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Compression plating (compression osteosynthesis) of mandible fractures
COMPRESSION PLATING (COMPRESSION OSTEOSYNTHESIS) OF MANDIBLE FRACTURES ROBERT M. KELLMAN, MD
Compression osteosynthesis implies the use of rigid fixation across a fracture or osteotomy so that the fragments are compressed together even when the body part is at rest (no functional load). It must be applied in such a way that the addition of a functional load will not reverse the compressive force. So long as a positive (compressive) force is maintained at all times, no motion of the fragments relative to each other will occur, and healing will likely ensue. The principles and techniques for achieving dependable compression osteosynthesis across mandibular fractures are described, including the use of the dynamic compression plate, the eccentric dynamic compression plate, and lag screw compression fixation. Proper application, with indications and contraindications, is included, along with a discussion of the complications that may be encountered.
Although m a n y readers may be familiar with the basic principles, one cannot approach the topic of compression plating of mandible fractures without some discussion of the biomechanical principles on which the techniques are based. In fact, m a n y of the complications encountered by surgeons (and described in the literature) can be attributed to a failure to adhere to these principles. (Note that the biomechanical principles remain the same regardless of what techniques are used; ie, compression plating, [neutral] mini-plating, wire osteosynthesis, or even conservative treatment with arch bars and mandibulo-maxillary fixation [MMF].) However, it is the understanding of these principles that allows the surgeon to choose among the various techniques available and then to apply the selected one appropriately in a given case, so as to thereby achieve a high rate of success with a minim u m of complications. The goal of fixation is to achieve bony union across a fracture or osteotomy dependably, rapidly, and in a controlled fashion (ie, in the desired position). In order to accomplish this, the bone edges must be brought together into the proper alignment and maintained there while healing takes place. If this can be accomplished with a minimum amount of disruption of the patient's life and function (eg, avoiding a prolonged period of MMF), this is generally believed to be preferable. Therefore, an ideal fixation technique will result in the maintenance of the proper alignment of the bones during the healing process, without preventing function. With careful attention to principles and with proper case selection, miniplating, compression plating, lag screw fixation, and reconstruction plating will all provide this outcome. By being familiar with all of these techniques and how to apply them, the surgeon will be able to select the optimal approach for a given case that is likely to maximize the From the Department of Otolaryngology and Communication Sciences, SUNY Health Smence Center at Syracuse, Syracuse, NY. Address reprint requests to Robert M. Kellman, MD, 750 E Adams St, Syracuse, NY 13210 Copyright © 1995 by W.B. Saunders Company 1043-1810/95/0602-0012505.00/0
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simplicity and success while minimizing the morbidity and the complications.
OVERCOMING FUNCTIONAL FORCES At rest, the mandible is unloaded. Any fixation that holds the fragments together (even wire osteosynthesis) would facilitate bone healing if the mandible was to remain unloaded at all times. Unfortunately, this is not the case. Even the act of swallowing loads the mandible. Therefore, a dependable fixation must be designed and applied to overcome any forces that will act to distract and mobilize the fractured fragments; otherwise relative motion will result in at best a delay in healing, and often a much worse outcome such as a malunion, a nonunion or even an osteomyelitis and loss of bone. Numerous studies have looked at the forces operating on the mandible during function. 1 Though the forces vary with the presence and status of the dentition, as an oversimplification, the forces along the alveolar (dental) border tend to distract fractured fragments w h e n loaded, whereas those along the basal border tend to actually compress the fragments together during f u n c t i o n .2:3 ' Behind the dentition, in the region of the mandibular angle, these forces actually fluctuate between distraction and compression at various points during the course of masticating and swallowing activity. 4'5 In the symphyseal region, torsional forces are seen as well. Proper fixation will overcome these forces and keep the fragments immobilized even w h e n loaded in function. What both Spiessl and Champy realized early was that chewing tends to distract the dental border of a fracture line, whereas the basal border tends to be compressed. 2"3 Fixation along the more accessible basal border does little to overcome the distracting forces occurring superiorly (Fig 1). This explains w h y early attempts at plate fixation of mandible fractures generally failed, because plates were generally placed along the inferior border. Logically, therefore, plates should be applied superiorly, where they will overcome the forces of distraction. Un-
O P E R A T I VTECHNIQUES E IN OTOLARYNGOLOGY--HEAD AND NECK SURGERY, VOL 6, NO 2 (JUN), 1995: PP 80-85
FIGURE 1. Direction of forces imposed by chewing on dental and basal borders of mandible fractures. fortunately, the presence of teeth and their roots as well as the inferior alveolar nerves seemed to preclude the possibility of applying what should be the ideal fixation. This problem was solved in several ways that have now proved clinically dependable over time. Spiessl advocated the use of a tension band arch bar. 2 This is applied securely to the teeth across the fracture, so that forces applied to the mandible during chewing cannot pull this area apart. In fact, the result is that the compressive force, normally produced by function along the basal border only, is now distributed along the length of the fracture; this explains w h y arch bar fixation alone has so frequently been successful. Spiessl then applied a compression plate across the basal border. This plate, w h e n properly applied (see below), places a compressive force across the fracture beneath the plate, even at rest. The presence of the tension band arch bar results in this compressive force being distributed along the length of the fracture (Fig 2). Champy et al solved the same problem by placing a mini-plate just below the tooth roots. 3 This has to be applied using mono-cortical screws so as to avoid inadvertent injury of the tooth roots or the nerve. They found that by placing a mini-plate in this area, it would overcome the distracting forces seen in function, so long as the patient did not fully load the fractured area of the mandible (ie, the patient would not chew on that side). Although Champy et al do not refer to it as such, the mini-plate is functioning as a tension band (Fig 3). Note that this technique prevents distraction of the fragments and holds them immobilized, but they are not compressed together at rest. Note further that in the area of
FIGURE 2. Distribution of chewing force over entire fracture by tension band arch bar. KELLMAN
FIGURE 3. Mini-plate acts as a tension band, immobilizing the fragments but not compressing them when at rest. the mandibular angle and in the symphyseal region, two mini-plates should be applied to overcome the varying and torsional forces. Mini-plating technique generally refers to the use of 2.0-mm neutral mandibular plates.
