J Oral Maxillofac 49:13-21.
Surg
1991
Lag Screw Fixation of Anterior Mandibular Fractures EDWARD ELLIS III, DDS, MS,* AND G.E. GHALI, DDSt A technique of applying lag screws for treating fractures of the anterior mandible is presented. A review of 41 patients who had lag screws placed to treat such fractures showed that it is a successful method of providing rigid internal fixation. The advantages of this technique over bone-plate fixation are discussed.
more commonly used in maxillofacial surgery than the true lag screws. The lag screw technique was first introduced to maxillofacial surgery by Brons and Boering in 1970, who cautioned that at least two screws are necessary to prevent rotational movement of the fragments in oblique fractures of the mandible.’ Others have similarly illustrated the versatility of lag screws for mandibular fractures.‘33 The purpose of this report is to describe the technique of lag screw placement in fractures of the anterior mandible and to review our early experience in their use.
Fractures of the anterior mandible are common facial injuries. Although many of these can be treated satisfactorily with closed reduction, open reduction and internal fixation are commonly used to align the fragments and keep them in contact, which promotes osseous union. With the recent enthusiasm for rigid forms of internal fixation, experimentation with various forms of plate and screw fixation have been attempted. Fractures in the anterior mandible are readily treated by application of either bone plates and/or bone screws. A useful method of providing rigid fixation in the anterior mandible is by using lag screws. The term lag screw is probably the most misunderstood of all terms involved with rigid internal fixation, probably because it is used both to describe a type of screw, as well as a technique of screw placement. A true lag screw has threads only on its terminal end (Fig 1). When used, the threads engage the far cortex, while the head seats against the near cortex, providing compression upon tightening. A lag screw technique (resulting in compression) is achieved with a cortical screw (Fig l), which has threads along its entire length, by overenlarging the hole in the near cortex. This latter procedure has been
Anatomy and Biomechanics of the Anterior Mandible The anterior mandible, from mental foramen to mental foramen, is uniquely suited to the application of lag screw fixation for three reasons. The most important is the curvature of the anterior mandible. This allows placement of lag screws across the symphysis, from one side to the other, for sagittal fractures, and from anterior to posterior for oblique fractures and those of the anterior body region. The second reason the anterior mandible is well suited to lag screw fixation is the thickness of the bony cortices, which provide extremely secure fixation when the screws are properly inserted. The final reason is that there are no anatomic hazards below the apices of the teeth until the mental foramina are encountered. This makes lag screw placement extremely simple. The direction of forces that are distributed through the anterior mandible vary with the activity of the mandible. This means that the classic zones of tension on the superior and compression on the inferior surfaces of the mandible are not absolute.
Received from the Department of Oral and Maxillofacial Surgery, University of Texas Southwestern Medical Center, Dallas. * Associate Professor. t Resident. Supported in part by a grant from the Chalmers J. Lyons Academy-James R. Hayward Research Fund. Address correspondence and reprint requests to Dr Ellis: Division of Oral and Maxillofacial Surgery, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75235. 0 1991 American geons
Association
of Oral and Maxillofacial
Sur-
0278-2391/91/4901-0004$3.00/O
13
14
LAG SCREW FIXATION OF ANTERIOR MANDIBLE
FIGURE 1. Top, A lag screw. Note the absence of threads except at the terminus of the screw. Below, Cortical screw. This screw can be used to impart compression to a fracture by overdrilling the outer (near) cortex so the threads only engage the far cortex.
Instead, the anterior mandible undergoes shearing and torsional (twisting) forces during functional activities.4.5 Therefore, application of fixation devices must take these factors into consideration. This is why Champy, who advocates only one small bone plate in most regions of the mandible, always places two bone plates in the symphysis.4 When using bone screws to secure fixation, one bone screw may not provide adequate stability, since the shear forces may allow rotation of the mandibular fragments around the screw. The only resistance to rotation about one screw is the compaction (friction) of the fragments into one another by virtue of the compression imparted from the lag screw. Application of an arch bar to the teeth may prohibit the rotational force; however, application of a second lag screw is the best insurance for providing rigidity.’ Fortunately, there is usually ample space available for the routine placement of two screws in fractures of the anterior mandible. Technique The application of lag screw fixation for fractures of the anterior mandible requires relatively few instruments; however, correct instruments are essential to the technique. (AO/ASIF instruments are available from Synthes Maxillofacial Instrument Company, Paoli, PA, or from other manufacturers.) The necessary instruments are included in the standard mandibular fracture kits; however, longer screws than those that normally accompany the set are necessary. The lag screw technique for the anterior mandible can require 2.7-mm screws up to 40 mm in length. Therefore, every screw length up to
40 mm should be available before attempting to treat fractures with lag screws. Following application of maxillary and mandibular arch bars, a vestibular incision is made from just posterior to one mental foramen to the same area on the other side. Anterior to the mental foramina, the incision is made out in the lip, splitting the mentalis muscle to facilitate a two-layer closure. Subperiosteal dissection of the anterior, lateral, and inferior borders of the mandible from one mental foramen to the other is essential for complete exposure of the fracture and for proper instrumentation. Dissection under, or between the bundles of the mental nerves when necessary for adequate retraction and exposure, helps protect the nerve from injury due to stretching. The entire fracture is examined following slight distraction to note the obliquity and the relationship of the cortices. If there are extensive areas of comminution, the lag screw technique should be abandoned, because it has little chance of success in cases where the continuity of the cortices is disturbed. Fortunately, this is unusual in fractures of the anterior mandible. Once the fracture has been examined and cleaned of extraneous debris, the mandible is placed into maxillomandibular fixation (MMF) while simultaneously reducing the fracture. A towel clip with the tips bent slightly outward can be used to assist in firmly reducing the fracture before application of lag screws. A small bur is used to drill holes approximately 10 mm away from each side of the fracture to provide a purchase for the modified towel clip. The towel clip is inserted into these holes and tightened, reducing the fracture. The location of the towel clip must not be an area where the lag screws are to be inserted. Frequently, it must be inserted in the region of the root apices, taking care to avoid them. The lingual cortices should also be checked to assure that they are in firm apposition, since other fractures of the mandible, especially those of the condyle and ramus, may cause an increase in the radius of the dental arch and inferior border. Therefore, the surgeon must not be lulled into a false sense of security that the fracture is properly reduced by solid apposition of the buccal cortices. It is helpful to dissect below the inferior border of the mandible in the area of the fracture to directly expose the lingual cortex and assure its proper reduction. Selecting the point of entry into bone and alignment of the drill is crucial since it will determine the success of the procedure and, when improperly executed, may cause undesirable complications. Although the lag screw technique in other bones usually involves drilling the screw hole at an angle that
ELLIS AND GHALI
15
FIGURE 2. Illustration demonstrating the A0 orthopedic technique for determining angulation of screw placement. The angle between the outer cortex and the line of fracture is bisected to determine the proper drill path. This technique of screw placement makes little sense in the anterior mandible and may cause overriding of the fragments when the screw is tightened. Instead, the screw should be placed perpendicular to the fracture.
