J Oral Maxillofac Surg 48:587-592,1990

A 3- Year Evaluation of Skeletal Stability of Mandibular Advancement With Rigid Fixation MICHAEL J. KIERL, DDS, MS,* RAM S. NANDA, DDS, MS, PHD,t AND G. FRANS CURRIER, DDS, MSD, MED:f: The postsurgical changes associated with mandibular advancements using the sagittal ramus osteotomy and rigid fixation were evaluated. This retrospective study was based on examination of lateral cephalometric radiographs of 19 individuals (16 females and 3 males) with a mean age of 26.6 years. These radiographs were evaluated presurgically, immediately postsurgery, and 3 years postsurgically (2 years, 9 months to 4 years, 5 months). The mean amount of sagittal surgical advancement was 6.7 ± 2.3 mm, and the mean amount of postsurgical relapse was 1.3 ± 2.0 rnrn, representing a 14% relapse of the original surgical advancement. However, individual variation in the amount and direction of movement of the mandible was found during the follow-up period. Postsurgical relapse was found to be related to the amount of surgical advancement. Linearregression analysis between these two variables resulted in an R2 value of 0.448. Fourteen of the subjects relapsed in the posterior direction, with 2 relapsing more than 50% of the surgical advancement. Five of the subjects moved further anteriorly, with 1 advancing as much as 50% more than the original advancement. The findings of this study suggest that mandibular advancement with the sagittal ramus osteotomy and rigid fixation does not provide consistently stable postsurgical results, However, when compared with previously reported relapse studies using nonrigid fixation techniques, rigid fixation yielded superior results.

Surgical treatment of mandibular retrognathia has steadily improved since the introduction of the sagittal ramus osteotomy by Trauner and Obwegeser in 1957. 1-5 Before 1974, the postsurgical stability of the

osseous segments in cases with surgical mandibular advancement was achieved through intraosseous and interdental wiring. The postsurgical relapse reported in these cases was substantive and not always predictable.v!" Also, patient discomfort was a serious problem because the mandible had to be immobilized from 6 to 8 weeks. With the advent of rigid fixation using titanium screws, patient discomfort has been overcome to a large extent. Early reports on postsurgical relapse after mandibular advancements using rigid fixation have yielded promising results.U'!" Some of these studies reported that the mandible actually moved farther anteriorly during the postsurgical follow-up period. 11- 13, 15 , 16 The results of these studies should be viewed with caution as they were based on the immediate postoperative radiographs with an occlusal splint still in place. The removal of the splint

Received from the Department of Orthodontics, University of Oklahoma, College of Dentistry, Oklahoma City, OK. * Former Graduate Resident; in private practice, Oklahoma City, OK. t Professor and Chairman. :j: Associate Professor. Based on a thesis submitted to faculty of Graduate Studies, University of Oklahoma, College of Dentistry, in partial fulfillment of the requirements for the degree of Master of Science. Address correspondence and reprint requests to Dr Nanda: Department of Orthodontics, PO Box 26901, 1001 Stanton L. Young Blvd, Oklahoma City, OK 73190. © 1990 American Association of Oral and Maxillofacial Surgeons 0278-2391/90/4806-0005$3,00/0

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MANDIBULAR ADVANCEMENT WITH RIGID FIXA nON

and subsequent autorotation would bring the mandible slightly forward giving erroneous comparisons of immediate postsurgical and follow-up radiographs. Kirkpatrick et al 14 did adjust for the presence of the occlusal splints and reported that postsurgical relapse was minimal. Their evaluation period was 6 months postsurgery. Only two studies evaluated postoperative periods longer than 12 months.P:" However, neither study accounted for the anterior translation of the mandible after the occlusal splint was removed. Long-term documentation of postsurgical changes following mandibular advancement procedures using the rigid fixation technique is lacking. The purpose of this study was to examine the longterm skeletal changes associated with internal rigid fixation in surgical mandibular advancements using the sagittal ramus osteotomy.

