Bone pathology Flashcards
Bone pathology, bone disease
What is the bone matrix composed of?
- Organic component: osteoid (90% type 1 collagen, 10% water, non-collagenous proteins, lipids, proteoglycas)
- Inorganic component of mineralised tissue (hydroxyapatite = hydroxylated calcium phosphate)
What is the consequence of the loss of inorganic matrix of the bone?
Flexible bones
What is the consequence of the loss of organic matrix of the bone?
Brittle bone
Describe the appearance and role of osteoclasts
Multinucleate, remove calcium from bone
Describe the histological appearance of osteocytes
Sit in lacunae, surrounded by matrix
Compare the ossification of long and flat bones
- Long: endochondral ossification at the metaphyseal growth plates (physes)
- Flat: intramembranous ossification, bone formed directly from he periosteum
Briefly describe the histological appearance of the physes of long bones
- Growth starts at hyaline cartilage (dark purple)
- Moves down into medullary cavity
- Then mineralises and ossifies, becomes pink
- Medullar cavity and spongy bone
What is the most common response of injured periosteum?
Formation of new bone e.g. around a fracture site
What is meant by brachygnathia?
Abnormally short jaw
What is meant by prognathia?
Abnormal projection of jaw
What is meant by kyphosis?
Dorsal curvature of the spinal column
What is meant by lordosis?
Ventral curvature of the spinal column
What is meant by scoliosis?
Lateral deviation of the spinal column
What is amelia?
Absence of limbs
What is hemimelia?
Absence of distal limb part
What is polydactyly and which animals are predisposed?
Presence of supranumerary digits, most common in cats, esp. Hemignway cats
What is adactyly?
Absence of a digit
What is syndactyly?
Fusion of digits
What causes chondrodysplasias?
Hereditary disorder of bone growth as a result of primary lesions in the growth cartilage
Which bones are affected by chondrodysplasias and why?
Long bones only, as only endochondral ossification is affected
Describe the appearance of an animal with chondrodysplasia
- Short legs and normal sized heads (dogs)
- Sheep usually normal length of legs but abnormal appearance of these (aka spider lamb syndrome)
- Also seen in cattle (bulldog cattle)
What causes osteopetrosis?
Defect in bone resorption by osteoclasts - plenty of osteoclasts but are not functioning correctly
Describe the consequences of osteopetrosis
- Bone mineral density increased, but bones are more fragile
- Not enough collagen
Which species are most commonly affected by osteopetrosis?
Cattle, sometimes horses
Give examples of congenital bone disorders
- Chondrodysplasia
- Osteopetrosis
- Osteogenesis imperfecta
- Congenital hyperostosis
- Osteochondromatosis
Give the main metabolic bone diseases
- Osteoporosis
- Rickets/osteomalacia
- Fibrous osteodystrophy
What are common causes of metabolic bone diseases?
Nutritional, toxic or endocrine
Describe the structure of bone affected by osteoporosis
Reduced bone mass, normal bone quality, well mineralised
List the main causes of osteoporosis
- Malnutrition Physical inactivity - Dietary calcium deficiency - Advanced age - Glucocorticoid excess (e.g. long term steroid administration) - Oestrogen or androgen deficiency
What are the consequences of osteoporosis?
- Brittle bones
- Fractures
Explain the difference between rickets and osteomalacia
- Failure ofmineralisation in growing skeleton (rickets) and adults (osteomalacia)
List the main causes of rickets/osteomalacia
- Calcium/vit D deficiencies
- Phosphorous deficiency
- Chronic renal disease (calcium phosphorous imbalance)
What are the consequences of rickets/osteomalacia?
- Bone deformities
- Thickening of growth plates
- Fractures
Describe the appearance of rachitic rosaries
- Occurs with rickets/osteomalacia
- Increased cartilage and fibrous connective tissue at costrochondral junctions
What is fibrous osteodystrophy?
- Similar to rickets but more severe, osteoclasts destroy bone
- Increased widespread osteoclastic resorption of bone and replacement by fibrous tissue
- Aka rubber jaw in dogs, bran disease in horses
List the causes of fibrous osteodystrophy
- Primary hyperparathyroidism
- Secondary hyperparathyroidism (renal/nutritional)
- Pseudohyperparahthyroidism (certain neoplasia)
- Lack of UV in reptiles
- Can also be seen as part of rickets
What are the consequences of fibrous osteodystrophy?
