- Email: [email protected]
Labial sensory function following sagittal split osteotomy
11996) 34. 75-8 I cc 1996 The Brltlsh Aasoaation of Oral and Maxdlofdcial Surgeons
I
I
I
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Labial sensory function following sagittal split osteotomy C. A. Pratt, H. Tippett, J. D. W. Barnard, D. J. Birnie Maxill~f~~cicrl
Unit, Queen Alexandm Hospital, Portsmouth, UK
SUMMAR Y. A retrospective assessment of labial sensory function following sagittal split osteotomy was undertaken by a combination of record analysis, postal questionnaire and objective sensory testing. Case records for 90 sides operated upon by a single consultant surgeon between 1979 and 1992 identified a prevalence of persisting sensory change at 2 years of 6.7%. A higher incidence of sensory change was seen in patients treated with intermaxillary fixation/upper border wires than those managed with buccal monocortical miniplates. Postal questionnaire returns for 67 consultant operated sides identified a higher incidence of sensory change than recorded in the notes. 5.9% had long term persisting anaesthesia. Another 28% bad more variable subtle sensory impairment. A similar relation to method of fixation was seen. An association between duration of temporary sensory change and magnitude of forward mandibular advance was noted. Objective sensory testing validated the subjectively reported sensory status but also identified many patients self-assessed as normal had some undetected sensory impairment. Possible mechanisms for the above findings and implications for clinical practice are presented.
related to neuropraxia. The subsequent split and bicortical screw fixation did not appear to be related to altered nerve conduction. Takeuchit2 presented CT scan evidence suggesting that paraesthesia in mandibular setback procedures may be related to direct bundle compression at the mandibular foramen. This study was devised to further elucidate the prevalence of labial sensory disturbance following sagittal split osteotomy in a UK Maxillofacial Unit. A retrospective analysis of consecutive cases was instituted and an attempt was made to identify statistically significant variables which may have influenced labial sensory outcome.
INTRODUCTION The management of mandibular prognathism and retrognathism was revolutionised by the advent of the technique of sagittal split osteotomy as described by Trauner and Obwegeser.’ There have been many modifications to the technique, all designed to minimise morbidity and maximise the stability of the procedure. These include the variations described by Dal Pont2 Hunsuck and Epker.4 Following the establishment of the procedure, a commonly noted sequaelae of the surgery was altered labial sensation, although the reported prevalence of this complication varied widely in the literature. Macintosh’ reported a prevalence of 85% sensory disturbance in the immediate postoperative period, which fell to 9% at 1 year. Pepersack and Chausse6 reported some labial sensory disturbance in 60% of cases at 5 years which remained undetected in 40% of these patients. Cochlan and Irvine7 also reported that the incidence of objectively assessed sensory change 2 years post operation was 34.2% of operated sides. There have been many attempts to explain the mechanisms of labial sensory change. Fiamminghi and Aversa’ performed a cadaver based study and suggested that the greatest risk of nerve disruption occurred at the time of the actual split. Brusati’ concurred, suggesting the use of a fine spatula to effect precise sagittal cleavage which he proposed would minimise persisting sensory disturbance. However, the work of Jones and Wolford,‘“~” using intraoperative recording of somatosensory evoked potentials indicated that the initial retraction of the bundle medial to the ramus during the preparation for the osteotomy cuts was the only consistent factor
METHOD A retrospective analysis of consecutive cases involving a sagittal split osteotomy were performed. These included cases which had concurrently undergone a Le Fort I osteotomy. Initially, this involved assessment of 122 patients who had undergone surgery between 1979 and 1992 for suitability for admission to the study. Formal case record analysis of eligible patients was followed up with a questionnaire posted to all patients. Subsequently, all such patients were invited to attend the clinic for objective sensory testing. All patients studied were at least 1 year post operation. In all cases, a standard technique was employed, utilising a short lingual split with minimal buccal periosteal stripping, as popularised by Epker. Prior to 1988, fixation was routinely achieved with upper border wires and intermaxillary fixation. Since 75
76
British Journal of Oral and Maxillofacial
Surgery
1988 however, a single buccal monocortical miniplate each side has been used as the method of fixation of choice. Operator difference was eliminated by considering only those sides which had been operated upon by a single consultant surgeon. Of the 122 consecutively treated patients assessed for suitability for inclusion in the case record analysis, those with incomplete records or who had not been operated upon by the designated surgeon were eliminated from the study. 94 operated sides were eligible for further consideration. Of these, 4 sides had been fixed with miniplates initially but had subsequently received adjuvant IMF, leaving 90 sides eligible for formal case record analysis. This included 51 sides treated by IMF and upper border wires and 39 sides treated with buccal monocortical miniplates. The case records were assessed to identify the following variables: the direction and magnitude of movement; the first entry in the notes reporting normal labial sensation; the nature of any persisting sensory change. A questionnaire was posted to all patients who had undergone case record analysis asking them to comment on the duration of sensory change or the nature of any persistant sensory deficit. Functional problems resulting from any residual deficit were also enquired of. 55 patients responded to the questionnaire, comprising 67 sides for the designated consultant operator. Objective sensory testing of labial sensation was Qerforrned by invitation to the clinic. 21 patients attended for assessment and 15 unoperated controls were included for comparison. Lower labial sensory function was determined by four non-invasive neurological tests (Fig. 1). All the tests were performed by a single observer, using a standardised technique. For each side, both lip and gingiva was assessed. These tests comprised: (a) two point discrimination; (b) sensory thresholds using a modified Von Frey probe; (c) sharp/blunt discrimination; (d) time to appreciate a hot or cold stimulus. Additionally, a follow-up questionnaire was completed at this stage to assess levels of satisfaction following treatment and also the nature of any other residual problems.
RESULTS
Fig. 1
- Devices used for assessmentof labial sensory function.
