J Oral Maxillofac 49234-243.
Lag Screw Fixation of Mandibular Angle Fractures EDWARD ELLIS III, DDS, MS,* AND G.E. GHALI, DDSt This article presents a technique of applying lag screws for treating fractures of the mandibular angle. A review of 30 patients who had lag screws placed to treat such fractures showed that it is an extremely useful, but technique-sensitive, method of providing rigid internal fixation. The advantages and complications of this technique over bone-plate fixation are discussed.
contour of the lateral mandible also takes a considerable amount of time and skill. The use of a transbuccal trochar is essential for drilling and screw placement, but instrumentation through the trochar is difficult, and more than one transbuccal puncture is necessary in the majority of instances. Because of these difficulties with large bone plates, miniplate systems have become quite popular. The advantage to the miniplate technique is that the small plates are secured along the external oblique ridge, facilitating access. The main problem with this technique is that it is not truly a “rigid” technique. After placement of the plate, one can readily appreciate their lack of rigidity by pushing medially on the ramus with an instrument or retractor and observe the instability at the inferior border. These plates essentially provide stable fixation only at the superior border of the mandible, neutralizing the tension zone during function. The nonrigidity of this technique has prompted most surgeons in the United States to use varying periods of maxillomandibular fixation (MMF) following surgery and to limit the diet to very soft foods. In 1981, Niederdellmann described a method of internal fixation of mandibular angle fractures using lag screws.* At first glance, this may seem an absurd method for treating angle fractures. However, once the anatomy of the mandible and technique of screw placement is understood, lag screw fixation makes very good sense. Like the miniplate system, its effectiveness relies heavily on securing the tension zone of the mandible during function. Also, like the miniplate technique, it is much easier to place than a large bone plate at the inferior border. A distinct advantage over the miniplate system, however, is the ability to apply great amounts of
Fractures of the mandibular angle are common injuries, comprising approximately 30% of mandibular fractures sustained in altercations.’ Because of the frequent displacement of the fragments, open reduction and internal fixation are commonly employed to align the fragments and maintain them in contact to promote osseous union. With the recent enthusiasm in the United States for rigid forms of internal fixation, experimentation with various forms of plate and screw fixation has been attempted. In general, this can be divided into those techniques that use large bone plates (with or without compression) secured near the inferior border of the mandible, or miniplates (without compression) applied to the superiolateral border of the mandible. Both of these techniques have advantages and disadvantages. The large bone plates are more difficult than miniplates to place in the mandibular angle region through a transoral approach. Those who have attempted their use for mandibular angle fractures know the difficulties encountered. Access is often extremely limited, especially when edema is present. Adapting the plate to the unique Received from the Division of Oral and Maxillofacial Surgery, The University of Texas Southwestern Medical Center, Dallas. * Associate Professor. t Resident. This research was supported in part by a grant from the Chalmers J. Lvons Academy-James R. Hayward Research Fund. Address correspondence and reprint requests to Dr Ellis: Division of Oral and Maxillofacial Surgerv, University of Texas Southwestern Medical Center, 5323 Harry Hines Bkd, Dallas, TX 75235. 0 1991 American geons
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compression between the fragments to promote healing and to stabilize the entire length of the fracture. We began to use the lag screw technique in January 1989 and found it to be an extremely rapid and simple method of treating fractures of the mandibular angle. In a I-year period, we have treated 42 angle fractures in 40 patients using this technique. The purpose of this article is to describe the technique and to review our early experience in 30 of these patients. Technique The application of lag screw fixation for angle fractures requires relatively few instruments; however, those instruments necessary are essential to the technique. The necessary instruments are included in the standard AO/ASIF mandibular fracture kit (Synthes Maxillofacial