D E P A R TM E N T O F O R T H O P A E D IC S G A N D H I M E D IC A L C O L L E G E , B HOPAL S e m inar O n PRINC IPL E S A ND TE C HNIQUE S OF A OModerator : Presented by :D r . J . S h u k la D r . S u n ilD r. A. S in s in w a r
HISTORY OF OSTEOSYNTHESIS• The term osteosynthesis was coined by Albin Lambotte a Belgian surgeon regarded universally has the father of the modern internal and external fixation. He devised an external fixator and numerous different plates and screws.• Robert Danis as surgeon in Brussel published two books on osteosynthesis in 1932 and 1949.
• A young swiss surgeon E. muller read his second book and he drew around himself a group of interested swiss surgeons and in 1958, at an historical weekend meeting in chur they decided to form a study group concerning issue of internal fixation of bone- the Arbeitgemeinschaft fur Osteosynthe- sefragen, or AO.
Principles of AO :• 1. Anatomical Reduction.• 2. Stable internal fixation.• 3. Preservation of Blood supply• 4. Early active pain free mobilisation.
BIOMECHANICAL ASPECTS OFTHE AO TECHNIQUE• Neutralization Plate or Protection Plate• Compression Plating• Lag screw• Tension Band Principle• Intra Medullary Nailing• External Fixation.
PLATESIntroduction :• Bone plates are like internal splints holding together the fractured ends of a bone.• A bone plate has two mechanical functions. It transmits forces from one end of a bone to the other, bypassing and thus protecting the area of fractures. It also holds the fracture ends together while maintaining the proper alignment of the fragments throughout the healing process.
Special Plates• T Plates• T&L Buttress plates• Lateral Tibial head buttress plates• Condylar butters plate• Narrow lenthening plates• Broad Lengthening plate• Spoon plate• Clover leaf plate
CLASSIFICATION• Regardless of their length, thickness, geometry, configuration or type of holes, all pates may be classified in four groups according to their function.• Neutralization Plates.• Compression Plates.• Buttress Plates.
Buttress Neutral LoadPosition Position Position
NEUTRALIZATION PLATE• A neutralization plate acts as a ""bridge". It transmits various forces from one end of the bone to the other, bypassing the area of the fracture. Its main function is to act as a mechanical link between the healthy segments of bone above and below the fracture. Such a plate does not produce any compression at the fracture site.• The most common clinical application of the neutralization plate is to protect the screw fixation of a short oblique fracture, a butterfly fragment or a mildly comminuted fracture of a long bone, or for the fixation of a segmental bone defect in combination with bone grafting.
COMPRESSION PLATE• A compression plate produces a locking force across a fracture site to which it is applied. The effect occurs according to Newtons Third Law (action and reaction are equal opposite). The plate is attached to a bone fragment. It is then pulled across the fracture site by a device, producing tension in the plate. As a reaction to this tension, compression is produced at the fracture site across which the plate is fixed with the screws. The direction of the compression force is parallel to the plate.
BONE UNDER COMPRESSION• Superior stability – Utilization of physiological forces.• Improved milieu for bone healing.• Early mobilization.
BUTTRESS PLATE• The mechanical function of this plate, as the name suggests, is to strengthen (buttress) a weakened area of cortex. The plate prevents the bone from collapsing during the healing process. It is usually designed with a large surface area to facilitate wider distribution of the load.• A buttress plate applied a force to the bone which is perpendicular (normal) to the flat surface of the plate.
• The fixation to the bone should begin in the middle of the plate, i.e. closest to the fracture site on the shaft. The screws should then be applied in an orderly fashion, one after the other, towards both ends of the plate.• A representative clinical example of a buttress plate is the T-plate used for the fixation of fractures of the distal radius and the tibial plateau.
DCP (Dynamic Compression Plate):Principle :- Its a self compression plate due to the special geometry of screw holes which allow the axial compression.
Dynamic compression principle: The holes of the plate areshaped like an inclined and transverse cylinder. Like a ball, thescrew head slides down the inclined cylinder. Because the screwhead is fixed to the bone via the shaft, it can only move verticallyrelative to the bone. The horizontal movement of the head, as itimpacts the angled side of the hole, results in movement of thebone fragment relative to the plate and leads to compression ofthe fracture.
