Bone pathology 2 Flashcards
Outline how fracture management can lead to osteopaenia
- Stress protection
- Implants reduce stress on bone
- No early mobility due to repair, leads to reduced mineral deposition on bone
- Weakened and at risk of pathological fracture
Compare the radiographic appearance of a traumatic fracture compared with a pathological fracture?
Pathological fracture usually has more bony changes around the fracture site, more lytic areas
Compare osteitis and osteomyelitis
Osteitis: centripetal i.e. moving towards marrow
Osteomyelitis: centrifugal i.e. starts in marrow and moves out
Describe the appearance of osteomyelitis on radiography
- Disorganised, areas of lucency
- Soft tissue swelling
- Irregular, semi-aggressive periosteal reaction
- More extensive than fracture callus
- Area of sclerosis around focus
What features are assessed in the determination of an aggressive vs non-aggressive lesion on radiography?
- Lysis
- Periosteal reaction pattern
- Lytic edge character
- Cortical disruption
- Transition zone
- Rate of change (10-14 days)
Briefly outline the bone lysis patterns that may be seen and rank these from non-aggressive to aggressive
- Geographic (single, well demarcated focus)
- Geographic (more aggressive if affecting only medulla)
- Moth eaten lysis (multiple areas)
- Permeative lysis (most aggressive)
Describe the benign (continuous) periosteal reaction patterns
- Lines parallel to the cortex typically
- Solid, lamellar (flat line), lamellated (slight rounding)
Briefly describe the interrupted (aggressive) periosteal reaction patterns and rank these from least to most aggressive
- Thick brush like (thick lines of periosteum perpendicular to the cortex)
- Think brush like (think lines)
- Sunburst (lines of periosteum from focus moving outwards in a divergent pattern)
- Amorphous bone production (no lines visible, disorganised)
What determines a radiographic lesion as aggressive, semi-aggressive or non-aggressive?
The most aggressive radiographic sign is used to determine the lesions degree of aggressiveness
What disease may be suggested by non-aggressive, slow developing radiographic signs?
Degenerative joint disease
Compare the radiographic appearance of neoplasia and infection in terms of degree of aggression
- Neoplasia: aggressive if malignant
- Non-aggressive/semi-aggressive if benign
- Infection: often semi- aggressive
Describe the orientation for viewing a lateral radiograph
- Proximal part of limb at top of image
- Cranial aspect of limb to the left
Describe the orientation for viewing a craniocaudal radiograph
Proximal part at the top
Describe the orientation for viewing a ventrodorsal radiograph
- Cranial part at the top
- Left marker on the right of the image when viewed
What normal feature of bone may commonly be mistaken as a small fracture?
Nutrient foramen
What are the advantages of MRI for imaging of the spinal column?
- Cross sectional image avoids superimposition
- Excellent soft tissue definition
Describe the appearance of discospondylitis on MRI
- Loss of signal from nucleus pulposus so appears hypointense
- Maybe some dislocation of vertebrae
Outline the advantages of CT in imaging of the spinal column
- Can be combined with myelography
- Can be useful where MRI not feasible e.g. metal implants
- Avoids superimposition
- Better for osseous structures vs. MRI
Describe the appearance of the subarachnoid space on a transverse CT myelogram
Radiopaque circle within the vertebral canal
Briefly outline the principles for myelography
- Injection of water-soluble non-ionic iodine contrast medium into the subarachnoid space
- Use of non-ionic medium in order to reduce side effects
What locations are used for the injection of contrast medium for myelography?
- Cisterna magna
- Caudal lumbar suubarachnoid space
What are the risks associated with myelography?
- Short term side effects e.g. incoordination
- Injection into spinal cord itself can result in permanent paralysis, or rarely, death
Compare cisternal and lumbar puncture for myelography
- Cisternal technically easier but less useful for thoracolumbar lesions as contrast may not reach that far
- Lumbar technically more difficult, better for thoracolumbar or lumbar lesions, may have less risk as not injecting near to proximal spinal cord
What modalities can be used for head and neck imaging?
- Radiography
- Ultrasound
- CT
- MRI
Outline the limitations of radiography for imaging of the skull
- Anatomy complex
- Structures bilaterally symmetrical, can be impossible to distinguish on lateral views
- Accurate positioning difficult
What radiographic views can be taken of the skull?
