Evolution of Intrameduallry nails

1. EVOLUTION OF
OSTEOSYNTHESIS WITH
INTRAMEDULLARY NAILS
DR. PRATEEK GOEL
3RD
YEAR ORTHO RESIDENT
LOK NAYAK HOSPITAL

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.
Long bone fractures represent the true domain of nailing due to the fact that all
other fixation techniques such as external fixation or plating cannot compete with
the benefits of the less invasive surgical approach, a no touch technique at the site
of the fracture, reasonable fixation strength, load sharing and early weight bearing.
INTRODUCTION

3. HISTORY
 Historically, the first written record is from the 16th
century from interaction with
the Spanish and the Aztecs in the New World.
 The Aztecs physicians have placed wooden sticks into the medullary canals of
patients with long bone non-union.
 In Mid 1800’s Ivory pegs were inserted into the medullary canal for non-union. In
1890, Gluck recorded the first description of an ivory intramedullary interlocked
device that contained 2 holes at the end for ivory pins.

4.  In 1917, Lejahrs introduced the concept of longer devices for stability.
 Also in 1917, Hoghid of USA reported use of autogenous bone as intramedullary
implant. He described a method whereby a piece of cortical bone was cut and
passed up the medullary canal across the fracture site.
 During World War I, in 1918, Hey Groves of England reported the use of
metallic rods for the treatment of gunshot wounds. Steel rods were passed into
the medullary cavity through an incision made over the fracture site. This
technique appeared to have a high infection rate and was not universally
accepted.

5. HEY GROVES Technique for Intramedullary nailing
of the femoral shaft

6.  Dr. Smith Petersen in 1925, introduced the “three-flanged” nail , which provided very
good results regarding rotation control and a shorter time of restraint (from 4 to 2 weeks)
for treatment of Neck of femur fracture; eliminating the use of a cast for the pelvis and
ankle.
 Americans L. V. Rush and H. L. Rush worked with their father J. Rush Hack in Meridian,
Mississippi. In 1937, they published a paper on the treatment of Monteggia fractures by
axial fixation using long thin flexible steel wires positioned antegrade olecranon.
 They claimed, that biomechanical forces exerted by muscles abductors on the proximal
fragment of the femur were similar to those of the triceps on the olecranon fragment.
The Rush nails became the most common method of osteosynthesis in North America.
 The method continued in Vienna as the Ender school of fracture fixation and survives
today in flexible pinning for pediatric fractures.

7. SMITH PETERSON NAIL
Three Flanged Nail

8. RUSH NAILS
SOLID, CIRCULAR IN CROSS
SECTION, STRAIGHT,WITH A
SHARP BEVELLED TIPS AND
A HOOK AT THE DRIVING
END.

9. ENDER NAILS
SOLID PINS WITH AN OBLIQUE TIP AND AN
EYE IN FLANGE AT THE OTHER END, WERE
ORIGINALLY DESIGNED FOR PERCUTANEOUS,
CLOSED TREATMENT OF EXTRA CAPSULAR
HIP FRACTURES

10.  , a German born military surgeon, reported about his first clinical case
of medullary nailing of a subtrochanteric fracture of the femur in 1940.
He instituted three important advances which were -
 insertion of nails from an entrance point at a distance from fracture site,
 the use of implant of sufficient caliber to allow for mechanical function of a fractured limb,
 placement of a medullary implant the full length of the marrow canal.
First he devised the nails which he called “marrow nail”. The initial nail was ‘V’ shaped
stainless steel nail which he initially inserted without reaming but later changed to a hollow
nail with slot and clover leaf section which was inserted ante-grade. He proposed that nail
would act as an internal splint that created an elastic union with the inner medullary cavity.

11.  The use of the nail was first described in the US in a march 12, 1945,
Time Magazine article, entitled “Amazing Thighbone”.
 American surgeons on discovering V-shaped metallic rods implanted in american
soldiers, sought information from Germany and were amazed at the reduction of
infections, risks, reduced blood loss, early mobilization and decrease of non unions
and decrease in overall morbidity.

12. AMAZING THIGHBONE - TIME MAGAZINE. MARCH 12, 1945;XLV:11

13. Advantage of K-Nail over Solid nail:
•Solid nail will not occupy the full width of the
medullary canal in most places since its diameter must
be selected to fit the narrowest portion of the canal. K-
nail with an elastic cross section will adjust to the
constrictions of the canal.
•Bone resorption will soon loosen a solid rod, even
though at first this rod accurately fit inside canal.
However nail with a compressible cross section will
expand during bone resorption. This nail is designed to
render the mechanical effects of bone resorption
ineffective.

