Long-term airway space changes after mandibular setback using bilateral sagittal split osteotomy
Joan M. Greco, Uwe Frohberg, Joseph E. Van Sickels Department of Oral & Maxillofacial Surgery, Dental School, The University of Texas Health Science Center at San Antonio, Texas, USA
J. M. Greco, U. Frohberg, J. E. Van Sickels: Long-term airway space changes after mandibular setback using bilateral sagittal split osteotomy. Int. J. Oral Maxillofac. Surg. 1990; 19: 103-105. Abstract. Eleven patients were evaluated retrospectively for their long-term changes in hypopharyngeal airway space after surgical correction of mandibular hyperplasia. All patients had undergone mandibular setbacks by way of bilateral sagittal split osteotomies using rigid fixation. The cephalometric evaluation of hypopharyngeal airway space was based on stable craniofacial landmarks. The results of this study indicate that mandibular setback procedures create relative narrowing of the hypopharyngeal airway space, as seen on lateral cephalometric radiographs, which in isolated cases might contribute to the development of an obstructive sleep apnea syndrome. The 2-dimensional evaluation of hypopharyngeal airway space and the clinical implications of the results are discussed.
Surgical procedures designed to correct dentoskeletal deformities, inevitably affect the size and position of the surrounding soft tissues by altering the preexisting soft tissue-hard tissue relationship. This alteration is a well-known phenomenon with established ratios for soft to hard tissue changes for chin and lips. The effects on the pharyngeal tissues have not been studied as thoroughly. BEag & PRIEST2 and Kou et al. 7 noted that mandibular advancements improved sleep apnea. RILEYet al.14 and VILA et a l l 9 reported simultaneous maxillary and mandibular advancements as a treatment modality for sleep apnea. If, by inference, advancements will improve the pharyngeal depth then will setbacks have an adverse effect? Early investigations showed that the tongue adapted to the mandibular setback2L However, mandibular setbacks have been implicated in obstruction of the posterior airway space with resultant sleep apnea 6,15. Apneas during sleep are physiologic events. When these apneic episodes occur with frequency, however, the possibility of sleep apnea syndrome increases. There are both central and obstructive causes for sleep apnea. Obstructive apneas are induced by intermittent upper airway collapse during sleep. Obstruction has been shown to occur at a number of locations within
the pharynx. Only after arousal from sleep does muscle tone return after which pharyngeal obstruction is eliminated and airflow resumes. Repetitive alveolar hypoventilation leads to pulmonary-arterial hypertension and cor pulmonale. The resultant sympathetic activations can cause systemic hypertension or serious cardiac arrhythmias. The consequence of the continuous arousals is sleep fragmentation, which is eventually responsible for excessive daytime sleepiness, intellectual deterioration, personality disorders and behavioral changes10.16.18. Thus far, no systematic investigations of mandibular setbacks have reported a long-term change in hypopharyngeal airway space (HAS), where one site of obstruction is noted to occur. The purpose of this project was to study a group of patients with mandibular hypefptasia without evidence of obstructive sleep apnea syndrome (OSAS), who underwent surgical correction, and to evaluate the long-term effects of mandibular posterior repositioning on the soft tissues of HAS.
