Controversias en Cirugía Oral y Maxilofacial: Parte II

---

Sagital split ramus osteotomy of the mandible in orthognathic surgery
Osteotomía sagital de rama mandibular en cirugía ortognática

 

L.A. Quevedo Rojas

---

Abstract: Bilateral Sagittal Split Osteotomy represents the most frequent surgical procedure being used in Orthognathic Surgery. Since Obwegeser first described has been modified in design, extension and instrumentation. With a revision of the most important modifications, this paper describe the technique being used by the author. Advantages, disadvantages and probable complications are also mentioned. Key words: Sagital split osteotomy; Orthognathic surgery.

Resumen: La Osteotomía Sagital Bilateral de Rama Mandibular (OSBRM) representa la técnica más frecuentemente utilizada en Cirugía Ortognática. Desde su aparición ha sido modificada tanto en diseño, extensión e instrumentación. Se hace un recuento de algunas modificaciones y en esa perspectiva, se explica la técnica que el autor utiliza. Se revisan las ventajas, desventajas, y las posibles complicaciones intra y post operatorias con relación a la Técnica. Palabras clave: Osteotomía sagital; Cirugía ortognática.

---

Prof. Asociado Cirugía Bucal y Máxilo Facial. Facultad de Odontología, Univ. de Chile. Santiago de Chile, Chile

Correspondencia:
Av. Kennedy 5735. Torre Poniente
Oficina 407. Las Condes
Santiago, Chile

 

Introduction

Since Hugo Obwegeser described bilateral sagittal split ramus osteotomy (BSSROM) of the mandible in 1955,¹ there have been many modifications of this surgical procedure, which undoubtedly is one of the surgical techniques most often used in orthognathic surgery. The most important contributions and modifications have been made by Gregorio Dal Pont, who in 1961² suggested that the osteotomy be extended forward, then taken through the mandibular body to the height of the second and first molars, and from there, vertically downward to the basilar edge. This increased the contact surface, which theoretically improved and enhanced the versatility of the technique because it made possible all sorts of clockwise and counterclockwise rotations and forward and backward mandibular displacements. This was important at the time because this osteotomy was used to resolve many kinds of skeletal problems without resorting to maxillary surgery. (See Figures 1 and 2).

In February 1977, Bruce Epker³ published what may be the most significant modification of the technique, which made it much more versatile, predictable, and easy to perform. This modification eliminates the need to continue the cut to the posterior edge of the mandibular ramus, it is only necessary to bring it forward and up behind the Spix spine; the lower edge of the body must be approached as perpendicularly as possible and completely transected, to guide the surgical fracture through the lower alveolar canal. This can be done using osteotomes to split the ramus progressively and much less traumatically because it generally eliminates the need to use hammer and chisels. (see figure 3)

This allows the direct visualization and care of the dental nerve, increasing the predictability of the surgical fracture and shortening operating times.

In May 1977, Dr. WH Bell,⁴ who as the author of this article became the conceptual father of modern orthognathic surgery, established the biological bases of sagittal split ramal osteotomy. This enhanced the development of the technical modifications that in effect made it friendlier, less laborious, and less prone to complications. His study identified the recommended work areas for new techniques where the blood supply was ensured and potential suffering and complications could be prevented.

With technological advances and the appearance of the reciprocating surgical saw with an ad hoc design, Larry Wolford et al.⁵ published a modification that was designed to ensure that ramal splitting took place along the lower edge instead of the alveolar canal, extending the osteotomy along the edge itself. This increases the contact surface between parts and, in particular, provides a larger surface for segment fixation.

Thus, BSSROM evolved in design, extension, and instrumentation. These modifications definitely made it the friendly, predictable, biologically acceptable, and tremendously versatile technique that it now is. Arising from these key modifications, many others have appeared and the author has observed on several occasions that experienced surgeons adapt the technique to their own style. In fact, the author’s own technique is described below. This method was developed over the course of several years and it protects the mandibular nerve more since the techniques previously described usually involve handling the mandibular nerve to separate it from the work area, which inevitably results in different degrees of neurapraxia.

Description of the technique

The subperiosteal approach to the anterior edge of the ramus and retromolar trigone is the usual approach. To restrict the spitting of the internal face of the mandibular ramus to what is strictly necessary, imaginary reference triangles like those shown in the figures are identified. There are three of these triangles, the first of which can be represented by the area of third molar, if it has erupted. The third triangle corresponds to the coronoid process and is located at the junction of the base of the coronoid process with the vertex of the second triangle, where the Spix spine is found. It is recommended that this area be entered only to open the tunnel necessary to find the spine, work in the area, and place the separator that will protect the mandibular vasculonervous package during internal horizontal osteotomy (see  figures 4 to 7).

