J Oral Maxillofac
Surg
50:338-339.1992
The Facial Nerve Function Coefficient: Analysis of 100 Normal Subjects NINIAN S. PECKITT, AND
FRCS ED, FFD RCS,
RITA V. WALKER, GEOFFREY R. BARKER,
FDS
RCS,*
NATCERTBlOL,t FRCS ED, FDS RCS*
MSc,
The Facial Nerve Function Index (FNFI) is a measure of asymmetrical facial movement and is a quick and easy method of monitoring the improvement of function in patients with facial nerve palsy. However, purely as a consequence of the way the index is formulated, and not primarily because of any tendency to biological asymmetry favoring one particular direction in the population, the FNFI has a highly skewed distribution. To remove the inherent asymmetry of the index, a modified index, the Facial Nerve Function Coefficient (FNFC), for which a symmetrical distribution is obtained, is proposed. A reference range for this index was derived.
the video screen and the coordinates were plotted. The image magnification was standardized prior to commencement of the measurements. One image capture at rest and one smiling were subjected to a single set of measurements according to the principles of the FNFI (Fig 2). This produced a skewed distribution, with a wide reference range. The same measurements were also used to calculate a new index (Fig 3) from which a symmetrical distribution would be expected. The inherent asymmetry of the distribution seen with the FNFI was improved, and
Methods of assessment of facial nerve function in relation to facial nerve palsy have been reviewed by Fields and Peck&’ and the Facial Nerve Function Index (FNFI) defined (Fig 1). A study to determine the limits of normal variation of this index between individuals was undertaken using computerized video image capture (Microsclase 2 Digithurst, Mertex 386 Bucon, Swansea, Wales) of the facial muscles at rest and in the smiling posture. Materials and Method One hundred white subjects without history of facial palsy were selected at random from staff at the Dental Hospital Cardiff. The ages ranged from 18 to 5 5 years. These subjects underwent surface measurements of facial muscle tone at rest and in the smiling position. The position of the commissure of the lip and outer canthus of the eye were determined by naked eye on Received from the Dental School, University Hospital of Wales, Heath Park, Cardiff, Wales. * Senior Registrar, Department of Oral and Maxillofacial Surgery. t Research Technician, Department of Oral Surgery. $ Professor and Head, Department of Oral Surgery, Medicine, and Pathology. Address correspondence and reprint requests to Mr Peckitt: Department of Oral and MaxilIofacial Surgery, Dental School, University Hospital of Wales, Heath Park, Cardiff, Wales, UK.
AT REST
SMILING
FIGURE I. The Facial Nerve Function Index (FNFI). Measurements in millimeters are taken from the outer canthus of the eye to the lateral commissure of the mouth at rest and when smiling. The FNFI is very easy to calculate and expressed as a percentage: FNFI = b - d/a - c X 100.
0 1992 American Association of Oral and Maxillofacial Surgeons 0278-2391/92/5004-0005$3.00/0
338
339
PECIUTT, WALKER, AND BARKER
.
. . . .....
. .
...................
. . . . . . .. . ........ ” ......... ..“........”
. . . ; . .... ... . ...
. . . . ...
. .
.
.
.
. .
;0
105
140
l
.
.
.
.
.... . .
.
.
...
.
. . . . . . . . . ...*... . . . . . . . . . . . . . . . . . ..~............. .........
. . . . .
.
.”
.
. . . . .
.
. .
.
~0.16
-0.32 3;
. . .
175
0.0
0.16
0.32
0.48
210
FIGURE 2. The Facial Nerve Function Index (FNFI). Analysis of 100 normal subjects (mean, 92.25 f 60.94). A skewed distribution is produced, related to asymmetrical movements in the normal face when smiling. Therefore, an accurate definition of normal values is not possible, and clinical improvement of facial nerve palsy is only crudely assessed using the FNFI.
FIGURE 4. The Facial Nerve Function Coefficient (FNFC). Analysis of 100 normal subjects. The normal distribution of the FNFC is limited by the way this coefficient is mathematically derived: FNFC = (a - c) - (b - d)/(a - c) + (b - d). The FNFC shows a more normal distribution than the FNFl and more accurate definition of normal values can be determined.
no wide reference range of the distribution was ob., served. We call this modified index The Facial Nerve Coefficient (FNFC). The results are displayed in Figure 4.
deviations. Although the FNFI will remain as a quick clinical indicator of improvement, useful in the outpatient assessment of patients with facial palsy, the FNFC mathematically produces a more symmetrical distribution.
