J Oral Maxillofac 49:1264-1266.
Surg
1991
Sensory Disturbances Associated Rigid Internal Fixation of Mandibular Fractures TATEYUKI
IIZUKA, MD, DDS,* AND CHRISTIAN
LINDQVIST,
With
MD, DDS, PHDT
Sensory status of the inferior alveolar nerve was monitored in 133 patients with 150 fractures in the region of the mandibular canal treated with rigid internal fixation preoperatively and 6 weeks postoperatively. Eighty-five of the patients were reevaluated on final follow-up at an average of 15.9 months. Preoperative sensory disturbance (58.5%) correlated significantly only with the presence of fracture displacement. The occurrence of postoperative paresthesia (76.0% at 6.2 weeks, 46.6% at 15.9 months) correlated significantly with the degree of mandibular edentulousness. Patients with edentulous mandibles, especially when a compression plate was used, suffered significantly more often from nerve injury than fully dentate patients. The results indicated that the sensory disturbance was caused by the surgical procedure. In contrast to previous assumptions, displacement of the fracture and preoperative sensory status did not correlate with postoperative occurrence of paresthesia.
Rigid internal fixation allowing early mobilization has increasingly been used during the last decade in the treatment of mandibular fractures.“6 However, it has been claimed that rigid fixation causes postoperative paresthesia more often than the other treatment methods.’ Theoretically, there are several different factors that may result in sensory disturbances. Nerve injury can be caused by the trauma, but also by the treatment. During the operative procedure, the nerve may be involved in traction and/or compression. Manipulation of fragments during reduction and stabilization of the fracture or extraction of a third molar also could cause injury to
the inferior alveolar nerve. Additionally, a bicortical screw placed near the mandibular canal might irritate or damage the nerve. Conventional follow-up studies usually include mandibular fractures in different locations treated by different methods. Yet, injuries to the inferior alveolar nerve resulting in paresthesia are usually observed only in association with fractures in the body and angle regions. Detailed analysis of sensory disturbances can thus become difficult. The effect of factors such as treatment delay and followup time has not always been taken into consideration. In this respect, the incidence and recovery of nerve damage associated with mandibular fractures are poorly documented in the literature.8 In the present study, preoperative and postoperative sensory disturbances and recovery from nerve injury were monitored in patients undergoing rigid internal fixation of body and angle fractures situated in the area traversed by the mandibular canal and the inferior alveolar nerve. These fractures were chosen because they represent a uniform fracture type that is frequently associated with nerve injury and because displaced fractures in these regions are often treated by open reduction. Data
Received from the Department of Oral and Maxillofacial Surgery, IV Department of Surgery, Helsinki University Central Hospital, Finland. * Senior Maxillofacial Surgeon. t Head. Address correspondence and reprint requests to Dr Iizuka: Department of Oral and Maxillofacial Surgery, Helsinki University Central Hospital, Kasarmikatu 11-13, SF-00130 Helsinki 13, Finland. 0 1991 American geons
Association
of Oral and Maxillofacial
Sur-
0278-2391/91/4912-0002$3.00/O
1264
1265
IIZUKA AND LINDQVIST
were analyzed to determine how the nerve injury was affected by different factors connected with the trauma and the surgical technique. Materials
and Methods
Between 1983 and 1989, 168 mandibular fractures of the angle and body regions, which are traversed by the mandibular canal, were treated in 149 patients following the AO/ASIF (A0 Study Group for Internal Fixation) principle’ of rigid internal fixation at the Department of Oral and Maxillofacial Surgery, Helsinki University Central Hospital, Finland. The number included neither body fractures in which the fracture line passed through the mental foramen, nor cases with extensive comminution or defects, often due to gunshot injuries, in which nerve section was obvious. The sensory status of the alveolar inferior nerve was monitored routinely on admission and postoperatively at approximately I- to 2-week intervals for 3 to 11 weeks (mean, 6.2 weeks) and then at the time of plate removal (average, 15.9 months; range, 8 to 36 months). Two patients were lost from follow-up immediately after hospitalization. Cases that required further surgical intervention because of postoperative complications were also excluded from the analysis. A total of 133 patients with 150 fractures (38 body fractures and 112 angular fractures) ultimately were studied. There were 108 males and 25 females, with a mean age of 33.5 years (range 16 to 83). Eightyfive patients with a total of 103 fractures (84 angle fractures and 19 body fractures) were reevaluated on final follow-up in connection with plate and screw removal. Fracture healing was uneventful in all these patients. To study sensory function, the patients were asked about the presence of a subjective sensation of hypesthesia in the mental region and about the difference in the nature of the sensation when compared with the noninjured side and with the skin of the cheek. Sensory testing was performed using light touch with cotton wool and sharp/blunt differentiation with a sharp dental probe on the skin of the chin and the lower lip. The clinical features characterizing the types of injury and treatment were compared with the sensory status on admission and at the two different postoperative stages (6.2 weeks and 15.9 months on average). Such features included degree of displacement, dental status (dentate or edentulous) of the mandible, presence of a tooth in the line of fracture, time delay before treatment, surgical approach, plate types, extraction of a tooth from the line of fracture, and use of maxillomandibular fixation
