CT Analysis of Structural Buttresses in the Traumatised Nose
Condition: Fractures
MeSH terms: Fractures, Bone
Study type: Observational

Summary: 
      Hypothesis: There are 5 support buttresses in the complex osteocartilaginous architecture of
      the nose.

        1. The membranous septum;

        2. The Right nasal bone;

        3. The Left nasal bone;

        4. The perpendicular plate of the ethmoid;

        5. The vomer, vomerine groove and anterior nasal spine.
    

Detailed description: 
      Aim:

        1. Study the 3-dimensional anatomy of the nasal buttresses.

        2. Diagnose fracture patterns in the nasal buttresses.

        3. Identify the buttress fractures associated with deviation of the external nasal
           morphology.

        4. Identify the buttress fractures associated with septal deviation.

        5. Assess the airflow patterns and its associated distribution of flow velocity, pressure,
           and wall shear stress in the nasal cavity for patient specific models with nose
           fracture.

        6. Assess the stress distribution in the nasal bone structures subject to various scenarios
           of loading conditions.

      Methodology:

      67 consecutive patients admitted for facial fractures and who undergo routine CT scans of the
      face with our protocol of axial and coronal sections taken at 0.6mm and gantry 0 are to be
      studied. The CT scans are evaluated to assess the position, comminution and displacement of
      the 5 said buttresses.

      The buttresses are graded Grade 1 Simple fracture without displacement Grade 2 Simple
      fracture with displacement Grade 3 Comminuted fracture without displacement Grade 4
      Comminuted fracture with minimal displacement Grade 5 Comminuted fractured with displacement

      The septum is graded from Grade 0 Septum is straight Grade 1 Septum is deviated by less than
      1 half the distance from the midline to the nasal turbinate Grade 2 Septum is deviated by
      more than 1 half the distance from the midline to the nasal turbinate Grade 3 Septum is
      almost touching the nasal turbinate

      Variables to be assessed included

        1. Grade of Severity of Nasal and Septal fracture

             1. Which is the weakest buttress that is most commonly broken?

             2. Which is the least often fractured and strongest buttress?

             3. Which buttress or buttresses are involved in a undisplaced septal fracture?

             4. Which buttress or buttresses are involved in a displaced septal fracture?

             5. Which buttresses or buttresses are involved in a undisplaced nasal fracture?

             6. Which buttress or buttresses are involved in a displaced nasal fracture?

             7. For a buttress to be displaced, the number of fractures in a single buttress?

        2. Assessment of biomechanical stability

             1. Assessment of stress distribution in the nasal buttresses for various scenarios of
                external loadings

             2. Assessment of nasal fracture patterns in different traumatic forces

             3. Assessment of stress wave propagation in the nasal bones during impact.

        3. Assessment of nasal air-flow via the nasal airways

      Methods for data management and analysis (incl. Biostatistical check)

        1. Segmentation and Reconstruction of 3D Nasal Model

           Given the CT images of a patient, the nasal bones and surrounding facial bones are
           segmented and a 3D model of the bones is reconstructed. This can be accomplished using a
           segmentation and 3D reconstruction software. We have developed a preliminary version of
           the software for segmenting and reconstructing 3D model of craniofacial bones based on
           fast marching method. The software can be adapted to focus on reconstructing 3D model of
           the nasal buttresses.

        2. Nonlinear Registration with Reference Model

           The 3D fractured model is registered with a normal reference model for fracture
           analysis. A novel nonlinear registration technique is required to decouple normal
           variations among normal people and variations due to fractures. In this way, the normal
           reference model can be deformed in a manner consistent with normal variations to
           register to the fractured model. After registration, the registered reference could
           serve as a model of the patient prior to the injury. Moreover, differences between the
           fractured model and the registered reference would indicate variations due to fractures.
           The extent of the fractures and displacements of bones can also be measured.

           To accomplish the novel nonlinear registration, a generalized form of source separation
           method is needed. In particular, the idea of discriminates subspace analysis (Zhang and
           Sim) developed by our colleagues for analyzing variations of facial images for face
           recognition may be applicable. The method can decouple variations due to different
           people and variations due to illumination and view point.

           To enhance the accuracy of analysis, multiple normal reference models may be required
           for the patients in different ethnic groups.

        3. Visualization of 3D Models

           Generic visualization tools do not discriminate between the nasal bones and other
           craniofacial bones. It is difficult and inconvenient to use them to visualize only the
           nasal structure. So, a software tool will be developed to visualize the nasal structure
           of the fractured models. It can also be used to visualize the registration of the
           fractured models with the normal reference and other fracture analysis results.

        4. Classification of Fracture Patterns

      After detecting and measuring the fractured bones, the fractured models can be classified
      according to their fracture patterns. This can be accomplished manually with the assistance
      of classification software.

      Subsequently,

        1. Refinement of Nonlinear Registration Method

           Refinement of the nonlinear registration method will be performed to improve its
           accuracy.

        2. Biomechanical studies

      Three dimensional finite element models of the nose, in particular the septum will be
      constructed from the CT scans. Finite element analysis will be carried out to assess the
      deformation, stress wave propagation and stress distribution in the nasal structures. Flow
      simulation using computational fluid dynamics will also be carried out to assess the flow
      pattern in the nasal cavity due to the nasal fracture.

      Finally,

      1. Biomechanical studies

      Three dimensional finite element models of the nose with various proposed techniques for the
      correction of nasal fracture will be carried out to assess the strength and weakness of the
      resulting nasal structures due to the corrective surgical procedure. Computation fluid
      dynamics will also be carried out to assess the flow pattern or nasal patency of the airway
      after the proposed surgical corrections.
    

Observational model: Case-Only
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        67 consecutive patients admitted for facial fractures and who undergo routine CT scans of
        the face with our protocol of axial and coronal sections taken at 0.6mm and gantry 0 are to
        be studied. The CT scans are evaluated to assess the position, comminution and displacement
        of the 5 said buttresses.
      
Keywords: Nasal fracture; Nasal buttresses; Septal deviation; Nasal morphology; CT Scan