Arthritis 11 Flashcards
(15 cards)
Describe the growth of bones in a foetus.
Chondroblasts (cartilage-producing cells) build the initial template for bone formation in the wmbryonic stage. Hyaline cartilage is used as the “model” upon which osteoblasts build bone matrix in a process called ossification.
As the foetus grows the cartilage is digestes forming a bone-enclosed cavity called the medulla (medullary cavity)
At birth, only the epiphyseal plate and articular cartilage have not been converted to bone. New cartilage is formed continuously at both of these locations, making the bone longer.
Increase in bone width is APPOSITIONAL growth - to widen the bone osteoblasts in the periosteum add bone tissue to the outside of the bone shaft. At the same time osteoclasts remove bone from the medulla, maintaining thickness of the bone.
Once an osteoclast has grown bone aroud itself and becomes trapped in bone matric inside a lacuna, it differentiates into a mature osteocyte.
What are epiphyseal plates? How do they differ in adulthood?
- Epiphyseal plates are where interstitial growth happens
- In childhood the epiphyseal plates can be seen on an X ray and maintain their thickness
- In adulthood as interstitial growth slows the epiphyseal growth plates can no longer be seen and there is an epiphyseal line instead
Describe the zones of the epiphyseal plate.
- Zone of resting cartilage (top) - nearest to the epiphysis and is composed of small chondrocytes throughout the matrix; it resembles hyaline cartilage and it secures the epiphysis to the epiphyseal plate. These chondrocytes conttibute to…
- Zone of proliferating cartilage where there is interstitial gorwth - rapid mitotic division occurs and columns of chondrocytes form which are parallel to the diaphysis
- Zone of hypertrophic(enlargement) cartilage and the walls on the sides of the lacunae begin to get thinner
- Zone of calcified cartilage = 2-3 layers of chondrocytes and minerals become deposited between the columns of lacunae . As these minerals are laid down the chondrocytes are destroyed
- Zone of ossification - walls break down between the lacunae in the columns and osteoblast and osteoclast progenitors invade. Osteoblasts can then lead to more ossification.
Describe Hueter-Volkmann’s Law.
= increased compression at the growth plate slows down longitudinal growth, increasing tension at the growth plate speeds up longitudinal growth.
- i.e. stretching a child (as they have growth plates that are unfused), can increase longitudinal growth.
- This law can be applied when addressing/correcting malformations in children
What are the different alignments of the knee and who do they most occur in?
Varus deformity – more common in sports players. Varus knee is associated with higher osteoarthritis.
Valgus deformity– more common in models/slim-women.
Neutral alignment – more common in desk job people.
Why is growth in childhood not decreased due to compression?
Loads are constantly changing e.g. as a child when walking and also a lot of growth occurs when you sleep. The problem occurs when you are applying too much pressure e.g. from a particular sport.
What are the risks of Varus deformity?
2 times greater risk of osteoarthritis
What can be done surgically when someone has misalignment of the knee?
OSTEOTOMY
If younger than 40 then the bone can be cut across and hinnged open, and a growth plate added to straighten out the leg.
However, this is a procedure which requires 6 months rehabilitation after in a person that currently has nothing wrong with their joints.
What is Wolff’s law? Give examples.
“bone in general adapts to load”
Healthy human/animal bone will adapt/remodel to loads/stresses applied to it
- If loading on bone increases –> remodels over time –> stronger + resists loading
- If load decreases –> bone less dense, weaker b/c no stimulus for continued remodelling = E.g. going to space, footballers, tennis players, runway models
What is developmental dysplasia of the hip?
AKA congenital hip dislocation/dyslasia
In-utero malformation due to an unknown cause
Patient is much more likely to develop osteoarthritis in older age - acetabular labrum will be worn down on the superior aspect
Features:
- Acetabulum has a steeper slope
- Femur is at a higher insertion point
Causes:
- Genetic
- Kicking in utero
- Probably a combination of both
Describe what is meant by CAM and PINCER impingements of the hip and describe how they develop.
CAM impingement:
- The neck of the femur may grow in response to activity forming a bump on the femur neck.
- This growth may hit the acetabular labrum and will ultimately affect deep flexion of the hip.
PINCER impingement:
- The socket may be too deep and again sport activity (increased flexion of the hip) may lead to increased growth of the acetabular labrum causing a pincer impingement.
- Pincer grip deformity – another femur deformity.
Treatment:
- Hip arthroscopies can shave off the bumps or inappropriate appositional bone growth.
Which ligament can become damaged when the knee is displaced too far forward? What is the consequence?
Anterior cruciate ligamnet of the knee
You would then have unrestricted movement of the knee so meniscial injury risk goes up as the menisci resist the femur sliding backward
Footballers are unable to go back to playing in the same way
How do you treat a ruptured meniscus?
A partial meniscectomy if the menisci cannot be re-woven together
Why does a lack of meniscus lead to arthritis?
In the past the whole meniscus would have been removed but menisci can’t heal and so this led to arthritis within 6 months - this is because menisci act to distribute compressive forces and without it all the forces are targeted in one point on the tibia
So when you run and have 8 times more load on the knee hthe menisci prevent point loading and in turn damage to the cartilage in the long term.
What are the functions of the menisci, ACL and PCL?
ACL function – prevent anterior displacement of tibia to femur, hyperextension of the knee (same thing).
PCL function – prevent posterior displacement of tibia to femur.
Menisci function – resist compressive forces, prevent over rotation of the tibia to femur.
