SN1
SHORT NOTE
5M
★ High-yield
Describe the epiphyseal plate with its zones. Add a note on the Salter–Harris classification.
Definition
The epiphyseal (growth) plate is a disc of hyaline cartilage between the epiphysis and the metaphysis of a growing long bone, responsible for growth in length.
Zones of the Growth Plate
| Zone | Feature |
|---|---|
| 1. Resting (reserve) | Small quiescent chondrocytes; anchors the plate to the epiphysis |
| 2. Proliferation | Cells divide and stack in columns like coins — the source of growth |
| 3. Hypertrophy | Cells enlarge and accumulate glycogen; the weakest zone |
| 4. Calcification | Matrix calcifies; chondrocytes die |
| 5. Ossification | Blood vessels invade; osteoblasts lay down bone on the calcified scaffold |
- Fractures separate through the zone of hypertrophy, because the cells are large and the matrix scanty there
- Growth occurs on the epiphyseal side; replacement by bone on the metaphyseal side — so the plate maintains its thickness while the bone lengthens
Salter–harris Classification of Epiphyseal Injuries
| Type | Description | Prognosis |
|---|---|---|
| I | Straight through the plate (separation) | Good |
| II | Through the plate and a triangle of metaphysis — the commonest (75%) | Good |
| III | Through the plate and the epiphysis into the joint | Fair — intra-articular |
| IV | Through epiphysis, plate and metaphysis | Poor — risk of growth arrest |
| V | Crush injury of the plate | Worst — growth arrest is usual; often diagnosed only in retrospect |
- Mnemonic — SALTR: Straight across, Above, Lower, Through, Rammed (crush)
Fusion and its Timing
- Fusion is under hormonal control — growth hormone and thyroxine promote growth; oestrogen and testosterone cause fusion
- Girls fuse 1–2 years earlier than boys, which is why they stop growing sooner
- Most plates fuse between 16 and 21 years
- The last to fuse are the medial end of the clavicle and the iliac crest — used in age estimation
Applied Aspects
- Growth arrest after injury causes shortening if the whole plate is damaged, and angular deformity if only part is — the intact portion continues to grow
- Precocious puberty causes short adult stature, because early sex steroid exposure closes the plates prematurely despite an initial growth spurt
- Eunuchoid tall stature — delayed fusion from hypogonadism gives disproportionately long limbs
- Slipped capital femoral epiphysis occurs through the hypertrophic zone in obese adolescents and causes hip and knee pain
- Bone age is assessed from radiographs of the hand and wrist and compared with chronological age in growth disorders
All questions in General Anatomy & Osteology
- Q1Classify bones with examples. Describe the parts of a long bone and its blood supply. Add a note on the types of epiphysis. ★
- Q2Classify joints with examples. Describe the structure of a synovial joint and add a note on Hilton's law. ★
- Q3Classify skeletal muscle according to shape and action. Describe its nerve supply and add a note on the functional groups of muscles. ★
- Q4Describe the types of blood vessels. Define anastomosis and end artery with examples, and add a note on portosystemic anastomoses. ★
- Q5Describe the structure of skin and fascia. Add a note on the lymphatic system and the thoracic duct. ★
- SN1Describe the epiphyseal plate with its zones. Add a note on the Salter–Harris classification. ★
- SN2Classify cartilage with its sites and features. Add a note on articular cartilage. ★
- SN3Describe the structure and types of a synovial joint. Add a note on synovial fluid. ★
- SN4Define end artery. Give its types with examples and the consequences of its occlusion. ★
- SN5Describe the types of ossification with examples. Add a note on the cells of bone. ★
- SN6Describe the deep fascia with its modifications and functions. Add a note on compartment syndrome. ★
- SN7Describe the anatomical position, the planes of the body and the terms of movement.