Lame - bone pathology Flashcards
What are the two causes of fracture?
Traumatic - normal bone with excessive force
Pathological - abnormal bone with minimal trauma
What are the 3 locations of bone fractures?
Growth plate
Trabecular bone
Cortical bone
What do fractures that cross/crush the growth plate cause?
Angular limb deformities
What type of fractures of the growth plate are more likely to heal easily?
Fractures that involve only the growth plate and primary bone trabeculae
What type of fractures of the growth plate are more likely to cause irreversible damage?
Fractures crossing growth plate through metaphysis/epyphisis
Crush of growth plate
What is the first step of fracture repair?
Formation of a haematoma around fracture site
What does damage to blood vessels from a fracture cause?
Reduced blood flow
Necrosis of bone fragments
Release of growth factors by macrophages from dying bone
What is formed from the haematoma in fracture repair?
Soft tissue callus/procallus
How is the procallus formed in fracture repair?
Blood vessels proliferate and undifferentiated mesenchymal cells penetrate, forming loose collagenous tissue
What is formed from the procallus in fracture repair? How?
A primary callus - metaplasia of the collagenous tissue into cartilage and woven bone
What is the secondary callus made of? What is it?
Replaces the primary callus over time with lamellar bone
What does the makeup of the primary callus depend on?
Blood an oxygen supply
The poorer the blood and o2 supply, the greater amount of cartilage in a callus - takes bone longer to heal
How does the bone return to its original shape over time?
The portions of callus that dont undergo physical stress are reabsorbed over time
What can complicate bone repair?
Insufficient bone supply
Instability
Infection poor nutrition
What happens when there is instability during bone repair?
Non union - procallus cant mature into bone so forms fibrous tissue instead
Fibrous tissue not strong enough
What can be formed by a non-union of bone due to instability?
Cysts
False joints
Pseudoarthritis
What is common in open fractures?
Septic bone inflammation/infection
Why is it easier for bacteria to invade under the articular epiphyseal cartilage complex?
Capillaries bend sharply to joining veins so there is turbulent blood flow and a discontinuous endothelial lining - easier for bacteria to invade
What pathogens cause osteomyelitis?
Almost always bacterial eg. strep, staph, truperella, E. coli
What causes inflammation during osteomyelitis?
Bacteria invade
Neutrophils recruited to the site causing inflammation
What does inflammation stimulate during osteomyelitis? What does this cause?
Inflammation stimulates osteoclasts to reabsorb bone and enzymes released - bone loss
What does the density of bone cause during osteomyelitis?
Density of bones means exudate cant get out of bone - the increased pressure is very painful, compresses blood vessels
Leads to thrombosis and infarction of intramedullary fat, marrow and bone
What is deposited at the side of osteomyelitis?
Fibrous tissue
What are sequelae?
Complications of osteomyelitis
What are some sequelae?
Inflammation extending to the surrounding soft tissues causing abcesses
Skin fistula
Septic arthritis
Sepsis
Pathologic fractures
Bone sequestra
Where can osteomyelitis spread to?
Surrounding soft tissues
Adjacent bones
Across joints
Into the bloodstream
What are bone squestra?
fragments of pale, chalky necrotic bone that are cut off from their blood supply and surrounded by exudate
Have no blood supply so cant resorb
Why are bone sequestra bad?
They can interrupt/undermine bone healing
What can cause bone sequestra?
Bone fractures
Osteomyelitis
What mechanism causes bone growth in width?
Intramembranous bone formation - osteoblasts for new concentric layers of cortical bone
What mechanism causes bone growth in length?
Endochondral ossification in the metaphyseal growth plates
When are growth plates thickest?
When growth is most rapid, closes at skeletal maturity
What are the 4 different cartilage zones in the growth plate?
The reserve/resting zone
Proliferative zone
Hypertrophic zone
Calcifying zone
What is the reserve/resting zone for?
A source of cells for the proliferating zone
What happens in the proliferative zone?
Cells multiply
Produce matrix
Become arranged in longitudinal columns
What happens in the hypertrophic zone?
Chondrocyte volume expands
Chondrocytes modify the matrix to allow capillary invasion
Initiation of matrix mineralisation
What happens in the calcifying zone?
Blood vessels from metaphysis invade into advancing growth plate
Cartilage mineralisation
What do the invading blood vessels from the metaphysis allow?
They provide entry for the osteoblasts - critical step
What is the primary spongiosa?
The junction between cartilage and bone in the metaphysis
A fragile lattice of bone covered spicules of calcified cartilage
What is the secondary spongiosia? What is it made up of?
More mature trabeculae when growth plate advances - fewer, thicker and made up of mostly bone
What is chondrodysplasia?
Hereditary disorders of bone growth - primary lesions in growth cartilage of the physeal/epiphyseal cartilage of long bones
What are some disorders of bone growth in chondrodysplasia?
Growth plates reduced
Disorganised chondrocytes
Cartilage matrix less dense
Trabeculae/spongiosa thickened
Cartilage retained in the secondary spongiosa
What type of dwarfism is caused by chondrodysplasia?
Disproportionate dwarfism - normal sized head with short legs
Why does disproportionate dwarfism not affect the head?
Bones of the head are not formed by endochondral ossification
What is not caused by chondrodysplasia?
Proportionate dwarfism - due to endocrine disease, malnutrition, or artificial breeding selection instead
Just small dogs
What causes angular limb deformities?
Partial or complete premature closure of growth plates
What is the most common site of angular limb deformities?
Distal ulnar physis - most stress on this growth plate
What causes angular limb deformities in horses?
Physeal osteochondrosis
What area is the most commonly affected thing in physeal osteochondrosis?
Hypertrophic cartilage layer
What is the result of physeal osteochondrosis?
A well demarcated wedge of retained cartilage in the physis - columns of chondrocytes that dont mineralise
Can cause growth plate fractures?
What is the weakest part of the bone?
Metaphyseal cortex adjacent to the growth plate
What breed of dogs most commonly get elbow dysplasia?
Large to giant breed dogs
What are some elbow abnormalities that cause elbow dysplasia?
Medial coronoid disease
Humeral osteochondrosis
Ununited anconeal process
Elbow instability
What disease does a short radius cause?
Medial coronoid disease
What disease does a short ulna cause?
Ununited anconeal process
What can cause aseptic/ischaemic necrosis?
Trauma causing vascular damage
Neoplasm infiltration
Thromboembolism
What does ischaemic necrosis of the metaphysis of the bone and bone marrow cause?
Retained growth cartilage - conversion of epiphyseal cartilage to bone is impaired
What does ischaemic necrosis of the epiphysis of the bone cause?
Premature growth plate closure - death of the proliferating chondrocytes
What can aseptic/ischaemic necrosis lead to?
Avascular necrosis of the femoral head (legg-calve-perthes)
What breeds are predisposed to avascular necrosis of the femoral head (legg-calve-perthes)?
Minature poodle
Yorkie
Why does ischaemic necrosis cause avascular necrosis of the femoral head?
Ischaemia causes dead femoral head bone to be replaced by fibrous tissue - this is not supportive enough so femoral head collapses
What does not happen in avascular necrosis of the femoral head because it is a sterile disease?
Bone sequestra
