Facial motion analysis of acid burn victims—Development of a new facial motion impairment index

JBUR-2422; No of Pages 10

Facial motion analysis of acid burn victims—Developmentof a new facial motion impairment index

Samuel Ghani a,*, Ashim Mannan a, Ahmed Kaucer a, Samanta Lal Sen b, Alex Clarke c,Peter Butler c, Annabel Cartwright d

aThikhana House, Acid Survivors Foundation, Dhaka, BangladeshbDhaka Medical College Hospital, Dhaka, BangladeshcDepartment of Plastic Surgery, Royal Free Hospital, London, UKdDepartment of Astrophysics, University of Cardiff, Cardiff, UK

b u r n s x x x ( 2 0 0 7 ) x x x – x x x

a r t i c l e i n f o

Article history:

Accepted 5 August 2006

Keywords:

Acid assault

Facial burns

Facial motion analysis

Facial motion impairment index

a b s t r a c t

Objectives: Evaluation of facial movement is necessary for the assessment of motor deficits

and planning reconstructive surgery in facial burns. Clinicians recognise the need for an

accurate and reproducible method of functional assessment. We propose a new facial

functional impairment index (FFII) for assessing facial motor dysfunction due to severe

burn injury and provide inter/intra-patient comparison for documenting rehabilitation.

Methods: The maximal static response assay (MSRA) was used to compare facial movement

in 20 acid burn victims with 20 control subjects. Data compiled from 12 soft tissue landmarks

was used to quantify rest and dynamic asymmetry, anatomic and non-anatomic motion

and calculate the FMII. The Katz score, Nottingham index and number of affected aesthetic

units provided insight into FFII efficacy.

Results: Patients with greater aesthetic disfigurement demonstrated significantly poorer

anatomic function (c = 0.62; p = 0.03) as well as larger global facial functional impairment

(c = 0.52; p = 0.08).

Conclusion: Acid burns caused severe asymmetry and functional impairment. The FFII is a

composite score of global function based on a reproducible method of data collection and it

differentiated between acid burn victims and provided objective comparative measures.

Software automation, integration of video and 3D data, appropriate graphical and pictorial

depiction of variables and measurements, and further research into the accuracy of FFII as a

marker of clinical recovery and assessment of function in facial burns, will enhance future

clinical applications and potentially aid surgical reconstruction.

# 2006 Elsevier Ltd and ISBI. All rights reserved.

avai lab le at www.sc iencedi rec t .com

journal homepage: www.e lsev ier .com/ locate /burns

1. Introduction

The need for an accurate and reproducible method of

assessing facial function, and planning surgical reconstruc-

tion, has long been recognised by clinicians. Most efforts

focussed on patients suffering congenital and/or acquired

* Corresponding author at: 34 Miles Drive, Thamesmead, London SE28E-mail address: [email protected] (S. Ghani).

0305-4179/$30.00 # 2006 Elsevier Ltd and ISBI. All rights reserved.doi:10.1016/j.burns.2006.08.024

Please cite this article in press as: Ghani S, et al., Facial motion ana

impairment index, Burns (2007), doi:10.1016/j.burns.2006.08.024

facial paralysis [1–15]. Traditional assessments of facial

movement and the degree of facial dysfunction relied on

the subjective judgement of a trained observer.

Numerous subjective facial functional grading scales have

been proposed. Most notable of these include the House–

Brackman grading scale (HBGS), Toronto (Sunnybrook) facial

0JA, UK.

lysis of acid burn victims—Development of a new facial motion

mailto:[email protected]

http://dx.doi.org/10.1016/j.burns.2006.08.024


b u r n s x x x ( 2 0 0 7 ) x x x – x x x2


grading system and the facial clinimetric evaluation scale

(FACE) [5,16,17]. The HBGS is regarded as the gold standard.

However, recent advances in objective grading systems,

using photographic and video analysis of the mimic muscle

system, have rendered subjective assessments unsuitable for

detecting clinically important change over the course of time

and/or treatment [15]. Most objective grading systems are

based on measuring displacement of pre-defined soft tissue

landmarks [7–9,13]. Photographic analysis yielding displace-

ment vectors, following a series of voluntary facial anima-

tions, is defined as the maximal static response assay (MSRA).

Recently emphasis has shifted to perfecting the measurement

of mimic movements in three dimensions as opposed to two

[18–20].

Despite new methods of objective measurement of facial

motion, authors found it difficult to integrate these into an

objective ‘facial functional impairment index’. Murty et al.

