Introduction Endochondral bone formation occurs in longitudinal physeal growth embryonic long bone formation non-rigid fracture healing (secondary healing) Cell biology endochondral bone formation occurs with a cartilage model chondrocytes produce cartilage which is absorbed by osteoclasts osteoblasts lay down bone on cartilaginous framework (bone replaces cartilage, cartilage is not converted to bone) forms primary trabecular bone bone deposition occurs on metaphyseal side type X collagen associated with endochondral ossification Molecular biology chondrocytes play a critical role in endochondral bone formation throughout the formation of the cartilage intermediate transcription factors involved in regulation of chondrocytes include Sox-9 considered a major regulator of chondrogenesis, regulates several cartilage-specific genes during endochondral ossification, including collagen types II, IV, and XI and aggrecan PTHrP delays differentiation of chondrocytes in the zone of hypertrophy Biomechanics variables that affect growth across the physis Hueter-Volkmann Law compression across the growth plate slows longitudinal growth tension accelerates longitudinal growth Anatomy Blood supply perichondrial artery You have not been heard from for a while. major source of nutrition to physis Longitudinal Physeal Growth Longitudinal physeal growth Reserve zone (B) Cells store lipids, glycogen, and proteoglycan aggregates for later growth and matrix production Low oxygen tension Gaucher's Diastrophic dysplasia Kneist Pseudoachondroplasia Proliferative zone (C) Proliferation of chondrocytes with longitudinal growth and stacking of chondrocytes. Highest rate of extracellular matrix production Increased oxygen tension in surroundings inhibits calcification Achondroplasia Gigantism MHE Hypertrophic zone (D) Zone of chondrocyte maturation, chondrocyte hypertrophy, and chondrocyte calcification. Three phases occur in the hypertrophic zone Maturation zone: preparation of matrix for calcification, chondrocyte growth Degenerative zone: further preparation of matrix for calcification, further chondrocyte growth in size (5x) Provisional calcification zone: chondrocyte death allows calcium release, allowing calcification of matrix Chondrocyte maturation regulated by local growth factors (parathyroid related peptides, expression regulated by Indian hedgehog gene) Type X collagen produced by hypertrophic chondrocytes important for mineralization SCFE (not renal) Rickets (provisional calcification zone) Enchondromas Mucopolysacharide disease Schmids Fractures most commonly occur through zone of provisional calcification Primary spongiosa (E) (metaphysis) Vascular invasion and resorption of transverse septa. Osteoblasts align on cartilage bars produced by physeal expansion. Primary spongiosa mineralized to form woven bone and then remodels to become secondary spongiosa (below) Metaphyseal "corner fracture" in child abuse Scurvy Secondary spongiosa (metaphysis) Internal remodeling (removal of cartilage bars, replacement of fiber bone with lamellar bone) External remodeling (funnelization) Renal SCFE Physis Periphery Groove of Ranvier During the first year of life, the zone spreads over the adjacent metaphysis to form a fibrous circumferential ring bridging from the epiphysis to the diaphysis. This ring increases the mechanical strength of the physis and is responsible for appositional bone growths Supplies chondrocytes to the periphery Osteochondroma Perichondrial fibrous ring of La Croix Dense fibrous tissue that is the primary limiting membrane that anchors and supports the physis through peripheral stability Perichondrial artery Major source of nutrition to physis Embryonic Long Bone Formation Overview allows growth in width and length formed from mesenchymal anlage around 6th week in utero. Steps of formation include cartilage model forms mesenchymal cells differentiate into chondroblasts (cartilage cells) that form the hyaline cartilaginous skeletal precursor of the bones vascularization vascular buds invade the mesenchymal model primary ossification centers form (at ~ 8 weeks) osteoprogenitor cells migrate through vascular buds and differentiate into osteoblasts forming the primary ossification centers. Marrow is simultaneously formed by resorption of central