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Enchondral Ossification

- See:
- Limb Development
- Longitudinal Growth:
- Pediatric Bone Circulation
- Salter Harris
- Epiphyseal Physis:

- Discussion:
- cartilage model includes three elements,
- articular cartilage:
- formation of articular cartilage depends on:
- interzone formation
- resorption of the interzone
- intersitial growth of the articular cartilage and underlying epiphyseal cartilage
- calcification of the lowest zone  of articlar cartilage at skeletal maturity;
- future epiphysis;
- these centers make their appearance in a specific order:
- center at distal end of femur is always present at birth;
- center at the proximal end in head of femur appears between 2 and 8 months following birth;
- center in proximal end of radius is not present until after 3 years of age;
- as ossification center enlarges, it does so at first in all directions at expense of surrounding cartilage, until it becomes bounded on the metaphyseal side by
epiphyseal plate & on other sides by articular cartilage;
- epiphyseal physis
- at time that varies in ea epiphysis, cartilage cells in center of mass hypertrophy, there is ingrowth of blood vessels, and bone replaces cartilage
just as it did in shaft at an earlier stage;

- Cartilagenous Model:
- cartilaginous model of long bones in fetus undergoes series of changes occurring in definite sequence that  will ultimately transform this minute structure
into an adult bone many times its size;
- covering cells of the cartilage model, the perichondrium, change from cartilage-producing cells to bone-forming cells, osteoblasts, in middle portion of shaft;
- newly created periosteum forms a thin shell of bone about middle of cartilage model;
- cells w/in center of model hypertrophy, and vessels grow into shaft from surface;
- as vessels come into contact w/ cartilage cells, these cells are destroyed and replaced by bone;
- bone nucleus spreads lengthwise in both directions from middle of model, until bone reaches level of future epiphyseal plate;
- growth in length by cartilage ends keeps pace w/ growth in length by the bony portion;
- what remains at this point is shaft of bone covered on both ends by a large mass of cartilage cells;
- this is the status of most long bones at the time of birth.

- Structural Stages:
- in the report by Rivas R and Shapiro F, the authors sought to classify the events involved in development of long bones and the
developmental age at which these events occur in order to help to elucidate the genetic and molecular mechanisms associated with these events;
- report describes the sequence of histologic events involved in the formation of long bones and their epiphyses in the New Zealand White rabbit.
- prenatal studies were performed on twelve, fourteen, fifteen, sixteen, eighteen, twenty-one, twenty-four, and twenty-seven-day-old rabbit embryos, and
postnatal studies were performed on newborn rabbits and on three-to-four-day-old; one, two, four, and six-week-old; and two, three,
four, six, and eight-month-old rabbits.
- stages included:
- limb-bud formation with uniform distribution of mesenchymal cells and formation of an apical ectodermal ridge (stage 1);
- mesenchymal condensation (stage 2);
- cartilage differentiation (stage 3);
- formation of a primary center of ossification (stage 4a);
- epiphyseal cartilage vascularization with formation of cartilage canals (stage 7);
- vascular invasion of the developing secondary ossification center (stage 9);
- bone formation and marrow cavitation in the secondary ossification center with formation of hematopoietic marrow (stage 10);
- fullest relative extent of secondary-ossification-center development in epiphyseal cartilage (stage 14);
- thinning of the physis (stage 15);
- resorption of the physis with establishment of continuity between epiphyseal and metaphyseal circulations (stage 16);
- Structural Stages in the Development of the Long Bones and Epiphyses. A Study in the New Zealand White Rabbit

- Contribution to Growth of Each Plate:
- proximal humerus: 80%
- distal humerus: 20%
- proximal radius: 25%
- distal radius: 75%
- proximal ulna: 20%
- distal ulna: 80%
- proximal femur: 30%
- distal femur: 70%
- proximal tibia: 57%
- distal tibia, 43%
- proximal fibula: 60%
- distal fibula: 40%

Morphometric analysis of chondrocyte hypertrophy.

Earliest evidence of cartilage and bone development in embryonic life.

Longitudinal growth and growth-plate activity in the lower extremity.

Two patterns of calcification in primary (physeal) and secondary (epiphyseal) growth cartilage.

Mechanisms Responsible for Longitudinal Growth of the Cortex: Coalescence of Trabecular Bone into Cortical Bone.

Development of the distal femoral epiphysis: a microscopic morphological investigation of the zone of Ranvier.

Cartilage Slide Show