[13] proposed the Nottingham system for scoring unilateral

facial paralysis—an objective facial functional grading tool

measuring inter-landmark distances during eyebrow raise,

maximal eye closure and closed lip smile and expressing

them as a ratio of affected side to unaffected. However,

Linstrom demonstrated flaws in this approach. He showed

that unilateral facial paralysis patients with synkinesis move

not only remote regions of the face on the affected side, but

also remote regions on the normal side in an attempt to

compensate for the loss of function on the affected side [21].

Hence, the Nottingham index, reliant on comparison between

both sides of the face, is inherently compromised by this

overcompensation. In addition this scale is not applicable in

bilateral facial pathology.

The vast majority of functional assessment has been

within the context of facial paralysis with little attention to

facial trauma. The concept of developing a facial functional

analysis protocol for reliable assessment of facial pathology

ranging from paralysis to trauma and their associated

complications has not been actively considered.

House defined the requirements of an effective facial

grading system as follows: scoring should differentiate

between patients who are different; should represent some-

thing meaningful and defined; and should measure secondary

defects—for example synkinesis, crocodile tears, eye dryness

and taste disturbances in facial paralysis. Facial dysfunction

should also be measured on a continuum, to effectively

measure intermediate levels and differentiate subtle differ-

ences in facial function [22,23]. This was reinforced by

Linstrom’s suggestion of an international facial nerve grading

system, emphasising the importance of a composite score of

several different observations yielding both a total picture

(Gestalt) of the whole and regional pictures of facial expression

[18]. The aim of this study was to develop a new facial

functional impairment index (FFII) to allow effective inter-

patient comparison and objective quantification of facial

function.

2. Materials and methods

We conducted this study in Bangladesh and performed facial

functional analysis of acid burn victims using MSRA. Acid



attacks are a unique form of vicious violence resulting in

permanent physical stigmata including devastating facial

scarring, visual impairment and blindness [24,25]. Bangladesh

has the highest reported incidence of acid attacks in the world

constituting 9% of all burns [25,26]. Perpetrators normally

target the face, although burns to the scalp, neck and arms are

frequent. Ethical approval was obtained from the Royal Free

Hospital, London.

2.1. Patient group

Twenty female acid burn victims were recruited from the

Acid Survivors Foundation—a non-government organisation

set up to cater for the medical, surgical and psychological

needs of acid burn survivors. Patients ranged from 16 to 25

years of age. All were of Bangladeshi origin and had been

attacked with sulphuric acid. All burns were due to refusal of

sexual advances or marriage proposals from male perpe-

trators. A lack of first aid knowledge resulted in none of

these patients receiving immediate irrigation of wounds and

mean time of presentation to a tertiary care centre was 4.5

days. All patients underwent a minimum of two full

thickness skin grafts and prior to our assessment had not

been subjected to any surgical intervention for at least 2

years. Scarring ranged from mild to severe hypertrophic

scarring. Patients with keloids were excluded from this

assessment.

2.2. Control group

Twenty females with no history of facial disfigurement or

facial pathology were selected. They ranged from 16 to 21

years of age and were all of Bangladeshi origin and similar

socio-economic status.

2.3. Aesthetic assessments

Digital AP photographs (SONY DSC-L1) of the control and

patients groups were taken at rest. The inner canthal–lateral

oral commissure, outer canthal–lateral oral commissure and

alar–lateral oral commissure distances were measured and

expressed as a ratio of right to left. Individual patient ratios

were statistically compared to mean control group measures.

z-Scores were calculated based on control group mean and

standard deviations. For patients with z-scores greater than 2,

cumulative probability scores were used to devise a contin-

uous asymmetry index from 0 to 1. All those with z-scores less

than 2 (i.e. within 95% confidence interval) had an asymmetry

index of 0.

Mean control facial shape was calculated and expressed as

the ratio of bizygomatic width to face height (nasion to most

inferior midpoint on the chin). Subsequently the facial shape

index was calculated for each patient and statistically

compared to the control group [27].

Patient group facial disfigurement was assessed using the

Katz score and the number of affected aesthetic units based on

Gonzales–Ulloas’s original regional classification [28,29]. The

presence and magnitude of scleral show was noted in acid

burn patients as well as ectropion, corneal scarring and

presence/absence of complete loss of the auricle.



