othopaedics basics

1. HISTOLOGY OF BONE
DR. SAJIL KRISHNA K

2. BONE
• Modified connective tissue
• Structural unit :- osteon
• Consists of organic (30 – 35%) &
inorganic(65- 70%) component

3. • Inorganic component
mainly calcium and phosphorous in the form of
calcium hydroxyl apatite

4. • Organic compound
matrix(90-95%) & cells(5- 10%)

5. • Matrix
collagenous and non collagenous
proteins & enzymes(alkaline phosphatase)

6. • Cells
*osteoblast
*osteocytes
*osteoclasts
*osteoprogenitor cells

7. Osteoprogenitor cells
• Stem cells(mesenchymal in origin)
• Convert themselves into osteoblast
• Resembles fibroblast
• Present in bone surfaces( periosteal and
endosteal)

8. osteoblast
• Bone forming cells
• Found in growing surface of bone
• Varied in shape & numerous gap in between
adjacent cells
• ovoid euchromatic nucleus , basophilic
cytoplasm, have abundant rough endoplasmic
reticulum,well developed golgi complex
• Cytoplasmic processes

9. • Responsible for laying down organic matrix &
also calcification
• Has ALP in the cell membrane
• Osteoma – benign
• osteosarcoma - malignant

10. osteocyte
• Most abundant cell
• Cells of mature bone
• Lie in the lacunae
• “imprisoned” osteoblast
• Cytoplasmic processes to establish contact
with other cell
• Eosinophilic/ lightly basophilic cytoplasm and
only small amount of endoplasmic reticulum

11. • Functions
* maintain the integrity of lacunae &
canaliculi
* keep open the channels for diffusion of
nutrients
* role in removal/ deposition of matrix &
calcium

12. osteoclast
• Bone removing cells
• Occupy in pits called “resorption bag/ lacunae
of howship”
• Large cells( 20-100 microm)
• Multiple nuclei(up to 20)
• Have numerous mitochondria &
lysosomes(acid phosphatase)

13. • Surface have many folds :- ruffled membrane
along the bone resorption surface

15. ? Lamellar bone
• Made up of layers called lamellae
• Each lamellus consists of collagen fibres ,
mineral salts deposited in a gelatinous ground
substance
• Space b/w lamellae:- Lacunae
• Canal b/w lacunae: -canaliculi

17. Woven bone
• Newly formed bone
• Not have a lamellar structure
• Collagen bundles arranged in randomly
• Replaced by lamellar bone
• PAGETS DISEASE

18. Structure of cancellous bone
• Meshwork of cancellous bone :- trabeculae
• Each trabeculae have number of lamellae
• Trabeculae encloses wide spaces filled by
bone marrow

20. Structure of compact bone
• Lamellae arranged in concentric rings that
surround a narrow HAVERSIAN canal
• Haversian canal + lamellae= Haversian system
(osteon)
• b/w adjoining osteon :- interstitial lamellae
• Near the surface:- circumferential lamellae

22. • Haversian canal communicate with marrow
and out side by VOLKMANN CANAL

23. PERIOSTEUM
• Covering membrane
• Sharpeys fibre connects periosteum to bone
• Two layers
* outer( fibrous)
* inner (cellular)- cambium
• In young bone inner layer have numerous
osteoblast- osteogenic layer
• Rich blood supply

24. Functions
Medium through which muscles , tendons ,
ligaments are attached to bone
 Nutrition
Help in repair of bone
Limiting membrane and prevents spilling out
of bone tissue

25. Formation of bone
• Ossification
• Two types
endochondral ossification- cartilage bone
intramembranous ossification- membrane
bone

26. Intramembranous ossification

27. 1. Mesenchymal condensation
2. Region become highly vascular

28. 3. Some mesenchymal cells lay down bundles of
collagen fibers

29. 4. These mesenchymal cells enlarges & become
osteoblast
secrete gelatinous matrix
collagen fibers swells up
OSTEOID

