 OMFS lecture series. So far in the management of mandibular fractures, we have discussed the basics, principles, closed reduction, surgical approaches and open reduction with intermaxillary fixation for mandibular fractures. In this lecture, we shall have a detailed discussion on open reduction with rigid internal fixation, where we shall see the various plating systems used in managing mandibular fractures. There are certain principles of rigid fixation as given by association for the study of internal fixation. The first goal of anatomical reduction of bone fragments imply that occlusion and basal reduction is of equal importance. In closed reduction, we aim to achieve only an occlusion reduction. In order to achieve basal reduction, we perform open reduction and internal fixation, thereby the reduction is complete. Rigid fixation and semi-rigid fixation, which is also called functionally stable fixation, reduces the interfragmentary motion. What is interfragmentary motion? It is a relative motion between the plates and the bone and also between the bone ends. Interfragmentary motion or interfragmentary gap will result in osteolysis and poor healing of the fracture. Therefore, open reduction and internal fixation is highly essential to avoid interfragmentary gap and provide stabilization. We know that fracture healing is highly dependent on its soft tissue coverage and blood supply. Therefore, try to preserve maximum vascular supply to the fracture fragment through atraumatic surgery. Early active and pain-free mobilization is very important and this makes open reduction superior to closed reduction or conventional intermaxillary fixation. Patients can also take normal diet, speed normally and interact socially. So, these set goals are universal principles of surgical fracture management. In the previous lectures, we had discussed techniques of closed reduction and intermaxillary fixation. We had also seen open reduction methods used in combination with IMF. In this lecture, we shall be discussing in detail the osteosynthesis without intermaxillary fixation. That is, the bone implant alone is sufficient to provide a stable fixation and there is no requirement of intermaxillary fixation. The most important osteosynthesis techniques are non-compression mini plates, compression plates and lag screws. Before going into the technical details of these plates and screws, it is very important to understand the principles and certain terminologies related to internal fixation. Let us see each of these terms one by one. Rigid, non-rigid and functionally stable fixation. Rigid fixation is any form of fixation applied directly to the bones which is strong enough to prevent interfragmentary motion across the fracture when actively using skeletal structure. We know interfragmentary motion is the relative motion between the plates and the bones. So when a functional load is applied, rigid fixation will prevent this interfragmentary motion when the mandible is back to function like mastication. It will not even allow micro movements between the fragments. This is rigid fixation. What is non-rigid fixation? It is any form of bone fixation that is not rigid enough to prevent interfragmentary motion when actively using the skeletal structure. So non-rigid fixation is just opposite to rigid fixation. Therefore it needs an additional support like IMF to stabilize the fragment. So all the techniques we discussed earlier on osteosynthesis with IMF like transorcius wiring, circumferential wiring, k wires. Everything falls under the category of non-rigid fixation. The third entity is the functionally stable fixation. Here there is adequate stability to allow function of the skeletal structure even though it doesn't allow a direct bone union. It means the fixation is not as rigid as in rigid fixation but functional load can be applied even without the period of IMF or immobilization. Primary bone healing takes place with rigid fixation whereas secondary bone healing that is with callus formation takes place in functionally stable fixation. Examples for functionally stable fixation is a single lag screw or mini plates. The next set of terms is compression and non-compression. Here you need to understand that compression and non-compression is the principle or the property within the bone implants that we use. Compression is the property of rigid fixation. So what is the purpose of compression? A compression plate creates inter fragmentary compression which in turn produce a large frictional force between the bone fragments and it is this friction between the fragments that prevent gliding of the metal implant and the bone. This enables rigid fixation. Bending torsion and shear forces associated with mastication are the major factors that disturb the fracture healing. A compression plate can withstand all these forces still stabilizing the fracture without the help of IMF. Again osteosynthesis with IMF doesn't have these features and hence fall under non compression category. Another concept of fixation is load bearing and load sharing osteosynthesis. These terms are self-explanatory. Load bearing fixation is a device that is of sufficient rigidity to bear the entire load applied to the mandible during functional activities. That means it takes all the forces upon itself. It doesn't transmit any force to the mandible. An example of load bearing osteosynthesis is the reconstruction plate used in community fractures of mandible or fractures where there is a loss of a portion of mandible. It is used in fractures with bone defect. Whereas a load sharing fixation device is of insufficient stability to bear all the functional load itself. It distributes the load across the fracture. Therefore the fractured mandible also has to bear a portion of the functional load. Many plates and lag screws are examples of load sharing osteosynthesis and is used in simple linear fractures of mandible. One more concept of fixation is the locking and non locking plates used for osteosynthesis. An important thing to consider while plating the bone is to accurately adapt the plate to the bone surface. This is important because if the adaptation is not proper, torsional forces can cause instability of the implant and the fracture. In locking system, the threads on the screw head lock into the congruent threads of the plate and as they are tightened the plate and screw becomes a single unit. That means the screw gets completely locked or the screw head gets completely locked into the plate thus becoming one single unit. The fixation here is thus rigid with high mechanical