Bone Pathology Flashcards
how do osteocytes and osteoblasts interact
connected by long cytoplasmic processes
changes in bone tissue fluid (BTF) when changes in stress/strain on bone or microcracks
osteocytes detect changes in BTW flow –> signal to osteoblasts –> bone formation or resorption
what can osteoclasts not bind to
unminderalized bone
what role does parathyroid hormone play (4)
- osteoblasts retract and secrete collagenases –> osteoclasts have access to bone
- osteblasts secrete RANKL –> activates resorption process
- osteoblasts also produce osteoprotegrin –> inhibition of formation of osteoclasts
- osteoblasts can both upregulate and downregulate osteoclastic bone resorption
what is the organic matrix made up of
type I collagen arranged in parallel
what is the ground susbtance of bone matrix made up of
non-collagenous proteins, proteoglycans, lipids
what is the mineral of bone matrix
hydroxyapatite
contains minderals (Ca and P) –> hardness
how do flat bones develop
intramembranous ossification
how do long bones develop
endochondral ossification
how do bones grow in length
metaphyseal growth plates via endochonral ossification
how do bones grow in width
osteogenic layer of periosteum
what is the cortex and subchondral bone made of
osteons –> concentric layers of lamellae
what is the bone in the medullary cavity made of
trabecular bone –> lamellae arranged in parallel to sruface of trabecules
what is bone remodelling
change of shape or contour of bone in response to normal growth, changed mechanical use or disease
what is the reaction to a bone injury
- change of size and shape
- change of density
- disruption of endochondral ossification –> change to metaphyseal trabeculae
- rapidly deposited bone is woven (not lamellar)
- injured periosteum often also forms bone
what is a traumatic bone fracture
force exceeding design
what is a pathological bone injury
force below design
abnormal bone (osteomyelitis, neoplasm, metabolic bone disease) is broken by minimal trauma or normal weight bearing
what is a stable fracture
fracture ends have been immobilized (clinical stability) –> callus formation
what is a unstable fracture
callus formation
what is a rigid fracture
usually surgical intervention
bone ends in close contact or close proximitity
ideally contact feeding
what is an external callus
formed by the periosteum
what is an internal callus
between ends of fragments and in medullary cavity
what is the function of a callus
bridge the gap
encircle the fracture site
stabilize the area
what does a callus contain
hyaline cartilage if the blood supply is less than optimal –> not as strong but eventually undergoes endochondral ossification
what are the steps in callus formation
- hematoma –> immediate
- invasion of mesenchymal cells and neovascularization –> 24-48h
- earliest woven bone: 36h –> primary callus 4-6 wks
- months to years for secondary cells (trabecular bone) and restoration of normal bone
what is the histological difference between woven and lamellar bone
collagen not in parallel
irregularly arranged
what are the advantages of healing by callus
- natural process
- minimal intervention - minimal risk
- minimal intervention - lowest cost option
what are the disadvantages of healing by callus
- callus may not be able to stabilize fracture
- callus takes time to stabilize fracture
- large callus may interfere with function of joints or tendons
what is healing with fixation or by 1st intention
direct osteonal bridging of fracture site, no callus formation
what occurs if the gap is less than 1mm in healing by fixation
osteoblasts form lamellar bone at right angle to fracture line –> become osteons parallel to long axis
what occurs if the gap is greater than 1mm in healing by fixation
first formation of woven bone –> remodelled into osteons
what are the complications of fracture healing (8)
- inadequate blood supply/O2 –> cartilage formation; if anoxia –> necrosis
- instability (movement and high tension) –> development of fibrous tissue –> no bone formation –> non-union, false joint/pseudarthrosis
- infection –> osteomyelititis, sequestra
- malnutrition, age
- tissue between fracutre 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
what are the disorders of bones
- vascular
- inflammatory (infectious/immune-mediated)
- traumatic
- anomaly (congenital)
- metabolic/toxic
- idiopathic/iatrogen
- neoplastic
- degenerative
(VITAMIND)
what are the terms used to describe bone inflammation
- osteitis: inflammation of bone
- periostitis: inflammation of periosteum
- osteomyelitis: involves the medullary cavity
- sequestrum: fragment of dead bone isolated from blood supply and surrounded by a pool of exudate
what are the portals of entry for bone infection
- direct
- hematogenous
what are the causes of direct trauma that cause infectious inflammation
trauma (may or may not break bone)
extension from direct inflammation (eg. periodontitis/otitis)
how does indirect entry of infectious inflammation of bone occur
mostly young animals
usually bacterial (embolic) –> suppurative inflammation
most commonly on metaphyseal side of growth plate at articular-epiphyseal complex
capillaries with sharp bends to join medullary viens (slow flow, turbulence, lower phagocytic capacity, discontinuous endothelial lining, no anastomosis)
what are the consequences of infectious inflammation of bone
- 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
what are the 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
what occurs when there is a fractrure of growht plates or trabecular bone
metaphyseal cortex is very thin (weakest part) –> growth plate fractures in young animals
what are the types of growth plate fractures
type I and II: few or no complications
type III-V: may have growth abnormalities as growth plate involved
what is an infraction
fracture of trabeculae without involvment of cortex
what are the congential/anomaly abnormalities in growth and development
- osteopetrosis
- osteogenesis imperfecta
- chondrodysplasia
what is osteopetrosis
too much bone
defect in bone resorption by osteoclasts (also infectious)
what is osteogenesis imperfecta
too little bone
mutations in genes for collagen I
what is chondrodysplasia
disproportionate dwarfism
mutations in genes which control formation of cartilage, storage dx (MPS)
what is metabolic bone disease
osteoporosis
rickets/osteomalacia
fibrous osteodystrophy
what is osteoporosis
less bone (reduction in the amount of normally mineralized bone)
malnutrition, immobilization, low dietary Ca, oestrogen/androgen deficiency
what is rickets/osteomalacia
soft bones (defect in mineralization of bone)
Vit D/phosphorus deficiency
rubberjaw
what is fibrous osteodystrophy
replacement of bone by fibro-osseus tissue
hyperparathyroidism
what are the types of primary neoplasms of bone (7)
- fibroma: ex. ossifying fibroma –> maxilla and mandible of horse and cattle
- fibrosarcoma: ex. oral masses in dogs
- chondroma: often arise from flat bones, very rare
- chondrosarcoma: most often flat bones, large breed dogs and sheep, grow slower than osteosarcomas, develop metastases later
- osteoma: usually bone of head
- osteosarcoma
- liposarcoma, hemangiosarcoma
what is an osteosarcoma
malignant neoplastic cells form osteoid, bone or both
most common tumour of bone in dogs and cats
where do osteosarcomas most commonly occur
giant breed dogs; metaphyses (distal radius, distal tibia, proximal humerus)
early hematogenous spread to lungs and soft tissues and other bones
what is a secondary neoplasm
carcinoma is most common
dogs: rib shafts, vertebral bodies, humoral and femoral metaphyses; most common primary site: mammary gland, lung, liver, prostate gland
cats: rare; mets to appendicular skeleton; lung carcinoma to digits