(MMF). In the angle fractures, presence of a third molar in the line of fracture, position of the third molar, location of the fracture line in relation to the third molar, and removal or retention of the third molar were additionally taken into consideration. Based on the analyses of preoperative panoramic and Towne’s view radiographs, the degree of fracture displacement was classified into three groups: diastasis without displacement (35 cases), displacement less than 5 mm (71 cases), and displacement more than 5 mm (44 cases) observable in at least one of the projections. Ninety-nine diagnoses of fracture were made in 94 dentate mandibles and 51 diagnoses of fracture in 39 endentulous mandibles. The tooth involved in the line of fracture was a second molar in 21 cases and a first molar in 10. In 66 cases, a third molar was situated in the line of fracture. This tooth was impacted in 45 cases (10 vertical impactions and 35 horizontal impactions). In 18 cases, the fracture was mesial to the third molar, in 27 it was distal, and in 21 the fracture was located at the tooth apex. A tooth in the line of fracture was removed at surgery in 72 cases. The mean delay from injury to hospital admission was 2.6 days (range, 0 to 29 days) and the delay from injury to surgery on average was 3.7 days (range, 0 to 31 days). Fracture reduction and fixation were performed using an extraoral approach through a submandibular or retromandibular incision in 143 cases. Only seven fractures were treated using an intraoral approach. The types of plate used are shown in Table 1. Maxillomandibular fixation was used postoperatively for 2 to 4 weeks in 28 cases because of other associated fractures. Categorical variables were analyzed using contingency tables and by computing a x2 statistic. Analysis of variance was used to assess the statistical Table 1. Types of Plate and Number of Screws Used in the Treatment of 150 Mandibular Fractures Plate Type*
No. of Fractures Operated on?
DCP4 DCP2 + DCP4 EDCPS DCP6 RP6 RP7 RP8 Lag screw Total
41 (3) 29 (2) 5 43 (9) 21 6 2 3 150
Abbreviations: DCP, dynamic compression plate; EDCP, eccentric dynamic compression plate; RP, reconstruction plate. * Numeral indicates number of holes in plate. t Number in parentheses indicates use of EDCP instead of DCP.
1266
SENSORY DISTURBANCE AND MANDIBULAR FRACTURES
significance of differences between groups. Student’s t test for paired values was used to assess the statistical significances of differences within groups. P values less than .05 were considered to indicate statistical significance. Results The frequency of sensory disturbance at different stages of treatment is shown in Figure 1. On admission, 54 cases were considered to have normal sensory status of the mental nerve. Hypesthesia, in which an anesthetic zone was detectable by objective testing of the skin under the lower lip, was diagnosed in 76 cases. In 20 cases, the sensory status could not be determined. The most common reason for failure of sensory testing on admission was either unconsciousness or poor compliance of the patient. Marked edema in the mental region or significant pain also made testing difficult. The frequency of hypesthesia increased to 91.3% (137 cases) in the immediate postoperative stage, but diminished during the follow-up. On average, 6.2 weeks postoperatively marked hypesthesia was detectable by objective testing in 38 cases (25.3%). In 76 cases (50.7%), there was slight hypesthesia characterized by an asymmetry of skin sensation in the region of the chin or the lower lip, with otherwise normal reaction to light touch and sharp/blunt differentiation (hyposensibility) (Fig 1). On the final examination about 1 year postoperatively, 48 (46.6%) of 103 fractures still had some degree of sensory disturbance. In 37 fractures (35.9%), this disturbance was hyposensibility in the region of the chin or the lower lip only. In a majority of these instances, the patients subjectively claimed to have normal sensation. In nine fractures (8.7%),
sensory disturbance was represented by severe hypesthesia and two (1.9%) had hyperesthesia (Fig 1). Analysis of the 130 fractures in which sensory function had been studied on admission showed that a sensory disturbance in the preoperative stage correlated significantly only with the presence of fracture displacement (P < .OOl), but there were no marked difference between the two groups with displaced fractures. Eight (25.8%) of 3 1 fractures without displacement, but 43 (66.2%) of 65 fractures with displacement less than 5 mm and 25 (73.5%) of 34 fractures with displacement greater than 5 mm, resulted in total loss of sensation (Fig 2). Treatment delay, dental status, presence of a tooth in the line of fracture, position of the third molar, and location of the fracture line in relation to the third molar had no effect on the preoperative sensory status. Postoperative hypesthesia correlated significantly only with mandibular dentulousness (P < .005). At an average of 6.2 weeks postoperatively, 71 of 99 fractures in dentate mandibles (71.7%) had some degree of sensory disturbance, but only 17 (17.2%) showed severe hypesthesia. Of 5 1 fractures in edentulous patients, however, 43 (84.3%) mental regions showed some degree of disturbed sensation, of which severe hypesthesia was observed in 21 (41.2%) (Fig 3). This correlation with dentulousness was also observed on final follow-up at an average of 15.9 months postoperatively (P < .005). Sensory disturbance was recorded in 27 (36.5%) of the 74 dentate mandibles and in 21 (72.4%) of the 29 edentulous mandibles (Fig 3). There was no correlation n-3 1
%
26.5 (0) 33.6 (22)
80 n-130
?4loo1n
“.I
“1103
n-1 50
50
(8.70
-1
n-34
n-65
loo-
-1
74.2 (23) 60 -
40 -
NoDtSPUCEkENT POSTaP
6.2 WEEKS
15.9 MONTHS
S1P~OS Of treatment
FIGURE 1. Sensory status of the alveolar inferior nerve in different stages of treatment. Number in parentheses indicates number of fractures. q, Normal; n , hypesthesia; H, hyposensibility; K!, hyperesthesia.