COMPRESSION FIXATION When using compression plates, the fragments are actually compressed together at rest, thereby increasing the frictional forces between the fragments and decreasing the likelihood of mobility. Another important aspect of compression fixation is that it seems to speed up the rate at which the bone itself becomes capable of supporting stress. In an elegant study by Luhr, 6 he fixed experimental osteotomies in dog mandibles using rigid fixation with and without compression. At 12 weeks postoperatively, the bending strengths of the healing bones were the same, with both groups exhibiting approximately 50% of the strength of the unfractured mandible. However, at 2 weeks, the noncompressed but rigidly fixed bones had no strength as compared with about 16% for the compressed bones, and at 4 weeks after repair, the compressed bones had more than 30% of normal strength as compared with approximately 10% to 15% for the noncompressed bones. Compression fixation is thus a somewhat safer technique, particularly in the noncompliant patient who is less likely to avoid full loading of the fractured area. However, it does require the use of bicortical screws; thus, compression plates cannot be used along the tension side of the fracture. There are also several additional options available to the surgeon, and these become particularly important when a tension band arch bar cannot be applied (eg, poor or absent dentition). When dentition is absent or inadequate for the placement of a tension band arch bar, compression fixation of the basal border of the mandible would obviously lead to distraction of the alveolar border and instability. One way of overcoming this problem is to apply a tension band plate superiorly, such as a neutral 2.0-mm, mono-cortical mini-plate. Another option is to use an eccentric dynamic compression plate (EDCP). This is a plate with compression holes directed both horizontally and superiorly. When properly applied, the horizontal compression screws compress the basal border, whereas the superiorly directed compression screws rotate the bone a r o u n d the initially applied screws, thereby compressing the alveolar border of the fracture together (Fig 4). Although not actually a plating technique, lag screw 81
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!'i' : FIGURE 4. Eccentric dynamic compression plate with horizontally and superiorly directed screw holes compresses alveolar fracture borders. fixation is another form of compression fixation. It is used specifically w h e n fragments of bone overlap. The lag screw is placed so that its thread does not catch in the proximal fragment, although it does hold securely in the second fragment. As the screw is tightened, the proximal fragment is pressed between the head of the screw and distal fragment, thereby compressing the two bone fragments firmly together. This technique works nicely in the symphyseal and parasymphyseal regions of the mandible, where the curvature of the mandible results in cortical overlap (Fig 5). 7 Though more difficult technically, it can also be used to repair angle fractures, s The screw is applied from an inferolateral position in the anterior buccal cortex in a superomedial direction into the posterior fragment (Fig 6), with extreme caution not to injure the inferior alveolar nerve. Finally, there is the mandibular reconstruction plate. This is a plate designed to be strong enough to replace a missing segment of mandible. It has to be bendable in three dimensions, and it must contain many holes, so that numerous fixation points for screw placement are available. This plate can be used to stabilize the mandible w h e n an area is defective or structurally defective (such as an area of comminution), but at least three and preferably four screws must be applied in the solid bone on either side. Because this fixation is strong enough to replace a defective area, it is obviously strong enough to fix a fracture. It is thus a good "fall-back" technique for the fixation of any difficult fracture, particularly when the bone is thin and weak, such as in the angle region or in the atrophic, edentulous mandible.
FIGURE 5. Lag screw fixation for use in cases with overlapping bone fragments. 82
FIGURE 6. Lag screw fixation used to repair an angle fracture. It is important to note that most of the research and clinical experience with mandibular compression plating has been performed using the 2.7-ram systems (eg, stainless steel, titanium, and Vitallium®). A 2.4-ram mandibular compression system has recently been introduced to provide smaller, lower profile plates. Although surgeons have been quick to accept this new system, it is not yet clear that the degree of stabilization is comparable to the 2.7-ram systems. ~ In general, caution should be exercised w h e n selecting untried and unproven new devices.
INDICATIONS Compression fixation is an option for all mandible fractures, except w h e n there is a gap at the fracture site due to bone loss. There are generally multiple options available for the repair of a given fracture, and the surgeon's preference and experience, as well as the needs of the individual patient, will all play a role in determining which repair option is selected. In the presence of good dentition, if a solidly placed arch bar results in a clinically stable fixation, a period of 3 to 6 weeks of MMF may be the preferred approach, if the patient prefers a noninvasive technique. However, if a fracture in a dentate segment occurs in association with a subcondylar fracture, an open reduction and internal fixation of the distal fracture may allow for earlier mobilization of the mandible and hopefully better joint function. When a relatively stable fracture is encountered in the compliant patient, virtually any fixation that will work for a given site can be selected. In the symphysis, parasymphysis, and angle regions, this will include mini-plates, compression plates, three-dimensional plates, lag screws, and reconstruction plates (as well as the EDCP plate, though its use is not generally recommended). In the body region, lag screw fixation is not an option, unless the fracture is oblique and the fragments overlap. In COMPRESSION PLATING OF MANDIBLE FRACTURES
fact, w h e n the fracture is oblique, creating overlapping fragments, the lag screw technique is indicated regardless of the site of fracture. Note that w h e n extra stabilization is required, lag screws can be applied through a plate. When the patient is noncompliant and is likely to chew on the side of the fracture, compression fixation is recommended as opposed to mini-plate fixation. The additional friction created by compression fixation should decrease the likelihood of movement of the bone fragments relative to each other. For this reason, it may also be wise to select a compression plate (or a reconstruction plate) w h e n the patient's initial presentation is delayed and/or complicated by local soft-tissue infection. Compression fixation seems to impart some degree of protection against the development of osteomyelitis by rigidly fixin~ the fragments together and promoting rapid healing. ~ Note that this refers to soft-tissue infection. If the bone is involved (ie, osteomyelitis), compression fixation is contraindicated, and a reconstruction plate should be used. Rigid fixation, w h e t h e r mini-plate or compression plate, is recommended for patients who wish to avoid MMF, whether for professional purposes or for reasons of personal preference. It is also recommended in elderly and malnourished patients, because a period of MMF could lead to debilitation. In the neurologically impaired or brain-injured patient, compression plating will not only eliminate the need for MMF, but the high degree of stability imparted may resist the forces created by bruxism, which is common in this patient population. Rigid fixation is also preferred in the seizure-prone patient, so that the risks associated with MMF in this patient group may be avoided.