portion of the cartilage anlage by myeloid precursor cells that migrate in through the vascular buds. cartilage model continues to grow Cartilage and chondrocytes continue to grow at ends of the bone while medullary cavity expands and remodels. secondary ossification centers form develop at bone ends and lead to epiphyseal ossification center (growth plate) Non-Rigid Fracture Healing Overview mechanism of bone formation is similar to physeal endochondral ossification Cell biology soft callus is the cartilage intermediate bone replaces callus via same chondrocyte proliferation, chondrocyte hypertrophy, and finally chondrocyte calcification Examples include casting and bracing intramedullary nailing allows for motion at the fracture site, which promotes bone formation both directly (intramembranous ossification) and through a cartilage intermediate (endochondral ossification)
QUESTIONS 1 of 8 1 2 3 4 5 6 7 8 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (OBQ12.123) Which of the following would lead to accelerated maturation in the zone of hypertrophy at the physis? QID: 4483 Type & Select Correct Answer 1 An activating mutation in TGF-ß 25% (1052/4207) 2 A deactivating mutation in the parathyroid hormone-related peptide (PTHrP) receptor 32% (1329/4207) 3 A deactivating mutation in prostaglandin E2 5% (222/4207) 4 An activating mutation in the SMAD-3 protein 15% (626/4207) 5 An activating mutation in the Indian Hedgehog (Ihh) protein 21% (903/4207) L 1 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic (OBQ10.146) A 10-year-old male presents to the emergency department after his left ankle came into contact with the rotating blades of a lawn mower. He has a deep open laceration over his medial malleolus, and a radiograph is shown in Figure A. There is concern for a peripheral growth plate injury in the region of the groove of Ranvier. What is this region of the growth plate responsible for? QID: 3234 FIGURES: A Type & Select Correct Answer 1 Longitudinal bone growth 15% (456/3024) 2 Appositional bone growth 60% (1824/3024) 3 Supplying cartilage cells to the articular surface 7% (213/3024) 4 Calcification of the matrix within the growth plate 7% (215/3024) 5 Organization of the growth plate into distinct zones of proliferation and hypertrophy. 10% (299/3024) L 3 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic (OBQ09.215) Sustained compression applied to a growth plate under experimental conditions has what effect? QID: 3028 Type & Select Correct Answer 1 No effect 1% (25/1696) 2 Accelerated longitudinal growth 8% (130/1696) 3 Decelerated longitudinal growth 88% (1489/1696) 4 Decelerated apposition growth 2% (38/1696) 5 Decreased bending strength of the bone 0% (7/1696) L 1 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ07.191) Gigantism affects which region of the growth plate labeled in Figure A? QID: 852 FIGURES: A Type & Select Correct Answer 1 A 2% (26/1417) 2 B 13% (189/1417) 3 C 53% (750/1417) 4 D 28% (393/1417) 5 E 4% (55/1417) L 3 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ07.201) What region of the physis does collagen type X play a prominent role? QID: 862 Type & Select Correct Answer 1 resting zone 10% (100/1014) 2 proliferative zone 25% (251/1014) 3 zone of hypertrophy 60% (611/1014) 4 metaphysis 4% (39/1014) 5 diaphysis 1% (8/1014) L 3 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ07.113) The fracture seen in Figures A and B is most likely to occur in which of the following growth plate zones? QID: 774 FIGURES: A B Type & Select Correct Answer 1 Resting zone 1% (11/2062) 2 Proliferative zone 32% (661/2062) 3 Zone of maturation 8% (167/2062) 4 Zone of degeneration 3% (64/2062) 5 Zone of provisional calcification 56% (1151/2062) L 3 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 5 Review Tested Concept Review Full Topic (OBQ06.34) Salter-Harris type I fractures typically occur through which zone of the physis? QID: 145 Type & Select Correct Answer 1 Resting zone 3% (29/1116) 2 Proliferative zone 36% (399/1116) 3 Zone of maturation 9% (103/1116) 4 Zone of degeneration 2% (23/1116) 5 Zone of provisional calcification 50% (556/1116) L 3 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 5 Review Tested Concept Review Full Topic
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