Response of bone to injury

Which bone cell is primarily responsible for bone resorption?

osteoclasts

What are growth arrest lines?

areas where growth was temporarily disrupted by debilitating disease, malnutrition, etc. growth plate becomes narrow, metaphyseal face of the plate can be sealed by a layer of bone as a result of transverse trabeculation, immediately subjacent to the growth plate. Once theres bone growth again, a growth arrest line forms parallel to the physis

What is growth retardation lattice?

acquired impairment of osteoclastic resorption of bone within the primary spongiosa; canine distemper, bovine viral diarrhea, lead poisoning “lead line”

What is focal damage or closure of growth plate?

premature closure of the distal ulnar physis (particularly susceptible to trauma, presumably because of its conical shape) or focal injury to growth plate (most common in distal radius in dogs) can cause angular limb deformities (bent-leg)

What can also cause focal damage or closure of growth plate and cause angular limb deformity?

retained endochondral cartilage core can be clinically silent but may interfere with longitudinal growth of the ulna

What is wolff’s law?

ability of bone to change its shape and size (modeling) to accommodate altered mechanical use

Bone changes its shape and mass in response to what?

mechanical forces

Where is formation of bone favored?

sites of compression

Where is resorption of bone favored?

sites of tension

What are the effects of mechanical forces during normal growing animal?

increase thickness of cortical bone and increase density of metaphyseal trabecular bone

What are the effects of mechanical forces on normal adult animal?

conserves amount of bone already present by decreasing remodeling

What are the effects of disuse of bone in a growing animal?

reduced accumulation of cortical (compact) bone, increased loss of metaphyseal trabecular bone, enlargement of marrow cavity

What are the effects of disuse of bone in an adult animal?

decreased outside diameter and cross-sectional area of bone, thinner cortex and reduced density or metaphyseal trabecular bone; osteopenia, osteoporosis

What are the main effects of disuse to bone?

retarded dense bone in cortex, increased diameter of marrow cavity, reduced external diameter

What is lamellar bone?

deposited in an ordered, layered manner; all normal bone is lamellar (except in the fetus); comprises cortical and trabecular (cancellous) bone

What is woven bone?

fetal bone; initial bone produced during growth and following bone injury or pathological conditions, collagen fibers laid down in disorganized/irregular pattern, later removed by osteoclasts and replaced by lamellar bone

What is periosteal new bone formation?

bone deposited rapidly is woven rather than lamellar, injured periosteum often response by forming bone

What is traumatic growth plate damage?

generally at hypertrophic zone of the growth plate, growth plate is weakest structure in the ends of long bones, fastest growth plates are most susceptible to injury (distal radial physis)

What is a slipped epiphysis (epiphysiolysis)?

complete separation through growth plate

What is a salter-harris fracture?

fractures involving the physis in immature animals

What are the common versus uncommon salter-harris fractures?

common with types III, IV, and V while its uncommon with types I and II

What is the overall most common type of salter-harris fracture?

type II

With what types does the salter-harris fracture line not cross the growth plate?

types I and II

With what types does the salter-harris fracture line cross the growth plate?

type III and IV

What is primary intention?

fractured ends in tight apposition (no to minimal gap present), no endochondral ossification, no cartilage formation, direct osteonal bridging of the fracture site

What is secondary intention?

(usual method) when there is a gap to fill

What are the properties of osteogenic mesenchyme progression to bone?

under normal developmental (mechanical) conditions and stable healing processes

What are the properties of osteogenic mesenchyme progression to fibrous tissue?

increased mobility, movement, instability (placed under tension)

What are the properties of osteogenic mesenchyme progression to cartilage?

proliferating in an unstable and hypoxic environment

What factors complicate repair?

infections (bacterial), excess mobility, malnutrition, poor vascularity, excessive distance between fracture ends, loss of periosteum results in decreased blood supply and lack of precursor cells for one formation, communication with large amounts of dead bone (sequestra)

What is an unstable fracture?

fractured edges are improperly aligned with excessive distance between the fragments

What is a nonunion fracture?

fracture site that does not deal whether it be due to soft tissue in fracture, excessive motion, infection, or poor blood supply; has persistence of granulation tissue that does not form bone, may lead to pseudoarthrosis

What are the steps of simple secondary intention fracture repair?

formation of a blood clot thats invaded by fibroblasts, endothelial cells, and macrophages. Production of primary callus is followed by remodeling