stability. Screw loosening is unlikely here and an accurate plate adaptation like that in non locking system is also not needed. Whereas in non locking system a precise plate adaptation is required and chances of screw loosening is also very high. Having understood the various concepts of fixation, let us now see in detail some of the internal fixation devices. The first among them is the compression plate. Compression plates provide rigid fixation with axial compression between the fractured bone ends. Need for inter-maxillary fixation is obviated and primary bone healing takes place. Even with these desirable features, the indications and uses of compression plates are limited due to its bulkiness in size. It is indicated in minimally oblique fractures or linear fractures with sound butt verses. It means there shouldn't be any bony defect in the mandible while applying compression plate. A precise plate adaptation is absolutely necessary, failure of which may cause overriding of the fracture fragments, spleying of lingual cortex and eventually malocclusion. These are the disadvantages of compression plates. There are two types of compression plates. Dynamic compression plate and eccentric dynamic compression plates. Let's see how a dynamic compression plate is designed and how it works. Dynamic compression plate or DCP has in total four holes. Two central holes are called the compression holes and the two terminal holes are called the retention holes. The screws placed in the central holes provide inter-fragmentary compression and the screws at the ends helps in plate retention. The shape of these holes also vary. The central holes are pure shaped or oval shaped and the retention holes are spherical. The inter-fragmentary compression is created through a principle called spherical gliding principle. What is spherical gliding principle? Imagine a hollow cylinder as you can see in this figure. This hollow cylinder has a bend or an angle which gives the cylinder two components an oblique and a horizontal component. Now imagine you are passing a ball or sphere through this cylinder. The ball first passes through the inclined or the oblique component and then it has to glide through the bend to enter the horizontal part. The same design applies to the central holes of the compression plate. The screw head which is placed in the oblique part of the central hole glides and settles at the horizontal part as the screw is tightened. As it glides through the bend in the hole it approximates the fracture fragments by pulling it together. While the screw is tightened in the central compartment or the central hole it provides an inter-fragmentary pressure thus compressing the two fragments together and the fracture gets reduced. The retentive screws are then tightened after the central ones. So this is how a dynamic compression plate act by providing inter-fragmentary compression in between the fracture fragments. The compression plates are designed in such a way that it is bulky and cannot be placed at the upper border of the mandible. It can only be placed at the lower border. Even though the compression plates provide a rigid fixation the upper border tends to open up during the compression or tightening of the screws. This is because there is always a constant tension at the superior border that tends to pull the fracture fragments apart. Therefore an additional fixation is required to compensate the tension at the superior border. Either a mini plate can be fixed to the upper border or a tension band can be applied. The tension can the tension band can be an arch bar that can counteract the opening up of superior border. So this is the condition when you apply only the compression plate at the inferior border. To avoid opening up of the superior border you either place a mini plate at the upper border or you can place an arch bar to the teeth. Excentric dynamic compression plate is similar to dynamic compression plate with the only difference at the terminal plate holes. The outer holes are positioned oblique to the long axis of the plate. If this is the plate axis the end screws are placed at an angulation. Various modifications have been made for the EDCP with the oblique holes at 45 degree, 75 degree and 90 degrees. The main purpose of this angulation is to resolve the plane at the superior border. This specific design will compress the superior border thus obviating the use of an additional mini plate or a tension band. EDCP is used in fractured identulous mandible where IMF is not possible. It is also used in identulous or partially identulous cases where the height of the mandible is not sufficient enough to accommodate two plates. Comparing dynamic compression plate and eccentric dynamic compression plate. The central compression design is the same for both. Spherical gliding principle. EDCP in addition has oblique outer compression holes to compress the upper border. Therefore tension band is required for DCP and not for EDCP. This is all about compression plate osteosynthesis. The most common, convenient, technically easier, feasible and least complicated osteosynthesis technique is the semi-rigid or functionally stable fixation, the mini plates. Shampi and his co-workers argued that compression plates were unnecessary because there is a natural line of compression existing along the lower border of the mandible. It was observed that physiologically coordinated muscle function produced tension at the upper border, compression at the lower border and torsional or rotational forces anterior to the canine region. Shampi at all determined the ideal osteosynthesis lines also known as shampi's lines of osteosynthesis where mini plate fixation is most stable. Therefore ideal osteosynthesis line is nothing but the sites where mini plate fixation can be most effectively performed in a mandible. Let us see which are those ideal regions of mini plate fixation. In the body of mandible the ideal position for fixer mini plate is between the upper border and the lower border. To be precise it is placed just below the roots and above the inferior alveolar canal. As you can see in the figure here the lines marked in pink are the lines of osteosynthesis. Behind the foramen the blue plate is fixed in between the teeth roots and the canal. In the angle region shampi's line is present at the external oblique ridge. Therefore the plate is fixed on to the broad surface of the external oblique ridge as high as possible. In the anterior region two plates are fixed one sub-apically that is below the root apices and one plate near the lower border. The two