DSPLACEWENT .c 5mm
Displacement
of
the
DISPMCEMNT B 5mm fractures
FIGURE 2. Percentage distribution of cases with preoperative hypesthesia in relation to degree of fracture displacement. Number in parentheses indicates number of fractures. Cl, Normal; n , hypesthesia.
1267
IIZUKA AND LINDQVIST
found between the frequency of postoperative paresthesia and other factors, such as delay to treatment, the presence of a tooth in the line of fracture, position of the third molar, location of the fracture line in relation to the third molar, removal or retention of the third molar, and use of MMF. The preoperative sensory status, influenced by the presence of fracture displacement, also did not affect the postoperative situation (Fig 5). Discussion 6.2
weeks
posloperaII~eIy stages
I
15.9
months
porIoparallvely
Of follow-up
FIGURE 3. Percentage distribution of cases with postoperative sensory disturbances in relation to dentate and edentulous patients in the two different stages of follow-up. Number in parentheses indicates number of fractures. 0. Normal; n , hypesthesia; a, hyposensibility; 0, hyperesthesia.
with type of plate in the patient material as a whole. However, analysis of the patient group with edentulous mandibles at an average of 6.2 weeks postoperatively showed a significant difference between types of plate. In the edentulous mandible, sensory disturbance was observed more frequently after stabilizing the fracture using a dynamic compression plate than after using a reconstruction plate (P < .OOl) (Fig 4). At the final follow-up, this difference caused by plate type was not determined because the number of patients was insufficient for detailed statistical analysis. No further correlation was
Various methods of determining sensory function of the mental region have been presented.“.” These include thermal stimulation, von Frey tactile sensation, Weber two-point discrimination, and brush directional measures. The sensitivities of these methods appear to be different. Comparative studies have shown that thermal tests are most sensitive and two-point discrimination least sensitive. l1 The tests used in the present study measure mainly mechanoreception. To evaluate nerve dysfunction accurately, better testing procedures than those used in this study are needed. The present methods were chosen because they are commonly used in follow-up studies of surgically treated mandibular fractures,2*‘2*‘3 and because they are simple and suitable for trauma patients, especially on admission and in the immediate postoperative stage. In clinical practice, simple methods such as light touch and testing for sharp/blunt differentiation, together with a subjective evaluation, give sufficient information about the patient’s sensory problems. According to the results of this study, 76% of the n-54
“-76
,- In--
n-38
n-51
,,,,bCP4
DCP2+4 I_
Types
of plsle
GRCWA
6.2 FIGURE 4. Distribution of sensory disturbances of 49 fractures in edentulous mandibles in relation to type of plate at an average of 6.2 weeks postoperatively. DCP~, Four-hole dynamic compression plate; DCP~+ 4, four-hole dynamic compression plate with a two-hole tension band plate; DC& six-hole dynamic compression plate; RP, reconstruction plate. Two fractures treated with lag screws were excluded. 0, Normal; H, hyposensibility; n , hypesthesia.
weeks
I
GWWE
portoper9tlvely stage*
I
GROWA 15.9
months
postoperatlvely
Of follow-up
FIGURE 5. Percentage distribution of postoperative sensory disturbances in patients with preoperatively normal (group A) and disturbed (group B) sensation. There were no significant differences between the groups. Number in parentheses indicates number of fractures. Cl, Normal; n , hypesthesia; IR, hyposensibility; 8, hyperesthesia.
