INTRODUCTION

 

The zygomaticomaxillary complex (ZMC) plays a key role in the structure, function, and aesthetic appearance of the facial skeleton. The ZMC fracture is the second most frequent facial fracture¹. The reported incidence of posttraumatic sensory disturbance of ION in ZMC fractures varies from 24- 94% due to the close proximity of the nerve to the ZMC with higher incidence in displaced than non displaced fractures.²

Various methods have been used to evaluate the ION function including patient questionnaire and sophisticated examination modalities. The selection of technique includes time considerations because the most reliable and accurate methods require multiple repetitions of stimuli.³ Sensory assessment helps acquiring a clinical diagnosis, distinguishing the degree of nerve injury and monitoring its recovery, determining the need of micro-surgery, monitoring sensory nerve recovery following micro-surgery and to help medico legal evaluation.⁴ Hence, the purpose of this study was to evaluate the efficacy of trigeminal somatosensory evoked potential (TSEP) as an objective neurosensory test pre and post operative, after rigid fixation of the ZMC fracture.

PATIENTS AND METHODS

 

Twelve patients with unilateral ZMC fractures were included in the present study. They were selected from the out-patient clinic of Oral and Maxillofacial Surgery Department, Faculty of Oral and Dental Medicine, Cairo University.

 

Diagnosis was made on clinical features and confirmed on basis of radiographic findings. The selected patients were treated with open reduction and internal rigid fixation using 2.0 mm titanium plates and screws, and assigned into one of the study groups.

-        Group I: included 6 patients with displaced ZMC fracture.

-        Group II: included 6 patients with non displaced ZMC fracture.

 

All patients were operated under general anesthesia (GA). The surgical field was scrubbed and draped according to the regular surgical standards. Temporary tarsorrhaphy suture was performed to protect the cornea and to retract the lower eyelid superiorly. Surgical access was usually performed through subcillary, buccogingival and lateral eyebrow approaches.

Neurosensory Examination

Assessment of the infraorbital nerve function was performed preoperatively, 2 and 12 weeks post-operatively for both sides (affected and non affected) in each group through:

 

A)           Patient's questionnaire:

Patient's questionnaire was used to assess neurosensory disturbance of infraorbital nerve.

 

B) Trigeminal somatosensory evoked potential technique:

Trigeminal somatosensory evoked potentials were recorded by Schwarzer-Myos Unit (Schwarzer GmbH, Myos4, Serial Number 500588). The recording electrode was placed contra lateral to the side of stimulation 2cm posterior to C₃ and C₄ at the coronal suture (according to the international 10-20 system recording sites). A reference electrode was placed at mid frontal site and the array was earthed by ground electrode placed around neck.

The electrical stimulator provided stimuli at a rate of 2/second and each stimulus lasted for 0.1 sec. The stimulus intensity was adjusted by gradual increasing up to the level where minimal lower eye lid twitch could be observed. In order to achieve pure sensory stimulation with maximum activation of the nerve fibers and minimum electrical artifact, the ION stimulation was performed at the ION foramen using the stimulator electrode of TSEP. TSEP was at least repeated twice to confirm the reproducibility and reliability of the response; TSEP were recorded for both sides. Latencies and amplitudes for each TSEP were determined and tabulated.

Obtained data were represented as mean, standard deviations, frequencies, and percentages. Chi-square was used for comparison between subjective assessments at each observation period.

 

RESULTS

 

The current study was applied on 12 patient, 10 males and 2 females. Their age at time of injury ranged from 20-42 with a mean of 31 years. The main etiological factors of fracture in this study were, motor vehicle accident in 7 patients, while 5 patients were due to inter-personal violence. Healing was uneventful except: Shortening in the lower eyelid was observed in 2 patients (16.6%) in group II. Intraoral wound dehiscence was observed in 1 patient (8.3%) in group I.

 

Neurosensory testing results

1)            Patient's questionnaire:

Comparing the two groups regarding subjective assessment results revealed that at 12 weeks postoperatively only one patient of group I reported numbness sensation over the upper lip of the affected side while 2 patients of group II reported persistence of numbness; one of them reported numbness over the lower eyelid and the upper lip of the affected side, while the other one over the upper lip only.

