Musculoskeletal Pathology - Bone Flashcards
Examination of bone - methods
◼ Diagnostic imaging
<><>
◼ Macroscopic
> Debone and saw
> ‘bug’ box (sarcophagus beetles)
<><>
◼ Histological
> Requires demineralization (aka decalcification) and thus longer processing time.
bone anatomy from middle to end
diaphysis
metaphysis
physis (gowth plate)
epiphysis
articular - epiphyseal cartilage (AEC) complex
cortical vs trabecular bone
Cortical bone is dense and solid and surrounds the marrow space, whereas trabecular bone is composed of a honeycomb-like network of trabecular plates and rods interspersed in the bone marrow compartment.
subchondral bone
Subchondral bone refers to the bony layer beneath the hyaline cartilage and cement line
lamellar bone
Histology:
Lamellar bone is a mature bone that results from the remodeling of immature woven bone
Histology of Bone: Bone formation mechanisms
Endochondral ossification
◼ Growth plates
> Metaphyseal = physis
> Epiphyseal = AEC
<><><>
Intramembranous ossification
◼ Any membrane
◼ Periosteum mainly
Histology of Bone; constituents of bone - cells and matrix
Cells of bone
◼ Bone lining cells
◼ Osteocytes
◼ Osteoblasts
◼ Osteoclasts
<><>
Matrix
◼ Mineral
◼ Osteoid
Bone lining cells - where are they, what do they do?
◼ Line the endosteal surface forming a functional barrier between interstitial fluid and bone.
◼ Activate bone formation and resorption
◼ Source of osteoblasts
◼ Haematopoietic functions
Osteoblasts - what do they do?
◼ Form bone on the surface of bone
◼ Respond to bone lining cells, osteocytes and parathyroid hormone
◼ Stimulate osteoclasts
Osteocytes - where do they come from, where are they found? what do they do?
◼ Derived from osteoblasts
◼ Are surrounded by bone and are in lacunae
◼ Connect to each other with cytoplasmic processes in bone channels.
◼ Couple bone formation and resorption
Osteoclasts - what are they, what do they do? inhibition?
◼ Monocyte–macrophage lineage (excavators)
◼ Respond to parathyroid hormone, and paracrine inflammatory cytokines
◼ Inhibited by calcitonin
Histology: Bone; matrix - what is it? components?
Bone Matrix (osteoid)
◼ Type 1 collagen
◼ Ground substance
> Water
> Proteins
> Proteoglycans
> Glycosoaminoglycans (GAG)
<><>
◼ Mineral
lamellar bone vs woven bone? organization?
Lamellar bone
◼ Collagen arranged in lamellae
◼ Takes time to form
◼ Examples
> Trabecular bone
> Cortical bone (arranged in osteons)
<><>
Woven bone
◼ Rapidly produced new bone
◼ Reactive bone
◼ Periosteal or endosteal new bone
what is bone remodelling?
◼ Gradual replacement of bone
◼ Repairs microcracks from bone strain/fatique. Microcracks lead to microfractures
◼ Results in production of lamellar bone.
> not to be confused with modelling! (eg. fracture repair is modelling)
what is bone modelling?
◼ Change in size and shape of bone with use - implies quicker change
◼ Mechanical forces change bone
> fluid movement through bone channels,
> piezoelectrical forces.
> Race horses running clockwise have larger bones of left side!
Case Example:
‘Powder’, Great Pyrenees, 5 yr old
◼ Sudden onset of forelimb lameness
◼ Pain of distal radius.
◼ Radiographical osteolysis and new bone formation.
Ddx?
◼ Osteosarcoma
◼ Osteomyelitis
◼ Osteoarthritis (degenerative joint disease)
◼ Other
Biopsy of Bone: Best technique
◼ Do not biopsy if referring for limb sparing surgery
<><>
◼ Bone biopsy instrument (Jamshidi biopsy needle, Michelle’s
trephine)
◼ Deep biopsies
> Aggressive – through one cortex to other
> 3 different sites
> Radiograph when finished to ensure sample is representative
◼ Increases probability of successful diagnosis.
