AFC Arthritis Flashcards
Where do bones grow from?
Growth plate (epiphyseal plate)
State Hueter-Volkmann’s Law
Increased compression at the growth plate slows longitudinal growth
Increased tension at the growth plate speeds up longitudinal growth
Give an example of where Hueter-Volkmann’s Law can be used to correct an abnormality.
8 Growth Plate – if abnormal growth on 1 side of the distal tibial physis, insert a metal plate with pins on either side of the growth plate to prevent further growth on normal side + allow the other side to catch up
What are the three different types of knee alignment?
Normal/Neutral
Varus – bowed legs, weight bearing on medial knee
Valgus – knocked knees, weight bearing on lateral knee
What types of athletes get varus alignment?
Which part of the knee joint would be loaded most? What are the consequences of this?
Footballers
Medial surface
Wears out the cartilage + causes osteoarthritis
What surgical intervention can be performed before the onset of osteoarthritis to realign the knee joint?
Osteotomy: cutting the tibia to realign the knee joint
State Wolff’s Law.
Who does this effect?
Give an example that illustrates Wolff’s law.
Bone in a healthy person will adapt to the loads under which it is placed
Effects kids + adults
Surfer’s knots
What are the two surfaces of the cortical bone?
Periosteal surface (outer) Endosteal surface. (lining)
Load on the bones causes an increase in cortical thickness – how is this response to loading different in children compared to adults?
Children: have an active periosteum + endosteum so get increased bone growth at BOTH surfaces
Adults: periosteum is less active – so response to increased loading is mainly at endosteal surface
A lot of problems to do with body shape occur in utero. Give an example of such a problem that is associated with osteoarthritis and 3 associated risk factors
Developmental Dysplasia of the Hip (DDH)
Breech presentation
Female sex
Infant positioning in 1st year of life
Describe the appearance of the hip joint in someone who had DDH.
Hip joint may be higher than normal
Acetabulum is shallow + doesn’t cover much of the femoral head
Leads to increased load + wear
Why is it important to spot the deformities of DDH early?
If caught early, can realign + cause a remodelling of the joint to allow normal stance
Name and describe two abnormalities of the hip joint.
Cam – bump on the femoral neck
Pincer – extra bone makes acetabulum much deeper than normal
What are the negative consequences of Cam abnormality?
Deep flexion causes repeated impact between the bump on the femoral neck + acetabular rim leading to the wearing away of cartilage + osteoarthritis
What are the negative consequences of Pincer abnormality?
Femoral neck impinges + crushes the labrum causing labral tears + levers the femoral head into the postero-inferior acetabulum leading to a contrecoup cartilaginous injury
Name the two cruciate ligaments of the knee joints and state their roles with regards to sliding at the knee joint.
Anterior: stops tibia sliding forwards
Posterior: stops tibia sliding backwards
What is a synovial joint?
A joint covered with hyaline cartilage or fibrocartilage that is surrounded by a fibrous capsule with a synovial membrane on the inside producing synovial fluid to lubricate the joint
What is the structural difference between the medial and lateral menisci?
The lateral meniscus has a much tighter C shape
What are the two main functions of cartilage?
Shock absorption
Low friction
Which type of collagen is found in cartilage?
Type 2
Describe the arrangement of collagen in the superficial layer and explain why they are arranged like this.
Horizontal
Resists shear forces
Describe the arrangement of collagen in the deep layer and explain why they are arranged like this.
Vertical
Resists compressive forces
What provides the nutrition to the tissue above the tidemark?
Synovial fluid
What is the downside to the lack of blood supply above the tidemark?
If cartilage superficial to subchondral bone is damaged, it can’t really heal itself
What is the name given to the pattern of fibres that form the collagen network in bone?
Arcades
What happens to your tibia when the ACL snaps and what other structures will try to hold it in place?
It slides forwards
The meniscus will try to hold it in place
If ACL is not repaired, meniscal tears will result due to being strained in attempt to keep the femur in place on the tibial plateau
Describe the vascularity of the menisci.
Only the peripheral 1/3 has a blood supply
What influence does sport in childhood have on knee alignment?
May cause misalignment due to increased pressures
How are collagen fibres arranged in the middle transitional zone of cartilage? Why?
Obliquely
Needs to resist compression + shearing forces
What is the tidemark? What is its function?
Interface between non calcified cartilage + calcified cartilage
Calcified cartilage acts as a barrier, stops blood (+ thus pathogens) passing into joint
What results from loss of ACL function?
Loss of stability (esp. when suddenly changing direction)
Loss of protection of cartilage
Back of meniscus takes increasing pressure + may tear
How does weight bearing area and pressure across the knee vary with an intact and excised meniscus?
Intact: Even distribution of pressure across knee
Excised: Huge decrease in weight bearing area + increased pressure in centre
