1) The document discusses principles of intramedullary nailing, including that it is commonly used to treat long bone fractures and acts as an internal splint. 2) Intramedullary nails can be classified as centromedullary, cephalomedullary, or condylocephalic. They provide load sharing characteristics and stability depending on nail characteristics, number of locking screws, and reaming versus non-reaming. 3) Reaming of the intramedullary canal facilitates nail insertion and provides a larger diameter nail for improved stability, while non-reamed nails avoid trauma to the bone and vasculature but provide less stability.

1. PRICIPPRILES OF
INTRAMEDULLARY NAILING

2. • The intramedullary nail is commonly used for long-bone fracture
fixation and has become the standard treatment of most long-
bone diaphyseal and selected metaphyseal fractures

3. INTRODUCTION
• Today any fracture is stabilized by one of the two
• systems of fracture fixation .
• 1. compression system
• 2. splinting system
• Intramedullary fixation belongs to internal splinting
• system.
• Splintage may be defined as a construct in which
• micromotion can occur between bone & implant,
• providing only relative stability without interfragmentary
• compression.

4. INTRAMEDULLARY DEVICES ARE
BROADLY CLASSIFIED INTO:
• A.) CENTROMEDULLARY- K NAIL,FIRST
• GENERATION IM NAIL
• B.) CEPHALOMEDULLARY- GAMMA NAIL,
• RUSSELL TAYLOR NAIL,UNIFLEX, PFN
• C.) CONDYLOCEPHALIC NAIL- ENDER
• NAIL,LOTTES ETC

5. BIOMECHANICS
• When placed in a fractured long bone, IM nails act as internaL
splints with load-sharing characteristics.
• Various types of load act on an IM nail: torsion, compression, tension and bending
• Physiologic loading is a combination of all these forces

6. • Nail cross section is round resisting loads equally in all
directions.
• • Plate cross-section is rectangular
• resisting greater loads in one plane
• versus the other

7. The amount of load borne by the nail depends on the
stability of the fracture/implant construct.
• This stability is determined by
• 1.Nail Characteristics
• 2.Number and orientation of locking screws
• 3.Distance of the locking screw from the fracture site
• 4.Reaming or non reaming
• 5.Quality of the bone
• IM nails are assumed to bear most of the load initially, then
• gradually transfer it to the bone as the fracture heals.

8. Several factors contribute to the overall biomechanical profile
and resulting structural stiffness of an IM nail.
• Chief among them are:
• a)Material properties
• b)Cross-sectional shape
• c)Diameter Curves
• d)Length and working length
• e)Extreme ends of the nail
• f) Supplementary fixation devices

9. • The cross-sectional shape of the nail ,Diameter determines
• its bending and torsional strengths( Resistance of a
• structure to torsion or twisting force is called polar
• movement of inertia )
• Circular nail has polar movement of inertia proportional to
• its diameter, in square nail its proportional to the edge
• Length
• Nails with Sharp corners or fluted edges has more polar
• movement inertia
• Cloverleaf design resist bending most effectively .
• Presence of slot reduces the torsional strength . It is more rigid when
• slot is placed in tensile side

10. • Diameter :
• Nail diameter affects bending rigidity of nail.
• For a solid circular nail, the bending rigidity is proportional
• to the third power of nail diameter
• Torsional rigidity is proportional to the fourth power of
• diameter .
• Large diameter with same cross-section are both stiffer and
• stronger than smaller ones.
• • Some nails are designed in a such a way that stiffness
• doesn’t vary with diameter.

11. • The diameter of a nail should always be measured with a
circular guage.
• •In reamed nailing, the width of nail is better determined by the
feel of the
• reamers than by radiographic measurements, although the
approximate size to be used can be determined from
preoperative radiographs.

