DEPARTMENT OF ORTHOPAEDICSGANDHI MEDICAL COLLEGE, BHOPAL

Seminar OnPRINCIPLES AND TECHNIQUES OF AO

Moderator : Dr. J. ShuklaDr. A. Gohiya

Presented by :Dr. Radheyshyam

HISTORY OF HISTORY OF OSTEOSYNTHESISOSTEOSYNTHESIS• The term osteosynthesis was coined by The term osteosynthesis was coined by

Albin Lambotte a Belgian surgeon Albin Lambotte a Belgian surgeon regarded universally as the father of the regarded universally as the father of the modern internal and external fixation. modern internal and external fixation. He devised an external fixator and He devised an external fixator and numerous different plates and screws.numerous different plates and screws.

• Robert Danis as surgeon in Brussel Robert Danis as surgeon in Brussel published two books on osteosynthesis published two books on osteosynthesis in 1932 and 1949.in 1932 and 1949.

•A young swiss surgeon E. muller A young swiss surgeon E. muller read his second book and he drew read his second book and he drew around himself a group of interested around himself a group of interested swiss surgeons and in 1958, at an swiss surgeons and in 1958, at an historical weekend meeting in chur historical weekend meeting in chur they decided to form a study group they decided to form a study group concerning issue of internal fixation concerning issue of internal fixation of bone- the Arbeitgemeinschaft fur of bone- the Arbeitgemeinschaft fur Osteosynthe-sefragen, or AO.Osteosynthe-sefragen, or AO.

Principles of AO :Principles of AO :• 1.1. Anatomical Reduction.Anatomical Reduction.• 2.2. Stable internal fixation.Stable internal fixation.• 3.3. Preservation of Blood supplyPreservation of Blood supply• 4.4. Early active pain free mobilisation.Early active pain free mobilisation.

BIOMECHANICAL ASPECTS BIOMECHANICAL ASPECTS OF THE AO TECHNIQUEOF THE AO TECHNIQUE• Neutralization Plate or Protection PlateNeutralization Plate or Protection Plate• Compression PlatingCompression Plating• Lag screwLag screw• Tension Band PrincipleTension Band Principle• Intra Medullary NailingIntra Medullary Nailing• External Fixation.External Fixation.

PLATESPLATESIntroduction :Introduction :• Bone plates are like internal splints holding Bone plates are like internal splints holding

together the fractured ends of a bone.together the fractured ends of a bone.• A bone plate has two mechanical A bone plate has two mechanical

functions. It transmits forces from one end functions. It transmits forces from one end of a bone to the other, bypassing and thus of a bone to the other, bypassing and thus protecting the area of fractures. It also protecting the area of fractures. It also holds the fracture ends together while holds the fracture ends together while maintaining the proper alignment of the maintaining the proper alignment of the fragments throughout the healing process.fragments throughout the healing process.

Standard PlatesStandard Plates

• Narrow DCP-4.5 mmNarrow DCP-4.5 mm• Broad DCP – 4.5 mmBroad DCP – 4.5 mm• 3.5 mm DCP3.5 mm DCP• LC-DCP 3.5 & 4.5mmLC-DCP 3.5 & 4.5mm• Reconstruction plate 3.5 & 4.5mmReconstruction plate 3.5 & 4.5mm• 1/3 tubular plate 2.7, 3.5 & 4.5 mm1/3 tubular plate 2.7, 3.5 & 4.5 mm

Special PlatesSpecial Plates• T PlatesT Plates• T&L Buttress platesT&L Buttress plates• Lateral Tibial head buttress platesLateral Tibial head buttress plates• Condylar buttress plateCondylar buttress plate• Narrow lenthening platesNarrow lenthening plates• Broad Lengthening plateBroad Lengthening plate• Spoon plateSpoon plate• Clover leaf plateClover leaf plate

CLASSIFICATIONCLASSIFICATION• Regardless of their length, thickness, Regardless of their length, thickness,

geometry, configuration or type of geometry, configuration or type of holes, all pates may be classified in holes, all pates may be classified in four groups according to their four groups according to their function.function.

• Neutralization Plates.Neutralization Plates.• Compression Plates.Compression Plates.• Buttress Plates.Buttress Plates.

Buttress Position

Neutral Position

Load Position

NEUTRALIZATION PLATENEUTRALIZATION PLATE• A neutralization plate acts as a ""bridge". It A neutralization plate acts as a ""bridge". It

transmits various forces from one end of the transmits various forces from one end of the bone to the other, bypassing the area of the bone to the other, bypassing the area of the fracture. Its main function is to act as a fracture. Its main function is to act as a mechanical link between the healthy segments mechanical link between the healthy segments of bone above and below the fracture. Such a of bone above and below the fracture. Such a plate does not produce any compression at the plate does not produce any compression at the fracture site.fracture site.

• The most common clinical application of the The most common clinical application of the neutralization plate is to protect the screw neutralization plate is to protect the screw fixation of a short oblique fracture, a butterfly fixation of a short oblique fracture, a butterfly fragment or a mildly comminuted fracture of a fragment or a mildly comminuted fracture of a long bone, or for the fixation of a segmental long bone, or for the fixation of a segmental bone defect in combination with bone grafting.bone defect in combination with bone grafting.