Table 1 -The prevalence of sensory change with time for the two methods of fixation (data derived from the case record analysis)
Percentage of caseswith persisting sensory change
IMF group Plated group Average Chi square=4.37;
1 year
2 years
3 years
29.4 10.3 21.1
9.8 2.6 6.7
7.8 2.4 5.0
1 D.F; ~~0.05.
was 9.8% but was only 2.6% in the plated group. In both groups, the prevalence of sensory disturbance decreased progressively with time, with the relative risk of persisting change in the IMF group versus the plated group being nearly 3 : 1. The mean period of sensory change for the two groups are shown in Table 2. In the plated group, the mean duration of temporary change was 14.8 weeks, but this increased to 32.4 weeks in the IMF treated group.
Case record analysis Assessment of 122 case records resulted in 90 consultant operated sides being eligible for analysis. In no case was division of the bundle at operation noted. The case records identified that the movements achieved at operation ranged from 9 mm setbacks to 13 mm advances. From the records, the overall prevalence of persisting sensory change was 6.7% at 2 years. Comparison of the cases treated with miniplates with those treated with IMF and upper border wires showed a striking difference in duration of sensory disturbance (Table 1). At 2 years, the incidence of persisting change in the IMF treated group
Postal questionnaire Replies received for the 67 consultant operated sides demonstrated a higher incidence of persisting sensory 2 - Duration of temporary disturbance for the two methods of fixation (Data derived from the case record analysis)
Table
Mean period of temporary sensory disturbance (weeks) SE diff=5.705;
IMF group
Plated group
32.4
14.8
no. SDs=3.08; p
Labial
1979
sensory
function
following
sagittal
change
for all patient
sides (in weeks)
osteotomy
77
1992
i 988
Fig. 2 - Duration of labial sensory change of any degree of severity).
split
(positive
bar = temporary
change;
negative
bar = permanent
change than recorded in the notes. Overall, 5.9% of cases had long term persisting anaesthesia of the lower lip. In addition, 14 patients reported more subtle sensory changes in 19 sides (equivalent to 28% of patient sides). The chronological occurrence of both temporary and permanent sensory disturbance between 1979 and 1992 is demonstrated in Figure 2. Those cases with permanent change are shown as bars below the x axis. It can also be seen that in only 4 cases of temporary change did the paraesthesia persist beyond 24 weeks. A similar relation of sensory outcome to the method of fixation noted above was seen. Here, plating was associated with persisting sensory change in 5 of 33 plated sides ( 15.1X), while IMF and upper border wires was associated in 11 of 26 sides (42.3%) (Table 3). Any patient treated by miniplate fixation who subsequently had IMF placed to correct an occlusal discrepancy was excluded from this analysis. For each group, no association between patient age and sensory outcome was noted. In the group of patients self assessed as normal, the mean age was 20.1 years (range 13-37 years) while the mean age of the group self assessed as abnormal was 23.9 (15538 years) (p>O.l). Replies received from the postal questionnaire were compared with the magnitude and direction of movement achieved at operation. Prior to the routine use of miniplate fixation, the routine treatment for mandibular prognathism in Portsmouth was an intraoral
vertical subsigmoid osteotomy. Hence, there were only a small number of sagittal split setback procedures immobilised with IMF and wires in this series. Analysis of the relation of mandibular movement to sensory outcome was therefore restricted to advancement surgery only. In this analysis, no statistically significant association between the magnitude of forward advance and the prevalence of permanent sensory impairment was seen. However, in those patients with resolved sensory change, it was noted that there was a significant association between increasing advance and the duration of such alteration. It would appear that forward advances beyond 5 mm trebled the mean duration of temporary sensory disturbance (Table 4).
Table 3 - Prevalence of permanent for the two methods of fixation questionnaire)
Table 4 -The association of the degree temporary sensory change
sensory change (data derived
IMF Percentage persisting Chi
square
of sides with sensory change = 18.06:
I D.F.:
42.1
group
(of (rrzq severity) from the postal
Plated 15.1
group
Objective sensory testing Objective sensory testing of both lower lip and gingivae in 21 patients and 15 controls was performed to attempt to validate the subjective result reported by patients. Each side was separately assessed. A striking difference between the groups self assessed as either normal or abnormal following surgery was noted, especially when two point discrimination and sensory threshold data was examined (Table 5). However, the time taken to appreciate a hot or cold thermal stimulus was not significant due to a high degree of scatter in the results (Table 6).
Movement advancement
achieved (mm)
by
o-5
S-IO p < 0.001.
SE diff = 2.08; no. SDS = 2.78;
of mandibular
Mean duration change (weeks) 2.6 8.4
p < 0.01.
advance
of sensory
and
78
British
Journal
Table 5 -Objective controls
2-point (mean Lip
of Oral
and Maxillofacial
sensory
function
in
Surgery patients
and
normal
Controls
Subjective assessment by the patient Normal Abnormal
8.7
8.8
7.4
7.8
1.7
5.5
4.2
6.2
discrimination values in mm)
Gingivae
Sensory thresholds (mean values in g) Lip
Gingivae
Table 6 - Labial
thermal
sensitivity
in patients
15.1 SE diff=l.38 pio.001 10.5 SE diff= 1.12 p 10.046
9.8 SE diff= 1.51 p
and normal
controls
Controls
Subjective assessment by the patient Normal Abnormal
2.1 l-4 0.72
2.8 o-7 1.913
3.7* 2-5* 0.848 SE diff = 0.49 p>o.5
1.0 0 0
1.8 04 1.203
3.0* o-7* 1.66 SE diff =0.504 p>o.5
Heat sensitivity (mean number of seconds to respond) Range Standard
deviation
Cold sensitivity (mean number of second to respond) Range Standard
deviation
*Using only data for those responders were excluded.
who
responded
to the stimulus.
