- See:
-
Enchondral Ossification:
-
Limb Development
-
Growth Deformities of the Limbs:
-
Pediatric Bone Circulation:
-
Physeal Bone Bridge
-
Salter Harris Classification
- Undifferentiated or Resting Cartilage Cells:
- immediately adjacent to epiphysis are irregularly scattered cartilage cells, called the resting cell zone;
- this is germinal layer that supplies the developing cartilage cells;
- ratio of extracellular matrix to cell volume is high and the cells are in a relatively quiescent state;
- injury to this layer results in cessation of growth;
- the groove of Ranvier contains cells which flow into the into the cartilage in this layer of the growth plate;
- the function is to supply chondrocytes for increasing the width of the growth plate;
- Zone of Proliferating Cartilage:
- location in which bone length is created by active growth of cartilage cells;
- chondrocytes assume a flattened appearance, begin to divide, and become organized into columns
- on metaphyseal side, cartilage cells become aligned into well-defined columns, known as zone of cellular proliferation;
- it is at base of these columns that mitotic activity is found;
- in this small area, two or three cells thick, occurs cell division upon which entire growth in length of bone depends;
- failure of these cells to thrive results in cessation of growth at end of bone;
- Hypertrophic Cell Zone (Maturation Zone):
- there is no active growth in this layer (no cellular division) and the chondrocytes begin to terminally differentiate;
- layer in which chondrocytes become enlarged, swollen, and vacuolated in process of maturation leading to cell death;
- they hypertrophy at expense of extracellular matrix (
collagens and
proteoglycans), & these enlarged cartilage cells;
- synthesis of extracellular matrix permits newly divided cells to separate from each other;
- columns of cartilage cells extend toward metaphysis, being constantly lengthened by cell division occurring at the base;
- cells nearer the metaphysis begin to undergo changes that ultimately lead to their destruction;
- marked increase in
alkaline phosphatase enzyme activity;
- this enzyme increases the concentration of phosphate ions, which are required in the calcification process;
- in
hypophosphatasia, there is an absence of alkaline phosphatase and there is deficient mineralization of the matrix and widening of the growth plate;
- this is
weakest portion of the epiphyseal plate (
salter harris fractures occur thru this zone);
- in
rickets, there is failure of calcification which causes accumulation of cells in the hypertrophic layer;
- type X collagen production:
- short-chain collagen found only in the hypertrophic zone;
- mutations here may cause
Schmid metaphyseal chondrodysplasia;
- Zone of Provisional Calcification:
- is area where, w/ death of chondrocyte & production of AP, longitudinal bars of cartilage matrix become calcified;
- these chondrocytes prepare the matrix for calcification, which then serves as a template for osteoblastic bone formation;
- last two or three cells in column of cartilage cells are in fourth zone, the zone of provisional calcification.
- it is in this area that extracellular chondroid matrix becomes impregnated with calcium salt;
- this calcification of matrix is required for subsequent steps, including:
- invasion of cartilage cells by
blood vessels from metaphysis;
- destruction of cartilage cells;
- this provides space for the ingress of vascular channels and bone-marrow stromal cells;
- formation of bone along remaining walls of calcified cartilage matrix;
- juncture between epiphyseal plate & metaphysis is secured by welding of metaphyseal bone to calcified cartilage matrix.
-
collagen type X, may play a role in the calcification of this cartilage;
- references:
- Localization of type X collagen in canine growth plate and adult canine articular cartilage. JM Gannon. J. Orthop. Res. Vol 9. 1991. p 485-494.
-
Does osteoarthrosis depend on growth of the mineralized layer of cartilage
- Physeal Growth Arrest:
- differential diagnosis:
- internal fixation (K wires)
- chemotherapy
- radiation
- thermal injury
- immobilization
- infection
- arterial insufficiency
- extravasation of IV medicinces
Characterization of aggregating proteoglycans from proliferative, maturing, hypertrophic, and calcifying zones of cartilaginous physis;
Growth plate physiology and pathology.
Quantitation of chondrocyte performance in growth-plate cartilage during longitudinal bone growth
Differential growth by growth plates as a function of multiple parameters of chondrocytic kinetics.
