Presentation about intramedullary Nailing Biomechanics, application, indications

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