Lecture 11 - Bone pathology

What is the function of osteoblasts? How is it measured?

-Line bone surfaces

-Make osteoid and initiate mineralization

-Measured indirectly through ALP

What is the function of osteocytes? Where are they found?

-Mature osteoblasts surrounded by mineralized bone

-Found in lacunae

What are osteoclasts?

-Cause bone resorption

What is the bone matrix composed of?

Osteoid and bone mineral (hydroxyapatite crystals)

What is osteoid composed of?

Type I collagen and ground substance

What are the two types of bone?

-Cortical bone (dense and strong, surrounds spongy bone)

-Trabecular/spongy bone (found in marrow cavity)

What is Wolff’s law?

-Bone is deposited in sites where it’s needed and resorbed where it’s not

-Allows for remodeling based on mechanical demands

What is the weakest part of bone in young/growing animals?

Growth plate (distal radial physis most commonly affected)

What is a slipped epiphysis/epiphysiolysis?

Complete separation of the growth plate

What causes angular limb deformities?

Growth plate damage is only on one side, other side continues growing

What is a valgus deformity?

Lateral deviation of the limb distal to affected growth plate

What is a varus deformity?

Medial deviation of the limb

What is codman’s triangle? What diseases is it found with?

-Pyramid shaped region of new bone formation

-Osteosarcoma and osteomyelitis

What is exostoses?

Localized outgrowth of new bone beneath periosteum

What are the two main types of bone fractures?

1. Traumatic - normal bone broken by excessive force

2. Pathological - abnormal bone broken by minimum trauma

What is a salter harris fracture? What are the 5 types? Which ones heal with few to no complications?

-Fracture of the growth plate

-Type I: through growth plate (heal w/ no complications)

• S (Separated)

-Type II: through growth plate and metaphysis (heal w/ few complications)

• A (Above GP)

-Type III: through growth plate and epiphysis

• L (beLow GP)

-Type IV: through growth plate, metaphysis and epiphysis

• T (Through GP)

-Type V: crushed growth plate

• ER (ERasure of GP)

What is a comminuted fracture?

Bone shattered into multiple small fragments

What is an avulsed fracture?

Fracture caused by traction of a ligament at point of insertion onto bone

What is a greenstick fracture?

One side of the cortex is broken, no separation or displacement

What is a transverse/spiral/oblique fracture?

Orientation of fracture line

What is a compression/impaction fracture?

Bone fragments are pressed together

What is a displacement fracture?

Orientation of distal fracture compared to rest of bone

What are the four processes of fracture repair? How long does each last?

1. Inflammation (days)

2. Soft callus (weeks)

3. Hard callus (months)

4. Remodeling (months to years)

What is a soft callus?

-Growth factors stimulate mesenchymal cells to form granulation tissue and cartilage

-Anchors fractured bone ends

What is a hard callus?

Disorganized meshwork of woven bone forming from a soft callus

What is sequestrum?

Fragment of bone becomes separated from blood supply and dies but body is unable to remove

What is pseudoarthrosis? What is this a result of?

Formation of false joint caused from bone healing with fibrous tissue

What is osteomyelitis?

Infection of the bone

What is osteopetrosis? What does it cause?

-Increased bone density due to failure of bone resorption by osteoclasts

-Causes increased amount of trabecular bone and reduced cortical bone causing pathological fractures

-Insufficient bone marrow space causes reduced hematopoiesis

What causes osteogenesis imperfect? What does it cause?

-Mutations in collagen 1 formation (major collagen type)

-Causes increased bone fragility (including teeth), joint laxity, and blue sclera

What causes chondrodysplasia? What does it usually result in?

-Abnormality in growth cartilage

-disproportionate dwarfism (short legged with normal sized heads)

What is spider lamb syndrome? What species?

Condrodysplasia in sheep

What causes spider lamb syndrome? What does it lead to?

-Point mutation in fibroblast growth factor receptor 3

-Causes uninhibited chondrocyte growth and unusually long legs

What are the four main metabolic bone diseases?

1. Ricketts

2. Osteomalacia

3. Fibrous osteodystrophy

4. Osteopenia/osteoporosis

What is osteoporosis? What are potential causes?

-Decreased bone thickness (normal quality, reduced quantity)

-Calcium deficiency, starvation/malnutrition, physical inactivity, hypogonadism, hyperadrenocorticism, age

What does osteoporosis look like grossly? What may be the first evidence of osteoporosis?

-Grossly: decreased cancellous bone and formation of reinforcement trabeculae

-First sign is usually bone fracture without excessive trauma

What is the green arrow pointing to?

Sequestrum

What is this bone showing?

Osteopetrosis

What is wrong with this bone? What are the arrows pointing to?

-Osteoporosis

-Reinforcement trabeculae

What is the difference between rickets and osteomalacia?

Rickets usually occurs in young animals while osteomalacia occurs in adults

What are rickets/osteomalacia?

Abnormal endochondral ossification causing defective bone formation

What is the pathogenesis of rickets/osteomalacia?

-Dietary Vit D/Phos deficiency causing failure of mineralization

-Chronic renal disease, GI malabsorption, hereditary

What are the clinical signs of rickets/osteomalacia?

Pain, pathologic fractures, stiff and lame, reluctance to stand

What are the gross lesions found with rickets?

-Most common in sites of rapid growth (metaphyseal and epiphyseal regions, CCJ)

-Rachitic rosary - abnormally enlarged CCJ

What are the gross lesions found with osteomalacia?