Material and methods The database consisted of patient records of 11 subjects who were treated for mandibular hyperplasia between 1982 and 1986. All pa-
Key words: orthognathic surgery; obstructive sleep apnea syndrome; mandibular hyperplasia. Accepted for publication 21 September 1989
tients underwent bilateral sagittal split osteotomies to set back the mandible. Rigid fixation was applied to the proximal and distal segment according to the procedure described by VAN SICKELS& JETER2°. After the proximal segment was seated, both segments were held in position with a modified Kocher clamp while screw fixation with 2.0 mm bicortical self-tapping bone screws was accomplished. Maxillomandibular fixation was not used. Lateral cephalometric radiographs were taken preoperatively (T1), immediately postoperatively (T2), and the longest postpoperative follow-up (T3), with a range of 2-6 years. The landmarks sella and nasion were transposed from the T1 cephalogram to each successive radiograph by superimposing on anterior and posterior cranial base structures. Registered at nasion each radiograph had constructed both a horizontal plane 7° above the sella-nasion (SN) line and vertical perpendicular plane, the nasion vertical (NV)3. To define HAS in its vertical dimension, 2 points were chosen. The posterior gonion point (PGP), a mid-planed point on the posterior border of the ramus near gonion, was the landmark for the superior measurement. The point used for the inferior measurement was the ramal osteotomy point (ROP), a midplaned point on the inferior border of the mandible representing the junction of the lateral osteotomy of a ramus procedure with the inferior border. Lines were drawn perpendicular to NV through PGP and ROP and extended back through the posterior pharyngeal wall. HAS was thus defined as an area between the base of the tongue and the posterior pharyngeal wall in the anterioposterior
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direction and vertically between the two planes perpendicular to NV (Fig. 1). The coordinates of each landmark were stored in an Apple liE computer (Apple Computer Inc., Cupertino, CA) by the investigator (J.M.G.). Using the BioQuant software (R&M Biometrics Inc., Knoxville, TN) and a digitizer (Hipad Scriptal Corp., Columbus OH), point coordinates were converted into areas (ram2) for evaluation of HAS. Statistical analysis was performed with the StatViewTM 512 + program (BrainPower Inc., Calabasas, CA). The changes in each parameter from T1-T2 and TI-T3 were determined for each of the periods. Digitizing errors for the sample were calculated by digitizing a subset of radiographs twice. The question was whether there was a long-term change in HAS following mandibular setbacks. Paired t-tests were used to examine the hypothesis. Eleven patients, 9 women and 2 men, were included in the study. At the time of the surgical procedure the patients' ages ranged between 16-56 years with a mean of 27 years. The longest postoperative follow-up time period ranged between 2 and 6 years with an average of 3 years. The mean setback was 5.1 mm with a range of 3-12 mm.
Results Paired t-tests revealed a significant difference between times T1-T2 and T 1 T 3 with a confidence level p
Joan M. Greco, Uwe Frohberg, Joseph E. Van Sickels Department of Oral & Maxillofacial Surgery, Dental School, The University of Texas Health Science Center at San Antonio, Texas, USA
J. M. Greco, U. Frohberg, J. E. Van Sickels: Long-term airway space changes after mandibular setback using bilateral sagittal split osteotomy. Int. J. Oral Maxillofac. Surg. 1990; 19: 103-105. Abstract. Eleven patients were evaluated retrospectively for their long-term changes in hypopharyngeal airway space after surgical correction of mandibular hyperplasia. All patients had undergone mandibular setbacks by way of bilateral sagittal split osteotomies using rigid fixation. The cephalometric evaluation of hypopharyngeal airway space was based on stable craniofacial landmarks. The results of this study indicate that mandibular setback procedures create relative narrowing of the hypopharyngeal airway space, as seen on lateral cephalometric radiographs, which in isolated cases might contribute to the development of an obstructive sleep apnea syndrome. The 2-dimensional evaluation of hypopharyngeal airway space and the clinical implications of the results are discussed.