• Screw hole and the spherical gliding principle.• Axial compression result from the an interplay between screw hole geometry and eccentric placement of the screw in the screw hole. The screw hole is a combination of incline and horizontal cylinder which permits the downward and the horizontal movement of a sphere the screw hand. Sideway movement of screw head is impossible. The aim is to position the screw head at the intersection of inclined and the horizontal cylinder. At this point screw head has a spherical contact in the screw hole which result in the maximum stability without completely blocking the horizontal movement of the screw.
The shape of the holes of the dynamic compressionplate allows inclination of the screws in a transverse direction of +7° and in a longitudinal direction of 25°.
Advantage of DCP :1. Inclined insertion 25° longitudinal and 7° sideways.2. Placement of a screw in neutral position without the danger of distraction of fragments.3. Insertion of a load screw for the compression.4. Usage of two load screws in the main fragments for axial compression.5. Compression of several fragments individually in comminuted fractures.6. Application as a buttress plate in articular area.
Short Coming of DCP :1. Flat under surface.2. Inclination upto 25°3. Plate hole distribution (extended middle segment)
LC-DCPThe structure of a limited-contact dynamic compression plate.
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 development of the DCP is used for the same indications as the DCP, but the improved design offers additional advantage.• The evenly distributed undercuts reduces the contact area between bone and plate to a minimum. This significantly reduces impairment of the blood supply of the underlying cortical bone undercuts also allow for the formation of a small callusbridge.• The enlarged cross section at the plate holes and the reduced cross section between holes offer a constant degree of stiffness along the long axis of the plate.
• The trapezoid cross section of the plate results in a smaller contact area between plate and bone.• The plate holes are uniformaly spaced, which permits easy positioning of the plate.• Undercuts plate holes; undercut at each end of the plate hole allows 40 tilting of screws both ways along the long axis of the plate. Lag screw fixation of short oblique fractures is thereby possible.
ADDITIONAL PRINCIPLES OFPLATE FIXATION• The engineering principle of the tension band is widely used in fracture fixation. It applies to the conversion of tensile forces to compression forces on the convex side of an eccentrically loaded bone.
PREBENDING PLATES• Contour to fit the bone surface snugly.• Make a sharp bend opposite the fracture site; midsection is elevated.• Fix to the bone, starting on either side of the fracture and then moving outwards.• Plate then compresses the far cortex also.• Apply only to two fragment fractures.
HOW MANY SCREWS ?• Hands-on experience suggests that, in the humerus, screws grip seven cortices on each side of the fracture ; in the radius and the ulna, five; in the tibia, six, and in the femur, seven. Bones No. of Cortices No. of Holes Type of PlateForearm 5 to 6 Cortex 6 holes Small 3.5Humerus 7 to 8 Cortex 8 holes Narrow 4.5Tibia 7 to 8 Cortex 7 holes Narrow 4.5Femur 7 to 8 Cortex 8 holes Narrow 4.5Clavicle 5 to 6 Cortex 6 holes` Small 3.5
HOW CLOSE TO THE FRACTURE SITE?• A screw, as a result, should not be placed closer than one centimeter from the fracture line.
Reconstruction Plates :• Can be bent and twisted in two dimensions.• Decrease stiffness than DCP.• Should not be bent more than 15°.• Used were the exact and complex contouring is required. eg. Pelvis, 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 andstiffer precurved lengths. As with tubular plates, they have oval screw holes, allowing potential for limited compression.
One Third Tubular Plates :• Plates have the form of one third of the circumference of a cylinder.• Low rigidity (1mm thick).• Oval holes – Axial compression can be achieved.• Uses – Lateral malleolus, distal ulna, 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 (LCP) Principle :• The basic principle of LCP is its angular stability whereas stability of conventional plate osteosynthesis relies on the friction between the plate and bone.• The principle of fixation of LCP is screw locking.• The functional LCP screw is like that of external fixator pins, that is why they are called as internal fixator.• LCP provides the relative stability.• # heals by the callus formation (Secondary Healing).
The mechanical principle of a locked screw plate. (A) Theplate sits slightly of the bone. (B) Tightening of the screwlocks the screw head within the plate. The plate is notdrawn toward the bone and there is no compression b/wthe bone and the plate. The flux is bone/ screw/ plate/screw/ bone.