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2.4. Functional assessment

A MSRA analysis of the control and patient groups was

conducted. Twelve soft tissue landmarks were highlighted on

all subjects using a surgical marker pen (Fig. 1):

1. Below lower lip at the midpoint of the left and right lateral

oral commissures.

2. Right lateral oral commissure.

3. Left lateral oral commissure.

4. Above upper lip at the midpoint of the left and right lateral

oral commissures.

5. Right infraorbit.

6. Rhinion (bony-cartilaginous junction along the nasal

dorsum).

7. Left infraorbit.

8. Right lateral canthus.

9. Right superiority.

10. Point directly above the rhinion in line with the left and

right supraorbit.

11. Left superiority.

12. Left lateral canthus.

Patients were asked to stand to their full height and place

their head within a fixed space frame measuring

30 cm � 30 cm. They rested their chin on a chin rest and head

was secured using the head clamp. A series of digital

photographs were taken of the following facial animations:

Fig. 1 – Facial motif illustrating soft tissue landmarks

highlighted for maximal static response assay

measurement.



1. Neutral pose (Rest).

2. Eyebrow raise (ER).

3. Maximum eye closure—eyes closed as tightly as possible

(MEC).

4. Minimum smile—smile without opening the mouth (MINS).

5. Maximum smile—smile showing the teeth (MAXS).

6. Purse lip (PL).

Each patient repeated these facial animations three times.

Images were downloaded and edited on Adobe Photoshop

5.5ME (Adobe Systems Inc., Mountain View, CA). All twelve

points marked on the face at rest, were given a (x, y) coordinate

based on an origin sited at the midpoint of the inter-tragal

distance [21,30]. Following each facial expression the new

positions of each of the 12 points were measured and resultant

vectors relative to neutral pose, were calculated.

Soft tissue displacement was subdivided into anatomic and

non-anatomic components. Anatomic motion is termed the

motion of specific facial points studied by the MSRA that can

be attributed solely to the pull of the regional facial muscles

that govern the movement of these points [31]. Non-anatomic

motion is described as movement at points elsewhere on the

face. Designation of anatomic and non-anatomic motion was

standardised based on the facial action coding sequence

(FACS). This is a database consisting of breakdown of facial

expressions into action units that correspond to specific facial

muscles responsible for the facial expression under consid-

eration [32,33] (Table 1).

For each facial expression, markers within the ‘active’

regions of the face demonstrated activity of specific muscle

groups defined by the FACS. Movement at all other landmarks

was considered non-anatomic. This classification was carried

out for each facial expression enabling functional analysis of

the upper, mid and lower thirds of the face. In addition the

Nottingham score was also calculated for all patients.

2.5. Facial functional impairment index (FFII)

Statistical comparison of patient derived vectors for each soft

tissue landmark for each facial expression with corresponding

mean control group vectors was carried out. z-Scores of

greater than 2 were regarded as being significantly abnormal.

Cumulative probability scores for significantly abnormal

vectors were used to calculate a continuous impairment

index, ranging from 0 to 1, for a variety of parameters

consisting of: (1) x-directional movement; (2) y-directional

movement; (3) total magnitude; (4) bearing. These were

totalled to produce the facial functional impairment index

(FFII). The FFII was subsequently broken down into anatomic

and non-anatomic components based on soft tissue designa-

tions described above. The complete method for FFII calcula-

tion was reviewed by a mathematician and found to be sound.

2.6. Statistical analysis

Rest asymmetry, facial shape index, Katz score, affected

aesthetic units, Nottingham score and facial functional impair-

ment index were all measured and calculated for the patient

group.Statistical analysis of relationship between aesthetic and

functional measures of disfigurement was conducted.



Table 1 – Table listing the action units and muscles actively involved in each facial expression assessed

Facial expression (AU: action unit) Anatomic (blue) and non-anatomic (red)

Eyebrow raise (ER)

AU 1: frontalis, pars medialis

AU 2: frontalis, pars lateralis

Maximum eye closure (MEC)

AU 4: corrugator supercilli, depressor supercilli

AU 43: orbicularis oris, pars palpebralis

Minimum smile (MINS)

AU 6: orbicularis oculi, pars orbitalis

AU 12: zygomaticus major

AU 14: buccinator

AU 24: orbicularis oris (lips pressed together)

Maximum smile (MAXS)

AU 6: orbicularis oculi, pars orbitalis

AU 12: zygomaticus major

AU 20: risorius with platysma

AU 25: depressor labii inferioris

Purselip (PL)

AU 18: incisive labii superioris, incisive labii inferioris

Adjacent facial motifs showing designated anatomic and non-anatomic soft tissue landmarks. This designation is later used to derive

anatomic and non-anatomic facial functional impairment scores.

