RIGID INTERNAL FIXATION

Made by-ROSHALMARIA THOMASIV YEAR B.D.S.RIGID INTERNAL FIXATION

What is fixation?Fixationinorthopedicsis the process by which an injury is rendered immobile. This may be accomplished byinternal fixation, or byexternal fixation.What is internal fixation?Internal fixationis anoperationinorthopedicsthat involves the surgical implementation ofimplantsfor the purpose of repairing a bone

What is osteosynthesis?Osteosynthesisis thereductionandinternal fixationof abone fracturewith implantable devices that are usually made of metal. It is a surgical procedure with an open or per cutaneous approach to the fractured bone. Osteosynthesis aims to bring the fractured bone ends together and immobilize the fracture site while healing takes place. In a fracture that is rigidly immobilized the fracture heals by the process ofintramembranous ossification

INDICATIONS for internal fixationTrauma- facial bone fractureOrthognathic surgeryReconstruction of craniofacial deformitiesReconstruction of bony defects 2 to ablative tumour surgery.Augmentation of atrophic mandible in the elderlyIatrogenic -2 to anterior/lateral mandibulotomy

History of Fracture Treatment and Development Of Modern Osteosynthesis

In the Preantibiotic era, closed reduction of fractures was understandably the rule for most fractures. However, when closed reduction was insufficient, external fixation appliances served to maintain skeletal units in position, frequently without the need for MMF (Maxillo-mandibular fixation) .Following the development of antibiotics, the open treatment of fractures began to be used on a more frequent basis. Rigid internal fixation (RIF) is Any form of fixation applied directly to the bones which is strong enough to permit active use of the skeletal structure during the healing phase and also helps in healing.

Bone fractures have been treated with various conservative techniques for centuries and it was not until the eighteenth century that internal fixation was first documented.Icart, a French surgeon in Castres, performed ligature fixation with brass wire on a young man with a humeral fracture. 1886, when Hansmann of Hamburg published a technique using retrievable metal bone plates with transcutaneous screws. Soon after, a Belgian surgeon, Albin Lambotte, improved these techniques and coined the term internal fixation.Lambotte developed and manufactured a variety of bone plates and screws and much of his armamentarim remained in use until the 1950s.In the twentieth century, Sherman improved on Lambottes designs and created parallel, threaded, finepitched, self-tapping screws. This hardware was made of corrosion-resistant vanadium steel, which was a strength improvement over silver and ivory fixation materials.

1970s-titaniumIn the 1930s, Eggers rediscovered an older design for sliding slot plates, which eventually led to the development of a compression plate by Danis in 1947. Luhr helped advance the principles of compression and dynamic compression, but it wasnt until 1977 that he developed these techniques to the maxillofacial skeleton.Spiessl later popularized dynamic compression bone plating of the mandible using Arbeitsgemeinschaft fr Osteosynthesefragen-Association for the Study of Internal Fixation (AO-ASIF) techniques.From Luhr and Spiessls work, eccentric dynamic compression plating was developed and adapted for craniomaxillofacial trauma use, but lost popularity due to its highly technique-sensitive nature and no proven benefits over other modern fixation methods.

BIOLOGY OF BONE AND BONE HEALING

Bone is a complex and ever-evolving connective tissue and serves multiple purposes. Besides being the main constituent of the human skeletal system, bone is highly metabolically active and essential for the regulation of serum electrolytesnamely, calcium and phosphate.Marrow cavities are filled with hematopoietic elements necessary to manufacture and maintain blood components and regulate the immune system. Bone is comprised of calcified bone matrix and three major cell types, osteocytes, osteoblasts, and osteoclasts.Bones organized structure is illustrated in cross section revealing the haversian system, or osteon. Each osteon contains concentric layers of compact bone surrounding a central haversian canal, which harbors the neurovascular bundle supplying the unit. Cells suspended in this highly calcified, highly vascular structure are perfused via small capillary-containing cylindrical cavities called canaliculi