COMPRESSION PLATECOMPRESSION PLATE• A compression plate produces a locking A compression plate produces a locking

force across a fracture site to which it is force across a fracture site to which it is applied. The effect occurs according to applied. The effect occurs according to Newton's Third Law (action and reaction Newton's Third Law (action and reaction are equal opposite). The plate is attached are equal opposite). The plate is attached to a bone fragment. It is then pulled across to a bone fragment. It is then pulled across the fracture site by a device, producing the fracture site by a device, producing tension in the plate. As a reaction to this tension in the plate. As a reaction to this tension, compression is produced at the tension, compression is produced at the fracture site across which the plate is fixed fracture site across which the plate is fixed with the screws. The direction of the with the screws. The direction of the compression force is parallel to the plate.compression force is parallel to the plate.

Application of Compression Plate

BONE UNDER BONE UNDER COMPRESSIONCOMPRESSION• Superior stability – Utilization of Superior stability – Utilization of

physiological forces.physiological forces.• Improved milieu for bone healing.Improved milieu for bone healing.• Early mobilization.Early mobilization.

BUTTRESS PLATEBUTTRESS PLATE• The mechanical function of this plate, as the The mechanical function of this plate, as the

name suggests, is to strengthen (buttress) a name suggests, is to strengthen (buttress) a weakened area of cortex. The plate prevents the weakened area of cortex. The plate prevents the bone from collapsing during the healing process. bone from collapsing during the healing process. It is usually designed with a large surface area to It is usually designed with a large surface area to facilitate wider distribution of the load.facilitate wider distribution of the load.

• A buttress plate applied a force to the bone A buttress plate applied a force to the bone which is perpendicular (normal) to the flat which is perpendicular (normal) to the flat surface of the plate.surface of the plate.

• The fixation to the bone should begin The fixation to the bone should begin in the middle of the plate, i.e. closest in the middle of the plate, i.e. closest to the fracture site on the shaft. The to the fracture site on the shaft. The screws should then be applied in an screws should then be applied in an orderly fashion, one after the other, orderly fashion, one after the other, towards both ends of the plate.towards both ends of the plate.

• A representative clinical example of A representative clinical example of a buttress plate is the T-plate used a buttress plate is the T-plate used for the fixation of fractures of the for the fixation of fractures of the distal radius and the tibial plateau.distal radius and the tibial plateau.

DCP (Dynamic Compression DCP (Dynamic Compression Plate):Plate):

Principle :Principle :-- Its a self compression plate due to Its a self compression plate due to

the special geometry of screw holes the special geometry of screw holes which allow the axial compression.which allow the axial compression.

Dynamic compression principle: The holes of the plate are shaped like an inclined and transverse cylinder. Like a ball, the screw head slides down the inclined cylinder. Because the screw head is fixed to the bone via the shaft, it can only move vertically relative to the bone. The horizontal movement of the head, as it impacts the angled side of the hole, results in movement of the bone fragment relative to the plate and leads to compression of the fracture.

• Screw hole and the spherical gliding Screw hole and the spherical gliding principle.principle.

• Axial compression result from the an interplay Axial compression result from the an interplay between screw hole geometry and eccentric between screw hole geometry and eccentric placement of the screw in the screw hole. The placement of the screw in the screw hole. The screw hole is a combination of incline and screw hole is a combination of incline and horizontal cylinder which permits the horizontal cylinder which permits the downward and the horizontal movement of a downward and the horizontal movement of a sphere the screw hand. Sideway movement of sphere the screw hand. Sideway movement of screw head is impossible. The aim is to screw head is impossible. The aim is to position the screw head at the intersection of position the screw head at the intersection of inclined and the horizontal cylinder. At this inclined and the horizontal cylinder. At this point screw head has a spherical contact in point screw head has a spherical contact in the screw hole which result in the maximum the screw hole which result in the maximum stability without completely blocking the stability without completely blocking the horizontal movement of the screw.horizontal movement of the screw.

General principles of internal fixation.

The shape of the holes of the dynamic compression plate allows inclination of the screws in a transverse

direction of +7° and in a longitudinal direction of 25°.

Advantage of DCP :Advantage of DCP :1.1. Inclined insertion 25° longitudinal and 7° Inclined insertion 25° longitudinal and 7°

sideways.sideways.2.2. Placement of a screw in neutral position without Placement of a screw in neutral position without

the danger of distraction of fragments.the danger of distraction of fragments.3.3. Insertion of a load screw for the compression.Insertion of a load screw for the compression.4.4. Usage of two load screws in the main fragments Usage of two load screws in the main fragments

for axial compression.for axial compression.5.5. Compression of several fragments individually in Compression of several fragments individually in

comminuted fractures.comminuted fractures.6.6. Application as a buttress plate in articular area.Application as a buttress plate in articular area.

Short Coming of DCP :Short Coming of DCP :

1.1. Flat under surface.Flat under surface.2.2. Inclination upto 25°Inclination upto 25°3.3. Plate hole distribution (extended Plate hole distribution (extended

middle segment) middle segment)

The structure of a limited-contact dynamic compression plate.

LC-DCP

In the dynamic compression plate (A), the area at the plate holes is less stiff than the area between them.

During bending, the plate tends to bend only in the areas of the hole. The limited-contact dynamic compression

plate (B) has an even stiffness without the risk of buckling at the screw holes.

• The LC-DCP (limited contact DCP) is a further The LC-DCP (limited contact DCP) is a further development of the DCP is used for the same development of the DCP is used for the same indications as the DCP, but the improved indications as the DCP, but the improved design offers additional advantage.design offers additional advantage.