Non-
DISCUSSION
The assessment of sensory outcome is fraught with difficulties especially since subjective estimation by the patient is often hard to quantify or classify. Despite this, patient assessment of their labial sensory outcome is probably the single most important criterion of the success of the procedure. The current study demonstrated a significant under recording of residual sensory deficit in the case records when compared to the postal questionnaire, although rates of profound sensory change were similar for the two sources. The postal questionnaire highlighted a variety of more minor subtle sensory changes ranging from mild paraesthesia to blunting of light touch. It is interesting to conjecture on the origin of this discrepancy. In almost all cases, the patients expressed a high level of satisfaction in the surgery carried out and this may have influenced their willingness to admit to minor sensory changes in the review clinics. The low prevalence of functional impairment (such
as burning or biting of the lips) would support the proposal that these changes were relatively minor. A prevalence of profound sensory change of around 6% and of subtle change of around 28% would compare well with rates reported by other workers.6,7,13-15 Data derived from both case records and from the postal questionnaire demonstrate the influence of the method of fixation on labial sensory outcome. However, there is a paucity of evidence in the literature to back up this assertion. Previously, many studies have concentrated on the role of the construction and execution of the split in the aetiology of labial sensory disturbance. Both Fiammonghi and Aversi* and also Brusati’ demonstrated how nerve trauma may be sustained if an exact and meticulous technique is not followed during the procedure. Both groups felt that direct bundle trauma at the time of surgery accounted for the postoperative morbidity. Leirai5 reported that macroscopic bundle trauma seen at operation correlated well with sensory outcome and went on to assert that in the absence of obvious trauma, all such patients regained normal sensation within 6 months. Jones and Wolford,“,” using somatosensory evoked potentials demonstrated that medial ramus dissection and retraction was the only significant factor in nerve conduction delay. Interestingly, they showed no decrease in nerve function during performance of the split or in placement of bicortical screws for fixation. In the current study, a significant association between the use of intermaxillary fixation (with an upper border wire) and increased nerve morbidity was noted (Tables 1, 2 & 3). This contradicts the assertion of others that the use of IMF was associated with the lowest prevalence of prolonged sensory disturbance. MacIntosh5 advised the use of prolonged intermaxillary fixation (up to 8 weeks) where sagittal split procedures were performed in patients over 40 years of age to reduce nerve morbidity. He felt that the delayed healing in this age group may contribute to their sensory impairment. Why then should this study identify a very different relationship? A number of proposals are suggested for the increased risk of nerve injury in this IMF treated group. 1. It may be argued that the data merely reflects increasing experience by the designated surgeon since IMF was used as an earlier method of fixation than miniplates. For this proposition to be tenable, one would expect a concentration of cases with sensory impairment early in the series. However, as Figure 1 demonstrates, there was a completely random scatter of cases throughout both the ‘IMF’ period (i.e. 1979-1988) and the ‘plated’ period (1988-1992). There appears to be no demonstrable ‘learning curve’ effect. Throughout both periods, a standardised technique had been followed, the only change was the method of fixation. 2. Placement of an upper border wire usually involves distraction and rotation of the distal relative to proximal mandibular fragments in order to allow correct placement of a bone hole
Labial
for the wire. This manoevre may result in a traction injury of the bundle. Placement of a buccal monocortical miniplate should not involve such distraction, minimising the risk of potential trauma. 3. If the upper border wire is excessively tightened, interfragmentory compression may result, directly crushing the nerve bundle. Alternatively, where the wire is left loose, little rotational stability is imparted to the osteotomy site. Hence, relative movement of opposing bone surfaces may directly tramatise the bundle, resulting in more prolonged sensory impairment. However, correct placement of a buccal miniplate will minimise the rotational forces at the operative site and may therefore be expected to reduce the risk of nerve injury. Figures 3 and 4
Fig. 3 - Postoperative
radiograph
of a patient
treated
with
upper
Fig. 4 - Postoperative
radiograph
of a patient
treated
with buccal
border
sensory
function
following
sagittal
split
osteotomy
79
demonstrate the differences in alignment and stability at the osteotomy for the two methods of fixation. Relative rotation of the fragments has occurred in the wire and IMF treated case but not in the plated one. 4. The plating technique employed in this study involved the entirely passive alignment of the proximal and distal fragments, with no lingually directed force on the buccal segment. This may be an additional factor to consider since compression forces on the bundle are minimised. Assessment of the data with respect to magnitude of forward advance achieved at operation demonstrated a correlation with duration of temporary sensory disturbance (Table 4). It is of interest that no association with permanent impairment was seen.