Weak bones, increased fragility

What is fibrous osteodystrophy (rubber jaw)?

-Extensive bone resorption and proliferation of fibrous tissue causing poorly mineralized and immature bone

-Will see weak, flexible bones

What are the main causes of fibrous osteodystrophy?

-Primary hyperparathyroidism (excessive PTH → increased bone resorption)

-Secondary hyperparathyroidism - renal (renal failure) or nutritional (Ca or Vit D deficiency, excess phosphorus)

-Pseudohyperparathyroidism (neoplasms producing PTH)

What are common signs of fibrous osteodystrophy?

-Pliable jaw with protruding tongue

-Bilateral and symmetrical maxillary/facial swelling

What is this picture showing?

Rickets

What is legg-calve-perthes disease? What species is it common in?

-Avascular necrosis of femoral head

-Small breed dogs

What causes legg-calve-perthes disease? What is the pathogenesis?

-Autosomal recessive

-Idiopathic disruption of capital epiphysis leading to ischemic necrosis

What is this picture showing?

Legg-Calve-Perthes disease

What is osteitis/osteomyelitis?

Inflammation of the bone and medullary cavity

What is periostitis?

Inflammation of the periosteum and bone

What is physitis?

Inflammation at the physis of the bone

What is diskopondylitis?

Inflammation of the vertebral discs and adjacent vertebrae

What are three routes of infection of bacterial osteomyelitis? Which one is common in young animals?

1. Hematogenous (young animals, especially horses and ruminants)

2. Local extension

3. Implantation

Where is a major location for bacterial osteomyelitis in young animals?

Physis

How does bacterial osteomyelitis occur with local extension?

Overlying inflammation extends into bone

How does implantation lead to bacterial osteomyelitis?

Penetrating wound into bone

What is the lesion seen with bacterial osteomyelitis?

Suppurative to necrosuppurative inflammation

What bacteria causes lumpy jaw? What animals?

-Actinomyces bovis

-Cattle

What bone lesions are seen with coccidioides immitis? Where is the predilection site?

-Often subclinical but may see pyogranulomatous inflammation

-Distal diaphysis of long bones

What is the route of infection of cryptococcus? What does this present as?

-Nasal, nasal cavity, lungs

-Swelling on the bridge of the nose (roman nose)

What is the route of infection of blastomyces dermatitidis? What is the most common presentation? What other organs can also be affected?

-Respiratory (inhalation)

-Pneumonia is most common

-Bone, eyes, lymph nodes, skin

What is metaphyseal osteopathy (hypertrophic osteodystrophy)? What animals is it commonly seen in?

-Aseptic osteomyelitis in young, large breed dogs

-Commonly resolves on its own

What are the clinical signs seen with metaphyseal osteopathy? What are the common sites?

-Fever, anorexia, malaise, lameness, swelling and pain

-Loves distal radius and ulna

What will you see on rads with metaphyseal osteopathy (hypertrophic osteodystrophy)? Grossly? On histo?

-Rads: Early lesions with alternating radiodense and radiolucent zones

-Gross: Infractions within medullary bone, bilaterally symmetrical swelling

-Histo: Intratrabecular suppurative inflammation with necrosis

What organism is this slide showing?

Cryptococcus (soap bubble appearance)

What organism is this slide showing?

Blastomyces dermatitidis (broad, blue based budding)

What are clinical signs seen with canine panosteitis? What kind of dogs does it usually affect?

-Mild to severe lameness, usually resolve after several months

-Usually affects young large and giant breed dogs

What lesions are found on radiographs with canine panosteitis?

Diaphyses of one or more long bones will have increased density in nutrient foramen

What species is hypertrophic osteopathy common in? What is the common lesion found? What is it usually found secondary to?

-Dogs

-Progressive, bilateral new bone formation in diaphyseal and metaphyseal regions

-Usually occurs secondary to space occupying lesion

Where is a bone cyst found? What is found on rads?

-Subchondral, simple, or aneurysmal

-Rads: well-demarcated lucent areas without evidence of aggressive growth

What are 7 primary neoplastic bone lesions? Which is most common?

1. Ossifying fibroma

2. Fibrosarcoma

3. Hemangiosarcoma

4. Chondroma

5. Chondrosarcoma

6. Osteoma

7. Osteosarcoma (most common)

What are three secondary neoplastic lesions found in bone?

1. Carcinomas

2. Sarcomas

3. Round cell tumors

What are three benign neoplastic lesions commonly found in bone?

1. Ossifying fibroma

2. Chondroma

3. Osteoma

What are 4 malignant neoplastic lesions of bone?

1. Osteosarcoma

2. Fibrosarcoma

3. Chondrosarcoma

4. Metastatic tumors

What is the site predilection of osteosarcoma in dogs?

-Away from the elbow: proximal humerus and distal radius

-Towards the knee: distal femur and proximal tibia

How do you diagnose osteosarcoma?

-Based on production of osteoid by neoplastic cells

-Do not cross joints

What is a fibrosarcoma? What is a common characteristic?

-Malignant neoplasma of fibroblasts

-No cartilage or osteoid production

What is a chondroma?

Benign term for cartilage lesions

What are the characteristics of a chondrosarcoma? What species is it most common in? What bones does it usually affect?

-Malignant mesenchymal tumors producing cartilaginous or fibrillar matrix (not osteoid)

-Most common in dogs

-Involves flat bones