rior mandibular body will generally need to be placed using a trans-buccal approach through a trocar placed through a stab incision made in a direction parallel to the branches of the facial nerve. Great care should be used to avoid injury to the mental nerve and the mandibular ramus of the facial nerve.
COMPRESSION PLATE A compression plate is designed so that proper placement of the screws will result in a relative motion between the plate and the screws that will force the bone fragments together, compressing them across the fracture line. This is accomplished by designing the plate with elliptical or oblong holes. The screw is designed with a head large enough to overlap the metal of the plate, w h e n it is properly positioned in the hole (Fig 7A). When the screw is placed into the bone, it forms a "screw-bone unit." Thus, any relative motion between the plate and the screw will bring the bone with the screw. As the screw is tightened, the screw will move relative to the plate until the screw is seated in the plate hole. The amount of movement will be equal to the amount that the screw head overlaps the plate (Fig 7B). If a screw has II II
CONTRAINDICATIONS There are two main contraindications to compression plating of mandible fractures. One is bone loss, because compression fixation in this situation will alter the position of the bone fragments, thereby creating a malunion. In the presence of dentition, this creates a malocclusion, but even in the absence of dentition, this will put undue stress on the temporomandibular joints, and it will make dental rehabilitation more difficult as well. The other contraindication is the presence of infection in the bone. Osteomyelitis requires debridement of bone, thus creating a bone loss situation. This requires pretreatment with intravenous antibiotics, followed by aggressive debridement of involved bone. The solid bone segments are repositioned using a long mandibular reconstruction plate, placing at least four screws in each fragment at a distance from the infected area, and leaving several empty holes in the area of the infection and defect. n Of course, w h e n the fracture is oblique, compression plating will result in the fractures gliding across each other into a malposition. Lag screw fixation is therefore indicated in this situation.
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TECHNIQUES Compression fixation techniques can be performed either via extra-oral or intra-oral incisions. Note that w h e n intra-oral incisions are used, screws posterior to the anteKELLMAN
FIGURE 7. The compression plate and screw heads are designed so that when the screws are tightened, the two bone fragments are compressed together. 83
been at least partially inserted into the other fracture fragment, its position in the plate will prevent the opposing fragment from moving away as this screw is tightened. This will cause the fragments of bone to be compressed together. Tightening of the screw in the opposite fragment will add additional compression of the bones together (Fig 7C). Additional screws are placed neutrally to increase the stability of the fixation.
ECCENTRIC DYNAMIC C O M P R E S S I O N PLATE This plate is generally used to compress a fracture w h e n no tension band has been applied. It is critically important to precompress the fracture using a technique that holds the alveolar portion of the fragments firmly together. Otherwise, this area will pull apart w h e n axial compression is applied across the basal border of the mandible. Precompression can be applied using a modified towel clip or a mandibular reduction forceps with side rollers (Fig 8). The EDCP is then applied. First, the horizontal compression screws are placed as described previously. Next, the compression screws are placed in the diagonal holes (pointing toward the superior portion of the fracture). These screws are positioned in the inferior portion of the screw holes, so that the screw head-plate interaction will push the screw-bone unit in a superior direction, thereby compressing the alveolar portion of the fracture (Fig 9). The remaining screws are placed neutrally. Note that w h e n using an EDCP, it is r e c o m m e n d e d that at least a six-hole plate be used for adequate stability. It is important to recognize that the successful use of the EDCP requires intact bone along the alveolar border. Thus, its use is not advised w h e n a tooth at the alveolar border has been acutely lost or needs to be extracted.
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FIGURE 9. Tightening of screws forces bone in a superior direction, compressing alveolar borders of fracture.
LAG S C R E W T E C H N I Q U E The key to lag screw fixation is having the thread glide through the first fragment and catch in the second bone fragment. Tightening will result in compression of the fragments together. A hole is drilled in the first fragment that is the size of the thread diameter of the screw to be used. The appropriate drill is then placed through this hole, and the second fragment is drilled using the drill that is the size of the screw shaft. The surface of the first hole is countersunk for better seating of the screw head. The depth of the hole is measured. The second hole is tapped if a non-self-tapping system is being used. The appropriate length screw is then placed and tightened (Fig 10). For overlapping fragments (oblique fractures), at least two and preferably three screws should be placed. For the symphysis, two lag screws are used. Only the mandibular angle is repaired using a single lag screw.
COMPLICATIONS The most c o m m o n complication of rigid fixation of the mandible is early local soft-tissue infection. This can generally be managed with drainage and appropriate (culture-specific) antibiotic therapy, without removal of
FIGURE 8. Precompression of bone fragments in preparation for application of eccentric dynamic compression plate.