Bone healing can be broadly categorized in two ways, primary and secondary. Primary, or direct bone healing, requires rigid fixation and immobility of fracture segments with a minimal gap between them (less than 100 m). Osteoclasts migrate to the fracture site and widen adjacent haversian systems, allowing osteoblasts to deposit bone matrix, or osteoid, eventually to calcify into organized mature lamellar bone.Secondary, or indirect bone healing, is more complex and occurs when a significant gap or interfragmentary motion is present. Secondary bone healing involves the formation of a fibrocartilaginous intermediary bone callous There are four distinct stages of indirect bone healing but the end product is the same as mature bone formed in primary healing. The initial insult propagates the inflammatory stage. A hematoma between and around the fracture develops and stabilizes, drawing inflammatory cells to the site.Necrotic and nonviable bone near the fracture is cellularly dbrided and repair is initiated by angiogenesis and the activation of osteoprogenitor cells and fibroblasts.

The second, or soft callus, stage is characterized by conversion of the hematoma to a fibrocartilaginous mass to bridge the fracture.Fibroblasts and mesenchymal elements are highly active in laying down new collagen to create the substrate into which the third phase, or hard callus stage, develops. During this period, osteoid is calcified and periosteal and endosteal bone ingrowth starts to replace the soft callus as a result of endochondral bone formation. Finally, in the remodeling stage, the woven bone of the hard callus matures and organizes to a trabecular structure to re-create the native preinjury structure.Although distinct, both types of bone healing may occur simultaneously in the same fracture. As three-dimensional structures, bones may have varying levels of contact and fracture reduction in the same general site, resulting in endochondral and lamellar elements in different areas at the same point in time

BIOPHYSICS OF THE FACIAL SKELETON

Although complex, the facial skeleton does not consist of many moving parts. The major axis of bony motion in the face is around the mandibular condyles, or temporomandibular joints (TMJs). The muscles of facial expression originate on various bones of the craniomaxillofacial skeleton, are invested in the superficial musculoaponeurotic system, and insert on each other and the facial skin. These have little effect on forces exerted on facial bones.The muscles of mastication and suprahyoid muscles, however, produce significant forces on the jaws and surrounding osseous structures. Bite force is generated by contracture of the masseters, temporalis, and medial pterygoids; the sum of these vectors allows for occlusion of the teeth via movement of the mandible.Due to its dynamic nature, the mandible bears most of the forces applied by facial musculature to the skeleton.

Aponeurosis- sheet of pearly white fibrous tissue which takes the place of a tendon in sheet-like muscles having a wide area of attachment.

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Mechanical Stress on mandible under FunctionThe force of the masseter, medial pterygoid, and temporalis muscle results in upward and forward vector of force on the posterior aspect of the mandible.The suprahyoid musculature places a downward and posterior force on the anterior portion of the mandible.With the pterygomasseteric sling functioning as a point of fulcrum, the superior border of the angle/posterior mandible is placed under tension while the inferior border is placed under compression

Beam mechanics dictates that the mandible is a class III lever, with the condyle being the fulcrum, the muscles of mastication acting as the applied force, and bite load acting as the resistance This rationale applies to one side of the mandible at a time, but as a horseshoe-shaped bone, the mandible is more than a simple class III lever.When loaded, the mandible exhibits maximum tension at the superior border and maximum compression at the inferior border . This is a gradient and, between the zones of tension and compression, lies a neutral zone in which opposite forces total zero. In this model, it would be mechanically advantageous to apply rigid fixation hardware along the zone of tension, or superior border. Biologically, this is complicated by the presence of teeth, thin cortical bone, and thin overlying soft tissue. The neutral zone is dynamic and depends on from bilateral muscle contracture on a unilateral fracture

Adequate exposure of fracture segments is carried out while not compromising the adjacent blood supply. Maintaining vital periosteum aids in fracture healing, preventing postoperative wound breakdown and decreasing the rate of hardware infection. Primary closure of the wound may or may not require local flaps to maintain well-vascularized soft tissue coverage.Cases in which surgical exposure of fracture sites may interrupt blood supply, such as severely comminuted fractures or contaminated wounds, pose a risk for hardware infection and may be an indication for skeletal pin external fixation.

