Craniomaxillofacial Reconstructive and Corrective Bone Surgery - part 9 potx

51. Genioplasty Techniques and Considerations for Rigid Internal Fixation 625 a c b d FIGURE 51.3 Clinical example of passive genioplasty. Presurgical and postsurgical photographs of a 22-year-old man with Angle class II/1 (deep bite) corrected by surgical advancement of the mandible (bi- lateral sagittal split osteotomy). Note the improvement of the chin position, lengthening of the anterior height, and stretching of the in- ferior labial fold. (a) Presurgical frontal view. (b) Presurgical in pro- file. (c) Postsurgical frontal view. (d) Postsurgical in profile. 626 F.H.M. Kroon a c d b Classifications for genioplasties are most practical if they are related either to the direction of the change in position of the chin (Table 51.1) or to the proposed clinical change in ap- pearance (Table 51.2). Prediction Measurements Measurements for prediction can be drawn on lateral cephalo- metric radiograph tracings. This method gives acceptable and sufficient information about the surgical possibilities in the hard tissue and the clinical effect at the site of the soft tis- sue. 6,16,17 In recent years, three-dimensional computerized hard- and soft-tissue prediction programs have become available. 18 After analysis of the lateral cephalometric x-ray, the re- quired transposition of the bony chin can be drawn and mea- sured (Figure 51.5). To have a controlled clinical prediction, it is wise to correlate the drawing to the position of the lower incisor. An equilateral rhomboid parallelogram can be con- structed by drawing crosspoint X between the lower incisor line and an occlusal line connecting the tips of the molars, cuspids, and incisors. Parallel to this occlusal line, the base- line is drawn from where the incisor line crosses the inferior mandibular border (point Y). The length XY is used as mea- sure for the four sides of the parallelogram. The next step is to choose how to divide the angle between baseline and in- cisorline. In case of the bisector, the transposition effects in both the horizontal and vertical directions are of equal length. If the inclination is less steep (i.e., ␣ Ͻ ␤ ), the horizontal ef- fect will be greater than the vertical effect. If the inclination is steeper (i.e., ␣ Ͼ ␤ ), the vertical effect is bigger than the hor- izontal effect. Earl and Foster described an apparatus that can be used during surgery to maintain the orientation with the planned angle during bone sawing. Depending on the re- quired transposition, the angle of the inclination can be chosen and the horizontal and vertical coordinates can be measured. 19 In the case of asymmetry, an anteroposterior x-ray and a submentovertex x-ray should be taken and analyzed to mea- sure the discrepancies and to determine the extent of bony corrections. Several methods have been described. 20 Surgical Approach A genioplasty procedure can be performed completely intra- orally. Preferably, the mucosal incision lies in the nonattached gingiva deep enough in the vestibular sulcus to have enough soft tissue to close the incision afterwards. Laterally, the in- cision should be superior to the mental nerve. Generally, it is wise to first identify the mental foramen and preserve its nerve through a safe and correct orientation of the osteotomy. Inci- sions that extend further out in the labial part of the lateral vestibule tend to cross the fine branches of the mental nerve. The periosteum should always be kept attached to the frontal part of the chin to maintain sufficient vascular blood supply. The periosteum should be kept in good condition to 51. Genioplasty Techniques and Considerations for Rigid Internal Fixation 627 F IGURE 51.4 Clinical result of a passive genioplasty procedure to cor- rect a severe Angle class II/1 malocclusion. (a) Presurgical lateral x-ray. (b) Postsurgical situation after sagittal split procedure in con- junction with segmental intrusion of the lower cuspids and incisors. (c) Postsurgical situation after 6 months. Hardware removed except for the central lag screw. (d) Orthopantomogram to show the posi- tion of plates and screws. T ABLE 51.1 Classification for genioplasties related to the main direction of change in position of the chin. 1. Horizontal a. Backward b. Forward 2. Vertical a. Upward b. Downward 3. Lateral to correct asymmetry 4. Combinations TABLE 51.2 Classification for genioplasties related to the main clinical change in appearance. 