The physis or growth plate in a bone is the region that separates the epiphysis from the metaphysis. It is the zone of endochondral ossification in an actively growing bone or the epiphyseal scar in a mature bone.
Structure of Physis(Zones of Growth plate)–
Extending from Epiphysis to Diaphyseal ends of the Growth Plate/Physis
- ZONE OF RESTING CARTILAGE/GERMINAL ZONE: –adjacent to epiphysis
– cells small, irregularly arranged
- ZONE OF PROLIFERATING CHONDROCYTES: -cells larger
-undergo rapid mitosis
-arranged in parallel columns→ separated by bars of intercellular matrix
- ZONE OF HYPERTROPHY: -cells gradually mature, grow larger & accumulate Glycogen & Alkaline Phosphatase; Type X collagen-a distinguishing feature of hypertrophic chondrocyte.
- ZONE OF PROVISIONAL CALCIFICATION: -thinner
-abuts directly on the bone of diaphysis
-matrix become calcified
-continuous transformation of the epiphyseal cartilage to bone.
Zone/Groove of Ranvier: –a triangular microscopic structure at the periphery of the physis,
-containing fibroblasts, chondroblasts, and osteoblasts
-responsible for peripheral growth of physis.
Perichondral ring of LaCroix: -a fibrous structure overlying the Zone of Ranvier
-connects metaphyseal periosteum to cartilaginous epiphysis
-important mechanical function→ stabilizes the epiphysis to the metaphysis.
Clinical Significance of different zones of growth plate(see table):-
Histologically, most physeal fractures occur through the proliferative zone-the weakest region of the physis; however, they can occur through any zone.
The different zones of the physis are concerned for different diseases as shown in the table.