2. Introduction
These implants are introduced into the bone
remote to the fracture site and share
compressive, bending, and torsional loads with
the surrounding osseous structures
IM nails act as internal splints
with load-sharing characteristics.
3. HISTORY
Stimson in 1883 described the insertion of an ivory peg in
medullary canal.
Rush brothers described their IM pinning system in 1927.
6. Mechanics
Act by stabilizing fractures with three or four point
compression
Equilibrium between the tensioned pin and the bone
with its soft attached tissues will hold the alignment.
Bending movements are neutralized but telescopining
and rotational torsion are not prevented.
11. MechanicsElastic Deformation is principle of nail stability
Nail insertion causes radially oriented force
Force is proportional to the contact area between the bone and
nail
Produced friction stops the nail from pulling out
“Elastic Locking”
12. Elastic Locking
Bending of the nail (curvature)
Cross-sectional shape (particularly the geometry of the
surface of the implant), and its diameter
The corresponding properties of the canal (eg, size, shape,
bone quality)
13. Interlocking Nailing
These nails have proximal and distal locking
screws.
The resistance to axial and torsional forces
is mainly dependant on screw bone
interphase.
14. Interlocking screws placed proximal and
distal to the fracture site restrict translation
and rotation at the fracture site; however,
minor movements occur between the nail
and screws, allowing toggling of the bone.
17. Extrinsic Factors
Reaming of the medullary canal
Fracture stability (comminution)
The use and location of locking bolts
18. Stability
Nail size
Number of locking screws or bolts, and
Distance of the locking screw or bolt from the
fracture site.
19. Nail Diameter
Bending rigidity is proportional to the nail diameter to the
third power,
The torsional rigidity is proportional to the fourth power
20. Working Length
It is the distance between proximal and distal locking screws
The working length influences nail stiffness in bending and
torsion.
22. Screw Breakage
With cortical bone contact
weight is transmitted through
bone also.
However in its absence four
point bending can occur
23. Implant Failures
Unlocked nails typically fail either at the fracture site or
through a screw hole or slot.
Locked nails fail by screw breakage or fracturing of the nail
at locking hole sites, most commonly at the proximal hole of
the distal interlocks
25. Local effects
Damage to endosteal blood supply
Heat necrosis
With intact soft tissue envelop reaming increases the
circulation in the surrounding muscles
Rate of non union is less with reamed nail as compared to
unreamed nail.
26. SystemicReaming causes transient raise of the pulmonary arterial pressure
IM instrumentation causes liberation of bone marrow contents to
blood stream
They undergo an increase in size due to platelet adhesions
27. Leads to a transient decrease in perfusion
Subsequent cascade reaction follows.
28. Unreamed nails
It is said that unreamed nailing is advantageous in treatment
of Gustilo IIIB open fractures.
It has got less amount of superficial infection and malunion as
compared to external fixation.
34. Principles
A motor with sub-cutaneous receiver for gradual lengthening
A mechanical function with one way cluches
35. Advantages over external
fixators
Limb lengthening by external fixators is associated with
problems such as
Pain at the pin tracts
Pin tract infections
Reduced joint motion and
Prolonged fixation time.
37. Hydroxyapatite coated implants
The extraction torque of HAP coated
implants found to be higher.
Coating of the dynamic screw reduced
significantly rate of cutout
38. Growth Factors
Local application of the growth factors significantly
accelerates the fracture healing in early phase
The sustained release of growth factors doesn’t induce HO.