wires
monocortical
and intermaxillary
miniplates
fixation
80
British
Journal
of Oral
and Maxillofacial
Surgery
The reason for this finding may be partly due to the exclusion of all setback procedures for the reasons described above. As discussed by Takeuchi et al,” the bundle is particularly vulnerable to compression at the mandibular foramen. Since the short split technique creates a line of fracture just posterior to this foramen, setback procedures are more likely to compress the bundle at its point of entry into the medial aspect of the ramus. Advancement procedures may have the opposite effect by increasing the dimension of the mandibular foramen and decompressing the nerve. The mechanism of the effect of increasing advance on temporary change may involve progressively greater traction on the bundle, resulting in a traction neuropraxia. This type of nerve injury may be expected to improve since there is no disruption of perineural integrity. Objective sensory testing was performed to validate the patient reported subjective sensation and also to provide quantifiable data for valid statistical comparison. Sensory thresholds and two point discrimination were both impaired in those patients who reported some persisting sensory change. However, this study was unable to support the work of others6,“,16 who commented on the value of thermal sensitivity in the assessment of sensory impairment. The lack of statistically significant discrimination for this test may be due to several factors. Firstly, the test critically relies on verbal response time so that inter patient variability in this respect may hide a subtle true relationship here. Alternatively, it may be argued that there may not be any difference between the groups and that this data may have identified a true differential neuropraxia. Indeed, different types of nerve fibres do have a differing sensitivity to a variety of insultslarge A alpha fibres mediating light touch are differentially sensitive to the effects of direct compression and local anaesthetics when compared to the smaller A delta and C fibres which mediate pain and thermal sensibility. I5 More study is required to identify the true patho-physiological effect on nerve function of sagittal split osteotomy. The data presented in this paper highlighted a persisting subclinical sensory deficit in many patients who had self-assessed their lip sensation as normal when sensory thresholds were considered. This phenomenon had been previously reported by Pepersack and Chausse6 and also by Cochlan and Irvine.7 The mechanism of this discrepancy may lie in the adaptation in perception of these patients sensory function. However, not all studies concur with these findings. Leira” was unable to demonstrate any detectable deficit in those patients who were selfassessed as normal. It is possible that the sensitivity and specificity of the methods used or inter-operator variability may account for the discrepancy reported in the literature. CONCLUSION
The present study has assessed the prevalence of persisting and temporary labial sensory change fol-
lowing sagittal split osteotomy. An attempt has been made to show that what is recorded in the notes or what patients will admit to often gives an unrealistic view of the true rates of labial sensory morbidity. Many patients appear to suffer from subtle subclinical sensory impairment, the significance of which remains undetermined. In general terms, factors shown to adversely influence labial sensation include the use of IMF and bone wires when compared to the outcome achieved with miniplates. Temporary sensory impairment correlates with the magnitude of forward advance, although there is no association with permanent change. What then are the implications for clinical practice? Evidence derived from this and other studies demonstrate the frequency and also the unpredictability of persisting sensory disturbance following sagittal split osteotomy. The traditionally held view that intermaxillary fixation and direct bone wiring offers the best opportunity for normal labial sensation postoperatively must now surely be challenged. However, statistically valid comparison (for a single operator) between plating and other methods of direct fixation such as bicortical screws or with ‘lag’ screws has still not been performed. This area of research should be explored so that surgeons and their patients may make an informed choice of the method of fixation employed. Other factors relevant to the decision include evidence regarding the adverse effects of IMF on respiratory function, airway compromise, late masticatory function and weight loss. The medicolegal implications of this decision are becoming increasingly relevant.
References 1. Trauner R, Obwegeser H. The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. Oral Surg Oral Med Oral Path01 1957; 10: 677-689. 2. Dal Pont G. Retromolar osteotomy for the correction of prognathism. J Oral Surg 1961; 19: 42-47. 3. Hunsuck EE. A modified intraoral sagittal splitting technique for the correction of mandibular prognathism. J Oral Surg 1968; 26: 249-252. 4. Epker B. Modifications in the sagittal osteotomy of the mandible. J Oral Surg 1977; 35: 157-159. 5. Macintosh RB. Experience with the sagittal osteotomy of the mandibular ramus; a 13 year review. J Maxillofac Surg 198 1; 9: 151-165. 6. Pepersack WJ, Chausse JM. Longterm follow-up of the sagittal splitting technique for the correction of mandibular prognathism. J Maxillofac Surg 1978; 6: 117-140. 7. Cochlan KM, Irvine GH. Neurological damage after sagittal split osteotomy. Int J Oral Maxillofac Surg 1986; 15: 369-371. 8. Fiamminghi L, Aversa C. Lesions of the inferior alveolar nerve in sagittal osteotomy of the ramus-experimental study. J Maxillofac Surg 1979; 7: 125-128. 9. Brusati R, Fiamminghi L, Sesenna E, Gazzotti A. Functional disturbance of the inferior alveolar nerve after sagittal osteotomy of the mandibular ramus: operating technique for prevention. J Maxillofac Surg 1981; 9: 123-125. 10. Jones DL, Wolford LM. Comparison of methods to assess alterations following orthognathic surgery. Int J Adult Orthod Orthognath Surg 1990; 5: 35542.
Labial II.
12.
13.
14.
15.
16.
Jones DL, Wolford LM. Intraoperative recording of trigeminal evoked potentials during orthognathic surgery. Int J Adult Orthod Orthognath Surg 1990; 5: 167- 174. Tacheuchi T, Furusawa K, Hirose I. Mechanism of transient mental nerve paraesthesia in sagittal split mandibular ramus osteotomy. Br J Oral Maxillofac Surg 1994: 32: 105-108. Guernsey LH, DeChamplain RW. Sequelae and complications of the intraoral sagittal osteotomy in the mandibular rami. Oral Surg 1971; 32: 176-191. Alfaro R. Correction of mandibular prognathism with associated apertogonia by intraoral sagittal osteotomy of rami. Oral Surg 1969; 27: 2855289. Leira JI, Gilhuus-Moe OT. Sensory impairment following sagittal split osteotomy for correction of mandibular retrognathism. Int J Adult Orthod Orthognath Surg 1991: 6: 161-167. Robinson PP. Observations on the recovery of sensation following inferior alveolar nerve injuries. Br J Oral Maxillofac Surg 1988: 26: 177 ~189.
