Questions and Answers
What is the most common type of osteomyelitis?
In which age group are benign bone-forming tumors like osteoid osteoma and osteoblastoma most common?
What is the characteristic feature of Ewing sarcoma on radiographic findings?
What is the name of the syndrome associated with enchondromas and secondary chondrosarcomas?
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Which of the following is a characteristic feature of osteomyelitis?
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What is the name of the benign tumor of hyaline cartilage that occurs in bones of endochrondral origin?
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What is the location of osteomyelitis in neonates?
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What is the name of the malignant matrix-producing tumor of bone that commonly occurs in the axial skeleton?
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Which of the following describes Osteomalacia?
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What is a key characteristic of Paget Disease?
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What is the most common cause of Osteonecrosis?
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Which of the following is a common symptom of Osteomyelitis?
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In Paget Disease, which population is primarily affected?
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What type of fracture is most likely associated with Osteonecrosis?
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What clinical manifestation characterizes Rickets in children?
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What is the characteristic sign of Pyogenic Osteomyelitis?
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How does hyperparathyroidism affect bone health?
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Study Notes
Bones
- Basic histology:
- Matrix: extracellular component of bone composed of osteoid (Type 1 Collagen, GAGs, proteins, Osteopontin/Osteocalcin) and minerals (Calcium hydroxyapatite)
- Cellular components: osteoblasts, osteoclasts, and osteocytes
- Developmental disorders:
- Dysostoses: localized disruption of migration and condensation of mesenchyme, caused by mutations in homeobox genes, cytokines, and cytokine receptors
- Dysplasia: fibroblast growth factor 3 (FGF3) mutations leading to achondroplasia and thanatophoric dysplasia
Skeletal Dysplasias
- Achondroplasia:
- Most common skeletal dysplasia and major cause of dwarfism
- Autosomal dominant: gain-of-function mutations in FGF3 → inhibition of endochondral growth
- Non-lethal
- Thanatophoric dysplasia:
- Most common lethal form of dwarfism
- Mutations lead to more ↑ FGF3 signaling → more severe manifestations than achondroplasia
- Usual cause of death: respiratory insufficiency (underdeveloped chest cavity)
Metabolic Pathways
- Osteogenesis imperfecta "brittle bone disease":
- Most common inherited disorder of connective tissue
- Autosomal dominant: fundamental abnormality of extreme skeletal fragility due to too little bone
- Four major types: Type 2 is the most lethal
- Osteopetrosis "marble bone disease":
- Autosomal recessive: impaired osteoclast function → excessive bone formation
- Deposited bone is woven
- Albers-Schönberg disease: mild autosomal dominant form
Metabolic Bone Disease
- Osteopenia and osteoporosis:
- Osteopenia: decreased bone mass
- Osteoporosis: severe osteopenia, increasing the risk of fractures
- Bone resorption exceeds formation
- Most common forms: senile and postmenopausal
- Hallmark: histologically normal bone, but ↓ in quantity
- Rickets and osteomalacia:
- Manifestations of Vitamin D deficiency
- Abnormal mineralization of bone
- Decreased mineral content of bone
Hyperparathyroidism
- Biologic effects of PTH: ↑ Ca2+ levels
- Bone: osteoclast activation → bone resorption
- Kidneys:
- ↑ Ca2+ tubular reabsorption
- ↑ PO43- excretion (PTH = Phosphate trashing hormone)
- ↑ Vitamin D synthesis → ↑ Intestinal Ca2+ absorption and ↑ Bone Ca2+ mobilization
Renal Osteodystrophy
- Skeletal changes in chronic renal failure (including dialysis)
