Normal Facial Function in the Sunnybrook Facial Grading System: Is the 100% Score too Restrictive?

The Sunnybrook Facial Grading System (SFGS) is a widely recognized tool for assessing facial palsy and its subsequent recovery, offering a standardized approach for quantifying facial movements [1]. This scale compares the paralyzed hemiface to the healthy hemiface of patients using a total composite score between 0% and 100%, where 100% corresponds to full recovery of facial function. The SFGS evaluate five facial movements, symmetry at rest and the presence of synkinesis. The total composite score is calculated by subtracting the symmetry and synkinesis scores from the dynamic movement score.

This scale and total composite score have proven to be a gold standard in clinical practice and research [2]. Even if it has been shown to be more sensitive in detecting changes following therapeutic intervention, the SFGS remains largely subjective [3]. Moreover, the widespread assumption of achieving a perfect 100% may not deal with the natural variations of face symmetry observed in healthy individuals and in patients with facial palsy [4]. Indeed, there is valuable evidence of asymmetry in the production of facial expressions in the general population, even in the absence of facial palsy [5].

This study aims to provide a more comprehensive understanding of the natural range of SFGS scores among healthy participants, thereby redefining the normative standards and advocating for a more patient-centred and holistic approach to facial rehabilitation.

Upon analyzing the SFGS scores, it was observed that the range differed depending on whether the right or left hemiface was considered the reference. Taking the right hemiface as a reference, SFGS-Total scores ranged from 65% to 100% (median = 96, IQR [91–100]). When the left hemiface was considered as the reference, scores ranged from 78% to 100% (median = 95; IQR [90–100]). No participants showed any synkinesis. No significant differences between the SFGS-Total scores according to the reference hemiface were found on the whole sample (p = 0.517). The data are reported by age and gender in Table 1. Data distribution using violin plots is reported in Figure 1.

Consistency between evaluators were high for right and left SFGS-Total scores (respectively α = 0.953 and α = 0.926). Right and left SFGS-Rest scores showed also high inter-rater reliability (respectively α = 0.860 and α = 0.886) as well as right and left SFGS-Movement scores (respectively α = 0.957 and α = 0.816).

There was a slight negative correlation between age and SFGS-Total scores. Indeed, the older the participants, the lower their scores (right side as reference: ρ (109) = −0.37, p < 0.0001, 95% CI [−0.52, −0.20]; left side as reference: ρ (109) = −0.25; p = 0.009; 95% CI [−0.42, −0.06], Figure 2). Post hoc comparisons using Kruskall–Wallis test indicated that there was a significant difference in the SFGS-Total scores (right side as reference) across age categories (χ² [2, n = 111] = 13.89, p = 0.001). The median scores were 96/100 for participants aged (18–39 years), 96/100 for participants aged (40–59 years) and 93/100 for participants aged (60–79 years).

Although women appear to have better scores than men when the left hemiface is the reference (women's median SFGS-Total scores = 95, IQR [91–100], men's median SFGS-Total scores = 95, IQR [88–100]), no significant difference was found between SFGS scores in women versus men (p = 0.091). When the right hemiface is the reference, no significant difference was found (p = 0.631).

The results of this study show the different total scores of the SFGS according to the hemiface taken as reference. Right and left SFGS Total scores showed high inter-rater reliability consistent with findings by Cabrol et al. [6]. Facial movements on the right and left sides are not significantly different, whereas the literature reports a greater expressiveness of the left hemiface in right-handers [5].

Picard et al. [7], who standardized an oro-facial motor assessment scale (the MBLF protocol), found an age- and gender-related effect on normal facial function in their validation study. An age effect was also found in our study: older participants demonstrated lower SFGS-Total scores. This phenomenon can be attributed to the reduced tonicity of the cheeks observed in elderly adults, resulting from the aging of soft tissues or alterations in the stomatognathic system [8]. There was no significant gender effect in our study, although women's facial expressivity appeared to be greater than men's when the reference hemiface was on the left side.

The current emphasis on achieving perfect facial symmetry as the ultimate goal may then create unrealistic expectations for patients. Being aware of the natural variations in face symmetry is crucial to patient-centered care. The patient and the practitioner should be aware that the normal SFGS score ranges from 65% to 100% (median = 96, IQR [91–100]). The results of our study are consistent with those of Neely et al. [9], where patients with Grade 1 according to the House-Brackmann classification, indicating normal facial function, had scores ranging from 95% to 100%. This range constitutes a more realistic and achievable target. This will reassure the patient who is dissatisfied with his recovery. The main limitation of the study lies in the subjectivity of the scale. The development of automated systems would take better account of the degree of asymmetry in normal participants and patients with facial palsy [10].

It is essential, especially for young practitioners clinical guidance, to consider that normal facial function does not necessarily correspond to perfect facial symmetry. This awareness contributes to a more realistic clinical practice tailored to patients experiencing facial palsy. Patients who have made significant progress in their recovery journey may still have minor residual asymmetries, which should not overshadow their overall functional improvements. By solely focusing on achieving perfect symmetry, we risk overlooking the broader aspects of facial rehabilitation, such as restoring functional movements, improving emotional expression and enhancing quality of life.

We are also aware that the SFGS score can be lowered by the simple presence of synkinesis complicating a previous facial palsy. Thus, it is obvious that a patient with this type of sequelae will be much more disabled than a healthy participant with the same SFGS score, less than 100%, but without any history of facial palsy.

By embracing a more realistic approach that acknowledges natural variations and asymmetry in facial movements, we can enhance patient care, foster a sense of achievement and promote a more holistic understanding of facial rehabilitation outcomes.

Diane Picard: conceptualization, formal analysis, investigation, methodology, project administration, supervision, validation, visualization, writing – original draft preparation. Remi Hervochon: resources, supervision, validation, writing – review and editing. Elodie Lannadere: conceptualization, project administration, supervision, validation, writing – review and editing. Cloe Cabos: data curation, investigation, writing – review and editing. Loeiza Gourves: data curation, investigation, writing – review and editing. Frederic Tankere: resources, supervision, validation, writing – review and editing. Peggy Gatignol: conceptualization, investigation, methodology, project administration, supervision, validation, writing – review and editing.

This study adhered to the Declaration of Helsinki and was registered with the CNIL declaration (no 2 217747). Each participant was recruited voluntarily. They signed an informed consent form to take part in the research and were given an anonymity number.

The authors declare no conflicts of interest.