• The evenly distributed undercuts reduces the The evenly distributed undercuts reduces the contact area between bone and plate to a contact area between bone and plate to a minimum. This significantly reduces minimum. This significantly reduces impairment of the blood supply of the impairment of the blood supply of the underlying cortical bone undercuts also allow underlying cortical bone undercuts also allow for the formation of a small callusbridge.for the formation of a small callusbridge.

• The enlarged cross section at the plate holes The enlarged cross section at the plate holes and the reduced cross section between holes and the reduced cross section between holes offer a constant degree of stiffness along the offer a constant degree of stiffness along the long axis of the plate.long axis of the plate.

• The trapezoid cross section of the plate The trapezoid cross section of the plate results in a smaller contact area between results in a smaller contact area between plate and bone.plate and bone.

• The plate holes are uniformaly spaced, The plate holes are uniformaly spaced, which permits easy positioning of the which permits easy positioning of the plate.plate.

• Undercuts plate holes; undercut at each Undercuts plate holes; undercut at each end of the plate hole allows 40 tilting of end of the plate hole allows 40 tilting of screws both ways along the long axis of screws both ways along the long axis of the plate. Lag screw fixation of short the plate. Lag screw fixation of short oblique fractures is thereby possible.oblique fractures is thereby possible.

Bridge Plating :Bridge Plating :

Bridge Plating for comminuted fracture

Wave Plating :Wave Plating :

Wave Plating for non union.

ADDITIONAL PRINCIPLES OF ADDITIONAL PRINCIPLES OF PLATE FIXATIONPLATE FIXATION• The engineering principle of the The engineering principle of the

tension band is widely used in tension band is widely used in fracture fixation. It applies to the fracture fixation. It applies to the conversion of tensile forces to conversion of tensile forces to compression forces on the convex compression forces on the convex side of an eccentrically loaded bone.side of an eccentrically loaded bone.

PREBENDING PLATESPREBENDING PLATES

• Contour to fit the bone surface snugly.Contour to fit the bone surface snugly.• Make a sharp bend opposite the fracture Make a sharp bend opposite the fracture

site; midsection is elevated.site; midsection is elevated.• Fix to the bone, starting on either side of Fix to the bone, starting on either side of

the fracture and then moving outwards.the fracture and then moving outwards.• Plate then compresses the far cortex also.Plate then compresses the far cortex also.• Apply only to two fragment fractures.Apply only to two fragment fractures.

HOW MANY SCREWS ?HOW MANY SCREWS ?• Hands-on experience suggests that, in the Hands-on experience suggests that, in the

humerus, screws grip seven cortices on each humerus, screws grip seven cortices on each side of the fracture ; in the radius and the ulna, side of the fracture ; in the radius and the ulna, five; in the tibia, six, and in the femur, seven.five; in the tibia, six, and in the femur, seven.

BonesBones No. of No. of CorticesCortices

No. of No. of HolesHoles

Type of Type of PlatePlate

ForearmForearm 5 to 6 Cortex 5 to 6 Cortex 6 holes6 holes Small 3.5Small 3.5HumeruHumeru

ss7 to 8 Cortex7 to 8 Cortex 8 holes8 holes Narrow 4.5Narrow 4.5

TibiaTibia 7 to 8 Cortex7 to 8 Cortex 7 holes7 holes Narrow 4.5Narrow 4.5FemurFemur 7 to 8 Cortex7 to 8 Cortex 8 holes8 holes Narrow 4.5Narrow 4.5ClavicleClavicle 5 to 6 Cortex5 to 6 Cortex 6 holes`6 holes` Small 3.5Small 3.5

HOW CLOSE TO THE FRACTURE HOW CLOSE TO THE FRACTURE SITE?SITE?•A screw, as a result, should not be A screw, as a result, should not be

placed closer than one centimeter placed closer than one centimeter from the fracture line.from the fracture line.

Reconstruction Plates :Reconstruction Plates :

• Can be bent and twisted in two Can be bent and twisted in two dimensions.dimensions.

• Decrease stiffness than DCP.Decrease stiffness than DCP.• Should not be bent more than 15°.Should not be bent more than 15°.• Used were the exact and complex Used were the exact and complex

contouring is required. eg. Pelvis, contouring is required. eg. Pelvis, Distal Humerus, Clavicle.Distal Humerus, Clavicle.

Reconstruction plates are thicker than third tubular plates but not quite as thick as dynamic compression plates. Designed with deep notches between the holes, they can be contoured in 3 planes to fit

complex surfaces, as around the pelvis and acetabulum. Reconstruction plates are provided in straight and slightly thicker and stiffer precurved lengths. As with tubular plates, they have oval screw

holes, allowing potential for limited compression.

One Third Tubular Plates :One Third Tubular Plates :• Plates have the form of one third of Plates have the form of one third of

the circumference of a cylinder.the circumference of a cylinder.• Low rigidity (1mm thick).Low rigidity (1mm thick).• Oval holes – Axial compression can Oval holes – Axial compression can

be achieved.be achieved.• Uses – Lateral malleolus, distal ulna, Uses – Lateral malleolus, distal ulna,

metatarsals.metatarsals.

limited stability. The thin design allows for easy shaping and is primarily used on the lateral malleolus and distal

ulna. The oval holes allow for limited fracture compression with eccentric screw placement.

LOCKING COMPRESSION PLATE LOCKING COMPRESSION PLATE (LCP)(LCP)Principle :Principle :• The basic principle of LCP is its angular The basic principle of LCP is its angular stability whereas stability of conventional stability whereas stability of conventional plate osteosynthesis relies on the friction plate osteosynthesis relies on the friction between the plate and bone.between the plate and bone.

