arthritis 11 lecture (pathophysiology) Flashcards
describe effect of exercise when young on bone growth, and Heuter-Volkmann principle
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)
weight bearing axis of varus (bow-legged) and valgus
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
ratio for weight-bearing axis
IC (inter-condylar): IM (inter-malleolar)
effect of sport on weight-bearing axis
more exaggerated vagus due to compression of inside of knee (Heuter-Volkmann principle)
effect of pelvis width on weight-bearing axis
as women typically have larger pelvises, affects gait and causes some valgus
effect of weight-bearing axis on intitial presentation of arthritis
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
what is diagnosis of arthritis based on in practice
imaging and clinical symptoms
osteotomy as a way of potentially delaying, or even preventing, arthritis
cut bone to hinge it and change shape of leg, re-alligning weight-bearing axis
describe Wolff’s law
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)
who is affected by developmental dysplasia of hip
affects foetus in utero, as if hip has slipped out of femur, acetabulum capsule doesn’t strengthen (Wolff’s law)
risk factors for developmental dysplasia of hip
female (oestrogen means ligaments become more lax, so hip can slip out), if foetus is breached (hip pushed into abnormal position)
treatment for developmental dysplasia of hip
put in harness so that hip joint is in acetabular socket (flex and abduct), so bone responds to form capsule (Wolff’s law)
why does risk of arthritis increase in developmental dysplasia of hip
head of femur rubs against hip acetabulum, wearing out more quickly
describe CAM impingement of hips
instead of slender neck, due to exercise femoral neck stresses are large, so more bone laid down (Wolff’s law), forming bump on outside
describe PINCER impingement of hips
very deep socket even though femoral head and neck normal
3 groups predisposed to arthritis
elderly (cartilage erodes), injured (torn structures e.g. labrum), shape of hip (CAM or PINCER driven by activity when young)
how can CAM lead to arthritis
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
how can PINCER lead to arthritis
socket is too deep, so linear impact between neck and acetabulum, hitting and eroding both sides of cartilage
treatment for CAM impingement
use burr to shave away bump on femoral neck (doesn;t treat arthritis as cartilage already worn out)
why is joint replacement not appropriate in young person
effects only lasts 20 years (metal cap means bone beneath is protected, so begins to dissolve - Wolff’s law)
best treatment for arthritis
exercise, as if muscles become weaker, more stress on joints, increasing pain
describe alternative exercise as possible prevention for arthritis caused by specific exercise
alternative exercise which causes offset changes, so both balance out (e.g. weight lifting as cartilage responds to load)
define synovial joint
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)
structure of cartilage (superficial to deep: arcade model of Benninghoff)
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)
