cartilage erodes), injured (torn structures e.g. labrum), shape of hip (CAM or PINCER driven by activity when young)

Question 17

how can CAM lead to arthritis

Answer 17

bump on femoral neck rubs against and erodes labrum during deep flexion, tearing labrum and causing cartilage to not be flat, and thus wear out

Question 18

how can PINCER lead to arthritis

Answer 18

socket is too deep, so linear impact between neck and acetabulum, hitting and eroding both sides of cartilage

Question 19

treatment for CAM impingement

Answer 19

use burr to shave away bump on femoral neck (doesn;t treat arthritis as cartilage already worn out)

Question 20

why is joint replacement not appropriate in young person

Answer 20

effects only lasts 20 years (metal cap means bone beneath is protected, so begins to dissolve - Wolff’s law)

Question 21

best treatment for arthritis

Answer 21

exercise, as if muscles become weaker, more stress on joints, increasing pain

Question 22

describe alternative exercise as possible prevention for arthritis caused by specific exercise

Answer 22

alternative exercise which causes offset changes, so both balance out (e.g. weight lifting as cartilage responds to load)

Question 23

define synovial joint

Answer 23

2 bones articulating with each other and covered with cartilage, bathed in synovial fluid (released from synovial membrane), reinforced by fibrous capsule (e.g. meniscus, acting as shock absorbers and increasing stability by deepening socket)

Question 24

structure of cartilage (superficial to deep: arcade model of Benninghoff)

Answer 24

superficial layer (collagen fibres horizontal as main stress in shear sliding stress) -> middle transitional zone (collagen fibres oblique to resist shear and compression) -> deep radial zone (vertical to resist compression) -> TIDEMARK -> calcified cartilage (prevents blood passing from bone into joint, preventing infection of cartilage)

Question 25

downside of no blood supply to cartilage

Answer 25

no repair

Question 26

issue with rupturing cruciate ligament

Answer 26

prevent knee sliding from front to back (unstable), so cartilage not lined up and abnormally loaded (weight-bearing axis altered, predisposing to arthritis)

Question 27

3 functions of ACL

Answer 27

stability (when changing direction), protect cartilage (correct weight-bearing axis), prevent meniscal tears (if torn, massively loads cartilage and causes it to wear out)

Question 28

treatments of ACL

Answer 28

coper (increase muscular stability in knee, but can’t do sport), operation (ACL reconstruction)

Question 29

aim and advantage of partial knee replacement

Answer 29

keeps everything else the same, but widenssjoint space between two bones which have come together (compressed)