• The principle of fixation of LCP is screw The principle of fixation of LCP is screw locking. locking.

• The functional LCP screw is like that of The functional LCP screw is like that of external fixator pins, that is why they are external fixator pins, that is why they are called as internal fixator. called as internal fixator.

• LCP provides the relative stability.LCP provides the relative stability.• # heals by the callus formation (Secondary # heals by the callus formation (Secondary

Healing). Healing).

The mechanical principle of a locked screw plate. (A) The plate sits slightly of the bone. (B) Tightening of the screw locks the screw head within the plate. The plate is not drawn toward the bone and there is no compression b/w the bone and the plate. The flux is bone/ screw/ plate/ screw/ bone.

Maintenance of primary reductionOnce the locking screws engage the plate, no further tightening is possible. Therefore, the implant locks the bone segments in their relative positions regardless of degree of reduction. Precontouring the plate minimizes the gap between the plate and the bone, but an exact fit is not necessary for implant stability. This feature is especially advantageous in minimally or less invasive plating techniques because these techniques do not allow exact contouring of the plate to the bone surface.

Bridge/Locked Plating Using Locking Screws

• Screws lock to the plate, forming a fixed-angle construct.

• Bone healing is achieved indirectly by callus formation when using locking screws exclusively.

Stability under loadBy locking the screws to the plate, the axial force is transmitted over the length of the plate. The risk of a secondary loss of the intraoperative reduction is reduced.

Blood supply to the boneLocking the screw into the plate does not generate additional compression. Therefore, the periosteum will be protected and the blood supply to the bone preserved.

Plate Design :Plate Design :• LC DCP LC DCP

features :features :• Tapered end for Tapered end for

sub sub muscular muscular insertion.insertion.

• Locking holes Locking holes

Screw :• Conical screw head• Large core diameter.• Self tapping.• Star drive recess.

Principle of internal fixation Principle of internal fixation using LCP :using LCP :1.1. 11stst reduced the # as anatomical as possible. reduced the # as anatomical as possible.2.2. Cortical screw should be used 1Cortical screw should be used 1stst in a fracture in a fracture

fragment.fragment.3.3. If the locking screw have been put, use of the If the locking screw have been put, use of the

cortical screw in the same fragment without cortical screw in the same fragment without loosening and retightening of the locking loosening and retightening of the locking screw is not recommended.screw is not recommended.

4.4. If locking screw is used first avoid spinning of If locking screw is used first avoid spinning of plates. plates.

5.5. Unicortical screws causes no loss of stability.Unicortical screws causes no loss of stability.

6.6. Osteoporotic bones bicortical Osteoporotic bones bicortical screws should be used. screws should be used.

7.7. In the comminuted # screw holes In the comminuted # screw holes close to the fracture should be close to the fracture should be used to reduce stain.used to reduce stain.

8.8. In the fracture with small or no gap In the fracture with small or no gap the immediate screw holes should the immediate screw holes should be left unfilled to reduced the be left unfilled to reduced the strain.strain.

Plate length and No. of Plate length and No. of Screws :Screws :Plate span ratio Plate span ratio Plate lengthPlate length

# length # length Comminuted # Comminuted # PSR 2PSR 2Simple # Simple # PSR 8PSR 8Plate Screw density Plate Screw density No. of ScrewsNo. of Screws

No. of Plate holes No. of Plate holes PSDPSD 0.5 to 0.40.5 to 0.4-- At least 4 cortices per main fragment for At least 4 cortices per main fragment for

comminuted fracturecomminuted fracture-- At least 3 cortices per main fragment for simple At least 3 cortices per main fragment for simple

fracture. fracture.

Plate screw density and fracture plate quotient

Indications :Indications :1.1. Osteoporotic #Osteoporotic #2.2. Periprosthetic #Periprosthetic #3.3. Multifragmentry #Multifragmentry #4.4. Delayed change from external fixation to internal Delayed change from external fixation to internal

fixation.fixation.Advantages :Advantages :1.1. Angular stability Angular stability 2.2. Axial stabilityAxial stability3.3. Plate contouring not requiredPlate contouring not required4.4. Less damage to the blood supply of bone.Less damage to the blood supply of bone.5.5. Decrease infection because of submuscular Decrease infection because of submuscular

techniquetechnique6.6. Less soft tissue damage. Less soft tissue damage.

Timing of Plate Removal, Timing of Plate Removal, Recommendations for removal Recommendations for removal of plates in the lower limb :of plates in the lower limb :• Bone / FractureBone / Fracture• Time after implantation in monthsTime after implantation in months• Malleolar fracturesMalleolar fractures• 8-128-12• The tibial pilonThe tibial pilon• 12-1812-18• The tibial shaftThe tibial shaft• 12-1812-18• The tibial headThe tibial head• 12-1812-18

• The femoral condylesThe femoral condyles• 12-2412-24• The femoral shaft: Single plate, Double PlateThe femoral shaft: Single plate, Double Plate• 24-3624-36• From month 18, in 2 steps ( Interval 06 months)From month 18, in 2 steps ( Interval 06 months)• Pertrochanteric and femoral neck fractures Pertrochanteric and femoral neck fractures

Upper extremityUpper extremity• 12-1812-18• OptionalOptional• Shaft of radius / ulnaShaft of radius / ulna• 24-2824-28• Distal radiusDistal radius• 8-128-12• MetacarpalsMetacarpals• 4-64-6

Cortical Screw :Cortical Screw :-- Use in the hard cortical bone mainly Use in the hard cortical bone mainly

in the diaphysis of the long bones. in the diaphysis of the long bones. -- Large core diameter Large core diameter -- Non self cuttingNon self cutting-- Tapping is required.Tapping is required.Cancellous Screw :Cancellous Screw :-- Large thread depth Large thread depth -- Large pitch.Large pitch.-- Non self tapping.Non self tapping.-- Tapping only near cortex.Tapping only near cortex.