Prior to the development of modern internal fixation, Maxillomandibular fixation (MMF) was the mainstay of facial fracture treatment. By stabilizing the dentition in its known pretraumatic occlusion, bone segments will assume an anatomically acceptable configuration. Because MMF compresses fractures at the alveolus, the inferior border of the mandible may still demonstrate a gap. By combining this method with compression of the inferior border with bone reduction forceps and application of internal fixation methods, an ideal reduction can be achieved. MMF is still used as a primary modality of fracture treatment in patients for whom internal fixation may not be indicated. Minimally or nondisplaced biomechanically favorable fractures in patients with a sufficient complement of teeth to provide a stable premorbid occlusion, severely comminuted fractures, or intracapsular condylar fractures in which occlusion can be reestablished are some common scenarios for which 2 to 8 weeks of MMF without surgery may be indicated. MMF is considerably less invasive and more cost-effective and reduces complications associated with open surgery

INTERNAL FIXATIONInternal fixation permits more precise anatomical bone reduction of the fracture site but requires direct surgical exposure of fractures, especially for transosseous wiring or plate fixationInternal fixation of mandibles can be undertaken in the following waysCircumferential wiring or nylon strapsTransosseous wiring;upper and lower borderIntramedullary pins; kirschners wire or Steinmann pinRigid internal fixations

PRINCIPLES OF FIXATION

AO-ASIF guidelines of rigid fixation follow four basic principles to ensure adequate treatment of fractures: bony segment reduction, stable fixation and immobilization of fragments, maintaining blood supply, and early function.

Reductionis asurgical procedureto restore afractureordislocationto the correct alignment. This sense of the term "reduction" does not imply any sort of removal or quantitative decrease but rather implies a restoration20

Materias used for RIFMetallic and Resorbable(biodegradable) osteosynthetic devices.1. Metallic Stainless steelVitallium- trade name for alloy of chromium, cobalt & molybdeniumTitanium 2. Resorbable materialsPolylactic acid(PLA)Polyglycolic acid(PGA)Polydioxanone(PDA)Copoloymers e.g PLLA+PDLA; PLLA + PGA(Lacto Sorb)

Metabolism of biodegradable implants:Hydrolysis short chained fragments phagocytosis(macrophages+ PMNs)Lactate(monomers)Pyruvate(gluconeogenesis &/or Krebs cycle) CO +HOExcretion- urine, faeces, expired air. Degradation time depends on - temperature, pH, presence of water, mechanical strain on implant, polymer configuration

Varios concepts of FixationRigid internal fixation & Non rigid fixation

Load-bearing & load-sharing fixation

Compression & Non compression plates osteosynthesis

Locking & Non locking plate-screw system

Although functionally stable fixation of the mandibular angle reduces operative time, risk of dental injury, and cost, it is not ideal in all situations. When fracture occurs at the angle, the upward and forward rotation of the posterior mandible combined with the downward and posterior movement of the anterior mandible results in distraction at the superior border and with bony contact remaining at the inferior border of the mandible .Concomitant fractures of the mandible must be treated rigidly to prevent motion at multiple sites. The Champy method relies on the contralateral condyle being seated correctly in the glenoid fossa, without disruption of the temporomandibular relationship. If a contralateral fracture is present and not treated rigidly, bite forces across the angle can transmit to the distal segment, causing rotation around the opposite fracture line. This may result in widening of the mandible and subsequent malocclusion and facial width alteration. By treating the other fracture site rigidly, the angle can essentially be treated as an isolated injury.

Examples of rigid fixation of a fracture include application of a reconstruction plate, two bone plates, two lag screws, or a compression plate and arch bar across a fracture.

COMPRESSION OSTEOSYNTHESISZero movement occurring between bones across the fracture, as well as complete immobility of the hardware against the bone. Today, most mandibular plating modules include dynamic compression plates for surgeons who wish to use compression osteosynthesis. compressive plating techniques are extremely technique-sensitive and prone to operator error

Dynamic compression plates are designed with eccentric holes with inclined planes.On either side of the midline of the plate, the plate holes are elongated, with the lateral side having the highest portion of the inclined plane and the medial with the lowest portion, or closest to the bone, of the inclined plane. The plate should be adapted so that one eccentric hole is on each side of the fracture, closest to the fracture line. The outer planes of each hole are the active, or compression, sites. As screws are drilled and fastened into this high point of the inclined plane, they follow the plane down toward the bone as friction is created between the screw head and plane surface. When completely tightened, they lie on the innermost portion of the hole closest to the bone. Because this is completed on either side of the fracture, the bone segments are compressed toward each other while the plate remains static, minimizing the bone gap and achieving compression. The remainder of the holes distal to the fracture line are then drilled and secured with bone screws in a passive position so as to not compress or distract the bones and hardware further.

