Subangular Deep Fascia Fixation for Submental U-Shaped Cogged Thread Lifting

Submental "double-chin" deformity is multifactorial and may reflect the volume and boundaries of preplatysmal fat, variability in platysmal decussation, and aging-related changes at the cervicomental angle. U-shaped cogged thread lifting is increasingly used as a minimally invasive option for submental contouring, yet the mandibular angle/antegonial notch region contains facial vessels and nerve branches that can be injured when the cannula or thread deviates into a deeper plane.

To describe cadaveric anatomical observations relevant to submental U-shaped cogged thread lifting and to propose a fixation concept using a regionally condensed fibrous layer beneath the platysma near the mandibular angle (herein referred to as the "subangular deep fascia"), representing a functional fascial interface rather than a formally defined anatomical layer, to reduce off-target traversal and potential injury.

Cadaveric thread simulations were performed to reproduce common U-shaped submental thread trajectories. Layer-by-layer dissections were used to identify the relationship of the simulated thread path to the platysma, facial artery/vein at the antegonial notch region, parotid tail, sternocleidomastoid muscle, and superficial sensory nerves. Representative photographs were compiled as figures.

When the trajectory was directed toward a posterior mastoid fixation, the thread pathway tended to approach deeper tissue planes near the mandibular angle, placing it in close proximity to vertically ascending facial vessels; a representative specimen demonstrated direct arterial penetration. A relatively thick and resistant fibrous layer was consistently appreciable beneath the platysma near the mandibular angle, which may represent a regional fascial condensation rather than a distinct named anatomical structure, and provided a plausible alternative fixation point. Conceptually, a subangular deep fascia fixation corridor allows the thread to remain predominantly preplatysmal while limiting posterior traversal through the parotid-sternocleidomastoid region.

The mandibular angle/antegonial notch region represents a critical transition zone in submental thread lifting. Anchoring within a dense subangular deep fascial layer beneath the platysma may improve procedural safety by reducing the need for deep posterior passage and by supporting a stable lifting vector. Further quantitative cadaveric mapping and prospective clinical studies are needed.