Cartilage and Joint Pathology Flashcards
Does inflammation play a part in cartilage injury?
No, but cartilage can be affected by inflammation in the synovium, subchondral bone or growth cartilage
How can repetitive stress damage cartilage?
It damages the matrix and chondrocytes leading to inappropriate cellular responses e.g. production of degradative enzymes, chondrocyte death and a cycle of injury.
Proteoglycan and collagen interactions are disrupted.
What is the response to injury?
- Response to injury is limited due to cartilage having a minimal capacity for repair
- If proteoglycans are lost, collagen fibres condense and fray (fibrillation)
- Clefts and fissures form in the vertical axis - this allows synovial fluid to enter subchondral bone and cause inflammation
- Fibrillation is accompanied by erosion
- Erosion doesn’t penetrate into the subchondral bone but is persistent. It doesn’t heal but does not progress either
- Necrosis of chondrocytes is subsequent to fibrillation and erosion (hypocellularity)
- Limited regenerative hyperplasia of chondrocytes
How does eburnation occur?
- Ulceration of cartilage causes the full thickness to be lost, gets filled with vascular fibrous tissue
- Often undergoes metaplasia to fibrocartilage but rarely hyaline cartilage
- Exposed subchondral bone develops an increased density due to increased mechanical use (eburnation)
What are the stages in degenerative joint disease?
- Cellularity of cartilage declines with age and turnover of collagen and cells occurs at a lower rate
- Chondromalacia (softening)
- Erosion and fibrillation
- Ulceration
Define ‘periarticular osteophytes’
- Bony outgrowths/spurs, initiated by mechanical instability of the joint and/or inflammatory cytokines.
- Don’t grow continuously but persist once formed
- Can form within joint cavity (perichondrium) or from the periosteum at the junction with the joint capsule
- Often get secondary synovial inflammation and hyperplasia
Define ‘pannus’
- Fibrovascular and inflammatory tissue that arises in the synovium and spreads over the articular cartilage, destroying it (macrophages and collagenases are responsible)
- Happens with chronic infectious synovitis or immune mediated disease
- Joint may be fused
Define ‘osteochondrosis’
- Disease of the outgrowth plate of cartilage, focal or multifocal failure of ossification. Involves the metaphyseal growth plate (accumulation of viable hypertrophic chondrocytes) and articular-epiphyseal complex (necrosis of epiphyseal cartilage)
- Basic lesion formed by failure of cartilage to become mineralised and replaced by bone
Describe osteochondrosis latens
Initial lesions due to necrosis of blood vessels in the epiphyseal cartilage of the articular epiphyseal complex. Overlying cartilage and underlying subchondral bone are not affected (microscopic lesion)
Describe osteochondrosis manifesta
- Grossly visible area of necrotic epiphyseal cartilage
- Lesion is highly vulnerable to further damage
What is the origin of synovial fluid?
From the synovium
Describe the structure of a synovial membrane
- Not an epithelium as it doesn’t have a BM. Contains specialised CT which as a secretory component
- Intima - 2-4 cells deep, Type A macrophages, Type B fibroblasts
- Subintima - supportive tissue of loose CT and fatty tissue, capillaries which run just beneath the intima
What are the components of synovial fluid?
- plasma dialysate
- small number of cells - lymphocytes, monocytes, neutrophils
What is the function of synovial fluid?
- Lubrication
* fluid squeezed out onto articular cartilage- Nutrient transport
- articular cartilage is avascular
- most AC is in close apposition with synovial membrane
- synovial fluid provides it with nutrition
What are the indications for arthrocentesis?
- Joint effusion
- If suspect and infection (sudden onset, pyrexia, pain)
- Multiple joints are affected
- Pyrexia of unknown origin
What are the general principles of arthrocentesis?
- GA or sedation
- Prep - hair clip, aseptic skin prep, ‘no touch’ or surgical gloves
- Needle size - 23g 0.6mm (blue) or 21g 0.8mm (green)
- Gentle flexion and extension can help aspiration
What are the explanations for finding blood in a joint tap?
- Latrogenic - distinctly defined area, sharp border
- Pathogenic - homogenous appearance
What volume of fluid should there be present in dogs and cats normally?
- Dogs - 0.1-1.0ml
- Cats - 0ml can be normal
- Volume increased in most diseased joints
What appearance should synovial fluid have?
- Normal - egg white, won’t clot but will gel
- Degenerative disease - clear to pale yellow
- Inflammatory disease - increased turbidity
- Septic - dark, bloody, smell bad
- Viscosity is subjective, shouldn’t be watery. Inflammatory joint disease will be reduced
How can synovial fluid be analysed?
- Cell counts - microscope or haematology analyser (hyalluronidase can be used to prepare samples for machine counts to reduce viscosity)
- Cytology - examine background, assess RBC no., platelet count, differential count (WBC), assess NCC
What signs will be present in a synovial fluid sample that would indicate haemorrhage?
- Streaks of blood at time of collection
- Acute haemartrosis - differentials similar to peripheral blood, platelets will be seen
- Longstanding haemorrhage - no platelets, increased WBC, erythrophagocytosis, haematiodin crystals in macrophages (golden crystals in cytosol), haemosiderin deposits in macrophages (RBC breakdown products)