Discussion FNFC
The FNFI,’ as originally formulated, displays a skewed distribution related to asymmetrical movements occurring in the normal face. Normal variation is wide and, although the index is a quick and easy parameter to clinically assess, the skewness of the scale makes it awkward to interpret. This limits the usefulness of the FNFI to a crude determination of clinical improvement, for example, in assessment of facial nerve palsy, without accurate definition of normal values. A case of facial nerve palsy monitored using the FNFC is illustrated in Figure 5. It can be seen that the FNFC level decreases as the palsy disappears. By week 5, the FNFC is within the normal range of two standard
0.7 .
.
WEEK 1 0.63 WEEK 2 0.64 WEEK 5 0.21 WEEK 7 -0.03
‘2SD
i
0.35 . -MEAN
(0.07)
O-
b .
FIGURE 5. The Facial Nerve Function Coefficient (FNFC) in a patient with facial nerve palsy. The FNFC recordings over a 7-week period are shown in a 20-year-old patient with a lower motor neuron (Bell’s) palsy. The patient was treated with high-dose steroid therapy (prednisolone, 60 mg/d) within 12 hours of the onset of the palsy. The FNFC returned to within two standard deviations of the mean by the fifth week after onset of the palsy (mean, 0.07). This implies recovery of the facial nerve to normal ranges of function.
Acknowledgment The authors are grateful for the assistance of Dr Robert G. Newcombe, Senior Lecturer in Medical Statistics, University of Wales College of Medicine, for suggesting the formulation of the FNFC and for statistical assistance.
AT REST
SMILING
FIGURE 3. The Facial Nerve Function Coefficient (FNFC). The FNFC has been formulated to produce a more symmetrical distribution with a narrower reference range (mean, 0.07 f 0.34).
References 1. Fields MI, Peck&t NS. Facial Nerve Function Index: .4 clinical measurement of facial nerve activity in patients with facial nerve palsies. Oral Surg Oral Med Gral Path01 69:68 1, 1990
Surg
50:338-339.1992
The Facial Nerve Function Coefficient: Analysis of 100 Normal Subjects NINIAN S. PECKITT, AND
FRCS ED, FFD RCS,
RITA V. WALKER, GEOFFREY R. BARKER,
FDS
RCS,*
NATCERTBlOL,t FRCS ED, FDS RCS*
MSc,
The Facial Nerve Function Index (FNFI) is a measure of asymmetrical facial movement and is a quick and easy method of monitoring the improvement of function in patients with facial nerve palsy. However, purely as a consequence of the way the index is formulated, and not primarily because of any tendency to biological asymmetry favoring one particular direction in the population, the FNFI has a highly skewed distribution. To remove the inherent asymmetry of the index, a modified index, the Facial Nerve Function Coefficient (FNFC), for which a symmetrical distribution is obtained, is proposed. A reference range for this index was derived.
the video screen and the coordinates were plotted. The image magnification was standardized prior to commencement of the measurements. One image capture at rest and one smiling were subjected to a single set of measurements according to the principles of the FNFI (Fig 2). This produced a skewed distribution, with a wide reference range. The same measurements were also used to calculate a new index (Fig 3) from which a symmetrical distribution would be expected. The inherent asymmetry of the distribution seen with the FNFI was improved, and
Methods of assessment of facial nerve function in relation to facial nerve palsy have been reviewed by Fields and Peck&’ and the Facial Nerve Function Index (FNFI) defined (Fig 1). A study to determine the limits of normal variation of this index between individuals was undertaken using computerized video image capture (Microsclase 2 Digithurst, Mertex 386 Bucon, Swansea, Wales) of the facial muscles at rest and in the smiling posture. Materials and Method One hundred white subjects without history of facial palsy were selected at random from staff at the Dental Hospital Cardiff. The ages ranged from 18 to 5 5 years. These subjects underwent surface measurements of facial muscle tone at rest and in the smiling position. The position of the commissure of the lip and outer canthus of the eye were determined by naked eye on Received from the Dental School, University Hospital of Wales, Heath Park, Cardiff, Wales. * Senior Registrar, Department of Oral and Maxillofacial Surgery. t Research Technician, Department of Oral Surgery. $ Professor and Head, Department of Oral Surgery, Medicine, and Pathology. Address correspondence and reprint requests to Mr Peckitt: Department of Oral and MaxilIofacial Surgery, Dental School, University Hospital of Wales, Heath Park, Cardiff, Wales, UK.
