Bone and Joints (pathology)

Question 1

What makes up normal bone?

Answer 1

Outer solid cortical bone
Inner trabecular (spongy bone)
Outer surface - periosteum
Inner space (medulla) contains fat or haemopoietic marrow
Inorganic (ca hydroxyapatite) 65%
Organic 35%

Question 2

Functions of bone?

Answer 2

Mineral homeostasis
Houses haemopoietic system
Mechanical - not a static scaffold (constantly remodelled)

Question 3

What are the types of bone diseases?

Answer 3

Infecs, tumours, trauma/degeneration
Specific derangements of bone’s particular specialised processes and function
Specific bone diseases: disorders of matrix formation, mineralisation and bone turnover

Question 4

What occurs in the bone remodelling cycle?

Answer 4

Activation of osteoclasts
Resorption of bone
Death of osteoclasts
Formation of new matrix by osteoblasts
Mineralisation of new matrix
Quiescence

Question 5

What cells form and resorb bone?

Answer 5

Osteoblasts = form
Osteoclasts = resorb

Question 6

How does bone resorption and bone formation work together?

When is coupling lost?

Answer 6

Coupling of bone formation and resorption usually balances, except where a local imbalance is required for the purposes of growth
Coupling is lost in osteoporosis = loss of bone volume

Question 7

Types of bone matrix formation diseases?

Answer 7

Mutations in collagen type 1 in bone:
- Osteogenesis imperfecta
- Also affects ears / eyes / skin / teeth
Other abnormalities of bone matrix
Mucopolysaccharidoses
- Morquio syndrome
- Hurler syndrome

Question 8

How do cartilage matrix formation disorders occur?

Answer 8

Failure of cartilage maturation at the growth plate
Caused by a mutation of fibroblast growth receptor receptor 3 which causes it to be continually activated (it is a negative regulator of bone growth)

Question 9

Examples of cartilage matrix formation disorders?

Answer 9

Achondroplasia = Autosomal dominant

Question 10

Examples of mineralisation diseases?

Answer 10

Osteomalacia / Ricketts

Question 11

Causes of mineralisation diseases?

Answer 11

Caused by deficiency in vitamin D or calcium
Can be dietary or metabolic
Failure to mineralise ->cartilage overgrowth, failure of longitudinal growth

Question 12

Bone remodelling problems (osteoporosis) due to?

Answer 12

Increased porosity of bone due to a reduction in bone mass
Age
Hormonal influences
Lifestyle (smoking, alcohol)
Activity
Genetics (Vit D receptor polymorphisms)
Nutrition (including malabsorption)

Question 13

How does osteoporosis occur?

Answer 13

Uncoupling of bone resorption and formation - too much bone resorption, too little bone formation
Loss of trabecular then cortical bone

Question 14

Complications of osteoporosis?

Answer 14

Fragility fractures (vertebrae, femoral neck, distal radius)
Kyphosis (dowager’s hump)
Loss of height

Question 15

Tx of osteoporosis?

Answer 15

Inhibit bone resorption (bisphosphonates)

Increase bone formation (experimental treatments)

Question 16

Abnormal turnover: Paget’s disease?

Answer 16

Excess turnover

Genetic

Question 17

Bone infection: Osteomyelitis features?

Answer 17

Complication of compound fractures
Blood borne
Necrosis of bone fragments
New bone formation
Sinuses drain pus

Question 18

What are most tumours in bone?

Answer 18

Metastases

Question 19

Features of primary bone tumours?

Answer 19

Many are benign

Malignant ones = rapidly fatal

Question 20

Chondrogenic features?

Answer 20

60% benign:
Osteochondroma
Chondroma

40% malignant:
Chondrosarcoma

Question 21

Osteogenic features?

Answer 21

13% benign:
Osteoid osteoma
Osteoblastoma

87% malignant:
Osteosarcoma

Question 22

Examples of malignant bone tumours?

Answer 22

Osteosarcoma
Chondrosarcoma
Ewing’s sarcoma
Undifferentiated sarcoma

Question 23

Site and age of osteosarcoma?

Answer 23

Metaphyses, most commonly knee

15-30

Question 24

Site and age of Chrondrosarcoma?

Answer 24

Pelvis, ribs, proximal long bones

Middle aged - elderly

Question 25

Site and age of Ewing’s sarcoma?

Answer 25

Diaphyses

<20

Question 26

Site and age of undifferentiated sarcoma?

Answer 26

Mainly metaphyses

Middle aged - elderly

Question 27

Types of joint diseases?

Answer 27

Infections
Crystal arthropathies
Chronic inflammatory arthritis
Osteoarthritis
Tumours

Question 28

Septic arthritis features?

Answer 28

Can be very trivial causes
Insect bites / small cuts near joints
punching people in teeth
Very painful
IV antibiotics +/- drainage

Question 29

Name the types of crystal arthropathies, features?

Answer 29

Gout = urate crystals 2ndry to raised serum uric acid
Pseudogout = calcium pyrophosphate crystals, age related

Question 30

Chronic inflammatory arthritis features?

Answer 30

Generally autoimmune

Rheumatoid arthritis is the commonest form
There are a variety of other types:
HLA B27-associated diseases such as ankylosing spondylitis and psoriatic arthritis
Systemic lupus and related conditions

Question 31

Features of rheumatoid arthritis?

Answer 31

Inflammation of synovium

• Lymphocytyes / plasma cells / macrophages
• ‘Pannus’ formation (inflamed fibrous tissue)

Multiple joints
Extra articular features
Joint destruction caused by a cascade of cytokines driven by tumour necrosis factor-alpha

Anti-TNF-alpha antibodies are an effective treatment of severe rheumatoid disease

Question 32

Osteoarthritis/osteoarthrosis features?

Answer 32

Common
Degenerative disease
Cartilage erosion - minimal inflam, leads to changes in underlying bone
Mechanical
Predisposed by pervious joint damage

Question 33

What occurs in ostoearthritis?

Effective tx?

Answer 33

Fragmentation of cartilage
(‘fibrillation’)

Osteophyte formation

Cysts in underlying bone

The only effective treatment is arthroplasty (surgical removal of the joint and replacement with a prosthesis)