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- most common disease of the growth plate
- is the most common form of dwarfism


- autosomal dominant, point mutation in gene that encodes FGF receptor 3 (constant activation of this receptor --> inhibition of cartilage formation)
- gain of function mutation (normally, FGFR3 inhibits cartilage proliferation


- disorganized and narrowed zone of proliferation in growth plate
- premature bone formation seals the plate
- intramembranous (periosteal) bone formation is normal


- mainly long tubular bones affected
- short extremities, relatively normal trunk, enlarged head with bulging forehead and depression of root of nose
- normal intelligence and life span

thanatophoric dwarfism

- mutation of FGFR3 different from achondroplasia (but is also a gain of function mutation)
- much less common form of dwarfism

thanatrophoric dwarfism

- lethal (perinatal age...die at birth or soon after)
- limb shortening and small chest
- death from respiratory insufficiency
- affects all bones, not just longitudinal ones
- histologically, shows diminished proliferation of chondrocytes and poor columnization in the zone of proliferation

osteogenesis imperfecta

- type 1 collagen disease
- abnormal collagen and brittle bones

type II osteogenesis imperfecta
type I osteogenesis imperfecta

- this type = lethal in utero, multiple intrauterine fractures
- this type = normal life spain, increased number of fractures, blue sclerae, hearing loss, misshapen teeth

osteogenesis imperfecta

- too little bone
- cortical thinning, attenuated trabeculae, hypercellular woven bone


- increased bone porosity due to decrease in bone mass (localized or generalized)
- bone is too lite and porous


- complications include fracture of femoral neck, pelvis, spine
- also pulmonary embolism or pneumonia secondary to fractures (cause of 40,000-50,000 deaths each year)
- shape of bone collapses, sinks in

senile osteoporosis

- low turnover variant (bone doesn't remodel as quickly)
- osteoblasts from older individuals have reduced reproductive and biosynthetic potential
- age-related bone loss (.7% per year)
- *Haversian system widened

postmenopausal osteoporosis

- high turnover variant (but slow process, so don't see enzyme abnormalities)
- hormone-dependent acceleration of bone loss after menopase (estrogen deficiency)
- decreased estrogen = increased secretion of cytokines = stimulation of osteoclast recruitment
- up to 50% trabecular bone loss
- osteoclasts absorb bone more than it is produced
- *vertebral collapse

disuse osteoporosis

- mechanical forces are important stimuli for normal bone remodeling
- muscle contraction important source of skeletal loading
- decreased physical activity leads to bone loss

- vitamin D
- calcium

- genetic polymorphism in _____________ receptor molecule leads to variation in maximum bone mass
- _________ intake is also important


- thinned trabeculae, microfractures, vertebral collapse (postmenopausal variant), cortex thinned, Haversian system widened (senile variant)
- specialized radiographic imaging required for diagnosis


in postmenopausal women, decreased estrogen levels promote increased osteoclastic activity by increasing production of cytokines with recruit and activate osteoclasts by increasing _________ expression while reducing OPG synthesis

Paget disease

- increased osteoclastic activity with numerous absorption pits, then prominent osteoblasts lining bone surfaces
- adjacent marrow hypervascular
- focal increase in bone mass

Paget disease

- woven bone formation followed by lamellar bone with mosaic pattern (jigsaw puzzle)
- prominent cement lines* annealing haphazardly oriented units of lamellar bone

Paget disease

- bone is thicker, but structurally abnormal and therefore breaks easily because it is weaker
- coarsely thickened trabeculae and cortices that are soft and porous --> increased vulnerability to deformation and fracture

axial skeleton (spine) and proximal femur

most common sites for Paget disease

serum alkaline phosphatase

What is increased in Paget disease and is a sign of increased bone turnover?

Paget disease

- pain, deformities (bowing of femur/tibia), increased blood flow may lead to high output cardiac failure (AV shunting), malignant transformation (high grade sarcoma) in 5-10% of patients with severe polyostotic disease

comminuted frature

a fracture in which the bone has broken into a number of pieces (bone is splintered)

displaced fracture

a fracture in which the bone ends are not aligned

- non-union
- psuedoarthrosis
- infection

complications which inhibit fracture healing (3)

osteonecrosis (avascular necrosis)

- bone necrosis secondary to ischemia
- due to mechanical vascular interruption (fracture), corticosteroids (unknown mechanism), thrombosis and embolism (sickle cell anemia), vasculitis/radiation injury, increased intraosseous pressure, venous HTN, often unknown (idiopathic*)

osteonecrosis (avascular necrosis)