- Lateral
- Dorsoventral
- Lateral oblique
- Rostrocaudal
- Rostrocaudal open-mouth
- Dorsoventral intraoral
- Ventrodorsal open-mouth oblique
Outline the positioning and centring for a lateral radiograph of the skull
- Lateral recumbency, nose and mandible raised with lucent pads to ensure sagittal plane of skull is parallel to the cassette
- Centre beam mid-way between eye and ear
Outline the positioning and centring for a dorsoventral radiograph of the skull
- Sternal recumbency, nose and mandible raised with lucent pads so transverse plane of skull is parallel to the cassette
- Centre beam mid way between medial canthi of eyes
What are the indications for use of a lateral oblique radiograph of the skull?
Imaging of the temporomandibular joints or bullae
Outline the positioning for a lateral oblique radiograph of the skull
- Wedge pad to raise rostral aspect of the head
- Lateral recumbency
What are the indications for use of a rostrocaudal “skyline” radiograph of the skull?
Imaging for frontal sinuses, zygomatic arch, temporal region, sagittal crest
Outline the positioning for a rostrocaudal “skyline” radiograph
- Dorsal recumbency
- Skull secured with tape around nose so hard palate is perpendicular to cassette
- Beam angled at 5-10degrees in rostrocaudal direction
What are the indications for a rostrocaudal open-mouth view in dogs and what modification is used in cats?
- Closed mouth in cats
- Used for tympanic bullae
Outline the positioning for a rostrocaudal open mouth radiograph
- Dorsal recumbency
- Mouth held open using tape
- Primary beam centred on base of skull
What are the indications for a dorsoventral intraoral radiograph?
demonstration of nasal chambers, premaxilla, upper incisors, rostral portions of maxilla and premolar teeth
Outline the positioning of a dorsoventral intraoral radiograph
- Sternal recumbency
- Screen film used for incisor region but non-screen film for fuller examination of maxillary arcades
- For incisors, angle beam around 20degrees
- ET tube tied to lower jaw
- Film placed above tongue and tube
What are the indications for ventrodorsal open-mouth oblique radiographs?
- Nasal chambers
- Is alternative to dorsoventral intraoral
- Preferred view for feline nasal cavity
Outline the positioning for a ventrodorsal open-mouth oblique radiograph
- Dorsal recumbency and mouth held wide open with tapes attached to the table and radiolucent gag
- Place sandbag or bandage roll under neck to ensure hard palate is parallel to table top
- Tongue and ET tube tied to mandible
- X-ray tube angle 20degrees rostrocaudally
- Centre beam on midline of palate at third premolar teeth
What are the general indications for radiography of the head?
- Trauma
- Malformation
- Foreign body
- Neoplasia
- Dental investigation
- Intracranial pathology
- Ear disease
- Nasal disease
Describe the radiographic appearance of hydrocephalus
- Exaggerated dome shape of skull
- Thinned bones of calvarium
- Open fontanelle and suture bones
Describe the possible appearance of ear disease on radiography
- Otitis media: increased soft tissue/fluid opacity of the tympanic bulla, thickened +/- irregular bulla wall
- Loss of air shadow in external ear canal may be seen in cases of severe otitis, polyps and neoplasia
- External ear cartilages may be calcified in chronic otitis
Describe the radiographic appearance of rhinitis
Increased nasal cavity radiopacity with retention of underlying turbinate pattern
Describe the radiographic appearance of nasal neoplasia
Increased radiopacity with loss of turbinates
Describe the radiographic appearance of fungal rhinitis
Decreased radiopacity with loss of turbinates
When might ultrasonography of the head be useful?
If fontanelle still open, can visualise ventricles and determine if they are enlarged e.g. in hydrocephalus
List the treatment options for osteosarcomas
- Euthanasia
- Analgesia only (poor prognosis, unlikely to be enough to remove pain)
- Limb sparing surgery or limb amputation
- Chemotherapy
- Palliative radiation
- Chemo + limb sparing surgery
Describe limb sparing surgery with chemotherapy as a treatment for osteosarcomas
- Remove tumour with a margin and fill gap with plate
- Fill with bone graft (prevents bending of plate)
What chemotherapeutic agents are used in the treatment of osteosarcomas?