the bisection of the angle between the line of fracture and the outer cortex (Fig 2),6 the curvature of the anterior mandible and frequent lack of fracture obliquity make this impossible and/or undesiris
able in most fractures of the anterior mandible. Therefore, the path of screw insertion should disregard this principle of lag screw insertion for long bones, and instead traverse the fracture in as per-
FIGURE 3. Attempting to use the A0 orthopedic principle demonstrated in Figure 2 for fractures of the anterior mandible, often results in improper/inadequate placement of screws. A, The screw is placed obliquely to sagittal fractures of the symphysis. The tightening of this screw tends to cause displacement of the fragments. This is similar to using a compression plate on a very tangential (oblique) fracture, which also causes overriding of the segments. Attempting to use the A0 orthopedic principle frequently results in placement of the screw into or very near the fracture on the lingual cortex (B), or misses the lingual cortex altogether (C and D). C, The screw glances off the lingual cortex although it may feel as if the screw is secure. However, upon tightening, it shears and loosens. D, Screw misses the lingual cortex and ends up in medullary bone. A screw inserted into medullary bone has insufficient strength to resist displacement of the fracture during function. The management of this problem is to continue drilling until the buccal cortex is reached, and a long screw is used (see Fig 4B).
16
LAG SCREW FIXATION OF ANTERIOR MANDIBLE
FIGURE 4. Ihustration showing proper placement of screws for fractures of the anterior mandible. A, The screw is placed perpendicular, or B, nearly perpendicular, to the line of fracture when it is sagittal. C and D, When the fracture is oblique, screws are simply inserted across the fracture in as perpendicular a manner as possible.
pendicular a manner as possible. When the screw is perpendicular to the line of fracture, the compressive load imparted by the lag screw becomes extremely effective in securing rigid stabilization of the fragments without causing displacement upon tightening. For the same reason that compression plates are not applied to oblique fractures, lag screws applied obliquely to the fracture cause displacement of the fracture. Figure 3 shows examples of improper placement of lag screws, which results in inaccurate reduction, complications, and/or instability. One must remember that medullary bone offers insufficient resistance to bone screw fixation and, therefore, a bony cortex must be engaged with the terminal threads of the screw. Figure 4 shows proper screw placement for various types of fractures in the anterior mandible. Selection of the proper point of entry for the drill in the buccal cortex is based on placing it suffL ciently away from the fracture so that an ample amount of bone is present between the head of the screw and the fracture after drilling and countersinking. This is especially important when drilling along the curved surface of the anterior mandible. The remaining bony bridge must resist all forces of mastication, since the screw head rests directly on it. Another factor to consider in determining the location of the bone screw is providing sufficient space for a second screw. Thus, the first screw should be placed just above the inferior border. Once the proper angulation and point of entry has been established, the 2.7-mm drill is initially placed almost perpendicular to the buccal cortex at the selected point of entry to prevent skidding of the drill bit, and a hole is begun in the buccal cortex. The
drill is then redirected to the previously selected angulation and the drilling completed through the buccal cortex and medullary bone of the first (near) fragment only (Fig 5A). The drill and drill guide are withdrawn from the wound and a countersinking tool is used at slow speed to provide a smooth platform for screw-head seating (Fig 5B). It is imperative that two facts be considered while countersinking the hole. First, the same angulation should be used as established by the initial 2.7-mm drill hole. To facilitate this, a countersinking tool with an adjustable guide-pin that extends beyond the countersinking flutes into the drill hole can be used. Second, countersinking must be adequate to allow complete seating of the screw head. This means that a considerable amount of buccal cortex must be removed when a screw is inserted into a rounded surface or in an oblique manner on a straight surface (Fig 6). The most appropriate method to determine the adequacy of countersinking is to place the 2.0mm (“centering”) drill guide into the drill hole. This drill guide, to be used in the next step, has a tip that fits tightly into the 2.7-mm hole and a shank with an outer diameter slightly larger than the head of the screw. If insertion into the drill hole cannot be smoothly accomplished without binding on the bone medial to the drill hole, countersinking is inadequate and must be completed (Fig 7). However, one must avoid countersinking deeper and deeper into the bone to the point where the screw head rests on medullary instead of cortical bone. Drilling through the second (far) fragment with a 2.0-mm drill is the next step. To ensure that the 2.0-mm drill is perfectly centered in the 2.7-mm hole previously drilled through the near cortex, a
ELLIS AND GHALI
FIGURE 5. Illustration showing technique of placing lag screws for sagittal fracture of the anterior mandible. A, Drilling near cortex with 2.7mm drill. Note that the drilling extends only to the fracture. A drill guide should be used to stabilize the drill and protect soft tissues. B, The near cortex is countersunk using countersinking tool with guide pin, which extends into 2.7-mm hole. C, Drilling 2.0-mm hole completely through mandible using centering drill guide. The tip of the drill guide has an outer diameter of 2.7 mm, allowing it to seat firmly into the previously drilled hole in the near cortex. The inner diameter of the drill guide is 2.0 mm, centering the 2.0-mm drill in the 2.7-mm hole. D, Result after drilling. Note the near cortex (right) has been drilled to 2.7 mm diameter, and the far cortex to 2.0 mm diameter. E, Depth gauge used to determine length of screw. F, Tapping the far cortex. Note that the tap (and screw in next step) slides through the near cortex, since it has the same outer diameter (2.7 mm). G, Result following tapping. Note screw threads only in far cortex. H, Screw inserted. Since the threads only engage the far cortex, compression is applied during tightening.