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3. Results

3.1. Aesthetic assessments

Control subjects were of poor socioeconomic status and had

no history of facial trauma, otologic or neurotologic

disorders, facial plastic or otologic surgery; and no known



lesion which would predispose the individual to facial

paralysis [21]. Patient group consisted of 10 individuals with

unilateral burns and 10 with bilateral. Facial lesions involved

both skin and muscle. Contractures and hypertrophic scars

were widespread and all injuries were full thickness. Specific

facial injuries included scalp burns (45%), ear injuries and/or

complete loss of the auricle (55%), nose injuries (85%), lips



Fig. 2 – Graph showing excellent positive correlation

between Katz score and the number of affected aesthetic

units.

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(55%) and neck involvement (40%). Ophthalmic injuries

consisted of scleral show (65%), eyelid injuries (75%),

ectropion (25%) and corneal scarring (30%). They were

initially treated in Bangladesh and received localised

pressure therapy and steroid injections in addition to basic

surgical scar treatments.

3.2. Asymmetry index

The control group demonstrated level horizontal inner canthi,

outer canthi and lateral oral commissures with no scleral

show. There was no significant rest asymmetry. The mean left

outer canthal–lateral oral commissure distance was slightly

greater than the right (t-test: p = 0.56, p > 0.05). Mean right

inner canthal–lateral oral commissure and alar–lateral oral

commissure distances were greater than the left (t-test:

p = 0.09 and p = 0.069). Mean total difference between right

and left measures was 0.37 cm with a standard deviation of

0.21 cm.

Most patients complained of significant tightening of the

skin, pruritis, pain, and muscle spasm. Ten acid burn victims

demonstrated significant canthal asymmetry. These

patients had widespread unilateral or bilateral burns and

resultant abnormal displacement of the canthi was the

net result of contractual forces acting from above and/or

below.

Amongst the patient group, the inner canthi, outer canthi

and lateral oral commissures were found to be asymmetric in

the horizontal plane. Mean right left measure differences were

significantly greater for patients than control group (p = 0.003;

p < 0.05). Unilateral and bilateral burns, individually, had

significantly greater asymmetry than control group (p = 0.006

and p = 0.005, respectively). There was no significant differ-

ence in asymmetry between patients with unilateral and

bilateral burns.

3.3. Facial shape

There was no significant difference between patient and

control bizygomatic ( p = 0.53), facial height (p = 0.29) and

subsequent facial shape index (p = 0.14).

Fig. 3 – Total, anatomic and non-anatomic marker displacemen

maximum eye closure; MINS: minimum smile; MAXS: maximu



3.4. Katz score and aesthetic units

The mean Katz score was 6.9 (range = 6) with five patients

scoring � 8 (maximum score = 9). Standard deviation was 1.5.

The mean number of burn affected aesthetic units was 5.4

units with a standard deviation of 2.6. The Katz score and

number of affected aesthetic units are both markers of

aesthetic disfigurement and correlated well. A correlation

coefficient of 0.86 was achieved with a p-value of <0.01 for

ANOVA single factor analysis (Fig. 2).

3.5. Functional assessment

All normal subjects were able to carry out each facial

animation. Acid burn victims demonstrated reduced mean

total marker displacement (sum of vector magnitude for each

soft tissue marker) for each facial expression, except eyebrow

raise (ER), relative to control group. Total displacement was

subdivided into anatomic and non-anatomic components for

each facial expression. Total patient mean anatomic displace-

ment was reduced in maximum eye closure (MEC), maximum

smile (MAXS), and significantly in minimum smile (MINS).

t for patients and controls. ER: eyebrow raise; MEC:

m smile; PL: purse lip.



Table 2 – Two tailed t-test p values for mean totaldisplacement (cm) for control subjects and acid burnpatients

Facial animation Two tailed t-test p values

Total Anatomic Non-anatomic

Eyebrow raise 0.42 0.38 0.57

Max eye closure 0.15 0.12 0.86

Min smile 0.20 0.01 0.43

Max smile 0.20 0.08 0.78

Purse lip 0.65 0.63 0.19

There was no significant difference in total displacement between

controls and patients for any expression.

Fig. 4 – Graph showing global FFII scores for each patient

with global anatomic FFII (blue) and global non-anatomic

FFII (red) components. (For interpretation of the references

to colour in this figure legend, the reader is referred to the

web version of the article.)

