gsafsaf's version from 2015-05-22 18:04

Bone Basics

Question Answer
Epiphyseal platewhere new bone formation takes place in growing long bones
Endochondral ossificationAxial + appendicular skeleton + base of skull
1st step in endochondral ossificationChondrocytes make cartilaginous model
2nd step in endochondral ossificationCartilage remodeled into woven and then lamellar bone by osteoclasts/blasts
Woven boneHaphazard organization of collagen fibers; result of rapid osteoblast production; mechanically weak; occurs after fractures + in Paget's
Lamellar boneRegular parallel alignment of collagen into sheets; mechanically strong
Membranous ossificationBones of calvarium + facial bones
1st step in membranous ossificationWoven bone formed directly without cartilage
2nd step in membranous ossificationWoven bone remodeled into lamellar bone by osteoclasts/blasts
OsteoblastsDifferentiate from mesenchymal stem cells
OsteoclastsDifferentiate from monocytes, macrophages
AchondroplasiaFailure of endochondral ossification; membranous ossification not affected
AchondroplasiaConstitutive activation of fibroblast growth factor receptor (FGFR3) inhibits chondrocyte proliferation
AchondroplasiaMajority of mutations = sporadic - assctd w advanced paternal age; autosomal dominant with full penetrance; homozygosity is lethal
If both parents have achondroplasia......25% homozygosity - death in utero; 50% heterozygous - achondroplasia, 25% no mutation
If one parent has achondroplasia, the other does not......50% of passing on mutated gene
AchondroplasiaProximal segments of limbs shorter than distal segments, frontal bossing, may have bowing of tibias
CanaliculiHow osteocytes communicate w each other; small canals connecting lacunae
LacunaSmall space in between lamellae containing an osteocyte in bone (or chondrocyte in cartilage)
OsteocyteOsteoblast that has been incorporated into bony matrix it has created
OsteoblastSecrete collagen + catalyze mineralization
OsteoclastMultinucleated giant cells found at surface of bone

Bone tumors

Question Answer
OsteochondromaYoung <25 yo male
OsteochondromaMost common benign bone tumor; bone spurs w cartilage cap; hamartoma
Osteoclastoma20-40 younger adults
Osteoclastoma"Soap-bubble" lucent X-ray; giant cell tumor
OsteoclastomaNear distal femur or proximal tibia; around knee
OsteosarcomaMost common primary malignant bone tumor of children
OsteosarcomaBoys 10-20
OsteosarcomaCodman's triangle on X-ray; tumor pushes periosteum up from surface of bone
OsteosarcomaSunburst pattern
Ewing SarcomaBoys <15
Ewing SarcomaGrows on surface of cortical bone; shaft of long bone
Ewing SarcomaDestruction of cortex on X-ray
Ewing SarcomaOnion-Skin appearance on X-ray
Ewing Sarcomat(11;22)
Lung mets to the boneLytic
Prostate mets to the boneBlastic
Breast mets to the boneLytic or Blastic
Blastic metsnew bone; weak, breaks easily; epidural spinal cord compression
Lytic metsbreak down bone; hypercalcemia

Bone Neoplasm Mnemonics

Question Answer
osteoCHondromaCHunk of bone
osteoCLastomaCLean "soap bubble"
osteoSarComaSunburst; Codman's triangle
eWING sarcomachicken WINGs and ONION RINGS
"Permanently Relocated Tumors Like Bones"Prostate, Renal cell cancer, Testes/Thyroid, Lung, Brest