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.Maintenance of primary reductionOnce the locking screws engage the plate, no furthertightening is possible. Therefore, the implant locks the bonesegments in their relative positions regardless of degree ofreduction. Precontouring the plate minimizes the gapbetween the plate and the bone, but an exact fit is notnecessary for implant stability. This feature is especiallyadvantageous in minimally or less invasive platingtechniques because these techniques do not allow exactcontouring of the plate to the bone surface.
Stability under loadBy locking the screws to theplate, the axial force istransmitted over the length of theplate. The risk of a secondaryloss of the intraoperativereduction is reduced.Blood supply to the boneLocking the screw into the platedoes not generate additionalcompression. Therefore, theperiosteum will be protected andthe blood supply to the bonepreserved.
Plate Design :• LC DCP features :• Tapered end for sub muscular insertion.• Locking holes
Screw :• Conical screw head• Large core diameter.• Self tapping.• Star drive recess.
Principle of internal fixationusing LCP :1. 1st reduced the # as anatomical as possible.2. Cortical screw should be used 1st in a fracture fragment.3. If the locking screw have been put, use of the cortical screw in the same fragment without loosening and retightening of the locking screw is not recommended.4. If locking screw is used first avoid spinning of plates.5. Unicortical screws causes no loss of stability.
6. Osteoporotic bones bicortical screws should be used.7. In the comminuted # screw holes close to the fracture should be used to reduce stain.8. In the fracture with small or no gap the immediate screw hoses should be left unfilled to reduced the strain.
Plate length and No. of Screws :Plate span ratio Plate length # lengthComminuted # PSR 2Simple # PSR 8Plate Screw density No. of Screws No. of Plate holesPSD 0.5 to 0.4- At least 4 cortices per main fragment for comminuted fracture- At least 3 cortices per main fragment for simple fracture.
Plate screw density and fracture plate quotient
Indications :1. Osteoporotic #2. Periprosthetic #3. Multifragmentry #4. Delayed change from external fixation to internal fixation.Advantages :1. Angular stability2. Axial stability3. Plate contouring not required4. Less damage to the blood supply of bone.5. Decrease infection because of submuscular technique6. Less soft tissue damage.
Timing of Plate Removal,Recommendations for removal ofplates in the lower limb :• Bone / Fracture• Time after implantation in months• Malleolar fractures• 8-12• The tibial pilon• 12-18• The tibial shaft• 12-18• The tibial head• 12-18
• The femoral condyles• 12-24• The femoral shaft: Single plate, Double Plate• 24-36• From month 18, in 2 steps ( Interval 06 months)• Pertrochanteric and femoral neck fractures Upper extremity• 12-18• Optional• Shaft of radius / ulna• 24-28• Distal radius• 8-12• Metacarpals• 4-6
Cortical Screw :- Use in the hard cortical bone mainly in the diaphysis of the long bones.- Large core diameter- Non self cutting- Tapping is required.Cancellous Screw :- Large thread depth- Large pitch.- Non self tapping.- Tapping only near cortex.
The screw thread is defined by its major or outsideand minor or root diameters, pitch, lead, and number of threads. Bottom: Screw head drive types.
Indication :- Metaphyseal and epiphyseal areas- Partially Threaded (for lag screw)- Fully threaded (for plates)- Cannulated or Non cannulated
Drill Bit :Used for drilling the hole in the bone.- Sizes 2.5 mm, 3.2 mm, 2 mm, 4.5 mm.- Always use the drill bit with the sleeve.- Standard drill bits – 2 flutes – air drill.- Three flutes drill bits – Better for drilling at oblique angles.- During the drilling normal saline should be used.- Canulated drill bit used for drilling over guide wires.
Cutting lip Cutting Edge Flute Margin Axis of drillDrill Bit
Taps :Used for cutting the thread in the bone.Cortical Tap :- Used to cut threads in the bone of same size as the screw.- Have 3 flutes.- Entire far cortex must be taped.- Taping should be done manually.- Two turn forward and half turn in the reverse direction.Cancellous Tap :- Short and wide threads slightly smaller than the screw.- One near cortex tapping is required.
