Finite Element Model Analysis of Cephalic Trim on Nasal Tip Stability

Alar rim retraction is the most common unintended consequence of tissue remodeling that results from overresection of the cephalic lateral crural cartilage; however, the complex tissue remodeling process that produces this shape change is not well understood.

To simulate how resection of cephalic trim alters the stress distribution within the human nose in response to tip depression (palpation) and to simulate the internal forces generated after cephalic trim that may lead to alar rim retraction cephalically and upward rotation of the nasal tip.

A multicomponent finite element model was derived from maxillofacial computed tomography with 1-mm axial resolution. The 3-dimensional editing function in the medical imaging software was used to trim the cephalic portion of the lower lateral cartilage to emulate that performed in typical rhinoplasty. Three models were created: a control, a conservative trim, and an aggressive trim. Each simulated model was imported to a software program that performs mechanical simulations, and material properties were assigned. First, nasal tip depression (palpation) was simulated, and the resulting stress distribution was calculated for each model. Second, long-term tissue migration was simulated on conservative and aggressive trim models by placing normal and shear force vectors along the caudal and cephalic borders of the tissue defect.

The von Mises stress distribution created by a 5-mm tip depression revealed consistent findings among all 3 simulations, with regions of high stress being concentrated to the medial portion of the intermediate crus and the caudal septum. Nasal tip reaction force marginally decreased as more lower lateral cartilage tissue was resected. Conservative and aggressive cephalic trim models produced some degree of alar rim retraction and tip rotation, which increased with the magnitude of the force applied to the region of the tissue defect.

Cephalic trim was performed on a computerized composite model of the human nose to simulate conservative and aggressive trims. Internal forces were applied to each model to emulate the tissue migration that results from decades of wound healing. Our simulations reveal that the degree of tip rotation and alar rim retraction is dependent on the amount of cartilage that was resected owing to cephalic trim. Tip reaction force is marginally reduced with increasing tissue volume resection.

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