The screw thread is defined by its major or outside and minor or root diameters, pitch, lead, and number

of threads. Bottom: Screw head drive types.

Common screw.

Indication :Indication :

-- Metaphyseal and epiphyseal areasMetaphyseal and epiphyseal areas-- Partially Threaded (for lag screw) Partially Threaded (for lag screw) -- Fully threaded (for plates)Fully threaded (for plates)-- Cannulated or Non cannulated Cannulated or Non cannulated

Drill Bit :Drill Bit :Used for drilling the hole in the bone.Used for drilling the hole in the bone.-- Sizes 2.5 mm, 3.2 mm, 2 mm, 4.5 mm.Sizes 2.5 mm, 3.2 mm, 2 mm, 4.5 mm.- Always use the drill bit with the sleeve.Always use the drill bit with the sleeve.- Standard drill bits – 2 flutes – air drill.Standard drill bits – 2 flutes – air drill.- Three flutes drill bits – Better for drilling Three flutes drill bits – Better for drilling

at oblique angles. at oblique angles. - During the drilling normal saline should During the drilling normal saline should

be used. be used. - Canulated drill bit used for drilling over Canulated drill bit used for drilling over

guide wires. guide wires.

Cutting EdgeFluteMargin

Axis of drill

Cutting lip

Drill Bit

Taps :Taps : Used for cutting the thread in the bone.Used for cutting the thread in the bone.Cortical Tap :Cortical Tap : - Used to cut threads in the bone of same Used to cut threads in the bone of same

size as the screw. size as the screw. - Have 3 flutes.Have 3 flutes.- Entire far cortex must be taped. Entire far cortex must be taped. - Taping should be done manually.Taping should be done manually.- Two turn forward and half turn in the Two turn forward and half turn in the

reverse direction. reverse direction. Cancellous Tap :Cancellous Tap :-- Short and wide threads slightly smaller Short and wide threads slightly smaller

than the screw.than the screw.-- One near cortex tapping is required. One near cortex tapping is required.

DIFFERENT AO SCREWSDIFFERENT AO SCREWS LARGE STANDARD SCREWS.LARGE STANDARD SCREWS. 4.5 mm Cortex Screw4.5 mm Cortex Screw

6.5 mm Cancellous 6.5 mm Cancellous ScrewScrew

Malleolar Screw 4.5Malleolar Screw 4.5CANNULATED SCREW CANNULATED SCREW

SYSTEMSYSTEM6.5 Cannulated Screw6.5 Cannulated Screw4.0 mm Cannulated 4.0 mm Cannulated

ScrewScrew3.5 Cannulated Screw3.5 Cannulated Screw

SMALL FRAGMENT SCREWSMALL FRAGMENT SCREW 3.5 mm Cortical Screw3.5 mm Cortical Screw4.0 Canceleous Screw4.0 Canceleous Screw-Partially Threaded.-Partially Threaded.-Fully Threaded-Fully Threaded

MINI SCREWMINI SCREW 2.7 mm Cortex Screw2.7 mm Cortex Screw2.0 mm Cortex Screw2.0 mm Cortex Screw1.5 mm Cortex Screw1.5 mm Cortex Screw

THE LAG SCREW

A lag screw is the most effective way to achieve compression between two bone fragments; it pulls the fragments together producing pressure across the fracture line. It achieves this by providing purchase on the distal fragment while being able to turn freely in the proximal. If the screw threads engage both cortices, the fragments remain apart like two nuts on the same bolt.

Top: Biomechanics of cannulated and noncannulated screws. Bottom: Ideally, lag screw fixation produces maximum interfragmentary compression when the screw is placed perpendicular to the fracture line.

Optimal inclination of the screw in relation to a simple fracture plane.

T-lag screw.

PRINCIPLE PRINCIPLE • The screw must glide freely through The screw must glide freely through

the near fragment and engage only the near fragment and engage only the far fragment.the far fragment.

• Wherever a screw crosses a fracture Wherever a screw crosses a fracture line it should be inserted as lag line it should be inserted as lag screw.screw.

• Two small screws produce a more Two small screws produce a more stable fixation than one large screw.stable fixation than one large screw.

