J Oral Maxillofac 4S:92-94.
Surg
1990
The Mandibular A Modification
Inferior Border Split:
in the Sagittal Split Osteotomy
LARRY M. WOLFORD, DDS,* AND WILBUR McL. DAVIS JR, DDSt The mandibular ramus sagittal split osteotomy (SSO) was first described by Trauner and Obwegeser in 1957.’ Since then, numerous modifications have been developed, including those by Hunsuck,* Epker,3 and Wolford et a1.4 With all the previous modifications, a constant finding has been that a split usually does not occur at the inferior border of the mandible, but rather on the lingual aspect of the mandible somewhere between the inferior border and the superior aspect of the inferior alveolar canal. In addition, other unpredictable and unfavorable splits, such as the buccal cortex splitting off from the mandible, or vertical fracturing in the third molar area so that the posterior part of the distal segment remains attached to the proximal segment, also occasionally occur. The primary contributing factor to these complications is a failure of the thick cortical bone at the inferior border of the mandible to split. When the fractures occur on the medial aspect of the ramus above the level of the cortical bone of the inferior and/or around the level of the neurovascular bundle, it is virtually impossible to place a bone screw below the level of the inferior alveolar nerve. Another problem that occurs when the medial fracture is in approximation to the neurovascular bundle is that the bundle frequently will remain attached to the proximal segment upon completion of the split. Significant injury to the neurovascular bundle can occur from stretching it during the splitting procedure and/or during the technical manuevers to release it from the proximal segment. If the split can be created at the inferior border of the mandible, there may be a greater chance of the nerve remaining with the distal segment. Unfortu-
nately, with the surgical modifications that presently exist, the mandible rarely splits at the inferior border. This report describes a new technique to create a predictable sagittal split at the inferior border of the mandible that should facilitate good stability and minimize complications. Technique The modified technique involves an inferior border osteotomy as part of the preliminary bone cuts made before sagittally splitting the mandible. Specially designed blades (Techmedica, Camarillo, CA) have been developed to allow cutting of the inferior border of the mandible with the reciprocating saw (Fig 1). The blades are offset to the left or right side to provide access for cutting on either side of the mandible (Fig 2). Once the medial, ascending ramus, and buccal vertical osteotomies are completed, the blade is used. It is best to begin the cut anteriorly adjacent to the vertical buccal osteotomy (Fig 3). The blade should be oriented so that the cutting edge is parallel to the inferior border of the mandible and it bisects the buccal-lingual thickness of the cortex. The saw blade is 5 mm at its maximum height, which will allow it to penetrate through most inferior border cortices and not damage the neurovascular bundle. The panoramic radiograph should be evaluated to determine the thickness of the inferior cortex and see where the level of the neurovascular bundle is in relationship to the inferior border of the mandible. If the nerve is extremely low and/ or the cortex is relatively thin, care must be taken not to damage the nerve. The reciprocating action of the saw blade is started at half speed and it is sunk to the appropriate depth before increasing the speed. The blade is then directed posteriorly toward the distal aspect of the antegonial notch area. It is then directed medially so that it will come out through the lingual cortex anterior to the angle of the mandible (Fig 4). The operator should be very conscious when making the inferior border cut to realize the shape and contour of the inferior border as well as the shape of the
* In private practice, Baylor University Medical Center; Clinical Professor, Oral and Maxillofacial Surgery, Baylor College of Dentistry, Dallas, TX. t In private practice, Orlando, FL. Address correspondence and reprint requests to Dr Wolford: Baylor University Medical Center, 3409 Worth St, Dallas, TX 75246. 0 1990 geons
American
Association
of Oral
and Maxillofacial
Sur-
0278-2391/90/4801-0019$3.00/O
92
1ND DAVIS
FIGURE I. The inferior border sagittal cutting saw blade is seen in the lateral view. The vertical height of the blade is 5 mm at its maximum.