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Conversely total patient mean non-anatomic displacement

was greater in ER, MINS and MAXS. However, this was not

statistically significant. There was no significant difference in

total displacement between controls and patients for any

facial expression. These findings are summarised in Fig. 3 and

Table 2.

3.6. Facial functional impairment index

The Nottingham score and facial functional impairment index

(FFII) were calculated for each patient. ‘Global’ FFII scores were

subdivided into anatomic and non-anatomic components.

The FFII scores are based on a continuous scale with a

maximum possible impairment score of 100. Hence, impair-

ment scores are expressed as percentages and listed in Table 3,

as well as corresponding affected aesthetic units, Katz and

Nottingham scores. The global FFII score is the sum of the

anatomic and non-anatomic error components and is pre-

sented in the bar chart in Fig. 4.

Table 3 – Table presenting all error indices used to assess fac

Patient Unilateralbilateral burn

Katzscore

Aestheticunits

Notts

1 Unilateral 6 4 N

2 Bilateral 7 5 5

3 Bilateral 7 3.5 5

4 Unilateral 6 3.5 9


6 Bilateral 9 8 8

7 Bilateral 8 10 4

8 Bilateral 9 9.5 7


10 Bilateral 7 3.5 8









19 Bilateral 9 9 7


Patients highlighted in bold were unable to carry out satisfactorily all fa



All measures of facial function were statistically com-

pared to the area of facial injury (i.e. number of burn affected

aesthetic units score). Correlation coefficients and the

results of ANOVA analysis are presented in Table 4 and

Fig. 5.

Nottingham score was negatively correlated with burn area

and not significant (coefficient = �0.43/�0.31; p-values = 0.064/

0.327). On categorising patients into unilateral and bilateral

burns the number of affected aesthetic units for bilateral

ial function for 20 acid burn patients

inghamcore

Facial motion impairment index

Anatomicerror (%)

Non-anatomicerror (%)

Combinederror (%)

/A N/A N/A 12.42354

4 7.35547 6.817455 14.17293

9.65 7.654775 8.276555 15.93133

5.86 7.02042 7.603165 14.62358

7.42 5.341415 5.01655 10.35797

0.80 8.32016 10.1482 18.46836

4.44 5.63272 7.54895 13.18167

9.73 10.26859 9.438335 19.70692

7.86 6.192495 7.350405 13.54289

0.43 4.656638 6.202345 10.85898

8.08 2.423861 7.547545 9.971406

5.52 4.507253 5.62656 10.13381

4.11 6.39942 11.84373 18.24314

8.92 3.278456 3.259306 6.537762

0.97 5.719715 5.12563 10.84535

3.64 4.598169 7.244425 11.84259

5.27 1.979135 10.56925 12.54838

7.14 5.82001 7.542485 13.3625

9.10 7.235915 5.69976 12.93568

5.49 6.71591 5.97117 12.68708

cial expressions.



Table 4 – Correlation coefficients and F p-values for ANOVA analysis comparing measures of facial motion impairmentwith burn affected aesthetic units

Measures of facial motion impairmentcompared to correspondingaesthetic units score

Twenty acid burns patientsa Twelve acid burns patientsb

Correlationcoefficient

ANOVA F:p-value

Correlationcoefficient

ANOVA F:p-value

Katz score 0.86 6.55ES07 0.91 3.29ES05

Nottingham score �0.43 0.063961 �0.31 0.326796

Global FMII 0.38 0.101599 0.52 0.082273

Anatomic FMII 0.39 0.101912 0.62 0.032389

Non-Anatomic FMII 0.13 0.573347 0.38 0.223339

Global FMII + rest asymmetry index 0.41 0.071649 0.52 0.081146

Anatomic FMII + rest asymmetry index 0.42 0.073641 0.57 0.052568

5% significance level was used. There was a significant positive correlation between anatomic FMII and aesthetic units affected (amongst

patients able to perform all facial expressions). Graphs displaying important correlations are presented below.a Twenty acid burns victims assessed by MSRA for facial function.b Twelve acid burns victims were able to complete all facial expressions satisfactorily for complete MSRA analysis.

b u r n s x x x ( 2 0 0 7 ) x x x – x x x 7


burns was significantly greater than unilateral (t-test p = 0.004,

p < 0.05). However, based on the Nottingham index, there was

poorer correlation between facial function and burn area for

bilateral burns (c = �0.05; F significance = 0.89, p > 0.05) than

for unilateral (c = �0.40; F significance = 0.29, p > 0.05). Indeed,

bilateral burn Nottingham scores were significantly less than

unilateral (p = 0.04).