1266 patients had some degree of sensory disturbance 6 weeks postoperatively and 46.6% experienced sensory disturbance more than 1 year postoperatively. The study by Campbell et al of 21 patients with mandibular body fractures treated with internal fixation reported that postoperatively 81% had poor sensation to thermal stimuli and 67% to von Frey tactile stimulation. l1 Central anesthetic zones on the skin under the lip on the injured side were found in 43% of Campbell’s cases, which corresponds to the rate found in this study. In most studies concerning rigid internal fixation, the rates of postoperative sensory deficit have been lower, varying from 0.9% to 34%.1Y2,5*‘3These rates have, however, always been calculated from the total number of surgically treated mandibular fractures, including those in the symphysis and parasymphysis regions, Fractures in these regions are seldom, if ever, associated with sensory problems. Additionally, as seen in this study, paresthesia diminished with time, and differences in follow-up time in previous studies make it difficult to compare the rates di-
rectly . Another reason for differences in results is that most patients regarded their sensation as normal in their daily activities, although objective testing showed slight sensory disturbance characterized as hyposensibility. This phenomenon has also been observed after mandibular sagittal split osteotomy (SSO). In the study by Coghlan and Irvine, “normal” sensation was demonstrated in 74% of patients after SSO, but objective tests showed normal sensation in 34% only. l4 Cases with slight neurosensory deficits also have probably not always been noted in earlier studies concerning fracture patients. Sensory disturbances after rigid fixation in the body and angle regions are probably more frequent than the rates generally presented. Disturbed sensation following open reduction and rigid fixation has been explained by the fact that major fracture displacements usually have been treated surgically. ‘,12 The results of the present study indicate, however, that preoperative sensory status corresponding to the presence of fracture displacement did not affect the degree of the postoperative sensory disturbance. It seems that the sensory disturbance was also affected by the surgical procedure. Theoretically, the nerve can be involved in traction and/or compression caused by manipulation of fragments during fracture reduction and stabilization. Extraction of a tooth from the line of fracture could also cause injury to the inferior alve-
SENSORY DISTURBANCE
AND MANDIBULAR
FRACTURES
olar nerve. In addition, a bicortical screw placed near the mandibular canal might irritate or damage the nerve. The postoperative sensory deficits observed in this study were possibly a result of the combined effects of all these factors. However, the decisive factor seems to be edentulousness of the mandible; paresthesia was often observed in patients with edentulous and atrophic mandibles. A possible explanation for this correlation is that, due to lack of space, a screw is more likely to be placed in or close to the mandibular canal, thereby causing damage to the inferior alveolar nerve. Therefore, especially in atrophic mandibles, care must be taken to bend the plate to the correct shape and to place it exactly along the inferior border of the mandibule. From this point of view, three-dimensionally bendable reconstruction plates are probably preferable to other plates. References 1. Tu HK, Tenhulzen D: Compression osteosynthesis of mandibular fractures. A retrospective study. J Oral Maxillofac Surg 43585, 1985 2. Lindqvist C, Kontio R, Pihakari A, et al: Rigid internal tixation of mandibular fractures. An analysis of 45 patients treated according to the ASIF method. Int J Oral Maxillofac Surg 15:657, 1986 3. Pogrel MA: Compression osteosynthesis in mandibular fractures. Int J Oral Maxillofac Surg 15:521, 1986 4. Schwimmer AM, Greenberg AM: Management of mandibular trauma with rigid internal fixation. Oral Surg 62:630, 1986 5. Ardary WC: Prospective clinical evaluation of the use of compression plates and screws in the management of mandible fractures. J Oral Maxillofac Surg 47: 1150, 1989 6. Peled M, Laufer D, Helman J, et al: Treatment of mandibular fractures by means of compression osteosynthesis. J Oral Maxillofac Surg 47:566, 1989 7. Bochlogyros PN: A retrospective study of 1,521 mandibular fractures. J Oral Maxillofac Surg 43597, 1985 8. Bruce R, Fonseca RJ: Mandibular fractures. in Fonseca RJ, Walker RV (eds): Oral and Maxillofacial Trauma. Philadelphia, PA, Saunders, 1991, p 414 9. Soiessl B: Internal fixation of the mandible: A manual of _ AO/ASIF principles. Berlin, Springer-Verlag, 1989, p 189 10. Zaytown HS, Phillips C, Terry BC: Long-term neurosensory deficits following transoral vertical ramus and sagittal split osteotomies for mandibular prognathism. J Oral Maxillofac Surg 44: 193, 1986 1I. Campbell RL, Shamaskin RG, Harkins SW: Assessment of recovery from injury to inferior alveolar and mental nerves. Oral Surg 64:519, 1987 12. Niederdellmann H, Shetty V: Solitary lag screw osteosynthesis in the treatment of fractures of the angle of the mandible: A retrospective study. Plast Reconstr Surg 80:68, 1987 13. Raveh J, Vuillemin T, Ladrach K, et al: Plate osteosynthesis of 367 mandibular fractures: The unrestricted indication for the intraoral approach. J Craniomaxillofac Surg 15:244, 1987 14. Coghlan KM, Irvine GH: Neurological damage after sagittal split osteotomy. Int J Oral Maxillofac Surg 15:369, 1986
Surg
1991
Sensory Disturbances Associated Rigid Internal Fixation of Mandibular Fractures TATEYUKI
IIZUKA, MD, DDS,* AND CHRISTIAN
LINDQVIST,
With
MD, DDS, PHDT
Sensory status of the inferior alveolar nerve was monitored in 133 patients with 150 fractures in the region of the mandibular canal treated with rigid internal fixation preoperatively and 6 weeks postoperatively. Eighty-five of the patients were reevaluated on final follow-up at an average of 15.9 months. Preoperative sensory disturbance (58.5%) correlated significantly only with the presence of fracture displacement. The occurrence of postoperative paresthesia (76.0% at 6.2 weeks, 46.6% at 15.9 months) correlated significantly with the degree of mandibular edentulousness. Patients with edentulous mandibles, especially when a compression plate was used, suffered significantly more often from nerve injury than fully dentate patients. The results indicated that the sensory disturbance was caused by the surgical procedure. In contrast to previous assumptions, displacement of the fracture and preoperative sensory status did not correlate with postoperative occurrence of paresthesia.