Cisplatin and doxorubicin
Which breeds are predisposed to osteosarcomas?
- Large to giant breed dogs with late closing growth plates
- Taller for breed more at risk
- Scottish deerhound, Rottweiler, Irish wolfhound, St Bernard, Great Dane, Doberman, German shepherd
Where are osteosarcomas typically found?
- Close to the knee, away from the elbow
- Metaphyses typically affected
- Thoracic limb > pelvic
- Distal radius, proximal humerus, uncommon in ulna
- Typically appendicular, can affect axial and soft tissues
Outline the signalment for osteosarcomas
- 7-8yo
- Neutered
- Large/giant breeds, tall individuals
Outline the diagnosis of osteosarcomas
- Initial clinical presentation
- Radiographic findings
- FNA and cytology (ALP staining to differentiate osteosarc from other primary bone tumours)
- Bone biopsy
Describe the typical clinical presentation for osteosarcomas
- Progressive lameness, leg swelling
- Lameness usually intermittent and progressive and severe (initially mild)
- Mass site firm and painful
- Often pathological fractures
Outline the staging of osteosarcomas
- Radiography, assess joint above and below
- MRI and CT ideal
- MRI best before operation to indicate medullar extent
- CT best for lung mets
Outline the metastatic rate of osteosarcomas
- 90% have mets at diagnosis but only 10% are identifiable at diagnosis
- Appendicular OSA are highly malignant
Describe the common sites of metastasis for osteosarcomas
- Lungs most common initially
- Bone mets more prevalent following tx with surgery and chemotherapy vs surgery alone
- Distant limp nodes, kidney, spleen, myocardium, diaphragm, mediastinum, spinal cord, small intestine, gingiva and subcut tissue also sites of metastasis
Where do osteocytes originate from and where are they located?
- Originate from osteoblasts
- Surrounded by bone matrix (osteoid) in bone spicules
How is lamellar bone formed and arranged?
Newly formed bone is woven, remodelled by osteoclasts into lamellar bone arranged into Haversian systems
Outline the structure of an osteon
- Central nerve, lymphatic vessel, vein and artery
- Surrounded by lamellae
- Osteocytes between layers of lamellae, enclosed by lucunae
- Around outside are osteoblasts, and occasional osteoclasts
Where is hyaline cartilage found?
- Joint surfaces
- Physes
- Nose
- Trachea
Where are chondrocytes located?
Often as groups of 2-4 within lucanae, in amorphous matrix
Where are chondroblasts found?
In perichondrium
Where is elastic cartilage found?
Ears
What is the main difference between elastic and hyaline cartilage?
Increased numbers of elastic fibres in elastic cartilage
Describe the structure and location of fibrocartilage
- No periochondrium
- Intermediate between connective tissue and hyaline cartilage
- Found in intervertebral discs only
Describe the histological appearance of a new fracture
- Similar to tumour in terms of increased number of cells
- No bizarre cells present
- Lots of osteoblasts (producing osteoid to form lamellae)
Describe the histological appearance of older fractures
- Spicules of spongy bone beginning to make lamellae
- Contain osteocytes
Describe the immediate response to structural damage within the bone
- Haematoma forms containing inflammatory mediators
- e.g. kinins, complement, histamine, serotonin, prostaglandins, leukotrienes
→ vasodilation, chemotaxis of white blood cells, platelet aggregation and release, mesenchymal cell proliferation
What are the 3 phases of bone reparation?