Instrument Company, Paoli, PA); however, one must have longer screws available than those that normally accompany the set. The lag screw technique for the mandibular angle require screws up to 40 mm in length. Following application of maxillary and mandibular arch bars, a vestibular incision is made from the retromolar area to the mandibular canine, leaving 4 to 5 mm of mucosa on the alveolar process to facilitate closure. When a terminal molar is present and is to be removed, the incision incorporates the attached gingiva around this tooth following removal. Subperiosteal dissection of the lateral and inferior borders of the mandible from the mental foramen to just behind the fracture is essential for exposure of the fracture and for instrumentation. The entire fracture is examined following slight distraction to note the mediolateral obliquity and the relationship of the cortices. If there are areas of comminution, the lag screw technique should be abandoned because it has little chance of success in cases where the continuity of the buccal cortex is disturbed. Once the fracture has been examined and cleaned of extraneous debris, the mandible is placed into MMF while simultaneously reducing the fracture. Securing MMF prior to exposure of the fracture is not recommended, because one frequently will have difficulty reducing the fracture while the jaws are wired shut. Appropriate retractors should be placed under the inferior border of the mandible to expose the entire lateral surface. One should not attempt to perform the lag screw placement through solely a transoral approach. When this is attempted, it is almost impossible to achieve the proper angulation of the drill, resulting in improper screw placement. Therefore, a 4-mm stab incision is made through skin at the inferior
border of the mandible in the area of the first premolar. A hemostat is used to bluntly tunnel through the subcutaneous tissues in a posteromedial direction until the elevated periosteum is punctured. The hemostat, when visible through the intraoral incision, should exit beneath and just posterior to the mental foramen. A 2.7-mm drill guide is then inserted through this tunnel followed by a 2.7-mm drill. The next step, selecting the point of entry in the bone and alignment of the drill, is crucial because, when properly executed, it will determine the success of the procedure and, when improperly executed, it may cause undesirable complications. The lingual cortex in the third molar area is of ins&icient thickness and density to maintain rigidity of the lag screw. Therefore, the path of screw insertion is predicated on securing the terminal screw threads in bone that is dense enough to provide rigid fixation. This can usually be achieved by a path of screw insertion that is approximately 10” to 20” from the buccal cortex (Fig 1). Using this path of insertion, the screw will come out posterior to the temporal crest of the mandible, in dense cortical bone. However, if placed almost parallel to the buccal cortex, the inferior alveolar neurovascular bundle can be encountered. Thus, one must determine the proper buccolingual angulation necessary to obtain sound bone without endangering the contents of the mandibular canal (Fig 2). The method we have found useful for this determination is to lay the 2.7-mm drill over the top of the mandible, with the tip passing just medial to the external oblique ridge (Fig 3). The angle the drill makes with the mandible both in a mediolateral and superioinferior direction can be used to determine proper drill angulation. The drill is then backed out of the drill guide until it contacts the mandible in the area where it is to perforate the buccal cortex. Selection of the proper point of entry for the drill in the buccal cortex is based on two factors. First, the point of entry must be sufficiently anterior to the fracture so that an ample amount of bone is present between the head of the screw and the fracture after drilling and countersinking. One must remember that this bony bridge is the bone that must resist all forces of mastication because the screw head rests directly on it. Because the angulation of drilling is only approximately 10” to 20” from parallel with the buccal cortex, countersinking the screw head may use several millimeters of bone, resulting in the head of the screw being much more posterior than the point of initial entry of the drill. Therefore, the initial point of entry should be approximately 12 to 15 mm anterior to the fracture. Most commonly, the point of entry will correspond with the anterior
LAG SCREW FIXATION OF MANDIBULAR
FIGURE 1. Radiographs (A) and illustration (B) showing proper angulation of screw placement.
