Flap design and the LeFort III osteotomy: Blood flow investigation

J Oral Maxillofac 41314-321.

Surg

1983

Flap Design and the LeFort Ill Osteo tomy: Blood GERALD J. WITTENBERG,

Flow Investigation DMD, MS, AND MAURICE W. MEYER, DDS, PHD

The effect on local blood flow of flap design in a LeFort III osteotomy was examined in this study. The radioactive microsphere technique was used to make serial flow determinations in two groups of macaque monkeys. The use of seven skin and mucosal incisions was compared with a coronal flap procedure. Significant blood flow reductions to the midface segment were measured when a coronal incision was the sole access in performance of the osteotomies. The findings indicate that the multiple incision approach is more biologically sound than the coronal incision approach in the LeFort Ill osteotomy. Important information about the surgical techniques can be determined from the data and applied to a more successful performance of the LeFort III osteotomy.

Clinical Background

Various surgical techniques have been used to treat craniofacial anomalies. In particular, the LeFort III osteotomy is used for the treatment of orbitofacial deformities associated with Crouzon’s disease and Apert’s syndrome as well as for specific traumatic midface deformities. Satisfactory results based on clinical evaluation have been reported, although substantial complications related to tissue vascularity have also been reported. A blood flow investigation to provide a better understanding of the biologic basis of the LeFort III osteotomy has not, to our knowledge, been previously done. This study quantitated blood flow to specific extracranial tissues when a LeFort III osteotomy was accomplished by either multiple facial incisions or the single coronal incision approach. A comparison of these two methods helped identify which approach causes a greater disturbance of local blood flow. The radioactive microsphere method, which has previously been used to assess the effect of other surgical techniques,lP3 was also used in this study.

This investigation represents an evaluation of local blood flow after a LeFort III osteotomy. A brief review of this procedure will provide a basis for understanding the experimental design and implications of the results. The LeFort III osteotomy is based on the original description of facial fracture by Rene LeFort in 1901. He examined the effect of blunt trauma to the faces of cadavers in order to determine “linea minoris resistentiae” (lines of least resistance) along which the facial bones would predictably break. His observations were not clinically applied until 1950, when Gillies attempted to correct a craniofacial anomaly by a midface osteotomy. Subsequently, TessieP” established the basis for craniofacial surgery and described procedures for the correction of orbital hypertelorism, craniostenosis with midface hypoplasia, and traumatic deformities of the midface. He also was the first to describe an intracranial approach for use in craniofacial surgery. LeFort III osteotomies were subsequently combined with frontal bone advancements, hypertelorism corrections, and frontal bone remodeling procedures as required in the correction of Apert’s syndrome. Tessier7zg accomplished a dysjunction osteotomy using classic LeFort III fracture lines within the orbit with multiple extraorbital modifications (Fig. 1). These modifications included a sagittal splitting of the lateral orbital wall, a step oste-

Received from the Department of Oral and Maxillofacial Surgery, School of Dentistry and Department of Physiology, University of Minnesota, Minneapolis, Minnesota. Supported by NIDR Grant No. DE02212. Presented in part at the Annual Session of the American Association for Dental Research, March 20-23, 1980, Los Angeles, California. Address correspondence and reprint requests to Dr. Meyer: Department of Physiology, 6-255 Milkrd Hall, University of Minnesota, Minneapolis, MN 55455

314

WITTENBERG

AND

MEYER

FIGURE 1. Various approaches that have been suggested for accomplishing the LeFort III osteotomy. Combined modified LeFort II1 and LeFort osteotomy, after Obwegeser. C. Modified with sagittal splitting step osteotomy of the zygoma. D. Tripartite osteotomy of the midface after converse.

otomy of the malar bone, a “keel-shaped” frontonasal osteotomy, and a spur osteotomy at the lateral orbital rim. Other workers have also contributed to technical advancements in midfacial surgery at the LeFort III level. ObwegeseP added a variation in the treatment of midface hypoplasia by combining a LeFort III osteotomy with a LeFort I osteotomy (Fig. 1). This allowed correction of the occlusion

