Bone Flashcards
Achondroplasia
Impaired cartilage proliferation in the growth plate leading to short stature or DWARFISM due to ACTIVATING MUTATION of fibroblast growth factor receptro FGFR3. Over expression of FGFR3 inhibits growth.
Clinically see short extremities with normal sized head and chest due to poor endochondrial bone formation (how long bones grow)
Endochondral vs Intramembranous Bone Formation
Endochondral = formation of a cartilage MATRIX which is then replaced by bone. Mechanism of LONG BONE growth
Intramembranous = formation of bone WITHOUT preexisting cartilage MATRIX. Way FLAT bones grow (skull and rib cage)
Osteogenesis Imperfecta
Congenital defect in bone formation from auto dominant defect in Collagen Type bONE synthesis.
Get weak bone that fractures easily, if middle ear bones fracture get hearing loss, and thinning of scleral collagen reveals underlying CHOROIDAL VEINS which leads to BLUE SCLERA
Osteoperosis
Inherited defect of osteoclast/bone resorption resulting in abnormally thick heavy bones that fracture easily.
Usually see carbonic anhydrase II mutation leading to lack of acidic environement needed for bone resorption.
Clinically see
1) Bone fractures
2) Anemia, thrombocytopenia, and leukopenia with extramedullary hematopoiesis (bony replacement of marrow (myelophthisic process)
4) hydrocephalus if foramen magnum is narrowed
5) Renal tubular acidosis = lack of carbonic anhydrase II results in impaired ability to makde bicarb leading to a metabolic acidosis
Treat with BONE MARROW TRANSPLANT since osteoclasts are derived from monocytes
Vitamin D
Derived from sunlight and diet Activation requires 25-hydroxylation by the liver followed by 1-alpha-hydroxylation by proximal tubule cells of the kidney Raises serum calcium and phosphate by 1)increasing absorption in intestine 2) Increasing reabsorption in kidney 3) increasing resorption of bone
Deficiency seen in poor diet, malabsorption, and kidney and liver failure
Rickets
Defective mineralization of OSTEOID (layed down by osteoblasts then mineralized with calcium and phosphate to form bone)
Due to low vitamin D in children.
Clinically see:
1) Pigeon breast deformity = inward bending of the ribs with anterior protrusion of the sternum
2) Frontal bossing/enlarge forehead = osteoid deposition in skull
3) Rachitic rosary = osteoid deposition in costochondral juntion
4) Bowing of the legs
Osteomalacia
Low vitamin D in adults. Inadequate mineralization results in weak bone with increased risk for fracture. Labs show: Decreased serum calcium and phosphate increased PTH Increased alkaline phosphatase
Osteoperosis Pathophys Clinically Labs Treatment
Reduction in trabecular bone mass that results in porous bone with increased risk of fracture
Peak bone mass is achieved at 30 and based on genetics, diet and exercise. Thereafter bone mass is lost. Lost more quickly when dont exercise, poor diet, and loss of estrogen
Clinically see: Bone pain and fractures in weight bearing areas such as vertebrae (shrinking and kyphosis), hi p and distal radius
Labs = serum calcium, phosphate, PTH and alkaline phosphatase are normal
Treatment (1) exercise, vitamin D, and calcium (2) Bisphosphonates = induce apoptosis of osteoclasts (3) estrogen replacemnt in theory (increases cancer) (4) NOT glucocorticoids
Paget Disease of Bone
Imbalance between osteoclasts and osteoblasts function, generaly in adults above 60.
May have viral etiology
Localized process involving one or more bones NOT entire skeleton
Distinct stages are 1)osteoclastic= osteoclasts break down bone independently of PTH and osteoblasts directions 2) mixed osteoblastic and ostecolastic = osteoclastic eventually burn out leading to 3)osteoblastic
Get thick sclerotic boens that fracture easily and have mosaic pattern of lamellar bone
Clinically see: bone pain, increasing hat size, hearing loss, lion like facies, isolated elevated alkaline phosphatase
Treatment = calcitonin (inhibits osteoclasts fxn) or bisphosphonates (induce apoptosis of osteoclasts)
Complications include high output cardiac failure (formation of AV shunts in bone) and osteosarcoma
Osteomyelitis
Infections of marrow and bone (more common in CHILDREN)
Transient bacteremia (children) seeds metaphysis while open wound bacteremia (adults) seeds epiphysis
Causes
1) Staph aureus = most common
2) n gonorrhoeae = sexually active
3) salmonella = SICKLE CELL DISEASE
4) Pseudomonas = DIABETICS or IV users
5) Pasteurella = cat/dog bite/scratch
6)myobacterium = involves vertebrae(potts disease)
Clinically get bone pain with systemic signs of fever and leukocystosis. See lytic focus surrounded by sclerosis on x-ray
Avascular Aseptic Necrosis
Ischemic necrosis of bone and bone marrow
Causes include trauma or fracture (most common), steroids, SICKLE CELL ANEMIA, and caisson disease (gas emboli like nitrogen precipitates out of blood and into the bone)
Osteoarthritis and fracture are major complications
Osteoma
Benign tumor of bonethat most commonly arises on surface of facial bones
associated with Gardner Syndrome (familail adenomatous polyposis, fibromatosis in retroperitoneum, osteoma of facial bone)
Osteoid Osteoma
Benign tumor of osteoblasts (that produce osteoid) surrounded by a rim of reactive bone.
See in young adults and more commonly in males
Arises in CORTEX of LONG BONES (femur)
Presents as bone pain that RESOLVES with aspirin
bony mass <2cm with a radioluscent core (osteoid)
Osteoblastoma
Similar to osteoid osteoma but is GREATER than 2cm, arises in vertebrae, and NOT respond to aspirin
Osteochondroma
Tumor of bone with an overlying cartilage cap that arises a lateral projection of the growth plate (metaphysis).
Overlying cartilage can transform rarely to chondrosarcoma