1. Augmentation a. Horizontal b. Vertical 2. Reduction a. Horizontal b. Vertical 3. Correction of asymmetry 4. Combinations FIGURE 51.5 Line drawing of construction of parallelogram to ori- ent the preferable direction of osteotomy line and required transpo- sition of genial bone fragment. (Incisor line crosses occlusal line at point X and the inferior border at point Y. If ␣ ϭ ␤ , vertical and horizontal transpositions are of equal length. If ␣ Ͻ ␤ , the horizon- tal transposition increases. If ␣ Ͼ ␤ , the vertical transposition in- creases.) For further explanation see text. use for final closure procedures in layers. To achieve this type of closure, it can be helpful to split the periosteal and mu- cosal layers more extensively. Figure 51.6 shows traction mattress-sutures to step the periosteum directly to the bone. Complete degloving procedures are unnecessarily danger- ous and have lead to necrosis and infections. 21,22 Surgical Procedures After a straight full mucoperiosteal incision or after stepwise incisions and separation of mucosal and periosteal layers, the periosteum at both sides of the incision is elevated just enough to provide sufficient bone surface to carry out the bone cut. The frontal segment of the chinbone can always be left at- tached to the periosteum. With references to the position of the mental foramen, a sliding osteotomy can be carried out according to the chosen angle to the bone surface (related to the position of the lower incision). To indicate the exact location of a sliding osteotomy, some landmarks can be made with a small, round drill. The final cutting can be carried out with a thin saw blade. If a more complicated design is planned, as in rotation and reduction procedures, landmarks made by means of a small, round burr are even more important. Anteroposterior reduction that can- not be achieved by a sole sliding osteotomy and translation of the segment should be realized by an osteotomy. If neces- sary, such an osteotomy can be designed as a wedge to allow additional rotation of the frontal segment around a transverse axis. Figure 51.7 shows the clinical situation after removal of an intermediate bone segment. Note the relative thickness of the cortex suitable for fixation by means of plates and screws. The chinbone should never be reduced by simply cutting off a frontal segment. The reduction effect is minimal because of the lack of support in transposition of the soft tissues. More- over, due to the excision of the bone segment, the soft tissues are weakened in a very undesirable way. 23 Fixation Techniques Because plates and screws are available in an extensive vari- ety of sizes and configurations, the use of wire osteosynthe- sis has lost its justification as a fixation technique in genio- plasty procedures. Figure 51.8 shows the result of insufficient support and positioning of a genial segment fixed by wire os- teosynthesis. The locations of the wire osteosyntheses are quite the same if plate fixation is carried out (Figure 51.13g). Similar to the stabilization of segments and fragments in frac- ture treatment, 1,24 the technique of lag screw fixation is very useful and relatively easy to perform in genioplasty proce- dures. Precision in position and drilling procedures is essential. 25,26 Stable fixation by means of plates, screws, or a combina- tion of the two contributes to predictable surgical results re- garding positioning, avoids undesired resorption effects due to instability, and allows relative extensive distances of ad- vancements or transposition procedures. 628 F.H.M. Kroon FIGURE 51.6 Photograph of mattress-sutures to close in layers by stepping the periosteal layer directly to the bone surface; picture shows the situation just before tightening the sutures. F IGURE 51.7 (a) Frontal view of reduced chin area. (b) Frontal view of resected bone segment. Note the relative thickness of the cortical layers, suitable for proper stable fixation. a b Craniofacial osteotomy instrumentation sets usually con- tain four sizes of plates. The regular (mandibular) 2.4 system has screw diameters of 2.4 mm. Miniplate systems 2.0 and 1.5 have screw diameters of 2.0 and 1.5 mm, respectively, in- cluding additional 2.4-mm screws as “emergency screws.” Microplate systems 1.0 and 1.2 have screw diameters of 1.0 and 1.2 mm, respectively. Systems 2.0 and 1.5 are the most convenient and practical for fixation of genioplasty segments. The strength of the 2.0 screws is sufficient to stabilize segments using either three separate lag screws or a combination of one screw in the central part and miniplates or microplates at both sides. The feasibility of screws as the sole means of fixation, using either as a lag screw or a positioning screw as shown in Figure 51.9, depends entirely on the type and direction of the osteotomy line (Table 51.3). The use of the lag screw technique is only possible if enough holding power in the cortical layers can be achieved. If this cannot be realized, the transposition gap can better be bridged with plates with the preferred minimum of at least two monocortical screws on either side of the osteotomy line. The 2.4-mm size is usually