EXTERNALFIXATORS

• External fixation is a method of immobilizing fractures by means of pins passed through the skin and bone.

• Pin pierces the limb completely or from one side and these pins are joined outside the limb by a rigid scaffolding .. hence the name External fixator.

• Minimum metal exists inside the tissue• Fracture elements are at will realigned,

distracted, or compressed.• Wound area is well exposed, local lavage,

flushing, dressing and surgical procedures – easy and convenient.

• Efficient stabilization• Facilitates limb elevation• Early movts of adjacent joint

• The history of external fixation goes back to the ancient times when Hippocrates in about 400 BC wrote about a simple external fixator.

• Hippocrates described a form of external fixation to splint a fracture of the tibia with the device consisting of closely fitting proximal and distal Egyptian leather rings connected by four wooden rods from a cornel tree.

• Malgaigne in 1840 has been credited with the first use of “pins” when he created a simple metal pin in a leather strap for the percutaneous pin treatment of a tibial fracture

• Parkhill 1894 Threaded pins and clamp

Lambotte 1902, self tapping threaded pins, rod, adjustable clamps

• In 1917. Humphry is the 1st man who uses threaded pins, but he uses only one pin above fracture and one below the fracture site.

• In 1948, Charnley popularized his compression device to facilitate arthrodesis of joints.

• In 1966 and 1974,Anderson et al. uses transfixing pins incorporated into a plaster cast for management of large series of tibial shaft fractures .

Aim of application of External Fixator is to achieve an environment conducive to fracture and soft tissue healing

Two main typesPin fixators and Ring fixators

PIN FIXATORS

Applied quicklyStabilize most diaphyseal #Adequate wound access – Mx of soft tissue

Disadv :# has to be reduced before construction of frame.Presence of a fixed bar, remote from the axis of the bone, limits adjustability of frame to control angulatory and rotatory deformities.Cantilevered System does not allow axial loadingHigh incidence of delayed union or non union unless fixator is modified or bone grafting is carried out.Angular deformities may occur.

• RING FIXATORS– Used in treatment of problems requiring complex reconstruction– These frames replicate structure of long tubular bone like

exoskeleton.– Bone is stabilized by tensioned wires acting like elastic band– Provides sufficient stability for most complicated diaphyseal

fractures– Multiplane deformity correction can be achieved– Excellent for Progressive deformity correction, limb lengthening

and Mx of non union

– Disadvantages :– Heavy, cumbersome– Time consuming procedure to plan and construct– Poor access to soft tissues– Risk of neurovascular damage

• Components of Pin fixatorBone screws or pinsClampsConnecting rods or tubes

• Pin – Schanz screw or half pinIt has threads at one end and a rounded tip at the other.3 mm to 6 mm diameterStabilizing hold on bone segmentDoes not pass much beyond far cortexModified cortical screw but the core diameter is slightly larger than the corresponding cortical screw (3.4 mm instead of 3mm for a 4.5mm screw)Torsional and bending strength increasesSteinman Pin. Available in 3, 4 and 5mm

Pin is described under 4 headingTip, Thread, Core and Shaft

TipTriangular tip cuts its own threads in the bone.Pilot hole is drilled before inserting the pin.A variety of pin tips are in use

• ThreadsThreads take hold in the bone and provides a secure purchase.Cutting threads initiate bone thread formation;Sizing threads bring this up to the required shape and size.Depending on the length of threaded portion, a pin may have a hold in one or both corticesShort thread engages distal cortex

CoreCore diameter affects the strength of the pinTorsional strength – cube of core diameterTensile strength – square of core diameter

ShaftStrongest part of the pinMore rigid then the threaded portionUsed to fasten pins to clamps

• CLAMPSProvides connection between pins and other componentsPermits multiplanar adjustment of the pin – tube interfaceTwo types Pin to RodRod to Rod

• UNILATERAL UNIPLANARSimple to constructStiffness in sagittal plane is higher Fewer skin entry holes – less chances of infection, less scarsPins applied in safe corridorsSufficient stability is achievedReduction has to be done before frame is complete

• UNILATERAL BIPLANARMost stable of unilateral framesUsed for treatment of tibia #Stable fixation achievedUseful in prolonged application of the fixator in cases of bone loss or open wounds

• BILATERAL UNIPLANARSteinman pin is used In cases of transverse or short oblique # or in osteotomy – axial compression is achieved by preloading the Steinman pin.For long oblique or spiral # - Lag screw might be inserted along with the construct - for stability.Complete elimination of lateral movementsUniform distribution of stresses on the corticesSkin exposed to two possible sources of contamination, double scar markUsed only for lesions of leg and supracondylar region of femurWeaker than unilateral frame in sagittal plane

• BILATERAL BIPLANARIndicated mainly in tibia, occasionally distal femur and rarely elbow, in large bony defects, for arthrodesis of knee and elbowGreat torsional stability

• MODULAR FRAMEModification of unilateral uniplanar frame.Two pins of one segment are connected to a short tube with a pin – tube clamp. Another tube and a tube to tube clamps are used to connect short tubes in two bone segments.All tubes can be rotated and fixed to reduce the fracture.Used in humerus #, for stabilization of pelvis #, open tibial #

• Important factors affecting stiffness :Number of pins used

more number of pins – more stability2 pin / segment for tibia and 3 for femurpins closer to # - more rigid more pin to pin distance in a segment – more is the bending stiffnesspin angled at 90 degree – increases torsional stiffness

Pin diameter4.5mm to 5.5mm for tibia and femur, 3.5mm for radius ulna and 2.5mm for metacarpals or metatarsalsMore the diameter – more is the stiffness