14.  Lottes at the same time designed three flanged femur and tibial nail. Both
nails employed a screw-on driver-extractor.
 In 1942, Fischer has reported in German literature use of intramedullary
reaming to increase area of contact with the nail and bone. In the 1950s
Kunstcher developed flexible reamers thereby allowing smooth reaming.
 In 1946, Soeur reported on his use of a U-shaped nail in the femur, tibia
and humerus.

15.  In America, Hansen-Street nail was introduced in 1947. It was a solid
diamond shaped nail designed to resist fracture rotation by its compressive
fit within cancellous bone. They were initially inserted by closed method to
avoid infection but later changed to open retrograde nailing after
introduction of penicillin.
 In 1950, Schneider designed his nail which incorporated a double ended
stud, self broaching and fluted with a square cross section.
 Modny and Bambara introduced the transfixion intramedullary nails in
1953. This nail was cruciate shaped with multiple holes the length of the
nail to allow for placement of screws at 90° angles from each other.

16. HANSEN STREET NAIL SCHNEIDER NAIL

17.  Enthusiasm for compression plating of long bone fractures exploded during the 1960s, and
general advancement in the use of intramedullary nails “went on hiatus.” Despite the
emergence of compression plating, there were several advancements that changed the
future practice of intramedullary nailing.
 Cephalomedullary nails were first introduced in the 1960s, highlighted by the
development of the Zickel nail in 1967. The Zickel nail contained a hole in the proximal
portion in order that a separate screw could be placed through the lateral cortex of the
proximal femur into the neck and head to prevent backout of nail.
 During the 1940s and 1950s, many surgeons abandoned early radiological techniques, such
as head worn fluoroscopy, because of the potential side effects to both surgeon and
patient. This forced these surgeons to adopt an open nailing technique. The development
of radiological image intensification, in the 1960s, allowed surgeons to readopt closed
nailing techniques with a much lower risk to patient and surgeon alike.

18. SECOND GENERATION NAILING
 The enthusiasm of compression plating of the femur diminished in the 1970s and
renewed interest in refining closed intramedullary nailing techniques.
 The use of reaming gained acceptance and unreamed nailing was left only for the
open fractures. Also reamed nailings were introduced for the humerus and tibia.
 Second generation nailing’s main improvement was the use of bicortical screw
fixation above and below the fracture to satisfy the requisite control of length
and rotation Initially, first generation manufacturing and designs simply had holes
drilled into the nails.

19.  Kempf introduced a semiclosed interlocking nail in the late 1970s with a welded
proximal cylinder for proximal locking and an image mounted device for distal
targeting and interlocking. This device was used in the early 1980s in the United
States with excellent results and surpassed closed treatment and open nailing.
 These initial devices were used in dynamic and static modes based on the
surgeon’s estimate of stability, which led to a 10% malunion rate. Also, the
patients were treated non–weight bearing to minimize implant failure.
 The Russell–Taylor nail was the first closed section interlocking nail, and they
reported the clinical results in 1986.

20. RUSSELL TAYLOR NAIL KEMPF NAIL

21.  Cephalomedullary nails originally conceived and developed by Kuntscher, for
proximal femoral fractures were designed with the new manufacturing techniques
and Gamma nails by Dr. Grosse and Kempf, and reconstruction nails by Russell
and Taylor largely replaced plates and traction for subtrochanteric fractures i.e.
slotted cloverleaf-shaped interlocked nail.
 As surgical technique continued to expand during this time, there was a surge in
clinical data regarding the use of reamed interlocking nails of both the femur and
tibia.
 This was culminated by a three-part study of reamed interlocked femoral nails by
Brumback and colleagues in 1988. His work reported a 98% healing with no
malunions with the Russell– Taylor femoral nail in a static locked configuration
with 1% implant failure rate with immediate weight bearing.

22.  In the 1990s, the issue of intramedullary vascularity was used to reconsider the
advantages of reaming of the femur. These unreamed nails frequently did not
attain adequate translational stability and were proven to have a lower union rate
than by following Kuntscher’s prescription for stable translational construct.
 In 1996, the AO/ASIF developed the proximal femoral nail (PFN) as an
intramedullary device for the treatment of unstable peritrochanteric femoral
fractures.
 Brumback and associates reported a two-part study looking at immediate
weightbearing in patients with comminuted femoral shaft fractures that were
treated with intramedullary nailing.
 These investigators concluded that immediate weightbearing is advisable in
patients who had their femur fractures fixed with larger diameter nails with high
fatigue strength, as this allows for more rapid mobilization for the trauma patient
with multiple injuries of the extremities.