DIFFERENT AO SCREWSLARGE STANDARD SCREWS. 4.5 mm Cortex Screw 6.5 mm Cancellous Screw Malleolar Screw 4.5CANNULATED SCREW SYSTEM 6.5 Cannulated Screw 4.0 mm Cannulated Screw 3.5 Cannulated ScrewSMALL FRAGMENT SCREW 3.5 mm Cortical Screw 4.0 Canceleous Screw -Partially Threaded. -Fully ThreadedMINI SCREW 2.7 mm Cortex Screw 2.0 mm Cortex Screw 1.5 mm Cortex Screw
THE LAG SCREWA lag screw is the most effective way toachieve compression between two bonefragments; it pulls the fragments togetherproducing pressure across the fracture line. Itachieves this by providing purchase on thedistal fragment while being able to turn freelyin the proximal. If the screw threads engageboth cortices, the fragments remain apart liketwo nuts on the same bolt.
Top: Biomechanics of cannulated and noncannulatedscrews. 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.
PRINCIPLE• The screw must glide freely through the near fragment and engage only the far fragment.• Wherever a screw crosses a fracture line it should be inserted as lag screw.• Two small screws produce a more stable fixation than one large screw.
Screw Core Thread Pitch Drill bit Drill bit Tap diamet diamet for for diamet er er gliding thread er hole holeLarge 7mm 4.5mm 7mm 2.75mm 4.5mm 7mmStandard CancellouScrews s Screw 6.5mm 3.5mm 6.5mm 2.7mm 3.2mm 4.5mm 6.5mm cancellous screw 4.5mm 4.5mm 3.1mm 1.75mm 3.2mm 4.5mm cancellous screw 4.5mm 3mm 4.5 mm 1.75mm 4.5mm 3.2mm 4.5mm cortical
DYNAMIC HIP SCREW & DYNAMICCONDYLAR SCREW• The dynamic hip screw (DHS) implant system has been designed primarily for the fixation of trochanteric fractures. It may also be used for certain subtrochanteric fractures as well as for selected basi-cervical femoral fractures.• The implant is based on the sliding nail principle which allows impaction of the fracture. This is made possible by the insertion of a wide diameter screw into the femoral head. A side plate, which has barrel at a fixed angle is slid over the screw and fixed to the femoral shaft.
DYNAMIC CONDYLAR SCREW• The dynamic condylar screw (DCS) is similar to the DHS in its design and concept. The fixed angle between plate and barrel is 95 and the plate is contoured to fit the lateral surface of the distal end of the femur.• The main indications are fractures of the distal femur and inter-condylar fractures. It may also be used for certain intertrochanteric fractures and very proximal subtrochanteric fractures. Impaction of compression of the fracture is achieved by using the compression screw.
Canulated Cancellous Screw Fixation in Fracture Neck Femur :- Parallel 6.5mm CCS are used in triangular or inverted triangular configuration.- After fracture reduction antiversion is determined.- 2mm threaded guide wire is inserted in the centre of the neck in both AP and lateral view.- Parallel wire guide is replaced over the central guide wire.- 2mm guide wire are inserted into the subchondral bone of the femoral head starting with the most superior.- Parallel wire guide is removed and length is determined.- Canulated drill bit is used.- Tapping is done with 6.5mm tap.- Appropriate screws are inserted.
TENSION BAND PRINCIPLE Tension-band principle.
• Tension Band Principle :- Its describes how the tensile forces are converted into compressive forces by applying a devise eccentrically or to the convex side of a curved tube or bone.• Indications :- Fracture Patella, olecranon, medial malleolus, greater trochanter of the femur.• Static• Dynamic
Pitfalls and Complications:• The most complication is failure of the implant. A wire put under pure tension is very strong. However, if bending forces are added, it will break by fatigue quite rapidly. As this also holds true for plates, it appears essential that in the diaphysis, the tension side of the bone is known and the opposite cortex is able to withstand the compression forces.
INTRAMEDULLARY NAILING• Load sharing device• Axial and rotational stability• Maintains the length• Biological fixation• Minimal soft tissue exposure• Early weight bearing
Intramedullary Nailing :• The principle of fixation is based on the compression between the bone and the nail.Interlocking Intramedullary Nail :• Nail have the proximal and distal screw holes. Nail is locked by the interlocking screws. The resistance to the torsial and axial force depend on the screw bone interface.Working Length :• Distance between the proximal and distal interlocking screws.