FIGURE a LeFort

2. Various sites for soft tissue incisions III osteotomy.

to accomplish

A. According of the lateral

to Tessier. B, orbital rim and

by the LeFort I osteotomy and correction of the orbital deformity by the LeFort III procedure. Converse” introduced a tripartite osteotomy (Fig. 1) for increased flexibility and selectivity in treatment planning of orbitofacial anomalies. His design allowed for differential mobilization of a central nasomaxillary segment and two lateral orbitozygomatic segments. The sites of soft tissue incisions used for exposure of the osteotomy sites to perform a craniofacial dysjunction osteotomy have often varied.‘,7.Y,1c’.1z1” Generally, the approaches can be grouped into the multiple incision type and the single coronal incision type, both of which can involve intraoral posterior vestibular incisions for access to the pterygomaxillary junction (Fig. 2). The intraoral incisions have recently been avoided to reduce contamination. The multiple incision approach can include any combination of nasal, lateral orbital, infraorbital, and zygomatic incisions, with further variations on the exact design and positioning of each incision. Tessier” advocated the use of a bitemporal or coronal flap for improved exposure of the orbital roof, the lateral orbital wall down to the sphenomaxillary fissure, and the frontonasal angle and medial orbital wall. He believed that this approach provided better control of the symmetry of operation. The coronal flap replaced the nasal and lateral canthal incisions, although Tessier recommended continued use of the infraorbital incision, which he later modified to a conjunctional approach.14 Subsequently, craniofacial surgeons have performed the entire LeFort III osteotomy via the coronal flap alone. The pterygomaxillary junction

316

FLAP DESIGN AND LEFORT III OSTEOTOMY

FIGURE 3. Leff, Frontal center, lateral,and righr, inferior views of LeFort III osteotomy sites in the

macaque monkey.

osteotomy can be accomplished via the coronal flap without grossly endangering the internal maxillary artery, and the infraorbital incision can be avoided because the orbital floor osteotomy can be made from a combined medial and lateral orbital approach. The description of areas of exposure for the various styles by others6,15*16provide the basis for the incisions selected in this study. Materials and Methods GENERAL

PROCEDURES

The experimental groups consisted of ten macaque monkeys, six in Group I and four in Group II, with a weight range of 5 to 14 kg. One week before surgery, each animal underwent phlebotomy so that blood could be obtained for autotransfusion during surgery. Anesthesia at the time of surgery was induced with ketamine and maintained with incremental doses of sodium pentobarbital, with the animal ventilated to obtain a Pace, of 35 to 40 mm Hg. Cannulations of the right and left femoral arteries and left femoral vein were performed for blood pressure monitoring and arterial gas sampling, reference blood sampling, and anesthetic and fluid injections. For microsphere injections, the right axillary artery was cannulated and a catheter advanced to the left ventricle in eight animals. In two animals, a thoracotomy was done and a pulmonary vein was cannulated. The catheter was advanced to the left atrium and the thoracotomies closed before the microspheres were injected. A continuous recording of blood pressure and heart rate was made in all experiments, and arterial blood gases were intermittently evaluated to aid in maintaining animal stability. Prior to the LeFort III osteotomy a measured amount of microspheres (15 p) labeled with cerium 141 was injected for baseline determinations. In Group I animals, seven skin and mucosal incisions were used for access, whereas in Group II, a single coronal incision was done. Blood loss was estimated from weighed sponges and hematocrit determinations of aspirated

fluid. Approximately 30 minutes after surgery, a measured amount of scandium 46 labeled microspheres (15 p) was injected. Animals were then killed with saturated KCl, and specific tissues were sampled for determining their radioactivity. SURGICAL