Rigid internal fixation allowing early mobilization has increasingly been used during the last decade in the treatment of mandibular fractures.“6 However, it has been claimed that rigid fixation causes postoperative paresthesia more often than the other treatment methods.’ Theoretically, there are several different factors that may result in sensory disturbances. Nerve injury can be caused by the trauma, but also by the treatment. During the operative procedure, the nerve may be involved in traction and/or compression. Manipulation of fragments during reduction and stabilization of the fracture or extraction of a third molar also could cause injury to
the inferior alveolar nerve. Additionally, a bicortical screw placed near the mandibular canal might irritate or damage the nerve. Conventional follow-up studies usually include mandibular fractures in different locations treated by different methods. Yet, injuries to the inferior alveolar nerve resulting in paresthesia are usually observed only in association with fractures in the body and angle regions. Detailed analysis of sensory disturbances can thus become difficult. The effect of factors such as treatment delay and followup time has not always been taken into consideration. In this respect, the incidence and recovery of nerve damage associated with mandibular fractures are poorly documented in the literature.8 In the present study, preoperative and postoperative sensory disturbances and recovery from nerve injury were monitored in patients undergoing rigid internal fixation of body and angle fractures situated in the area traversed by the mandibular canal and the inferior alveolar nerve. These fractures were chosen because they represent a uniform fracture type that is frequently associated with nerve injury and because displaced fractures in these regions are often treated by open reduction. Data
Received from the Department of Oral and Maxillofacial Surgery, IV Department of Surgery, Helsinki University Central Hospital, Finland. * Senior Maxillofacial Surgeon. t Head. Address correspondence and reprint requests to Dr Iizuka: Department of Oral and Maxillofacial Surgery, Helsinki University Central Hospital, Kasarmikatu 11-13, SF-00130 Helsinki 13, Finland. 0 1991 American geons
Association
of Oral and Maxillofacial
Sur-
0278-2391/91/4912-0002$3.00/O
1264
1265
IIZUKA AND LINDQVIST
were analyzed to determine how the nerve injury was affected by different factors connected with the trauma and the surgical technique. Materials
and Methods
Between 1983 and 1989, 168 mandibular fractures of the angle and body regions, which are traversed by the mandibular canal, were treated in 149 patients following the AO/ASIF (A0 Study Group for Internal Fixation) principle’ of rigid internal fixation at the Department of Oral and Maxillofacial Surgery, Helsinki University Central Hospital, Finland. The number included neither body fractures in which the fracture line passed through the mental foramen, nor cases with extensive comminution or defects, often due to gunshot injuries, in which nerve section was obvious. The sensory status of the alveolar inferior nerve was monitored routinely on admission and postoperatively at approximately I- to 2-week intervals for 3 to 11 weeks (mean, 6.2 weeks) and then at the time of plate removal (average, 15.9 months; range, 8 to 36 months). Two patients were lost from follow-up immediately after hospitalization. Cases that required further surgical intervention because of postoperative complications were also excluded from the analysis. A total of 133 patients with 150 fractures (38 body fractures and 112 angular fractures) ultimately were studied. There were 108 males and 25 females, with a mean age of 33.5 years (range 16 to 83). Eightyfive patients with a total of 103 fractures (84 angle fractures and 19 body fractures) were reevaluated on final follow-up in connection with plate and screw removal. Fracture healing was uneventful in all these patients. To study sensory function, the patients were asked about the presence of a subjective sensation of hypesthesia in the mental region and about the difference in the nature of the sensation when compared with the noninjured side and with the skin of the cheek. Sensory testing was performed using light touch with cotton wool and sharp/blunt differentiation with a sharp dental probe on the skin of the chin and the lower lip. The clinical features characterizing the types of injury and treatment were compared with the sensory status on admission and at the two different postoperative stages (6.2 weeks and 15.9 months on average). Such features included degree of displacement, dental status (dentate or edentulous) of the mandible, presence of a tooth in the line of fracture, time delay before treatment, surgical approach, plate types, extraction of a tooth from the line of fracture, and use of maxillomandibular fixation