sensory
function
following
sagittal
split
osteotomy
The Authors C. A. Pratt BSc, BDS, MB, BS, FDSRCS (Eng), FRCS (Edin) Higher Surgical Trainee in Oral and Maxillofacial Surgery South Coast Training Programme H. Tippett BDS Senior House Officer J. D. W. Barnard BDS, FDSRCS (Eng), FDSRCPS (Glasg) Consultant Oral and Maxillofacial Surgeon D. J. Birnie FDSRCS (Edin), FDSRCS (Eng), MOrthRCS (Eng) Consultant Orthodontist Maxillofacial Unit Queen Alexandra Hospital Cosham Portsmouth PO6 3LY Correspondence
and requests
Paper received 17 January Accepted 29 March I995
for otfprints
1995
to Mr C. A. Pratt
81
I
I
I
-
Labial sensory function following sagittal split osteotomy C. A. Pratt, H. Tippett, J. D. W. Barnard, D. J. Birnie Maxill~f~~cicrl
Unit, Queen Alexandm Hospital, Portsmouth, UK
SUMMAR Y. A retrospective assessment of labial sensory function following sagittal split osteotomy was undertaken by a combination of record analysis, postal questionnaire and objective sensory testing. Case records for 90 sides operated upon by a single consultant surgeon between 1979 and 1992 identified a prevalence of persisting sensory change at 2 years of 6.7%. A higher incidence of sensory change was seen in patients treated with intermaxillary fixation/upper border wires than those managed with buccal monocortical miniplates. Postal questionnaire returns for 67 consultant operated sides identified a higher incidence of sensory change than recorded in the notes. 5.9% had long term persisting anaesthesia. Another 28% bad more variable subtle sensory impairment. A similar relation to method of fixation was seen. An association between duration of temporary sensory change and magnitude of forward mandibular advance was noted. Objective sensory testing validated the subjectively reported sensory status but also identified many patients self-assessed as normal had some undetected sensory impairment. Possible mechanisms for the above findings and implications for clinical practice are presented.
related to neuropraxia. The subsequent split and bicortical screw fixation did not appear to be related to altered nerve conduction. Takeuchit2 presented CT scan evidence suggesting that paraesthesia in mandibular setback procedures may be related to direct bundle compression at the mandibular foramen. This study was devised to further elucidate the prevalence of labial sensory disturbance following sagittal split osteotomy in a UK Maxillofacial Unit. A retrospective analysis of consecutive cases was instituted and an attempt was made to identify statistically significant variables which may have influenced labial sensory outcome.
INTRODUCTION The management of mandibular prognathism and retrognathism was revolutionised by the advent of the technique of sagittal split osteotomy as described by Trauner and Obwegeser.’ There have been many modifications to the technique, all designed to minimise morbidity and maximise the stability of the procedure. These include the variations described by Dal Pont2 Hunsuck and Epker.4 Following the establishment of the procedure, a commonly noted sequaelae of the surgery was altered labial sensation, although the reported prevalence of this complication varied widely in the literature. Macintosh’ reported a prevalence of 85% sensory disturbance in the immediate postoperative period, which fell to 9% at 1 year. Pepersack and Chausse6 reported some labial sensory disturbance in 60% of cases at 5 years which remained undetected in 40% of these patients. Cochlan and Irvine7 also reported that the incidence of objectively assessed sensory change 2 years post operation was 34.2% of operated sides. There have been many attempts to explain the mechanisms of labial sensory change. Fiamminghi and Aversa’ performed a cadaver based study and suggested that the greatest risk of nerve disruption occurred at the time of the actual split. Brusati’ concurred, suggesting the use of a fine spatula to effect precise sagittal cleavage which he proposed would minimise persisting sensory disturbance. However, the work of Jones and Wolford,‘“~” using intraoperative recording of somatosensory evoked potentials indicated that the initial retraction of the bundle medial to the ramus during the preparation for the osteotomy cuts was the only consistent factor
METHOD A retrospective analysis of consecutive cases involving a sagittal split osteotomy were performed. These included cases which had concurrently undergone a Le Fort I osteotomy. Initially, this involved assessment of 122 patients who had undergone surgery between 1979 and 1992 for suitability for admission to the study. Formal case record analysis of eligible patients was followed up with a questionnaire posted to all patients. Subsequently, all such patients were invited to attend the clinic for objective sensory testing. All patients studied were at least 1 year post operation. In all cases, a standard technique was employed, utilising a short lingual split with minimal buccal periosteal stripping, as popularised by Epker. Prior to 1988, fixation was routinely achieved with upper border wires and intermaxillary fixation. Since 75
76
British Journal of Oral and Maxillofacial
Surgery
1988 however, a single buccal monocortical miniplate each side has been used as the method of fixation of choice. Operator difference was eliminated by considering only those sides which had been operated upon by a single consultant surgeon. Of the 122 consecutively treated patients assessed for suitability for inclusion in the case record analysis, those with incomplete records or who had not been operated upon by the designated surgeon were eliminated from the study. 94 operated sides were eligible for further consideration. Of these, 4 sides had been fixed with miniplates initially but had subsequently received adjuvant IMF, leaving 90 sides eligible for formal case record analysis. This included 51 sides treated by IMF and upper border wires and 39 sides treated with buccal monocortical miniplates. The case records were assessed to identify the following variables: the direction and magnitude of movement; the first entry in the notes reporting normal labial sensation; the nature of any persisting sensory change. A questionnaire was posted to all patients who had undergone case record analysis asking them to comment on the duration of sensory change or the nature of any persistant sensory deficit. Functional problems resulting from any residual deficit were also enquired of. 55 patients responded to the questionnaire, comprising 67 sides for the designated consultant operator. Objective sensory testing of labial sensation was Qerforrned by invitation to the clinic. 21 patients attended for assessment and 15 unoperated controls were included for comparison. Lower labial sensory function was determined by four non-invasive neurological tests (Fig. 1). All the tests were performed by a single observer, using a standardised technique. For each side, both lip and gingiva was assessed. These tests comprised: (a) two point discrimination; (b) sensory thresholds using a modified Von Frey probe; (c) sharp/blunt discrimination; (d) time to appreciate a hot or cold stimulus. Additionally, a follow-up questionnaire was completed at this stage to assess levels of satisfaction following treatment and also the nature of any other residual problems.
RESULTS
Fig. 1
- Devices used for assessmentof labial sensory function.