gery, and finally, approximately 3 years postsurgically. The final radiograph was taken, on an average, 3 years and 4 months following surgery with a range of 2 years, 9 months to 4 years, 5 months. All cephalometric radiographs were traced, and the following cephalometric landmarks were digitized. Points nasion (N), anterior nasal spine (ANS), point B, and menton (Me), were located according to Enlow. IS An additional point used was symphysis posterior (SymP), which is the most posterior point on the outline of the mandibular symphysis. The palatal plane was selected as a primary reference plane to measure the sagittal and vertical postsurgical movements of the mandible because no maxillary surgery was performed on any individual in the sample. Also, this comparison allowed suitable assessment of the presurgical and postsurgical relation of the mandibular landmarks to the maxilla. Perpendiculars were drawn to the palatal plane from N, SymP, Me, and B. These intersections to the palatal plane were referred to as N P , SymP P , Me P , and BP , respectively. The following cephalometric measurements were used (Fig 0: linear sagittal measurementsdistance from BP to N P (S-l), and distance from

Materials and Methods

Serial lateral cephalometric radiographs of 19 subjects who had surgical mandibular advancements using the bilateral sagittal ramus osteotomy and rigid fixation were evaluated in this study. The sample consisted of three white males and 16 white females, with a mean age of 26.6 years and a range of 14 to 47 years. The three men were aged 23,27, and 29 years. Three surgeons performed the operations, with one of the three present as either the primary surgeon or assisting surgeon on all 19 cases, thus ensuring that a similar technique was used in every patient. Modified bilateral sagittal ramus osteotomies were completed as described by Epker.? The rigid fixation was applied using the technique of Jeter et al 17 with some minor modifications. The segments were stabilized by a curved Kocher clamp placed on the medial and lateral aspects of the ramus. The condylar segment was positioned in the glenoid fossa by applying gentle posterior-superior pressure, and the Kocher clamp was tightened slowly. Three Synthes stainless steel screws, 2 mm in diameter, were placed with a Synthes screwdriver inserted through a transcutaneous puncture placed at the angle of the mandible. The most commonly used screw lengths were 10, 12, and 14 mm. The details of the surgical and rigid fixation techniques have been described by Kirkpatrick et al. 14 Six of the patients received genioplasties: 4 augmentations and 2 reductions. Similarly, 16 subjects received orthodontics before and after surgery. None of the subjects had any suprahyoid myotomies performed. The radiographs were taken within 3 weeks before surgery, within 1 week after sur-

5-2

Me FIGURE 1. Cephalometric linear measurements used to show surgical and postsurgical sagittal and vertical changes were sagirral distances: Sol BP to N P , and S-2 SymP P to N P ; vertical distances: V-I B to BP , V-2 Me to MeP , and V-3 SymP to SymP P •

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KIERL, NANDA, AND CURRIER

SymPP to N P (S-2). Linear vertical measurements-« distance from B to BP (V-I), distance from Me to Me P (V -2), and distance from SymP to SymP P (V-3). Each subject was wearing an interocclusal splint when the immediate postsurgical cephalometric radiograph was taken. The splint prevented the teeth from occluding in centric occlusion as the mandible was propped open. Therefore, it was necessary to make a template of the mandible and rotate it upward and forward around a midcondylar point until the maxillary and mandibular incisors were in contact. Subsequent cephalometric measurements were made from this corrected mandibular position. The analysis of error of tracings, location of landmarks, and measurements was made on 25 cephalometric radiographs selected randomly from the sample. Each cephalometric radiograph was traced and digitized. Two weeks later, the same cephalometric radiographs were traced and digitized again without access to the measurements of the first tracings. The absolute mean error and their standard deviations were calculated for each measurement. The error in reproducibility of each of the cephalometric measurements was within 0.5 mm. STATISTICAL ANALYSIS