blade. The reciprocating saw handpiece and blade should be oriented so that the blade will cut maximally up into the bone. This means that once the saw blade has been engaged, the handpiece is rotated superiorly so that the triangular blade can cut most effectively (Fig 3). There is a protective, rounded shaft at the inferior aspect of the blade that will prevent the blade from going further up into the osteotomy area. If there is inadequate vertical cutting of the inferior border, then there is still the risk that a buccal cortical fracture or the standard medial fracture above the inferior border might occur. Once the inferior border cut is finished, the sagittal split is completed by prying the segments apart; no malleting is necessary. The less force used to separate the segments, the less intraoperative trauma to the temporomandibular joints. Once the segments are separated, they are managed in the appropriate manner and stabilized with either rigid or nonrigid methods495 (Fig 5). Discussion We have used this new technique in over 150 patients with no unfavorable splits. The nerve will occasionally remain attached to the proximal segment if there is dense cortical bone in the canal wall or if
FIGURE 2.
The offset saw blades are viewed from above.
FIGURE 3. The inferior border cut should begin adjacent to the vertical buccal osteotomy. The blade is oriented parallel to the inferior border and should bisect the buccal-lingual thickness of the inferior border cortex.
the neurovascular bundle is positioned extremely laterally. However, the instances of this occurring are fewer than with the other, more traditional techniques. This technique has also allowed placement of a screw at the inferior border in most cases. From a technical standpoint, surgeons using this method should have significant experience with sagittal split osteotomies and understand the anatomy of the mandible. The use of this blade is somewhat awkward at first until the proper feel and dexterity are developed. Once the surgeon learns how to use this particular instrument, and realizes the increased ease and predictability of the splitting, it is difficult to go back to the more traditional procedures. This technique provides several advantages: 1) it provides predictable and controlled splitting of the inferior border of the mandible; 2) it increases the bony interface of the proximal and distal segments,
FIGURE 4. The inferior border of the mandible is viewed. The blade is directed posteriorly to the posterior aspect of the gonial notch. It is then directed medially so that it will come out through the lingual cortex anterior to the angle of the mandible.
94
THE MANDIBULAR
INFERIOR BORDER SPLIT
tation of the proximal segment; 5) it may improve the esthetics of the angle of the mandible and gonial notch area; 6) it may decrease the incidence of the inferior alveolar nerve remaining in the proximal segment; 7) it requires less recontouring of the medial aspect of the proximal segment to facilitate passive interface of the proximal and distal segments; 8) it may decrease the incidence of intraoperative traumatization to the temporomandibular joints; 9) it increases the ease of separating the segments, particularly on cases with severe vertical deticienties of posterior mandibular height and ramus width; and 10) it facilitates performing predictable sagittal splits on previously split mandibles. The use of this instrument may increase the surgical time slightly because of the additional time needed to complete this cut. However, because of the easier and more predictable splitting of the mandible, it may, in fact, save surgical time. References
FIGURE 5. Radiograph showing the controlled quality of the inferior border splitting technique, which generally allows placement of a screw below the neurovascular canal.