- medullary infarcts involve cancellous bone and marrow (cortex not affected due to collateral blood flow)
- subchondral infarct
- dead bone

subchondral infarct

- part of osteonecrosis
- chronic pain (collapse of dead bone leads to severe osteoarthritis)

medullary infarct

- part of osteonecrosis
- often silent, rarely undergoes malignant transformation to high-grade sarcoma

creeping substitution

- in the healing response, osteoclasts resorb the necrotic trabeculae; however, those that remain act as scaffolding for the deposition of new bone in a process known as ___________________

pyogenic osteomyelitis

- almost always bacterial
- infection is hematogenous (most common), contiguous, or direct implantation
- S. aureus is most common organism (80-90%), but can be others

- metaphysis and epiphysis
- metaphysis
- epiphysis (due to growth plate closure)

pyogenic osteomyelitis location:
- neonates?
- children?
- adults?

pyogenic osteomyelitis

- acute systemic illness or more subtle symptoms
- X ray findings: lytic focus surrounded by sclerosis
- bone biopsy may be necessary to culture organism
- complications include fracture, endocarditis, sepsis, squamos cell carcinoma

pyogenic osteomyelitis

sequestrum, draining sinus, involucrum, Brodie abscess

- sequestrum
- draining sinus
- involucrum
- Brodie's abscess

- dead piece of bone
- rupture of the periosteum leads to a soft-tissue abscess and the eventual formation of a _____________
- when the newly deposited bone forms a sleeve of living tissue around the segment of devitalized infected bone, it is known as an ____________
- is a small intraosseous abscess that frequently involves the cortex and is walled off by reactive bone

tuberculous osteomyelitis

- 1-3% of pulmonary or extra-pulmonary TB
- usually solitary but may be multifocal
- festers for years
- sites most commonly involved: spine, knees, hips
- more destructive and more difficult to control than pyogenic osteomyelitis

Pott disease

- when tuberculous osteomyelitis involves the spine, it is called _______________
- the infection breaks through the intervertebral discs to involve multiple vertebrae and extends into the soft tissues forming abscesses

Skeletal syphilis

- congenital intrauterine or acquired infection
- bones frequently involved if acquired include the nose, palate, skull, and extremities
- saber shin is produced by massive reactive periosteal bone deposition on the medial and anterior surfaces of the tibia
- if congenital, lesion appear in 5th month of gestation and are fully developed at birth


- most common joint disease
- progressive erosion of articular cartilage (not an inflammatory disease)
- primary = idiopathic (aging phenomenon)
- secondary = predisposing condition such as development deformity, diabetes, marked obesity, repeated trauma (athletes)


- alterations in proteoglycans and collagen lead to decreased tensile strength and secretion of cytokines
- chondrocyte proliferation followed by fibrillation
- sclerosis and remodeling of underlying bone
- eburnation


- deep pain
- osteophytes may cause nerve compression
- typically only few joints involved (hip, knees, lumbar/cervical spine, interphalangeal and first carpometacrapal and tarsometatarsal joints


- Herberden nodules (osteophytes at DIPs)
- joint mice

rheumatoid arthritis

- thick, hyperplastic synovium with villous fronds
- prominent lymphoplasmacytic infiltrate
- organizing fibrin may float in joint space "rice bodies"

rheumatoid arthritis

- juxtaarticular erosions
- pannus (fibrocellular mass of synovium and stroma containing inflammatory cells and fibroblasts, causes erosion of cartilage --> late sequelae: fibrous and bony ankylosis

rheumatoid arthritis

- occur in areas subject to pressure (ulnar aspects of forearms and elbows)
- vasculitis if disease is severe in small to medium arteries (possible complication of vasculitis is gangrene)


often happens after a meal rich in protein (meat)


- swollen joints
- acute arthritis: dense neutrophilic infiltrate
- chronic tophaceous arthritis: urate deposits encrust articular surfaces, eventually leading to ankylosis
- urate crystals needle shaped, negatively birefringent


- are defined as large aggregations of urate crystals surrounded by inflammatory cells and multinucleated foreign body giant cells
- white, cheesy looking material
- characteristic of gout


- articular cartilage, ligaments, and soft tissue
- usually affects distal extremities (toes)
- cardiovascular disease including aterosclerosis and HTN is common

gouty nephropathy

- when deposition of urate crystals in medulla causes the formation of stones

pseudogout (chondrocalcinosis) (CCPD)

- crystals deposit in the articular matrix, menisci, and intervertebral discs --> seeding into the joint --> inflammatory response with neutrophils produce damage

pseudogout (chondrocalcinosis) (CPPD)

- chalky white friable deposits, weakly positive birefringent (rarely deposit in masses to form tophi)
- more square, not needle shaped
- crystals stain as blue-purple aggregates

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