3D Stereophotogrammetric assessment of pre- and postoperative volumetric changes in the cleft lip and palate nose

Article Outline

• Abstract
• Materials and methods
  • Operative procedure
  • Pre- and postoperative 3D documentation
  • 3D measurements
  • Statistical analysis
• Results
• Discussion
• Funding
• Competing interests
• Ethical approval
• Financial interest in this study
• References
• Copyright

Abstract 

In cleft lip and palate patients the shape of the nose invariably changes in three dimensions (3D) due to rhinoplastic surgery. The purpose of this study was to evaluate stereophotogrammetry as a 3D method to document volumetric changes of the nose in patients with a cleft lip (CL) or cleft lip and palate (CLP) after secondary open rhinoplasty. 12 patients with unilateral CL or CLP were enrolled in the study prospectively. 3D facial images were acquired using 3D stereophotogrammetry preoperatively and 3 months postoperatively. A 3D cephalometric analysis of the nose was performed and volumetric data were acquired. The reliability of the method was tested by performing an intra- and inter-observer analysis. Left, right and total nasal volumes and symmetry were compared. No statistically significant differences (p<0.05) were found within and between observers for the measured volumes and symmetry. Postoperatively, the total volume of the nose increased significantly, especially the volume at the cleft side. No significant volume difference pre- and postoperatively was found for the non-cleft side. The symmetry of the nose improved significantly. 3D stereophotogrammetry is a sensitive, quick, non-invasive method for evaluating volumetric changes of the nose in patients with cleft lip or cleft lip and palate.

Keywords: stereophotogrammetry, cleft lip and palate, rhinoplasty, volumetric 3D measurements, reproducibility, surface registration, maxillofacial surgery, otorhinolaryngology, plastic and reconstructive surgery

The nose is known to be aberrant in appearance and function in patients with a cleft lip (CL) or a cleft lip and palate (CLP)³. Distortions of the nose can vary from almost invisible to catastrophic, mostly dependent on the severity and type of cleft²⁹. To correct the nasal deformity in CL or CLP patients is a challenge. In the Netherlands, for the last 25 years, a primary rhinoplasty correction has been performed at the time of primary lip closure in unilateral CL or CLP patients. This usually involves reducing the asymmetry by undermining and rotating the nose without altering bony tissue. Nevertheless, as the children grow older, the nasal shape remains deformed. There is usually an underprojection of the dome at the cleft side and surgery mainly focuses on correcting this asymmetry by increasing the projection (which enhances the volume of the nasal pyramid) on the cleft side.

Various studies have been undertaken to evaluate the result of different rhinoplastic procedures³, ¹⁰, ¹², ¹³, ¹⁶, ¹⁹, ²¹, ²⁵, but quantification of surgical changes remains difficult. Besides direct anthropometric measurements⁷, two-dimensional (2D) photographs and radiographs are used to document and calculate the changes after surgery²³. Until now, studies comparing pre- and postoperative nasal changes in patients with clefts have been limited to these techniques¹⁵. The human body however, is a three-dimensional (3D) entity and any change, whether from movement during facial expression or from surgery, occurs in three dimensions. Various 3D imaging techniques have been developed to overcome the shortcomings of conventional 2D imaging. These include 3D cephalometry²⁶, Moiré topography²⁸, 3D laser scanning⁶, 3D optoelectronic digitizers⁸ and 3D stereophotogrammetry¹¹, ¹⁴, ²⁴. The latter method has gained popularity over the last years as digital 3D data sets of the face can be acquired rapidly and non-invasively, while simultaneously being archived for future analysis². Recent studies have shown 3D cephalometric measurements acquired with a 3D stereophotogrammetrical camera setup to be valid and reproducible², ²².

To the best of the authors’ knowledge, no stereophotogrammetry studies have been performed on the volumetric 3D changes of the nose after secondary rhinoplasty in CL and CLP patients. The purpose of this study was to evaluate the value of 3D stereophotogrammetry for volumetric documentation of the nose in CL and CLP patients who underwent secondary rhinoplastic surgery.