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FIGURE 10. Lag screw fixation of overlapping bone fragments. COMPRESSION PLATING OF MANDIBLE FRACTURES
the hardware, so long as the fixation is stable and the screws are tight. Sometimes surgical exploration a n d evaluation of the stability of the hardware are necessary. Late infection is more ominous a n d generally implies loosening of one or more screws. W h e n this occurs, the w o u n d should be explored and the hardware should be removed. If the fracture is healed, antibiotic treatment should resolve the problem. If healing is incomplete, or if bone infection is found, t h e n replacement of the fixation plate with either a reconstruction plate or an external fixator s h o u l d be considered. In an excellent metaanalysis of rigid fixation of mandible fractures, Iizuka 12 noted that infection rates varied b e t w e e n 0% a n d 27%. Higher infection rates have been seen at the mandibular angle. 5 Other authors have suggested that rigid fixation techniques in general result in higher complication rates than either conservative m a n a g e m e n t with MMF alone or w h e n combined with wire osteosynthesis. 13 However, there is evidence to suggest that at least some of these complications were technical. The report by E1 Degwi a n d Mathog 13 involved multiple surgeons in several specialties at different hospitals, m a n y of w h o m had limited experience with the techniques. It is thus likely that at least some complications could be attributed to variance from strict biomechanical principles in the application of the techniques. In the review by Iizuka, 12 it was f o u n d that their o w n overall infection rate using compression osteosynthesis over a 7-year period was 6.1% (13 of 214). W h e n looked at over time, it was n o t e d that the infection rate was 10.9% b e t w e e n 1983 a n d 1986, 4.8% in 1987 a n d 1988, and only 3.6% in 1989. Levy et al 5 were able to reduce their complication rate w h e n plating angle fractures from 26.3% to 3.1% by routinely a d d i n g a second plate. Thus, there is good evidence to suggest that strict adherence to biomechanical principles a n d increasing surgical experience can result in high rates of success with acceptably low complication rates. Other complications include malocclusion, nerve injury, a n d tooth root injury. Malocclusion is obviously the result of rigid fixation of the bones in an improper position. Difficulties with plate b e n d i n g make this complication more likely with larger plates. However, attention to detail a n d an unwillingness to accept a less-thansatisfactory result at the time of plate application should minimize this complication. For complex, c o m m i n u t e d fractures in which total failure is a high risk, a malocclusion should be preferable to a n o n u n i o n . Mental nerve injury is more c o m m o n w h e n using the intra-oral approach, a n d facial nerve injury is obviously more likely via the external approach. Care should be exercised to minimize these complications. Injury to tooth roots a n d to the inferior alveolar nerve in its b o n y canal should be avoided by placing compression plates along the basal border of the mandible. W h e n placing compression plates via the intra-oral route, it is possible
KELLMAN
to position t h e m more superiorly t h a n is obvious, a n d caution should be exercised in this situation. Pain, palpability, a n d cold i n t o l e r a n c e all occur. These can be easily resolved by removing the h a r d w a r e after healing is complete.
SUMMARY In s u m m a r y , compression fixation of mandible fractures is an important technique that should be part of the arm a m e n t a r i u m of the facial trauma surgeon. A complete u n d e r s t a n d i n g of the biomechanical principles a n d techniques will result in high rates of surgical success with a m i n i m u m of complications.
REFERENCES 1. Koolstra JH, van Eijden TMGJ, Weijs WA, Naeije M: A threedimensional mathematical model of the human masticatory system predicting maximum possible bite forces. J Biomechanics 21:563576, 1988 2. Spiessl B: New Concepts in MaxillofacialBone Surgery. New York, NY, Springer-Verlag, 1976 3. Champy M, Pape HD, Gerlach KL, et al: The Strasbourg mini plate osteosynthesis, in Kruger E, Schiili W, Worthington P (eds): Oral and MaxdlofacialTraumatology. Chicago, IL, Quintessence Publishing, vol 2, 1986 4. Kroon F: Effectsof three-dimensional loading on stabihty of internal fixation of mandible fractures, in Spiessl B (ed): Internal Fixation of the Mandible. Berlin, Spnnger-Vedag, 1989 5. Levy FE, Smith RW, Odland RM, Marentette LJ: Monocortical miniplate fixation of mandibular angle fractures. Arch Otolaryngol Head Neck Surg 117:149-154, 1991 6. Luhr HG: Basic research, surgical technical and results of fracture treatment with the LUHR-Mandibular-Compression-Screw-System (MCS-System). Oral and MaxillofacialSurgery: Proceedings from the 8th International Conference on Oral and MaxillofacialSurgery. Chicago, IL, Quintessence Publishing Co, 1985, pp 124-137 7. Ellis E III, Ghalh GE: Lag screw fixation of anterior mandibular fractures. J Oral MaxfllofacSurg 49:13-21, 1991 8. NlederdeUmann H, Akuamoa-Boateng E, Uhlig G: Lag-screw osteosynthesis: A new procedure for treating fractures of the mandibular angle. J Oral Surg 39:938, 1981 9. Ellis E III, Sinn DP: Treatment of mandibular angle fractures using two 2.4-mm dynamic compression plates. J Oral Maxillofac Surg 51:969-973, 1993 10. Beckers HL: Treatment of inlbally infected mandibular fractures with bone plates. J Oral Surg 37:310, 1979 11. KellmanRM: One stage vs. two stage management of mandibular osteomyelitis using the AO mandibular reconstruction plate. Free Paper Abstracts, Vith International Symposmm. Presented at the Sixth International Symposium of the American Academy of Facial Plastic & ReconstructiveSurgery. San Francisco, CA, June 19, 1993 12. hzuka T: Rigid internal fixation of mandibular fractures. Academic Dissertation. Helsinki, Finland, 1992 13. E1-Degwi A, Mathog RH: Mandible fractures--Medical and economic considerations. Otolaryngol Head Neck Surg 108:213-219, 1993
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Compression osteosynthesis implies the use of rigid fixation across a fracture or osteotomy so that the fragments are compressed together even when the body part is at rest (no functional load). It must be applied in such a way that the addition of a functional load will not reverse the compressive force. So long as a positive (compressive) force is maintained at all times, no motion of the fragments relative to each other will occur, and healing will likely ensue. The principles and techniques for achieving dependable compression osteosynthesis across mandibular fractures are described, including the use of the dynamic compression plate, the eccentric dynamic compression plate, and lag screw compression fixation. Proper application, with indications and contraindications, is included, along with a discussion of the complications that may be encountered.