Osteotomy is performed with a reciprocating saw. For the medial horizontal cut, the saw should be placed about 5 mm above the Spix spine in order to enter with the saw at a 45° angle with respect to the medullary core and then continue directly along the anterior edge of the ramus. This cut must be complete from the anterior edge to just behind the spine and through the entire thickness of the medial cortex. The cut continues in a straight line that crosses the retromolar trigone and then goes outwards, continuing with an equally straight line along the external face of the mandibular body towards the lower rim, avoiding angular cuts. The full depth of the saw should enter the retromolar trigone zone from the beginning of the vertical line and perpendicularly. When the cut reaches the distal part of the last molar in the mouth, the saw should be withdrawn enough to avoid damaging the vasculonervous mandibular package. The angle should be more tangential to the bone as the cut progresses to the lateral wall of the mandibular body, where it should form an angle of approximately 50° with the basilar edge. 

When the saw reaches the basilar edge, it is inverted to cut the mandible upward, maintaining a 50° slant and making sure that the edge is completely cut, thus guiding the surgical fracture needed to split the ramus. Using the reciprocal saw in this way, the ramus can generally be split more easily and lateral to the alveolar canal, leaving the nerve, or at least its distal segment, in the canal, where we can avoid manipulating it. Once the rami are split, it is important to remember to separate the insertion of the pterygoid muscle from the medial face of the ramus, as Epker suggests, and to take care to avoid causes of neurological damage when realigning the fragments. (see  figures 8 to 13)

Rigid internal fixation has been an extraordinary advance in BSSROM. Even though many authors recommended avoiding the use of plates and/or screws to fix the segments in the early years, because it was thought that this would originate problems in the temporomandibular joints, reports in the literature and by specialists in the technique indicate that they are abandoning the use of wires in favor of rigid medial fixation with an increasing frequency. Whether plates and monocortical screws or bicortical screws are used, since both techniques adequately immobilize the segments (rigid fixation), particularly when securing the position of the mandibular condyle in the articular glenoid fossa, the technique must satisfy certain important requirements to prevent problems in the temporomandibular joint.

Indications

At present, we can certainly say that bilateral sagittal split ramal osteotomy of the mandible is indicated whenever skeletal mobilization of the mandibular ramus is required. This means that BSSROM is useful in cases requiring forward or backward repositioning of the mandible, to which any type or degree of rotation, whether clockwise or counterclockwise, can be added. It is also indicated for posterior vertical repositioning, as a complement to posterior intrusion of the maxillary in the case of bimaxillary surgery, or for the opposite movement, although this is less common due to biomechanical reasons. In a cross-sectional direction, it is the technique of choice for cases of mandibular asymmetry, in which the mandibular arc has to be moved forward on one side and backward on the other side.

Whenever a surgical technique is applied in different cases and situations, it must be adapted to the requirements of the case. This is especially important in cases in which BSSROM is used in asymmetrical jaw repositioning, in which the degree of divergence of the mandibular rami can cause unwanted rotation of the proximal segments, which may produce undesirable aesthetic results due to the asymmetry of the mandibular body or, what is worse, functional alterations of the temporomandibular joint.

Advantages of BSSROM

Among the many advantages of BSSROM when performed as described, the most noteworthy are 1) the versatility of its indications, 2) the possibility of using rigid internal fixation to join osteotomized fragments, which has innumerable advantages, and 3) the absence of surgical complications related to segment viability, segment stability, or bone healing.

Disadvantages of BSSROM

The disadvantages of the technique refer mainly to the demands of the technique. While it is not technically difficult to perform the bone cuts or separate the rami, ensuring the proper condylar position of each of the proximal mandibular segments requires special attention. The experience of the surgeon is the best guarantee against complications but it is unacceptable to gain experience by a process of trial and error. This is why we must insist that surgeons have sufficient training in the use of plates and screws before performing a BSSROM like the one described in this article, with rigid internal fixation. In addition, it is highly desirable that the surgeon be capable of managing surgical orthodontic planning, which involves the use of semi-adjustable articulators, techniques of neuromuscular deprogramming, and taking impressions in a relation to a central point. These skills are needed for planning, performing model surgery, and preparing surgical splints in relation to the mandibular center, which is the starting point of all planning and the best way to handle temporomandibular joints.

The details of the rigid fixation method or technique per se are beyond the scope of this article and surely will be the topic of a future publication.

Possible complications

The complications of BSSROM can be divided into intraoperative and postoperative complications. The intraoperative complications are attributable to the technique:

• Unwanted fractures. In any of the modifications of the technique, including the form used by the author, a fracture of the proximal segment of the external face of the ramus can occur. Such fractures are usually partial and leave a fragment of variable size with no connection to any soft or hard tissue pedicle. If the fracture is high and lateral to the alveolar canal, the proximal segment may remain joined to the dental arc and the surgeon will not notice that the mandibular condyle has slipped out of the glenoid fossa when placing the teeth in occlusion. This complication will almost certainly require immediate re-operation. It is always advisable to check the proximal and distal segments and the dissociation that should exist between them; segments should move freely with respect to each other.