12. Size – length
• Obtain preoperative radiographs of the fractured long bone, including the proximal and
distal joints.
• If there is any question, obtain an anteroposterior radiograph of the opposite normal limb
at a tube distance of 1meter.
• A nail of the appropriate size should be taped to the side of the limb for reference, or a
radiographic ruler can be used, alternatively a Kuntscher measuring device – the
ossimeter may be used to measure length and width.
• The ossimeter has two scales, one of which takes into account the magnification caused
by the X-ray at a 1 – m tube distance.
• In most cases, a nail reaching to within 1 to 2 cm of the subchondral bone distally is
indicated.

13. CURVES:
• Longitudinal (Anterior) bow
• • Governs how easily a nail can be inserted as well as bone/ nail mismatch, in turn
influences the stability of fixation of the nail in the bone.
• • Complete congruency minimizes normal forces and hence
• little frictional component to nail’s fixation.
• • Conversely, gross mismatch increases frictional component of fixation and
inadequate fracture reduction.
• Femoral nail designs have considerably less curve, with
• radius ranging from 186 to 300 cm

14. • Mismatch in the radius of curvature between the nail and the
femur can lead to distal anterior cortical perforation

15. • When inserting nail , axial force is necessary as the nail must
• bend to fit the curvature of the medularly canal .
• The insertion force generates hoop stress in the bone
• ( Circumferential expansion stress )
• Greater the insertion force higher the hoop stress. Larger hoop
stress can split the bone

16. • Over reaming the entry hole by 0.5 - 1mm ,selecting entry point posterior
to the central axis reduce the hoop stress
• Example :
• The ideal starting point for insertion of an antegrade femoral nail is in
the posterior portion of the piriformis fossa . It reduces the hoop stress

17. Length and working length:
• A-Total nail length- total anatomical length
• B-Working length- -Length of a nail spanning the fracture
site from its distal point of fixation in the proximal fragment
to proximal point of fixation in the distal fragment

18. INTERLOCKING
• Interlocking screws are recommended for most cases of IM nailing.
• The number of interlocks used is based on fracture location,
• amount of fracture comminution , and the fit of the nail
• within the canal.
• Placing screws in multiple planes may lead to a reduction
• of minor movement
• The principle of interlocking nailing is different. The nail is
• locked to the bone by inserting screws through the bone
• and the screw holes.
• The resistance to axial and torsional forces is mainly dependent on the screw – bone interface,
• and the length of the bone is maintained even if there is a
• bone defect.

19. STATIC LOCKING
• when screws placed proximal and distal to the fracture site.
• This restrict translation and rotation at the fracture site.
• Indications – communited , spiral, pathological fractures fractures
with bone loss lengthning or shortening osteotomies , atropic non
union
• it achieves BRIDGING FIXATION through which fracture is often
held in distraction , a favourable environment for periosteal callus
formation exists and healing rather than nonunion is rule.

21. DYNAMIC LOCKING
• It achieves additional rotational control of a fragment with large
medullary canal or short epimetaphyseal fragment.
• It is effective only when the contact area between the major
fragments is atleast 50% of the cortical
• circumference.
• With axial loading, working length in bending and torsion is reduced
as nail bends and abuts against the cortex near the fracture,
improving the nail-bone contact

23. DYNAMISATION:
• •No longer std. practice to dynamize an interlocked nail by removing the locked screws .
• •It is indicated when there is a risk of development of
• nonunion or established pseudoarthrosis.
• •The screws are then removed from the longer
• fragments, maintaining adequate control of shorter
• fragment.
• Premature removal may cause shortening,
• instability and nonunion.

24. POLLER SCREW
• when malalignment develops during
Nail insertion,placement of blocking
screw, and nail reinsertion improves alignment.
• •Most reliable in proximal and distal
shaft fractures of tibia.
• A posteriorly placed screw prevents
anterior angulation and laterally placed screw prevents valgus
angulation

25. • Stability depends on the locking screw diameter for a given
• nail diameter.
• In general, 4 to 5 mm for humeral nails and 5 to 6 mm for tibial and femoral nails.
• Nail hole size should not exceed 50% of the nail diameter.
• Interlocking screws undergo four-point bending loads, with
• higher screw stresses seen at the most distal locking sites
• The number of locking screws is determined based on
• fracture location and stability.
• In general, one proximal one distal screw is sufficient for
• stable fractures.

