| Objective:Unilateral cleft lip with nasal deformation is the most common oromaxillofacial congenital deformation, better correction of nasal deformation has been one major problem of plastic surgery. Surgery is the major treatment of unilateral cleft lip nasal deformation. Surgical methods are various. Because the complexity of cleft lip nasal deformation, the high demand of the entire rehabilitation in patients, constraint of surgical methods and implant materials, we are often difficult to obtain the most satisfactory tectonic effects. We acquired imaging data of unilateral cleft lip nasal deformation through the CT, MRI and other imaging methods, then obtained morphological information of the unilateral cleft lip nasal deformation by computerized three-dimensional reconstruction. Finally we used finite element method to analyze biomechanical regularity of nasal deformation in unilateral cleft lip, hoped to explain the cause of the formation of cleft lip nasal deformation from the view of biomechanics, reveal biomechanical regularity of unilateral cleft lip nasal deformation, measure biomechanical properties of unilateral cleft lip nasal deformation, conduct the treatment of unilateral cleft lip nasal deformation, establish a good biomechanical theoretical basis for treatment of patients with unilateral cleft lip nasal deformation.Methods:All the objects in this study—unilateral cleft lip nasal deformation—were obtained from patients who visited the Department of Plastic Surgery, Changhai Hospital and Shanghai Ninth People's Hospital from 2007 to 2009. We collected 10 cases of patients with unilateral cleft lip nasal deformation, whose age range from 10～18 years old, 7 male patients, 3 female patients, all the patients were left unilateral cleft lip nasal deformation. All the collected patients were secondary cleft lip nasal deformation. They had a cleft lip repair between 0～3 years old age, after that they had not been pre-treated nasal deformation, and now asked for treatment of nasal deformation. Collected patients with unilateral cleft lip nasal deformation mainly expressed in the affected side of the alar collapse deformation, or simultaneously with the deflection nasal columella, nasal tip separation deformation, etc. All the collected cases were carried out pre-operative CT and MRI scanning, image data collected with the document form of DICOM files, transferred to HP graphics workstation, computerized three-dimensional reconstruction by the software MIMICS. We obtained the nasal deformation with three-dimensional reconstruction images and adjusted to separate the images of nasal cartilage, defined the form and structure of nasal deformation. Then we measured 10 cases of adult cadavers nasal alar, lateral and septal cartilage through modern mechanical measuring instruments, to obtain the elastic modulus of above three part structure of nasal cartilage, then to obtain more accurate nasal cartilage elastic modulus data through statistical analysis. At the same time, according to the relevant literature, we obtained nasal soft tissue biomechanical properties, mainly were elastic modulus and Poisson's ratio. Finally we established three-dimensional finite element analysis model of unilateral cleft lip nasal deformation, defined the model's constraint conditions and carried out biomechanical measurement and analysis of unilateral cleft lip nasal deformation. We carried out two kinds of finite element biomechanical analysis in each model: 1, static structural analysis; 2, displacement load analysis. After the analysis of unilateral cleft lip nasal deformation, we obtained the deformed nasal's stress and strain distribution figure, and finally statistical analyzed the results, summarized biomechanical conclusions and the regularities of unilateral cleft lip nasal deformation.Results:1. Nasal three dimensional reconstruction of patients with unilateral cleft lip and nasal alar collapse1.1 CT scan for nasal three dimensional reconstruction of patients with unilateral cleft lip and nasal alar collapseWe scanned deformed noses of patients with unilateral cleft lip by GE light speed 64 slice CT. Scanning thickness of each slice was 0.625mm. Because nasal cartilage and soft tissue have different density, multi-slice CT can distinguish different tissues and obtain better gray image of cartilage. Then adjusted gray-scale images by post-processing software, we could obtain a better imaging of nasal cartilage and better segmentation of nasal cartilage, finally we could obtain a better three-dimensional reconstruction model.1.2 MRI scan for nasal three dimensional reconstruction of patients with unilateral cleft lip and nasal alar collapseWe scanned deformed noses of patients with unilateral cleft lip by Philips Achieva 3.0T MRI machine, respectively, in T1 and T2 scan sequence. Scanning thickness of each slice was 1mm. MRI scan showed nasal cartilage as a middle-high brightness shadow in T1 sequence, showed middle-low brightness shadow in T2 sequences. MRI imaging results showed that image of nasal cartilage is blurred, some artifacts and noise, and its imaging was significantly worse than CT scanning imaging. For these reasons, the segmentation of nasal cartilage was difficult, the three-dimensional reconstruction model was rough, MRI image post-processing was difficult, so we discarded the MRI scanning to establish three-dimensional finite element models of nasal structure .2. Measurement of biomechanical