PROCEDURES

The design of the LeFort III osteotomy was similar in the two groups (Fig. 3). Anatomically, the line of osteotomy crossed the frontonasal junction, descended the medial orbital wall posteriorly to the lacrimal fossa, and crossed the orbital floor to reach the inferior orbital fissure. The osteotomy line then traversed the lateral orbital wall to a point slightly superior to the frontomalar suture. The zygomatic arch was divided in the middle of the arch, and the pterygomaxillary junction was separated. These osteotomies were accomplished bilaterally, by use of rotating cutting instruments and hand osteotomes. The midline nasal structures were sectioned with a chisel introduced through the frontonasal osteotomy. Leverage was applied at various sites to separate the midface from the cranial base, and the midface segment was then mobilized extensively to stretch the tissues and imitate an advancement situation. Hemostasis was obtained and skin closure performed. For Group I, the seven skin and mucosal incisions included bilateral lateral brow, zygomatic, and intraoral incisions combined with a single vertical nasal incision (Fig. 4). Access was very good in all instances, the orbital floor osteotomy being accomplished through the nasal and lateral brow incisions. For Group II, the bitemporal incision was the sole access to the site of the LeFort III osteotomy (Fig. 4). Good access to all osteotomy sites was obtained. Of particular note, the pterygomaxillary junction was separated from a superolateral approach without complication, and a complete separation of the oral cavity from the midface operative sites was achieved. The orbital floor was approached from a medial and lateral direction.

WITTENBERG

AND MEYER

BLOOD

FLOW DETERMINATIONS

The use of radioactive labeled microspheres to quantitate regional blood flow is termed the particle distribution method. The technique has been extensively evaluated.‘7P”’ The validity of the method depends upon various assumptions, which involve the application of the Fick principle to measure blood flow by some suitable tracer. If the venous concentration of an injected tracer is assumed to remain at 0, then the tracer (e.g., microspheres) must be completely trapped during one circulation. The average arterial concentration time curve must be the same for all organs and tissues, and the microspheres must be distributed according to flow. Thus, to measure tissue blood flow, we obtain a measurement of some other flow. This flow has been termed reference flow. By withdrawing arterial blood before, during, and after the injection of the microspheres, the withdrawal time is recorded and the concentration of each isotope can be determined. The product of these two variables represents the average concentration time curve, assuming that microspheres are uniformally mixed to obtain a representative arterial sample. By determining the weight of the sample, all blood flows can be expressed as flow per gram of tissue. Since the total number of microspheres (or total radioactivity) injected was measured, it is possible to calculate the cardiac output and cardiac index (cardiac output per kg body weight). The mean and standard error were calculated for blood flow to each tissue. Subsequent comparison of preoperative and postoperative results was done using Student’s paired t test with or without prior logarithmic transformation. A nonparametric analysis was also applied to assess the significance of any differences by using the nonparametric sign test. Results

Generally, the preoperative cardiovascular status and blood flow to tissues of concern in Group I (multiple incisions) and Group II (coronal incision) were similar. However, changes in cardiovascular status and local blood flow were observed at 30 minutes after the LeFort III procedure. The average cardiac index (ml/min/kg) decreased from 118 to 104, or 12%) for Group I animals, but decreased from 94 to 73, or 21%, for animals in Group II. The average blood loss was 43 ml in Group I, which represented 7.8% of the average animal’s blood volume, whereas Group II animals lost an average of 114 ml. or 16.4% of the average animal’s blood volume.

FIGURE4. Completed LeFort III osteotomies by the multiple incision technique (Group I) (above) and the coronal incision technique (Group II) (h&w).