(MMF). In the angle fractures, presence of a third molar in the line of fracture, position of the third molar, location of the fracture line in relation to the third molar, and removal or retention of the third molar were additionally taken into consideration. Based on the analyses of preoperative panoramic and Towne’s view radiographs, the degree of fracture displacement was classified into three groups: diastasis without displacement (35 cases), displacement less than 5 mm (71 cases), and displacement more than 5 mm (44 cases) observable in at least one of the projections. Ninety-nine diagnoses of fracture were made in 94 dentate mandibles and 51 diagnoses of fracture in 39 endentulous mandibles. The tooth involved in the line of fracture was a second molar in 21 cases and a first molar in 10. In 66 cases, a third molar was situated in the line of fracture. This tooth was impacted in 45 cases (10 vertical impactions and 35 horizontal impactions). In 18 cases, the fracture was mesial to the third molar, in 27 it was distal, and in 21 the fracture was located at the tooth apex. A tooth in the line of fracture was removed at surgery in 72 cases. The mean delay from injury to hospital admission was 2.6 days (range, 0 to 29 days) and the delay from injury to surgery on average was 3.7 days (range, 0 to 31 days). Fracture reduction and fixation were performed using an extraoral approach through a submandibular or retromandibular incision in 143 cases. Only seven fractures were treated using an intraoral approach. The types of plate used are shown in Table 1. Maxillomandibular fixation was used postoperatively for 2 to 4 weeks in 28 cases because of other associated fractures. Categorical variables were analyzed using contingency tables and by computing a x2 statistic. Analysis of variance was used to assess the statistical Table 1. Types of Plate and Number of Screws Used in the Treatment of 150 Mandibular Fractures Plate Type*
No. of Fractures Operated on?
DCP4 DCP2 + DCP4 EDCPS DCP6 RP6 RP7 RP8 Lag screw Total
41 (3) 29 (2) 5 43 (9) 21 6 2 3 150
Abbreviations: DCP, dynamic compression plate; EDCP, eccentric dynamic compression plate; RP, reconstruction plate. * Numeral indicates number of holes in plate. t Number in parentheses indicates use of EDCP instead of DCP.
1266
SENSORY DISTURBANCE AND MANDIBULAR FRACTURES
significance of differences between groups. Student’s t test for paired values was used to assess the statistical significances of differences within groups. P values less than .05 were considered to indicate statistical significance. Results The frequency of sensory disturbance at different stages of treatment is shown in Figure 1. On admission, 54 cases were considered to have normal sensory status of the mental nerve. Hypesthesia, in which an anesthetic zone was detectable by objective testing of the skin under the lower lip, was diagnosed in 76 cases. In 20 cases, the sensory status could not be determined. The most common reason for failure of sensory testing on admission was either unconsciousness or poor compliance of the patient. Marked edema in the mental region or significant pain also made testing difficult. The frequency of hypesthesia increased to 91.3% (137 cases) in the immediate postoperative stage, but diminished during the follow-up. On average, 6.2 weeks postoperatively marked hypesthesia was detectable by objective testing in 38 cases (25.3%). In 76 cases (50.7%), there was slight hypesthesia characterized by an asymmetry of skin sensation in the region of the chin or the lower lip, with otherwise normal reaction to light touch and sharp/blunt differentiation (hyposensibility) (Fig 1). On the final examination about 1 year postoperatively, 48 (46.6%) of 103 fractures still had some degree of sensory disturbance. In 37 fractures (35.9%), this disturbance was hyposensibility in the region of the chin or the lower lip only. In a majority of these instances, the patients subjectively claimed to have normal sensation. In nine fractures (8.7%),
sensory disturbance was represented by severe hypesthesia and two (1.9%) had hyperesthesia (Fig 1). Analysis of the 130 fractures in which sensory function had been studied on admission showed that a sensory disturbance in the preoperative stage correlated significantly only with the presence of fracture displacement (P < .OOl), but there were no marked difference between the two groups with displaced fractures. Eight (25.8%) of 3 1 fractures without displacement, but 43 (66.2%) of 65 fractures with displacement less than 5 mm and 25 (73.5%) of 34 fractures with displacement greater than 5 mm, resulted in total loss of sensation (Fig 2). Treatment delay, dental status, presence of a tooth in the line of fracture, position of the third molar, and location of the fracture line in relation to the third molar had no effect on the preoperative sensory status. Postoperative hypesthesia correlated significantly only with mandibular dentulousness (P < .005). At an average of 6.2 weeks postoperatively, 71 of 99 fractures in dentate mandibles (71.7%) had some degree of sensory disturbance, but only 17 (17.2%) showed severe hypesthesia. Of 5 1 fractures in edentulous patients, however, 43 (84.3%) mental regions showed some degree of disturbed sensation, of which severe hypesthesia was observed in 21 (41.2%) (Fig 3). This correlation with dentulousness was also observed on final follow-up at an average of 15.9 months postoperatively (P < .005). Sensory disturbance was recorded in 27 (36.5%) of the 74 dentate mandibles and in 21 (72.4%) of the 29 edentulous mandibles (Fig 3). There was no correlation n-3 1
%
26.5 (0) 33.6 (22)
80 n-130
?4loo1n
“.I
“1103
n-1 50
50
(8.70
-1
n-34
n-65
loo-
-1
74.2 (23) 60 -
40 -
NoDtSPUCEkENT POSTaP
6.2 WEEKS
15.9 MONTHS
S1P~OS Of treatment
FIGURE 1. Sensory status of the alveolar inferior nerve in different stages of treatment. Number in parentheses indicates number of fractures. q, Normal; n , hypesthesia; H, hyposensibility; K!, hyperesthesia.
