Leading Clinical Paper

Orthognathic Surgery

Int. J. Oral Maxillofac. Surg. 2010; 39: 756–760doi:10.1016/j.ijom.2010.04.001, available online at http://www.sciencedirect.com

Bilateral sagittal splitosteotomies versus mandibulardistraction osteogenesis:a prospective clinical trialcomparing inferior alveolarnerve function andcomplications

A. Ow, L. K. Cheung: Bilateral sagittal split osteotomies versus mandibulardistraction osteogenesis: a prospective clinical trial comparing inferior alveolarnerve function and complications. Int. J. Oral Maxillofac. Surg. 2010; 39: 756–760.# 2010 International Association of Oral and Maxillofacial Surgeons. Published byElsevier Ltd. All rights reserved.

0901-5027/080756 + 05 $36.00/0 # 2010 Inte

rnational Association of Oral and Maxillofacial Surge

A. Ow, L. K. CheungDiscipline of Oral and Maxillofacial Surgery,Faculty of Dentistry, The University of HongKong, Prince Philip Dental Hospital, 34Hospital Road, Hong Kong SAR

Abstract. The aim of this study was to conduct a prospective clinical trial comparingthe neurosensory function of the inferior alveolar nerve (IAN) after mandibularadvancement surgery with either bilateral sagittal split osteotomies (BSSO) ormandibular distraction ostoegenesis (MDO). 23 Class II mandibular hypoplasiapatients requiring mandibular advancement were randomized into two groups foreither BSSO or MDO. Subjective and objective neurosensory evaluations wereperformed preoperatively and at the following postoperative times: 2 weeks(TBD1), 6 weeks (TBD2), 12 weeks (TBD3), 6 months (TBD4) and 12 months(TBD5). Subjective evaluation included the use of a visual analogue scale (VAS).Objective evaluation included the use of light touch (LT), two-point discrimination(2PD) and pain detection threshold (PD) tests. Intra-operative or postoperativecomplications were recorded. Using a mixed model, no significant differences werereported in subjective VAS scores and objective LT, 2PD and PD scores betweenthe BSSO and MDO groups over 12 months (p > 0.05). Common postoperativecomplications included localized wound infection (BSSO = 2, MDO = 6) andcondylar resorption (BSSO = 1, MDO = 1).

Keywords: bilateral sagittal split osteotomies;mandibular distraction osteogenesis; inferioralveolar nerve; complications.

Accepted for publication 6 April 2010Available online 7 May 2010

ons. Published by Elsevier Ltd. All rights reserved.

Comparison of BSSO and MDO 757

Persistent neurosensory disturbance of theinferior alveolar nerve (IAN) is a well-known complication of bilateral sagittalsplit osteotomies (BSSO). Since the incep-tion of this technique, there have beennumerous investigations into the risk fac-tors and recovery patterns associated withthis postoperative complication. Thepatient’s age, particularly for those over40 years of age, has been reported inseveral studies1,12,15 to have a significantinfluence on persistent neurosensory def-icits. Intra-operative risk factors such asexcessive nerve manipulation, nervelaceration, dissection trauma to the medialsoft tissue of the ramus, splitting techni-que, degree of mandibular advancementand unfavourable fractures have also beenimplicated1,3,7,10–12,15. Anatomical varia-tions of the mandible such as the corpusheight and location of the IAN canal nearthe inferior border of the mandible havealso been reported to be risks for nerveinjury11. Most risk factors can be mini-mized during surgery by experienced sur-geons, but postoperative neurosensorydisturbance remains a common postopera-tive morbidity.

In recent years, mandibular distractionosteogenesis (MDO) has been applied totreat patients with Class II mandibularhypoplasia. This technique has beenreported to have a lower incidence ofpostoperative neurosensory disturbanceof the IAN13, but it has been associatedwith other minor complications. There hasbeen no comparison of such morbiditiesbetween these two surgical techniques.This clinical trial aims to compare theneurosensory function of the IAN andthe complications after mandibularadvancement surgery with either BSSOor MDO in the treatment of patients withClass II mandibular hypoplasia.

Materials and methods

This was a prospective clinical trial andethical approval was obtained from theEthics Committee, Faculty of Dentistry,The University of Hong Kong. The inclu-sion criteria comprised patients with askeletal diagnosis of Class II mandibularhypoplasia, aged 16 years or older withradiographic evidence of completion ofskeletal growth using a hand-wrist radio-graph and requiring surgical mandibularadvancement. Patients with systemic dis-eases, facial asymmetry and craniofacialsyndromes were excluded from the study.Patients fulfilling the inclusion criteriawere randomly assigned to a BSSO or aMDO group based on a computer gener-ated randomization table. Informed con-

sent was obtained from each patient beforeany treatment was carried out.