The average blood flow to specific tissues in animals of both groups is presented in Tables 1 and 2. Blood flow to the maxillary alveolar mucosal tissue, which was sampled in the region of the posterior access incision, increased 175% after the osteotomy. The soft palate tissue also showed an increase flow of 29%. Both changes were statistically significant (P < .05), as was the 20% decrease in blood flow to maxillary skin. The changes calculated for blood flow to the palatal mucosa and maxillary attached gingiva were not statistically significant. Soft tissue flow changes in Group II animals were significant at a P value less than 0.05 only in the anterior palatal and nasal mucosa. Blood flow to the posterior palatal mucosa decreased 83%, but the P value was 0.06 rather than 0.05 or less. Flow to the maxillary alveolar mucosa decreased 74%

318

FLAP DESIGN AND LEFORT III OSTEOTOMY

Table 1. Average Blood Flow (ml/min/g f SLY) to Soft and Bony Tissues Before and 30 Minutes After a LeFort Ill Osteotomy: Multiple Incisions (Group I) Tissue Soft

After

tissues

Maxillary alveolar mucosa Maxillary skin Maxillary attached gingiva Soft palate Nasal mucosa and concha Anterior palate mucosa Posterior palatal mucosa Eye Bony

Before

.20 .lO .32 .31 .69 .lS .19 .72

2 * 2 ? ? ? + ?

.03 .03 .08 .07 .15 .06 .05 .26

.55

k

.08 .39 .40 .25 .lO .14 .54

+ + 2 5 * * +

.lO .02 .12 .08 .ll .os .os .13

tissues

Proximal to osteotomy site Frontonasal Zygomatic Frontomalar Distal to osteotomized site Nasal Zygomatic Frontomalar Vomer Midface segment Maxillary Alveolar Anterior Palate Posterior Palate

(P = .06), in contrast to the increased

flow in Group I animals. The eye tissue was specifically sampled for evaluation of the effects of the orbital manipulation associated with LeFort III osteotomies. Significant changes in blood flow to the eye tissue samples were not observed for either group. The changes in blood flow to the bone proximal to the osteotomy for Group I were variable (Table l), but the average decrease was 50%. In three of the six animals, no change occurred; therefore, the P value was ~0.05. However, in Group II, blood flow decreased significantly, averaging 83% (Table 2). Significant decreases in flow to the lateral orbital rim and nasal bones distal to the osteotomies were observed in both groups, with greater percentage decreases seen in the coronal incision group (71% vs 90%, respectively). The calculations showed a decrease in flow to the vomer in both groups. The flow to the zygomatic arch remained relatively unchanged on either side of the osteotomy. The blood flow to bones on the mobilized midface segment was altered dramatically in the coronal incision group. An overall average of 85% flow reduction in Group II was calculated as opposed to 29% in Group I animals. Statistically, only the flow reductions in Group II were significant. Blood flow to the maxillary alveolar bone in Group I decreased 17%, vs 81% in Group II, and the maxillary bone flow decreased 31% in Group I vs 85% in Group II.

.08 ? .02 .12 * .03 .08 ? .03

.04 + .Ol .ll + .02 .04 c .Ol

.I7 .07 .07 .25

* 2 * ”

.04 .Ol .Ol .06

.06 .07 .02 .06

* + 5 2

.02 .Ol .Ol .Ol

.16 .12 .I2 .12

+ 2 r -t

.03 .03 .05 .03

.I1 .lO .08 .08

+ 2 + ?

.02 .03 .03 .02

Blood flow to the anterior and posterior regions of the palatal bone decreased an average of 86% in the coronal incision group, which was consistent with the previously noted 86% decrease in flow tc the soft tissue to the same region. Discussion

The surgical management of patients with craniofacial anomalies is a complex problem, requiring a detailed understanding of specific anatomic and functional characteristics. A multidisciplinary approach is essential, and continual evaluation and documentation are necessary for assessing a patient’s progress and for projecting treatment of patients with similar deformities. No single surgical procedure can achieve complete correction of major craniofacial deformities. The LeFort III osteotomy, however, is a major component is the reconstruction of orbitofacial deformities associated with two craniofacial anomalies-Crouzon’s disease and Apert’s syndrome. It is frequently used at major craniofacial surgical centers, with many published reports detailing technique6 and describing related complications. 13,22-26This extensive procedure separates the skeletal components of the midface from the cranial base, thereby allowing a repositioning of the midfacial structures to accomplish esthetic and functional goals. Various complica-