ScrewScrew Core Core diamediame

terter

ThreaThread d

diamediameterter

PitchPitch Drill Drill bit for bit for glidingliding holeg hole

Drill Drill bit for bit for thread thread holehole

Tap Tap diamediame

terter

Large Large StandarStandard d ScrewsScrews

7mm 7mm CancelloCancellous Screwus Screw

4.5m4.5mmm

7mm7mm 2.75m2.75mmm

4.5m4.5mmm

7mm7mm

6.5mm 6.5mm cancellocancellous screwus screw

3.5m3.5mmm

6.5m6.5mmm

2.7mm2.7mm 3.2m3.2mmm

4.5m4.5mmm

6.5m6.5mmm

4.5mm 4.5mm cancellocancellous screwus screw

4.5m4.5mmm

3.1m3.1mmm

1.75m1.75mmm

3.2m3.2mmm

4.5m4.5mmm

4.5mm 4.5mm corticalcortical

3mm 3mm 4.5 4.5 mmmm

1.75m1.75mmm

4.5m4.5mmm

3.2m3.2mmm

4.5m4.5mmm

Small Small FragmeFragment nt Screws Screws

3.5mm 3.5mm cancelloucancellous screws screw

2.5m2.5mmm

3.5m3.5mmm

1.25m1.25mmm

2.7m2.7mmm

3.5m3.5mmm

4mm 4mm CancellouCancellous screw s screw

1.9m1.9mmm

4mm4mm 1.75m1.75mmm

2.5m2.5mmm

4mm4mm

3.5mm 3.5mm Cortex Cortex ScrewScrew

2.4m2.4mmm

3.5m3.5mmm

1.25m1.25mmm

3.5m3.5mmm

2.5m2.5mmm

3.5m3.5mmm

Mini Mini FragmeFragment nt ScrewsScrews

2.7mm 2.7mm Cortex Cortex ScrewScrew

1.9m1.9mmm

2.7m2.7mmm

1mm1mm 2.7m2.7mmm

2mm2mm 2.7m2.7mmm

2mm 2mm Cortex Cortex ScrewScrew

1.3m1.3mmm

2mm2mm 0.6mm0.6mm 2mm2mm 1.5m1.5mmm

2mm2mm

1.5mm 1.5mm Cortex Cortex ScrewScrew

1mm1mm 1.5m1.5mmm

0.5mm0.5mm 1.5m1.5mmm

1.1m1.1mmm

1.5m1.5mmm

DYNAMIC HIP SCREW & DYNAMIC DYNAMIC HIP SCREW & DYNAMIC CONDYLAR SCREWCONDYLAR SCREW• The dynamic hip screw (DHS) implant system The dynamic hip screw (DHS) implant system

has been designed primarily for the fixation of has been designed primarily for the fixation of trochanteric fractures. It may also be used for trochanteric fractures. It may also be used for certain subtrochanteric fractures as well as for certain subtrochanteric fractures as well as for selected basi-cervical femoral fractures.selected basi-cervical femoral fractures.

• The implant is based on the sliding nail principle The implant is based on the sliding nail principle which allows impaction of the fracture. This is which allows impaction of the fracture. This is made possible by the insertion of a wide made possible by the insertion of a wide diameter screw into the femoral head. A side diameter screw into the femoral head. A side plate, which has barrel at a fixed angle is slid plate, which has barrel at a fixed angle is slid over the screw and fixed to the femoral shaft.over the screw and fixed to the femoral shaft.

• The dynamic condylar screw (DCS) is similar The dynamic condylar screw (DCS) is similar to the DHS in its design and concept. The to the DHS in its design and concept. The fixed angle between plate and barrel is 95 fixed angle between plate and barrel is 95 and the plate is contoured to fit the lateral and the plate is contoured to fit the lateral surface of the distal end of the femur.surface of the distal end of the femur.

• The main indications are fractures of the The main indications are fractures of the distal femur and inter-condylar fractures. It distal femur and inter-condylar fractures. It may also be used for certain intertrochanteric may also be used for certain intertrochanteric fractures and very proximal subtrochanteric fractures and very proximal subtrochanteric fractures. Impaction of compression of the fractures. Impaction of compression of the fracture is achieved by using the compression fracture is achieved by using the compression screw.screw.

DYNAMIC CONDYLAR SCREW

DHS :DHS :• Example of measurements :Example of measurements :• Length of measurements :Length of measurements :• Length measuredLength measured 105 mm105 mm• Reamer settingReamer setting 95 mm95 mm• Tapping depthTapping depth 95 mm95 mm• DHS/DCS Screw lengthDHS/DCS Screw length 95 mm95 mmDCSDCS• Length measuredLength measured 85 mm85 mm• Reamer settingReamer setting 75 mm75 mm• Tapping depthTapping depth 75 mm75 mm• DCS ScrewDCS Screw 70 mm70 mm

Cannulated Cancellous Screw Fixation in Cannulated Cancellous Screw Fixation in Fracture Neck Femur :Fracture Neck Femur :

-- Parallel 6.5mm CCS are used in triangular or inverted Parallel 6.5mm CCS are used in triangular or inverted triangular configuration. triangular configuration.

- After fracture reduction antiversion is determined.After fracture reduction antiversion is determined.- 2mm threaded guide wire is inserted in the centre of 2mm threaded guide wire is inserted in the centre of

the neck in both AP and lateral view.the neck in both AP and lateral view.- Parallel wire guide is replaced over the central guide Parallel wire guide is replaced over the central guide

wire.wire.- 2mm guide wire are inserted into the subchondral bone 2mm guide wire are inserted into the subchondral bone

of the femoral head starting with the most superior. of the femoral head starting with the most superior. - Parallel wire guide is removed and length is Parallel wire guide is removed and length is

determined. determined. - Canulated drill bit is used. Canulated drill bit is used. - Tapping is done with 6.5mm tap.Tapping is done with 6.5mm tap.- Appropriate screws are inserted. Appropriate screws are inserted.

TENSION BAND PRINCIPLE

Tension-band principle.

Tension-band principle at the femur.