aspect of the external oblique ridge as it tapers down into the mandibular body. In this manner, a sound bony buttress will remain following countersinking. The second factor to be considered in selecting the point of initial drill entry is the superioinferior position. The best method to determine this is by laying the 2.7-mm drill over the top of the mandible, establishing proper mediolateral and superoinferior angulation, retracting the drill until the proper anteroposterior position is found, and using the superoinfetior angulation thus established in drilling the hole (Figs 3 and 4). It is best to try and enter the bone just superior to the position of the mandibular canal; however, because of the lingual position of the canal in the first-second molar area,3 injury is avoided even when entrance is made directly over the canal. The surgeon inexperienced in the lag screw technique will find that considerable time may be spent deciding on the proper point of entry and angulation; with experience, this becomes easier. Once the proper angulation and point of entry have been established, drilling the outer cortex should proceed. 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 made through 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 distal fragment only (Figs 4 and 5A). It is not necessary to have the proximal segment perfectly reduced at this time, as no crossing of the fracture with this drill occurs. The drill and drill guide are withdrawn from the wound and a countersinking tool is placed through the same stab incision. It is not necessary to protect the skin, because the shank is smooth and will not damage the skin at the slow speed used for countersinking. It is imperative that while countersinking the hole, two facts be considered. 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 cortical bone must be removed anterior and medial to the drill hole (Fig 6). Because the head of a 2.7-mm screw is 5.0 mm in diameter, another 1.2 mm of bone must be removed from the buccal cortex on the medial side of the drill hole. The bone removal must be in perfect line with the direction of the drill hole, or the screw will bind on
ELLIS AND GHALI
FIGURE 2. Radiographs (A) and illustration (B) showing improper angulation of screw placement. The screw was not adequately retentive (note MMF wires). It must engage the dense cortical bone on the lingual aspect of ramus to be secure. When angled too far lingually, the bone is less retentive. - _
the bone medially on insertion, causing undue forces on the cortex buccal to the screw, which will fracture (Fig 7). Once countersinking has provided an even plateau of bony cortex both on the medial and the lateral side of the drill hole, the countersinking tool is removed from the wound. The most appropriate method to determine the adequacy of countersinking is to place the 2.0-mm centering drill guide through the stab incision and insert it into the drill hole. This drill guide, to be used in the next step, fits tightly into the 2.7-mm hole and its shank has an outer diameter slightly larger than the head of the screw (Fig 8). 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 9). One must, however, 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 proximal fragment with a 2.0mm 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 buccal cortex, a special centering drill guide is used (Figs 5C, 8, and 9). This drill guide had an outer diameter of 2.7 mm on its
working end, allowing a snug fit into the hole previously drilled through the buccal 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 buccal cortex. During drilling of the proximal fragment with the 2.0-mm drill, it is imperative that the fracture be anatomically reduced. It is unnecessary in most instances to use bone clamps or transosseous wires to accomplish this. Simple use of retractors placed along the buccal cortex of the proximal fragment allow easy manipulation into proper relationship with the distal fragment. Once properly reduced, drilling through the proximal segment with the 2.0mm drill is performed (Fig 5C). During the drilling, it is important to use slow speed and repeatedly withdraw the drill from the drill guide to clear bony debris. If not done, one will note that the drill becomes quite warm, owing to both the inability of irrigant to reach the flutes and clogging of flutes with debris, A long depth gauge is inserted through the stab incision and the screw length determined (Fig 5E). However, it is usually possible to determine screw length during drilling the 2.0-mm hole, because it is easy to feel when the drill exits the lingual cortex.
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cause it will not Iit through the stab incision. Before the last few turns of the screw are accomplished, attention to the fracture site is mandatory to assure that it is perfectly reduced along its entire length. While the final tightening proceeds, one must carefully observe the bony cortices around the head of the screw for signs of crazing. The screw can frequently be over-tightened to the point of creating microfractures around the screw head. This should be avoided, if possible. It is essential that the screw exit the lingual cortex of the proximal segment for maximal strength. Maxillomandibular fixation should be released at this point and the rigidity of the fracture tested. The fracture should be exposed and observed while the mandible is forcefully opened and manipulated through various movements. If any movement of the fracture is observed, the rigidity of the fixation is in question. One must then decide on one of two courses. The first is to supplement the fixation with a bone plate placed more inferiorly or to use a period of MMF. The second is to place the patient on a soft diet and frequent observations. However, this requires that the patient be extremely cooperative. The intraoral incision is closed in one layer with resorbable sutures, obtaining closure over extractions sockets, if possible. One monofilament suture is placed to close the dermal surface of the trochar incision. Study Methods
FIGURE 3. Method of determining the buccolingual angulation for drilling initial hole. The 2.7-mm drill is laid across the external oblique ridge to determine proper angulation.