drill guide is used (Fig 50. special “centering” This drill guide has an outer diameter of 2.7 mm on its working end, allowing a snug fit into the hole previously drilled through the near cortex. It has an inner diameter of 2.0 mm, acting as a drill guide for the 2.0-mm drill, perfectly centering it within the 2.7-mm hole in the near cortex. Drilling through the second (far) segment with the 2.0-mm drill is then performed (Fig 5C). During the drilling, it is important to use slow-speed, copious irrigation, and repeatedly withdraw the drill flutes from the drill guide to clear bony debris. If not done, the drill becomes quite warm due to both the inability of irrigant to reach the flutes and clogging of flutes with debris. A depth gauge is inserted through the drill hole and the screw length is determined (Fig 5E). The hole in the far segment is then tapped using a long
tap (Fig 5F). To prevent tissue entanglement and to help avoid wobble, the same drill guide as used in drilling the 2.7-mm hole should be used as a tapguide. Care should be taken to ensure that the same direction used during drilling is used for tapping. The hole should be thoroughly irrigated before placing the screw. After selection of the appropriate length screw, it is inserted on a screw driver into the screw hole. The outer hole (or clearance hole) is free of threads and the screw should slip through until it contacts the threads in the far segment (Fig 5D and G). Thus, when tightened, the screw will compress the two segments of bone together. While the final tightening proceeds, the surgeon must carefully observe the bony cortices around the head of the screw for signs of crazing. Frequently, the screw is overtightened to the point of creating microfrac-
18
LAG SCREW FIXATION OF ANTERIOR MANDIBLE
FIGURE 6. Illustration demonstrating the importance of properly countersinking the screw. If inadequate or no countersinking is performed (A), tightening of an obliquely placed screw will cause premature contact and binding of the screw on the bone, resulting in displacement of the screw and/or segments or causing fractures of the near cortex. B, Proper countersinking.
tures around the screw head. This should be avoided if possible. It is essential that the screw exit the far cortex for maximal strength (Fig 5H). A second screw is then inserted in the same manner as just described (Fig 8). With sagittal fractures of the mandible between the incisors, it frequently is easier to place the second screw from the opposite direction. Because the buccal cortex on the other side of the fracture has not yet been disrupted, a greater area of bone for screw placement is provided (Fig 9). In fractures of the anterior mandibular body (Fig lo), placing a second screw may not be possible without damaging the mental nerve. There are two choices in this instance. The first is to supplement the fixation with a bone plate placed superior to the lag screw (Fig 1OD). The second is the maintenance of the arch bar and compression (bridle) wire, and placement of the patient on a soft diet (Fig 1OC). However, the rigidity produced by one lag screw and an arch bar is not yet known and is therefore not recommended routinely. If used, it requires that the patient be extremely cooperative. The intraoral incision is closed in two layers with resorbable sutures. The MMF is then removed and the patient is maintained on a soft diet.
Material and Methods All patients treated by open reduction and internal fixation of fractures between the mental foramina by the lag screw technique previously described between November 1, 1988, and November 31, 1989, were included in this retrospective study. The patients’ charts were reviewed for information about additional fractures, and the presence of a tooth in the line of fracture. Notes on the operative findings and postsurgical course were evaluated for extraction of the tooth in line of fracture, duration of MMF if used, postsurgical occlusal relationship, infection, and need for further intervention because of complications. When possible, clinical examinations were performed in December 1989 and January 1990. Otherwise, only the patients’ charts, including postsurgical notes, were used for tabulation of the above data. Results Forty-one patients were identified who were treated using bone screws for anterior mandibular fractures. Seven were female, the remainder male.
FIGURE 7. Illustration showing effect of inadequate countersinking for an obliquely placed screw. The 2.0-mm drill guide does not seat securely, causing the 2.0-mm drill to become misaligned with respect to the 2.7-mm hole. A, Inadequate countersinking. B, Proper countersinking.
ELLIS AND GHALI
They ranged in age from 14 to 59 years. Two lag screws were placed in the majority of patients (29); however, in two patients, three lag screws were used. A single lag screw was placed in seven patients; a single lag screw combined with a small compression plate (using 2.0-mm screws) was used in three patients. The anterior mandibular fracture was the only mandibular fracture in 13 patients. Twenty-nine patients had associated mandibular fractures, of which 17 were fractures of the angle, nine were subcondylar (six unilateral, three bilateral), one was in the body, one was in the ramus. and one was a dentoalveolar fracture. All patients had a tooth in the line of fracture. Five patients had the tooth in the line of fracture removed at surgery. Because of associated fractures, MMF was used in nine patients: two patients for 1 week, four for 4 weeks, and three for 6 weeks. No MMF was used as a supplement to lag screw fixation of a symphyseal fracture. Follow-up ranged from 4 to 61 weeks, with a mean of 12 weeks. All fractures except the one noted below were found to be stable at follow-up appointments. No postsurgical malocclusion resulted. Two patients developed postsurgical infections (4.9%), both thought to be due to a nonvital tooth in the line of fracture that was subsequently removed. Both patients had two lag screws placed to secure the two halves of the mandible. In one patient, a soft-tissue infection developed 1 week following surgery and the tooth in the line of fracture, which was noted to be loose, was removed. This patient had a large segment of
FIGURE 8. Example of lag screws in symphyseal fracture. A, Preoperative panoramic radiograph showing sagittal fracture of midsymphysis. B, Postoperative panoramic radiograph showing placement of two lag screws perpendicular to fracture. from one buccal cortex to the other.
19
FIGURE 9. Lag screws placed from opposite sides of a sagittal fracture. A, Intraoperative view. B, Postoperative view following healing of fracture. The crisscross technique of screw placement may be easier, because more bone is available for drilling and countersinking on the side opposite the initial screw.
bone that included the inferior border maintained in position using a third lag screw during surgery. The patient had also been placed in MMF for an associated subcondylar fracture. The infection persisted at a subclinical level, and at 6 weeks postsurgery, the labial soft tissue had a dehiscence, exposing some granulation tissue and nonvital bone. A sequestrectomy was performed at this time and the previously repositioned bony segment, which was found to be loose and necrotic, was removed. However, the fracture was united and the patient healed uneventfully. The second patient developed a soft tissue swelling 3 weeks postsurgery. This patient had no extraction at the time of surgery. One tooth associated with the fracture was removed. The following week, more swelling was noted and the other tooth adjacent to the fracture was noted to be loose and was removed. The fracture was noted to have slight mobility at that time. The patient was placed into MMF, but was uncooperative and repeatedly removed the fixation. At 8 weeks’ postsurgery, the patient was taken to the operating room where the lag screws (which were slightly loose) were removed and external pin fixation was placed. He had a satisfactory course thereafter. One addi-
20
LAG SCREW FIXATION OF ANTERIOR MANDIBLE
FIGURE 10. Illustration showing application of lag screws for fractures of the anterior mandibular body in the vicinity of the mental foramen. Placing screws from buccal to buccal (A), or buccal to lingual (B) both have utility. C, Use of a single lag screw combined with arch bar and bridle wire for fractures around the mental foramen. D, Supplementation of fixation by application of a 2.0-mm bone plate, using monocortical screws to avoid roots, if necessary.