plates are positioned to neutralize the torsional forces or the rotational forces acting at the anterior mandible. Here is the armamentarium for mini plate fixation. This is the bone plating kit with plate benders. These are the plate benders and plate holders. These are the mini plates and the screws used for fixing them. Plates are available in different designs with different number of holes and lengths. Screws also comes in various lengths and head diameters. This is a screw holder with which you carry the screws into the bone and with a screwdriver you tighten it. Dwells are available in different sizes to drill the bone through the plate holes. This photo shows two mini plates fixed at the anterior mandible. A deed loving incision is made in the anterior vestibule. Mentalism muscle is incised and subperiostal dissection is performed to expose the lower border. The fracture is then reduced in its anatomical position and the temporary IMF is performed to achieve occlusion. The plate is then adapted to the bone contour and fixed in position with the screws. This is how a mini plate fixation is performed. Having discussed about both compression and mini plates, let us compare both the systems. Compression plate is bulky and difficult to use, hence applied extra orally, whereas mini plates are smaller, need lesser soft tissue dissection and hence applied intra-orally. Compression plates are difficult to adapt. It causes nerve injury and cannot be applied to the upper border. On the other hand, mini plates can be placed at both the upper and lower borders with fewer complications. Compression plate provides rigid fixation with no interfragmentary motion and mini plates provide functionally stable fixation with little interfragmentary motion under functional loading. That's all about the two important plating systems. Third type of osteosynthesis is the lag screw. Stable union of two bone fragments can be achieved by means of lag screws. The principle is that the axial tensile stress within the screws while tightening it is converted into a compressive stress acting upon the fracture surface. The special feature of lag screw is that the threads are confined to one half of the shaft. The threads are confined to the lower half of the shaft and the remainder near to the screw head is smooth. This part of the screw is smooth and the lower part is threaded. First a hole is made through both the fracture fragments using a drill bit of 2mm. Then you use something called a screw tap. It is used to make a gliding and a thread hole of required size. The threaded part of the lag screw that is the lower part fits into the thread hole and the upper smooth part fits into the gliding hole. As the screw is being tightened the threaded lower tip engages the lingual cortex. This is the buckle cortex and this is the lingual cortex. So as the screw is tightened the threaded lower tip engages the lingual cortex and pulls it towards the buckle and the two cortices are compressed against each other. This way fracture is reduced and lag screws are used for stabilizing or it is used as a fixation device. Lag screws are ideal for oblique surface fracture which means the length of the fracture surface should be greater than or equal to the manipular height. Such fractures are considered oblique and ideal number of lag screws is three or more in number to neutralize the functional forces that acts in all directions but two screws are an absolute minimum. Other indications are fractures in the identialist mandible with concomitant fractures of body and condyle. It is helpful in patients in whom IMF is contraindicated and also in non or malunion fractures. Reconstruction plates as the name suggests is used to reconstruct the lowest part of mandible following a fracture or surgical resection. They are load bearing and provide rigid fixation. It makes up for the bony defect and restore the continuity of the bone. This particular slide has been included only to make you understand which fixation devices fall under rigid fixation and which under semi-rigid fixation. By now you would have understood the different concepts of fixation and the working principles of each devices. Therefore you may use them in combinations to achieve the desired type of fixation. For example a single reconstruction plate or a single six hole 2.4 mm compression plate is sufficient to provide rigid fixation whereas for certain other devices you need a combination. Only a combination can provide rigid fixation. For example two bone plates. The bone plates can be either two compression plates or two mini plates or it can be one compression plate and one mini plate. So a combination of two bone plates, a combination of two lag screws, one bone plate and one lag screw and one compression plate and arch bar. These four combinations will give rigid fixation and reconstruction plate and one six hole compression plate will provide rigid fixation. Now coming to semi-rigid fixation. If you place one 2 mm mini plate at the angle region without arch bar then you achieve functionally stable fixation or semi-rigid fixation. Whereas elsewhere in the mandible you need to place one 2 mm mini plate along with an arch bar for semi-rigid fixation. Also one lag screw and arch bar and one four hole 2.4 mm compression plate without arch bar are examples of semi-rigid fixation. So here one four hole compression plate with arch bar will provide rigid fixation whereas the same plate same compression plate without arch bar will provide semi-rigid fixation. Lastly let us have a look at the advantages and disadvantages of open reduction and internal fixation. Advantages are that there is accurate reduction and fixation of the fractures with primary bone healing. There is early return to normal jaw function. The patient can maintain a good oral hygiene and there is a lower risk of major complications. Disadvantages are that the procedure requires surgical exposure under general anesthesia which makes the treatment expensive. Compared to the IMF technique open reduction is difficult and risky. You are leaving foreign body inside the tissues because you are placing a bone implant. The risk of neurovascular structure and teeth is also more when compared to closed reduction. If required a second surgery also has to be performed to remove the hardware. So these are few advantages and disadvantages of open reduction and internal fixation. That's all about the topic and with this we have completed the management of mandibular fractures. In the next lecture we shall be discussing condylar fractures exclusively. Thank you.