Osteo-articular Pathology Flashcards
Name developmental osteo-articular disorders (x3)
- Osteogenesis imperfecta
- achondroplasia
- osteopetrosis
Name systemic / generalised osteo-articular disorders (x5)
- infections - osteomyelitis
- osteoporosis
- rickets / osteomalacia
- hyperparathyroidism (skeletal effects)
- Paget’s disease
Name neoplastic osteo-articular disorders (x4)
- bone forming tumours
- cartilage tumours
- fibrous tumours
- tumours of uncertain histogenesis
Name joint osteo-articular diseases (x2)
- osteoarthritis
- rheumatoid arthritis
What is the outer section of bone called?
Cortex
- compact bone
What is the inner section of bone called?
Medulla
- cancellous bone
- spongy
- trabeculae
What is in the trabeculae?
Bone marrow
What does bone marrow do?
makes RBC / WBC
What are the functions of bone? (x4)
- support
- protect organs
- host and protect bone marrow
- supplies calcium and phosphate
Describe intramembranous ossification
- ossification centre in fibrous connective tissue membrane
- mesenchymal cells differentiate into osteoblasts - Bone matrix (osteoid) is secreted within fibrous mem
- osteoblasts secrete osteoid
- osteoid is mineralised / calcified within a few days = bone matrix
- trapped osteoblasts become osteocytes - Woven bone and periosteum form
- osteoid laid down between embryonic blood vessels - random network = trabeculae
- vascularised mesenchyme condenses on external surface of woven bone to become periosteum - bone collar of compact bone forms and red marrow appears
- trabeculae thicken just deep to periosteum = woven bone collar - later replaced by mature lamellar bone
- spongy bone remains internally and its vascular tissue becomes red bone marrow
What bones are created by intracmembranous ossification?
Flat bones
- skull (not occipital bone)
- part of mandible / maxilla
- part of clavicles
How long does is take for ostoid to become calcified once secreted from osteoblasts?
a few days
What bones are created by endochondrial ossification?
long bones
How are bone created by endochondrial ossification?
- Mesenchymal cells form hyaline cartilage
- bone collar forms on sides of long bone
- Blood vessels enter central ossification centre (cartilage can’t survive if O2 present, so bone forms) from periosteal bud
- spongy bone formed
- medullary cavity forms
- secondary ossification centres form
- epiphyseal blood vessels enter secondary ossification centres
- ossification of the epiphyses
- hyaline cartilage remains on epiphyseal plate and articular cartilage
What is a periosteal bud?
Blood vessels from the periosteum which enter the centre of ossification in endochondrial ossification
What is the medullary cavity?
aka marrow cavity
- central part of bone where marrow stored
What are the following:
- diaphysis
- epiphysis
- epiphyseal
diaphysis
- bone between epiphyseal plates (middle part)
epiphysis
- bone above eiphyseal plates (top / bottom)
epiphyseal
- plate of cartilage
Describe the growth plate in bone
aka epiphyseal plate
- well ordered columns of chondrocytes
- chondrocytes release matrix (proteoglycans, water, collagen)
- hypertrophy of chondrocytes are they get closer to zone of bone formation - reduced proteoglycan release, increased alkaline phosphatase - therefore increased calcification
- then they become calcified
- then converted to bone
What happens if bone does not calcify in growth plate?
bone does not grow
Where does alkaline phosphatase come from and what does it do in bone formation?
from chondrocytes in growth plates
causes calcification of hypertrophy chondrocytes to form bone
Name condition associated with short limbs
achondroplasia
What are physical symptoms of achondroplasia?
- short limbs
- trident hands
- smaller occipital bone / contracted base of skull
Normal - trunk/thorax
What are trident hands?
- fingers all similar length
- fingers splay at 1st joint
What type of bone formation is faulty in achondroplasia?
endochondrial ossification
how many births have achondroplasia?
1 in 30,000 live births
What % of achondroplasia is
- hereditary
- sporadic
hereditary = 25%
- autosomal dominant trait
Sporadic = 75%
- new mutations
Name long bones
humerus, ulna, radius
femur, fibula, tibia
How is cartilage different in long bones in achondroplasia|
epiphyseal plates don’t develop normally
cartiage at end of long bones is enlarged
What happens in achondroplasia endochondrial ossification?