30. 5. Calcium salts are deposited by the influence
of osteoblast (osteoid lamellus)

31. 6. Over this lamellae another layer of osteoid
laid down by osteoblast
7. In this way a number of lamellae formed
trabeculus

33. Endochondral ossification
1. Mesenchymal condensation

34. 2. some mesenchymal cells become
chondroblast & lay down hyaline cartilage
3. Mesenchymal cells on the surface cartilage
form perichondrium (P)

35. 4. Cartilage cells enlarges
5. Intercellular substance b/w cartilage cells
calcified ( ALP by cartilage cells)

36. 6. Nutrition to cells lost & die
7. Forms empty space- PRIMARY AREOLAE

37. 8. Some blood vessels from perichondrium
invade cartilaginous matrix with
osteoprogenitor cells( periosteal bud)
eats walls of primary areolae
secondary areolae(medullary spaces)

38. 9. Osteoprogenitor cell become osteoblast
and lie on the surface & produce osteoid
10. Osteoid calcified and form lamellus

39. Conversion of cancellous bone to compact bone

40. Blood supply of bone
• Diaphyseal nutrient artery (4)
• Epiphyseal (1) and metaphyseal artery (2)
• Periosteal artery (3)

41. Growth plate

42. • Cartilaginous remnant
between 2 centers of
ossification is known as
growth plate or physis

43. The growth plate consists of a fibrous component,
a cartilaginous component, and a bony
Component.
The fibrous component surrounds the growth
plate and is divided into an ossification groove
called the groove of Ranvier and a perichondrial
ring called the ring of LaCroix

45. Cartilagenous component
• Resting zone
• Zone of proliferation
• Zone of hypertrophy:
Maturation zone
Degenerative zone
Zone of provisional calcification

49. Resting zone
• It is adjacent to the secondary centre of
ossification
• Type 2 collagen content is highest
• Cellular proliferation is sporadic and the
chondrocytes do not contribute to
longitudinal growth
• Blood supply is via terminal branches of the
epiphyseal artery

50. • Resting zone stores lipids, glycogen and
proteoglycan aggregates for later growth and
matrix production
• Involved in the regulation of chondrocytes
proliferation by increasing expression of PTHrP
• Germinal cells of stem cell origin are found in
this zone
• Has the lowest intracellular and ionized
calcium content
• Gaucher’s disease affects this zone

52. Proliferative zone
• Characterized by longitudinal columns
flattened cells.
• Uppermost cell in each column is the
progenitor cell, which is responsible for
longitudinal growth
• Cellular proliferation and matrix formation
occurs

53. • Supplied by the terminal branches of the
epiphyseal artery
• This is an area of high oxygen concentration
• Achondroplasia typically affects this zone

55. Hypertrophic zone
• Chondrocytes are larger in size here, so that
there is less space for the ECM and hence it is
a weak zone
• It is the weakest layer of the physis under
tension, shear, and bending stress
• Rate of chondrocyte maturation is regulated
by the systemic hormones and growth factors
like parathyroid related peptide

56. • This zone is characteristically weakened in
rickets
• Mucopolysaccharidoses and
hypophosphatasia affects this zone
• Enchondromas originate here
• SCFE occurs through this zone except SCFE
associated with renal failure which occurs
through metaphyseal spongiosa

58. Zone of provisional calcification
• The calcification of matrix occurs as a result of
metaphyseal vascular invasion and apoptosis
of chondrocytes is initiated
• Here osteoblasts and osteoclasts enter with
vascular invasion and allows formation of
primary bone and subsequent remodelling

59. Blood supply
Physis is surrounded by 4 distinct
sources of blood supply.
1) Epiphyseal vessels -supply the
germinal layer. Damage leads
to closure.
2) Perichondral vessels -provide
nutrition and oxygen to the
peripheral portions.
3) Metaphyseal vessels and
4) Extensions of the nutrient
artery.

60. THANK YOU