To instrument the dynamic compression plate properly and achieve successful compression, the plate must first be bent and accurately adapted to the bony segments.The fracture must be stabilized and reduced by MMF, a superior border miniplate, bone reduction forceps, or a combination of these techniques prior to bending the dynamic compression plate. Once adapted to the reduced fracture, the compression elements can be drilled. Drill guides provided by the manufacturer for compression plating are helpful in placing the screw hole correctly to achieve maximum compression. The drill guide has active and passive positions, with arrows to indicate the orientation. The first hole adjacent to the fracture is drilled in a bicortical fashion with a drill guide with the active, or compression, arrow facing the fracture. This corresponds to the outer, or high, incline of the hole. A depth gauge is used to measure the desired screw length and the screw is inserted partially to stabilize the position of the plate. The most proximal hole on the opposite side of the fracture is drilled in the same fashion in the active position and the screw is inserted and tightened completely. As noted, the screw will migrate down the plane approaching the fracture line and draw the bone segment toward its counterpart. The first screw is then tightened completely, producing the same effect on the opposite side and creating compression between the bony segments.

The remainder of the holes are then drilled in the passive position and bicortical screws are inserted to stabilize the plate to the fractured mandible. These serve to share the load further and reduce forces that would tend to counteract interfragmentary compression. Dynamic compression plates actively draw fractured segments together. The resultant compression at this site, typically the inferior mandibular border, may result in excessive tension at the superior border or alveolus. It is necessary to neutralize these forces to prevent gap formation in the zone of tension of the mandible. This is typically achieved by the use of a tension band. An arch bar, superior lag screw, or monocortical miniplate can be used as a tension band to reduce the distraction at the superior border. This applies to any load-sharing internal fixation system but holds especially true for compression plating.Compression osteosynthesis is best applied in transverse fractures of the mandibular symphysis or body without comminution or bone loss. Obliquely oriented fractures can pose problems in this technique due to the nonsymmetrical nature of the fracture line. Plates are adapted and applied to the outer, or buccal, cortex of the mandible. Compression is applied parallel to the plate; equal distribution of forces occurs best in fractures that are completely perpendicular to the compression plate.

NONCOMPRESSION OSTEOSYNTHESIS

Noncompression osteosynthesis is widely used in managing traumatic injuries to the maxillofacial skeleton. This can be accomplished with a variety of methodsNon-compression bone plates and reconstruction plates, both of which are available with locking mechanisms. These methods have broader applications and less degree of operator error when compared with compression osteosynthesis.

MANDIBULAR FIXATIONFixation must be sufficient to withstand masticatory forces during the healing period. Fracture plates are manufactured in various widths and universal fixation systems generally allow interchangeable screw diameters to be used in multiple plates, depending on the level of fixation desired. Other factors that should be taken into account when selecting the width of the fracture plate are quantity and quality of overlying soft tissue, patient compliance, and risk of reinjury. Thicker plates provide more stability than thinner counterparts, but may be palpable under soft tissue, may require more dissection, are more difficult to adapt, and have higher rates of dehiscence.

INSTRUMENTATIONReduction forcepsTowel clip typeBone holding clampsReduction/Compression forcepsPlate holding forcepsScrew driver holding sleeve (hexa, cruciform, phillip)Plate bendersBending ironsBending pliers (flat, pronged, side bender)Plate cuttersTemplates Drilling machineDrill bitsDrill guides (neutral or eccentric)Depth guagesTap Transbuccal instruments (trocar + cannula, guide, retractor)

Locking plates- useful in securing plates that cannot be perfectly adapted to fractures or if bone quality is poor.Locking screws are double-threaded; the head of the screw has an additional larger diameter thread that secures into the thread pattern of the plate hole. Locking plate and screw systems prevent loosening and extrusion of the screw from the plate, even if it does not integrate to the mandible and resists mechanical yielding under stress.