suitable to achieve initial seg- ment stability. Infrequently, a 2.7-mm screw emergency will be required. Fixation Procedures Precise positioning of the genial segment is essential for a well-defined clinical result. A well-controlled sawing proce- dure results in an accurate translation of the planning and analysis to the clinical situation, and permits an exact trans- 51. Genioplasty Techniques and Considerations for Rigid Internal Fixation 629 a b FIGURE 51.8 Insufficient position and support of a reduced chin segment fixed by wire osteosyntheses. (a) Lateral skull x-ray. (b) Or- thopantomogram. position and fixation technique. Midline references should be marked on the bone segment. Even extraoral orientation on a line such as the Frankfurt horizontal can be very helpful. When introducing lag screws, the technical rules of prepa- ration should be strictly followed: 1. Preparation of the gliding hole in the genial segment. If necessary, gently adjust the cortical surface for an exact fit and avoid any sliding of the screwhead. 2. Prepare the opposite traction hole in the mandible using a centering drill guide to achieve coaxial preparation of the holes. 3. Measure the required screw length. 4. Pretap the traction hole, if a nonself-tapping screw is to be used. 5. Insert and position the screw. The need for pretapping is mainly determined by the thick- ness and the number of cortical layers to pass. Experimental work 27,28 has shown that length of the pathway in the cortex of more than 3 mm requires pretapping. Additionally, it is im- portant to realize that in case of using or passing through more cortical layers the length of the screw is critical and requires proper preparation of the drill holes. 630 F.H.M. Kroon a b c d e FIGURE 51.9 Photographs of (a) pre- and (b) postsurgical situation of a chin augmentation achieved by a sliding osteotomy according to the prediction described in Figure 51.5. (a) Presurgical situation. (b) Postsurgical situation. (c) Presurgical tracing. (d) Postsurgical tracing. (e) The combination of (c) and (d). Dotted lines are presur- gical. (Line drawings in (c,d,e) courtesy Dr. P.E. Swartberg) Rotation and Interposition of Bone Fragments Augmentation procedures sometimes need interposition of segmental fragments or additional bone transplants. Gener- ally, the technique of fixation of such configurations of ge- nioplasties is not different from the simpler sliding procedure. The position of the segments should be stabilized during the hole preparation procedure to achieve the planned clinical result. The space created in the vicinity of point B can easily be filled in with spongeous bone transplants or a cortical frag- ment from the osteotomy procedure can be used for that pur- pose. Preferably, stable fixation of such fragments should be realized by using the lag screw technique. Miniscrews 1.5- mm diameter or even the 1.0-mm microscrews can provide adequate stability. The surgical steps of such a procedure of slight rotation and interposition in a case of chin augmenta- tion is shown in Figure 51.10. The radiographic evidence of positioning and consolidation is shown in Figure 51.11. The clinical appearance is shown in Figure 51.12. Lateral defects at the inferior border can also be considered to be filled in with bone particles and eventually combined with artificial bone fragments (covered by resorbable membranes). Correc- tion of asymmetries should include thorough orientation of facial and dental midlines. Rigid fixation by means of lag screws, miniplates, or a combination, is even more important in these more complicated corrections. Wedge-type excisions and propeller-type segment inversions to correct asymmetries have been described. 20 Midline splits for widening may also be considered. Complications and Solutions Overdrilling of Holes In the case of overdrilling of holes, emergency screws that cor- respond to the planned type of screws should be available; that is, 1.2 (1.0), 1.5 (1.2), 2.0 (1.5), 2.4 (2.0), or 2.7 (2.4). If the proposed design of lag screws fails, monocortical fixation of well-adapted miniplates (or even microplates) should be the proper solution. During preparation of drill holes, careful cool- ing and rinsing procedures should be followed. Soft Tissue Closure With augmentation, inadequacy of soft tissues for closure in layers can be easily prevented by choosing a stepwise mu- cosal/periosteal incision and additional splitting of both lay- ers from each other before closing in layers. In the case of reduction, abundance of tissue could require shortening the soft tissue of the lower lip by reducing the buc- cal mucosa. Care must be taken in reapproximating the men- talis muscles, which at times may require bony suspension. 