Pathophysiology of osteomyelitis

Question 1

Infectious inflammation of bone

Answer 1

inflammation often associated with degeneration, necrosis, lysis and attempts at repair of bone due to infection.

Question 2

Causes of infectious inflammation of bone

Answer 2

Bacteria–sepsis in neonatal; traumatically inoculated at all ages (suppurative osteomyelitis)

Fungi–coccidiodomycosis (pyogranulomatous osteomyelitis)

Virus–not inflammation but canine distemper virus can kill osteoclasts

Question 3

Mechanisms of infectious inflammation of bone

Answer 3

Agent: toxins, lytic enzyme, proteins that “activate” host cells
Host: humoral factors, inflammatory cells, and degenerate, necrotic, reactive structural cells
Structural cells

Question 4

Structural cells of infectious inflammation of bone

Answer 4

osteoclasts: matrix lysis (acids and enzymes)
osteoblasts: reactive woven bone formation and/or lack of bone formation
fibroblasts: scar tissue, mechanically unstable

Question 5

Pathogenesis of infectious inflammation of bone

Answer 5

localization of embolic bacteria at growth plates in bone of young animals

Question 6

Physis/AE complex appear to favor bacterial colonization due to:

Answer 6

• -slow and turbulent flow in capillary loops
• -fenestrated endothelial cells
• -low resident histocyte population in region
• -no anastomosis-ease of thrombosis
• -selective receptors in cartilage/bone matrix for the bacteria (and possibly receptors for bacteria in the endothelium of the capillaries at these locations)

Question 7

Sequestrum formation

Answer 7

squestrum is a focus of coagulation necrosis that is separated from adjacent normal tissue by a reactive wall

Question 8

Non-infectious inflammation of bone

Answer 8

hypertrophic osteodystrophy (metaphyseal osteopathy)--this is an inflammatory lesion
seen in growing large breed dogs

Question 9

Characteristics of hypertrophic osteodystrophy (metaphyseal osteopathy)

Answer 9

metaphyseal suppuration, necrosis and infractions (suppurative metaphysitis in many long bones with fracturing of the primary trabeculae causing radiolucent line in parallel to growth plate)

Question 10

Cause of hypertrophic osteodystrophy (metaphyseal osteopathy)

Answer 10

causes unknown–the evidence that this is due to bacteria is very weak but many treat with antibiotics as well as treat for inflammation and pain relief.

Most likely sterile and immune mediated

Question 11

Involucrum

Answer 11

reactive wall of a sequestrumthat could be reactive fibrous tissue or, in the skeletal system, reactive bone

Question 12

causes of a sequestrum: inflammation

Answer 12

predisposing factor for development of coagulation necrosis in bone because pressure of exudate in a rigidly confined space can cause blood vessels to collapse resulting in coagulation necrosis

Question 13

causes of sequestrum: bacterial toxins

Answer 13

toxins that kill bone cells and prevent lysis of the dead bone.
Bacteria can stimulate lytic exudates to form at junction between viable and dead tissue separating and isolating dead bone fragment from viable tissue

Question 14

other ways of sequestrum formation

Answer 14

infected bone to fracture loose forming a fragment or for a fracture fragment to become secondarily infected

Question 15

Eosinophillic panosteitis

Answer 15

neither eosinophilis or inflammatory
growing dogs
diaphyseal
periosteal and endocortical woven bone formation. Endocortical lesion has significant reactive fibrosis
sometimes marked periosteal reactive woven bone formation

Question 16

Necrosis of Bone (inflammatory)

Answer 16

inflammation can cause pressure within the marrow space and result in ischemic bone necrosis in addition to damage done by the inflammation directly.
(Also see sequestrum)

Question 17

Necrosis of bone (sterile/noninflammatory)

Answer 17

coagulation necrosis of cells (bone cells and marrow) with retention of matrix.
cellular response dependent on cause and blood flow

Question 18

Dead bone resorption due to vascularization

IMPORTANT SLIDE

Answer 18

if dead bone becomes vascularized there commonly will be formation of new bone on top of dead bone prior to resorbing the dead bone

Question 19

Revascularization of dead bone

IMPORTANT SLIDE

Answer 19

can bring calcium (in solution in blood) to the site and this calcium can be precipitated (dystrophic mineralization) in the lacunae of dead osteocytes

Question 20

Cause of increased radio-opacity sometimes seen with bone necrosis

Answer 20

formation of new bone on top of dead bone and this mineralization of osteocyte lacunae

Question 21

Pathogenesis of sterile noninflammatory bone necrosis

Answer 21

1) Idiopathic avascualar–especially in growing animals (increased pressure in the joint causing occlusion of small epiphyseal vessels)–small breed dogs
2) trauma with disruption of blood supply
3) steroid/ radiation/ hyperbaric–in adult humans

Question 22

Features of bone that favor bacterial colonization

Answer 22

capillary loops into at the physis of bone have slow turbulent flow

Question 23

characteristic of embolism at physis

Answer 23

Red rim of reaction=separation between healthy bone and infected area