- disrupted columns of chondrocytes
- chondrocytes fail to hypertrophy
- defective calcification
- bone not formed
Which gene is responsible for achondroplasia and what is the type of mutation?
What does this gene do?
Fibroblast growth factor receptor 3 (FGFR3)
- point mutation
- in achondroplasia, FGFR3 is always active, so chondrocytes aren’t switched on for hypertrophy
What are three conditions caused by faulty FGFR3?
- achondroplasia (dwarfism)
- craniosynostosis (abnormal scalp/sutures)
- lethal dwarism (foetus doesn’t grow)
What is osteogenesis imperfecta?
aka brittle bones
- defective connective tissue
- abnormal synthesis of type 1 collagen
What % of ORGANIC matter of bone is made of collagen?
90%
What makes up 90% of organic matter of bone?
Collagen
What mutations cause osteogensis imperfecta?
point mutations of many genes.
mainly - COL1A1 and COL1A2
how many types of osteogensis imperfecta are there?
8
mild - severe
What determines the severity of osteogenesis imperfecta?
- number of point mutations
- type of point mutations (amino acid substitution at point mutation)
What is the pattern of inheritance for osteogensis imperfecta?
autosomal dominant or recessive
What is the organic matrix in bone?
collagen / osteoid
What is the inorganic matrix in bone?
Calcium
What are symptoms of mild osteogenesis imperfecta?
- delicate bones
- early osteoporosis
What are symptoms of severe osteogenesis imperfecta?
- can be lethal perinatally (just before / after birth)
- foetus can get fractures
Adults
- abnormal bone structure
- defective mineralisation
What are bones like in adults with osteogenesis imperfecta?
thin cortex = weak, bendy
epiphyseal cartilage is fine, so normal length bones
What other symptoms can be present in osteogenesis imperfecta? (none bone related)
blue/grey eyes
- sclera is thin, so choroidal veins below show through
Dentogenesis imperfecta
- irregular dentine formation (NB enamel = no collagen)
- blue /grey hue
- in type III and IV osteogenesis imperfecta?
- loose joints for slender weak tendons
- poor muscle tone
- early loss of hearing in some children (middle ear bones)
- protrusion of the eyes
What type of osteogenesis imperfecta gets dentogenesis imperfecta?
types Ib, III and IV
What is the most common type of osteogenesis imperfecta?
type I
What are symptoms of osteogenesis imperfecta type I?
- fragile bones (fracture, slight spinal curvature)
- loose joints for slender weak tendons
- poor muscle tone
- blue-grey sclera in eye (choroidal veins below show through)
- early loss of hearing in some children (middle ear bones)
- protrusion of the eyes
- type 1A = no dentogenesis imperfecta
- type IB = dentogenesis imperfecta
- reduced life exp (risk fatal bone fracture)
Why does life exp reduce in osteogenesis imperfecta?
risk of fatal bone fracture
Which type 1 osteogenesis imperfecta is associated with dentogenesis imperfecta?
Type IB (not type 1A)
NB type III and IV collagen issues are also linked to dentogenesis imperfecta
What is disorder with v dense bone?
osteopetrosis
What is osteopetrosis?
osteoclast defect bone formation > resorption become become denser reduced medullary cavity / space for marrow reduced haemoposesis, inc WBC increased risk infection
What is inhertiance pattern of osteopetrosis?
How common is it?
inherited
rare
What is haemoposesis?
Formation of blood cells in bone marrow
What does xray of osteopetrosis look like?
dense, bright white bone
can’t see medulla
with thick bone of osteopetrosis, is there an increase or decrease in risk of fracture?
increase
How many men / women get osteoporosis?
1 in 3 women (over 50)
1 in 10 men (over 50)
get fractures from osteoporosis
How many hip fractures are caused by osteoporosis each year?
70,000
How many wrist fractures are caused by osteoporosis each year?
50,000
How many spinal fractures are caused by osteoporosis each year?
40,000
What is most common fracture associated with osteoporosis?
hip (70,000 / year) - neck of femur fractures
then wrist (50,000) - radius in wrist - Colles fracture then spine (40,000) - vertebral crush
How much does osteoporosis cost the NHS each year?
£1.7billion!
Define osteoporosis
reduced bone mass / density
- thinner cortex
- increased trabeculae spaces
What is main cause of osteoporosis?
post-menopause