The means and standard deviations were determined for each measurement at the three time intervals (Table I). The mean differences between the same measurements were then calculated for the presurgical and immediate postsurgical observations. Similarly, the mean differences were calculated for the immediate postsurgical and 3-year follow-up observations. Two-tailed t tests were performed to test if any statistically significant changes occurred during the interval between immediate postsurgery and the 3-year follow-up. Pearson correlation coefficients were performed to determine whether there was any significant skeletal pattern which predisposed to postsurgical in-

stability. A multiple linear regression analysis was done to determine if there was any relationship between the extent of postsurgical relapse and the following factors: I) the amount of initial surgical change, 2) sex of the subjects, 3) age of the subjects, 4) a concurrent genioplasty, or 5) the rendering of orthodontic treatment in conjunction with the surgical procedures. Finally, an analysis of covariance test was performed to determine if there was any significant relationship between the amount of postsurgical relapse and the surgeon performing the mandibular advancement surgery. The covariate was the amount of surgical advancement. For all statistical analysis, the level of significance was set as P < .05).

Results

The mean amount of surgical advancement was 6.65 mm as measured by the distance between B and N on the palatal plane (n P to N P) . This compared to a mean advancement of 6.78 mm as measured by the distance between SymP P and N P • Because of surgery, the lower face height measured as the distance from menton to the palatal plane increased 0.77 mm. Also, the distance from points B and SymP to the palatal plane increased an average of 1.32 mm and 1.42 mm, respectively, as a result of surgery (Table 2). The mean changes in mandibular position between immediately postsurgery and 3 years postsurgery are shown in Table 2. Sagittally, the distance from BP and SymP P to N P increased an average of 1.28 mm and 1.14 mm, respectively. This reflected a posterior movement of the mandible and was found to be statistically significant. Vertically, the mean changes in the measurement from B, menton, and SymP to the palatal plane were 0.06 mm, 0.66 mm, and 0.22 mm, respectively. These changes were found to be statistically insignificant (Table 2).

Table 1. Values for Each Measurement at the Three Intervals Measurement Sagittal (mm) B P to N P SymP P to NP Vertic al (mm) B to palatal plane Me to palatal plane SymP to palatal plane Values arc given as mean ± SO.

Presurgery

Immediate Postsurgery

3 Years Postsurgery

-11.61 :!: 6.25 - 22.83 :!: 6.69

-4.49 :!: 6.39 - 15.70 :!: 6.70

-6.29 :!: 5.90 -17.28 ± 6.42

41.86 :!: 4.86 63.98 :!: 4.53 56.79:!: 4.92

43.24 ± 4.37 64.83 ± 4.88 51.54 :!: 4.30

43.04 ± 4.08 65.32 ± 3.78 51.41 ± 3.99

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MANDIBULAR ADVANCEMENT WITH RIGID FIXATION

Table 2.

Surgical and Postsurgical Changes

Measurement Sagittal B P to N P SymP P to N P Vertical B to palatal plane Me to palatal plane SymP to palatal plane

Surgical Changes

Postsurgical Changes

6.65 ± 2.25 6.78 ± 2.57

- 1.28 ± 2.03" -1.14 ± 2.31"

1.32 ± 2.55 0.77 ± 2.47 1.42 ± 2.21

-0.06 ± 2.01 0.66 ± 2.02 0.22 ± 1.63

Values are given as mean ± SD. The statistical significance as done by the two-tailed t test is also shown. "P < .05.

Of the various factors evaluated, the multiple linear regression analysis indicated that the amount of surgical movement was the only variable that showed a significant relationship with postsurgical relapse. This was further confirmed by a simple linear regression analysis performed between these two variables. This analysis again showed that a relatively strong relationship existed between the amount of sagittal surgical advancement and the amount of postsurgical sagittal relapse. Similarly, a statistically significant relationship existed between the surgical vertical change and postsurgical vertical changes; however, it was not as strong. None of the Pearson correlation coefficients suggested a significant relationship between cephalometric measures taken before surgery and changes during the postsurgical follow-up period. The analysis of covariance performed to see if there was any relationship between the amount of postsurgical relapse and the surgeons performing the surgery indicated that there was no significant difference. Discussion