26. • The location of the distal locking screws
• affects the biomechanics of the fracture .
• The closer the fracture to the distal
• locking screws, the nail has less cortical
• contact , which leads to increased stress
• on the locking screws.
• More distal the locking screw is from
• fracture site, the fracture becomes more
• rotationally stable

27. CLOSED AND OPEN NAILING
• Closed nailing :
• - Fluoroscopy is used to achieve fracture reduction .
• - Medullary cavity is entered through one end of the bone “
• antegrade .
• eg-Piriformis fossa in femur .
• Closed antegrade nailing is the method of choice .
• Open nailing :
• - Performed in lessthan ideal operation room conditions
• - Antegrade nailing is prefered .
• - In retrograde method nail is inserted in to the proximal
• fragment through fracture site and brought out at one end
• of the bone ,after reduction nail is driven in to the distal
• fragment
• - Infection and non union is six and ten times greater in open
• nailing

28. F R A C T U R E R E D U C T I O N
• The earlier a fracture is nailed,
• easier is the reduction.
• Shortly after injury, the hydraulic effects
• of edematous fluid can cause shortening and rigidity of the limb
segment, which may make
• fracture reduction extremely difficult.
• If nailing is not done before this degree of edema, gentle traction may
be required to regain length and alignment gradually

29. • In femur, the reduction is most easily achieved by placing the
distal fragment in neutral position, avoiding tightness of
• the iliotibial band, which could otherwise result in shortening
and a fixed valgus deformity

30. • As the tibia is subcutaneous, direct manipulation results in reduction in
• most cases.
• - In upper extremity, reduction is achieved by a combination of
• manipulation of the proximal fragment with the nail and direct
• manipulation of the distal fragment and fracture site .
- In open nailing, the key to reduction is to angle the fracture.
- The corners of the cortices of the proximal and distal fragments are
approximated at an acute angle, and the fracture is then straightened into
appropriate alignment.

31. ENTRY POINTS:
• With reamed rods, which are generally fairly rigid, the
• entry site must be directly above the intramedullary
• canal.
• Eccentric entry sites, particularly in the femur
• and tibia, can result in incarceration of the nail or
• comminution.
• For nonreamed, flexible nails, an eccentric entry site is
• usually used to take advantage of three – point fixation of the curved nail within the
medullary canal.
• Generally these nails are inserted distally through the
• supracondylar flares of the long bones

32. ANTEGRADE NAILING FOR FEMUR
• The entry point for reamed nails is in the thin cortex at the base
of the greater trochanter at the site of its junction with the
superior
• aspect of the femoral neck.

33. • Most usual entry point is just lateral to the to articular surface of
the humeral head and just medial to the greater tuberosity

34. • Tibia nailing direct route is through the patellar tendon into the
bone just proximal to the tibial tubercle , but to avoid injury to
the patellar tendon, most surgeons now enter just medial to the
patellar tendon

35. Retrograde IM nailing
• 3 cm longitudinal incision approximately 1 cm from the medial border of
patella, beginning about 2 cm proximal to distal pole of the patella

36. Intramedullary nailing—to ream or not to
ream?

37. Gerhardt Kuntscher (1900–1972)
• “Preserve” periosteal vascularity
• Indirect reduction
• IM reaming
• “Elastic nailing” and “tight fit”
• Cloverleaf nail

38. IM reaming
• The nail must be wide enough to occupy the entire cross section of the
medullary canal over its entire length” -G Kuntscher
•  IM canal diameter
•  IM nail diameter (stronger nail)
•  working length
•  fixation stability
• Axial forces
• Rotation
• Bending

39. Interlocked nailing (1980s)
• Multi-plane stability
• No need for
• Large diameter, tight fitting nails
• “Extensive” reaming

40. Unreamed nails (1990s)
• Interlocking techniques
• Implants designed for nonreamed insertion
• Initially for IM nailing of open fractures
• Unreamed nail
• Faster
• Option to reduce fracture with nail
• Less trauma to the bone and body?