D tional patient had further surgical intervention at 9 months. This patient had been treated with two lag screws, no MMF, and underwent an uneventful postoperative course. However, a 9-month radiograph showed a small radiolucency around the head of one of the bone screws. No symptoms were present. This screw was found to be loose and was removed. Dense fibrous connective tissue surrounded the head of the screw where the labial cortical bone had once been. The other screw was not loose, but was also removed. Discussion Besides the many advantages that rigid fixation of mandibular fractures offers, the use of lag screws as a type of rigid fixation has several unique advantages over bone-plate fixation. The major advantage is that lag screws can be applied more rapidly, since the time-consuming task of adapting a bone plate is obviated. This also allows a more anatomically accurate reduction, because it takes considerable skill to perfectly adapt a bone plate to the complex contours of the mandible. In our experience, displacement of bone fragments is much more common during placement of a bone plate, since the adequacy of plate contouring is not thoroughly known until the screws are inserted and the plate is drawn to the mandible. Displacement of bone segments almost never occurs while applying lag screw fixation when one adheres to the details previously described. Lag screws also permit the rapid application of fixation without a decrease in rigidity of the frac-
ture reduction. Although no research has yet been done that compares the rigidity of fixation with a bone plate versus lag screw fixation of anterior mandibular fractures, one frequently gets the impression that lag screws provide much more rigidity than do bone plates. This is especially evident when the screws are applied perpendicular to the fracture. The fracture gap frequently completely disappears from sight due to the great amount of compression that can be imparted with the screws. Another advantage is the costs incurred: these are greatly diminished because the screws cost much less than a bone plate. The results of this retrospective study show that lag screw fixation of anterior mandibular fractures is an extremely simple and successful method of rigidly securing the fragments, permitting active use of the mandible during healing. Only two patients experienced problems that required intervention. All seven patients treated with only one lag screw (in addition to an arch bar and bridle wire) had no postoperative difficulties. These patients were all cautioned to maintain a soft diet, because the rigidity of the fixation with only one screw is unknown. However, their compliance with this regimen was not determined. However, even in the face of these results, we still do not recommend the use of only one lag screw, because adequate numbers to justify its routine implementation are not yet available. We are in disagreement with Niederdellmann et al, who state that “lag screw osteosynthesis is not meant to replace osteosynthesis with plates,” and who reserved the use of lag screws for very special circumstances.’ We now use lag screw fixation as
21
ALAN SCHWIMMER
our first choice for providing rigid internal fixation of anterior mandibular fractures. Rarely do we have the need or desire to use bone plates in the anterior mandible. However, there are special circumstances where the use of lag screws are contraindicated. The most important is when there is comminution and/or bone loss in the fracture gap. One must understand completely that the lag screw technique of fixation is one that relies on compression of bone fragments. If the intervening bone is unstable due to comminution, or is missing, compressing across this region will cause displacement of intervening bone fragments, overriding of segments, and/or shortening of the fracture gap, resulting in problems with the occlusion. In such situations, applying a bone plate without compression across this gap can achieve rigid fixation without disturbing the occlusion. Fortunately, the vast majority of fractures of the anterior mandible result in fragments
J Oral Maxillofac
that are large enough to permit the application of lag screw fixation.
of the mandibular body treated by stable internal fixation: A preliminary report. J
1. Brons R, Boering G: Fractures
Oral Surg 28:407, 1970 2. Niederdellmann H, Schilli W, Dtiker J, et al: Osteosynthesis of mandibular fractures using lag screws. lnt J Oral Surg 5:117, 1976 3. Leonard MS: The use of lag screws in mandibular fractures. Otolaryngol Clin North Am 20:479, 1987 4. Charnpy M, Lodde JP, Schmitt R, et al: Mandibular osteosynthesis by miniature screwed plates via a buccal approach. J Maxillofac Surg 6:14, 1978 5. Niederdellmann H: Fundamentals of healing of fractures of the facial skull. 1. Biomechanics, in Kruger E, Schilli W teds): Oral and Maxillofacial Traumatology (vol 1). Chicago, IL, Quintessence, 1982, pp 125-128 6. Mtiller ME, Allgower M, Willenegger H: Manual of Internal Fixation. New York, NY, Springer-Verlag, 1970, p 24
Surg
49.21-22.1991
Discussion Lag Screw Fixation of Anterior Mandibular Fractures Alan Schwimmer,
DDS
Beth Israel Medical Center, New York, NY
Doctors Ellis and Ghali have presented an extremely innovative technique for the use of lag screws as a means of obtaining functionally stable fixation in mandibular fractures. Lag screws, or traction screws, provide maximum interfragmentary compression with a minimum amount of implanted material. Because of their efficiency, they represent an ideal method of internal fixation, and in orthopedic surgery lag screws are often the first choice when rigid fixation is used. Lag screw fixation also has been useful in the treatment of midface trauma. Direct lag screw fixation is often not practical for the stabilization of midface fractures; however, the use of lag screws has been shown to be effective in the stabilization of split calvarial grafts. Recent studies by Phillips, Rahn, and McCarthy have demonstrated improved retention of bone graft volume when cranial grafts have been stabilized with lag screws. Anatomic considerations often prevent the use of lag screw fixation in the treatment of mandibular fractures. Niederdellman has described the use of a single unprotected lag screw for the fixation of transverse fractures at the angle of the mandible.’ With this technique, the lag screw is placed on the tension side of the fracture; therefore, compression is achieved along the unstable portion of the fracture. Spiessl has recommended the use of lag screws in oblique fractures of the body of the mandible.2 However, in these cases a minimum of three lag screws
are used. In oblique fractures that allow placement of only a single lag screw, protection of the lag screw by a stabilization plate is recommended. With the publication of this technique, Drs Ellis and Ghali have expanded the use of lag screws for the functional stabilization of mandibular fractures. This procedure appears to be easily executed; however, any surgeon attempting to use this technique must be familiar with the basic principles of rigid internal fixation. A lack of understanding of these basic principles will result in failure. It is therefore advisable that one first develop proficiency in the more routine methods of plate and screw stabilization. Once experience is gained in these techniques, greater success can be expected when using the procedure described by Drs Ellis and Ghali. The technique described in this article does adhere to several principles of lag screw fixation. To begin with, it is important to note that the authors recommend using dedicated instruments when using this technique. Attempts to improvise instrumentation will compromise the success of the procedure. Of special importance is the use of the centering guide to align the traction hole and the gliding hole coaxially. Failure to pay close attention to this step will result in misalignment of the fracture and a decrease in the compressive force of the lag screw. It should also be reemphasized that a 20-mm screw is the longest available in the standard Synthes set. When using lag screws for the stabilization of transverse fractures, whether at the angle or in the anterior mandible, screws longer than 20 mm are often required. Therefore, if the surgeon is planning lag screw fiiation of a transverse mandibular fracture, it is essential that screws of 30 to 40 mm in length be available.