51. Genioplasty Techniques and Considerations for Rigid Internal Fixation 631 T ABLE 51.3 Preferable type of fixation and clinical effect of transposition of genial segment related to the inclination of the (sliding) osteotomy line to the incisor line and occlusal line (see Figure 51.5). Direction of Angulation of segmental Preferable type Type of genioplasty osteotomy line transposition Clinical effect of fixation A. Without bone reduction I. Parallel to a. Upward Vertical reduction Lag screw incisor line b. Downward Vertical augmentation Lag screw and/or miniplates II. Bisector a. Upward Vertical reduction ϩ horizontal augmentation Lag screw b. Downward Vertical augmentation ϩ horizontal reduction Miniplates III. Parallel to a. Forward Horizontal augmentation Miniplates occlusal line b. Backward Horizontal reduction Miniplates B. With segment excision I. Parallel to a. Upward Vertical ϩ horizontal reduction Lag screw incisor line b. Downward Vertical augmentation ϩ horizontal reduction Lag screw and/or miniplates c. No sliding Horizontal reduction Lag screw II. Bisector a. Upward Vertical reduction Lag screw b. Downward Vertical augmentation ϩ horizontal reduction Miniplates c. No sliding Horizontal reduction Lag screw III. Parallel to a. Forward Horizontal augmentation ϩ vertical reduction Miniplates occlusal line b. Backward Horizontal reduction ϩ vertical reduction Miniplates c. No sliding Vertical reduction Miniplates C. With segment interposition I. Parallel to a. Upward Horizontal augmentation ϩ vertical reduction Lag screw incisor line b. Downward Horizontal augmentation ϩ vertical augmentation Lag screw and miniplates c. No sliding Horizontal augmentation Lag screw II. Bisector a. Upward Horizontal augmentation ϩ vertical reduction Lag screw b. Downward Vertical augmentation Lag screw and miniplates c. No sliding Horizontal ϩ vertical augmentation Lag screw III. Parallel to a. Forward Horizontal ϩ vertical augmentation Miniplates occlusal line b. Backward Horizontal reduction ϩ vertical augmentation Miniplates c. No sliding Vertical augmentation Miniplates 632 F.H.M. Kroon a b c d FIGURE 51.10 Surgical steps of fixation of frontal genial segment, slightly rotated around a transverse axis. (a) Note the position of the mental nerve (see arrow). (b–d) Positioning of the 2.0 fixation lag screw and the fixation and stabilization of a cortical fragment to fill the gap at point B. 51. Genioplasty Techniques and Considerations for Rigid Internal Fixation 633 a c b d FIGURE 51.11 Lateral x-rays of the patient described in Figures 51.10 and 51.12. (a) Presurgical. (b) Direct postsurgical. (c) Three months postsurgical. (d) Consolidation after 15 months. No signs of resorption around screwheads (titanium screws). Wound Dehiscenses Wound dehiscense mostly occurs because of insufficient oral hygiene postoperatively or from a lack of temporary support by bandages. Reapplication of extraoral bandages and thor- ough cleaning instruction will solve these problems. Regular intensive dental hygiene should be advised and can be sup- ported by rinsing the mouth with salt water or chlorohexidine gluconate rinses. Infections To prevent infection, generally short prophylactic application of antibiotics (24 hours) should be sufficient. Infections, rarely occur, and most probably will be due to instability of the segments and loose hardware. Removal of loose hardware and reapplication of internal fixation is the treatment method of choice. 29 Only in the case of abscess formation is exten- sive empirical antibiotic therapy and culture and identifica- tion of the bacteria necessary. Nerve Damage The best solution to manage nerve damage is through pre- vention. Mucosal incision design superior to the mental fora- men avoids unneccesary division of small extensions of the mental nerve. Temporary hypoesthesia is expected in all cases, and the patient should be advised. Return of sensation of damaged mental nerves is very difficult to predict and should not be promised. Cosmetic Failures Patients’ final satisfaction with the cosmetic results can be a very delicate matter, especially when a genioplasty is done for cosmetic improvement only (see Figure 51.13). However, cosmetic changes that result from major facial corrections, such as extensive orthognathic surgery for functional reasons, also include risks for patient dissatisfaction. It has been pointed out that psychological aspects may play an important role as a predisposition to the development of jaw dysfunc- tion. 30 Preoperative attention to patient expectations and 634 F.H.M. Kroon a b FIGURE 51.12 Clinical photographs of the patient described in Fig- ures 51.10 and 51.11. (a) Presurgical. (b) Postsurgical after nose cor- rection (courtesy Dr. J.B. de Boer) and after chin augmentation. (c) Presurgical tracing. (d) Postsurgical tracing. (e) Combination of (c) and (d). Dotted line is presurgical. [(c,d,e,) Courtesy Dr. P.E. Swart- berg] [...]