MUSCULOSKELETAL - BONE INJURY AND INFLAMMATION

• Friable necrotic bone shown by scratching the bone with a sharp object

• Pale discolored bone

• Lack of visible osteocytes

• Lacunae are empty

• Lack of bone marrow cells

BONE NECROSIS

• Due to ischemia or necrosis

• As long as the blood circulation is not completely compromised, necrotic bone is reabsorbed by osteoclastic activity

Aseptic Necrosis

• Woven bone joins and replaces old fractured spicule with mature lamellar bone

• Woven bone is less compacted, and collagen fibers are in a crisscross fashion

FRACTURED BONE SPICULE

Necrosis → Resorption → Woven Bone → Mature Bone

FRACTURED BONE SPICULE

• Large necrosis with repair leaving a visible scar

• Enlargement of rib at callus site

  • Passing through the birth canal in neonates

  • Acquired trauma (kicking or hit by car)

CALLUS FORMATION

Necrosis → Resorption → Woven Bone → Callus

CALLUS FORMATION

Progression:

Healing fracture starts with hemorrhage and hematoma → gets invaded by fibrous connective tissue → forms a temporary fibrous bridge between fracture edges → infiltrated with osteoblasts laying osteoid to form woven bone → reabsorbed and replaced by mature lamellar bone forming a secondary callus

CALLUS FORMATION

Formed when a large piece of necrotic bone is isolated from circulation and cannot be reached by blood cells and osteoclasts. Involcrum surrounds the dead bone

BONE SEQUESTRUM

Band of CT that surrounds sequestered dead bone

Involcrum

• Extensive osteophyte proliferation

• Abnormal remodeling with growth of bone nodules (osteophytes)

• Severe cases: osteophytes cover large proportion of bone and obliterate entire epiphysis

CHRONIC PROLIFERATIVE OSTEOMYELITIS

• Affected bone is pale with purulent exudate

• Osteomyelitis due to bacteremia

• Exudate and dissolution of bone below the growth cartilage

• Aspirate reveals large number of neutrophils with bacteria

• Neutrophils induce lysis resulting in fractures

SUPPURATIVE OSTEOMYELITIS

Common site of septic osteomyelitis in farm animals

Metaphyseal blood vessels in the growth plate

Neutrophils induce lysis resulting in fractures

Septic myelitis

• Large clusters of leukocytes in the bone

• Bone infection is common sequel to neonatal bacteremia

• Bone infections are difficult to treat

Osteomyelitis

Trabecula reabsorbed by osteoclasts and replaced by fibrous tissue as first step of repair

CHRONIC OSTEOMYELITIS/FIBROSIS

• Swelling of the jaw

• Ulcerated skin with a fistula

• Macerated jaw reveals exuberant exostosis

• Unilateral pyogranulomatous inflammation

• Bone necrosis and exostosis persist with continued bone necrosis and repair

ACTINOMYCOSIS - LUMPY JAW

• Soft tissue trauma contaminated with Actinomyces bovis

ACTINOMYCOSIS - LUMPY JAW

• Common in cattle and pigs (unable to stand)

• Large vertebral abscess with compression of spinal cord leading to vertebral fractures

• Tail bite results in bacterial emboli lodging in vertebral bodies (spondylitis) → inflammation reaching the meninges → meningitis

SPINAL ABSCESS (SPONDYLITIS)

• Lytic lesion in the vertebra

• Bacterial emboli lodge in the epiphyseal vessels of long bones

• 70% of foals with joint-ill also have septic osteomyelitis

• Inflammation in the SC causes meningitis

• Omphalophlebitis - common source of bacterial embolism in neonates

CHRONIC OSTEOMYELITIS - Rhodococcus equi

Common source of bacterial embolism in neonates

Omphalophlebitis

• Osteomyelitis with exuberant exostosis

• Lytic lesion in the leg of a dog with weight loss, cough, and lameness history as well as ulcerated skin lesions and disseminated lymphadenomegaly

CHRONIC MYCOTIC OSTEOMYELITIS (BLASTOMYCOSIS)

• Type of mycoses that cause chronic disseminated osteomyelitis as part of multi-systemic infection involving multiple organs

• Dimorphic fungi disseminate through the blood and lymphatic system to bones

  • Blastomyces dermatitides

  • Coccidiodes immitis

  • Cryptococcus neoformans

CHRONIC MYCOTIC OSTEOMYELITIS (BLASTOMYCOSIS)

Positive PAS stain  in yeast wall inside multinucleated giant cell due to high CHO

CHRONIC MYCOTIC OSTEOMYELITIS (BLASTOMYCOSIS)

• Extensive proliferation of osteophytes in the entire appendicular skeleton

• Space-occupying mass in the thorax, like a large abscess or tumor, causes pulmonary hypertension, inducing vascular anastomosis allowing megakaryocytes to reach periosteal bone

• Severe hyperostosis along the periosteal surface

PULMONARY HYPERTROPHIC OSTEOPATHY

HUMAN Case of PULMONARY HYPERTROPHIC OSTEOPATHY

Marie’s Disease

• Localized rare disease in dogs of unknown etiology resulting in periosteal proliferation of the mandible and cranial bones

• Lesions only affect the head (e.g., tympanic bullae), bilaterally symmetrical, and self-limiting

CRANIOMANDIBULAR OSTEOPATHY

• Painful swelling and enlarged temporal-maxillary region

• Grossly and radiographically, there are proliferative changes in the temporal and maxillary bones causing bony bridging on the periosteal surface

CRANIOMANDIBULAR OSTEOPATHY

other term for CRANIOMANDIBULAR OSTEOPATHY

Lion’s Jaw

Common in

• West Highland White

• Scottish Terriers

CRANIOMANDIBULAR OSTEOPATHY (Lion’s Jaw)