DSPLACEWENT .c 5mm
Displacement
of
the
DISPMCEMNT B 5mm fractures
FIGURE 2. Percentage distribution of cases with preoperative hypesthesia in relation to degree of fracture displacement. Number in parentheses indicates number of fractures. Cl, Normal; n , hypesthesia.
1267
IIZUKA AND LINDQVIST
found between the frequency of postoperative paresthesia and other factors, such as delay to treatment, the presence of a tooth in the line of fracture, position of the third molar, location of the fracture line in relation to the third molar, removal or retention of the third molar, and use of MMF. The preoperative sensory status, influenced by the presence of fracture displacement, also did not affect the postoperative situation (Fig 5). Discussion 6.2
weeks
posloperaII~eIy stages
I
15.9
months
porIoparallvely
Of follow-up
FIGURE 3. Percentage distribution of cases with postoperative sensory disturbances in relation to dentate and edentulous patients in the two different stages of follow-up. Number in parentheses indicates number of fractures. 0. Normal; n , hypesthesia; a, hyposensibility; 0, hyperesthesia.
with type of plate in the patient material as a whole. However, analysis of the patient group with edentulous mandibles at an average of 6.2 weeks postoperatively showed a significant difference between types of plate. In the edentulous mandible, sensory disturbance was observed more frequently after stabilizing the fracture using a dynamic compression plate than after using a reconstruction plate (P < .OOl) (Fig 4). At the final follow-up, this difference caused by plate type was not determined because the number of patients was insufficient for detailed statistical analysis. No further correlation was
Various methods of determining sensory function of the mental region have been presented.“.” These include thermal stimulation, von Frey tactile sensation, Weber two-point discrimination, and brush directional measures. The sensitivities of these methods appear to be different. Comparative studies have shown that thermal tests are most sensitive and two-point discrimination least sensitive. l1 The tests used in the present study measure mainly mechanoreception. To evaluate nerve dysfunction accurately, better testing procedures than those used in this study are needed. The present methods were chosen because they are commonly used in follow-up studies of surgically treated mandibular fractures,2*‘2*‘3 and because they are simple and suitable for trauma patients, especially on admission and in the immediate postoperative stage. In clinical practice, simple methods such as light touch and testing for sharp/blunt differentiation, together with a subjective evaluation, give sufficient information about the patient’s sensory problems. According to the results of this study, 76% of the n-54
“-76
,- In--
n-38
n-51
,,,,bCP4
DCP2+4 I_
Types
of plsle
GRCWA
6.2 FIGURE 4. Distribution of sensory disturbances of 49 fractures in edentulous mandibles in relation to type of plate at an average of 6.2 weeks postoperatively. DCP~, Four-hole dynamic compression plate; DCP~+ 4, four-hole dynamic compression plate with a two-hole tension band plate; DC& six-hole dynamic compression plate; RP, reconstruction plate. Two fractures treated with lag screws were excluded. 0, Normal; H, hyposensibility; n , hypesthesia.
weeks
I
GWWE
portoper9tlvely stage*
I
GROWA 15.9
months
postoperatlvely
Of follow-up
FIGURE 5. Percentage distribution of postoperative sensory disturbances in patients with preoperatively normal (group A) and disturbed (group B) sensation. There were no significant differences between the groups. Number in parentheses indicates number of fractures. Cl, Normal; n , hypesthesia; IR, hyposensibility; 8, hyperesthesia.
