im nailing
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Interlocking Nail
IntroductionThese 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.
HISTORYStimson in 1883 described the insertion of an
ivory peg in medullary canal.
Rush brothers described their IM pinning system in 1927.
Gerhard KuntschnerFemoral Nail-1939
Stable Osteosynthesis
Principle of fixation was based on compression between bone and implant
Flexible NailsRush pins
Ender nails
Morote Nails
Nancy Nails
MechanicsAct 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.
ApplicationsChildren- Mainly for forearm fractures femur fracture.
Adults-Clavicle fracture Proximal humerus fracture Humeral shaft fracture Forearm fracture
DisadvantagesAdditional immobilization is often required.
Secondary loss of reduction
Shortening with loading
Intramedullary NailingUnlocked Nail
Interlocking Nail
Unreamed Nail
Reamed Nail
Unlocked Nail
Mechanics Elastic 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”
Elastic LockingBending 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)
Interlocking NailingThese nails have proximal and distal locking screws.
The resistance to axial and torsional forces is mainly dependant on screw bone interphase.
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.
Nail Bio-MechanicsIntrinsic
Extrinsic
Intrinsic FactorsMaterial properties
Cross-sectional shape Anterior bow
Diameter
Extrinsic FactorsReaming of the medullary canal
Fracture stability (comminution)
The use and location of locking bolts
Stability Nail size Number of locking screws or bolts, and
Distance of the locking screw or bolt from the fracture site.
Nail Diameter Bending rigidity is proportional to the nail
diameter to the third power, The torsional rigidity is proportional to the
fourth power
Working LengthIt is the distance between proximal and
distal locking screws
The working length influences nail stiffness in bending and torsion.
Physiological loading of the Nail
Screw BreakageWith cortical bone contact weight is transmitted
through bone also.
However in its absence four point bending can occur
Implant FailuresUnlocked 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
PATHOPHYSIOLOGY OF NAILINGLocal effects
Systemic effects.
These effects are described with reamed nailing.
Local effectsDamage to endosteal blood supplyHeat necrosisWith 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.
Systemic Reaming 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
Leads to a transient decrease in perfusion
Subsequent cascade reaction follows.
Unreamed nailsIt 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.
DisadvantagesNonunion
Distal Screw breakage
Special Designs Proximal Femoral Nails
Retrograde Nails
Distraction Nails
Knee Arthrodesis
Proximal Femoral NailSub trochanteric fracture
Fracture NOF
Intertrochanteric Fractures
Retrograde NailsDistal femur
fractures
Humeral fractures
Periprosthetic fractures
IM SKELETAL KINETIC DISTRACTOR
PrinciplesA motor with sub-cutaneous receiver for
gradual lengthening
A mechanical function with one way cluches
Advantages over external fixatorsLimb 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.
Coated ImplantsHydroxyapatite
Growth Factors
Antibiotics
Hydroxyapatite coated implants The extraction torque of HAP coated implants found to be higher.
Coating of the dynamic screw reduced significantly rate of cutout
Growth FactorsLocal application of the growth factors
significantly accelerates the fracture healing in early phase
The sustained release of growth factors doesn’t induce HO.
Antibiotics Gentamycin coated implants have shown
reduced rate of infection in animal studies.
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