Computational Modelling of Platysma Muscle Mechanics: Challenging the Isometric Contraction Paradigm and Implications...

Platysmal bands are among the most visible signs of cervical ageing, commonly attributed to focal isometric contraction zones requiring targeted chemodenervation. However, this paradigm is based primarily on indirect imaging and clinical observation, with limited biomechanical validation.

To develop a finite element model of platysma contraction incorporating realistic tissue mechanics and to test whether uniform shortening with fascial tethering alone can reproduce contour deformations classically ascribed to isometric contraction.

A high-resolution finite element framework was created using Abaqus/CAE to simulate a layered cervical composite comprising platysma, superficial fascia, and dermis. Geometries were parametrically defined and varied across a synthetic cohort of 1000 virtual anatomies using Latin hypercube sampling. Constitutive formulations included transversely isotropic hyperelastic muscle, viscoelastic fascia with Prony series relaxation, and nonlinear dermis. Simulations varied contraction amplitude (5-15%) and tether density (0-50%). Outputs included cranio-caudal displacement, regional thickness deformation, strain energy, and divergence. Supplementary sustained contraction simulations assessed viscoelastic creep over 300 s.

Uniform contraction combined with variable fascial tethering reproduced localized thickening and restricted gliding without requiring isometric contraction zones. Maximal midline thickness increased proportionally with tether density (0.17 mm at 0% tethering to 0.65 mm at 50%), and displacement divergence amplified radial contour deformation. Sensitivity analysis confirmed robustness to ±20% variations in tissue stiffness. Viscoelastic creep simulations suggested progressive strain accumulation (+7% midline thickness over 5 minutes).

These findings suggest that platysmal bands can emerge from predictable passive deformation driven by uniform shortening over heterogeneous anchoring, challenging conventional models of focal hyperactivity. This framework supports the hypothesis that distributed injection protocols targeting tension gradients rather than only visually prominent bands may warrant investigation and highlights the need for further clinical validation of simulation-informed strategies.

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