Fracture healing and anatomy of bone

1. Anatomy of Bone and Fracture healing
Orthopedics
“Journey from a disability
to an ability’’
Roll. No. 11
Aditya Rana ( 2018 )
Reference - Essential Orthopedics - J Maheshwari

2. Orientation
• Histology of bone
• Anatomy of bone
• Growth of bone
• Blood supply of bone
• Fracture healing
• Review questions

5. Bone cells: There are three main cell types in
the bone. These are:
A) Osteoblasts: Concerned with ossification,
these cells are rich in alkaline phosphatase,
glycolytic enzymes and phosphorylases.
b) Osteocytes: These are mature bone cells
which vary in activity, and may assume the
form of an osteoclast or reticulocyte. These
cells are rich in glycogen and PAS positive
granules.
c) Osteoclasts: These are multi-nucleate
mesenchymal cells concerned with bone
resorption.
These have glycolytic acid hydrolases,
collagenases and acid phosphatase enzymes.

6. ANATOMY OF BONE
Bones may be classified into four types on the basis
of their shape i.e., long, short, flat and irregular. For
practical purposes, anatomy of a typical long bone
will be discussed here.
Structure of a typical long bone:
In children, a typical long bone, such as the femur, has two
ends or epiphyses (singular epiphysis), and an
intermediate portion called the shaft or diaphysis.
The part of the shaft which adjoins the epiphysis
is called the metaphysis – one next to each epiphysis.
There is a thin plate of growth cartilage one at each end,
separating the epiphysis from the metaphysis. This is
called the epiphyseal plate.

7. At maturity, the epiphysis fuses with the
metaphysis
and the epiphyseal plate is replaced by
bone.
The articular ends of the epiphyses are
covered with articular cartilage. The rest
of the bone is covered
with periosteum which provides
attachment to
tendons, muscles, ligaments, etc.
The strands of fibrous tissue connecting
the bone to the
periosteum
are called Sharpey's fibres.

8. Microscopically, bone can be classified as either
woven or lamellar. Woven bone or immature bone
is characterized by random arrangement of bone
cells (osteocytes) and collagen fibres.
Woven bone is formed at periods of rapid bone
formation, as in
the initial stages of fracture healing.
Lamellar bone or mature bone has an orderly
arrangement of bone cells
and collagen fibres.
Lamellar bone constitutes all
bones, both cortical and cancellous.
Cortical – compact bone- diaphysis.
Cancellous – spongy – epi+ metaphysis.
1. SA increased , more bone cells,
2. vascular

9. The difference is, that in cortical bone the lamellae
are densely packed, and in cancellous bone loosely.
The basic structural unit of lamellar bone is
the osteon.
It consists of a series of concentric
laminations or lamellae surrounding a central canal,
the Haversian canal. These canals run longitudinally
and connect freely with each other and with
Volkmann's canals.
The latter run horizontally from
endosteal to periosteal surfaces.

10. GROWTH OF A LONG BONE
All long bones, with the exception of the clavicle,
develop from cartilaginous primordia (enchondral
ossification). This type of ossification commences
in the middle of the shaft (primary centre of
ossification) before birth. The secondary ossification
centres (the epiphyses) appear at the ends of the
bone, mostly* after birth.
The bone grows in length by a continuous growth
at the epiphyseal plate. The increase in the girth of
the bone is by subperiosteal new bone deposition.
The epiphysis of distal end of the femur is present
at birth.
At the end of the growth period, the epiphysis
fuses with the diaphysis, and the growth stops. The
secondary centres of ossification, not contributing
to the length of a bone, are termed apophysis (e.g.,
apophysis of the greater trochanter). The time and
sequence of appearance and fusion of epiphysis has
clinical relevance in deciding the true age (bone age)
of a child. Sometimes, an epiphyseal plate may be
wrongly interpreted as a fracture.

11. Interstitial

12. The junction between the two,
termed the cortico-cancellous junction
is a common site of fractures.
Remodeling of bone: Bone has
the ability to
alter its size, shape and structure
in response to
stress. This happens throughout
life though not
perceptible. According to Wolff's
law of bone
Remodeling , bone hypertrophy
occurs in the plane of stress.

14. BLOOD SUPPLY OF BONES
There is a standard pattern of the blood supply of a
typical long bone.
a) Nutrient artery: This vessel enters the bone
around its middle and divides into two branches,
one running towards either end of the bone.
b) Metaphyseal vessels: These are numerous small
vessels derived from the anastomosis around the
joint. They pierce the metaphysis along the line
of attachment of the joint capsule.
c) Epiphyseal vessels: These are vessels which
enter directly into the epiphysis.
d) Periosteal vessels:
Blood supply to the inner two-thirds of the bone
comes from the nutrient artery and the outer one third
from the periosteal vessels.

16. Fracture healing
Partial or complete loss of continuity in cortex = #
Primary Healing Secondary Healing
Direct healing. Indirect
No callus seen. Callus is formed.
Result of absolute stability. Result of relative stability.
Micromovements- very good for #
healing.
The healing of fractures is in many ways similar to the healing of soft tissue wounds,
except that soft
tissue heals with fibrous tissue, and end result of bone healing is mineralised
mesenchymal tissue, i.e. bone.