At this point, the amount of drill bit extending beyond the drill guide (next to the drill chuck) can be measured. If the drill shank is touching the drill guide, ie, completely seated, a 40-mm screw is necessary. This is the longest hole one can drill with the equipment, and the longest 2.7-mm screw available. If there is 4 mm of exposed drill at the drill guide, a 36-mm screw is necessary. The hole in the proximal segment is tapped using a long tap (Fig SF). To prevent tissue entanglement, the same drill guide as used in drilling the 2.7-mm hole should be used as a trochar through the stab incision. The hole should be thoroughly irrigated before placing the screw. After selection of the appropriate length screw, it is inserted through the stab incision on a screw driver into the screw hole (Fig 5H). The screw holder on the screw driver should be removed be-
All patients treated by open reduction and internal fixation of at least one mandibular angle fracture by the lag screw technique described above between January 1 and December 31, 1989, were included in this retrospective review. The patients’ charts were reviewed for indication of additional fractures and the presence of a tooth in the line of fracture. Notes on the operative findings and postsurgical course were evaluated for 1) extraction of teeth in line of fracture; 2) duration of MMF, if used; 3) postsurgical occlusal relationship; 4) infection; 5) dehiscence/exposure of bone; and 6) need for further intervention because of complications. When possible, clinical examinations were performed between January and March of 1990. Otherwise, charts, including postsurgical notes, were used for tabulation of the above data. Results Thirty patients were identified who were treated using bone screws for mandibular angle fractures and had adequate records for evaluation or were available for recall. Six were female, the remainder
ELLIS AND GHALI
FIGURE 4. Illustration showing inferosuperior angulation of 2.7-mm drill.
male. They ranged in age from 17 to 49. Fourteen patients had a unilateral angle fracture as their only mandibular fracture. Two patients had bilateral angle fractures, 11 had a combination of angle and symphysis fractures, and 3 had a combination of angle and body fractures. The additional fractures were treated with plate and screw, or lag screw tixation (with the possible exception of condylar fractures). Twenty-eight patients had a tooth in the line of fracture; all were removed during the surgery. Following application of the lag screw, 22 of the 30 fractures were determined to be stable to aggressive bimanual manipulation of the mandible. Eight patients had slight mobility of the fracture, necessitating supplemental methods of fixation. In one patient, a 2.0-mm compression bone plate was applied at the inferior border (Fig 10). In seven patients, postoperative MMF was used for varying periods (3 weeks in two, 4 weeks in four, and 8 weeks in one patient*). In six of these eight cases, the staff surgeon was not present during surgery. Follow-up ranged from 8 to 52 weeks, with a mean of I1 weeks. Postoperative radiographic evaluation showed excellent reduction in every patient. No patient developed nonunion or malunion. Two patients were found to have very minor occlusal discrepancies in the first 2 postoperative weeks. These were treated satisfactorily with 3 to 4 weeks of maxillomandibular elastics. No other postsurgical malocclusion resulted in any patient. One patient had radiographic evidence of probable impalement of the mandibular canal by the screw. In this case, the screw was directed insufftciently superiorly. However, because the patient was anesthetic before sur* This patient was not scheduled for 8 weeks of MMF, but did not return for scheduled follow-up.
gery, it was impossible to determine whether impalement actually occurred. In no patient was the 3to 4-mm incision for trochar placement a problem. Seven patients developed minor postsurgical soft-tissue infections/bone exposures (23%) within the first several weeks (no cases of osteomyelitis occurred). Three resolved after treatment with oral antibiotics without any further intervention. Four patients (13%) required further intervention, including removal of the hardware and small sequestra. One patient also had extraction of a terminal molar that was thought to be nonvital. Discussion The results of this retrospective study and our clinical experience indicate that lag screw fixation of mandibular angle fractures is a simple, yet extremely technique-sensitive, method of rigidly securing the fragments in mandibular angle fractures. In our experience, the time needed to place the screw is approximately 20 minutes, much faster than adapting and securing a bone plate at the inferior border through a transoral approach. Further, the reduction is more anatomically accurate, because it takes considerable skill to perfectly adapt a bone plate to the complex contours of the mandible. Displacement of bone fragments is much more common in our experience when securing a bone plate, because the adequacy of plate contouring is not completely 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 described. However, the use of the lag screw technique in angle fractures requires more attention to detail than any other technique of internal fixation.