Distance between the bone and the connecting rod

Closer the pin clamps can be to the pin – bone interface – more rigid fixationOptimal distance – 4 cms2 rods increases the stiffness (Instead of 1)Stiffness of the connecting rod

Pin clamp interface Slippage of clamp decreases stiffness Periodic tightening

• Pin – Bone InterfaceThere is a race between increasing load carrying capacity of a healing bone and failure of pin bone interface

Stress reducing factors at Pin Bone interface :Pin Large diameter High modulus material Multiple pin cluster Reduced Span PreloadingFixator 2 plane fixation constructPatient Reduced weight bearing

• Preloading :Preload is a static force of sufficient magnitude applied to an implant to overcome all dynamic and muscular contracture forces and to maintain uninterrupted pin bone contact.Lack of tension – leads to micro motion – leads to pin loosening- Osteoclast initiate bone resorption at periosteal and endosteal surfacesRadial preloading – best method of preloading, achieved by inserting a pin which is larger in diameter than the pre-drilled hole – a designed misfitOptimal misfit is 0.1 mm. Not more than 0.3mm

PROF. GABRIEL ABRAMOVITCH ILIZAROV(1921-1992)

History• Professor Gavril Abramovich Ilizarov was born in the

Caucasus, in the Soviet Union in 1921.

• He was sent, without much orthopedic training, to look after injured Russian soldiers in Kurgan,Siberia in the 1950s. With no equipment he was confronted with crippling conditions of unhealed, infected, and malaligned fractures.

• With the help of the local bicycle shop he devised ring external fixators tensioned like the spokes of a bicycle. With this equipment he achieved healing, realignment and lengthening to a degree unheard of elsewhere.

• His Ilizarov apparatus is still used today as one of the distraction osteogenesis methods.

RING FIXATORS

Main components : Standard elements used to correct skeletal deformityRingsWiresBolts and bucklesPinsPin clamps

Secondary components : necessary for assembly of fixatorRodsPlatesSupportsPostsHinges WasherSocketsBoltsNuts

RINGSFlat surface and multiple holes – principal componentProvides strong support for the frame, designed to bear high stresses of the tensioned wireInternal diameter of ring measures from 80 to 240 mmComplete set has 12 different diameter rings

• It has half ring and full rings• Full ring has more holes than two connected half

rings• Half ring has 18 to 28 holes – 4mm apart and are

of 8mm diameter

• Five-eighths ring facilitates joint motion• Deployed near knee and elbow joint• Used in middle of regular frame to provide access

for soft tissue• Weaker than full ring

Half ring with curved ends• It is modified 5/8

ring with ends curved outwards

• Configuration fits deltoid area of the shoulder

Arches• Used in femoral

trochanteric area and shoulder joint

• Available as 90 and 120 degree

Bolts and Nuts• Used to fasten various parts together• Bolt has hexagonal head of 10 mm and a threaded shaft of

6mmdiameter , pitch is 1mm• 10, 16 and 30 mm long• Nuts have a diameter of 6mm and comes in 6mm, 5mm and

3mm height• 1mm pitch of inside thread• Turn of a nut is used as a driving force in Ilizarov• 1/4th turn 4 times a day is the rate of distraction –

compression

Rods• 6mm thick stainless steel

threaded rod is the main connector

• Four equidistant rods connecting 2 neighbouring rings

• More bending stiffness in a 4 rod construct

• Can withstand high axial loading • Available in 10 lengths ranging

from 60 to 400mm• Pitch of the thread is 1mm

• A slotted cannulated rod has 2x2mm slot extending the length of 20 threads acts as a connecting rod and a pulling device

• K wires can be attached by locking nuts

• Partially threaded rods along with telescopic rods provides a more stable assembly.

• Connection plates used to reinforce ring fixator

• Used to construct oval rings for foot and large frames for correction of angulation

• Threaded sockets are used to reinforced a threaded rod

• Hollow and threaded from inside

Supports, Posts and Half hingesFacilitate creation of constructPlaced at any location and fixed at any angleSupport and posts bear tremendous loadHalf hinges have a supporting base with 2 flat surfaces matching 10mm wrench

Wire fixation bolts are of 2 types cannulated and slotted

• Washers fill space between a part and the ring

• Thickness ranges from 1.5mm to 4mm

• Wrenches used for constructing frame

• Two methodsComplete frame construction before the surgery or assemble frame piece by piece

Ring PositionStationary ring is located on the strongest and widest part of the bone – proximal end5cms distal to the jointDistal supporting ring located at distal epimetaphysis 3- 5 cms away from joint linePusher puller ring is movable and is used for distraction – compression, located 3 – 5 cms distal to Fracture/Osteotomy/Non union Reference Ring used as reference, determines the distribution of translating forces, applied at apex of bony angulation

• Ring inclination is perpendicular to the bony segment

• Space between skin and ring : 3cms

• Closer the ring to the bone fragment, more stable is the fragment during all movements

Wire and Schanz screw• Trocar Tip• Bayonet pointed• Olive • Interupted threaded• Full threaded

• 1.8mm for adults and 1.5mm for children

• Wires are inserted atleast 3 cms apart

• Olive wires prevents side to side shift

• Two wires crisscrossing at 90 degree has best stability

• Less angle permits displacement and parallel wires allows free movement

Indications…• Limb lengthening • Deformity Correction.• Infected Non-unions.• Congenital Pseudarthrosis.• Treatment of Joint Contractures e.g. resistant

congenital talipes euino varus, post burns contractures, post-traumatic stiffness

• Fixation of complex fractures • Bone transport & Osteomyelitis (treatment of

missing bone in the limb, due to various causes) • Arthrodesis (fusion or joining of two bones across a

joint)

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