Inflammation
Repair
Remodelling
Describe the inflammatory phase of bone healing
- Occurs within first 2-3 weeks
- Clearance of debris/necrotic/devitalised bone
- Fracture gap widens
- Influx of cytokines and growrth factors
- Phagocytosis of tissues
- Fragment end resoprtion
- By 4 weeks have callus formation
Describe the reparative phase of bone healing
- INdirect repair, healing under motion
- 2-12 months duration
- angiogenesis (initially in adjacent tissues, the medullary blood supply restored)
- Periosteal and endosteal callus formation
- Bone union
Describe the periosteal and endosteal callus formation in the reparative phase of bone healing, and what may suppress this
- Large surface area, not strong bone but large surface area provides good and rapid stabilisation
- Suppressed by rigid immobilisation, excessive mobilisation
Describe the bone union in the reparative phase of bone healing
- Cancellous bone formed by combination of intramembranous and endochondral ossification
- Cartilage component mineralised resulting in cancellous bone union, subsequently remodelled into lamellar bone
Explain the difference between the endochrondal and intramembranous ossification that occurs in the reparative phase of bone healing
- Endochondral: occurs at growth plates/fracture gap, initially get fibrous scaffold (fibroplasia, replaces haematoma) → cartilage (chondrogenesis)→ bone (mineralisation)
- Membranous ossification: fibrous structure → mineralised bone (NO cartilage stage)
Describe the remodelling phase of bone healing
- Bone resorption and bone formation
- Cortical callus undergoes Haversian remodelling to form lamellar bone
List the types of regulatory molecules involved in bone healing and give examples
- Growth factors (e.g. TGFbeta, IGF-1/2, FGF)
- Cytokines (IL-1, Il3, CSF, IL6)
- Others: osteoponin, osteocalcin, osteonectin, prostaglandins
What are the basic patterns of bone repair?
Primary (direct) or secondary (indirect) repair
Describe primary (direct) fracture healing
- Exact alignment
- Rigid fixation
- Sufficient blood supply
- Provides rapid strength to fracture
- No periosteal callus formation
- Contact healing or gap healing
Compare contact and gap healing in fracture healing
- Contact: secondary osteonal (Havesian) remodelling of the fracture at interfragmentary contact points
Gap: small gaps filled with woven then lamellar bone, secondary osteonal remodelling, grow across gap
What are the fixation principles of direct fracture repair?
- Anatomic reduction
- Stable internal fixation
- Interfragmentary compression
- Preservation of blood supply
- Early active, pain free mobilisation
What are the methods of direct/primary bone repair?
- External fixation (casts, braces, ESF)
- Internal fixation (screws, plates, IM pins)
How is compression of a fracture commonly achieved to facilitate primary (direct) healing?
- Dynamic compression plate
- Creates friction between plate and bone and compresses the 2 sides of a fracture together
What are the advantagesof secondary (indirect) bone healing?
- Allows rapid stabilisation
- Callus formation early on, provides strength
What are the disadvantages of secondary (indirect) bone healing?
- Long period of remodelling
- Repair pattern influenced by both biology and mechanics
- Not as successful in long bones in horses
What may lead to difficulty in achieving accurate reduction of a fracture site?
- Eburnation
- Muscle contraction (esp. if fracture older than 12-24 hours)
- Severe comminution
What are the potential consequences of not achieving accurate anatomical reduction of a fracture?
- Osteoarthritis (if articular misalignment)
- Cyclical implant loading which can lead to implant failure
How can muscle contraction, preventing accurate fracture reduction, be overcome in the horse?
- Early treatment
- Suspension of the limb with a mechanical hoist can allow better reduction
Discuss the complications that may occur with stable internal fixation
- Too stable and no motion at fracture gap → no callus formation
- Excessive motion at fracture gap → hypertrophic non-union due to persistence of fibrous tissue
Discuss the problems in fracture repair that are specific to horses
- Large animals, enormous mechanical loads on recovery from GA
- Rapid weight bearing following anaesthesia
- Bed rest not an option
- Often open fractures, soft tissue damaged
- Contralateral overload (laminitis, angular limb deformity in younger animals, elongation of stay apparatus, cartilage degeneration
List the potential consequences of prolonged limb immobilisation for fracture repair in the horse
- Osteoporosis
- Joint laxity
- Tendon laxity
- Cartilage degeneration
- Pressure or rub sores
Outline how surgical techniques can facilitate biological fracture healing
- Small incisions
- Minimal disruption to fractuer haematoma
- Periosteum largely left in tact
How can fracture repair be enhanced beyond standard techniques (i.e. direct, indirect fixation)?
Expensive, area of research
- Cancellous bone grafting
- Osteoconduction (scaffold)
- Osteoinduction (stimulation of osteogenesis)