Global FFII scores increased with increasing burn area. This

correlation improved with incorporation of the rest asymme-

try index (20 patients: coefficient = 0.38–0.41; p-value = 0.102–

0.072; 12 patients: coefficient = 0.5212–0.5228; p-value = 0.082–

0.081). There was a significant positive correlation between

anatomic FFII and burn area (coefficient = 0.62; p-value = 0.032;

p < 0.05). However, the anatomic FFII was not influenced by

the rest asymmetry index. Global and anatomic FFII scores

were significantly greater for bilateral burn victims than

unilateral (global FFII: t-test p = 0.041; anatomic FFII: t-test

p = 0.046). There was a poor correlation between the Notting-

ham score and global FFII (0.062).

There was no significant correlation between non-

anatomic FFII scores and number of affected aesthetic

Fig. 5 – Graph showing correlation between affected

aesthetic units and global FFII, anatomic FFII, non-

anatomic FFII.



units. There was also no significant difference between

non-anatomic FFII scores for unilateral and bilateral

burns.

4. Discussion

Facial expression reproduction has been shown to be a

justified and accurate means of functional assessment [34].

Johnson et al. [14] used the MSRA, to evaluate the success of

functional free muscle transfer in patients with chronic facial

paralysis and concluded it could be used to objectively assess

the results of facial reanimation. We used the MSRA for the

objective assessment of 20 control subjects and 20 female

patients with devastating facial burns following attacks with

sulphuric acid [25].

4.1. Control group

The control group consisted of 20 females matched for age,

facial shape index and ethnicity. Weedan demonstrated

significant positive correlation between facial shape index –

objective assessment of facial size – and facial motion.

Weedan et al. also demonstrated that males and females

showed differences in maximum facial movements after

adjusting for differences in facial size with males having

greater movement than females [27]. Tzou et al. demonstrated

the influence of ethnicity with significant differences in facial

motion between normal Asian and European faces, conclud-

ing that they were generally the result of differences in facial

size. Hence, Asians (with smaller faces) demonstrated smaller

facial excursion than Europeans [35]. Giovanoli [20] demon-

strated significant increase in facial motion with increasing

age.

These variables were all taken into consideration with

regards to control group selection. There were no significant

differences in facial shape between our control and patient

groups (bizygomatic distance: p = 0.53; face height: p = 0.29;

and facial shape index: p = 0.14) and all control subjects and

patients were female and of Bangladeshi origin, enabling valid

comparison for the purposes of calculating the facial func-

tional impairment index.



b u r n s x x x ( 2 0 0 7 ) x x x – x x x8


4.2. Patient group

The patient group consisted of 20 females sustaining acid

burns from sulphuric acid with no surgical intervention for at

least 2 years. The majority of patients had widespread facial

hypertrophic scars. Patients with keloid scars were not

included in this study. Based on Magliacani et al.’s [36]

classification of burn scars, hypertrophic scars can be

described as short or medium-term evolution and achieve

normalisation within 2 years. Hence, the patient group can be

described as homogenous and their respective scars being in

complete remission at time of assessment.

4.3. Facial functional impairment index (FFII)

We propose the ‘facial functional impairment index’ (FFII).

This consists of 7 separate measures of facial functional

impairment based on excursion at 12 soft tissue landmarks for

5 facial expressions. Linear displacement, vectors and bear-

ings were measured in acid burn victims and statistically

compared to mean normal values obtained from MSRA

analysis of a group of volunteers matched for age, sex, facial

shape and ethnicity—all factors shown to significantly

influence facial motion. The FFII accounts for abnormalities

in absolute displacement, proportional displacement and

absolute direction. The mathematical calculations involved

in derivation of the FFII were formally checked by a

mathematician based at the University of Cardiff.

For each facial expression, soft tissue landmarks were

designated as anatomic or non-anatomic based on the facial

action coding sequence (Table 1). As a result the FFII score for

each facial expression can be subdivided into anatomic and

non-anatomic components. As defined earlier, anatomic

motion is termed the motion of specific facial points studied

by the MSRA that can be attributed solely to the pull of the

regional facial muscles that govern the movement of these

points and hence non-anatomic motion is movement at points

elsewhere on the face. If we define the total of all FFII scores for

each facial expression as the global FFII, corresponding global

anatomic and global non-anatomic scores can be derived.

