Interlocking nails are bone implants inserted into the medullary canal to stabilize fractures remotely. They share loading with surrounding bone and act as internal splints. Early versions were simple metal pins, but modern locked nails provide stability through proximal and distal screws. Nail design factors like diameter, length, and screw placement influence stability. Reaming increases stability but also disrupts blood supply, so unreamed nails are preferred for severe injuries. Specialized nails are used for specific fractures. Coatings can further enhance healing and reduce complications.

1. Interlocking Nail

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.

4. Gerhard Kuntschner
Femoral Nail-1939
Stable Osteosynthesis
Principle of fixation was based on compression between bone
and implant

5. Flexible Nails
Rush pins
Ender nails
Morote Nails
Nancy Nails

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.

7. Applications
Children- Mainly for forearm fractures
femur fracture.
Adults-Clavicle fracture
Proximal humerus fracture
Humeral shaft fracture
Forearm fracture

8. Disadvantages
Additional immobilization is often required.
Secondary loss of reduction
Shortening with loading

9. Intramedullary Nailing
Unlocked Nail
Interlocking Nail
Unreamed Nail
Reamed Nail

10. Unlocked Nail

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.

15. Nail Bio-Mechanics
Intrinsic
Extrinsic

16. Intrinsic Factors
Material properties
Cross-sectional shape
Anterior bow
Diameter

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.

21. Physiological loading of the Nail

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

24. PATHOPHYSIOLOGY OF NAILING
Local effects
Systemic effects.
These effects are described with reamed nailing.

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.

29. Disadvantages
Nonunion
Distal Screw breakage

30. Special Designs
Proximal Femoral Nails
Retrograde Nails
Distraction Nails
Knee Arthrodesis

31. Proximal Femoral Nail
Sub trochanteric fracture
Fracture NOF
Intertrochanteric Fractures

32. Retrograde Nails
Distal femur fractures
Humeral fractures
Periprosthetic fractures

33. IM SKELETAL KINETIC
DISTRACTOR

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.

36. Coated Implants
Hydroxyapatite
Growth Factors
Antibiotics

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.

39. Antibiotics
Gentamycin coated implants have shown
reduced rate of infection in animal studies.