Table 1 -The prevalence of sensory change with time for the two methods of fixation (data derived from the case record analysis)
Percentage of caseswith persisting sensory change
IMF group Plated group Average Chi square=4.37;
1 year
2 years
3 years
29.4 10.3 21.1
9.8 2.6 6.7
7.8 2.4 5.0
1 D.F; ~~0.05.
was 9.8% but was only 2.6% in the plated group. In both groups, the prevalence of sensory disturbance decreased progressively with time, with the relative risk of persisting change in the IMF group versus the plated group being nearly 3 : 1. The mean period of sensory change for the two groups are shown in Table 2. In the plated group, the mean duration of temporary change was 14.8 weeks, but this increased to 32.4 weeks in the IMF treated group.
Case record analysis Assessment of 122 case records resulted in 90 consultant operated sides being eligible for analysis. In no case was division of the bundle at operation noted. The case records identified that the movements achieved at operation ranged from 9 mm setbacks to 13 mm advances. From the records, the overall prevalence of persisting sensory change was 6.7% at 2 years. Comparison of the cases treated with miniplates with those treated with IMF and upper border wires showed a striking difference in duration of sensory disturbance (Table 1). At 2 years, the incidence of persisting change in the IMF treated group
Postal questionnaire Replies received for the 67 consultant operated sides demonstrated a higher incidence of persisting sensory 2 - Duration of temporary disturbance for the two methods of fixation (Data derived from the case record analysis)
Table
Mean period of temporary sensory disturbance (weeks) SE diff=5.705;
IMF group
Plated group
32.4
14.8
no. SDs=3.08; p
Labial
1979
sensory
function
following
sagittal
change
for all patient
sides (in weeks)
osteotomy
77
1992
i 988
Fig. 2 - Duration of labial sensory change of any degree of severity).
split
(positive
bar = temporary
change;
negative
bar = permanent
change than recorded in the notes. Overall, 5.9% of cases had long term persisting anaesthesia of the lower lip. In addition, 14 patients reported more subtle sensory changes in 19 sides (equivalent to 28% of patient sides). The chronological occurrence of both temporary and permanent sensory disturbance between 1979 and 1992 is demonstrated in Figure 2. Those cases with permanent change are shown as bars below the x axis. It can also be seen that in only 4 cases of temporary change did the paraesthesia persist beyond 24 weeks. A similar relation of sensory outcome to the method of fixation noted above was seen. Here, plating was associated with persisting sensory change in 5 of 33 plated sides ( 15.1X), while IMF and upper border wires was associated in 11 of 26 sides (42.3%) (Table 3). Any patient treated by miniplate fixation who subsequently had IMF placed to correct an occlusal discrepancy was excluded from this analysis. For each group, no association between patient age and sensory outcome was noted. In the group of patients self assessed as normal, the mean age was 20.1 years (range 13-37 years) while the mean age of the group self assessed as abnormal was 23.9 (15538 years) (p>O.l). Replies received from the postal questionnaire were compared with the magnitude and direction of movement achieved at operation. Prior to the routine use of miniplate fixation, the routine treatment for mandibular prognathism in Portsmouth was an intraoral
vertical subsigmoid osteotomy. Hence, there were only a small number of sagittal split setback procedures immobilised with IMF and wires in this series. Analysis of the relation of mandibular movement to sensory outcome was therefore restricted to advancement surgery only. In this analysis, no statistically significant association between the magnitude of forward advance and the prevalence of permanent sensory impairment was seen. However, in those patients with resolved sensory change, it was noted that there was a significant association between increasing advance and the duration of such alteration. It would appear that forward advances beyond 5 mm trebled the mean duration of temporary sensory disturbance (Table 4).
Table 3 - Prevalence of permanent for the two methods of fixation questionnaire)
Table 4 -The association of the degree temporary sensory change
sensory change (data derived
IMF Percentage persisting Chi
square
of sides with sensory change = 18.06:
I D.F.:
42.1
group
(of (rrzq severity) from the postal
Plated 15.1
group
Objective sensory testing Objective sensory testing of both lower lip and gingivae in 21 patients and 15 controls was performed to attempt to validate the subjective result reported by patients. Each side was separately assessed. A striking difference between the groups self assessed as either normal or abnormal following surgery was noted, especially when two point discrimination and sensory threshold data was examined (Table 5). However, the time taken to appreciate a hot or cold thermal stimulus was not significant due to a high degree of scatter in the results (Table 6).
Movement advancement
achieved (mm)
by
o-5
S-IO p < 0.001.
SE diff = 2.08; no. SDS = 2.78;
of mandibular
Mean duration change (weeks) 2.6 8.4
p < 0.01.
advance
of sensory
and
78
British
Journal
Table 5 -Objective controls
2-point (mean Lip
of Oral
and Maxillofacial
sensory
function
in
Surgery patients
and
normal
Controls
Subjective assessment by the patient Normal Abnormal
8.7
8.8
7.4
7.8
1.7
5.5
4.2
6.2
discrimination values in mm)
Gingivae
Sensory thresholds (mean values in g) Lip
Gingivae
Table 6 - Labial
thermal
sensitivity
in patients
15.1 SE diff=l.38 pio.001 10.5 SE diff= 1.12 p 10.046
9.8 SE diff= 1.51 p
and normal
controls
Controls
Subjective assessment by the patient Normal Abnormal
2.1 l-4 0.72
2.8 o-7 1.913
3.7* 2-5* 0.848 SE diff = 0.49 p>o.5
1.0 0 0
1.8 04 1.203
3.0* o-7* 1.66 SE diff =0.504 p>o.5
Heat sensitivity (mean number of seconds to respond) Range Standard
deviation
Cold sensitivity (mean number of second to respond) Range Standard
deviation
*Using only data for those responders were excluded.
who
responded
to the stimulus.