23 subjects with a 6–12-month follow-up were presented, with 12 subjects (3males, 9 females) receiving BSSO and11 subjects (2 male, 9 females) receivingMDO. Additional maxillary surgery orlower anterior subapical osteotomies(Hofer) were carried out if necessary.Great care was taken during the Hoferosteotomy by keeping the osteotomy cuts5 mm anterior to the mental foramen toavoid the anterior loop of the mentalbranch of the IAN and to protect and avoidexcessive stretching of this branch. 9 sub-jects in the BSSO group and 7 in the MDOgroup had received a Hofer osteotomy. Inthe BSSO group, 3 subjects had undergonesingle jaw surgery while the remaining 11subjects had undergone double jaw sur-gery. In the MDO group, 2 subjects under-went single jaw surgery and 9 subjectsreceived double jaw surgery.

Standardized BSSO were performed inthe BSSO group, with fixation achievedusing titanium mini-plates. For the MDOgroup, bilateral vertical osteotomies wereperformed distal to the lower last molar.The distal and proximal segments werethen mobilized to a limited extent toensure that there were no bony hindrancesand to check the integrity of the IAN.Unidirectional intra-oral distractors wereplaced with a distraction vector parallel tothe upper occlusal plane. Fixation of thedistractors was achieved with titaniummini-screws.

A 5–7-day latency period was observedpostoperatively after which distraction wascommenced two to four times a day at a rateof 1 mm/day. The distraction process wascontinued until a Class I occlusion wasachieved. The distractors were kept in placefor a 3-month consolidation period. Fol-lowing radiographic evidence of bony heal-ing, a second operation was performed toremove the distractors.

Evaluation of IAN function was per-formed with subjective and objective neu-rosensory tests. These tests were performed1 week before surgery (T0) and at thefollowing time periods after surgery forthe BSSO group or after distraction forthe MDO group: 2 weeks (TBD1), 6 weeks(TBD2), 3 months (TBD3), 6 months(TBD4) and 12 months (TBD5).

Subjective evaluation was performedusing a patient questionnaire that con-sisted of a visual analogue scale (VAS),where a score of 0 was ‘normal sensation’and 10 was ‘abnormal sensation in itsgreatest severity’.

Objective evaluation involved testing ofthe IAN function in its area of distribution

on the mental region on both sides. Threesensory modalities were evaluated. First,light touch threshold (LT), which wasevaluated using Semmes-Weinstein pres-sure aesthesiometer monofilaments(Stoelting Co., IL, USA). These monofila-ments were used in increasing thicknessand applied to the mental region with justenough pressure to bend the hair. Thepatient was asked if he or she was ableto feel the monofilament as it was appliedand the force (g) corresponding to thatmonofilament was recorded. Second,two-point discrimination (2PD) was eval-uated using a pair of parallel pins mountedaround a plastic disc. These pins wereseparated at increasing distances rangingfrom 2 to 20 mm. They were applied tothe mental region in a horizontal direc-tion and the patient was asked if he or shewas able to discriminate whether the pinapplication felt like one or two points.The distance setting started from themaximum distance and decreased untilthe patient could no longer discriminatebetween the two points correctly. Thedistance between the pins at which thepins were felt as one point was recorded.Third, pain detection threshold (PD) wasevaluated using a stress and tensiongauge (Dentaurum, Ispringen, Germany).This gauge consisted of a pin calibratedto a gauge meter (10–100 g) that mea-sured the amount of force applied by thepin to the test area. The pin was appliedto the mental region with just enoughpressure for the patient to feel sharp pain.The force indicated on the gauge wasrecorded.

All testing procedures were performedwith the patient’s eyes closed. The testswere applied to one point in the centre ofthe mental region on both sides and wererepeated three times, following which thereadings were averaged.

Any intra-operative complications asso-ciated with the BSSO or MDO surgicaltechniques, such as IAN transaction (partialor total), hemorrhage and unfavourablefractures, were recorded. Postoperativecomplications were recorded for bothgroups at follow-up. For the MDO group,complications occurring during the distrac-tion process were also recorded.