There was no statistically significant difference between the two groups as regards the lower eyelid and lateral side of the nose sensory symptoms. While the upper lip showed no statistical significant difference between the two groups pre-operatively and after 12 weeks. After 2 weeks, displaced group showed statistical significant higher prevalence of numbness sensation than non-displaced group (Table 1).

 

2)            Trigeminal somatosensory evoked potentials:

Preoperatively: mean peaks latency of the affected side in group I was 11.06±2.5 msec and 9.27±1.4 msec in normal side of the same group. While in group II mean peaks latency of affected side was 9.98±2.9 msec and in normal side was 11.08±3.5 msec. The mean amplitude in group I was 183.1±110.5 mv while for group II it was 264.4±219 mv. Two weeks postoperatively: mean peaks latency of the affected side in group I was 9.69±3.4 msec and 9.40±4.2 msec of the normal side of the same group. While in group II mean peak latency of the affected side was 10.03±2.7 msec and 9.52±1.1 msec for normal side. The mean amplitude in group I 35.6±8.7 mv while for group II it was 93.4±57.2 mv. Twelve weeks postoperatively: mean peaks latency of the affected side in group I was 7.26±1.4 msec and 7.07±1.5 msec in the normal side. While for group II mean peak latency of the affected side was 8.10±2.6 msec and 7.52±1.8 msec in normal side the mean amplitude in group I 126.4±100.9 mv while for group II 75.9±21 mv. Comparing the mean and standard deviation (SD) values of latency in the two groups revealed that there was no statistically significant difference between mean latency in the two groups either in affected or normal side (Figure 1).

Comparing preoperative with 2 and 12 weeks postoperative results in group I revealed mean differences of latencies in the affected side -1.36±1.7 msec, -2.45±2.2 msec and -3.80±1.5 msec respectively. This revealed that there was no statistical significant change in mean latency after 2 weeks in the affected side. From 2-12 weeks, there was a statistical significant decrease in mean latency. Comparing the pre-operative measurement with 12 weeks measurement, a statistical significant decrease in mean latency was observed.

Comparing TSEPs preoperatively with 2 and 12 weeks postoperative intervals in affected sides in group II revealed that the mean differences in latencies in the affected side was 0.06±2 msec, -1.93±1.1 msec and -1.87±1 msec respectively. There were no statistical significant changes in mean latency after 2 weeks. From 2-12 weeks, there was a statistical significant decrease in mean latency. Comparing the pre-operative with 12 weeks measurements, there was a statistical significant decrease in mean latency. Comparing the 2 groups according to percentage changes in latency in both affected and normal sides showed that in the affected side there was no statistical significant difference between means % change in latency of the two groups after 2 weeks and from 2-12 weeks. Through the pre-operative - 12 weeks period, group I showed statistical significant lower mean % change than group II.

Comparing group I and group II according to percentage changes in amplitude revealed that there was no statistical significant difference between means % change in amplitude of the two groups after 2 weeks and through pre-operative -12 weeks period. From 2-12 weeks, group I showed statistical significantly lower mean % change than group II. Association between the subjective symptoms and latencies of TSEP revealed that there was no statistically difference between latencies in patients with or without numbness in both groups.

 

 

Table 1. Frequencies, percentages and results of chi-square test for comparison between subjective assessments in the two groups.

 

Site	Group Period	Displaced		Non-displaced		P-value
		Frequency	%	Frequency	%
Lower eyelid	Pre-operative	6	100	6	100	NC**
	2 weeks	1	16.7	2	33.3	0.505
	12 weeks	0	0	1	16.7	0.296
Lateral skin of the nose	Pre-operative	6	100	6	100	NC**
	2 weeks	2	33.3	0	0	0.121
	12 weeks	0	0	0	0	NC**
Upper lip	Pre-operative	6	100	6	100	NC**
	2 weeks	6	100	3	50	0.046*
	12 weeks	1	16.7	2	33.3	0.505

* Significant at p < 0.05, NC ** Not Computed because the variable is constant

 

 

 

Figure 1. Histogram showing comparison between means, standard deviation values of the latency in the two groups.

