New method to evaluate sequelae of static facial asymmetry in patients with facial palsy using three-dimensional scanning analysis

Objective: During the process of neural recovery after facial palsy, distressing sequelae of static and dynamic facial asymmetry develop in patients with facial palsy. A pronounced nasolabial fold is mainly responsible for static facial asymmetry, which leads to many psychological and social problems in patients. Objective and qualitative assessment of facial appearance is critical to determine the severity of sequelae of static facial asymmetry and whether an intervention is effective for treatment. In the present study, an attempt was made to develop three-dimensional analysis method to assess sequelae of static facial asymmetry after facial palsy.

Methods: Eight patients with sequelae of facial asymmetry after facial palsy and ten healthy volunteers were enrolled. We used three-dimensional scanning analysis with a portable non-contact optical scanner to obtain three-dimensional surface data from a patient's face and produced a three-dimensional digital model of the face. We then identified a reference plane fixed with the patient's face, and measured the depth of the nasolabial fold of the face.

Results: The nasolabial fold of the face on the affected side was significantly deeper than that on the unaffected side in patients with sequelae of static facial asymmetry after facial palsy. However, the depth of the facial nasolabial fold on the right side was not different from that on the left side in healthy volunteers. Affected-unaffected side differences in the depth of the nasolabial fold in patients with sequelae of static facial asymmetry after facial palsy were significantly larger than left-right differences in the depth of the nasolabial fold in healthy volunteers. Two weeks after treatment with botulinum toxin injection to the affected zygomaticus muscles, affected-unaffected side differences in the depth of the nasolabial fold were significantly decreased in the patients. In the patients who received botulinum toxin, the absolute values of affected-unaffected side differences in the depth of the nasolabial fold measured using the three-dimensional scanning analysis showed a significant positive correlation with the visual analog scale scores of facial asymmetry marked by independent doctors.

Conclusion: The present findings suggest that affected-unaffected side differences in the depth of the nasolabial fold of the measured using three-dimensional scanning analysis can be used as an index of sequelae of static facial asymmetry. It is also suggested that the index can evaluate whether interventions are effective for the treatment of sequelae.