WITTENBERG

319

AND MEYER

Table 2. Average Blood Flow (ml/min/g SW) to Soft and Bony Tissues Before and 30 Minutes After a LeFort III Osteotomy: Coronal Incision (Group II) Tissue Sofi

Before

After

tissues

Maxillary alveolar mucosa Maxillary skin Maxillary attached gingiva Soft palate Nasal mucosa and concha Anterior palate mucosa Posterior palatal mucosa Eye

.56 .13 .84 .27 .99 .54 .61 .89

2 + 2 t * + + t

.36 .06 .31 .I0 .35 .28 .26 .I4

.I5 .05 .35 .I8 .13 .06 .I1 .63

-t + i+ !I ? i2

.03 .Ol .I1 .06 .05 .03 .06 .23

EO/lJ~fi.\srrr.\

Proximal to osteotomy site Frontonasal Zygomatic Frontomalar Distal to osteotomized site Nasal Zygomatic Frontomalar Vomer Midface segment Maxillary Alveolar Anterior Palate Posterior Palate

tions include hemorrhage,~,‘“.?7,‘X blindness,23 premaxillary necrosis,‘” and death.2”*2” In this study two separate approaches were used to accomplish a LeFort III osteotomy. To provide a biologic basis for the procedure, the blood flow was determined in 36 extracranial tissues. This information could identify which approach maintains a better vascular supply and consequently an improved tissue viability. The design of the LeFort III procedure was selected to correspond with designs currently in clinical use and also meet specific requirements for tissue sampling for use with the radioactive microsphere technique. The locations of the experimental soft tissue incisions corresponded with those used in humans;4*ti.SJ0 however, the seven incisions did not include any in the infraorbital region. The experimental results indicated that the cardiovascular parameters varied only to a minor degree between the animal groups, and a comparison is therefore qualified. The particle distribution method has been extensively evaluated.1-3J-“1 The serial blood flow determinations using two differently labeled microspheres caused no measurable detrimental effect on hemodynamics. The accuracy of the blood flow value is dependent upon the number of microspheres in each tissue sample.lX Various bony tissues contained less than the desired quantity of microspheres, because of tissue size,

.07 * .O? .lO L .O? .07 ? .02

.02 t ,002

.20 .09 .09 .?I

.I1 + .04 .Ol ? ,002

* 2 5 t

.05 .O? .O? .07

.04 .07 .Ol .04

2 + i ?

.Ol .03 ,003 .Ol

.37 2 .16? .46 2 .39 t

.I? .OS .19 .I2

.06 .03 .06 .06

+- .Ol t .01 t .Ol t .Ol

low resting blood flow, or reduced postosteotomy blood flow. Despite the reduced accuracy of the flow to some tissues, the magnitude of the change can still be significant. The results support the hypothesis that the coronal flap causes a greater disturbance of blood flow to the midface segment than the multiple incision approach (Fig. 5). The significant decrease in flow to the frontomalar and frontonasal bones above the osteotomy sites in Group II animals emphasizes the effect of the more extensive soft tissue coronal flap. In both groups, the bone subadjacent to the osteotomies had similarily decreased flows. A most significant finding is the overall average decrease in blood flow of 85% to the mobilized midface bony tissues with the coronal flap approach. This is contrasted with a statistically insignificant decrease in flow averaging 29% to the same tissues when a multiple incision approach was used. This decrease was statistically insignificant because of variability among the animals. Further, the flow to the palatal soft tissues averaged 86% and 30% for Group II and Group I, respectively. This also suggests a great disturbance of blood flow in the midface region when the coronal flap approach is used. The effect of decreases in flow 30 minutes postosteotomy on subsequent healing can only be postulated. Tissues that remain significantly unaltered by the surgery are not likely to be adversely af-

