The clinical application of three-dimensional motion capture (4D): a novel approach to quantify the dynamics of facial animations

Abstract

The aim of this pilot study was to evaluate the feasibility of measuring the change in magnitude, speed, and motion similarity of facial animations in head and neck oncology patients, before and after lip split mandibulotomy. Seven subjects (four males, three females) aged 42–80 years were recruited. The subjects were asked to perform four facial animations (maximal smile, lip purse, cheek puff, and grimace) from rest to maximal position. The animations were captured using a Di4D motion capture system, which recorded 60 frames/s. Nine facial soft tissue landmarks were manually digitized on the first frame of the three-dimensional image of each animation by the same operator and were tracked automatically for the sequential frames. The intra-operator digitization error was within 0.4 mm. Lip purse and maximal smile animations showed the least amount of change in magnitude (0.2 mm) following surgery; speed difference was least for smile animation (−0.1 mm/s). Motion similarity was found to be highest for lip purse animation (0.78). This pilot study confirmed that surgery did influence the dynamics of facial animations, and the Di4D capture system can be regarded as a feasible objective tool for assessing the impact of surgical interventions on facial soft tissue movements.

Facial disfigurement after the surgical treatment of oral and oropharyngeal cancer has a major impact on a patient’s quality of life. Unconcealed alterations in facial appearance, social rejection, depression, and impaired self-esteem have a marked effect on how these patients are perceived in society. In addition to aesthetics and social interaction, functional impairment, which includes difficulty in swallowing, speech, and performing certain facial expressions, all reduce the quality of life in this group of patients.

The assessment of facial animations to date has been subjective and thus lacks reproducibility and is prone to human error. The most common subjective methods include the use of grading scales, panel assessments, and two-dimensional (2D) still photographic and video techniques. Objective methods have been suggested that include rulers and calipers, however these methods have limitations. Recent advances in technology have allowed the development of three-dimensional (3D) surface imaging methods such as stereophotogrammetry and laser scanning for the assessment of facial soft tissue dimensions and animations.

Four-dimensional (4D) facial imaging can be defined as ‘a time sequence of 3D models of facial animations’. The quantification of facial dynamics is considered to be an important aspect of craniofacial abnormality diagnosis, surgical planning, and outcome assessments. For this reason, motion capture stereophotogrammetric systems have been introduced to overcome the errors and limitations associated with direct anthropometry and to provide realistic information regarding the dynamics of facial animations rather than the static nature of orofacial morphology.

The removal of the oral and oropharyngeal tumour mostly requires access through a lower lip split mandibulotomy, which may cause deterioration of function of the lower lip and may lead to poor aesthetics. Until now, no objective assessment has been reported assessing the dynamics of facial muscles following surgical lower lip split mandibulotomy as an access procedure. The aim of this study was to introduce, for the first time, an objective method to characterize the dynamics of 3D lip movements in head and neck oncology patients before and after lower lip split mandibulotomy.

Our pilot study was carried out to assess the feasibility of measuring the change in magnitude, speed, and motion similarity of facial animations in patients following a lower lip split mandibulotomy access procedure for removal of the oral and oropharyngeal cancer.

Materials and methods

Study design

This pilot study was prospective in design. Following the approval of the local ethics committee, seven patients were recruited (four men, three women; age range 42–80 years) from a multidisciplinary treatment clinic for the management of head and neck cancer ( Table 1 ). All patients were planned for a resection of the oral and oropharyngeal cancer via a lower lip split mandibulotomy access procedure. Each subject was provided with a study leaflet and patient information sheet, and written consent was obtained from the participants.

Table 1
Demographic details of participants.
Patient no. Age, years Sex Diagnosis Site Clinical TNM
1 65 F Squamous cell carcinoma Right posterolateral tongue and right retromolar region T2N2b
2 79 M Squamous cell carcinoma Right posterolateral tongue and floor of mouth T2N1
3 54 M Squamous cell carcinoma Left posterolateral tongue T1N1
4 70 F Squamous cell carcinoma Right posterolateral tongue T4N1
5 58 M Squamous cell carcinoma Right posterolateral tongue T2N0
6 72 F Squamous cell carcinoma Left posterior tongue T2N1
7 43 M Squamous cell carcinoma Left posterolateral tongue T3N1
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Jan 19, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on The clinical application of three-dimensional motion capture (4D): a novel approach to quantify the dynamics of facial animations
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