DISCUSSION

 

Posttraumatic recovery of the injured ION drew the attention of many researchers⁵. Several studies have evaluated the ION function following treatment of the ZMC fractures by patient’s self assessment of pain, temperature and pressure ^6-7. Yekta et al.⁶, assessed patients after orofacial intervention using  psychophysical  means to monitor somatosensory deficits of trigeminal nerve dysfunction and proved to be a noninvasive way for assessment of sensory nerve functions.

Numbness sensation was the subjective symptom utilized to assess ION function in the present study. Research efforts have not yet evaluated ION response to the three point fixation of non displaced ZMC fractures using a reliable objective method. In our study, the use of TSEP as a quantitative measure to assess the nerve function was based on published studies that considered TSEP an objective, non-invasive way of testing neurosensory nerve function in maxillofacial region.⁸

The results of this study revealed that the infraorbital nerve sensory disturbances occurred in all patients (100%) regardless the group preoperatively. The recovery rate of ION of the displaced group (83.3%) compared favorably with the numbers given by other studies.  According to the literatures, the recovery rate of ION in zygomatic fractures ranges between 70-77% following open reduction and single point miniplate fixation along the ZF suture while closed reduction without osteosynthesis or open reduction with wire fixation of ZMC fracture yielded 47-57% cure rate.⁹ The high recovery rate of ION function in our series relative to the previous studies could be attributed to the miniplate fixation along the ZMC fracture sites with subsequent stability of the fractured bone during healing, minimize traction upon the nerve and allowing proper nerve regeneration. Furthermore, our finding is in agreement with that of Westermarck et al.¹¹, who stated that the incidence of the infraorbital nerve hypoesthesia following fracture of the zygomatic complex can be reduced if rigid fixation is applied on the infraorbital rim.

The rate of complete recovery of ION function in group II of the current study was 66.7% three months postoperatively which compared favorably to various authors.¹¹

In the present work, TSEP measurement revealed that latency prolongation of the first peak wave is the most marked feature of sensory impairment preoperatively. This is in general agreement with the study of Barker et al.¹² who found that the extent of latency delay between traumatized and control sides up to 2 or 3 msec is an indication for nerve injuries.

Comparison between the results of subjective assessment and latency values obtained from TSEP revealed no statistical significant difference between both groups. Our results contradict with Bailey et al.¹³ and Seif El-Din⁹, who found that the level of subjective complaint was higher when compared with TSEP. This difference might be attributed to the difference in procedures used. Bailey et al.¹³ evaluated the long term sensory changes following mandibular augmentation procedures. On the other hand Seif El-Din⁹, evaluated the neurosensory function of ION following bilateral sagittal split osteotomy either in case of mandibular advancement or mandibular setback.

In the present study, the amplitude measurement has been described but could not be used as a diagnostic parameter to assess the ION function as it showed great variability between the patients and even in the same patient in each observation period as its data did not follow normal distribution. We relied upon the waveform latency, in agreement with other literatures^14,15 that suggested waveform latency measurement to be the most informative reliable and diagnostic parameter of TSEP.

Although this study was based on limited number of patients (12 patients), the data suggests feasibility and reliability of the trigeminal somatosensory evoked potential test as an objective clinical method for assessment of ION function pre and post rigid fixation of ZMC fractures. The results of the present study emphasized the importance of presurgical patient counseling for medico-legal purpose.

 

Conclusion

1.        The insignificant difference between subjective and objective methods indicates the reliability of patient’s self assessment of neurosensory dysfunction.

2.        TSEP represents an objective, sensitive, non invasive method of testing neurosensory nerve function.

3.        TSEP is suggested to be used for medico-legal purpose.

4.        Further studies are needed to answer the questions of whether or not and to what extent the sensibility disorders are due only to the trauma or also to the tissue manipulation during open surgery.

 

[Disclosure: Authors report no conflict of interest]

 

 

REFERENCES

 

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