Surgical procedures designed to correct dentoskeletal deformities, inevitably affect the size and position of the surrounding soft tissues by altering the preexisting soft tissue-hard tissue relationship. This alteration is a well-known phenomenon with established ratios for soft to hard tissue changes for chin and lips. The effects on the pharyngeal tissues have not been studied as thoroughly. BEag & PRIEST2 and Kou et al. 7 noted that mandibular advancements improved sleep apnea. RILEYet al.14 and VILA et a l l 9 reported simultaneous maxillary and mandibular advancements as a treatment modality for sleep apnea. If, by inference, advancements will improve the pharyngeal depth then will setbacks have an adverse effect? Early investigations showed that the tongue adapted to the mandibular setback2L However, mandibular setbacks have been implicated in obstruction of the posterior airway space with resultant sleep apnea 6,15. Apneas during sleep are physiologic events. When these apneic episodes occur with frequency, however, the possibility of sleep apnea syndrome increases. There are both central and obstructive causes for sleep apnea. Obstructive apneas are induced by intermittent upper airway collapse during sleep. Obstruction has been shown to occur at a number of locations within
the pharynx. Only after arousal from sleep does muscle tone return after which pharyngeal obstruction is eliminated and airflow resumes. Repetitive alveolar hypoventilation leads to pulmonary-arterial hypertension and cor pulmonale. The resultant sympathetic activations can cause systemic hypertension or serious cardiac arrhythmias. The consequence of the continuous arousals is sleep fragmentation, which is eventually responsible for excessive daytime sleepiness, intellectual deterioration, personality disorders and behavioral changes10.16.18. Thus far, no systematic investigations of mandibular setbacks have reported a long-term change in hypopharyngeal airway space (HAS), where one site of obstruction is noted to occur. The purpose of this project was to study a group of patients with mandibular hypefptasia without evidence of obstructive sleep apnea syndrome (OSAS), who underwent surgical correction, and to evaluate the long-term effects of mandibular posterior repositioning on the soft tissues of HAS.
Material and methods The database consisted of patient records of 11 subjects who were treated for mandibular hyperplasia between 1982 and 1986. All pa-
Key words: orthognathic surgery; obstructive sleep apnea syndrome; mandibular hyperplasia. Accepted for publication 21 September 1989
tients underwent bilateral sagittal split osteotomies to set back the mandible. Rigid fixation was applied to the proximal and distal segment according to the procedure described by VAN SICKELS& JETER2°. After the proximal segment was seated, both segments were held in position with a modified Kocher clamp while screw fixation with 2.0 mm bicortical self-tapping bone screws was accomplished. Maxillomandibular fixation was not used. Lateral cephalometric radiographs were taken preoperatively (T1), immediately postoperatively (T2), and the longest postpoperative follow-up (T3), with a range of 2-6 years. The landmarks sella and nasion were transposed from the T1 cephalogram to each successive radiograph by superimposing on anterior and posterior cranial base structures. Registered at nasion each radiograph had constructed both a horizontal plane 7° above the sella-nasion (SN) line and vertical perpendicular plane, the nasion vertical (NV)3. To define HAS in its vertical dimension, 2 points were chosen. The posterior gonion point (PGP), a mid-planed point on the posterior border of the ramus near gonion, was the landmark for the superior measurement. The point used for the inferior measurement was the ramal osteotomy point (ROP), a midplaned point on the inferior border of the mandible representing the junction of the lateral osteotomy of a ramus procedure with the inferior border. Lines were drawn perpendicular to NV through PGP and ROP and extended back through the posterior pharyngeal wall. HAS was thus defined as an area between the base of the tongue and the posterior pharyngeal wall in the anterioposterior
104
Greco et al.
direction and vertically between the two planes perpendicular to NV (Fig. 1). The coordinates of each landmark were stored in an Apple liE computer (Apple Computer Inc., Cupertino, CA) by the investigator (J.M.G.). Using the BioQuant software (R&M Biometrics Inc., Knoxville, TN) and a digitizer (Hipad Scriptal Corp., Columbus OH), point coordinates were converted into areas (ram2) for evaluation of HAS. Statistical analysis was performed with the StatViewTM 512 + program (BrainPower Inc., Calabasas, CA). The changes in each parameter from T1-T2 and TI-T3 were determined for each of the periods. Digitizing errors for the sample were calculated by digitizing a subset of radiographs twice. The question was whether there was a long-term change in HAS following mandibular setbacks. Paired t-tests were used to examine the hypothesis. Eleven patients, 9 women and 2 men, were included in the study. At the time of the surgical procedure the patients' ages ranged between 16-56 years with a mean of 27 years. The longest postoperative follow-up time period ranged between 2 and 6 years with an average of 3 years. The mean setback was 5.1 mm with a range of 3-12 mm.
Results Paired t-tests revealed a significant difference between times T1-T2 and T 1 T 3 with a confidence level p