23. A – SCHNEIDER
B – HANSEN STREET (DIAMOND)
C – SAMPSON FLUTED
D – KUNTSCHER
E – RUSH
F – ENDER
G – MODNY
H – HALLORAN
I – HUCKSTEP
J – AO/ASOF
K – GROSSE AND KEMPF
L – RUSSELL-TAYLOR

24. THIRD GENERATION NAILING
 The third generation of Nailing from 1998 to 2008 resulted from an analysis of the
failures of second generation nailing.
 In the 1990s, entry portal errors and malalignment were the new problems.34
Also, as surgeons expanded the indications for surgery, metaphyseal fractures
emerged as a problem of inadequate stabilization and high screw breakage rates
with second generation designs.
 Third generation nailing involved a material and structural change in screw and
resulting nail design and tactical options for screw placement in the
centromedullary design of the nail.

25.  Titanium alloy screws were found to be more fatigue resistant than
stainless steel screws if the design of the screws was optimized.
 Interlocking screws primarily fail by axial load; however, if the screws are
loaded eccentrically due to instability, their fatigue life shortens.
 Multiaxial screw configurations permitted more stability especially in the
distal femur where its expanded geometry precludes a stable longitudinal
nail interference fit.
 Expansion of the proximal cross-section of the nail allowed differing hole
configurations for standard diagonal proximal fixation or reconstruction
type patterns with the same nail.

26.  Nail entry portal creation requires a precise portal acquisition using a 2 pin
targeted concept that is based on a piriformis or trochanteric entry portal
dependent on the respective nail design and follows a trajectory that best
matches the selected nail geometry in the proximal femur.
 Instrumentation of the femur for reduction and reaming is carried out
through the indwelling channel reamer to avoid entry portal erosion and
fracture.
 Reduction of the fracture has evolved from flexible wires and extensive
radiation imaging to intramedullary devices with curved geometries that
allow precannulation reduction of the proximal to distal femoral
components and subsequent reamer wire insertion only for length
measurement and reaming.

27.  Despite the wide use of PFNA and satisfactory outcomes with low major
complication rates, lateral cortex impingement in Asian patients has been
reported. A second version of PFNA (PFNA-II) was designed with a flattened lateral
surface, decreased mediolateral nail angle, and decreased proximal nail diameter.
 PFNA-II could avoid lateral cortex impingement while providing fast and stable
fixation of unstable pertrochanteric fractures.
 It has less blood loss, less operative time and less fluoroscopy time.
 When compared to a column screw, use of the helical blade results in increased
contact surface area between the device and the femoral head cancellous bone,
compressing rather than removing the limited amount of bone.

28.  Krettek made a significant contribution to nail stability
with his Poller screw concept that was initially created for
tibial applications.
 Poller is a german word meaning Bollard, a tubular
structure used to guide traffic
 Interlocking screws control rotation and length, but the
addition of the blocking screws allows the surgeon to
obtain nail stability by adjacent placement of bicortically
fixed screws ensuring translational and angular stability of
the nails.
 A posteriorly placed screw prevents anterior angulation
and laterally placed screw prevents valgus angulation.

29. FOURTH GENERATION NAILING
 We are now entering the fourth generation of nailing, which is a combination of
the 3 previous generations with the addition of the possibilities of surface
treatments to avoid infection and telemetry to ascertain the status of bone
regeneration and mechanical reconstitution.
 The two areas of future research are revolving around different biomaterials and
biologically active agents to promote bone healing.
 Two types of biomaterials that may hold promise include biodegradable polymers
and shape memory alloys. Biologically active agents, such as Bone Morphogenic
Protein-2 and 7, have been used with good success in the promotion of bone
healing in both animal models and humans.

30.  The design and improved metal will improve with possible impregnation with
biologically active biomaterials to promote bone healing.
 These new nails could also be impregnated with slow release antibiotics to
eliminate infections especially in open fractures.
 These new technologies include surface engineering with either passive or active
coupling with antibiotics, the addition of sensor technology to nails to allow non-
iodizing radiation targeting and screw insertion and telemetry through sensors as
to changes in the pH environment around the nail and load stress telemetry to
assess stiffness progression at the fracture site with bone regeneration.