- Lameness
- Fractures
- Deformities
Compare the bone mineralisation in rickets/osteomalacia, osteoporosis and fibrous osteodystrophy
- Rickets/osteomalacia: reduced bone mineralisation (increased connective tissue)
- Osteoporosis: normal mineralisation (loss of spicules of bone, diaphysis gone)
- Fibrous osteodystrophy: fibrous replacement
List toxicities and nutritional imbalances that affect bone
- Hypervitaminosis D
- Vitamin C deficiency
- Vitamine A deficiency or toxicity
- Lead toxicity
- Fluoride toxicity
List the common causes of hypervitaminosis D
- Ingestion of calcinogenic plans e.g. Solanum sp, Trisetum flavescens
- Feed overdoses (pigs, horses)
- Ingestion of certain drugs (e.g. rodenticide such as cholecalciferol)
Describe the consequences of hypervitaminosis D regarding bone (incl. location)
- Produces hypercalcaemia an/or hyperphosphataemia and consequently metastatic mineralisation
- Typically seen in vessels, lung, kidney, stomach
Explain the effect of vitamin C deficiency on bone
- Required for collagen synthesis
- Most primates, guinea pigs and some bats cannot synthesise vit C
- Leads to osteopaenia
What are the consequences of vitamin C deficiency in bone?
- Bone fragility
- Fractures
- Metaphyseal/articular/muscular/subcutaneous haemorrhages
Why do haemorrhages occur with vitamin C deficiency?
Vessels do not have proper collagen component so they burst
What is osteitis?
Inflammation of bone
What is periostitis?
Inflammation of bone with periosteal involvement
what is osteomyelitis?
Inflammation of bone with bone marrow involvement
What are potential sources of infectious inflammatory diseases of bone?
- Haematogenous spread
- Trauma
- Inflammation of adjacent tissues e.g periodontitis (maxilla/jaw), otitis (tympanic bulla)
What are the most common bacterial causes of bone infection?
- Trueperella pyogenes
- Strep spp
- Staph spp
- E. coli
- Salmonella spp.
Describe fungi as a cause of infectious bone disease and give examples
- Rare and difficult to treat
- Coccidioides immitis
- Blastomyces dermatitidis
Give examples of viral bone disease
- Canine distemper virus
- bovine viral diarrhoea
- NB will be sterile, no inflammation
In which animals is bacterial osteomyelitis most common and why?
- Young farm animals and foals
- As extension of navel/joint ill
What is the causative agent of lumpy jaw and describe the appearance
- Actinomyces bovis
- Chronic pyogranulomatous osteomyelitis
- Lots of necrotic tissue present with neutrophils (pus)
Describe the radiographic appearance of osteomyelitis
Increased radiopacity
In which breeds and ages is metaphyseal osteopathy most common?
Usually larger breeds e.g. Danes, Labs, young dogs 2-6mo
Describe the presentation of metaphyseal osteopathy
- Lameness
- Fever
- Swollen painful metaphyses in multiple long bones
- May look like infection
- Joint tap shows fibrin, cloudy, blood, but no bacteria
What is metaphyseal osteopathy?
Suppurative sterile and fibrinous ostemyelitis of the trabecular bone of the metaphysis
Give examples of non-neoplastic proliferative bone lesions
- Hypertrophic osteopathy
- Craniomandibular osteopathy
What is hypertrophic osteopathy?
Progressive, bilateral periosteal new bone formation in the diaphyses of distal limbs
What is the underlying cause of hypertrophic osteopathy?
Usually intra-thoracic neoplasia or inflammation (some kind of space occupying lesion)
Describe the radiographic appearance of hypertrophic osteopathy
- Joints unaffected
- Excess bone on the outside of bones, no bone destruction
- New woven bone, not lamellar bone
- Metacarpal/metatarsal bones affected first, then spreads proximally
Describe craniomandibular osteopathy
- Hereditary condition of westies/scotties
- Thickening of mandibles, occipital and temporal bones
- Generally only cosmetic issue, unless affecting TMJ which will cause difficulty opening hte mouth
List the benign tumours of bone
- Osteoma
- Chrondroma
- Fibroma
List the malignant tumours of bone
- Osteosarcoma
- Chrondrosarcoma
- Firbrosarcoma
Compare the prevalence of benign vs malignant bone neoplasia
Malignant more common, benign possible esp. in cartilage e.g. chondroma
What are the disadvantages of using biopsy in the diagnosis of bone neoplasia?
- Biopsies often contain reactive periosteum
- Fractures possible
Outline the occurrence of metastatic bone tumours
- Rare
- Mainly carcinomas e.g. pulmonary carcinomas in cats can metastasise to digits (to 3rd phalanx, sloughing claws)
Which bone neoplasia fits with the following characteristics?
- Osteoblast origin
- Rare
- Primary site: flat bones
- Benign behaviour
Osteoma
Which bone neoplasia fits with the following characteristics?
- Osteoblast origin
- Common
- Primary site: metaphyses of larger appendicular bones
- Hihgly malignant with early metastasis
Osteosarcoma
Which bone neoplasia fits with the following characteristics?
- Chondrocyte/chondroblast origin
- Rare
- Primary site: flat bones
- Benign behaviour
Chondroma
Which bone neoplasia fits with the following characteristics?
