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Original Investigation |

A Finite Element Model to Simulate Formation of the Inverted-V Deformity

Tjoson Tjoa, MD1; Cyrus T. Manuel, BS2; Ryan P. Leary, BA2; Rani Harb, PhD2; Dmitriy E. Protsenko, PhD2; Brian J. F. Wong, MD, PhD2,3
[+] Author Affiliations
1Department of Otolaryngology, Massachusetts Eye & Ear Infirmary, Boston
2Beckman Laser Institute, University of California, Irvine
3Department of Otolaryngology, University of California, Irvine
JAMA Facial Plast Surg. 2016;18(2):136-143. doi:10.1001/jamafacial.2015.1954.
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Importance  Computational modeling can be used to mimic the forces acting on the nasal framework that lead to the inverted-V deformity (IVD) after surgery and potentially determine long-range outcomes.

Objective  To demonstrate the use of the finite element method (FEM) to predict the formation of the IVD after separation of the upper lateral cartilages (ULCs) from the nasal septum.

Design, Setting, and Participants  A computer model of a nose was derived from human computed tomographic data. The septum and upper and lower lateral cartilages were designed to fit within the soft-tissue envelope using computer-aided design software. Mechanical properties were obtained from the literature. The 3 simulations created included (1) partial fusion of the ULCs to the septum, (2) separation of the ULCs from the septum, and (3) a fully connected model to serve as a control. Forces caused by wound healing were prescribed at the junction of the disarticulated ULCs and septum. Using FEM software, equilibrium stress and strain were calculated. Displacement of the soft tissue along the nasal dorsum was measured and evaluated for evidence of morphologic change consistent with the IVD.

Main Outcome and Measures  Morphologic changes on the computer models in response to each simulation.

Results  When a posteroinferior force vector was applied along the nasal dorsum, the areas of highest stress were along the medial edge of the ULCs and at the junction of the ULCs and the nasal bones. With full detachment of ULCs and the dorsal septum, the characteristic IVD was observed. Both separation FEMs produced a peak depression of 0.3 mm along the nasal dorsum.

Conclusions and Relevance  The FEM can be used to simulate the long-term structural complications of a surgical maneuver in rhinoplasty, such as the IVD. When applied to other rhinoplasty maneuvers, the use of FEMs may be useful to simulate the long-term outcomes, particularly when long-term clinical results are not available. In the future, use of FEMs may simulate rhinoplasty results beyond simply morphing the outer contours of the nose and allow estimation of potentially long-term clinical outcomes that may not be readily apparent.

Level of Evidence  NA.

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Figures

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Figure 1.
Finite Element Model of a Normal Human Nose

Models with intact attachments and separation of the upper lateral cartilages and dorsal septum were created in medical image-processing software (Mimecs; Materialise).

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Figure 2.
Application of Pressure

Red indicates areas where pressure was applied to the model.

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Figure 3.
Surface Plot of von Mises Stresses on the Nasal Cartilages

Stress values (in megapascals) are plotted on a color map scale where deep red indicates areas of highest stress and dark blue indicates no stress. Red arrows indicate the areas of peak stress.

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Figure 4.
Surface Displacement Plots With Partial Disarticulation of the Upper Lateral Cartilages and Dorsal Septum

The finite element model shows partial disarticulation between the dorsal septum and upper lateral cartilages. Color map scale indicates magnitude of displacement.

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Figure 5.
Surface Displacement Plots With Full Disarticulation

The finite element model shows full disarticulation between the dorsal septum and upper lateral cartilages. Color map scale indicates magnitude of displacement.

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