# Model-based simulations of the insertion of tensor threads in patient-specific face: a proof of concept

Marie-Charlotte Picard, Pascal Perrier, Mohammad Ali Nazari, Yohan Payan

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Marie-Charlotte Picard, Pascal Perrier, Mohammad Ali Nazari, Yohan Payan. Model-based simulations of the insertion of tensor threads in patient-specific face: a proof of concept. CMBBE 2023 - 18th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering (CMBBE 2023), May 2023, Paris, France. hal-03948826

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Submitted on 20 Jan 2023

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<figure><img src="image_1.png" /></figure>
MODEL-BASED SIMULATIONS OF THE INSERTION OF TENSOR
THREADS IN PATIENT-SPECIFIC FACE: A PROOF OF CONCEPT

Marie-Charlotte Picard (1), Pascal Perrier (2), Mohammad Nazari (1, 3), Yohan Payan (1)

1. Univ. Grenoble Alpes, CNRS, Grenoble INP, TIMC, 38000 Grenoble, France

2. Univ. Grenoble Alpes, CNRS, Grenoble INP, GIPSA-lab, 38000 Grenoble, France

3. School of Mechanical Engineering, University of Tehran, Tehran, Iran

**1. Introduction**

Facial paralysis is associated with the loss of motricity of facial muscles, inducing face sagging under the effect of gravity, with aesthetic and functional consequences. In order to compensate for the sagging, surgeons have proposed a clinical procedure consisting of inserting and anchoring biodegradable tensor threads under the skin of the face, in order to restore tension to the sagging areas. This study allowed the realization of a proof of concept of a software tool that uses simulations with a Finite Element (FE) biomechanical model of the face [1] in order for the surgeons to (1) predict the behavior of the face after addition of tensor threads and (2) visualize preoperatively in real-time the postoperative aesthetic appearance of the patient's face using reduced order models (ROM) [2].

**2. Materials and Methods**

Patient-specific FE face models are generated
by registrating a reference Face model using the
Elastix library (fig. 1).

<figure><img src="image_2.png" /><figcaption>**Figure 1:** Patient-specific mesh generation</figcaption></figure>

The mesh is composed of four layers, which
represent skin, dermis, hypodermis and
muscles, modeled by hyperelastic materials. An
FE replica of the thread is inserted in the third
layer of the FE face model and contacts between
thread (that includes a set of hollow cones) and
facial tissue are modeled. Nodal forces are then
applied at the tip of the thread to simulate its

traction (fig. 1) and the lifting of facial tissue. A
ROM is then built from a set of selected FE
simulations of the impact of the applied force on
the facial tissue shape, using the
StaticRomBuilder software of Ansys®.

**3. Results**

A interactive software has been developed
using the CamiTK library (camitk.imag.fr), in
order for the clinician to (1) build the patient-
specific biomechanical face model, (2) insert
the tensor thread (position and rotation) in the
model, (3) generate the corresponding ROM
and (4) test and display in real-time the shape of
the face resulting from tractions with the tensor
threads (fig. 2).

<figure><img src="image_3.png" /><figcaption>**Figure 2:** Simulated face appearance after tensile
wire traction of two forces imposed by the user.</figcaption></figure>

**4. Discussion and Conclusions**

We have demonstrated the feasibility of a
software that allows surgeons to evaluate for
each patient the extent to which the position of
the threads can compensate for facial lifting.

**5. References**

1. Nazari, M. A. et al. (2011). Shaping by stiffening: a modeling study for lips. Motor control, 15(1), 141-16

2. Cueto, E., & Chinesta, F. (2014). Real time simulation for computational surgery: a review. Advanced Modeling and Simulation in Engineering Sciences, 1(1), 1-18