Non-
DISCUSSION
The assessment of sensory outcome is fraught with difficulties especially since subjective estimation by the patient is often hard to quantify or classify. Despite this, patient assessment of their labial sensory outcome is probably the single most important criterion of the success of the procedure. The current study demonstrated a significant under recording of residual sensory deficit in the case records when compared to the postal questionnaire, although rates of profound sensory change were similar for the two sources. The postal questionnaire highlighted a variety of more minor subtle sensory changes ranging from mild paraesthesia to blunting of light touch. It is interesting to conjecture on the origin of this discrepancy. In almost all cases, the patients expressed a high level of satisfaction in the surgery carried out and this may have influenced their willingness to admit to minor sensory changes in the review clinics. The low prevalence of functional impairment (such
as burning or biting of the lips) would support the proposal that these changes were relatively minor. A prevalence of profound sensory change of around 6% and of subtle change of around 28% would compare well with rates reported by other workers.6,7,13-15 Data derived from both case records and from the postal questionnaire demonstrate the influence of the method of fixation on labial sensory outcome. However, there is a paucity of evidence in the literature to back up this assertion. Previously, many studies have concentrated on the role of the construction and execution of the split in the aetiology of labial sensory disturbance. Both Fiammonghi and Aversi* and also Brusati’ demonstrated how nerve trauma may be sustained if an exact and meticulous technique is not followed during the procedure. Both groups felt that direct bundle trauma at the time of surgery accounted for the postoperative morbidity. Leirai5 reported that macroscopic bundle trauma seen at operation correlated well with sensory outcome and went on to assert that in the absence of obvious trauma, all such patients regained normal sensation within 6 months. Jones and Wolford,“,” using somatosensory evoked potentials demonstrated that medial ramus dissection and retraction was the only significant factor in nerve conduction delay. Interestingly, they showed no decrease in nerve function during performance of the split or in placement of bicortical screws for fixation. In the current study, a significant association between the use of intermaxillary fixation (with an upper border wire) and increased nerve morbidity was noted (Tables 1, 2 & 3). This contradicts the assertion of others that the use of IMF was associated with the lowest prevalence of prolonged sensory disturbance. MacIntosh5 advised the use of prolonged intermaxillary fixation (up to 8 weeks) where sagittal split procedures were performed in patients over 40 years of age to reduce nerve morbidity. He felt that the delayed healing in this age group may contribute to their sensory impairment. Why then should this study identify a very different relationship? A number of proposals are suggested for the increased risk of nerve injury in this IMF treated group. 1. It may be argued that the data merely reflects increasing experience by the designated surgeon since IMF was used as an earlier method of fixation than miniplates. For this proposition to be tenable, one would expect a concentration of cases with sensory impairment early in the series. However, as Figure 1 demonstrates, there was a completely random scatter of cases throughout both the ‘IMF’ period (i.e. 1979-1988) and the ‘plated’ period (1988-1992). There appears to be no demonstrable ‘learning curve’ effect. Throughout both periods, a standardised technique had been followed, the only change was the method of fixation. 2. Placement of an upper border wire usually involves distraction and rotation of the distal relative to proximal mandibular fragments in order to allow correct placement of a bone hole
Labial
for the wire. This manoevre may result in a traction injury of the bundle. Placement of a buccal monocortical miniplate should not involve such distraction, minimising the risk of potential trauma. 3. If the upper border wire is excessively tightened, interfragmentory compression may result, directly crushing the nerve bundle. Alternatively, where the wire is left loose, little rotational stability is imparted to the osteotomy site. Hence, relative movement of opposing bone surfaces may directly tramatise the bundle, resulting in more prolonged sensory impairment. However, correct placement of a buccal miniplate will minimise the rotational forces at the operative site and may therefore be expected to reduce the risk of nerve injury. Figures 3 and 4
Fig. 3 - Postoperative
radiograph
of a patient
treated
with
upper
Fig. 4 - Postoperative
radiograph
of a patient
treated
with buccal
border
sensory
function
following
sagittal
split
osteotomy
79
demonstrate the differences in alignment and stability at the osteotomy for the two methods of fixation. Relative rotation of the fragments has occurred in the wire and IMF treated case but not in the plated one. 4. The plating technique employed in this study involved the entirely passive alignment of the proximal and distal fragments, with no lingually directed force on the buccal segment. This may be an additional factor to consider since compression forces on the bundle are minimised. Assessment of the data with respect to magnitude of forward advance achieved at operation demonstrated a correlation with duration of temporary sensory disturbance (Table 4). It is of interest that no association with permanent impairment was seen.