1266 patients had some degree of sensory disturbance 6 weeks postoperatively and 46.6% experienced sensory disturbance more than 1 year postoperatively. The study by Campbell et al of 21 patients with mandibular body fractures treated with internal fixation reported that postoperatively 81% had poor sensation to thermal stimuli and 67% to von Frey tactile stimulation. l1 Central anesthetic zones on the skin under the lip on the injured side were found in 43% of Campbell’s cases, which corresponds to the rate found in this study. In most studies concerning rigid internal fixation, the rates of postoperative sensory deficit have been lower, varying from 0.9% to 34%.1Y2,5*‘3These rates have, however, always been calculated from the total number of surgically treated mandibular fractures, including those in the symphysis and parasymphysis regions, Fractures in these regions are seldom, if ever, associated with sensory problems. Additionally, as seen in this study, paresthesia diminished with time, and differences in follow-up time in previous studies make it difficult to compare the rates di-
rectly . Another reason for differences in results is that most patients regarded their sensation as normal in their daily activities, although objective testing showed slight sensory disturbance characterized as hyposensibility. This phenomenon has also been observed after mandibular sagittal split osteotomy (SSO). In the study by Coghlan and Irvine, “normal” sensation was demonstrated in 74% of patients after SSO, but objective tests showed normal sensation in 34% only. l4 Cases with slight neurosensory deficits also have probably not always been noted in earlier studies concerning fracture patients. Sensory disturbances after rigid fixation in the body and angle regions are probably more frequent than the rates generally presented. Disturbed sensation following open reduction and rigid fixation has been explained by the fact that major fracture displacements usually have been treated surgically. ‘,12 The results of the present study indicate, however, that preoperative sensory status corresponding to the presence of fracture displacement did not affect the degree of the postoperative sensory disturbance. It seems that the sensory disturbance was also affected by the surgical procedure. Theoretically, the nerve can be involved in traction and/or compression caused by manipulation of fragments during fracture reduction and stabilization. Extraction of a tooth from the line of fracture could also cause injury to the inferior alve-
SENSORY DISTURBANCE
AND MANDIBULAR
FRACTURES
olar nerve. In addition, a bicortical screw placed near the mandibular canal might irritate or damage the nerve. The postoperative sensory deficits observed in this study were possibly a result of the combined effects of all these factors. However, the decisive factor seems to be edentulousness of the mandible; paresthesia was often observed in patients with edentulous and atrophic mandibles. A possible explanation for this correlation is that, due to lack of space, a screw is more likely to be placed in or close to the mandibular canal, thereby causing damage to the inferior alveolar nerve. Therefore, especially in atrophic mandibles, care must be taken to bend the plate to the correct shape and to place it exactly along the inferior border of the mandibule. From this point of view, three-dimensionally bendable reconstruction plates are probably preferable to other plates. References 1. Tu HK, Tenhulzen D: Compression osteosynthesis of mandibular fractures. A retrospective study. J Oral Maxillofac Surg 43585, 1985 2. Lindqvist C, Kontio R, Pihakari A, et al: Rigid internal tixation of mandibular fractures. An analysis of 45 patients treated according to the ASIF method. Int J Oral Maxillofac Surg 15:657, 1986 3. Pogrel MA: Compression osteosynthesis in mandibular fractures. Int J Oral Maxillofac Surg 15:521, 1986 4. Schwimmer AM, Greenberg AM: Management of mandibular trauma with rigid internal fixation. Oral Surg 62:630, 1986 5. Ardary WC: Prospective clinical evaluation of the use of compression plates and screws in the management of mandible fractures. J Oral Maxillofac Surg 47: 1150, 1989 6. Peled M, Laufer D, Helman J, et al: Treatment of mandibular fractures by means of compression osteosynthesis. J Oral Maxillofac Surg 47:566, 1989 7. Bochlogyros PN: A retrospective study of 1,521 mandibular fractures. J Oral Maxillofac Surg 43597, 1985 8. Bruce R, Fonseca RJ: Mandibular fractures. in Fonseca RJ, Walker RV (eds): Oral and Maxillofacial Trauma. Philadelphia, PA, Saunders, 1991, p 414 9. Soiessl B: Internal fixation of the mandible: A manual of _ AO/ASIF principles. Berlin, Springer-Verlag, 1989, p 189 10. Zaytown HS, Phillips C, Terry BC: Long-term neurosensory deficits following transoral vertical ramus and sagittal split osteotomies for mandibular prognathism. J Oral Maxillofac Surg 44: 193, 1986 1I. Campbell RL, Shamaskin RG, Harkins SW: Assessment of recovery from injury to inferior alveolar and mental nerves. Oral Surg 64:519, 1987 12. Niederdellmann H, Shetty V: Solitary lag screw osteosynthesis in the treatment of fractures of the angle of the mandible: A retrospective study. Plast Reconstr Surg 80:68, 1987 13. Raveh J, Vuillemin T, Ladrach K, et al: Plate osteosynthesis of 367 mandibular fractures: The unrestricted indication for the intraoral approach. J Craniomaxillofac Surg 15:244, 1987 14. Coghlan KM, Irvine GH: Neurological damage after sagittal split osteotomy. Int J Oral Maxillofac Surg 15:369, 1986