• Tension Band Principle :-Tension Band Principle :- Its Its describes how the tensile forces are describes how the tensile forces are converted into compressive forces by converted into compressive forces by applying a devise eccentrically or to applying a devise eccentrically or to the convex side of a curved tube or the convex side of a curved tube or bone.bone.

• Indications :-Indications :- Fracture Patella, Fracture Patella, olecranon, medial malleolus, greater olecranon, medial malleolus, greater trochanter of the femur. trochanter of the femur.

• StaticStatic• Dynamic Dynamic

Pitfalls and Complications:Pitfalls and Complications:• The most complication is failure of the The most complication is failure of the

implant. A wire put under pure tension implant. A wire put under pure tension is very strong. However, if bending is very strong. However, if bending forces are added, it will break by forces are added, it will break by fatigue quite rapidly. As this also holds fatigue quite rapidly. As this also holds true for plates, it appears essential true for plates, it appears essential that in the diaphysis, the tension side that in the diaphysis, the tension side of the bone is known and the opposite of the bone is known and the opposite cortex is able to withstand the cortex is able to withstand the compression forces.compression forces.

INTRAMEDULLARY NAILINGINTRAMEDULLARY NAILING• Load sharing device Load sharing device • Axial and rotational stabilityAxial and rotational stability• Maintains the length Maintains the length • Biological fixation Biological fixation • Minimal soft tissue exposureMinimal soft tissue exposure• Early weight bearingEarly weight bearing

Intramedullary Nailing :Intramedullary Nailing :• The principle of fixation is based on The principle of fixation is based on

the compression between the bone the compression between the bone and the nail.and the nail.

Interlocking Intramedullary Nail :Interlocking Intramedullary Nail :• Nail have the proximal and distal Nail have the proximal and distal

screw holes. Nail is locked by the screw holes. Nail is locked by the interlocking screws. The resistance to interlocking screws. The resistance to the torsial and axial force depend on the torsial and axial force depend on the screw bone interface. the screw bone interface.

Working Length :Working Length :• Distance between the proximal and Distance between the proximal and

distal interlocking screws. distal interlocking screws.

Dyanamization : Dyanamization : • Interlocking Nails can be locked in dynamic Interlocking Nails can be locked in dynamic

or static mode.or static mode.• Dyanamization means placing the screw at Dyanamization means placing the screw at

only one end of the bone.only one end of the bone.Static LockingStatic Locking means placing the screw at means placing the screw at

the both ends of the bone. the both ends of the bone. • Dynamization can be done at the 8-12 Dynamization can be done at the 8-12

weeks for delayed union.weeks for delayed union.• Screw is removed from the longer Screw is removed from the longer

fragment.fragment.

INDICATINOS FOR UNIVERSAL INDICATINOS FOR UNIVERSAL NAILING OF FEMUR AND TIBIA NAILING OF FEMUR AND TIBIA WITH AND WITHOUT LOCKINGWITH AND WITHOUT LOCKING

• Conventional nailing without locking for stable Conventional nailing without locking for stable fractures with bony support in the middle third fractures with bony support in the middle third of the bone, such as:of the bone, such as:

• Transverse fractures.Transverse fractures.• Short oblique fracturesShort oblique fractures• Delayed union or nonunionDelayed union or nonunion• Locked medullary nailing for unstable fractures Locked medullary nailing for unstable fractures

without bony support in approximately the without bony support in approximately the middle 60% of the bone, where axial and middle 60% of the bone, where axial and rotational stability has to be achieved, such asrotational stability has to be achieved, such as

Fractures near the metaphysic Fractures near the metaphysic Long torsional fracturesLong torsional fractures Segmental fracturesSegmental fractures Multifragmentary fracturesMultifragmentary fractures Fractures with bone defects.Fractures with bone defects.

TYPES OF INTRAMEDULLARY TYPES OF INTRAMEDULLARY NAILS :NAILS :

• Centromedullary nailsCentromedullary nails• Condylocephalic nailsCondylocephalic nails• Cephalomedullary nailsCephalomedullary nails

Blk screws.

Working Length

K wire : K wire : Used for the temporary and permanent Used for the temporary and permanent

fixation fixation - Trocar Tip :Trocar Tip : 0.6 mm, 0.8 mm, 1 mm, 0.6 mm, 0.8 mm, 1 mm,

1.25 mm, 1.6 mm, 2mm, 2.5 mm, 3 1.25 mm, 1.6 mm, 2mm, 2.5 mm, 3 mm. mm.

- Threaded Tip :Threaded Tip : 1.6 mm, 2 mm, 2.5 mm 1.6 mm, 2 mm, 2.5 mm- Double Trocar Tip :Double Trocar Tip : 0.6 mm, 0.8 mm, 0.6 mm, 0.8 mm,

1.25 mm, 1.6 mm, 2 mm.1.25 mm, 1.6 mm, 2 mm.

EXTERNAL FIXATION EXTERNAL FIXATION Introduction :Introduction :• An external fixator is a device placed outside An external fixator is a device placed outside

the skin which stabilizes the bone fragments the skin which stabilizes the bone fragments through wires or pins connected to one or through wires or pins connected to one or more longitudinal bars/ tubes. more longitudinal bars/ tubes.