Bone disorders

Question Answer
Osteopetrosis - osteoclasts are deficient in Carbonic anhydrase II
OsteopetrosisDefect of bone resorption; bone is thick yet weak - prone to fracture
OsteopetrosisOsteoclasts work too slowly
OsteoporosisOsteoblasts work too slowly
OsteoporosisCan be caused by chronic glucocorticoid/heparin use
OsteoporosisAssociated risk of hypogonadism
OsteoporosisVertebral compression fractures
OsteopetrosisLong bones
OsteopetrosisErlenmeyer flask appearance of long bones on Xray
OsteopetrosisNarrowing of foramina of skull -> CN palsies
OsteopetrosisObliteration of marrow space -> pancytopenia, anemia, thrombocytopenia, leukopenia
OsteopetrosisLabs usually normal; if severe may see: decreased Ca++, increased PTH; alk phos sometimes high
OsteopetrosisTHICK bone
Paget diseasebone ENLARGMENT (also bone pain + arthritis)
Paget diseaseLocalized disordered bone remodeling
Paget diseaseIncreased osteoclast + osteoblast activity; eventually only osteoclasts work overtime
Paget disease"My hat is too tight" -pt
Paget diseaseNarrowing of auditory foramen - hearing loss
Paget diseaseNormal: Ca++, PTH, Ph; High: alk phos
Paget diseaseIncreased risk of osteosarcoma
Why is Alk Phos elevated in Paget disease?increased boney turn-over
Why is phosphate elevated in Renal insufficiency?Nephrons cannot get rid of phosphate despite elevated PTH due to decreased Ca++ absorption
Why is phosphate decreased in vit. D intoxication?Due to increased serum Ca++, PTH goes down, allowing phosphate to increase
How does PTH generally affect Alk Phos levels?Increased PTH, increased bony turnover, increased Alk Phos; Alk Phos levels will either be normal or increased (never decreased) in bone disorders w increased PTH
Osteomalacia + RicketsReversible when vitamin D is replaced
Osteomalacia + Ricketssoft bones due to defective mineralization of osteoid
Osteomalacia + RicketsDecreased: Calcium, Ph; Increased: PTH; Increased or normal: alk phos
Osteitis fibrosa cysticaBony manifestation of endocrine disorder: either Hyperparathyroidism or Type IA pseudohypoparathyroidism
Osteitis fibrosa cystica"Brown tumors" - cysts lined by osteoclasts and filled w fibrous stroma + blood
Low bone mineral density on DEXA scanOsteitis fibrosa cystica
Low bone mineral density on DEXA scanOsteoporosis
Polyostotic fibrous dysplasiaBone replaced by collagen + fibroblasts; irregular bony trabeculae
Polyostotic fibrous dysplasia Part of McCune-Albright Syndrome (cafe-au-lait spots + precocious puberty)
Type IA pseudohypoparathyroidism Albright hereditary osteodystrophy
Type IA pseudohypoparathyroidism Endocrine disorder that manifests with osteitis fibrosa cystica
HyperparathyroidismEndocrine disorder that manifests with osteitis fibrosa cystica
Type IA pseudohypoparathyroidism PTH resistance at renal tubules -> low serum Ca++, high Ph; low Ca++ ultimately -> high PTH
HyperparathyroidismHigh PTH -> high serum Ca++, low Ph, high all phis

Bone Disorder Labs

Question Answer
Osteoporosis Ca++Normal
Osteoporosis PhosNormal
Osteoporosis Alk PhosNormal
Osteoporosis PTHNormal
Osteopetrosis Ca++Normal/Decreased
Osteopetrosis PhosNormal
Osteopetrosis Alk PhosNormal/Increased
Osteopetrosis PTHNormal/Increased
Paget disease Ca++Normal
Paget disease PhosNormal
Paget disease Alk PhosIncreased
Paget disease PTHNormal
Rickets/Osteomalacia Ca++Decreased
Rickets/Osteomalacia PhosDecreased
Rickets/Osteomalacia Alk PhosNormal/Increased
Rickets/Osteomalacia PTHIncreased
Renal insufficiency Ca++Decreased
Renal insufficiency PhosIncreased
Renal insufficiency Alk PhosNormal/Increased
Renal insufficiency PTHIncreased
Vitamin D intoxication Ca++Increased
Vitamin D intoxication PhosIncreased
Vitamin D intoxication Alk PhosNormal
Vitamin D intoxication PTHDecreased
Primary hyperparathyroidism Ca++Increased
Primary hyperparathyroidism PhosDecreased
Primary hyperparathyroidism Alk PhosIncreased
Primary hyperparathyroidism PTHIncreased
Osteitis fibrosa cystica Ca++Increased
Osteitis fibrosa cystica PhosDecreased
Osteitis fibrosa cystica Alk PhosIncreased
Osteitis fibrosa cystica PTHIncreased