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Original Investigation | Journal Club

Finite Element Model Analysis of Cephalic Trim on Nasal Tip Stability

Ryan P. Leary, MD1,2,3; Cyrus T. Manuel, BS1; David Shamouelian, MD2; Dmitriy E. Protsenko, PhD1; Brian J. F. Wong, MD, PhD1,2
[+] Author Affiliations
1Beckman Laser Institute and Medical Clinic, Irvine, California
2Department of Otolaryngology, University of California, Irvine, School of Medicine, Irvine
3currently with Department of Otorhinolaryngology, Montefiore Medical Center, Bronx, New York
JAMA Facial Plast Surg. 2015;17(6):413-420. doi:10.1001/jamafacial.2015.0941.
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Importance  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.

Objectives  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.

Design, Setting, and Participants  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.

Results  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.

Conclusions and Relevance  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.

Level of Evidence  NA.

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Figure 1.
Control Finite Element Model of the Human Nose

Gray indicates bone; light blue, cartilage, and semitransparent, soft tissue.

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Figure 2.
Frontal View of Simulated Resection of Cephalic Lower Lateral Cartilage
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Figure 3.
Area of the Tissue Being Depressed and Points to Measure Nasal Tip Movement

Pink region indicates surface area where the displacement was prescribed for nasal tip depression. Red dots indicate points on the alar rim and nasal tip where displacement is recorded and its data are used to calculate tip rotation.

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Figure 4.
Simulating the Movement of the Nose Decades After a Cephalic Trim

Top row: Green region marks the resected portion of cartilage. Red arrows indicate direction of migration of surrounding tissue. Last image in the top row is the net finding after decades of tissue remodeling, resulting in increased tip rotation and alar retraction. Bottom row: Green region is region of resected cartilage within the model. Superior and inferior edge of resected tissue volume were selected as boundary conditions. So the progression of this shape change can be observed, a range of forces (inward normal forces around the border of the resected tissue volume) was applied individually along these surfaces. The net force vector was normal to the triangular surfaces selected. The dots indicate nodes of the triangular element, and the purple highlighted region is where the stress is applied in minimal and maximal trim models. The dashed blue lines indicate the area of the surface element being described.

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Figure 5.
Stress Distribution in Response to Nasal Tip Depression
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Figure 6.
Simulated Tissue Migration of Conservative and Aggressive Trim Models

Oblique views: arrow indicates peak stress of 1.5 MPa (top row) and 1.3 MPa (bottom row) at 10N of tissue retraction force. Profile views: line denotes original location of columella.

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Figure 7.
Displacement Plot of Simulated Tissue Migration for Conservative and Aggressive Trim Models

A total force of 10N was applied along the caudal and cephalic boundaries of the tissue defect. Lines indicate amount of rotation.

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