31. FIRST GENERATION SECOND GENERATION THIRD GENERATION FOURTH GENERATION
- Primary splint
- Less Rotational stabliity
- Logitudinal slot over
entire length
- Locking Screw
- Improved rotational
stability
- Not Slotted
- Fit anatomical
- Titanium alloy
- Multi axial screw
fixation
- Reaming
- Surface treatment
- Telemetry
Eg- K-nail,
V-nail
Russel-Taylor Nail
PFN
Kempf Nail
PFNA

32. INDICATIONS
 Diaphyseal fractures of long bones.
 Peritrochanteric fractures
 High proximal and low distal fractures of long bones.
 Floating hip, floating knee, floating elbow
 Aseptic and septic non- union
 Osteoporotic long bone #
 Pathological #
 Open femoral & tibia grade 1 and 2

33. BIOMECHANICS
• Each nail is precurved to achieve 3-point fixation where the required precurve should
be
approximately 3 times the diameter of a long bone at its narrowest part.
o Upper Level – Entry site and proximal bone fixation
o Middle Level – Isthmus (Narrowest point of medullary cavity)
o Lower Level – Distal end (cancellous end)
• 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

34.  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
d) Length and working length
e) Extreme ends of the nail
f) Supplementary fixation devices

35.  Metallurgy less important than other parameters for stiffness of an IM Nail.
 Most of them are fabricated from stainless steel, with a small number from
titanium.
 The material must be stiff. Titanium are 1.6 times stiffer and elastic modulus is
50% lower than steel nail
 Titanium alloy has a modulus of elasticity closely approximates that of cortical
bone

36.  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

37. BASIC PRINCIPLES OF STABILITY
 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.

38.  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.

39.  When inserting nail, axial force is necessary as
the nail must bend to fit the curvature of the
medullary 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

40.  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

41.  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.

42. 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
 Interlocking can be Static or Dynamic.

43.  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.
 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

44. Static Locking
 When screws placed proximal and distal to the fracture site. This restrict
translation and rotation at the fracture site.
 It is indicated in communited , spiral, pathological fractures, fractures with bone
loss, lengthning or shortening osteotomies, Atropic non union.
 In comminuted fractures, it achieves BRIDGING FIXATION through which fracture
is often held in distraction, a favourable environment for periosteal callus
formation exists.

45. Dynamic Locking
 It achieves additional rotational control of a fragment with large medullary canal
or short epi-metaphyseal 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
 Dynamization is indicated when there is a risk of development of nonunion or
established pseudoarthrosis.

46. 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.
 Length between proximal and distal point of firm
fixation to the bone
 Unsupported portion of the nail between two
major fragments
 Whereas the total nail length is the total
anatomical length.

47.  The bending stiffness of a nail is inversely proportinal to the square of its
working length
 The torsional stiffness is inversely proportional to its working length.
 Shorter the working length stronger the fixation
 Medullary reaming prepares a uniform canal and improves nail - bone fixation
towards the fracture, thus reducing the working length.

48. BUNDLE PINNING
 These pins are C- or S – Shaped, they act like a spring.
 The equilibrium between the tensioned pin and the bone with its attached soft tissues
will hold the alignment.
 The principle of bundle nailing was introduced by Hackethal.
 He inserted many pins into the bone until they jammed within the medullary cavity to
provide compression between the nails and the bone.
 Both techniques should be seen more as IM splinting than rigid fixation.
 Bending movements are neutralized, but telescoping and rotational torsion are not
prevented with this technique.

49.  Part of the biomechanical stability is provided by the intact muscle
envelope surrounding the long bone.
 All currently available nails have beaked or hooked ends to allow
satisfactory sliding down on insertion along inner surface of the diaphysis
without impacting the opposite cortex.
 Insertion points that do not lie opposite to one another produce differing
internal tension and imbalance of the fracture stability and fixation.
 The apex of the curvature should be at the level of the fracture site.
 The nail diameter should be 40% of the narrowest medullary space
diameter.

50.  Two nails of the same diameter and similarly prebent to be used.
 Flexible nail are usually simpler to use and can be inserted more quickly.
 If infection intervenes, the complication of likely less severe. So can be used in
tibia open fracture because of its less blood supply and its subcutaneous
location.
 Because of small size of forearm bones reaming is technically difficult, so
unreamed nail have generally been used.

