Bone Pathology

M.8R, W.2, L.10

List the structure that connects osteocytes and osteoblasts

long cytoplasmic processes

When do changes in bone tissue fluid flow occur?

when there are:

• changes in stress/strain on bone or microcracks

What detects changes in BTF flow and what happens when they do detect this change?

Osteocytes detect change → signal osteoblasts → initiate bone formation or resorption

what can osteoclasts NOT bind to?

unmineralized bone

Describe osteoblasts (what they retract, secrete, produce and what this can lead to, and their overall function w/ bone resorption)

• Retract and secrete collagenases → osteoclasts have access to bone

• secrete RANKL → activates resorption process

• Produce osteoprotegerin → inhibition of formation of osteoclasts

• Osteoblasts upregulate and downregulate osteoclastic bone resorption

What is organic matrix made up of?

• Organic Matrix

  • Type I collagen

• GS

  • non-collagenous proteins, proteoglycans, lipids

• Mineral

  • hyroxyapartite; contains minerals including calcium and phosphate

List function of hydroxyapatite

gives bone its hardness

List the type of development for flat bones and long bones

• Flat bones

  • intramembranous ossification

• Long bones

  • endochondral ossification

List how bones grow length wise and width wise

• Length

  • metaphyseal growth plates via endochondral ossification

• Width

  • osteogenic layer of periosteum

Define (re-)modelling of bone

change of shape or contour of bone in response to normal growth, changed mechanical use or disease

List what a bone can do in reaction to injury

• Change of size and shape

• Change of density

• Disruption of endochondral ossification → change to metaphyseal trabeculae

• Rapidly deposited bone is woven

• Injured periosteum → forms bone

List the two types of causes of bone fractures and define them

• Traumatic

  • force put on bone exceeded the design; too much force for normal bone

• Pathological

  • abnormal bone broken by minimal trauma or normal weight bearing

• Stable

• unstable

• Rigid

Critical Factors:

• Correct alignment - Lack of movement - Asepsis - Adequate blood supply

• External

  • formed by periosteum

• Internal

  • between ends of fragments and in medullary cavity

• Function:

  • should bridge gap

  • encircle fracture site

  • stabilize area

List the 3 stages of callus formation

• Inflammation

• Proliferation

• Maturation

List advantages of healing by callus

• Natural process

• Minimal intervention - minimal risk

• Minimal intervention - lowest cost option

List disadvantages of healing by callus

• Callus may not be able to stabilise fracture

• Callus takes time to stabilise a fracture

• Large callus may interfere with function of joints or tendons

List complications of fracture healing

• Inadequate blood supply/02 cartilage formation; if anoxía necrosis

• Instability (movement and high tension) -> development of fibrous tissue -> no bone formation -> nonunion, false joint/pseudoarthrosis

• Infection -> osteomyelitis, sequestra

• Malnutrition, age

• Tissue between fracture ends delayed or non-union

• Too large metallic implants -> lack of mechanical force to bone → atrophy

• Intramedullary implants may damage blood supply

• Premature closure of growth plates deformed limbs

List and define terminology for inflammation of the bone

• Osteitis

  • inflammation of bone

• Periostitis

  • inflammation of periosteum

• Osteomyelitis

  • involves medullary cavity

Define Sequestrum

fragment of necrotic bone

List infectious agents of bone that cause inflammation

• Bacteria (most common)

  • Trueperella pyogenes

  • Staphylococcus spp.

  • Streptococcus spp.

  • Salmonella E.coli

• Fungi

• Viruses

• protozoa

• How do they get there?

  • hematogenous

  • direct extension

List two ways Direct extension can cause infectious inflammation of the bone and give two examples

• Trauma

• Extension from direct inflammation

• Ex:

  • Actinomyces bovis (“lumpy jaw”)

  • Pyogranulomatous osteomyelitis

List two ways Indirect extension can cause infectious inflammation of the bone and give two examples

• Bacterial (usually) —> suppurative inflammation

• 
  

List consequences of infectious inflammation of bone and possible sequela

• Thrombosis, infarction, inflammation —> bone resorption

• Possible Sequela

  • Extension into joint and periosteum

  • Formation of sequestra

  • Formation of sinus tracts

  • Spread to other bones and soft tissues

  • Pathological fractures

List and define types of fractures of cortical bone

• Closed

  • skin unbroken

• Open/compound

  • skin broken

• Simple

  • clean break into two parts

• Comminuted

  • bone shattered into fragments

• Greenstick

  • cortex on one side broken, on other side only bent (-> no displacement of fracture site)

• Transverse/spiral (depending on fracture line)

List the two types of growth plate fractures

• Type I and II: few or no complications

• Type III-V: may have growth abnormalities as growth plate involved

Define an infarction

Fracture of trabeculae without involvement of cortex

Metabolic Bone Disease (dx, define and causes)

• Osteoporosis

• less bone

• malnutrition, immobilization, low dietary Ca, estrogen/androgen deficiency

List two more types of metabolic bone disease

• Rickets / Osteomalacia

  • 
    

• Fibrous osteodystrophy

  • replacement of bone by fibro-osseous tissue (makes bone softer; mostly have collagen, no bone)

List Primary Neoplasms of bone

• Fibroma

• Fibrosarcoma

• Chondroma

• Chondrosarcoma

• Osteoma

• Osteosarcoma

• Liposarcoma

• Hemangiosarcoma

• Multilobular tumor of bone

• malignant neoplastic cells from osteoid

List sites where primary and secondary neoplasms of bone can show up in canines

• Common Primary Site

  • mammary gland

  • lung

  • liver

  • prostate gland

• Secondary

  • rib shafts

  • vertebral bodies

  • humoral

  • femoral metaphyses

List where secondary neoplasms of bone can show up in felines

• rare

• mets to appendicular skeleton

• lung carcinoma to digits