Reactions of bone to injury
◼ Replay of bone formation
> Endochondral ossification
> Membranous bone formation
◼ Archetype is a fracture
Reaction of Bone to Injury: Fracture repair
- primary vs secondary
Primary fracture repair
> when two ends of bones are held together > fixation
◼ Osteoclastic removal and bone formation to reform osteons
◼ Occurs with bone forced on bone – surgical fixation
> this fracture heals by remodelling > the normal physiologic process, as though they are repairing a normal microfracture
<><>
Secondary fracture repair
◼ Hematoma
> beneath periosteum > periosteum lifts away from bone > fracture, produces new bone
◼ Reparative phase and Callus formation
> Fibrous callus > granulation tissue that matures
> Primary callus (woven bone) > removed over time, and replaced with…
> Secondary callus (lamellar bone)
◼ Modelling and remodelling > ‘clean up’, to look the way it was before
Reaction of Bone to Injury: Blood flow, Pressure, Movement relationship and resulting tissues
◼ Blood + pressure – movement = bone
◼ Pressure – blood – movement = cartilage
◼ Movement = fibrous tissue
Bone lesions and diseases broad categories
- Metabolic bone disease
- Bone necrosis
- Inflammation
Metabolic bone disease
◼ Osteoporosis
◼ Rickets (young) and osteomalacia (adult)
> Vit D deficiency
> Phosphorous deficiency
◼ Fibrous osteodystrophy (FOD, ODF) > bone replaced by fibrous tissue
> Excess phosphorous
> Renal failure
Osteoporosis - causes
Humans
◼ Overactive osteoclasts
<><>
Animals
◼ Disuse atrophy
◼ Senile atrophy
◼ Starvation/Malnutrition > mostly production animals > lack of protein in particular
◼ Calcium deficiency
Rickets and osteomalacia
- what age do they affect?
- how it arises
◼ Rickets – young
◼ Osteomalacia - adult
<><>
◼ Bone fails to mineralize, osteoid forms but doesn’t mineralize
◼ Hypovitaminosis D (rare in animals > they produce their own vitamin D)
◼ Phosphorous deficiency (more commonly)
Fibrous osteodystrophy
- when do we see it? types?
Primary hyperparathyroidism
◼ Neoplasia
<><>
Nutritional hyperparathyroidism
◼ Phosphorous excess + calcium deficiency
> Dogs and cats fed meat only diet (BARF)
> Horses on bran diet
> Pigs on grain diet
<><>
Renal hyperparathyroidism
◼ Chronic renal disease
◼ hyperphosphatemia and vitamin D deficiency (needed to absorb Ca from intestine) and resistance
Bone Disease: Diseases with dead bone
- Sequestrum
- Necrosis of femoral neck
- Marrow necrosis
Sequestrum in the bone - what is it? how it arises?
dead tissue with liquid surround
<><>
Secondary to a primary problem
◼ Trauma and or fracture
◼ Lymphoma
◼ Osteomyelitis
Necrosis of femoral head
- how it arises?
blood supply is through the neck, or synovial membrane
> if we get fracture of the neck, the head dies
<><><><>
◼ Femoral neck fracture
> Trauma
◼ Avascular necrosis of femoral head (Legg Perthes disease, small dogs) > young dogs (<18 months)
◼ Physeal dysplasia with slipped capital epiphysis (cats) (overweight neutered males > slip their physis)
bone marrow necrosis often due to what condition
Lymphoma
Inflammation of Bone - called what?
Osteitis
Osteomyelitis - if it is in the marrow
osteitis vs periostitis vs osteomyelitis definitions?
- where we see bone inflammation in young vs older animals? origins?
◼ Osteitis – inflammation of bone
◼ Periostitis – inflammation of periosteum
◼ Osteomyelitis – inflammation of medulla of bone.
<><>
Young - Metaphyseal region.
◼ Bacteremia, localisation, proliferation, neutrophilic inflammation, bone lysis and osteomyelitis
<><>
Older – localized
◼ Fractures
◼ Local injection of bacteria – lumpy jaw
Osteomyelitis of metaphysis - can lead to what?
Osteomyelitis of metaphysis > formation of sequestrum