thereby enhancing healing; 3) it increases the possibility of placing a bone screw below the level of the inferior alveolar nerve; 4) it improves transverse stability of the segments by not allowing medial ro-
1. Trauner R, Obwegeser H: The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. I. Oral Surg Oral Med Oral Path01 10:677, 1957 2. Hunsuch EE: A modified intraoral sagittal splitting technique for correction of mandibular prognathism. J Oral Surg 26:250, 1968 3. Epker BN: Modification in the sagittal osteotomy of the mandible. J Oral Surg 35: 157, 1977 4. Wolford LM, Bennett MA, Rafferty CG: Modification of the mandibular ramus sagittal split osteotomy. Oral Surg Oral Med Oral Pathol 64: 146, 1987 5. Davis WMcL: A method to facilitate placement of screws for sagittal ramus osteotomy. Oral Surg Oral Med Oral Pathol 64:536, 1987
Surg
1990
The Mandibular A Modification
Inferior Border Split:
in the Sagittal Split Osteotomy
LARRY M. WOLFORD, DDS,* AND WILBUR McL. DAVIS JR, DDSt The mandibular ramus sagittal split osteotomy (SSO) was first described by Trauner and Obwegeser in 1957.’ Since then, numerous modifications have been developed, including those by Hunsuck,* Epker,3 and Wolford et a1.4 With all the previous modifications, a constant finding has been that a split usually does not occur at the inferior border of the mandible, but rather on the lingual aspect of the mandible somewhere between the inferior border and the superior aspect of the inferior alveolar canal. In addition, other unpredictable and unfavorable splits, such as the buccal cortex splitting off from the mandible, or vertical fracturing in the third molar area so that the posterior part of the distal segment remains attached to the proximal segment, also occasionally occur. The primary contributing factor to these complications is a failure of the thick cortical bone at the inferior border of the mandible to split. When the fractures occur on the medial aspect of the ramus above the level of the cortical bone of the inferior and/or around the level of the neurovascular bundle, it is virtually impossible to place a bone screw below the level of the inferior alveolar nerve. Another problem that occurs when the medial fracture is in approximation to the neurovascular bundle is that the bundle frequently will remain attached to the proximal segment upon completion of the split. Significant injury to the neurovascular bundle can occur from stretching it during the splitting procedure and/or during the technical manuevers to release it from the proximal segment. If the split can be created at the inferior border of the mandible, there may be a greater chance of the nerve remaining with the distal segment. Unfortu-
nately, with the surgical modifications that presently exist, the mandible rarely splits at the inferior border. This report describes a new technique to create a predictable sagittal split at the inferior border of the mandible that should facilitate good stability and minimize complications. Technique The modified technique involves an inferior border osteotomy as part of the preliminary bone cuts made before sagittally splitting the mandible. Specially designed blades (Techmedica, Camarillo, CA) have been developed to allow cutting of the inferior border of the mandible with the reciprocating saw (Fig 1). The blades are offset to the left or right side to provide access for cutting on either side of the mandible (Fig 2). Once the medial, ascending ramus, and buccal vertical osteotomies are completed, the blade is used. It is best to begin the cut anteriorly adjacent to the vertical buccal osteotomy (Fig 3). The blade should be oriented so that the cutting edge is parallel to the inferior border of the mandible and it bisects the buccal-lingual thickness of the cortex. The saw blade is 5 mm at its maximum height, which will allow it to penetrate through most inferior border cortices and not damage the neurovascular bundle. The panoramic radiograph should be evaluated to determine the thickness of the inferior cortex and see where the level of the neurovascular bundle is in relationship to the inferior border of the mandible. If the nerve is extremely low and/ or the cortex is relatively thin, care must be taken not to damage the nerve. The reciprocating action of the saw blade is started at half speed and it is sunk to the appropriate depth before increasing the speed. The blade is then directed posteriorly toward the distal aspect of the antegonial notch area. It is then directed medially so that it will come out through the lingual cortex anterior to the angle of the mandible (Fig 4). The operator should be very conscious when making the inferior border cut to realize the shape and contour of the inferior border as well as the shape of the
* In private practice, Baylor University Medical Center; Clinical Professor, Oral and Maxillofacial Surgery, Baylor College of Dentistry, Dallas, TX. t In private practice, Orlando, FL. Address correspondence and reprint requests to Dr Wolford: Baylor University Medical Center, 3409 Worth St, Dallas, TX 75246. 0 1990 geons
American
Association
of Oral
and Maxillofacial
Sur-
0278-2391/90/4801-0019$3.00/O
92
1ND DAVIS
FIGURE I. The inferior border sagittal cutting saw blade is seen in the lateral view. The vertical height of the blade is 5 mm at its maximum.