Surg
1991
Lag Screw Fixation of Anterior Mandibular Fractures EDWARD ELLIS III, DDS, MS,* AND G.E. GHALI, DDSt A technique of applying lag screws for treating fractures of the anterior mandible is presented. A review of 41 patients who had lag screws placed to treat such fractures showed that it is a successful method of providing rigid internal fixation. The advantages of this technique over bone-plate fixation are discussed.
more commonly used in maxillofacial surgery than the true lag screws. The lag screw technique was first introduced to maxillofacial surgery by Brons and Boering in 1970, who cautioned that at least two screws are necessary to prevent rotational movement of the fragments in oblique fractures of the mandible.’ Others have similarly illustrated the versatility of lag screws for mandibular fractures.‘33 The purpose of this report is to describe the technique of lag screw placement in fractures of the anterior mandible and to review our early experience in their use.
Fractures of the anterior mandible are common facial injuries. Although many of these can be treated satisfactorily with closed reduction, open reduction and internal fixation are commonly used to align the fragments and keep them in contact, which promotes osseous union. With the recent enthusiasm for rigid forms of internal fixation, experimentation with various forms of plate and screw fixation have been attempted. Fractures in the anterior mandible are readily treated by application of either bone plates and/or bone screws. A useful method of providing rigid fixation in the anterior mandible is by using lag screws. The term lag screw is probably the most misunderstood of all terms involved with rigid internal fixation, probably because it is used both to describe a type of screw, as well as a technique of screw placement. A true lag screw has threads only on its terminal end (Fig 1). When used, the threads engage the far cortex, while the head seats against the near cortex, providing compression upon tightening. A lag screw technique (resulting in compression) is achieved with a cortical screw (Fig l), which has threads along its entire length, by overenlarging the hole in the near cortex. This latter procedure has been
Anatomy and Biomechanics of the Anterior Mandible The anterior mandible, from mental foramen to mental foramen, is uniquely suited to the application of lag screw fixation for three reasons. The most important is the curvature of the anterior mandible. This allows placement of lag screws across the symphysis, from one side to the other, for sagittal fractures, and from anterior to posterior for oblique fractures and those of the anterior body region. The second reason the anterior mandible is well suited to lag screw fixation is the thickness of the bony cortices, which provide extremely secure fixation when the screws are properly inserted. The final reason is that there are no anatomic hazards below the apices of the teeth until the mental foramina are encountered. This makes lag screw placement extremely simple. The direction of forces that are distributed through the anterior mandible vary with the activity of the mandible. This means that the classic zones of tension on the superior and compression on the inferior surfaces of the mandible are not absolute.
Received from the Department of Oral and Maxillofacial Surgery, University of Texas Southwestern Medical Center, Dallas. * Associate Professor. t Resident. Supported in part by a grant from the Chalmers J. Lyons Academy-James R. Hayward Research Fund. Address correspondence and reprint requests to Dr Ellis: Division of Oral and Maxillofacial Surgery, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75235. 0 1991 American geons
Association
of Oral and Maxillofacial
Sur-
0278-2391/91/4901-0004$3.00/O
13
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LAG SCREW FIXATION OF ANTERIOR MANDIBLE
FIGURE 1. Top, A lag screw. Note the absence of threads except at the terminus of the screw. Below, Cortical screw. This screw can be used to impart compression to a fracture by overdrilling the outer (near) cortex so the threads only engage the far cortex.
Instead, the anterior mandible undergoes shearing and torsional (twisting) forces during functional activities.4.5 Therefore, application of fixation devices must take these factors into consideration. This is why Champy, who advocates only one small bone plate in most regions of the mandible, always places two bone plates in the symphysis.4 When using bone screws to secure fixation, one bone screw may not provide adequate stability, since the shear forces may allow rotation of the mandibular fragments around the screw. The only resistance to rotation about one screw is the compaction (friction) of the fragments into one another by virtue of the compression imparted from the lag screw. Application of an arch bar to the teeth may prohibit the rotational force; however, application of a second lag screw is the best insurance for providing rigidity.’ Fortunately, there is usually ample space available for the routine placement of two screws in fractures of the anterior mandible. Technique The application of lag screw fixation for fractures of the anterior mandible requires relatively few instruments; however, correct instruments are essential to the technique. (AO/ASIF instruments are available from Synthes Maxillofacial Instrument Company, Paoli, PA, or from other manufacturers.) The necessary instruments are included in the standard mandibular fracture kits; however, longer screws than those that normally accompany the set are necessary. The lag screw technique for the anterior mandible can require 2.7-mm screws up to 40 mm in length. Therefore, every screw length up to
40 mm should be available before attempting to treat fractures with lag screws. Following application of maxillary and mandibular arch bars, a vestibular incision is made from just posterior to one mental foramen to the same area on the other side. Anterior to the mental foramina, the incision is made out in the lip, splitting the mentalis muscle to facilitate a two-layer closure. Subperiosteal dissection of the anterior, lateral, and inferior borders of the mandible from one mental foramen to the other is essential for complete exposure of the fracture and for proper instrumentation. Dissection under, or between the bundles of the mental nerves when necessary for adequate retraction and exposure, helps protect the nerve from injury due to stretching. The entire fracture is examined following slight distraction to note the obliquity and the relationship of the cortices. If there are extensive areas of comminution, the lag screw technique should be abandoned, because it has little chance of success in cases where the continuity of the cortices is disturbed. Fortunately, this is unusual in fractures of the anterior mandible. Once the fracture has been examined and cleaned of extraneous debris, the mandible is placed into maxillomandibular fixation (MMF) while simultaneously reducing the fracture. A towel clip with the tips bent slightly outward can be used to assist in firmly reducing the fracture before application of lag screws. A small bur is used to drill holes approximately 10 mm away from each side of the fracture to provide a purchase for the modified towel clip. The towel clip is inserted into these holes and tightened, reducing the fracture. The location of the towel clip must not be an area where the lag screws are to be inserted. Frequently, it must be inserted in the region of the root apices, taking care to avoid them. The lingual cortices should also be checked to assure that they are in firm apposition, since other fractures of the mandible, especially those of the condyle and ramus, may cause an increase in the radius of the dental arch and inferior border. Therefore, the surgeon must not be lulled into a false sense of security that the fracture is properly reduced by solid apposition of the buccal cortices. It is helpful to dissect below the inferior border of the mandible in the area of the fracture to directly expose the lingual cortex and assure its proper reduction. Selecting the point of entry into bone and alignment of the drill is crucial since it will determine the success of the procedure and, when improperly executed, may cause undesirable complications. Although the lag screw technique in other bones usually involves drilling the screw hole at an angle that
ELLIS AND GHALI
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FIGURE 2. Illustration demonstrating the A0 orthopedic technique for determining angulation of screw placement. The angle between the outer cortex and the line of fracture is bisected to determine the proper drill path. This technique of screw placement makes little sense in the anterior mandible and may cause overriding of the fragments when the screw is tightened. Instead, the screw should be placed perpendicular to the fracture.