Dyanamization :• Interlocking Nails can be locked in dynamic or static mode.• Dyanamization means placing the screw at only one end of the bone.Static Locking means placing the screw at the both ends of the bone.• Dynamization can be done at the 8-12 weeks for delayed union.• Screw is removed from the longer fragment.
INDICATINOS FOR UNIVERSAL NAILING OF FEMUR AND TIBIA WITH AND WITHOUT LOCKING• Conventional nailing without locking for stable fractures with bony support in the middle third of the bone, such as:• Transverse fractures.• Short oblique fractures• Delayed union or nonunion• Locked medullary nailing for unstable fractures without bony support in approximately the middle 60% of the bone, where axial and rotational stability has to be achieved, such as
Fractures near the metaphysic Long torsional fractures Segmental fractures Multifragmentary fractures Fractures with bone defects.TYPES OF INTRAMEDULLARY NAILS :• Centromedullary nails• Condylocephalic nails• Cephalomedullary nails
K wire :Used for the temporary and permanent fixation- Trocar Tip : 0.6 mm, 0.8 mm, 1 mm, 1.25 mm, 1.6 mm, 2mm, 2.5 mm, 3 mm.- Threaded Tip : 1.6 mm, 2 mm, 2.5 mm- Double Trocar Tip : 0.6 mm, 0.8 mm, 1.25 mm, 1.6 mm, 2 mm.
EXTERNAL FIXATIONIntroduction :• An external fixator is a device placed outside the skin which stabilizes the bone fragments through wires or pins connected to one or more longitudinal bars/ tubes.Biomechanical Aspects :• Components of standard external fixators• Pins (Schanz screws/Steinmann pins)• Stainless steel tubes or carbon fibre rods• A variety of clamps to fasten pins/wires to tubes/rods• A variety of clamps to fasten pins/wires to tubes/rods.• Clamps to connect tubes/rods to tubes/rods
There are a variety of pins and wiresavailable:• Steinmann pins for bilateral frames• Schanz screws, either self drilling or requiring pre drilling• Schanz screws with small diameter tips for use in small bones.• 2.0 and 1.8 mm K-wires (#olives) for ring fixator.• Threaded K-wires for small external fixators.• The standard tubular system is employed for treatment of fractures in large bones, for arthrodesis, and for bone lengtheneing and transport systems. The small external fixator is used mainly for fractures or distal radius and forearm as well as for fractures in children and adolescents.
Types of external fixators:• Pin fixators:• Unilateral• V-shaped,• Bilateral frame,• Triangular,• Ring (wire fixators)• Hybrdfixators (wire pin)• Pinless external fixator.• Mefisto (Monolateral External fixator System in traumatology and orthopedics).• Considerations when applying the external fixator
• Frame Stiffness and Fracture stabilization of long bones.• Placing the main frame. in the sagital plane• Increasing the main frame in the sagital plane.• Preloading the Schanz screws by pre-drilling 4.5 mm and using the 5.0 mm• Schanz screws with 4.6 mm core size (radial pre load).• Increasing the no. of Schanz screws in each main fragment.• Reducing the distance between the bone and the tube.• Using double tube frame.
• Increasing the distance between the tubes.• Applying a two plane unilateral frame.• Insufficiently stable external fixation may delay fracture healing and lead to pin loosening. However, too much stiffness or rigidity of the external fixator construct may also delay fracture healing, expecially in open fractures. In the managmenet of such fractures it may be necessary to "dynamise" an initially quiet stable configuration or add stability in case of pin loosening.
Indications of External Fixator :• Stabilization and correction of extremity mal alignment and length discrepanicies in severe open fractures and infected non unions.• Initial stabilization of bony disruption and soft tissue injuries in poly traumatized patients.• Closed fractures associated with severe soft tissue damange.• Multifragmentary disaphyseal and periarticular lesions• Certain pelvic ring disruptions• Arthrodesis• Compression fixation in osteotomies.
Frame Construction :• Good pin insertion practice• Make a liberal skin incision; spread deeper soft tissues with haemostar.• Lift periosteum with small elevator to prevent damage by drill bit.• Use trocar to mark pin insertion point.• Employ sleeve to drill a pilot hole and to insert a pin.• Use a power drill.
• Sharp drill bit with simultaneous saline irrigation prevents thermal damage.• Clean drill bit flutes often• Use depth guage for accurate pin length.• 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