blade. The reciprocating saw handpiece and blade should be oriented so that the blade will cut maximally up into the bone. This means that once the saw blade has been engaged, the handpiece is rotated superiorly so that the triangular blade can cut most effectively (Fig 3). There is a protective, rounded shaft at the inferior aspect of the blade that will prevent the blade from going further up into the osteotomy area. If there is inadequate vertical cutting of the inferior border, then there is still the risk that a buccal cortical fracture or the standard medial fracture above the inferior border might occur. Once the inferior border cut is finished, the sagittal split is completed by prying the segments apart; no malleting is necessary. The less force used to separate the segments, the less intraoperative trauma to the temporomandibular joints. Once the segments are separated, they are managed in the appropriate manner and stabilized with either rigid or nonrigid methods495 (Fig 5). Discussion We have used this new technique in over 150 patients with no unfavorable splits. The nerve will occasionally remain attached to the proximal segment if there is dense cortical bone in the canal wall or if
FIGURE 2.
The offset saw blades are viewed from above.
FIGURE 3. The inferior border cut should begin adjacent to the vertical buccal osteotomy. The blade is oriented parallel to the inferior border and should bisect the buccal-lingual thickness of the inferior border cortex.
the neurovascular bundle is positioned extremely laterally. However, the instances of this occurring are fewer than with the other, more traditional techniques. This technique has also allowed placement of a screw at the inferior border in most cases. From a technical standpoint, surgeons using this method should have significant experience with sagittal split osteotomies and understand the anatomy of the mandible. The use of this blade is somewhat awkward at first until the proper feel and dexterity are developed. Once the surgeon learns how to use this particular instrument, and realizes the increased ease and predictability of the splitting, it is difficult to go back to the more traditional procedures. This technique provides several advantages: 1) it provides predictable and controlled splitting of the inferior border of the mandible; 2) it increases the bony interface of the proximal and distal segments,
FIGURE 4. The inferior border of the mandible is viewed. The blade is directed posteriorly to the posterior aspect of the gonial notch. It is then directed medially so that it will come out through the lingual cortex anterior to the angle of the mandible.
94
THE MANDIBULAR
INFERIOR BORDER SPLIT
tation of the proximal segment; 5) it may improve the esthetics of the angle of the mandible and gonial notch area; 6) it may decrease the incidence of the inferior alveolar nerve remaining in the proximal segment; 7) it requires less recontouring of the medial aspect of the proximal segment to facilitate passive interface of the proximal and distal segments; 8) it may decrease the incidence of intraoperative traumatization to the temporomandibular joints; 9) it increases the ease of separating the segments, particularly on cases with severe vertical deticienties of posterior mandibular height and ramus width; and 10) it facilitates performing predictable sagittal splits on previously split mandibles. The use of this instrument may increase the surgical time slightly because of the additional time needed to complete this cut. However, because of the easier and more predictable splitting of the mandible, it may, in fact, save surgical time. References
FIGURE 5. Radiograph showing the controlled quality of the inferior border splitting technique, which generally allows placement of a screw below the neurovascular canal.
thereby enhancing healing; 3) it increases the possibility of placing a bone screw below the level of the inferior alveolar nerve; 4) it improves transverse stability of the segments by not allowing medial ro-
1. Trauner R, Obwegeser H: The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. I. Oral Surg Oral Med Oral Path01 10:677, 1957 2. Hunsuch EE: A modified intraoral sagittal splitting technique for correction of mandibular prognathism. J Oral Surg 26:250, 1968 3. Epker BN: Modification in the sagittal osteotomy of the mandible. J Oral Surg 35: 157, 1977 4. Wolford LM, Bennett MA, Rafferty CG: Modification of the mandibular ramus sagittal split osteotomy. Oral Surg Oral Med Oral Pathol 64: 146, 1987 5. Davis WMcL: A method to facilitate placement of screws for sagittal ramus osteotomy. Oral Surg Oral Med Oral Pathol 64:536, 1987
