Bone pathology

Question 1

Composition of bone

Answer 1

65% inorganic (calcium hydroxyapatite)

35% organic (protein matrix, bone cells)

Question 2

3 types of bone cell + functions

Answer 2

Osteoblasts - build bone + stimulate osteoclast dev by RANKL
Osteoclasts - chew bone
Osteocytes - osteoblast-like

Question 3

2 types of mature bone

Answer 3

• Cortical (highly calcified, densely packed osteons, outer bone)
• Cancellous ‘trabecular’ (less calcified metabolic large SA, gaps filled with BM, inner bone + epiphyses)

Question 4

Stages of bone development

Answer 4

Woven bone (collagen fibres in irregular directions)
Lamellar bone (collagen fibres in parallel)

Question 5

Bone anatomy

Answer 5

Diaphysis = shaft, epiphysis = head, metaphysis = boundary

Diaphysis = inner cancellous, outer cortical

Question 6

Largest bone cells

Differentiation regulated by RANK-L

Answer 6

Osteoclasts

Question 7

First presentation NOF # (vertebrae, Colles, NOF)
Elderly woman falls over
Thin bone + enlarged Haversian canals
No demineralisation of bone
Bone density DEXA >2.5SD below normal

Answer 7

Osteoporosis

Question 8

Bone demineralisation
Pseudofractures, bone deformity + widened epiphyses
Proximal muscle weakness
Low calcium + phosphate

Answer 8

Osteomalacia (Rickets in children)

Question 9

Chaotic bone turnover
Raised ALP
Bony pain and deformity
Deafness due to CNVII compression
Mosaic lamellar bone + huge osteoclasts
Lytic + sclerotic lesions

Answer 9

Paget’s disease

Question 10

Osteitis fibrosis cystica
High calcium
Brown cell tumour

Answer 10

Hyperparathyroidism

Question 11

No periosteal reaction
Well developed bone
Intraosseous, even calcification

Answer 11

Benign neoplastic bone disease (osteoid osteoma, osteoma, enchondroma, osteochondroma, fibrous dysplasia, simple bone cyst, osteoblastoma)

Question 12

Acute periosteal reaction (e.g. Codman’s triangle, onion skin, sunburst)
Irregular bone formation
Extraosseous, irregular calcification

Answer 12

Malignant neoplastic bone disease

Osteosarcoma, chondrosarcoma, Ewing’s, giant cell

Question 13

Children + adolescents
Histology: Sheets of small round cells, scanty cytoplasm, droplets of glycogen
CD99+, T11;22 translocation
X-ray: ‘Onion skin reaction’ of perisoteum

Answer 13

Ewing’s sarcoma

Question 14

X-ray + organisms osteomyelitis

Answer 14

X-ray - lytic lesions 10d post onset

Organisms - S aureus adults, Hib / GBS children

Question 15

Histology: Malignant chondrocytes

X-ray: Fluffy calcification, axial skeleton

Answer 15

Chondrosarcoma

“Cloud like fluffy calcification”

Question 16

Codman’s triangle, sunburst appearance

Answer 16

Osteosarcoma

Question 17

Multinucleated giant osteoblasts with surrounding spindle cells
Soap bubble appearance (lytic lesions in epiphysis)

Answer 17

Giant cell tumour

Question 18

Renal osteodystrophy

Answer 18

Secondary hyperparathyroidism

Question 19

GI polyps + multiple osteomas + epidermoid cysts

Answer 19

Gardner’s syndrome

Question 20

Hands

Cotton wool calcification

Answer 20

Enchondroma (‘Ends in hands’)

Question 21

Bulls eye appearance

Answer 21

Osteoid osteoma

Question 22

Cartilage capped bony spurs (‘mushrooms’) on surface of bone

Teenage boys

Answer 22

Osteochondroma

Question 23

Soap bubble osteolysis
Shepherd’s croook deformity
Chinese letters
McCune Albright (precocious puberty, cafe au lait spots)

Answer 23

FIbrous dysplasia

Question 24

Lytic well defined lesion

Answer 24

Simple bone cyst

Question 25

Speckled mineralisation

Answer 25

Osteoblastoma

Question 26

Associated with Gardner’s syndrome (GI involvement)

Answer 26

Osteoma

Question 27

Bowed legs
Renal failure
Raised PTH, low calcium + low vitamin D

Answer 27

Secondary hyperparathyroidism with chronic renal osteodystrophy (renal failure prevents vitamin D activation)