51. REAMING
 IM reaming can act to increase the contact area between the nail and cortical
bone by smoothing internal surfaces.
 When the nail is the same size as the reamer, 1 mm of reaming can increase the
contact area by 38%.
 Reaming reduces the working length and increase the stability.
 More reaming allows insertion of a larger-diameter nail, which provides more
rigidity in bending and torsion. Biomechanically, reamed nails provide better
fixation stability than do unreamed nails

52.  Medullary canal is more or less like an
hour-glass than a perfect cylinder.
Reaming is an attempt to make the
canal of uniform size to adapt the bone
to the nail. The size of the canal limits
the size of the nail.
 Reaming improves the length of
contact, reduces the working length and
increases the stability of the ‘tube
within a tube’

53. Local Changes
 Both reamed and unreamed nails cause damage to the endosteal blood supply.
 Experimental data suggest that reamed nailing deleteriously affects nutrient
artery blood flow, but cortical blood supply is significantly reduced after reamed
nailing compared with unreamed nailing.
 Reaming is also associated with the potential risk of fat necrosis
 Blunt reamers and the use of reamers larger in diameter than the medullary canal
Lead to increased temperature , therefore it suggested that long bones with very
narrow canals should first be reamed manually or an alternative treatment method
should be used.

54.  Clinical studies of both tibial and femoral fractures show that reamed
nailing of fractures with low – grade soft tissue injuries significantly
reduces the rates of nonunion and implant failure in comparison with
unreamed nailing.
 In fractures with an intact soft tissue envelope, reaming of the medullary
cavity increases significantly the circulation within the surrounding
muscles. This increased circulation may improve fracture healing
 Reaming does not increase the risk of compartment syndrome.
 Some surgeons believe that unreamed nailing is advantageous in the
treatment of Gustilo III B open fractures, citing higher infection rates.

55. Systemic Changes
 Fat embolism due to IM reaming was described by Kuntscher. Fat embolism due
to passage of IM contents into the bloodstream can occur.
 The incidence of fat embolism is more with femoral reaming. Reaming of the
tibia does not lead to a significant increase of IM pressure, and intraoperative
echocardiography does not show significant fat embolism in reamed tibial
fractures.

56. Advantages
Allows insertion of larger-sized implants which helps in weight bearing and joint function
during the healing process.
Improves nail-bone cortical contact across the working length of the implant and directs
fracture fragments into a more anatomical position.
From a biologic standpoint, provides systemic factors to promote mitosis of osteogenic
stem cells and to stimulate osteogenesis.
Disadvantages
Eccentric reaming may lead to malreduction of the fracture.
Destroys all medullary vessels, resulting in a initial decrease in endosteal blood flow and in
turn decreased immune response and delay in early healing of the involved cortices.
In open fractures, avascular and nonviable fragments causes increased susceptibility to
infections.
Heat: a rise in temperature upto 44.60°C can have a negative effect on fracture healing as
the threshold value of heat induced osteonecrosis is 47°C.

57. Intramedullary nailing with reaming
Local
 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.
 Damage to endo steal blood supply
(rev.-8 to 12 weeks)
 Heat necrosis
 Rate of infection is high in open fractures- therefore
not indicated.
Systemic
- Pulmonary embolisation ( not used in polytrauma
patients)
ENTRY POINT
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.
Intramedullary nailing without reaming
 Less heat necrosis
 Infection –higher in tubullar than soild nail.
 It is said that unreamed nailing is advantageous
in treatment of Gustilo lllB open fractures.
 It has got less amount of superficial infection
and malunion as compared to external fixation.
 Preservation of blood supply, reduced blood
loss, shorter operative time( no significant
changes in pulmonary embolisation)
ENTRY POINT
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.

58. NAIL FAILURE
 With all metallic implants, there is a relative race between bone healing and
implant failure.
 Occasionally, an implant will break when fracture healing is delayed or when
nonunion occurs.
 IM nails usually fail in predictable patterns. 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

59. Z Effect
 Z-Effect is an unfortunate by-product of most intramedually nails that utilize two screws
placed up into the femoral neck and head.
 Typically, the superior screw is of smaller diameter than the inferior and bears a
disproportionate amount of load during weight bearing.
 Excessive varus forces placed on the smaller screw at the lateral cortex cause it to toggle
and either back out or migrate through the femoral head into the acetabulum.
 The larger inferior screw is neither keyed in rotation nor locked in place, and it too will
either back out or migrate medially.
 The resultant Z-Effect where the two screws move in opposite directions is one mode of
failure for the conventional two screw reconstruction device.

60. THANK YOU

61. CLOSED VS 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 :
- 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
- Performed in less than ideal operation room conditions
- Infection and non union is six and ten times greater in open nailing