the bisection of the angle between the line of fracture and the outer cortex (Fig 2),6 the curvature of the anterior mandible and frequent lack of fracture obliquity make this impossible and/or undesiris
able in most fractures of the anterior mandible. Therefore, the path of screw insertion should disregard this principle of lag screw insertion for long bones, and instead traverse the fracture in as per-
FIGURE 3. Attempting to use the A0 orthopedic principle demonstrated in Figure 2 for fractures of the anterior mandible, often results in improper/inadequate placement of screws. A, The screw is placed obliquely to sagittal fractures of the symphysis. The tightening of this screw tends to cause displacement of the fragments. This is similar to using a compression plate on a very tangential (oblique) fracture, which also causes overriding of the segments. Attempting to use the A0 orthopedic principle frequently results in placement of the screw into or very near the fracture on the lingual cortex (B), or misses the lingual cortex altogether (C and D). C, The screw glances off the lingual cortex although it may feel as if the screw is secure. However, upon tightening, it shears and loosens. D, Screw misses the lingual cortex and ends up in medullary bone. A screw inserted into medullary bone has insufficient strength to resist displacement of the fracture during function. The management of this problem is to continue drilling until the buccal cortex is reached, and a long screw is used (see Fig 4B).
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LAG SCREW FIXATION OF ANTERIOR MANDIBLE
FIGURE 4. Ihustration showing proper placement of screws for fractures of the anterior mandible. A, The screw is placed perpendicular, or B, nearly perpendicular, to the line of fracture when it is sagittal. C and D, When the fracture is oblique, screws are simply inserted across the fracture in as perpendicular a manner as possible.
pendicular a manner as possible. When the screw is perpendicular to the line of fracture, the compressive load imparted by the lag screw becomes extremely effective in securing rigid stabilization of the fragments without causing displacement upon tightening. For the same reason that compression plates are not applied to oblique fractures, lag screws applied obliquely to the fracture cause displacement of the fracture. Figure 3 shows examples of improper placement of lag screws, which results in inaccurate reduction, complications, and/or instability. One must remember that medullary bone offers insufficient resistance to bone screw fixation and, therefore, a bony cortex must be engaged with the terminal threads of the screw. Figure 4 shows proper screw placement for various types of fractures in the anterior mandible. Selection of the proper point of entry for the drill in the buccal cortex is based on placing it suffL ciently away from the fracture so that an ample amount of bone is present between the head of the screw and the fracture after drilling and countersinking. This is especially important when drilling along the curved surface of the anterior mandible. The remaining bony bridge must resist all forces of mastication, since the screw head rests directly on it. Another factor to consider in determining the location of the bone screw is providing sufficient space for a second screw. Thus, the first screw should be placed just above the inferior border. Once the proper angulation and point of entry has been established, the 2.7-mm drill is initially placed almost perpendicular to the buccal cortex at the selected point of entry to prevent skidding of the drill bit, and a hole is begun in the buccal cortex. The
drill is then redirected to the previously selected angulation and the drilling completed through the buccal cortex and medullary bone of the first (near) fragment only (Fig 5A). The drill and drill guide are withdrawn from the wound and a countersinking tool is used at slow speed to provide a smooth platform for screw-head seating (Fig 5B). It is imperative that two facts be considered while countersinking the hole. First, the same angulation should be used as established by the initial 2.7-mm drill hole. To facilitate this, a countersinking tool with an adjustable guide-pin that extends beyond the countersinking flutes into the drill hole can be used. Second, countersinking must be adequate to allow complete seating of the screw head. This means that a considerable amount of buccal cortex must be removed when a screw is inserted into a rounded surface or in an oblique manner on a straight surface (Fig 6). The most appropriate method to determine the adequacy of countersinking is to place the 2.0mm (“centering”) drill guide into the drill hole. This drill guide, to be used in the next step, has a tip that fits tightly into the 2.7-mm hole and a shank with an outer diameter slightly larger than the head of the screw. If insertion into the drill hole cannot be smoothly accomplished without binding on the bone medial to the drill hole, countersinking is inadequate and must be completed (Fig 7). However, one must avoid countersinking deeper and deeper into the bone to the point where the screw head rests on medullary instead of cortical bone. Drilling through the second (far) fragment with a 2.0-mm drill is the next step. To ensure that the 2.0-mm drill is perfectly centered in the 2.7-mm hole previously drilled through the near cortex, a
ELLIS AND GHALI
FIGURE 5. Illustration showing technique of placing lag screws for sagittal fracture of the anterior mandible. A, Drilling near cortex with 2.7mm drill. Note that the drilling extends only to the fracture. A drill guide should be used to stabilize the drill and protect soft tissues. B, The near cortex is countersunk using countersinking tool with guide pin, which extends into 2.7-mm hole. C, Drilling 2.0-mm hole completely through mandible using centering drill guide. The tip of the drill guide has an outer diameter of 2.7 mm, allowing it to seat firmly into the previously drilled hole in the near cortex. The inner diameter of the drill guide is 2.0 mm, centering the 2.0-mm drill in the 2.7-mm hole. D, Result after drilling. Note the near cortex (right) has been drilled to 2.7 mm diameter, and the far cortex to 2.0 mm diameter. E, Depth gauge used to determine length of screw. F, Tapping the far cortex. Note that the tap (and screw in next step) slides through the near cortex, since it has the same outer diameter (2.7 mm). G, Result following tapping. Note screw threads only in far cortex. H, Screw inserted. Since the threads only engage the far cortex, compression is applied during tightening.
