Lame - Joint pathology Flashcards by Mary Tilling

What are 3 types of joints in the body?

Fibrous joints
Cartilaginous joints
Synovial joints

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What are the three main components of synovial joints?

Joint cartilage
Joint capsule
Subchondral bone

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What does cartilage outside of synovial joints rely on for providing nutrients and new chondrocytes?

Perichondrium

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What is different about joint cartilage in synovial joints to normal cartilage?

It has no perichondrium so relies on alternating compression ad release of normal weight bearing to help the diffusion of fluid with nutrients and waste products into and out of the cartilage

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What can cause cartilage atrophy?

Constant static weight bearing
Lack of weight bearing

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What affects joint cartilage healing?

Lack of blood supply

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Where can inflammation in the synovial joint arise from?

The synovium or the subchondral bone
Subarticular growth cartilage of the epiphysis in young animals
Not the joint cartilage - lack of vasculature means no inflammatory response

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Where can pain originate from in the synovial joint?

Synovium and subchondral bone
Similar to inflammation - no nerves in joint cartilage so no pain

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What creates the cartilage matrix?

Chondroblasts

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What is the cartilage matrix made up of?

Collagen
Elastin fibres
Hyaluronic acid
Proteoglycans

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What gives cartilage its stiffness?

Bonds between collagen and elastin and glycosaminoglycans

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What gives cartilage its shock absorbing ability?

The water molecules in the matrix - if water retention is affected then cartilage integrity is affected

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How can cartilage be damaged?

Chondrocyte damage
Enzymes produced by inflammatory cells penetrating the matrix and degrading the collagen and proteoglycans

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What happens to the appearance of cartilage when its matrix is compromised?

Dehydrates, shrivels, turns dull yellow/brown
Eventually erodes away and exposes the subchondral bone

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What is ankylosis?

Fusion of joint surfaces

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What makes up the surface of the joint capsule?

Villi

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What are the villi in the joint capsule covered by?

The synovial lining

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What is the synovial lining made up of? What function do they have?

Synovial A cells - clear debris from synovial fluid
Synovial B cells - Produce components that make synovial fluid viscous and lubricating

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What are the three synovial responses to injury?

Villous hypertrophy and hyperplasia
Synovial cell hypertrophy and hyperplasia
Pannus formation

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Which synovial responses to injury are accompanied by inflammation (synovitis)?

Villous hypertrophy and hyperplasia
Synovial cell hypertrophy and hyperplasia

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What are the consequences of synovitis?

Impaired joint fluid drainage
Compromised fluid lubricating properties - B cells secrete other substances instead when there is inflammation

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What cells release inflammatory mediators into the synovial fluid?

Mononuclear cells
Synovial A cells

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What diseases is pannus formation in the synovial joint associated with?

Infectious fibrinous synovitis
Some immune-mediated diseases

What is a pannus?

A fibrovascular tissue that arises from the synovial membrane and spreads like a blanket over the joint cartilage, damaging it

What type of cell infiltrates the synovial joint during pannus formation?

Macrophages - inside the fibrovascular tissue, destroy the joint cartilage

What can pannus formation cause in the synovial joint?

The fibrous tissue of the pannus becomes a bridge between joint surfaces, creating an ankylosis, a fixed fusion of the joint

What is eburnation?

Exposure of subchondral bone due to loss of joint cartilage The subchondral bone is unprotected causing it to increase in density If the cartilage ulcerates, the subchondral bones can rub against each other making them smooth and shiny

What are osteophytes?

Bone spurs that project from the periosteum and persist once formed

Where are osteophytes found?

Sometimes just in the joint cavity Sometimes protrude from the periosteal surface of the bone

What causes osteophyte formation?

Joint injury Mechanical instability within the joint Inflammatory mediator release within the joint from cell death

What is the most common joint disease in animals?

Degenerative joint disease (DJD) (Also known as osteoarthritis)

What is degenerative joint disease?