Miniplates Champy method of mandibular angle fracture fixation and its use as a tension band.. These plates accept the same screws as standard mandibular fracture platesThe Champy method of mandibular angle fixation involves exposing and reducing a fracture, as described earlier, and using the biomechanical advantage to place a miniplate at the zone of tensionthat is, the superior border

This method has been proven to exhibit enough stability to withstand tensile forces at the superior border under function during the healing period.Care must be taken to place this plate in the zone of tension while avoiding tooth roots. Even with monocortical fixation, damage to dental structures can occur because the relationship of teeth to the mandibular buccal cortex vary from patient to patient. In the edentulous mandible, tension bands should be placed at the superior border to maximize tensile force resistance. Miniplates are also more prone to screw loosening and infectious complicationsMay be regular or 3DProfiles usually 1-1.3mm2.0mm used in mandible1.3, 1.5,mm used in middle and upper thirdMay accommodate locking mechanism in plates (small, medium, large, extra large profile mandibular plates)Come in different shapes and lengths May also come as meshes

Compression plates(Spiessel et al)There are basically two types:RegularEDCPReconstruction platesMandibular reconstruction plates are thickerHave a longer span than fracture platesDesigned to be load bearing to span gaps and defects. Reconstruction plates can be used to treat mandibular fractures that are comminuted, atrophic, or grossly unstable. When used to span a gap, four screws should be placed on each side of the defect to allow the plate to bear the most, if not all, the load of the mandible. Due to their size and thickness, reconstruction plates frequently pose problems in adapting to the mandible. The built-in locking mechanism can circumvent the need for perfect adaptation to bone. Reconstruction plates exhibit a high degree of elastic deformation. The locking mechanism proves to be essential in large spans with complex contours for which perfect plate adaptation is not possible. Can vary in thickness from 2mm and abovePlates not as thick as 3mm are not recommended for defect bridgingMay use 2.4, 2.7 or 3.0mm screws depending on system.

UFP (Universal Fracture Plate) 2.4mm

UFP

LAG SCREWS(Brons and Boering)Lag screw osteosynthesis is a fracture compression technique that can be carried out by using true lag screws or a lag technique with long bone screws fixation of transverse mandibular symphysis and parasymphysis fractures or obliquely oriented body and angle fractures. The premise of this technique is its ability to engage and pull, or lag, the distal cortex toward the proximal cortex across a fracture. This method provides a high degree of fracture compression, resulting in very stable fixation Lag screw osteosynthesis directly traverses the fracture line, more evenly distributing compressive forces between segments and resulting in excellent stability and minimal to no lingual splay. After the fracture is exposed and reduced, a gliding hold is prepared from the near-cortex to the fracture close to the inferior border.

This hole is of a larger diameter than the screw to be used to ensure that it does not actively engage this cortex. Next, a long drill guide is inserted into the glide hole and, using a drill of smaller diameter than the screw threads, the osteotomy is completed from the fracture line to the distal cortex. This is the traction portion of the osteotomy.A depth gauge is used to measure the distances between the cortices and the appropriate screw length is selected. A long bone screw or true lag screw is inserted passively through the gliding hole and purchased into the traction hole. When completely tightened, the engaged distal cortex will be drawn proximally and create compression at the fracture line. This process should be repeated with a second screw or second method of fixation to prevent rotation around a single axis When treating transverse or sagittal fractures of the symphysis, the screws should be placed through the outer cortex on either side. In oblique fractures, it may be necessary to engage the outer cortex proximally and inner cortex distally.