properties of nasal cartilage2.1 Compression elastic modulus data of cadaver's nasal cartilageStress-strain curves and statistical analysis showed that the compression modulus of elasticity of nasal alar cartilage was minimal, statistical value is 1.142±0.336 MPa; compression modulus of elasticity of lateral nasal cartilage was greatest, statistical value is 5.84±1.246 MPa; compression elastic modulus of septal cartilage was middle, statistical value is 3.85±1.685 MPa.2.2 Tensile elastic modulus data of cadaver's nasal cartilageStress-strain curves and statistical analysis showed that the tensile modulus of elasticity of nasal alar cartilage was minimal, statistical value is 4.679±1.641 MPa; tensile modulus of elasticity of lateral nasal cartilage was greatest, statistical value is 8.601±2.131 MPa; tensile elastic modulus of septal cartilage was middle, statistical value is 6.907±1.621 MPa.2.3 Elastic modulus data analysis of cadaver's nasal cartilageStatistical analysis showed that for nasal cartilage tensile elastic modulus generally was greater than compression elastic modulus; elastic modulus of lateral nasal cartilage > elastic modulus of septal cartilage > elastic modulus of alar cartilage.3. Nasal biomechanical analysis of patients with unilateral cleft lip and nasal alar collapse3.1 Nasal static analysis of patients with unilateral cleft lip and nasal alar collapseDeformed nasal static three-dimensional finite element analysis showed the stress distribution of nasal deformation. Twist positions of nasal septum cartilage were the most stress concentrated region, following were the bottom of nasal columella and the lateral feet of both nasal alar parts; Nasal tip was the weakest stress distribution region. It suggested that under static status, the nasal septum, nasal columella and the lateral feet of nasal alar were the most concentrated areas of stress distribution. They are key mechanical parts of deformed nasal.3.2 Nasal displacement load analysis of patients with unilateral cleft lip and nasal alar collapse Deformed nasal displacement load three-dimensional finite element analysis showed that if the ipsilateral and contralateral nasal parts obtain similar geometry, the positions around nasal columella in ipsilateral nostril were the most stress concentrated region, next parts were the nasal septum and the lateral nasal alar. It suggested that under displacement load status, to acquire contralateral nasal approximate geometry, ipsilateral nasal columella, nasal septum and lateral nasal alar were the most stress concentrated areas. They are also the key mechanical parts of deformed nasal rectify.3.3 Biomechanical analysis and summary of patients with unilateral cleft lip and nasal alar collapseStatic mechanical analysis and displacement load analysis of 10 cases of nasal deformation in patients with unilateral nasal showed that: under the static state, nasal deformation has a very small value of stress distribution. The value of the key stress points are followings: the nasal septum 0.00935±0.002 MPa, the bottom of nasal columella 0.0059±0.0021 MPa, lateral feet of nasal alar 0.00681±0.0013 MPa; under displacement load status, the deformed nasal has a large value of the stress distribution. The value of the key stress points are followings: ipsilateral nasal columella 25.51±3.98 MPa, nasal septum 7.882±1.35 MPa, ipsilateral nasal alar 8.184±1.58 MPa.Conclusion:Study of CT and MRI three-dimensional image reconstruction showed that: thin slice CT scan for the external nose and soft tissue had the highest accuracy. We can reconstruct the most precise three-dimensional geometry of the external nose and nasal cartilage. Because MRI imaging are thick slice, vague boundary, artifacts, noise and other problems, nasal cartilage segmentation was difficult, three-dimensional reconstruction model is rough.After testing three main kinds of nasal cartilage's biomechanical properties and statistical analysis, we find that for the main nasal cartilage tensile elastic modulus is generally greater than compression elastic modulus; elastic modulus of lateral nasal cartilage > elastic modulus of septal cartilage > elastic modulus of alar cartilage, addition, the elastic modulus of nasal cartilage are the same magnitude level (unit: MPa).After the biomechanical finite element analysis for the three-dimensional reconstruction model, we find the structure of the deformed nose showes the following characteristics: 1, Nasal septum, nasal columella, lateral feet of nasal alar, lateral nasal dorsum are stress concentrated regions, that is the key mechanical positions of deformed nose; 2, Under the static state, nasal deformation has a very small value of stress distribution, under displacement load status, the deformed nasal has a large value of the stress distribution; 3, Ipsilateral nasal columella are the the key mechanical parts of deformed nasal rectify. And lateral nasal alar is also the most stress concentrated areas.Finite element analysis for patients with unilateral cleft lip and nasal alar collapse shows that: 1, Affected side of nasal columella are the key mechanical part to rectify deformed nose, followed part is the ipsilateral nasal alar; 2, The stress concentration of the nasal septum suggests that the nasal septum rectification is very important, its rectification and fixation are perhaps the important content of deformed nose rectification .
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