Biomechanical simulation of correcting primary unilateral cleft lip nasal deformity

Abstract

For better outcomes of the primary correction of cleft lip nasal deformity, it is important to clarify the specific morphological and biomechanical consequences of major surgical maneuvers during cleft lip nose correction. In this study, a finite element model was established basing on the micro-MRI imaging of an infant specimen with unilateral complete cleft lip deformity. Alar base adduction was simulated as a medially-directed force on the lateral crus (F1); columella straightening was simulated as a laterally-directed force on the medial crus (F2); and nasal tip enhancement was simulated as an anteriorly-directed force on the intermediate crus (F3). The deformation and stress distribution consequent to each force vector or different force combinations were analyzed in details. Our biomechnical analyses suggested that W\when loaded alone, the three forces generated disparate morphological changes. The combination of different force loadings generated obviously different outcomes. F3 generated the most intensive stress when compared to F1 and F2. When F2 was loaded on top of F1-F3 combination, it further relieved nasal deviation without incurring significant increase in stress. Our simulation suggested that alar base adduction, columella straightening, and nasal tip elevation should all be included in a competent cleft lip nose correction.

Fig 1. CAD model construction and vectors of force loadings.

(A) Demonstration of a typical unilateral cleft lip nasal deformity. (B) Fetal specimen used for micro-MRI scanning. (C, D) The CAD model composed of both cartilage framework and skin envelope. (E, F) The directions of forces loaded on the alar cartilage.

Fig 2. Micro-MRI imaging reconstruction.

(A, B, C) Micro-MRI imaging of the fetal specimen. Red arrows indicated the position of cartilages, including the alar cartilages (AC), the upper lateral cartilages (ULC) and the nasal septum (NS). (D) Three dimensional reconstruction of the micro-MRI imaging.

Fig 3. Total deformation of the nasal cartilage framework consequent to different force loadings.

(A) F1 alone; (B) F2 alone; (C) F3 alone; (D) F1 plus F2; (E) F1 plus F3; (F) F1, F2 and F3 at the same time. Blue represented the fixed part of the model. The grey shadow represented the pre-simulation position of the model.

Fig 4. The deformation of the skin envelope consequent to different force loadings.

(A) F1 alone; (B) F2 alone; (C) F3 alone; (D) F1 plus F2; (E) F1 plus F3; (F) F1, F2 and F3 at the same time. The length and direction of the arrow represented the value and direction of the deformation respectively.

Fig 5. The TD and EQV at major landmarks on the skin envelope.

(A) Path one was defined by the alar bases at both sides (Landmarks one, five), the alar domes at both sides (Landmark two, four) and the nasal tip (Landmark three); (a) Path two was defined by the columella base (Landmark one), the nasal tip (Landmark two), the dorsum (Landmark three) and the nasal radix (Landmark four); (B, C, D, E, F, G) The vectors of TD on Path one; (b, c, d, e, f, g) The vectors of TD on Path two; (H) The TD on Path one; (I) The EQV on Path one; (h) The TD on Path two; (i) The EQV on Path two.