41. Pathophysiology of reaming
• IM blood supply
• Reaming and nail insertion
• Elevation of IM pressure
• Thermal injury
• Effect on bone healing mechanisms

42. • Inner 2/3 of cortex
• Nutrient medullary artery
• Outer 1/3 of cortex
• Periosteum
• Extra-osseous soft tissues

43. • Any manipulation of the IM canal will affect the IM blood
supply
• Unreamed
• Minimal reaming
• Extensive reaming

45. • Initial perfusion recovery may be faster in unreamed nail
• Compensatory  periosteal blood flow
• Revascularization
• Remodeling of bone over time
• Does reaming have any long-term adverse effects on bone healing?

46. • IM canal manipulation causes  IM pressure
• Resting
30–60 mmHG
• Opening of canal
200–300 mmHG
• Guide wire/1st reamer
500–1000 mmHG
• Sequential reaming
Variable
• Nail insertion
200 to more than 1000 mmHG

47. Local effects:  IM pressure
• Occlusion blood vessels
• Efferent veins
• Subperiosteal vessels
• Debris  Haversian canals and vessels
• Fat
• Marrow
• Bone
• Compartment pressure effect?

48. Systemic effects:  IM pressure
• Intraoperative trans-esophageal echo
• No emboli—60%
• Showers—25%
• Large emboli—15%
• Effect on:
• Pulmonary function
• Central nervous system?

49. Long-bone fractures and lungs
• Fixation of long bones beneficial
• Effect of reaming and IM fixation
• Minimal adverse effect on normal lungs
• Effect on injured lungs—YES
• Difficult to quantify pulmonary injury
• Are there high risk patients? YES:
•  Damage Control versus Immediate Total Care

50. Thermal injury—bone death at 50º C
• Same issues as with IM pressure
• Tourniquet versus no tourniquet
• Heat dissipation??
• Solutions
• Reamer design and utilization
• Proper technique

51. Reaming effect: biological
• Internal bone grafting?
• Stimulation  blood flow?
• Activates greater cellular/humoral response?
• Does this enhance fracture healing?
• Goal of fixation with IM nails is to achieve stable fixation resulting in
indirect fracture healing with callus

52. Reaming effect: mechanical
• Facilitates nail insertion
• Nail insertion with minimal force
• Facilitates use of larger implant
• Improved implant mechanical properties:
• bending R3 torsion R4
• Some locking options require a larger nail
• Improved fixation stability

53. Unreamed nails
• Mechanical properties affected by:
•  nail diameter
• Locking hole size related to nail diameter
•  locking screw size
• Solid unreamed nails
• Better performance (?)
• Fixation stability
• Patient rehabilitation issues?

54. Clinical application of available data:
• Unreamed versus reamed nailing
• Multiple studies (more than 1,500 in English)
• Most either unreamed or reamed nailing
• Most are Level II or III studies
• Some Level I studies (eg, SPRINT study)
• Femur versus tibia

55. • Infection: open and closed fractures
• No difference between unreamed versus reamed nails
• Reamed nails better than unreamed nails
• Time to union
• Nonunion and delayed union
• Reoperation
• Implant problems
• Femur (reamed nails superior in every study)
• Tibia (reamed nails generally have a higher rate of healing)

56. Summary: reaming
• Increased fracture union with reamed nails
• Better mechanical properties of larger implants
• Many IM nail systems require reaming to use larger diameter nails with
multidirectional locking options
• Minimal adverse effects from limited reaming using proper reaming
techniques and reamers
• Contraindication to reaming also a contraindication to IM fixation