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FIGURE 5. Illustrations showing placement of lag screw for mandibular angle fractures. A, Drilling 2.7-mm hole through the distal fragment using a drill guide as a trochar. Note that the hole does not enter the proximal segment. B, Countersinking the screw hole. C, Drilling through the proximal segment using a 2.0-mm centering drill guide. The drill guide centers the 2.0-mm drill within the previously drilled 2.7-mm drill hole. D, Result following above steps. Note that the proximal segment has 2.0-mm drill hole and the distal segment has a 2.7-mm gliding hole. E, Depth gauge used to determine screw length. F, Tapping of 2.0-mm hole in proximal segment to 2.7 mm. The tap does not engage the bone in the distal segment, as it is already drilled to 2.7 mm. G. Result following tapping. H, Screw placed.
FIGURE 6. Illustration showing countersinking of the drill hole. Note the amount of bone removed medial and anterior to the drill hole. A large round bur, shown here, on a drill inserted transorally, can also be used to perform countersinking.
ELLIS AND GHALI
FIGURE 7. Illustration demonstrating the importance of properly countersinking the screw hole. If inadequate or no countersinking is performed, 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.
Many steps in the application of the lag screw, when performed improperly, can lead to failure. The two most common errors made in lag screw fixation of angle fractures in our sample were the angulation of the screw and improper countersinking the screw hole. There is a tendency for the inexperienced surgeon to exaggerate the buccallingual angulation of the screw, resulting in a screw that engages the bone on the lingual aspect of the third molar area (Fig 2). This bone is of insufficient thickness and density to provide rigid fixation. One must resist the fear of impaling the inferior alveolar neurovascular bundle and angle the screw more posteriorly, exiting in the dense bone on the lingual aspect of the ramus. In our experience, damage to the inferior alveolar nerve is rare; only one patient
TIP OF 2.omm DRILL I
t FIGURE 8. Illustration showing tip of 2.0-mm centering drill guide. The working end has an outer diameter of 2.7 mm, which tits snugly into the 2.7-mm hole drilled into the distal segment. The inner diameter of the drill guide is 2.0 mm, perfectly centering the 2.0-mm drill within the 2.7-mm hole. The outer diameter of the shank of the drill guide is slightly larger than the head of a screw. When this instrument can easily slide into the 2.7-mm hole, countersinking has been adequate and the screw will not bind on adjacent bone during insertion.
had radiographic evidence of proximity between the screw and the mandibular canal. Improper countersinking of the hole has also led to problems. First, if the countersinking tool is allowed to penetrate too far along the screw hole, the cortical bone will be completely removed and the screw head will then rest on medullary bone. This bone offers insufficient rigidity to the screw head, resulting in nonrigid fixation. Secondly, if insufficient bone is removed anterior and medial to the screw hole, the 2.0-mm “centering” drill guide will not fit properly into the 2.7-mm hole, and the 2.0mm drill hole will then be directed too far to the lingual, engaging bone of insufficient density for rigid fixation. Thus, strict attention to detail is required for successful therapy using this technique. The value of experience with this technique can be highlighted by the fact that in the 10 cases where the staff surgeon was not present, 6 cases (60%) were determined to be of insufficient rigidity to permit active use of the mandible and supplemental fixation was necessary. On the other hand, in the 20 cases where the staff surgeon was present, 2 cases (10%) required supplemental fixation. Thus, in a training program where multiple residents are involved in treatment, constant reinforcement and guidance in the details of the technique are necessary. When the results of this study are considered, one must be cognizant of the fact that many residents were involved. Superior results, as demonstrated by Niederdellmann and Shetty,4 can be attained with more experience. The most disturbing result in this study was the incidence of postoperative infection/bone exposure. Seven patients (23%) developed some degree of
LAG SCREW FIXATION OF MANDIBULAR
postoperative wound infection or bone exposure, three that resolved with oral antibiotics, four that required intervention (13%). This is much higher than the 4% incidence reported by Niederdellmann and Shetty in 50 patients undergoing lag screw fixation of angle fractures.4 There are many possible
FIGURE 9. Illustration showing effect of inadequate countersinking an obliquely placed screw hole. The 2.0mm drill guide does not seat securely, causing the 2.0-mm drill to become malaligned with respect to the 2.7-mm hole.