Although m a n y readers may be familiar with the basic principles, one cannot approach the topic of compression plating of mandible fractures without some discussion of the biomechanical principles on which the techniques are based. In fact, m a n y of the complications encountered by surgeons (and described in the literature) can be attributed to a failure to adhere to these principles. (Note that the biomechanical principles remain the same regardless of what techniques are used; ie, compression plating, [neutral] mini-plating, wire osteosynthesis, or even conservative treatment with arch bars and mandibulo-maxillary fixation [MMF].) However, it is the understanding of these principles that allows the surgeon to choose among the various techniques available and then to apply the selected one appropriately in a given case, so as to thereby achieve a high rate of success with a minim u m of complications. The goal of fixation is to achieve bony union across a fracture or osteotomy dependably, rapidly, and in a controlled fashion (ie, in the desired position). In order to accomplish this, the bone edges must be brought together into the proper alignment and maintained there while healing takes place. If this can be accomplished with a minimum amount of disruption of the patient's life and function (eg, avoiding a prolonged period of MMF), this is generally believed to be preferable. Therefore, an ideal fixation technique will result in the maintenance of the proper alignment of the bones during the healing process, without preventing function. With careful attention to principles and with proper case selection, miniplating, compression plating, lag screw fixation, and reconstruction plating will all provide this outcome. By being familiar with all of these techniques and how to apply them, the surgeon will be able to select the optimal approach for a given case that is likely to maximize the From the Department of Otolaryngology and Communication Sciences, SUNY Health Smence Center at Syracuse, Syracuse, NY. Address reprint requests to Robert M. Kellman, MD, 750 E Adams St, Syracuse, NY 13210 Copyright © 1995 by W.B. Saunders Company 1043-1810/95/0602-0012505.00/0
80
simplicity and success while minimizing the morbidity and the complications.
OVERCOMING FUNCTIONAL FORCES At rest, the mandible is unloaded. Any fixation that holds the fragments together (even wire osteosynthesis) would facilitate bone healing if the mandible was to remain unloaded at all times. Unfortunately, this is not the case. Even the act of swallowing loads the mandible. Therefore, a dependable fixation must be designed and applied to overcome any forces that will act to distract and mobilize the fractured fragments; otherwise relative motion will result in at best a delay in healing, and often a much worse outcome such as a malunion, a nonunion or even an osteomyelitis and loss of bone. Numerous studies have looked at the forces operating on the mandible during function. 1 Though the forces vary with the presence and status of the dentition, as an oversimplification, the forces along the alveolar (dental) border tend to distract fractured fragments w h e n loaded, whereas those along the basal border tend to actually compress the fragments together during f u n c t i o n .2:3 ' Behind the dentition, in the region of the mandibular angle, these forces actually fluctuate between distraction and compression at various points during the course of masticating and swallowing activity. 4'5 In the symphyseal region, torsional forces are seen as well. Proper fixation will overcome these forces and keep the fragments immobilized even w h e n loaded in function. What both Spiessl and Champy realized early was that chewing tends to distract the dental border of a fracture line, whereas the basal border tends to be compressed. 2"3 Fixation along the more accessible basal border does little to overcome the distracting forces occurring superiorly (Fig 1). This explains w h y early attempts at plate fixation of mandible fractures generally failed, because plates were generally placed along the inferior border. Logically, therefore, plates should be applied superiorly, where they will overcome the forces of distraction. Un-
O P E R A T I VTECHNIQUES E IN OTOLARYNGOLOGY--HEAD AND NECK SURGERY, VOL 6, NO 2 (JUN), 1995: PP 80-85
FIGURE 1. Direction of forces imposed by chewing on dental and basal borders of mandible fractures. fortunately, the presence of teeth and their roots as well as the inferior alveolar nerves seemed to preclude the possibility of applying what should be the ideal fixation. This problem was solved in several ways that have now proved clinically dependable over time. Spiessl advocated the use of a tension band arch bar. 2 This is applied securely to the teeth across the fracture, so that forces applied to the mandible during chewing cannot pull this area apart. In fact, the result is that the compressive force, normally produced by function along the basal border only, is now distributed along the length of the fracture; this explains w h y arch bar fixation alone has so frequently been successful. Spiessl then applied a compression plate across the basal border. This plate, w h e n properly applied (see below), places a compressive force across the fracture beneath the plate, even at rest. The presence of the tension band arch bar results in this compressive force being distributed along the length of the fracture (Fig 2). Champy et al solved the same problem by placing a mini-plate just below the tooth roots. 3 This has to be applied using mono-cortical screws so as to avoid inadvertent injury of the tooth roots or the nerve. They found that by placing a mini-plate in this area, it would overcome the distracting forces seen in function, so long as the patient did not fully load the fractured area of the mandible (ie, the patient would not chew on that side). Although Champy et al do not refer to it as such, the mini-plate is functioning as a tension band (Fig 3). Note that this technique prevents distraction of the fragments and holds them immobilized, but they are not compressed together at rest. Note further that in the area of
FIGURE 2. Distribution of chewing force over entire fracture by tension band arch bar. KELLMAN
FIGURE 3. Mini-plate acts as a tension band, immobilizing the fragments but not compressing them when at rest. the mandibular angle and in the symphyseal region, two mini-plates should be applied to overcome the varying and torsional forces. Mini-plating technique generally refers to the use of 2.0-mm neutral mandibular plates.
