• paracrine signaling
  • elaboration of RANK ligand and RANK (TNF family R that activates osteoclasts)
• osteoblasts have receptors for:
  • PTH
  • vitamin D
  • estrogens
  • cytokines
  • GF's

• mechanisms
  • intramembranous ossification- occurs on membranes of CT
  • endochondral ossification- occurs on a model of cartilage
• major component of organic matrix and mineral component
  • matrix- collagen type I
  • mineral- hydroxyapatite

• Factors of deposition
  • circulatory factors
  • metabolic factors
  • mechanical factors (bone deposited in proportion to the stress load the bone must carry)

• lamellar bone represents adult bone (layering patttern according to stress lines)
• woven bone represents immature or pathologic bone

• cause- abnormal osteoblast synthesis of type I collagen
  • also affects collagen in the joints, eyes, skin, and teeth

• cause- abnormal osteoclast function
  • bones dense, but brittle and replaced by marrow space

bending of bone with break occuring only on convex side

• open wound of soft tissue and skin extending from fracture site (potential for contamination)
• cause- high force injury

• dislocations
• soft tissue injury involving nerves and vessels

• reduction- bringing the fractures end together (with or w/o surgery)
  • this will restore correct shape, length and angle of the bone

1. circulatory
   • hematoma
   • granulation tissue and organization
   • procallous
2. metabolic
   • matrix synthesis
   • conversion of procallus to fibrocatilagenous and osteoid callus
3. mechanical- production of osseous callus and bone remodeling according to stress line

• malalignment, incomplete immobilization, repeat trauma at fracture site
• necrotic bone fragments from comminuted fracture
• secondary bacterial infection
• impairment of vascular supply
• metabolic bone disease

• malunion or delayed union
• nonunion (pseudoarthrosis)- abnormal healing process during which osseous callus may not form
• secondary bacterial infection
• injury to soft tissue, vascular structures, and/or nerves

• trauma with a "dirty wound" exposing bone to contaminated material
• direct extension of an adjacent infection
• hematogenous spread resulting from bacteremia or septicemia

• causative agent- Staph. aureus
• epidemiology- usually growing children, young adults

• sickle cell anemia- Salmonella
• drug addicts- Pseudomonas
• neonates- Hib, Group B Strep

• presentation
  • acute febrile illness
  • pain, fever, leukocytosis
  • blood cultures positive the majority of the time
• long bones most frequently involved
  • femur > tibia > humerus > radius > ulna
• Xray signs (not seen till after a full week)
  • periosteal elevation
  • reactive bone formation
  • metaphyseal destruction

• acute inflammatory infiltrate
• suppurative osteolysis
• ischemic bone necrosis that may produce a sequestrum

• involvement of periosteum and new bone formation-involucrum
• may involve soft tissue infection, cellulitis, and chronic draining sinus penetrating through skin
• X ray- mottle appearance due to combined bone production and destruction

• septicemia and death
• abscess formation
• septic arthritis
• chronic osteomyelitis
• pathological fracture

• origin- pulmonary or mediastinal focus
• histopathology
  • caseating necrosis
  • granulomatous inflammation may destroy cortical bone and epiphyseal cartilage
• Pott's disease- TB osteomyelitis of spine usually involving multiple vertebrae and discs with soft tissue abscess

• composition
  • cells
  • matrix
    • type II collagen
    • proteoglycans (comp: hyaluronic acid and mucopolysaccharides that are hydrophilic)
  • water
• function of water and matrix- tensile/shearing force and compressive force resistance
• lacks blood supply, lymphatic drainage, and innervation

• synarthrosis- no mov't (ex: skull sutures)
• amphiarthrosis- lil mov't (ex: intervertebral joints)
• diarthrosis- movement about a synovial joint

• forms a sac enclosing synovial joint
• function- provide metabolic support for joint
• produces hyaluronic acid
• different synovial cell types provide protein synthetic and phagocytic functions
• synovial fluid provides lubrication and nutrition to articular cartilage

• pathogenesis
  • infectious arthritis from injection of infectious material through:
    • trauma
    • extension of adjacent infection (bone, joint, tissue)
    • hematogenous spread (MOST COMMON)
• causative agent- S. aureus

• presentation
  • usually involves one join
  • host response is typical of the agent
    • bacteria- suppurative
    • TB- granulomatous
    • virus (rubella)- lymphocytic response
• complications
  • loss of collagen (due to collagenases)
  • joint fusion (due to inflammatory organization and adhesions)

• definition- non-infectious, partially inflammatory progressive degeneration of articular cartilage associated with proliferation of new osteoarticular tissue (osteophytes)
• associated with:
  • aging
  • pre-existing pathology
    • joint dysplasia
    • trauma
    • avascular necrosis
    • inflammatory disease
    • metabolic disease

1. chondrocytes produce inflammatory mediators that degrade matrix and prevent matrix synthesis
2. decreases in proteoglycans lead to cartialge degeneration
3. secondary response is bone production and sclerosis

• gross
  • articular cartilage undergoes softening and fibrliation
  • with subsequent cartilage erosion, bone eburnation, and joint deformity
• histo
  • osteophytes, subchondral cysts, and loose bodies may develop
  • secondary inflammatory response of synovium

• classically seen in tabes dorsalis or DM
• pathogenesis
  1. deficient or abnormal neurovascular supply
  2. joint undergo progressive erosion, sclerosis, and marked destruction
  3. fragments of bone and cartilage may embed in synovial tissue

• chronic deforming and destructive arthritis
• multiple joints tend to be symmetrically involved in 85% of patients positive for rhematoid factor (anti- IgG)

• rheumatoid nodule
• pleural and pulmonary parenchymal disease
• myo-/peri-carditis
• myositis
• arterits

• genetics
• exogenous immunoreactive Ag's
• autoimmune synovitis and panus reaction
• initiation of mediators of joint injury

• gross
  • joints show erosive changes, deformities, subluxations, fusions
• histo
  • proliferative synovitis forming papillary synovial and granulation tissue mass
  • this mass overgrows and destroys articular cartilage

• definition- inflammatory arthritis with progressive bone ankylosing of spine and large limb joints
• pathogical changes
  • early changes- chronic synovitis and cartilage erosion (resemble RA)
  • later changes- fibrosis, bone fusion about the joint, and subsequent ossification
• associated with HLA-B27 Ag
• characteristic feature
  • syndesmophyte formation (ossification of scar tissue along lateral margin bridgin the vertebral bodies to give a rigid vertebral column)

• lab dx- seronegative for RF and have no rheumatoid nodules
• definition- RA-like inflammatory arthritis with the skin lesions of psoriasis
• in the hand:
  • usually affects DIP, not PIP or MCP joints
    • RA usually affects PIP and MCP joints
• histopathology- similar to RA

• histopathology- similar to RA
• clinical triad
  • urethritis (nongonococcal)
  • conjunctivitis
  • inflammatory arthritis
• usually involves ankle and knee

• infarction of bone (cortical and trabecular) and bone marrow
• etiology
  • idiopathic
  • secondary to:
    • fractures
    • vascular injury or obstruction
    • alcoholism
    • steroid therapy
    • radiation therapy
    • other disease
      • Gaucher's
      • sickle cell disease
      • caisson's

• necrosis of bone and bone marrow (fat necrosis) that is juxtaarticular (avascular necrosis) or metadiaphyseal (bone infarct) in location
• healing occurs at the reactive interface of viable and dead bone by woven bone deposition on dead bone and granulation tissue and fibrosis replacing dead marrow