EMERGENCY SCREWS1.0- 1.21.3- 1.71.5- 2.02.0- 2.42.4- 2.72.7- 3.0

MIDFACE AND UPPER FACE FIXATION

The zygoma is the only other bone that displays significant effects from the masticatory musculature. Complex craniomaxillofacial trauma involving the frontal sinus, orbits, naso-orbito-ethmoid (NOE) complex, zygomaticomaxillary complex, and maxilla-miniplate or microplate fixationThin soft tissue and overlying skin encasing the orbital and nasal complexes requires low-profile plates to prevent show-through, palpability, or dehiscenceCompared with the mandible, midface and upper facial bones are thinner and more fragile. It is important to take advantage of the facial buttresses in fixating fractures to achieve screw and fracture stabilityEven with the pull of the masseter attachment at the zygoma, zygomaticomaxillary complex fractures can be managed with miniplate or microplate fixation at multiple points, with stable results. The contraction of the masseter muscle produces distracting forces at the zygomaticofrontal and zygomaticomaxillary sutures, both of which are important points of fixation, with adequate bone stock for screw stability. Increased points of fixation resist these forces but may or may not make a clinical difference

BIOABSORBABLE PLATE FIXATION

The advent of bioabsorbable fixation devices negates the need for hardware removal and can prevent many complications associated with long-term retention of permanent hardware.Bioabsorbable implants were initially developed and used for pediatric craniofacial surgery in 1996, but have been described in the literature as early as 1971 for application in the facial skeletonThe advantage of a resorbable system for pediatric fractures lies in absorption of the plate in vivo before it can translocate to an unfavorable areaThere are several varieties of bioabsorbable materials; the most modern are permutations of a polylactic acid and/or polyglycolic acid polymerReported resorption rates for these materials range from 12 to 36 months, as described by manufacturers, but many reports indicate that these plates can be palpated past the 3-year mark. The most commonly reported complications associated with this technique include not only plate palpability, but foreign body reactions, effusions, and infections.Polylactic acid and polyglycolic acid plates, on average, provide half the strength of a traditional bicortically fixated bone plate across a fracture. In the mandible, this can produce negative outcomes

Surgical ApproachesUse of existing lacerationIntraoralMakes use of a vestibular incisionWith appropriate instruments and skill, can be used from symphysis to condyle.Use of transbuccal instruments, special contra-angled instruments and endoscope may be necessary in posterior regions. ExtraoralReserved for cases not treatable by intraoral access

Submental Simple or extendedSubmandibular Retromandibular Preauricular Facelift/ RhytidectomyOthers

SYMPHYSIS and PARASYMPHYSIS2 lag screws/ lag techniqueA lag screw and a miniplateArchbar and lower border plate2 miniplatesReconstruction plate (preferably locking)3D plates

BODYLag screwsOne miniplateTwo platesOne large plate (recon. Plate)3D plates

ANGLE AND RAMUSSingle miniplateOblique ridgeBuccal surfaceTwo miniplates3D platesReconstruction plate

CONDYLEIdeally, two miniplates should be applied in a triangular fashion with one plate below the sigmoid notch and one plate along the posterior border.Single DCPSingle large profile 2.0 mand plate3D plate

ORTHOGNATIC SURGERYDifferent plate systems are available for orthognathic surgeries.3D plates and plates with angles are frequently utilisedOther plates in mandibular modules may be usedRECONSTRUCTIONPlates may be used to retain bone graft or flapRecon plates which may be locking or non locking are usedLocking plates are preferredThey require at least 3 screws on either side for adequate stability.Condylar pieces are available for replacement

ADVANTAGES OF RIFPermits primary bone healingIncreases 3D mechanical and functional stabilityAllows precise anatomic reduction and enhance bone healingRequires no distraction of th efracture cleftRequires no additional fixationProvides greater patient comfort- airway maintained and function is immediately restored

LIMITATIONSStress shielding- osteopenia likely to occur with adaptational platesForeign body reactions- less likely with titaniumExpensive Interference with CT scans n radiotherapyMetal bulk

BIBLIOGRAPHYOral n maxillofacial trauma- fonsecaPeterson's Principles of Oral and Maxillofacial Surgery - Michael Miloro, G. E. Ghali, Peter Larsen, Peter WaiteMaxillofacial trauma and esthetic facial reconstruction- Peter Ward Booth et alTextbook of oral and maxillofacial surgery- Chitra ChakravarthyTextbook of oral and maxillofacial surgery-Rajiv M BorleMathog's Atlas of Craniofacial Trauma - Robert H Mathog, Terry Shibuya, Michael A. CarronIllustrated lecture notes in oral and maxillofacial surgery- George Dimitroulishttps://www.aofoundation.org