Payam Hard

Bone Cells and Structure

• Osteoblasts form bone cells
• Osteocytes are mature bone cells
• Osteoclasts break down bone matrix
• Osteogenic cells are stem cells in the periosteum and endosteum, giving rise to osteoblasts
• Woven bone is rapidly produced during fetal development or fracture repair, characterized by a haphazard arrangement of collagen fibers
• Lamellar bone is the mature bone found in adult skeletons, with a more organized structure (cortical and trabecular)
• Parallel collagen fibers characterize lamellar bone.

Bone Development

• Endochondral ossification develops long bones
• Intramembranous ossification develops flat bones

Osteoclast Regulation

• RANKL (on osteoblasts and marrow stromal cells) binds to RANK (on osteoclast precursors), stimulating osteoclast activity.
• Osteoprotegerin (OPG) blocks RANK-RANKL interaction, inhibiting osteoclast activity.
• Bone resorption and formation balance is controlled by PTH, Vitamin D3, sex hormones, and glucocorticoids.

Achondroplasia

• Autosomal dominant disorder affecting endochondral ossification
• Point mutation in FGFR3
• Shortened limbs, large head, and bulging forehead are characteristics
• No change to longevity, intelligence, or reproductive status.

Osteogenesis Imperfecta (OI)

• Brittle bone disease
• Defective synthesis of type I collagen
• Multiple extraskeletal manifestations (too little bone mass and extreme fragility)
• Various types with varying severity and lifespan
• Some types are uniformly lethal in utero or postpartum

Osteopetrosis

• Stone/marble bone disease
• Defective osteoclast-mediated bone resorption
• Increased bone density, making bones brittle and prone to fracture
• Many types with variations in symptoms

Hyperparathyroidism

• Increased PTH leads to increased osteoclastic activity, resulting in bone resorption and osteopenia (low bone mass)
• Some bones are more conspicuous on radiographs
• Central role in calcium homeostasis
• Increased osteoclastic activation
• Increased urinary excretion of phosphates
• Synthesis of active vitamin D3, affecting calcium absorption

Secondary Hyperparathyroidism

• Chronic renal failure
• Inability to produce enough active vitamin D3
• Reduction of PTH levels can correct the imbalance

Brown Tumor

• Manifestation of symptomatic untreated hyperparathyroidism
• Bone loss occurs most severely in phalanges, vertebra, and femur
• Micro-fractures and hemorrhages cause reparative fibrous tissue growth inside bone
• Brown color is due to vascularity, hemorrhage, and hemosiderin deposition

Paget Disease

• Increased, disordered bone in structure
• Osteolytic, osteoclastic-osteoblastic, and osteosclerotic phases
• Mosaic pattern of lamellar bone

Osteomyelitis

• Infection of bone and bone marrow
• Usually starts from a hematogenous source
• Different forms/types, leading to various complications

Bone Tumors

• Metastatic bone tumors are prevalent
• Benign bone tumors (osteoma) grow slowly, often asymptomatic, and are generally localized
• Malignant bone tumors, like osteosarcoma, grow quickly, spread aggressively, and present more severe health issues.
• Osteosarcoma arises in metaphyses of long bones: most common primary malignant bone tumor in children.

Other Bone Conditions

• Osteoid osteoma and osteoblastoma are benign bone tumors that differ by size
• Osteochondroma is a benign bony projection, often arising from growth plates
• Chondroma is a benign tumor arising from cartilage tissue that often presents in small tubular bones
• Chondrosarcoma is a malignant tumor arising from cartilage tissue. Typically arises from bones in the extremities, pelvis, and trunk.
• fibrous cortical defect and non-ossifying fibroma: benign, often discovered incidentally, developmental disorders; fibrous dysplasia is a benign process with pre-cancerous potential
• Ewing sarcoma/PNET is a malignant, aggressive tumor originating from bone marrow. It is associated with bone pain, swelling.

Osteoarthritis

• Degeneration of articular cartilage, often associated with aging and predisposing factors
• Secondary osteoarthritis can develop due to several causes.
• Rheumatoid arthritis is a systemic autoimmune disorder, leading to chronic progressive inflammation in many tissues.
• Some common sites of involvement include small joints.

Seronegative Spondyloarthropathies

• Include ankylosing spondylitis, Reiter's syndrome, and psoriatic arthritis.
• These disorders lack rheumatoid factor and show a prevalence of HLA-B27 presence.

Gout

• Caused by monosodium urate crystal deposits in joints.
• Several risk factors for gout development; alcohol consumption, purine-rich diets, kidney disease or impairment.
• Acute arthritis is common in the great toe
• Secondary gout can be associated with neurological conditions and other medical issues

Pseudogout

• Calcium pyrophosphate deposition in joints.