Definition:
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
    4 Zones:

1. ZONE OF RESTING CARTILAGE/GERMINAL ZONE: –adjacent to epiphysis
   – cells small, irregularly arranged
2. ZONE OF PROLIFERATING CHONDROCYTES: -cells larger
   -undergo rapid mitosis
   -arranged in parallel columns→ separated by bars of intercellular matrix
3. ZONE OF HYPERTROPHY: -cells gradually mature, grow larger & accumulate Glycogen & Alkaline Phosphatase; Type X collagen-a distinguishing feature of hypertrophic chondrocyte.
4. 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.

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