Data were analyzed with statistical ana-lysis computer software (SPSS 17.0 forWindows#, Chicago, IL). The normal dis-tribution of the quantitative variable valueswas confirmed using the Kolmogorov–Smirnov test. Paired t-tests were used todetermine whether there were any differ-ences between left and right sides at differ-ent time points in both groups. Mixed modelwas utilized to compare the postoperative

758 Ow, and Cheung

subjective VAS and objective (LT, 2PD andPD) scores between the BSSO and MDOgroups. Variance and covariance matriceswere chosen based on the Bayesian Infor-mation Criteria (BIC). The presence orabsence of a Hofer osteotomy was adjustedfor in the model. Interaction was not eval-uated due to the small sample size. A p-value of less than 0.05 was consideredstatistically significant.

Fig. 2. Light touch (LT) scores (mean � SE) from TBD1 to TBD5; BSSO group versus MDOgroup; No significant differences between groups over the 12-month postoperative period(p > 0.05).

Fig. 3. Two-point discrimination (2PD) scores (mean � SE) from TBD1 to TBD5; BSSO groupversus MDO group; No significant differences between groups over the 12-month postoperativeperiod (p > 0.05).

Results

The mean age in both groups was similar(26.5 years in the BSSO group and 25.3years in the MDO group). Mean mandibu-lar advancement (mean � SD, mm) wascomparable for both groups, 7.71 �2.19 mm in the BSSO group and 8.00 �2.47 mm in the MDO group (p > 0.05).

No intra-operative complications werereported for either group. The IAN wasexposed in 8 patients (2 unilateral and 6bilateral) in the BSSO group and allpatients in the MDO group.

VAS scores were elevated in the earlypostoperative/distraction period (TBD1)for both groups (Fig. 1). These scoresgradually reduced over time from TBD2to TBD5 but did not revert back to normalpreoperative values. From the mixedmodel, there were no significant differ-ences in VAS scores between the BSSOand MDO groups over the 12-month post-operative period (p = 0.69).

No significant differences were foundbetween the left and right mental regionsfor all tests in either group (p > 0.05). Assuch, data for the left and right mentalregions were averaged and the mean usedfor data analyses. Both groups reportedincreased LT, 2PD and PD scores inthe early postoperative/distraction period(Figs. 2–4). These scores graduallyreturned to near normal values fromTBD3 to TBD5 in both groups. The resultfrom mixed model showed that the main

Fig. 1. Visual analogue scale (VAS) scores (meversus MDO group; No significant differences beperiod (p > 0.05).

effect of the Hofer osteotomy on LT, 2PDand PD score was not significant (p = 0.69,p = 0.11, and p = 0.77, respectively). Whencomparing the BSSO and MDO groups, nosignificant differences were detected forLT, 2PD and PD scores throughout the12-month postoperative period (p = 0.55,p = 0.39, and p = 0.096, respectively).The mean differences for LT, 2PDand PD scores between these two groupswere 0.02 � 0.04 g, 1.00 � 1.15 mm, and3.78 � 2.16 g, respectively.

an � SE) from TBD1 to TBD5; BSSO grouptween groups over the 12-month postoperative

In the BSSO group, localized woundinfections were reported in 2 patients.These were treated with antibiotics andin one case, incision and drainage underlocal anaesthesia. 1 patient developed anincreased overjet 1 year postoperatively(TBD5), which was confirmed by radio-graphic examination to be due to condylarresorption. In the MDO group, 1 patientrequired replacement of the distractorsduring the distraction period due to insuf-ficient distractor length. This was attrib-uted to over-activation of the distractorduring the initial placement. During theconsolidation period (TBD1–TBD3), 1patient required early removal of the dis-tractors and the use of heavy elastics tocorrect a bilateral posterior open bite thathad developed during distraction. Persis-tent wound infection around the distractorrods was a common problem during theconsolidation period (n = 6). During thepost-distractor removal period (TBD3–TBD5), 1 patient developed a progressiveopen bite and asymmetry, which was con-firmed by radiographic examination andcephalometric analysis to be due to con-dylar resorption. Other complications arelisted for both groups in Tables 1 and 2.

Comparison of BSSO and MDO 759

Table 1. Postoperative complications in the BSSO group.

Postoperative complications No. of BSSO patients

Postoperative 0–2 weeks (TBD1)Bilateral posterior open bite* 1Localized wound infectiony 2

Postoperative 6 months to 1 year (TBD4–TBD5)Condylar resorption 1Mild anterior open bite 1* Intermaxillary fixation applied.y 1 patient required incision and drainage under local anaesthesia.

Table 2. Postoperative complications in the MDO group.

Postoperative complications No. of MDO patients

During distractionInsufficient length of distractors* 1

Consolidation period (2 weeks to 3 months; TBD1–TBD3)Bilateral posterior open bitey 1Persistent wound infection around distractor rodsz 6

Post-distractor removal period (3 months to 1 year; TBD3–TBD5)Condylar resorption 1Mild anterior open bite 1* Re-operation with replacement of distractors.yRe-operation with early removal of distractors and use of heavy elastics to correct open bite.z 2 patients required incision and drainage under local anaesthesia; 1 patient with oro-

cutaneous fistula.