The Katz score and distribution of affected aesthetic units

provided aesthetic measures of disfigurement. They were

consistent with a significant positive correlation (c = 0.86;

p < 0.01). The FFII was calculated for all patients and correlated

well with corresponding aesthetic measures. Larger burns and

more disfigurement resulted in worse facial function (c = 0.52;

p = 0.08, p > 0.05).

In particular, larger facial burns resulted in significantly

worse anatomic function (c = 62; p = 0.03, p < 0.05). Within the

context of facial paralysis, poor anatomic function is judged to

be the result of defective motor nerve innervation. Abnormal

non-anatomic motion was defined by Linstrom as synkinesis

[21] and by Bajaj-Luthra, as secondary to the pull of the

unaffected contralateral muscles, transmitted to the paral-

yzed hemiface [31].

In acid burn victims, all injuries are full thickness and

damage generally extends beyond dermal and epidermal

layers. Assuming intact motor nerve function, normal

anatomic motion is restricted by overlying, tight, scar tissue

as well as muscle necrosis, particularly at points of origin and



insertion. Hypertrophic scar tissue extending from anatomic

to non-anatomic regions may thus transmit anatomic move-

ment to non-anatomic landmarks, and hence represent

abnormal non-anatomic displacements.

4.4. Rest asymmetry index

Such was the severity of burns in some patients, hypertrophic

scars and grafts resulted in contractures pulling and displa-

cing certain soft tissue landmarks, at rest. The FFII is a

dynamic measure of functional impairment but does not take

into account static disfigurement that may potentially con-

found any active comparison. In other words certain soft

tissue landmarks and their surrounding relations in patients

may not relate accurately to the control group and hence

comparison of like with like is not quite accurate.

The rest asymmetry index was calculated prior to the FFII

and based on comparison of control and patient neutral pose.

Various inter-soft tissue landmark distances, on either side of

the face, were measured and expressed as a ratio of left to

right. Significant differences in ratios between patients and

the normogram, represent the effects of contractures produ-

cing a significantly asymmetric facial profile at rest. Anatomic

function was not significantly affected by any static facial

asymmetry. However, non-anatomic motion was significantly

affected with increased non-anatomic FFII scores ( p = 0.04).

The rest asymmetry index was factored into the FFII for

further accuracy.

4.5. FFII—advantages

Critical assessment of the FFII reveals several advantages, as

well as drawbacks, that bode well for its effective clinical

application. The FFII is able to differentiate between patients

and is not based on an exponential scale. It takes into account

five facial expressions representing active movement in the

upper third, tragal third (middle) and gonion (lower third)

region of the face. The FFII is a composite score of regional and

global function. Scores for specific facial animations represent

measures of regional function. Individual soft tissue landmark

scores provide geographical details of global and regional

facial functional deficit with specific areas of abnormal motion

relating to specific muscle groups based on the facial action

coding sequence.

The FFII accounts for movement in the x- and y-direction

and hence addresses angular direction indirectly but also

directly addresses absolute direction with the inclusion of a

bearing component. Earlier grading systems were based on

the assumption that abnormal displacement due to facial

dysfunction manifests as abnormally decreased excursion

and/or inter-landmark distances. Acid burn injuries are

capable of reshaping the normal soft tissue profile of the

face and hence, potentially compromising sites of origin and

insertion of facial muscles without necessarily directly

damaging muscle tissue. Hence, it is possible that resultant

anatomic excursions maybe of normal magnitude but have

radically altered bearing. Furthermore, the need for direc-

tional and proportional measures is emphasised with the

recognition of overcompensation and synkinesis in facial

paralysis. Linstrom’s and Frey’s objective measurement of



b u r n s x x x ( 2 0 0 7 ) x x x – x x x 9


movement in the x- and y-planes is not enough to account for

bearing, and the Nottingham index and HBGS do not consider

directional change at all [11,13,18].

Kahn noted that current facial grading systems work by

compartmentalizing facial movement. However, this is not a

true reflection of real facial function. Within a given

individual, separate facial zones’ movements, both ipsilateral

and contralateral, impact on adjoining zones [19]. The FFII

standardises normal impaction of movement across ipsilat-

eral and contralateral zones and hence is able to define and

quantify pathological non-anatomic, as well as anatomic,

motion.