reasons for this difference, not the least of which may be the nature of the populations of patients. Most of ours were extremely noncompliant, regularly missing their postoperative appointments and returning only when a problem was already wellestablished. Another probable reason for the differ-
FIGURE 10. Preoperative (A) and postoperative (B) radiographs of mandibular angle fracture where supplementation fixation with 2.0-mm bone plate was necessary to provide satisfactory immobility.
of lag screw
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ence between the results of these two studies is our inexperience. All of our cases were included in this study if they were available for recall and/or had adequate records, even our first cases. The results of our early cases were not as encouraging as those performed later. A difference between the management of our patients and that of Niederdellmann and Shetty is that none of our patients’ wounds were drained, whereas suction drains were placed in all of their patients. A further reason for the difference in incidence of infection between the two studies may be the difference in how teeth in the line of fracture were managed. Niederdellmann and Shetty recommend leaving teeth in the line of fracture unless they were grossly mobile or involved with pathology, and, if necessary, removing them later at the time of screw removal.4 They contend that maintenance of the teeth provides a broader surface area for adaptation of the bone fragments. In contrast, we routinely removed teeth in the line of fracture, as most of them had visible exposure of the apices, mobility, and/or pericoronitis. It may be that the removal of teeth reduced the rigidity of the repaired skeletal unit, leading to postoperative mobility and resultant infection. Of interest, however, was the development of an infection in one patient 7 weeks postoperatively while in MMF. When the screw was removed 1 week later, the fracture was found to be completely healed and a sequestrum was found in the wound. It is difficult to incriminate mobility of the fragments as the cause of the infection in this individual, because MMF was maintained since surgery. It should be noted that the infections in the patients were all very mild, consisting of minimal swelling, minimal purulence, and, predominately, of granulation tissue exiting from the wound. Because sequestra were noted in two of the four individuals in whom we removed screws (all via a transoral approach), we feel that an inflammatory reaction to devitalized cortical bone may have been the cause of the infections. Of interest is that the incidence of infection requiring intervention (13%) in the 30 patients is not much different than the incidence of infection reported by Dodson et al following conventional treatment with MMF (11.3%), and
is less than the incidence of infection when bone plates were used (17.9%).5 Besides the many advantages that rigid fixation of mandibular angle fractures offer, 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. Another advantage is the costs incurred; these are greatly diminished since the screws cost little compared to the cost of a bone plate. We now use lag screw fixation as our first choice for providing rigid internal fixation of mandibular angle fractures. There are 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 which relies upon compression of bone fragments. If the intervening bone is unstable due to comminution or is missing, compressing across this area 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 majority of fractures of the mandibular angle result in fragments that are large enough to permit the application of lag screw fixation. References 1. Ellis E, Moos K, El Attar A: Ten years of mandibular fractures: An analysis of 2,137 cases. Oral Surg 59:120, 1985 2. Niederdelimann H, Akuamoa-Boateng E, Uhlig G: Lagscrew osteosynthesis: A new procedure for treating fractures of the mandibular angle. J Oral Surg 39:938, 1981 3. Rajchel J, Ellis E, Fonseca RJ: The anatomical location of the mandibular canal: Its relationship to the sagittal ramus osteotomy. Int J Adult Orthod Orthogn Surg 1:37, 1986 4. Niederdellmann H, Shetty V: Solitary lag screw osteosynthesis in the treatment of fractures of the angle of the mandible: A retrospective study. Plast Reconstr Surg 80:68, 1987 5. Dodson TB, Perrott DH, Kaban LB, et al: Fixation of mandibular fractures: A comparative analysis of rigid internal fixation and standard fixation techniques. J Oral Maxillofat Surg 48:362,19!90