... Maxillofac Surg 199 2;50(2):1 19 123 Bähr W, Stoll P Pre-tapped and self-tapping screws in children’s mandibles A scanning electron microscopic examination of the implant beds Br J Oral Maxillofac Surg 199 1: 29 Phillips JH, Rahn BA Comparison of compression and torque of self-tapping and pretapped screws Plast Reconstruct Surg 198 9;83(3):447–456 Prein J, Beyer M Management of infection and nonunion in mandibular... with a 2-mm system Supplemental suspension wires were used with elastic traction between the maxillary and mandibular wires 1.5-mm Stabilization A 17-year-old female presented with apertognathia (3 mm) and horizontal mandibular excess After presurgical orthodontics, she underwent a one-piece impaction of 4-mm posterior with a 6-mm mandibular setback (Figure 52. 29) Twoand-one-half years after surgery, ... in Orthognathic and Reconstructive Surgery Vol 1 Philadelphia: WB Saunders; 199 2:523– 593 29 Van Sickels JE A comparative study of bicortical screws and suspension wires versus bicortical screws in large mandibular advancements J Oral Maxillofac Surg 199 1; 49: 1 293 –1 296 30 Hall HD, Chase DC, Paylor LG Evaluation and refinement of the intraoral vertical subcondylar osteotomy J Oral Surg 197 5;33:333–341... Phys Anthropol 195 8;16:213–234 8 Ricketts RM Perspectives in the clinical application of cephalometrics Angle Orthod 198 1;51:115–150 9 Sassouni VA A classification of skeletal facial types Am J Orthod 196 9;55:1 09 123 10 Solow B, Tallgren A Natural head position in standing subjects Acta Odontol Scand 197 1; 29: 591 –607 11 Steiner CC Cephalometrics for you and me Am J Orthod 195 3; 39: 7 29 12 Steiner CC The... J Oral Surg 197 7;35: 296 Noorman van der Dussen F, Egyedi P Premature aging of the face after orthognathic surgery J Craniomaxfac Surg 199 0;18: 335 Frodel JL Jr, Marentette LJ Lag screw fixation in the upper craniomaxillofacial skeleton Arch Otolaryngol Head Neck Surg 199 3;1 19( 3): 297 –304 Ellis E, Ghali GE Lag screw fixation of anterior mandibular fractures J Oral Maxillofac Surg 199 1; 49( 1):13–21 Ilg... maxillary excess (total facial height of 168 mm) and maxillary transverse deficiency and apertognathia, and horizontal mandibular excess Following presurgical orthodontics, he underwent a three-piece maxillary impaction with a differential movement (10-mm posterior, 4-mm anterior impaction) with a 5-mm BSSO setback (Figure 52.28) One -and- one-half years after surgery, there has been no change in his facial... J Oral Maxillofac Surg 199 2; 50:687– 690 38 Park HS, Ellis E, Fonseca RJ, Reynolds ST, Mayo KH A ret- 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 6 59 rospective study of advancement genioplasty Oral Surg Oral Med Oral Pathol 198 9;67:481–4 89 Van Sickels JE, Smith CV, Jones DL Hard and soft tissue predictability with advancement genioplasty Oral Surg Oral Med Oral Pathol 199 4;77:218–221 Wassamund... prognathism of the mandible corrected by vertical ramus osteotomy (a) Lateral x-ray presurgical (b) Lateral x-ray postsurgical (10 weeks) (c) Lateral x-ray postsurgical (4 years and 3 months) used as presurgical to chin surgery (d) Lateral x-ray postsurgical to genioplasty after 1 day (e) Lateral x-ray postsurgical (7 years and 7 weeks) after vertical ramus osteotomy, and (2 years and 9 months) after genioplasty... osteotomies, and arguably it is the most frequently performed maxillofacial corrective surgery It is used for mandibular advancements, setbacks, and asymmetry Each movement must be approached differently When the mandible is advanced, the arc of the mandible is enlarged 6 39 640 a b FIGURE 52.1 (a,b) Change in the arc of mandible with advancement and setback of the mandible (From Van Sickels, Jeter, and Aragon,43... have brought a major improvement of the feasibility and predictability of genioplasties by bone surgery References 1 Leonard MS The use of lag screws in mandibular fractures Otolaryngol Clin North Am 198 7;20(3):4 79 493 2 Spiessl B Internal Fixation of the Mandible A Manual of AO/ASIF Principles Berlin; Springer-Verlag; 198 9 3 McBride KL, Bell WH Chin surgery In: Bell WH, Proffit WR, White RP, eds Surgical . surgery. (d) Lateral x-ray postsurgical to genioplasty after 1 day. (e) Lateral x-ray postsurgical (7 years and 7 weeks) af- ter vertical ramus osteotomy, and (2 years and 9 months) after ge- nioplasty subjects. Acta Odontol Scand. 197 1; 29: 591 –607. 11. Steiner CC. Cephalometrics for you and me. Am J Orthod. 195 3; 39: 7 29. 12. Steiner CC. The use of cephalometrics as an aid to planning and assessing orthodontic. screws in mandibular fractures. Otolaryngol Clin North Am. 198 7;20(3):4 79 493 . 2. Spiessl B. Internal Fixation of the Mandible. A Manual of AO/ASIF Principles. Berlin; Springer-Verlag; 198 9. 3. McBride