Non infectious disease Structural and functional failure of joint homeostasis resulting in damage to the joint cartilage

What are the risk factors for degenerative joint disease?

Genetics Conformation Joint angles Pelvic muscle mass Diet/exercise/weight Age

What are some triggers of degenerative joint disease?

Accumulated repetitive micro‐damage A major traumatic event Secondary to metabolic and biochemical factors

What are the consequences of degenerative joint disease?

The inflammation and lesions cause cartilage damage, increased friction and grinding between adjacent subchondral bones Joint mobility is compromised

What is the most important predisposing factor for degenerative joint disease?

Osteochondrosis dissicans

What is osteochondrosis dissicans?

Focal failure of blood supply to growing cartilage so failure of endochondral ossification of the normal growth plate in young animals Then normal stresses or injury cause cracks and fissures in the cartilage

Where does endochondral ossification occur?

Occurs at the highly vascularized physeal growth plate and the articular-epiphyseal growth cartilage

What is the aetiology of osteochondrosis dissicans?

Multifactorial Genetics Rapid growth rate Vascular factors Trauma

What happens to the growth plate during osteochondrosis?

Cartilage is quickly replaced by bone - endochondral ossification The blood vessels feeding the cartilage cant penetrate so ischaemia and necrosis of cartilage occurs Dead growth plate cartilage is weak and causes subchondral bone above it to fracture up to the joint cartilage Synovitis occurs

What does osteochondrosis often result in formation of in horses?

Developmental bone cysts - subchondral bone cysts within the epiphyseal trabecular bone

What are 'true cysts' that result from osteochondrosis?

Develop after the vascular failure during osteochondrosis Microfractures cause bone to cave in and joint cartilage to fold and break Joint fluid enters the cyst

What is a 'pseudocyst' that results from osteochondrosis?

When an area of dead necrotic cartilage becomes surrounded by the ossification front, making the necrotic area appear as a radiolucent, ‘empty’ cavity on radiographs

What causes hip dysplasia?

Is a genetic inherited condition in large/giant breeds

What is hip dysplasia?

Lack of conformity of the femoral head and acetabulum causing instability and chronic subluxation of the hip joint Causes severe secondary DJD

What are the different routes of infection of joints?

Haematogenous spread - in blood Spread from osteomyelitis Spread from soft tissue Diagnostic or therapeutic procedures Penetrating damage

What is the name for inflammation of a joint?

Arthritis

What will acute inflammation of the synovial joint cause changes to?

Only the synovial fluid

What changes occur to the synovial joint in acute suppurative and fibrinous arthritis?

Fluid becomes watery and may be cloudy if neutrophils or fibrin are present May be red if there is haemorrhage

What changes occur to the synovial joint in subacute suppurative or fibrinous arthritis?

Thinned cartilage Exudates may be present Synovial membrane may be infiltrated by lymphocytes and plasma cells Hyperplasia of the synovial lining cells - to increase fluid production

What changes occur to the synovial joint in chronic suppurative arthritis?

Extensive cartilage erosion and ulceration Exudates reach subchondral bone Granulation tissue replaces synovial membrane Lymphoplasmacytic inflammation Joint capsule thickened and fibrotic Joint fusion

What changes occur to the synovial joint in chronic fibrinous arthritis?

Cartilage may ulcerate - especially if there is pannus formation Cartilage replaced with fibrous tissue, fusing joint

What pathogens more commonly cause fibrinous arthritis?

Gram negative bacteria eg. E. coli, mycoplasma

What pathogens more commonly cause suppurative arthritis?

Gram positive bacteria eg. staph, strep

What animals are bacterial arthritis common in?

Calves, lambs, foals, piglets Secondary to neonatal bacteraemia Not common in dogs and cats

What are the clinical signs of bacterial arthritis?

Lameness Swelling of synovial joints - fill of serofibrinous to suppurative exudate