17. Hematoma formation Fibroblast comes -
chemotactic
Granulation tissue
formation
Fibroblast – mature –
osteoid- callus – soft
structures
Because no minerals.
Rigid callus-
consolidation
Deposition of minerals.
calcium
Irregular – woven bone
Not strong enough
Consolidation
Remodeling Lamellated bone
strong
1st stage visible on Xray Callus, earliest
3rd week
1st stage of clinical union Consolidation stage

19. Stage of hematoma: This stage lasts up to 7 days.
Stage of granulation tissue: This stage lasts for about
2-3 weeks. In this stage, the sensitized precursor cells
(daughter cells) produce cells which differentiate
and organise to provide blood vessels, fibroblasts,
osteoblasts etc. Collectively they form a soft granulation
tissue in the space between the fracture fragments. This
cellular tissue eventually gives a soft tissue anchorage
to the fracture, without any structural rigidity.
Stage of callus: This stage lasts for about 4-12
Weeks . these cells lay down an intercellular
matrix which soon
becomes impregnated with calcium salts. This
results in formulation of the callus, also called woven
bone. The callus is the first sign of union visible on
X-rays, usually 3 weeks after the fracture (Fig-2.4).
The formation of this bridge of woven bone imparts
good strength to the fracture. Callus formation is
slower in adults than in children, and in cortical
bones than in cancellous bones.

20. Stage of remodeling: Formerly called the stage
of consolidation. In this stage, the woven bone is
replaced by mature bone with a typical lamellar
structure.
This process of change is multicellular
unit based, whereby a pocket of callus is
replaced by
a pocket of lamellar bone. It is a slow
process and
takes anything from one to four years.
Stage of modelling: Formerly called the stage of
remodeling. In this stage the bone is gradually
strengthened. The shapening of cortices occurs at
the endosteal and periosteal surfaces.
HEALING OF CANCELLOUS BONES
The healing of fractured cancellous bone follows
a different pattern. The bone is of uniform spongy
texture and has no medullary cavity so that there is
a large area of contact between the trabeculae. Union
can occur directly between the bony trabeculae.
Subsequent to haematoma and granulation formation,
mature osteoblasts lay down woven bone in the
intercellular matrix, and the two fragments unite.

21. Factors affecting bone healing
a) Age of the patient: Fractures unite faster in
children. On an average, bones in children
unite in half the time compared to that in
adults.
Failure of union is uncommon in fractures of
children.
b) Type of bone: Flat and cancellous bones unite
faster than tubular and cortical bones.
c) Pattern of fracture: Spiral fractures unite
faster
than oblique fractures, which in turn unite
faster
than transverse fractures. Comminuted fractures
are usually result of a severe trauma or occur in
osteoporotic bones, and thus heal slower.
d) Disturbed pathoanatomy: Following a
fracture,
changes may occur at the fracture site, and may
hinder the normal healing process. These are:
(i) soft tissue interposition; and (ii) ischemic
fracture ends. In the former, the fracture ends
pierce through the surrounding soft tissues,
and
get stuck.
This causes soft tissue interposition
between the fragments, and prevents the callus
from bridging the fragments. In the latter, due
to anatomical peculiarities of blood supply of
some bones (e.g. scaphoid), vascularity of one
of the fragments is cut off.
Since vascularised
bone ends are important for optimal fracture
union, these fractures unite slowly or do not
unite at all.

22. e) Type of reduction: Good apposition of the
fracture results in faster union. At least half
the
fracture surface should be in contact for
optimal
union in adults. In children, a fracture may
unite
even if bones are only side-to-side in contact
(bayonet reduction).
f) Immobilisation: It is not necessary to
immobilise
all fractures (e.g., fracture ribs, scapula, etc).
They heal anyway. Some fractures need strict
immobilisation (e.g., fracture of the neck of
the
femur), and may still not heal.
g) Open fractures: Open fractures often go
into delayed union and non-union.
h) Compression at fracture site: Compression
enhances the rate of union in cancellous bone.

23. Additional information: From the entrance exams
point of VIEW
Pathognomonic sign of traumatic and fresh fracture is crepitus / ABNORMAL
MOVEMENT
Most common cause of non-union is inadequate immobilization.
Markers of bone formation: Serum bone specific alkaline phosphatase(ALP)
Serum osteocalcin
Serum peptide of type 1 collagen
Markers of bone resorption: Urine and serum crosslinked ‘N’ telopeptide
Urine and serum crosslinked ‘C’ telopeptide
Urine total free deoxypyridinoline.
TRAP, HYDROXYPROLINE,
HYDROXYLYSINE
Rate of mineralization determined by labelled tetracycline.

24. Review questions
1. Articular cartilage is found
a) at the ends of the epiphysis.
b) on the outside of the diaphysis.
c) within the epiphyseal plate.
2.Bones store calcium ions . There are times when other parts of the
body need calcium ions for chemical reactions to occur. The bones can
supply those calcium ions by allowing calcium ions to leave the bones
and enter into the bloodstream. The cells that induce this absorption of
calcium ions into the bloodstream are the ‘bone destroying cells” called
a) Osteoblasts b) osteoclasts
c) Osteocytes

25. 3. Which x ray finding is visible earliest in fracture healing and when ?
a) Pannus 2 weeks
b)Callus 3 weeks
c) Hematoma 3 weeks
d) granulation 2 week
4. Which marker more related to bone formation –
a) TRAP
b) ALT
c) AST
d) ALP

26. Q . No. 1 Match the following fractures with the description given below
( JULY - INI CET 2021 )
Fracture Site
A. March fracture 1. between the base and shaft of the
fifth
metatarsal bone
B. Bennet fracture 2. 2nd metatarsal foot
C. Jones fracture 3. Injury of 1st metacarpal
base
D. Boxer fracture 4. transverse fractures of
the 5th metacarpal neck
1. A-2, B-3,C-1,D-4 2. A-1, B-3, C-4, D- 2
3. A-3, B-2, C-1, D-4 4. A-1, B-4,C-2,D-3