Lecture 55: Skeletal Disease Processes 2

What is a benign, bony growth projecting outward from bone- typically originating at the periosteum?

exostosis

What is a bony growth at the margins of joints?

osteophyte

What is ossification of a tendon or ligament (forming abnormal bony projections) at the point of its insertion into the bone?

enthesophyte

What is uniform thickening of bone along the periosteal surface?

hyperostosis

What is a bony growth within the medullary cavity that can result in obliteration of the medullary cavity?

enostosis

What is hypertrophic osteopathy?

Progressive, often bilateral, periosteal, new bone formation in the diaphyseal and metaphyseal regions, particularly of the distal limbs of dogs (most common) occurring as a secondary reaction to a primary space occupying lesion (usually intrathoracic neoplasm)

What has occurred in this canine tibia and fibula? note the dog also had an intrathoracic mass.

hypertrophic osteopathy

Where are osteochondromas located and in who?

adjacent to physes in young dogs and horses (mass usually stops growing when animal reaches skeletal maturity)

Where do osteochondromas NOT develop in dogs and horses?

on bones of intramembranous origins (ex. skull)

What makes osteochondromas in cats different?

they develop in mature animals and tend to be in flat bones instead of long bones

What is affecting this canine distal femoral metaphysis?

osteochondroma

What is this?

osteochondroma

What are multilobular tumors of bone?

single, nodular, smooth-contoured, immovable masses that occur on flat bones of the skull and hard palate in middle aged/older dogs and cats

What is this mass on this canine skull? note the mass is firm and immovable.

multilobular tumor of bone

What are the benign neoplasms of hyaline cartilage often arising from flat bones of dogs, cats, and sheep? They have a blue-white appearance on cut section.

chondroma

What are chondrosarcomas?

malignant neoplasms in which the neoplastic cells produce cartilaginous matrix but not osteoid or bone

Where are chondrosarcomas usually found?

flat bones in large breed dogs and sheep

dogs: nasal bones, ribs, and pelvis

sheep: ribs and sternum

What is affecting this feline rib? note the multilobulated white to gray mass with invasive destruction and loss of normal bone architecture.

chondrosarcoma

What are ossifying fibromas?

uncommon masses in the maxillae and mandibles of horses less than a year of age and cattle that can destroy adjacent cortical trabecular bone by expansile growth

What can be seen in this equine mandible?

ossifying fibroma

What bones does osteosarcoma have a predilection for in dogs and cats?

long bones (away from elbow - towards the knee)

ribs, vertebrae, bones of head etc

What is affecting this canine distal radius? note the reactive periosteal new bone formation and the large area of hemorrhage and necrosis.

osteosarcoma

What are the common skeletal sites of metastatic neoplasms in dogs? Where do they metastasize from?

rib shafts, vertebral bodies, and humoral/femoral metaphyses

mammary gland, liver, lung, and prostate

What is the difference between traumatic and pathologic bone fractures?

traumatic: normal bone broken by excessive force

pathologic: abnormal bone broken by minimal trauma or by normal weight bearing due to weakening from underlying disease

What two factors are important for callus formation during fracture repair?

hematoma and tissue necrosis → growth factors from hematoma and inflammation with necrosis begin process to stimulation proliferation of repair tissue (woven bone)

What is the primary (soft) callus in bone repair?

disorganized meshwork of woven bone formed by fibrous connective tissue and cartilage to bridge the gap, encircle the fracture site, and stabilize the area

What is the secondary (hard) callus?

more organized and stronger bone that replaces the primary callus at the fracture site

What are the 4 major steps of fracture repair?

1. hematoma formation

2. primary (soft) callus formation

3. secondary (hard) callus formation

4. bone remodeling (months to years): resolve callus and return to normal shape and architecture

What are the major complications of fracture healing?

• inadequate blood supply

• instability: excessive movement can result in too much fibrous tissue deposition that cannot act as a template for bone formation

• infection

What is the difference between a stable and unstable fraction?

unstable: fractured edges improperly aligned, abundant external callus trying to stabilize region

stable: fractured edges adequately aligned, fracture stabilized by abundant cartilaginous callus that is replaced by bone

How can you tell if joint fluid is diseased?

normal joint fluid should be clear to pale yellow and viscous

diseased joint fluid has decreased viscosity and is more opaque

What are the common routes of infectious arthritis?

• Neonatal bacteremia secondary to omphalitis or oral-intestinal entry commonly leads to polyarthritis in lambs, calves, piglets, and foals.

• Bacteria can also reach the joint by direct inoculation (as in a puncture wound)

• Direct extension from periarticular soft tissue

• Extension from adjacent bone

What are the macroscopic lesions of septic/infection arthritis?

articular cartilage: eroded or ulcerated

synovial fluid: reduced viscosity and turbid due to neutrophils or fibrin

synovial membrane:

• acute: hyperemia or mild edema

• subacute: synovial hyperplasia

• chronic: replacement of synovial membrane with granulation tissue and fibrosis

What is affecting this carpus of a calf? note the abundant yellow fibrin within the joint and the white glistening articular cartilage.

fibrinous synovitis

What is affecting this porcine stifle joint? note the villous hypertorphy of the synovial membrane.

chronic synovitis

What type of bacterial arthritis is expected with gram negative vs gram positive bacteria?

negative: fibrinous inflammation

positive: suppurative arthritis

What is a common cause of suppurative arthritis in cattle and pigs?

trueperella pyogenes

What is a common cause of acute serofibrinous polyarthritis in cattle?

histophilus somni

What is a cause of myocplasma (fibrinous) arthritis in pigs?

mycoplasma hyorhinis in pigs between 3-10 wks of age and mycoplasma hyosynoviae in pigs older than 3 months

What is a cause of myocplasma (fibrinous) arthritis in cattle?

mycoplasma bovis

What are the commonly seen lesions in goats with CAE (viral arthritis)?

• chronic firbinous arthritis that can look like “rice grains” attached to synovium

• carpal hygromas: fluid filled sac on dorsal aspect of joints (“big knee”)

What are the lesions commonly seen in nonerosive noninfectious - immune mediated polyarthritis?

• joint pain, swelling, lameness in multiple joints

• articular cartilage normal

• synovial villous hyperplasia - minimal to marked

• synovial fluid contains neutrophils with no bacteria

What concurrent sterile immune mediated diseases are associated with nonerosive noninfectious - immune mediated polyarthritis in dogs?

steroid responsive meningitis/arteritis, neoplasia, or SLE (systemic lupus erythematosus)