wires
monocortical
and intermaxillary
miniplates
fixation
80
British
Journal
of Oral
and Maxillofacial
Surgery
The reason for this finding may be partly due to the exclusion of all setback procedures for the reasons described above. As discussed by Takeuchi et al,” the bundle is particularly vulnerable to compression at the mandibular foramen. Since the short split technique creates a line of fracture just posterior to this foramen, setback procedures are more likely to compress the bundle at its point of entry into the medial aspect of the ramus. Advancement procedures may have the opposite effect by increasing the dimension of the mandibular foramen and decompressing the nerve. The mechanism of the effect of increasing advance on temporary change may involve progressively greater traction on the bundle, resulting in a traction neuropraxia. This type of nerve injury may be expected to improve since there is no disruption of perineural integrity. Objective sensory testing was performed to validate the patient reported subjective sensation and also to provide quantifiable data for valid statistical comparison. Sensory thresholds and two point discrimination were both impaired in those patients who reported some persisting sensory change. However, this study was unable to support the work of others6,“,16 who commented on the value of thermal sensitivity in the assessment of sensory impairment. The lack of statistically significant discrimination for this test may be due to several factors. Firstly, the test critically relies on verbal response time so that inter patient variability in this respect may hide a subtle true relationship here. Alternatively, it may be argued that there may not be any difference between the groups and that this data may have identified a true differential neuropraxia. Indeed, different types of nerve fibres do have a differing sensitivity to a variety of insultslarge A alpha fibres mediating light touch are differentially sensitive to the effects of direct compression and local anaesthetics when compared to the smaller A delta and C fibres which mediate pain and thermal sensibility. I5 More study is required to identify the true patho-physiological effect on nerve function of sagittal split osteotomy. The data presented in this paper highlighted a persisting subclinical sensory deficit in many patients who had self-assessed their lip sensation as normal when sensory thresholds were considered. This phenomenon had been previously reported by Pepersack and Chausse6 and also by Cochlan and Irvine.7 The mechanism of this discrepancy may lie in the adaptation in perception of these patients sensory function. However, not all studies concur with these findings. Leira” was unable to demonstrate any detectable deficit in those patients who were selfassessed as normal. It is possible that the sensitivity and specificity of the methods used or inter-operator variability may account for the discrepancy reported in the literature. CONCLUSION
The present study has assessed the prevalence of persisting and temporary labial sensory change fol-
lowing sagittal split osteotomy. An attempt has been made to show that what is recorded in the notes or what patients will admit to often gives an unrealistic view of the true rates of labial sensory morbidity. Many patients appear to suffer from subtle subclinical sensory impairment, the significance of which remains undetermined. In general terms, factors shown to adversely influence labial sensation include the use of IMF and bone wires when compared to the outcome achieved with miniplates. Temporary sensory impairment correlates with the magnitude of forward advance, although there is no association with permanent change. What then are the implications for clinical practice? Evidence derived from this and other studies demonstrate the frequency and also the unpredictability of persisting sensory disturbance following sagittal split osteotomy. The traditionally held view that intermaxillary fixation and direct bone wiring offers the best opportunity for normal labial sensation postoperatively must now surely be challenged. However, statistically valid comparison (for a single operator) between plating and other methods of direct fixation such as bicortical screws or with ‘lag’ screws has still not been performed. This area of research should be explored so that surgeons and their patients may make an informed choice of the method of fixation employed. Other factors relevant to the decision include evidence regarding the adverse effects of IMF on respiratory function, airway compromise, late masticatory function and weight loss. The medicolegal implications of this decision are becoming increasingly relevant.
References 1. Trauner R, Obwegeser H. The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. Oral Surg Oral Med Oral Path01 1957; 10: 677-689. 2. Dal Pont G. Retromolar osteotomy for the correction of prognathism. J Oral Surg 1961; 19: 42-47. 3. Hunsuck EE. A modified intraoral sagittal splitting technique for the correction of mandibular prognathism. J Oral Surg 1968; 26: 249-252. 4. Epker B. Modifications in the sagittal osteotomy of the mandible. J Oral Surg 1977; 35: 157-159. 5. Macintosh RB. Experience with the sagittal osteotomy of the mandibular ramus; a 13 year review. J Maxillofac Surg 198 1; 9: 151-165. 6. Pepersack WJ, Chausse JM. Longterm follow-up of the sagittal splitting technique for the correction of mandibular prognathism. J Maxillofac Surg 1978; 6: 117-140. 7. Cochlan KM, Irvine GH. Neurological damage after sagittal split osteotomy. Int J Oral Maxillofac Surg 1986; 15: 369-371. 8. Fiamminghi L, Aversa C. Lesions of the inferior alveolar nerve in sagittal osteotomy of the ramus-experimental study. J Maxillofac Surg 1979; 7: 125-128. 9. Brusati R, Fiamminghi L, Sesenna E, Gazzotti A. Functional disturbance of the inferior alveolar nerve after sagittal osteotomy of the mandibular ramus: operating technique for prevention. J Maxillofac Surg 1981; 9: 123-125. 10. Jones DL, Wolford LM. Comparison of methods to assess alterations following orthognathic surgery. Int J Adult Orthod Orthognath Surg 1990; 5: 35542.
Labial II.
12.
13.
14.
15.
16.
Jones DL, Wolford LM. Intraoperative recording of trigeminal evoked potentials during orthognathic surgery. Int J Adult Orthod Orthognath Surg 1990; 5: 167- 174. Tacheuchi T, Furusawa K, Hirose I. Mechanism of transient mental nerve paraesthesia in sagittal split mandibular ramus osteotomy. Br J Oral Maxillofac Surg 1994: 32: 105-108. Guernsey LH, DeChamplain RW. Sequelae and complications of the intraoral sagittal osteotomy in the mandibular rami. Oral Surg 1971; 32: 176-191. Alfaro R. Correction of mandibular prognathism with associated apertogonia by intraoral sagittal osteotomy of rami. Oral Surg 1969; 27: 2855289. Leira JI, Gilhuus-Moe OT. Sensory impairment following sagittal split osteotomy for correction of mandibular retrognathism. Int J Adult Orthod Orthognath Surg 1991: 6: 161-167. Robinson PP. Observations on the recovery of sensation following inferior alveolar nerve injuries. Br J Oral Maxillofac Surg 1988: 26: 177 ~189.
sensory
function
following
sagittal
split
osteotomy
The Authors C. A. Pratt BSc, BDS, MB, BS, FDSRCS (Eng), FRCS (Edin) Higher Surgical Trainee in Oral and Maxillofacial Surgery South Coast Training Programme H. Tippett BDS Senior House Officer J. D. W. Barnard BDS, FDSRCS (Eng), FDSRCPS (Glasg) Consultant Oral and Maxillofacial Surgeon D. J. Birnie FDSRCS (Edin), FDSRCS (Eng), MOrthRCS (Eng) Consultant Orthodontist Maxillofacial Unit Queen Alexandra Hospital Cosham Portsmouth PO6 3LY Correspondence
and requests
Paper received 17 January Accepted 29 March I995
for otfprints
1995
to Mr C. A. Pratt
81