COMPRESSION FIXATION When using compression plates, the fragments are actually compressed together at rest, thereby increasing the frictional forces between the fragments and decreasing the likelihood of mobility. Another important aspect of compression fixation is that it seems to speed up the rate at which the bone itself becomes capable of supporting stress. In an elegant study by Luhr, 6 he fixed experimental osteotomies in dog mandibles using rigid fixation with and without compression. At 12 weeks postoperatively, the bending strengths of the healing bones were the same, with both groups exhibiting approximately 50% of the strength of the unfractured mandible. However, at 2 weeks, the noncompressed but rigidly fixed bones had no strength as compared with about 16% for the compressed bones, and at 4 weeks after repair, the compressed bones had more than 30% of normal strength as compared with approximately 10% to 15% for the noncompressed bones. Compression fixation is thus a somewhat safer technique, particularly in the noncompliant patient who is less likely to avoid full loading of the fractured area. However, it does require the use of bicortical screws; thus, compression plates cannot be used along the tension side of the fracture. There are also several additional options available to the surgeon, and these become particularly important when a tension band arch bar cannot be applied (eg, poor or absent dentition). When dentition is absent or inadequate for the placement of a tension band arch bar, compression fixation of the basal border of the mandible would obviously lead to distraction of the alveolar border and instability. One way of overcoming this problem is to apply a tension band plate superiorly, such as a neutral 2.0-mm, mono-cortical mini-plate. Another option is to use an eccentric dynamic compression plate (EDCP). This is a plate with compression holes directed both horizontally and superiorly. When properly applied, the horizontal compression screws compress the basal border, whereas the superiorly directed compression screws rotate the bone a r o u n d the initially applied screws, thereby compressing the alveolar border of the fracture together (Fig 4). Although not actually a plating technique, lag screw 81
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!'i' : FIGURE 4. Eccentric dynamic compression plate with horizontally and superiorly directed screw holes compresses alveolar fracture borders. fixation is another form of compression fixation. It is used specifically w h e n fragments of bone overlap. The lag screw is placed so that its thread does not catch in the proximal fragment, although it does hold securely in the second fragment. As the screw is tightened, the proximal fragment is pressed between the head of the screw and distal fragment, thereby compressing the two bone fragments firmly together. This technique works nicely in the symphyseal and parasymphyseal regions of the mandible, where the curvature of the mandible results in cortical overlap (Fig 5). 7 Though more difficult technically, it can also be used to repair angle fractures, s The screw is applied from an inferolateral position in the anterior buccal cortex in a superomedial direction into the posterior fragment (Fig 6), with extreme caution not to injure the inferior alveolar nerve. Finally, there is the mandibular reconstruction plate. This is a plate designed to be strong enough to replace a missing segment of mandible. It has to be bendable in three dimensions, and it must contain many holes, so that numerous fixation points for screw placement are available. This plate can be used to stabilize the mandible w h e n an area is defective or structurally defective (such as an area of comminution), but at least three and preferably four screws must be applied in the solid bone on either side. Because this fixation is strong enough to replace a defective area, it is obviously strong enough to fix a fracture. It is thus a good "fall-back" technique for the fixation of any difficult fracture, particularly when the bone is thin and weak, such as in the angle region or in the atrophic, edentulous mandible.
FIGURE 5. Lag screw fixation for use in cases with overlapping bone fragments. 82
FIGURE 6. Lag screw fixation used to repair an angle fracture. It is important to note that most of the research and clinical experience with mandibular compression plating has been performed using the 2.7-ram systems (eg, stainless steel, titanium, and Vitallium®). A 2.4-ram mandibular compression system has recently been introduced to provide smaller, lower profile plates. Although surgeons have been quick to accept this new system, it is not yet clear that the degree of stabilization is comparable to the 2.7-ram systems. ~ In general, caution should be exercised w h e n selecting untried and unproven new devices.
INDICATIONS Compression fixation is an option for all mandible fractures, except w h e n there is a gap at the fracture site due to bone loss. There are generally multiple options available for the repair of a given fracture, and the surgeon's preference and experience, as well as the needs of the individual patient, will all play a role in determining which repair option is selected. In the presence of good dentition, if a solidly placed arch bar results in a clinically stable fixation, a period of 3 to 6 weeks of MMF may be the preferred approach, if the patient prefers a noninvasive technique. However, if a fracture in a dentate segment occurs in association with a subcondylar fracture, an open reduction and internal fixation of the distal fracture may allow for earlier mobilization of the mandible and hopefully better joint function. When a relatively stable fracture is encountered in the compliant patient, virtually any fixation that will work for a given site can be selected. In the symphysis, parasymphysis, and angle regions, this will include mini-plates, compression plates, three-dimensional plates, lag screws, and reconstruction plates (as well as the EDCP plate, though its use is not generally recommended). In the body region, lag screw fixation is not an option, unless the fracture is oblique and the fragments overlap. In COMPRESSION PLATING OF MANDIBLE FRACTURES
fact, w h e n the fracture is oblique, creating overlapping fragments, the lag screw technique is indicated regardless of the site of fracture. Note that w h e n extra stabilization is required, lag screws can be applied through a plate. When the patient is noncompliant and is likely to chew on the side of the fracture, compression fixation is recommended as opposed to mini-plate fixation. The additional friction created by compression fixation should decrease the likelihood of movement of the bone fragments relative to each other. For this reason, it may also be wise to select a compression plate (or a reconstruction plate) w h e n the patient's initial presentation is delayed and/or complicated by local soft-tissue infection. Compression fixation seems to impart some degree of protection against the development of osteomyelitis by rigidly fixin~ the fragments together and promoting rapid healing. ~ Note that this refers to soft-tissue infection. If the bone is involved (ie, osteomyelitis), compression fixation is contraindicated, and a reconstruction plate should be used. Rigid fixation, w h e t h e r mini-plate or compression plate, is recommended for patients who wish to avoid MMF, whether for professional purposes or for reasons of personal preference. It is also recommended in elderly and malnourished patients, because a period of MMF could lead to debilitation. In the neurologically impaired or brain-injured patient, compression plating will not only eliminate the need for MMF, but the high degree of stability imparted may resist the forces created by bruxism, which is common in this patient population. Rigid fixation is also preferred in the seizure-prone patient, so that the risks associated with MMF in this patient group may be avoided.