• Damage to vasculonervous structures. This complication is also attributable to the technique and related to both ramal splitting and rigid internal fixation. With regard to the osteotomies and ramal splitting, this complication is becoming increasingly less frequent due to the modifications described. Nevertheless, in no case can it be claimed that neurapraxia of the inferior dental nerve can be avoided, which is what causes the disturbances in the sensitivity of the lower lip and chin that are known to everyone and are related to BSSROM. In an evaluation made by the author of 400 operated cases, the results were: neurosensorial disturbances in 70% of the patients. Of this 70%, 20% suffered anesthesia 10 days after surgery. The rest were variable percentages of hypoesthesia or hyperesthesia. In 50% of the patients who suffered sensitivity disturbances, these remitted completely within 3 months. The other half of the patients with persistent disturbances recovered gradually. Almost 5% (19 patients) had disturbances that persisted for more than 6 months. Eight (8) patients, representing 2% of the patients evaluated, had functional hypoesthesia lasting more than a year. For the author, functional hypoesthesia produces a reduced response to testing (touch, directional and two-point discrimination, and pain), but does not create any problem for the patient’s daily life. This evaluation was made before the technique described in this article was put into routine practice. Although we have seen better results, no adequate evaluation has been made to obtain firm evidence.

The following postoperative complications are attributable to the technique:

• Immediate postoperative malocclusion. Any occlusion different from that planned in the surgery of models must be considered a complication. This malocclusion may or may not be accompanied by malposition of the condyle in the mandibular glenoid fossa, or may even be due to it. If the cause of the malocclusion is condylar distraction, which is the most likely, the author recommends re-operation to reposition the proximal segments, as necessary. Otherwise, the functional stability of any short-term or intermediate-term treatment would be at risk. If occlusal disturbances coexist with an adequate condylar position, it is recommended that the orthodontist evaluate the possibility of performing dental mobilizations to achieve objective functional occlusion, which is no more than a mutely protected organic occlusion. If feasible, this is the route to take, even though it involves prolonging postoperative orthodontic treatment time.

• Delayed malocclusion. In this case we should think about the presence of a problem of skeletal stability. Stability in orthognathic surgery is related, more than to the type of fixations used, to the structural and functional integrity of the temporomandibular joints and to the final occlusion and its functionality. Occlusal instability, which is of inorganic characteristics and produces deflective or premature contacts without canine and anterior guides, is the main factor in orthodontic and, ultimately, skeletal stability in patients who have undergone orthognathic surgery. This instability is not attributable to BSSROM. On the other hand, the structural integrity of the temporomandibular joint is specifically related to progressive condylar resorption, avascular necrosis, condylar lysis, or the preferred designation. This complication usually appears in patients who have undergone BSSROM as a single or combined technique and in young women who have a predisposing biochemical (hormonal) and biomechanical component. If it occurs, condylar resorption causes a loss of skeletal height, which translates into an anteriorly open bite that is proportional to the degree of condylar resorption. In the case of unilateral resorption, which is infrequent, an asymmetrical component toward the affected side can be expected. Nothing has been published that establishes a cause-effect relation between BSSROM and the appearance of condylar resorption. Nevertheless, we cannot ignore it because it appears in patients who have undergone orthognathic surgery and, specifically, the osteotomy that concerns us.

References

1. Trauner R, Obwegeser H. Zur Operationstechnik Bei der Progenie und anderen Unterkieferanomalien. Dtsch Zahn-Mund-Kieferheilk 23 (1955-56) 1.         [ Links ]

2. Dal Pont Giorgio. J Oral Surg. Anesth & Hosp.D. Serv Vol. 19. En. 1961.         [ Links ]

3. Epker N. Bruce. Modifications in the sagittal osteotomy of the mandible. J Oral Surgery 1977 Vol. 35.         [ Links ]

4. Bell H. William. Biological basis for modification of the sagittal ramus split operation. J Oral Surgery Mayo 1977 Vol. 35.         [ Links ]

5. Wolford L. The Mandibular Inferior Border Split. J Oral Surgery 1990;48:92-4.         [ Links ]

6. Quevedo L, Ruiz J, Figueroa L. Técnica Quirúrgica de Cirugía Ortognática para Ortodoncistas. Parte II. Rev Chil Ortodoncia 1989;6:31-5.         [ Links ]

7. Quevedo L, y cols. Estética Facial para el Cirujano Máxilo Facial. Rev Dental de Chile 1991;82:36-40.         [ Links ]