320

FIGURE 5. Areas of significant decrease in blood flow as shown by shaded portions. Lefr. Group I (multiple incisions). Right, Group II (coronal incision).

fected subsequently unless unusual complications develop. A major region of reported infectionsz4rz5 associated with LeFort III osteotomies is the infraorbital and anterior maxillary areas, where significant flow reductions were observed in the coronal incision group. The nose and paranasal structures are often cited as the source of the infective process, and many of the infections reported clinically have been associated with the multiple incision approach. However, the frontonasal region is not often a reported site of infection, although it too shares the hazard of contamination from the nasal mucosa. The significant decrease in blood flow in the anterior maxillary region observed with the coronal flap approach may further endanger the tissue viability so much that an infective process could supervene in the area. Further, bone grafts that require early reestablishment of blood supply to the surrounding tissues are often placed in the very sites where there was reduced flow, perhaps therefore contributing to a higher rate of complications. The addition of an infraorbital incision to the coronal incision can further reduce local blood flow. In view of the experimental results obtained, a limited soft tissue dissection in the infraorbital region, and performance of the orbital floor osteotomy via a combined superior medial and superior lateral approach, may be indicated to aid subsequent healing. Certainly, the relative absence of vital structures inferior to the thin orbital floor and the general lack of requirement for bone grafting of the floor support this idea should the surgeon elect not to perform a step osteotomy of the malar bone. Surgeons have often advised maximal muscle and soft tissue stripping in many regions to reduce the surgical relapse, although this technique may represent an even greater infringement on the blood flow to the mobilized skeletal structures. The use of combined LeFort III and LeFort I

FLAP DESIGN AND LEFORT III OSTEOTOMY

osteotomies at a single operation to correct certain orbitofacial deformities and dentoskeletal malrelationships simultaneously has been recommended.‘” The experimental results indicate that in these instances, a multiple incision approach may be preferred, as evidenced by the palatal tissue blood flows. The 86% decrease in palatal soft tissue flow combined with the 87% decrease in flow to palatal bone in the coronal incision group would indicate a greater risk to the combined procedures when the LeFort III is performed via a coronal flap. The correction of craniofacial deformities by use of a LeFort III osteotomy requires a certain degree of orbital tissue manipulation. Serious functional impairments of the eye due to optic nerve damage need not be caused by direct nerve damage but may result from hemorrhage at the orbital apex.15 Furthermore, traction on the eyeball may produce sufficient ischemia to cause permanent visual damage. Unilateral blindnessz3 from retraction and exposure keratitis with cornea1 opacity2” are the most serious reported ophthalmic complications. The blood flow to the eye tissues, as measured experimentally, remained significantly unaltered with both the multiple incision and coronal incision approaches. The avoidance, therefore, of an infraorbital incision does not seem to cause any undue trauma to the globe, as determined by measurement of blood flow. The result, however, cannot exclude the possibility of a temporary arterial occlusion during the operative procedure. The experimentally determined blood flows to the extracranial tissues prior to surgery correlate well with previously reported results obtained with the microsphere technique. 2,3 The flow changes observed at 30 minutes yielded quite low blood flow rates to certain bone tissues. However, it remains in doubt whether the observed decrease in flow jeapordizes the local tissue viability. Previous investigations of LeFort I osteotomies examined longitudinally with microangiographic and histological techniques in comparison with quantitative studies using the particle distribution technique suggest that the low blood flows are transient.2 Healing with revascularization subsequently occurred with no tissue loss. However, the microangiographic technique has failed to identify obvious tissue necrosis in certain experiments. 3o No microangiographic studies of the LeFort III osteotomy have been performed to date. Indeed, loss of tissue is unusual with clinically performed LeFort III osteotomies;24*25 yet, the results reported in the current study indicate that appropriate attention should be directed to the maintenance of an adequate soft tissue pedicle if the coronal flap is used to accomplish the craniofacial dysjunction osteotomy.

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