rior mandibular body will generally need to be placed using a trans-buccal approach through a trocar placed through a stab incision made in a direction parallel to the branches of the facial nerve. Great care should be used to avoid injury to the mental nerve and the mandibular ramus of the facial nerve.
COMPRESSION PLATE A compression plate is designed so that proper placement of the screws will result in a relative motion between the plate and the screws that will force the bone fragments together, compressing them across the fracture line. This is accomplished by designing the plate with elliptical or oblong holes. The screw is designed with a head large enough to overlap the metal of the plate, w h e n it is properly positioned in the hole (Fig 7A). When the screw is placed into the bone, it forms a "screw-bone unit." Thus, any relative motion between the plate and the screw will bring the bone with the screw. As the screw is tightened, the screw will move relative to the plate until the screw is seated in the plate hole. The amount of movement will be equal to the amount that the screw head overlaps the plate (Fig 7B). If a screw has II II
CONTRAINDICATIONS There are two main contraindications to compression plating of mandible fractures. One is bone loss, because compression fixation in this situation will alter the position of the bone fragments, thereby creating a malunion. In the presence of dentition, this creates a malocclusion, but even in the absence of dentition, this will put undue stress on the temporomandibular joints, and it will make dental rehabilitation more difficult as well. The other contraindication is the presence of infection in the bone. Osteomyelitis requires debridement of bone, thus creating a bone loss situation. This requires pretreatment with intravenous antibiotics, followed by aggressive debridement of involved bone. The solid bone segments are repositioned using a long mandibular reconstruction plate, placing at least four screws in each fragment at a distance from the infected area, and leaving several empty holes in the area of the infection and defect. n Of course, w h e n the fracture is oblique, compression plating will result in the fractures gliding across each other into a malposition. Lag screw fixation is therefore indicated in this situation.
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TECHNIQUES Compression fixation techniques can be performed either via extra-oral or intra-oral incisions. Note that w h e n intra-oral incisions are used, screws posterior to the anteKELLMAN
FIGURE 7. The compression plate and screw heads are designed so that when the screws are tightened, the two bone fragments are compressed together. 83
been at least partially inserted into the other fracture fragment, its position in the plate will prevent the opposing fragment from moving away as this screw is tightened. This will cause the fragments of bone to be compressed together. Tightening of the screw in the opposite fragment will add additional compression of the bones together (Fig 7C). Additional screws are placed neutrally to increase the stability of the fixation.
ECCENTRIC DYNAMIC C O M P R E S S I O N PLATE This plate is generally used to compress a fracture w h e n no tension band has been applied. It is critically important to precompress the fracture using a technique that holds the alveolar portion of the fragments firmly together. Otherwise, this area will pull apart w h e n axial compression is applied across the basal border of the mandible. Precompression can be applied using a modified towel clip or a mandibular reduction forceps with side rollers (Fig 8). The EDCP is then applied. First, the horizontal compression screws are placed as described previously. Next, the compression screws are placed in the diagonal holes (pointing toward the superior portion of the fracture). These screws are positioned in the inferior portion of the screw holes, so that the screw head-plate interaction will push the screw-bone unit in a superior direction, thereby compressing the alveolar portion of the fracture (Fig 9). The remaining screws are placed neutrally. Note that w h e n using an EDCP, it is r e c o m m e n d e d that at least a six-hole plate be used for adequate stability. It is important to recognize that the successful use of the EDCP requires intact bone along the alveolar border. Thus, its use is not advised w h e n a tooth at the alveolar border has been acutely lost or needs to be extracted.
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FIGURE 9. Tightening of screws forces bone in a superior direction, compressing alveolar borders of fracture.
LAG S C R E W T E C H N I Q U E The key to lag screw fixation is having the thread glide through the first fragment and catch in the second bone fragment. Tightening will result in compression of the fragments together. A hole is drilled in the first fragment that is the size of the thread diameter of the screw to be used. The appropriate drill is then placed through this hole, and the second fragment is drilled using the drill that is the size of the screw shaft. The surface of the first hole is countersunk for better seating of the screw head. The depth of the hole is measured. The second hole is tapped if a non-self-tapping system is being used. The appropriate length screw is then placed and tightened (Fig 10). For overlapping fragments (oblique fractures), at least two and preferably three screws should be placed. For the symphysis, two lag screws are used. Only the mandibular angle is repaired using a single lag screw.
COMPLICATIONS The most c o m m o n complication of rigid fixation of the mandible is early local soft-tissue infection. This can generally be managed with drainage and appropriate (culture-specific) antibiotic therapy, without removal of
FIGURE 8. Precompression of bone fragments in preparation for application of eccentric dynamic compression plate.