drill guide is used (Fig 50. special “centering” This drill guide has an outer diameter of 2.7 mm on its working end, allowing a snug fit into the hole previously drilled through the near cortex. It has an inner diameter of 2.0 mm, acting as a drill guide for the 2.0-mm drill, perfectly centering it within the 2.7-mm hole in the near cortex. Drilling through the second (far) segment with the 2.0-mm drill is then performed (Fig 5C). During the drilling, it is important to use slow-speed, copious irrigation, and repeatedly withdraw the drill flutes from the drill guide to clear bony debris. If not done, the drill becomes quite warm due to both the inability of irrigant to reach the flutes and clogging of flutes with debris. A depth gauge is inserted through the drill hole and the screw length is determined (Fig 5E). The hole in the far segment is then tapped using a long
tap (Fig 5F). To prevent tissue entanglement and to help avoid wobble, the same drill guide as used in drilling the 2.7-mm hole should be used as a tapguide. Care should be taken to ensure that the same direction used during drilling is used for tapping. The hole should be thoroughly irrigated before placing the screw. After selection of the appropriate length screw, it is inserted on a screw driver into the screw hole. The outer hole (or clearance hole) is free of threads and the screw should slip through until it contacts the threads in the far segment (Fig 5D and G). Thus, when tightened, the screw will compress the two segments of bone together. While the final tightening proceeds, the surgeon must carefully observe the bony cortices around the head of the screw for signs of crazing. Frequently, the screw is overtightened to the point of creating microfrac-
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LAG SCREW FIXATION OF ANTERIOR MANDIBLE
FIGURE 6. Illustration demonstrating the importance of properly countersinking the screw. If inadequate or no countersinking is performed (A), tightening of an obliquely placed screw will cause premature contact and binding of the screw on the bone, resulting in displacement of the screw and/or segments or causing fractures of the near cortex. B, Proper countersinking.
tures around the screw head. This should be avoided if possible. It is essential that the screw exit the far cortex for maximal strength (Fig 5H). A second screw is then inserted in the same manner as just described (Fig 8). With sagittal fractures of the mandible between the incisors, it frequently is easier to place the second screw from the opposite direction. Because the buccal cortex on the other side of the fracture has not yet been disrupted, a greater area of bone for screw placement is provided (Fig 9). In fractures of the anterior mandibular body (Fig lo), placing a second screw may not be possible without damaging the mental nerve. There are two choices in this instance. The first is to supplement the fixation with a bone plate placed superior to the lag screw (Fig 1OD). The second is the maintenance of the arch bar and compression (bridle) wire, and placement of the patient on a soft diet (Fig 1OC). However, the rigidity produced by one lag screw and an arch bar is not yet known and is therefore not recommended routinely. If used, it requires that the patient be extremely cooperative. The intraoral incision is closed in two layers with resorbable sutures. The MMF is then removed and the patient is maintained on a soft diet.
Material and Methods All patients treated by open reduction and internal fixation of fractures between the mental foramina by the lag screw technique previously described between November 1, 1988, and November 31, 1989, were included in this retrospective study. The patients’ charts were reviewed for information about additional fractures, and the presence of a tooth in the line of fracture. Notes on the operative findings and postsurgical course were evaluated for extraction of the tooth in line of fracture, duration of MMF if used, postsurgical occlusal relationship, infection, and need for further intervention because of complications. When possible, clinical examinations were performed in December 1989 and January 1990. Otherwise, only the patients’ charts, including postsurgical notes, were used for tabulation of the above data. Results Forty-one patients were identified who were treated using bone screws for anterior mandibular fractures. Seven were female, the remainder male.
FIGURE 7. Illustration showing effect of inadequate countersinking for an obliquely placed screw. The 2.0-mm drill guide does not seat securely, causing the 2.0-mm drill to become misaligned with respect to the 2.7-mm hole. A, Inadequate countersinking. B, Proper countersinking.
ELLIS AND GHALI
They ranged in age from 14 to 59 years. Two lag screws were placed in the majority of patients (29); however, in two patients, three lag screws were used. A single lag screw was placed in seven patients; a single lag screw combined with a small compression plate (using 2.0-mm screws) was used in three patients. The anterior mandibular fracture was the only mandibular fracture in 13 patients. Twenty-nine patients had associated mandibular fractures, of which 17 were fractures of the angle, nine were subcondylar (six unilateral, three bilateral), one was in the body, one was in the ramus. and one was a dentoalveolar fracture. All patients had a tooth in the line of fracture. Five patients had the tooth in the line of fracture removed at surgery. Because of associated fractures, MMF was used in nine patients: two patients for 1 week, four for 4 weeks, and three for 6 weeks. No MMF was used as a supplement to lag screw fixation of a symphyseal fracture. Follow-up ranged from 4 to 61 weeks, with a mean of 12 weeks. All fractures except the one noted below were found to be stable at follow-up appointments. No postsurgical malocclusion resulted. Two patients developed postsurgical infections (4.9%), both thought to be due to a nonvital tooth in the line of fracture that was subsequently removed. Both patients had two lag screws placed to secure the two halves of the mandible. In one patient, a soft-tissue infection developed 1 week following surgery and the tooth in the line of fracture, which was noted to be loose, was removed. This patient had a large segment of
FIGURE 8. Example of lag screws in symphyseal fracture. A, Preoperative panoramic radiograph showing sagittal fracture of midsymphysis. B, Postoperative panoramic radiograph showing placement of two lag screws perpendicular to fracture. from one buccal cortex to the other.
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FIGURE 9. Lag screws placed from opposite sides of a sagittal fracture. A, Intraoperative view. B, Postoperative view following healing of fracture. The crisscross technique of screw placement may be easier, because more bone is available for drilling and countersinking on the side opposite the initial screw.
bone that included the inferior border maintained in position using a third lag screw during surgery. The patient had also been placed in MMF for an associated subcondylar fracture. The infection persisted at a subclinical level, and at 6 weeks postsurgery, the labial soft tissue had a dehiscence, exposing some granulation tissue and nonvital bone. A sequestrectomy was performed at this time and the previously repositioned bony segment, which was found to be loose and necrotic, was removed. However, the fracture was united and the patient healed uneventfully. The second patient developed a soft tissue swelling 3 weeks postsurgery. This patient had no extraction at the time of surgery. One tooth associated with the fracture was removed. The following week, more swelling was noted and the other tooth adjacent to the fracture was noted to be loose and was removed. The fracture was noted to have slight mobility at that time. The patient was placed into MMF, but was uncooperative and repeatedly removed the fixation. At 8 weeks’ postsurgery, the patient was taken to the operating room where the lag screws (which were slightly loose) were removed and external pin fixation was placed. He had a satisfactory course thereafter. One addi-
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LAG SCREW FIXATION OF ANTERIOR MANDIBLE
FIGURE 10. Illustration showing application of lag screws for fractures of the anterior mandibular body in the vicinity of the mental foramen. Placing screws from buccal to buccal (A), or buccal to lingual (B) both have utility. C, Use of a single lag screw combined with arch bar and bridle wire for fractures around the mental foramen. D, Supplementation of fixation by application of a 2.0-mm bone plate, using monocortical screws to avoid roots, if necessary.