- Chondrocyte/blast origin
- Relatively rare
- Primary site: ribs, sternum, nasal cavity
- Metastases not common and late
Chondrosarcoma
Which bone neoplasia fits with the following characteristics?
- Fibroblast origin
- Uncommon
- Benign behaviour
Fibroma
Which bone neoplasia fits with the following characteristics?
- Fibroblast origin
- Relatively rare
- Primary site: diaphyses of bones of appendicular skeleton
- Metastasise relatively late
Fibrosarcoma
Where do osteosarcomas most commonly arise?
Metaphyses of long bone, close to the knee, away from the elbow
Describe the metastasis of osteosarcomas
Haematogenously - even if no metastases found are probably there, just not visible
Compare the relationship of osteosarcomas and chrondosarcomas with regards to joints
- Osteosarcomas do not cross joints
- Chondrosarcomas do cross joints
What are the advantages of CT over radiography?
- CT eliminates superimposition
- Produces 3D reconstructions
- Good for areas with lots of superimposition e.g. skull, elbow
What imaging modalities are useful for MSK investigations?
- Radiography
- CT
- MRI
Scintigraphy - (Ultrasonography)
What is scintigraphy and how is it used in MSK investigations?
- Radionuclide imaging
- Increased uptake of radioisotope in regions of inflammation
- Can be used to look for damage in bone, but non-specific
What are the possible ways in which bone can respond to pathological processes?
- Increased or decreased bone mass (main change): increase or loss (osteopaenia, always bad)
- Change in shape/contour
- Change in alignment
What is sclerosis?
Localised area of increased bone density
Why might sclerosis occur?
- Response of bone to “wall off” pathology e.g. infection, cyst
- Or response to increased/abnormal loading (Wolff’s law)
What may cause the appearance of artefactual sclerosis on a radiograph?
- Superimposition of structures
- Adjacent bone loss
- Foreign material on coat
What may cause the appearance of artefactual bone loss on a radiograph?
- Gas or defect in sof tissue
- Mach lines (overlapping of 2 bones, mimics hairline fracture)
How should radiographs be used in diagnosing a musculoskeletal disease?
Cannot give a definitive diagnosis, other than a fracture, but can indicate if a lesion is aggressive or non-aggressive and help form a differentials list
What are the following radiographic signs indicative of?
Soft tissue swelling, changes in subchondral bone opacity (mainly sclerosis), narrowing of joint space, osteophyte formation, osteochondral fragments in the joint cavity, joint subluxation, cyst formation?
Osteoarthritis
List the typical locations for osteophytes in the elbow
- Dorsal anconeal process
- Cranial joint aspect
lateral epicondylar crest of humerus - medial epicondyle of humerus
- Medial coronoid process of ulna
- Trochlear notch of ulna
Describe the radiogaphic signs of metabolic bone disease
- Generalised bone disease
- Usually osteopaenia
Describe the appearance of bone in nutritional secondary hyperparathyroidism
- Cortices thin
- Bones less obvious compared to soft tissue
Describe the radiographic appearance of vitA excess in cats and how this occurs
- Increased bone formation
- Feeding of raw liver
Outline metabolic bone disease in reptiles
- Imbalance in Ca, P, vitD
- Lethargy, reluctance to move
- Osteopaenia and pathological fractures
- Tx: correct deficiency, may recover if fractures not too bad
Describe the radiographic appearance of metaphyseal osteopathy
- Localised lesion, but affects multiple long bones esp. radius and ulna
- Early: radiolucent line adjacent to metaphyses
Later: periosteal new bone formation and sclerosis (lucency of metaphyses still present)
Describe the radiographic appearance of craniomandibular osteopathy
- Reactive periosteal new bone formation on mandible and ventral skull bones
- Increased bone density
Describe the clinical presentation of panosteitis
- Shifting (spontaneously switching) lameness in young growing dogs esp. GSD
- Self limiting
- Affects FL more than HL
Describe the radiographic appearance of panosteitis
- Increased opacity of medullary canal: irregular, heterogenous, inflammatory
- Thumb print lesions may be seen
- Eventually cortical thickening
- Often centred around nutrient foramina
Describe the clinical presentation of immune-mediated polyarthritis
- Painful, stiff, depressed animal
- Swollen joints
- Ligamentous laxity
- Affects all joints, changes most common/initially in carpi and hocks
Outline the radiographic apperance of immune mediated polyarthritis
Will only see bony changes in erosive form, multiple lytic lesions around and “crossing” joints
Describe the radiographic appearance of bone cysts
- Often single, can be multiple
- Usually oval/circular lucent area and well marginated +/- sclerotic rim
- Usually near joints
What are the predilection sites for bone cysts in the horse?
Stifle and fetlock
