7. Bones - General

Question 1

What layers make up the periosteum?

Answer 1

• Outer layer - vascular fibrous tissue
• Inner layer - osteoprogenitor / osteoblastic cells
• Sharpey fibres, attach to cortex

Question 2

Name the layers of the physis!

Answer 2

Question 3

What direction do nutrient foramen generally run in? In which bone is this reversed?

Answer 3

Periosteum (proximal) -> Endosteum (distal)

REVERSED IN ULNA

Question 4

Which cell type comprises the majority of compact bone? What other pertinent stuctural feature of compact bone is present?

Answer 4

• Osteocytes

=> HAVERSIAN system: interconnected canaliculi and Volkmann’s canals

Question 5

Define endochondral ossification

Answer 5

• MOST BONES DO THIS - develop from a cartilage model
• Ossifications centres form from hyaline cartilage centres IN UTERO
• Surrounded by perichondral new bone
• Ossification centres: All trabecular bone bone resorbed and replaced by marrow AT BIRTH

=> Trabecular bone persists at metaphyses

• Secondary ossification centres develop at epiphyses

=> Articular cartilage contributed to growth

Question 6

Which bones develop by intramembranous ossification?

Answer 6

Flat bones - e.g. SKULL

=> Form directly from connective tissue

Question 7

What are apophyses?

Answer 7

Non-articular cartilagenous protuberances -> ossify.

In young animal seperated from body of bone by cartilageneous band which fuse when mature

Sites of tendious attachement

Question 8

Describe the vascular supply to bone

Answer 8

Epiphyses: JOINT CAPSULE

Physis: Essentially avascular

Metaphysis: Nutrient foramen. PARTICULARLY BLOOD RICH -> osteomyelitis predisposition

Cortical bone: Medullary cavity via medullary arteries (centrifugal) to whole cortex, EXCEPT at sites of fascial attachment where outer 1/3rd supplied by small fascial arterioles

NB: Periosteum highly vascular in YOUNG DOG, vestigial with maturity. Facilitates component of intramembranous ossification

Question 9

Which portion of the bone is predisposed to osteomyelitis and osteosarcoma?

Answer 9

METAPHYSIS! Increased blood supply

Question 10

What is the cutback zone?

Answer 10

• Region of subperiosteal osteoclastic activity in region of metaphyseal zone as physis remodeleed to become diaphyseal

Question 11

List causes of endosteal / medullary osteosclerosis

Answer 11

Chronic osteomyelitis

Margins of neoplastic process / neoplastic new bone formation

Panosteitis

Bone infarction (e.g. malignancy associated in dogs, leukaemia in cats)

Question 12

List 7 periosteal reaction patterns in order of aggression

Answer 12

Question 13

List features of SOLID periosteal reaction

Answer 13

• Likely benign
• Periosteum slowly lifted over time
  e. g. fracture callus, chronic osteomyelitis, panosteitis, CODMANS TRIANGLE

=> the latter can be associated with neoplasoia

Question 14

List features of lamellar (parallel) periosteal reaction

Answer 14

• Periosteum lifted by e.g. exudate, haematoma or neoplastic cells (less commonly)
• Seperated from underlying cortex by radiolucent line
• Will fill with bone to beome solid reaction

Question 15

List features of Lamellated periosteal reaction

Answer 15

• More aggressive than lamellar = “onion skin” sequential elevations of periosteum
• Typically with fungal osteomyelitis and malignant neoplasai

Question 16

List features of brush like periosteal reaction

Answer 16

• Periosteum lifted rapidly, with osteoblastic activity along vertically oriented sharpey fibres
• Thicker brush = palisading: less aggressive as SLOWER growing
• Thinner = spiculated: faster, more aggressive

E.g osteomyelitis, neoplasia, hypertrophic osteopathy

Question 17

List features of sunburst periosteal reaction

Answer 17

• Highly aggressive process, typically OSA
• Periosteum lifte rapidly -> domed shape

Question 18

List features of amorphous bone production

Answer 18

NOT PERIOSTEAL REACTION -> neoplastic new bone, beyond confines of periosteum

=> cotton wool or candyfloss appearance

Highly suggestive of OSA

Question 19

What % of bone loss is detectable radiographically?

Answer 19

30-50%

Question 20

Define osteoporosis vs osteomalacia

Answer 20

Osteoporosis: Bone atrophy (local or generalised) without change to composition. Fewer / coarser trabeculae, thin cortex

Osteomalacia: Decreased bone mass with disturbance to composition due to insufficient / abnormal osteoid mineralisation. Usually affects whole skeleton and metabolic in origin

Question 21

List types of lysis

Answer 21

Question 22

Define differences between geographic, moth eaten and permeative lysis

Answer 22

Geographic

• Least aggressive
• Usually cancellous bone at extremitis

+- sclerotic rim. If present less aggressive, if not = “punched out”

• Cortical destruction may be present e.g. myeloma, metastasis

Moth eaten

• Larger seperate foci (2-3mm), ill-defined
• Intermediate aggressiveness

Permeative

• Numersous small foci, 1-2mm.
• Often with cortical scalloping or defects
• MOST aggressive

Question 23

Features of aggression!

Answer 23