The main reference plane used in this study was the palatal plane. Several previously reported studies on postsurgical stability used a line constructed seven degrees above the SoN as the main reference plane. lI , 13, 16 A line constructed seven degrees off the SoN line would be subject to the variability of the vertical position of sella (S) in the cranial base. Hence, perpendicular lines constructed off of this line would not necessarily measure in a truly sagittal direction. Kirkpatrick et al 14 recommended using the palatal plane for a horizontal reference. The palatal plane for horizontal reference seemed advantageous for several reasons. First, several studies have noted that the palatal plane was stable in its position relative to the cranial base. 19-21 In addition, the palatal plane was found to be nearly parallel to Frankfort

horizontal in a majority of cases.F Second, it was felt that the palatal plane was closer to the area being studied than the SoN line. This would result in a higher degree of accuracy in measurements because of the shorter distances used. Third, Frankfort horizontal, ifused, has a greater variability due to difficulty in locating landmarks. On the other hand, the palatal plane could be drawn more consistently, minimizing the geometric bias in taking the horizontal and vertical measurements. Point B is regarded to sometimes change with orthodontic treatment. To confirm this with another point on the mandible, measurements from SymP were taken. Comparison with the changes in reference to SymP indicated that point B was a stable measure to check the sagittal and vertical movements of the mandible during the postsurgical follow-up period. Evaluation of the mean data for the 3-year followup period (Table 2) revealed relatively small changes. In the sagittal dimension, the mean relapse was 1.28 mrn, or 14% of the original surgical advancement. These observations of the mean data are in disagreement with two previously reported stuclies 15 , 16 that had longer than a 6- to 12-month postoperative follow-up period. These investigators reported a mean postsurgical change in a further anterior direction. This difference may be related to the fact that they did not compensate for the presence of the splint in the immediate postsurgical radiographs. Hence, the autorotation of the mandible caused by removal of the splint would result in a relative anterior displacement of the mandible. Failure to take this into consideration would render all future measurements of postsurgical relapse of mandibular advancements subject to error. The mean surgical vertical increase was approximately 1 mm (Table I). It was felt, with the exception of a few individual cases, that the vertical dimension did not increase a great deal due to the preoperative orthodontics which leveled the occlusal plane. However, there were individual cases in which the vertical dimension increased as much as 6.2 mm and decreased as much as 4.3 mm, which were averaged in with the rest of the sample. The mean data for the 3-year follow-up suggested that the mandibular advancement using the sagittal ramus osteotomy and rigid fixation appeared to be a relatively stable procedure. However, the individual data (Fig 2) indicated that there was considerable variability in the amount of postsurgical change. Fourteen subjects in the sample experienced relapse; the largest noticed was 5.5 mm with a to-mm mandibular advancement. Two patients experienced relapse to the extent of over 50%; 3

591

KIERL, NANDA, AND CURRIER

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(MILLIMETERS)

FIGURE 2. Surgical mandibular advancement and the amount of movement of the mandible as measured by BP to N P during the follow-up period is shown as the black bar. The changes are rank ordered from the largest to the smallest surgical sagittal movement.

subjects relapsed from 35% to 50%; 4 subjects showed relapse between 20% to 35%, and 5 subjects experienced less than 20% relapse. It was interesting to note that in 4 subjects, the mandible moved farther anteriorly from its immediate postsurgical position. In I of these subjects, it was as much as 50% more than the original surgical movement. In all 4 patients that showed further anterior movement of the mandible, the surgical movement was less than 5 mm. The remaining 6 subjects showed less than 0.5 mm change during the 3-year follow-up period. It appears from the results of the study that on a long-term basis the stability of the mandibular advancement procedure with rigid fixation yields variable results. Nearly one half of the sample had over 20% relapse, and a fourth of the sample showed further anterior movement of the mandible. Kirkpatrick et al,14 from their study of 6 months follow-up of mandibular advancement found only 0.42 mm, or 8% relapse. Many of the patients included in this study are the same patients. The long-

term appraisal (over 3 years) has indicated that the stability of mandibular advancements cannot be predicted consistently. Compared with previously reported studies'

A 3-year evaluation of skeletal stability of mandibular advancement with rigid fixation.

The postsurgical changes associated with mandibular advancements using the sagittal ramus osteotomy and rigid fixation were evaluated. This retrospect...
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