Fig. 4. Pain detection threshold (PD) scores (mean � SE) from TBD1 to TBD5; BSSO groupversus MDO group; No significant differences between groups over the 12-month postoperativeperiod (p > 0.05).

Discussion

When compared with BSSO, the incidenceof persistent IAN disturbance after MDO isexpected to be lower. OW & CHEUNG

9

reported a lower incidence of persistentIAN disturbance (3%) after MDO com-pared with BSSO, of which the incidencewas 28%. Animal studies5,8 have shownthat the IAN undergoes gradual stretchingduring the distraction process, whichallows the nerve to adapt better and avoidany permanent damage when comparedwith the abrupt stretching of the IAN inBSSO advancement. This adaptation isinfluenced by the distraction rate, with ahigher rate resulting in more nerve damage.Surgical technique is another contributingfactor. With MDO, soft tissue dissection is

minimal and limited to the buccal muco-periosteum on the lateral body and part ofthe lingual surface, with no dissection at themedial ramus. After the osteotomy is per-formed, gradual mobilization of the seg-ments is carried out to ensure adequateseparation. Excessive separation of thebone segments to check for the positionof the IAN is not required. In contrast, theIAN is frequently trapped in the proximalsegment with BSSO and surgical dissectionis required to free the nerve. There is lesstraumatic manipulation of the IAN withMDO, but the number of clinical studiesinvestigating persistent IAN disturbanceafter MDO is low. In a retrospective study,VAN STRIJEN et al.13 reported persistent IANdisturbance in only 3 of 70 patients. Incontrast, in a case series of 5 patients by

WHITESIDES & MEYER14, minor parasthesia

was reported in all patients after MDOusing bilateral vertical body osteotomies.The reason for this difference could beattributed to the younger patient pool inthe former study, of whom a better adaptiveand regenerative capacity is expected.Similarly, in this study, patients reportedmildly elevated subjective VAS scoreseven at postoperative/distraction 1 year,indicating that some degree of persistentneurosensory disturbance existed, even forMDO. The reason for this could be relatedto the adaptive and regenerative capacity ofthese patients, who were older comparedwith the sample as reported by VAN STRIJEN

et al.13 and other studies9. The use of theHofer osteotomy in this study could havehad an effect on neurosensory recovery,although mixed model analysis had shownthis effect to be insignificant. The numberof patients in this study is small, so whetherMDO results in a better recovery patternthan BSSO remains to be seen.

Regarding other complications, in theMDO group, persistent wound infectionaround the distractor rods was a commonfinding despite meticulous oral hygiene.This was attributed to food trapping inand around the coils of the distractor rods,providing a portal of bacterial ingress intothe wound. 2 patients required incision anddrainage under local anaesthesia and 1patient developed an oro-cutaneous fistula.Prompt resolution of the infectionsoccurred on distractor removal. In laterMDO patients, this coiled type of distractorwas replaced with a smooth-surfaced type.There have not been any reports of severeinfection around these smooth-surfaceddistractor rods. Condylar resorption wasseen in 1 BSSO and 1 MDO patient inthe late postoperative period. OW &CHEUNG

9 reported a 6% and 1% incidenceof condylar resorption after BSSO andMDO, respectively. Risk factors for con-dylar resorption have been well-reportedfor BSSO and have included having a highmandibular plane angle, a posteriorlyinclined condylar neck, large advancement,screw fixation and pre-existing temporo-mandibular joint (TMJ) internal derange-ment4,6. For MDO, risk factors for condylarresorption have not been elucidated. Duringthe distraction process, MDO results insuperior and posterior displacement ofthe condyle process. Similar to the situationin BSSO, this condylar displacement isthought to produce unfavourable loadingof the condyle and disk, and may result incondylar resorption once the adaptive capa-city of the condyle is exceeded. AZUMI

et al.2 reported 4 patients with condylarresorption after MDO for lengthening.

760 Ow, and Cheung

All these patients were female and hadpreoperative TMJ internal derangement.In these cases, control of the rate andrhythm of distraction may be importantto allow physiologic adaptation of the con-dyle during the distraction process. The useof Class II elastics to pull the mandibleforward during the activation period mayalso reduce the risk of condylar resorptionby preventing the condyle from compres-sing against the fossa. Further long-termstudies are required to address this area.