D tional patient had further surgical intervention at 9 months. This patient had been treated with two lag screws, no MMF, and underwent an uneventful postoperative course. However, a 9-month radiograph showed a small radiolucency around the head of one of the bone screws. No symptoms were present. This screw was found to be loose and was removed. Dense fibrous connective tissue surrounded the head of the screw where the labial cortical bone had once been. The other screw was not loose, but was also removed. Discussion Besides the many advantages that rigid fixation of mandibular fractures offers, the use of lag screws as a type of rigid fixation has several unique advantages over bone-plate fixation. The major advantage is that lag screws can be applied more rapidly, since the time-consuming task of adapting a bone plate is obviated. This also allows a more anatomically accurate reduction, because it takes considerable skill to perfectly adapt a bone plate to the complex contours of the mandible. In our experience, displacement of bone fragments is much more common during placement of a bone plate, since the adequacy of plate contouring is not thoroughly known until the screws are inserted and the plate is drawn to the mandible. Displacement of bone segments almost never occurs while applying lag screw fixation when one adheres to the details previously described. Lag screws also permit the rapid application of fixation without a decrease in rigidity of the frac-
ture reduction. Although no research has yet been done that compares the rigidity of fixation with a bone plate versus lag screw fixation of anterior mandibular fractures, one frequently gets the impression that lag screws provide much more rigidity than do bone plates. This is especially evident when the screws are applied perpendicular to the fracture. The fracture gap frequently completely disappears from sight due to the great amount of compression that can be imparted with the screws. Another advantage is the costs incurred: these are greatly diminished because the screws cost much less than a bone plate. The results of this retrospective study show that lag screw fixation of anterior mandibular fractures is an extremely simple and successful method of rigidly securing the fragments, permitting active use of the mandible during healing. Only two patients experienced problems that required intervention. All seven patients treated with only one lag screw (in addition to an arch bar and bridle wire) had no postoperative difficulties. These patients were all cautioned to maintain a soft diet, because the rigidity of the fixation with only one screw is unknown. However, their compliance with this regimen was not determined. However, even in the face of these results, we still do not recommend the use of only one lag screw, because adequate numbers to justify its routine implementation are not yet available. We are in disagreement with Niederdellmann et al, who state that “lag screw osteosynthesis is not meant to replace osteosynthesis with plates,” and who reserved the use of lag screws for very special circumstances.’ We now use lag screw fixation as
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ALAN SCHWIMMER
our first choice for providing rigid internal fixation of anterior mandibular fractures. Rarely do we have the need or desire to use bone plates in the anterior mandible. However, there are special circumstances where the use of lag screws are contraindicated. The most important is when there is comminution and/or bone loss in the fracture gap. One must understand completely that the lag screw technique of fixation is one that relies on compression of bone fragments. If the intervening bone is unstable due to comminution, or is missing, compressing across this region will cause displacement of intervening bone fragments, overriding of segments, and/or shortening of the fracture gap, resulting in problems with the occlusion. In such situations, applying a bone plate without compression across this gap can achieve rigid fixation without disturbing the occlusion. Fortunately, the vast majority of fractures of the anterior mandible result in fragments
J Oral Maxillofac
that are large enough to permit the application of lag screw fixation.
of the mandibular body treated by stable internal fixation: A preliminary report. J
1. Brons R, Boering G: Fractures
Oral Surg 28:407, 1970 2. Niederdellmann H, Schilli W, Dtiker J, et al: Osteosynthesis of mandibular fractures using lag screws. lnt J Oral Surg 5:117, 1976 3. Leonard MS: The use of lag screws in mandibular fractures. Otolaryngol Clin North Am 20:479, 1987 4. Charnpy M, Lodde JP, Schmitt R, et al: Mandibular osteosynthesis by miniature screwed plates via a buccal approach. J Maxillofac Surg 6:14, 1978 5. Niederdellmann H: Fundamentals of healing of fractures of the facial skull. 1. Biomechanics, in Kruger E, Schilli W teds): Oral and Maxillofacial Traumatology (vol 1). Chicago, IL, Quintessence, 1982, pp 125-128 6. Mtiller ME, Allgower M, Willenegger H: Manual of Internal Fixation. New York, NY, Springer-Verlag, 1970, p 24
Surg
49.21-22.1991
Discussion Lag Screw Fixation of Anterior Mandibular Fractures Alan Schwimmer,
DDS
Beth Israel Medical Center, New York, NY
Doctors Ellis and Ghali have presented an extremely innovative technique for the use of lag screws as a means of obtaining functionally stable fixation in mandibular fractures. Lag screws, or traction screws, provide maximum interfragmentary compression with a minimum amount of implanted material. Because of their efficiency, they represent an ideal method of internal fixation, and in orthopedic surgery lag screws are often the first choice when rigid fixation is used. Lag screw fixation also has been useful in the treatment of midface trauma. Direct lag screw fixation is often not practical for the stabilization of midface fractures; however, the use of lag screws has been shown to be effective in the stabilization of split calvarial grafts. Recent studies by Phillips, Rahn, and McCarthy have demonstrated improved retention of bone graft volume when cranial grafts have been stabilized with lag screws. Anatomic considerations often prevent the use of lag screw fixation in the treatment of mandibular fractures. Niederdellman has described the use of a single unprotected lag screw for the fixation of transverse fractures at the angle of the mandible.’ With this technique, the lag screw is placed on the tension side of the fracture; therefore, compression is achieved along the unstable portion of the fracture. Spiessl has recommended the use of lag screws in oblique fractures of the body of the mandible.2 However, in these cases a minimum of three lag screws
are used. In oblique fractures that allow placement of only a single lag screw, protection of the lag screw by a stabilization plate is recommended. With the publication of this technique, Drs Ellis and Ghali have expanded the use of lag screws for the functional stabilization of mandibular fractures. This procedure appears to be easily executed; however, any surgeon attempting to use this technique must be familiar with the basic principles of rigid internal fixation. A lack of understanding of these basic principles will result in failure. It is therefore advisable that one first develop proficiency in the more routine methods of plate and screw stabilization. Once experience is gained in these techniques, greater success can be expected when using the procedure described by Drs Ellis and Ghali. The technique described in this article does adhere to several principles of lag screw fixation. To begin with, it is important to note that the authors recommend using dedicated instruments when using this technique. Attempts to improvise instrumentation will compromise the success of the procedure. Of special importance is the use of the centering guide to align the traction hole and the gliding hole coaxially. Failure to pay close attention to this step will result in misalignment of the fracture and a decrease in the compressive force of the lag screw. It should also be reemphasized that a 20-mm screw is the longest available in the standard Synthes set. When using lag screws for the stabilization of transverse fractures, whether at the angle or in the anterior mandible, screws longer than 20 mm are often required. Therefore, if the surgeon is planning lag screw fiiation of a transverse mandibular fracture, it is essential that screws of 30 to 40 mm in length be available.