- Osteopenia/osteoporosis
- Osteomalacia
- Secondary hyperparathyroidism
- Growth retardation
- Pathophysiology:
- Renal tubular acidosis → Systemic acidosis → ↑ Bone demineralization and osteomalacia
- Poor Ca2+ reabsorption + Poor PO43- excretion → ↑ PTH → ↑ Bone resorption
- ↓ Vitamin D synthesis and dysregulation of Ca2+-PO43- homeostasis between kidney and bone
Paget Disease (Osteitis Deformans)
- Increased, but disordered and structurally unsound bone mass
- Mosaic pattern of lamellar bone with cement lines “jigsaw puzzle”
- Clinical aspects:
- Primarily a disease of the elderly
- Most common bones: axial skeleton, proximal femur
- Clinically, bone pain (from microfractures or nerve compression)
- Complications:
- High-output failure: Pagetic bone as AV shunt
- Most dreaded complication: osteosarcoma and fibrosarcoma
Fracture Healing and Osteonecrosis
- Fracture healing:
- Osteonecrosis:
- Most common causes: trauma, steroids
- Morphology:
- Medulla more commonly affected
- Subchondral infarcts
- Necrotic bone: empty lacunae surrounded by necrotic adipocytes
- Saponification: Ca2+ + Fatty acids released from adipocytes
- Deposition of new bone with remaining trabeculae as scaffolding
- Resorption of necrotic trabeculae by osteoclasts
- Sequelae: collapse of necrotic bone, fracture, sloughing of articular cartilage
Osteomyelitis
- Pyogenic osteomyelitis:
- Route of infection: hematogenous, extension, direct implantation
- Causative agents:
- S. aureus (most common, 80-90%)
- E. coli, Pseudomonas, Klebsiella (GUT infections & IV drug users)
- H. influenzae, GBS (neonates)
- Salmonella (sickle cell disease)
- Location dependent on osseous vascular circulation
- Morphology:
- Subperiosteal abscesses
- Draining sinuses: consequence of periosteal rupture and soft tissue abscesses
- Sequestrum: dead bone
- Involucrum: newly developed sleeve of bone around dead bone
- Clinical manifestations:
- Systemic symptoms related to infection
- Pain over infected bone
- Radiograph: Lytic focus with surrounding sclerosis
Mycobacterial Osteomyelitis
- More destructive and more resistant to control
- Involves spine in 40% of cases (tuberculous spondylitis, Pott disease)
- Kyphoscoliosis and neurologic manifestations (due to disc and vertebral destruction)
Bone-Forming Tumors
- Osteoid osteoma and osteoblastoma:
- Benign tumors common in 10-20 years old
- Malignant transformation is rare
- Morphology:
- Haphazardly interconnected trabeculae of woven bone WITH osteoblastic rimming
- Cytologically benign cells
- Reactive bone surrounding the lesion
- Osteosarcoma:
- Bimodal age incidence
- Most occur in
- Pelvis, Scapula, Ribs
- Morphology:
- Cartilage cap: hyaline cartilage (disorganized growth plate-like) covered peripherally by perichondrium
- Underlying bone and marrow
- Bimodal age incidence
Cartilage-Forming Tumors
- Chondroma:
- Benign tumor of hyaline cartilage that occurs in bones of endochondral origin
- Enchondroma: intramedullary
- Most common intraosseous cartilage tumor
- Juxtacortical: bone surface
- Age: 20-50 years
- Location: metaphysis of hand and foot bones
- Associations: Ollier and Maffucci syndrome
- Enchondromatosis: multiple enchondromas
- Associated with secondary chondrosarcomas
- Chondrosarcoma, conventional type:
- Second most common malignant matrix-producing tumor of bone
- Age: usually a disease of the elderly (>40 years)
- Common location: axial skeleton (pelvis, shoulder, ribs)
- Morphology: anaplastic chondrocytes with varying cellularity, atypia, and mitosis (basis for three-tier grading)
- Grade is a prognostic factor
Tumors of Unknown Origin
- Ewing sarcoma:
- Second most common group of bone sarcomas in children
- Radiographic findings:
- Lytic lesion with infiltrative margins that may involve soft tissue
- Periosteal reaction: onion-skin like deposition of the reactive bone
- Age:
- Most common mutation: t(11;22)
- EWSR1-FLI1 fusion gene
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Description
This quiz covers the basics of bone histology, including the extracellular matrix, types of bone, and markers of osteoblasts. It's a great resource for students studying anatomy and physiology.