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FIGURE 10. Lag screw fixation of overlapping bone fragments. COMPRESSION PLATING OF MANDIBLE FRACTURES
the hardware, so long as the fixation is stable and the screws are tight. Sometimes surgical exploration a n d evaluation of the stability of the hardware are necessary. Late infection is more ominous a n d generally implies loosening of one or more screws. W h e n this occurs, the w o u n d should be explored and the hardware should be removed. If the fracture is healed, antibiotic treatment should resolve the problem. If healing is incomplete, or if bone infection is found, t h e n replacement of the fixation plate with either a reconstruction plate or an external fixator s h o u l d be considered. In an excellent metaanalysis of rigid fixation of mandible fractures, Iizuka 12 noted that infection rates varied b e t w e e n 0% a n d 27%. Higher infection rates have been seen at the mandibular angle. 5 Other authors have suggested that rigid fixation techniques in general result in higher complication rates than either conservative m a n a g e m e n t with MMF alone or w h e n combined with wire osteosynthesis. 13 However, there is evidence to suggest that at least some of these complications were technical. The report by E1 Degwi a n d Mathog 13 involved multiple surgeons in several specialties at different hospitals, m a n y of w h o m had limited experience with the techniques. It is thus likely that at least some complications could be attributed to variance from strict biomechanical principles in the application of the techniques. In the review by Iizuka, 12 it was f o u n d that their o w n overall infection rate using compression osteosynthesis over a 7-year period was 6.1% (13 of 214). W h e n looked at over time, it was n o t e d that the infection rate was 10.9% b e t w e e n 1983 a n d 1986, 4.8% in 1987 a n d 1988, and only 3.6% in 1989. Levy et al 5 were able to reduce their complication rate w h e n plating angle fractures from 26.3% to 3.1% by routinely a d d i n g a second plate. Thus, there is good evidence to suggest that strict adherence to biomechanical principles a n d increasing surgical experience can result in high rates of success with acceptably low complication rates. Other complications include malocclusion, nerve injury, a n d tooth root injury. Malocclusion is obviously the result of rigid fixation of the bones in an improper position. Difficulties with plate b e n d i n g make this complication more likely with larger plates. However, attention to detail a n d an unwillingness to accept a less-thansatisfactory result at the time of plate application should minimize this complication. For complex, c o m m i n u t e d fractures in which total failure is a high risk, a malocclusion should be preferable to a n o n u n i o n . Mental nerve injury is more c o m m o n w h e n using the intra-oral approach, a n d facial nerve injury is obviously more likely via the external approach. Care should be exercised to minimize these complications. Injury to tooth roots a n d to the inferior alveolar nerve in its b o n y canal should be avoided by placing compression plates along the basal border of the mandible. W h e n placing compression plates via the intra-oral route, it is possible
KELLMAN
to position t h e m more superiorly t h a n is obvious, a n d caution should be exercised in this situation. Pain, palpability, a n d cold i n t o l e r a n c e all occur. These can be easily resolved by removing the h a r d w a r e after healing is complete.
SUMMARY In s u m m a r y , compression fixation of mandible fractures is an important technique that should be part of the arm a m e n t a r i u m of the facial trauma surgeon. A complete u n d e r s t a n d i n g of the biomechanical principles a n d techniques will result in high rates of surgical success with a m i n i m u m of complications.
REFERENCES 1. Koolstra JH, van Eijden TMGJ, Weijs WA, Naeije M: A threedimensional mathematical model of the human masticatory system predicting maximum possible bite forces. J Biomechanics 21:563576, 1988 2. Spiessl B: New Concepts in MaxillofacialBone Surgery. New York, NY, Springer-Verlag, 1976 3. Champy M, Pape HD, Gerlach KL, et al: The Strasbourg mini plate osteosynthesis, in Kruger E, Schiili W, Worthington P (eds): Oral and MaxdlofacialTraumatology. Chicago, IL, Quintessence Publishing, vol 2, 1986 4. Kroon F: Effectsof three-dimensional loading on stabihty of internal fixation of mandible fractures, in Spiessl B (ed): Internal Fixation of the Mandible. Berlin, Spnnger-Vedag, 1989 5. Levy FE, Smith RW, Odland RM, Marentette LJ: Monocortical miniplate fixation of mandibular angle fractures. Arch Otolaryngol Head Neck Surg 117:149-154, 1991 6. Luhr HG: Basic research, surgical technical and results of fracture treatment with the LUHR-Mandibular-Compression-Screw-System (MCS-System). Oral and MaxillofacialSurgery: Proceedings from the 8th International Conference on Oral and MaxillofacialSurgery. Chicago, IL, Quintessence Publishing Co, 1985, pp 124-137 7. Ellis E III, Ghalh GE: Lag screw fixation of anterior mandibular fractures. J Oral MaxfllofacSurg 49:13-21, 1991 8. NlederdeUmann H, Akuamoa-Boateng E, Uhlig G: Lag-screw osteosynthesis: A new procedure for treating fractures of the mandibular angle. J Oral Surg 39:938, 1981 9. Ellis E III, Sinn DP: Treatment of mandibular angle fractures using two 2.4-mm dynamic compression plates. J Oral Maxillofac Surg 51:969-973, 1993 10. Beckers HL: Treatment of inlbally infected mandibular fractures with bone plates. J Oral Surg 37:310, 1979 11. KellmanRM: One stage vs. two stage management of mandibular osteomyelitis using the AO mandibular reconstruction plate. Free Paper Abstracts, Vith International Symposmm. Presented at the Sixth International Symposium of the American Academy of Facial Plastic & ReconstructiveSurgery. San Francisco, CA, June 19, 1993 12. hzuka T: Rigid internal fixation of mandibular fractures. Academic Dissertation. Helsinki, Finland, 1992 13. E1-Degwi A, Mathog RH: Mandible fractures--Medical and economic considerations. Otolaryngol Head Neck Surg 108:213-219, 1993
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