AT REST
SMILING
FIGURE I. The Facial Nerve Function Index (FNFI). Measurements in millimeters are taken from the outer canthus of the eye to the lateral commissure of the mouth at rest and when smiling. The FNFI is very easy to calculate and expressed as a percentage: FNFI = b - d/a - c X 100.
0 1992 American Association of Oral and Maxillofacial Surgeons 0278-2391/92/5004-0005$3.00/0
338
339
PECIUTT, WALKER, AND BARKER
.
. . . .....
. .
...................
. . . . . . .. . ........ ” ......... ..“........”
. . . ; . .... ... . ...
. . . . ...
. .
.
.
.
. .
;0
105
140
l
.
.
.
.
.... . .
.
.
...
.
. . . . . . . . . ...*... . . . . . . . . . . . . . . . . . ..~............. .........
. . . . .
.
.”
.
. . . . .
.
. .
.
~0.16
-0.32 3;
. . .
175
0.0
0.16
0.32
0.48
210
FIGURE 2. The Facial Nerve Function Index (FNFI). Analysis of 100 normal subjects (mean, 92.25 f 60.94). A skewed distribution is produced, related to asymmetrical movements in the normal face when smiling. Therefore, an accurate definition of normal values is not possible, and clinical improvement of facial nerve palsy is only crudely assessed using the FNFI.
FIGURE 4. The Facial Nerve Function Coefficient (FNFC). Analysis of 100 normal subjects. The normal distribution of the FNFC is limited by the way this coefficient is mathematically derived: FNFC = (a - c) - (b - d)/(a - c) + (b - d). The FNFC shows a more normal distribution than the FNFl and more accurate definition of normal values can be determined.
no wide reference range of the distribution was ob., served. We call this modified index The Facial Nerve Coefficient (FNFC). The results are displayed in Figure 4.
deviations. Although the FNFI will remain as a quick clinical indicator of improvement, useful in the outpatient assessment of patients with facial palsy, the FNFC mathematically produces a more symmetrical distribution.
Discussion FNFC
The FNFI,’ as originally formulated, displays a skewed distribution related to asymmetrical movements occurring in the normal face. Normal variation is wide and, although the index is a quick and easy parameter to clinically assess, the skewness of the scale makes it awkward to interpret. This limits the usefulness of the FNFI to a crude determination of clinical improvement, for example, in assessment of facial nerve palsy, without accurate definition of normal values. A case of facial nerve palsy monitored using the FNFC is illustrated in Figure 5. It can be seen that the FNFC level decreases as the palsy disappears. By week 5, the FNFC is within the normal range of two standard
0.7 .
.
WEEK 1 0.63 WEEK 2 0.64 WEEK 5 0.21 WEEK 7 -0.03
‘2SD
i
0.35 . -MEAN
(0.07)
O-
b .
FIGURE 5. The Facial Nerve Function Coefficient (FNFC) in a patient with facial nerve palsy. The FNFC recordings over a 7-week period are shown in a 20-year-old patient with a lower motor neuron (Bell’s) palsy. The patient was treated with high-dose steroid therapy (prednisolone, 60 mg/d) within 12 hours of the onset of the palsy. The FNFC returned to within two standard deviations of the mean by the fifth week after onset of the palsy (mean, 0.07). This implies recovery of the facial nerve to normal ranges of function.
Acknowledgment The authors are grateful for the assistance of Dr Robert G. Newcombe, Senior Lecturer in Medical Statistics, University of Wales College of Medicine, for suggesting the formulation of the FNFC and for statistical assistance.
AT REST
SMILING
FIGURE 3. The Facial Nerve Function Coefficient (FNFC). The FNFC has been formulated to produce a more symmetrical distribution with a narrower reference range (mean, 0.07 f 0.34).
References 1. Fields MI, Peck&t NS. Facial Nerve Function Index: .4 clinical measurement of facial nerve activity in patients with facial nerve palsies. Oral Surg Oral Med Gral Path01 69:68 1, 1990