The FFII is based on deliberate facial action tasks. Directed

facial action tasks may differ in appearance and timing from

spontaneously occurring expressions [33]. Deliberate and

spontaneous facial behaviour are mediated by separate motor

pathways—the pyramidal and extra pyramidal motor tracts

[33]. As a consequence fine motor control of deliberate facial

actions is often inferior and less symmetric to that which

occurs spontaneously. All normal subjects and patients were

asked to perform directed facial expressions and patients were

well trained beforehand.

4.6. FFII—disadvantages

The FFII still has significant drawbacks. The calculation of this

index is extremely labour intensive and at this stage remains a

clinical research tool at best. The FFII does not take into

account neck excursion. Neck burns and contractions can

have significant effects on facial function and further

refinement of the FFII will require incorporation of neck

excursion as a facial expression.

The FFII works on the assumption that expressions are

singular and begin and end from a neutral position. Mimetic

movement is in fact multi-vectored and the range of move-

ment is on a continuum from a relaxed state to a fully

contracted [37–39]. Unfortunately FFII and MSRA consider only

neutral and final maximally contracted states and are

restricted to two dimensions.

The incorporation of video and dynamic study of facial

motion accounts for multi-vectored movements. Video

motion analysis enables measurement of velocity and accel-

eration of facial excursion throughout the duration of move-

ment. Peak Motus Motion Measurement System, 3D Expert

Vision Hi Res motion analysis system, Facialis and FaciShow

have proved to be successful motion capture software in facial

functional assessment, but extremely expensive [18,21–

23,30,37–44].

The significance of velocity and acceleration in the

evaluation of facial function has not been definitively

elucidated. Linstrom showed that the presentation of accel-

eration and velocity in the form of time plots for normal versus

pathological facial nerve function clearly demonstrates

degrees of postoperative facial nerve recovery [21]. In the

context of facial nerve paralysis, loss of facial nerve function

appears to result in reduced acceleration. In the context of acid

burn victims, assuming no facial nerve damage, normal and

pathological excursion would be expected to accelerate at the

same rate until the effects of scar damage limit the maximum

possible displacement of the burn affected side and radically



reduce velocity. If this is the case this sort of analysis may help

to decide the borders of potential grafts.

Recently there has also been a shift towards three-

dimensional assessments of facial function and asymmetry

[18,21,23,30,41–43]. Comparisons of 2D and 3D measurements

of facial excursion in normal individuals by Lin et al. [30]

demonstrated that a 3D analysis may be more appropriate for

detecting clinical differences in facial function. According to

Frey et al. [18], important information is lost and accuracy of

measurement is sacrificed by projecting 3D data into 2D. Lin

et al. [30] found significant differences (p < 0.001) between 2D

and 3D excursion despite high correlation between the two

(r > 0.69) with 2D measurements underestimating 3D.

The FFII is a 2D based impairment index and hence may

underestimate facial functional impairment in acid burn

victims. The future incorporation of 3D data may improve the

accuracy of the FFII. Automation of FFII calculation is

necessary to allow routine clinical use. This automation

requires the development of software to work side by side with

affordable video based motion capture.

The degrees of movement as well as facial coordination

normally differ from person to person. Some people have

more expressive faces with larger smiles and greater eyebrow

excursion than others [43]. Also it might be expected that

subjects with larger faces would have greater displacements.

Hence, Lin accounted for this by normalising differences with

anthropometric measurements. The calculation of the FFII is

based on a normogram database for each facial expression.

Assuming a normal distribution for varying degrees of facial

expressiveness and facial size, there is a need for more

exhaustive normogram databases.

5. Conclusion

MSRA analysis of 20 acid burn victims was successfully

conducted. A normogram database enabled the develop-

ment of the facial functional impairment index (FFII)—a

composite score of global and regional measures of facial

function; able to differentiate patients; define anatomic and

non anatomic functional impairment and; correlate sig-

nificantly with aesthetic measures of disfigurement. Our

analysis of 20 female acid burn victims revealed some

significant findings. Anatomic facial function was signifi-

cantly compromised by larger burn injuries. Abnormal non-

anatomic motion was significantly increased in the presence

of rest asymmetry. Global facial function worsened with

increasing burn area.

Introduction of the FFII into clinical practice requires

automation, the integration of video, appropriate graphical

and pictorial depiction of variables and measurements, and

further research into the accuracy of FFII as a marker of

clinical recovery and assessment of facial function.

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Facial motion analysis of acid burn victims—Development of a new facial motion impairment index

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