Biomechanical Aspects :Biomechanical Aspects :• Components of standard external fixatorsComponents of standard external fixators• Pins (Schanz screws/Steinmann pins)Pins (Schanz screws/Steinmann pins)• Stainless steel tubes or carbon fibre rodsStainless steel tubes or carbon fibre rods• A variety of clamps to fasten pins/wires to A variety of clamps to fasten pins/wires to

tubes/rodstubes/rods• A variety of clamps to fasten pins/wires to A variety of clamps to fasten pins/wires to

tubes/rods.tubes/rods.• Clamps to connect tubes/rods to tubes/rodsClamps to connect tubes/rods to tubes/rods

There are a variety of pins and wires There are a variety of pins and wires available:available:• Steinmann pins for bilateral framesSteinmann pins for bilateral frames• Schanz screws, either self drilling or requiring Schanz screws, either self drilling or requiring

pre drillingpre drilling• Schanz screws with small diameter tips for use Schanz screws with small diameter tips for use

in small bones.in small bones.• 2.0 and 1.8 mm K-wires (#olives) for ring 2.0 and 1.8 mm K-wires (#olives) for ring

fixator.fixator.• Threaded K-wires for small external fixators.Threaded K-wires for small external fixators.• The standard tubular system is employed for The standard tubular system is employed for

treatment of fractures in large bones, for treatment of fractures in large bones, for arthodesis, and for bone lengthening and arthodesis, and for bone lengthening and transport systems. The small external fixator is transport systems. The small external fixator is used mainly for fractures or distal radius and used mainly for fractures or distal radius and forearm as well as for fractures in children and forearm as well as for fractures in children and adolescents.adolescents.

Types of external fixators:Types of external fixators:• Pin fixators:Pin fixators:• UnilateralUnilateral• V-shaped,V-shaped,• Bilateral frame,Bilateral frame,• Triangular,Triangular,• Ring (wire fixators)Ring (wire fixators)• Hybrdfixators (wire pin)Hybrdfixators (wire pin)• Pinless external fixator.Pinless external fixator.• Mefisto (Monolateral External fixator System in Mefisto (Monolateral External fixator System in

traumatology and orthopedics).traumatology and orthopedics).• Considerations when applying the external Considerations when applying the external

fixatorfixator

• Frame Stiffness and Fracture stabilization of Frame Stiffness and Fracture stabilization of long bones.long bones.

• Placing the main frame. in the sagital planePlacing the main frame. in the sagital plane• Increasing the main frame in the sagital Increasing the main frame in the sagital

plane.plane.• Preloading the Schanz screws by pre-drilling Preloading the Schanz screws by pre-drilling

4.5 mm and using the 5.0 mm4.5 mm and using the 5.0 mm• Schanz screws with 4.6 mm core size (radial Schanz screws with 4.6 mm core size (radial

pre load).pre load).• Increasing the no. of Schanz screws in each Increasing the no. of Schanz screws in each

main fragment.main fragment.• Reducing the distance between the bone Reducing the distance between the bone

and the tube.and the tube.• Using double tube frame.Using double tube frame.

• Increasing the distance between the tubes.Increasing the distance between the tubes.• Applying a two plane unilateral frame.Applying a two plane unilateral frame.• Insufficiently stable external fixation may Insufficiently stable external fixation may

delay fracture healing and lead to pin delay fracture healing and lead to pin loosening. However, too much stiffness or loosening. However, too much stiffness or rigidity of the external fixator construct rigidity of the external fixator construct may also delay fracture healing, especially may also delay fracture healing, especially in open fractures. In the management of in open fractures. In the management of such fractures it may be necessary to such fractures it may be necessary to "dynamise" an initially quiet stable "dynamise" an initially quiet stable configuration or add stability in case of pin configuration or add stability in case of pin loosening.loosening.

Indications of External Indications of External Fixator :Fixator :• Stabilization and correction of extremity mal Stabilization and correction of extremity mal alignment and length discrepancies in severe alignment and length discrepancies in severe open fractures and infected non unions.open fractures and infected non unions.

• Initial stabilization of bony disruption and Initial stabilization of bony disruption and soft tissue injuries in poly traumatized soft tissue injuries in poly traumatized patients.patients.

• Closed fractures associated with severe soft Closed fractures associated with severe soft tissue damage.tissue damage.

• Multifragmentary diaphyseal and Multifragmentary diaphyseal and periarticular lesionsperiarticular lesions

• Certain pelvic ring disruptionsCertain pelvic ring disruptions• ArthodesisArthodesis• Compression fixation in osteotomies.Compression fixation in osteotomies.

Frame Construction :Frame Construction :• Good pin insertion practiceGood pin insertion practice• Make a liberal skin incision; spread Make a liberal skin incision; spread

deeper soft tissues with haemostat.deeper soft tissues with haemostat.• Lift periosteum with small elevator to Lift periosteum with small elevator to

prevent damage by drill bit.prevent damage by drill bit.• Use trocar to mark pin insertion point.Use trocar to mark pin insertion point.• Employ sleeve to drill a pilot hole and to Employ sleeve to drill a pilot hole and to

insert a pin.insert a pin.• Use a power drill.Use a power drill.

• Sharp drill bit with simultaneous saline Sharp drill bit with simultaneous saline irrigation prevents thermal damage.irrigation prevents thermal damage.

• Clean drill bit flutes oftenClean drill bit flutes often

• Use depth guage for accurate pin Use depth guage for accurate pin length.length.

• Insert pin with hand instrument. Insert pin with hand instrument.

Bibliography

- AO/ASIF Instruments and Implants

- Manual of Internal Fixation

- The Elements of Fracture Fixation

- Rockwood and Green

- Campbel Operative Orthopaedics