In summary, this randomized clinicaltrial compared the incidence of persistentneurosensory disturbance between BSSOand MDO in the treatment of Class IImandibular hypoplasia. At present, somedegree of postoperative neurosensory dis-turbance exists for patients in both groups1 year postoperatively, although no sig-nificant differences between the twogroups were found. Despite its low inci-dence, condylar resorption was reported inboth groups and both techniques mayshare common risk factors for such acomplication. A larger sample size isneeded to compare the morbidities asso-ciated with these two techniques further.

Competing interests

None declared.

Funding

None.

Ethical approval

Yes.

Acknowledgements. The authors wouldlike to thank Dr. Shen Liang and Mr.Shadow Yeung for their contributions tothe manuscript.

References

1. August M, Marchena J, Donady J,Kaban L. Neurosensory deficit and func-tional impairment after sagittal ramusosteotomy: a long-term follow-up study.J Oral Maxillofac Surg 1998: 56: 1231–1235.

2. Azumi Y, Sugawara J, Takahashi I,Mitani H, Nagasaka H, Kawamura H.Positional and morphologic changes ofthe mandibular condyle after mandibulardistraction osteogenesis in skeletal classII patients. World J Orthodon 2004: 5:32–39.

3. Brusati R, Fiamminghi L, Sesenna E,Gazzotti A. Functional disturbances ofthe inferior alveolar nerve after sagittalosteotomy of the mandibular ramus: oper-ating technique for prevention. J Maxil-lofac Surg 1981: 9: 123–125.

4. Cutbirth M, Van Sickels JE, Thrash

WJ. Condylar resorption after bicorticalscrew fixation of mandibular advance-ment. J Oral Maxillofac Surg 1998: 56:178–182.

5. Hu J, Tang Z, Wang D, Buckley MJ.Changes in the inferior alveolar nerveafter mandibular lengthening with differ-ent rates of distraction. J Oral MaxillofacSurg 2001: 9: 1041–1045.

6. Hwang SJ, Haers PE, Seifert B, Sai-

ler HF. Non-surgical risk factors forcondylar resorption after orthognathicsurgery. J Craniomaxillofac Surg 2004:32: 103–111.

7. MacIntosh RB. Experience with thesagittal osteotomy of the mandibularramus: a 13-year review. J MaxillofacSurg 1981: 9: 151–165.

8. Makarov MR, Harper RP, Cope JB,Samchukov ML. Evaluation of inferioralveolar nerve function during distractionosteogenesis in the dog. J Oral MaxillofacSurg 1998: 56: 1417–1423.

9. Ow ATC, Cheung LK. Skeletal stabi-lity and complications of BilateralSagittal Split Osteotomies (BSSO) andMandibular Distraction Osteogenesis(MDO): An evidence-based review. J

Oral and Maxillofac Surg 2009: 67:2344–2353.

10. Panula K, Finne K, Oikarinen K.Neurosensory deficits after bilateralsagittal split ramus osteotomy of themandible—influence of soft tissuehandling medial to the ascending ramus.Int J Oral Maxillofac Surg 2004: 33:543–548.

11. Teerijoki-Oksa T, Jaaskelainen SK,Forssell K, Forssell H, Vahatalo

K, Tammisalo T, Virtanen A. Riskfactors of nerve injury during mandibularsagittal split osteotomy. Int J Oral Max-illofac Surg 2002: 31: 33–39.

12. Van Sickels JE, Hatch JP, Dolce C,Bays RA, Rugh JD. Effects of age,amount of advancement, and genio-plasty on neurosensory disturbance aftera bilateral sagittal split osteotomy. JOral Maxillofac Surg 2002: 60: 1012–1017.

13. van Strijen PJ, Breuning KH, Beck-

ing AG, Perdijk FB, Tuinzing DB.Complications in bilateral mandibulardistraction osteogenesis using internaldevices. Oral Surg Oral Med OralPathol Oral Radiol Endod 2003: 96:392–397.

14. Whitesides LM, Meyer RA. Effect ofdistraction osteogenesis on the severelyhypoplastic mandible and inferior alveo-lar nerve function. J Oral Maxillofac Surg2004: 62: 292–297.

15. Ylikontiola L, Kinnunen J, Oikari-

nen K. Factors affecting neurosensorydisturbance after mandibular bilateralsagittal split osteotomy. J Oral MaxillofacSurg 2000: 58: 1234–1240.

Address:Lim Kwong Cheung2/FOral and Maxillofacial SurgeryFaculty of DentistryPrince Philip Dental Hospital34 Hospital RoadHong Kong SARFax: +852 25599014E-mail: lkcheung@hkucc.hku.hk