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Materials and methods 

The study sample comprised of CL and CLP patients from the Cleft Palate Craniofacial Unit of the Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands, operated on between June 2007 and December 2007. Inclusion criteria were: unilateral CL or unilateral CLP; age above 12 years; and signed informed consent. Exclusion criteria were: associated cranio-facial deformities; syndromes; and earlier secondary rhinoplastic surgery.

Operative procedure 

All operative procedures were performed by one surgeon (PS). An open rhinoplasty (Rethi incision: rim incision traversing the columella) was performed in all patients. Depending on the deformity, the following nasal surgery components were employed: a septal deviation was corrected by remodelling the deviating septum and trimming the base. The lower lateral cartilages were reduced and sutured together in order to narrow the dome. A columellar strut was placed for nasal tip support. For this purpose part of the septal cartilage was used or cartilage was acquired from the auricular concha. Dome sutures, shield, tip or dorsal grafts were implemented if required. When correction of the nasal bone was mandatory a medial and lateral osteotomy including efracture and infracture was performed.

Pre- and postoperative 3D documentation 

A 3D stereophotogrammetrical camera setup with an integrated software program modular system V 1.0 (3dMDface™ System, 3dMD LLC, Atlanta, GA, USA) was used to capture 3D photographs of the face. The 3D photographs were generated from six 2D photographs taken simultaneously (four grey-scale photographs and two full colour photographs). A polygon light pattern was projected onto the four grey-scale photographs. Based on this pattern and its deformed image, a 3D photograph was reconstructed. These 3D photographs were automatically saved as ‘three-dimensional surface binary’ files (.tsb file) and were visualized and analyzed using 3D editing software (3dMDpatient V3.0.1. 3dMDpatient™ Software Platform, 3dMD LLC). With this system it was possible to capture 180 degrees of the subject's face, which concurred with an ear-to-ear 3D photograph.

The 3D photographs were taken in natural head position and habitual occlusion. Patients were asked to relax their facial musculature, swallow and keep their molars in occlusion after swallowing⁵. 3D photographs were acquired preoperatively as well as at the clinical control visit 3 months postoperatively. The preoperative surgical deformities of the nose were recorded using criteria proposed by Nakamura et al.²⁰

3D measurements 

To isolate the region of interest on the 3D photographs, the neck and parts of the hair were trimmed using 3dMDpatient V3.0.1 software. The 3D photograph was exported as a wavefront object file (.obj) and imported into Maxilim^® version 2.2.2.1 (Medicim NV, Mechelen, Belgium). A surface based matching procedure for the pre- and postoperative 3D photographs was performed in five steps as described previously¹⁷. On the matched 3D photographs a distance map was created giving an indication of the soft-tissue changes (Fig. 1). A modified 3D cephalometric analysis, based on 3D cephalometric soft tissue analysis on CT data²⁷ (Table 1), was performed to outline the region of interest for the volumetric measurements. This resulted in the matched 3D photographs on a Cartesian coordinate system with the nose lined by various planes (Fig. 2). These planes defined the borders of the volume of the nose and were used for further circumscription of the 3D photograph.

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• Fig. 1. 

  3D distance map of the pre- and postoperative soft tissue changes in patient 6. (a) Decrease (red) of volume on the non-cleft side; (b) patient 6 frontal view; (c) increase (green) in volume on the cleft side.

Table 1. Definitions of landmarks and planes used based on the 3D cephalometric soft-tissue analysis according to Swennen²⁷.

Landmark	Abbreviation	Description	View
Landmarks and planes
Alare (left)	al(l)	Left alare, most lateral point on the left alar contour.	Base view
Alare (right)	al(r)	Right alare, most lateral point on the right alar contour.	Base view
Cheilion (left)	ch(l)	Left cheilion, point located at the left labial commissure.	Frontal
Cheilion (right)	ch(r)	Right cheilion, point located at the right labial commissure.	Frontal
Cheilion (middle)	ch(m)	Soft tissue point automatically computed as the midpoint of the right cheilion and left cheilion.
Endocanthion (left)	en(l)	Left endocanthion, soft tissue point located at the inner commissure of the left eye fissure.	Frontal
Endocanthion (right)	en(r)	Right endocanthion, soft tissue point located at the inner commissure of the right eye fissure.	Frontal
Exocanthion (left)	ex(l)	Left exocanthion, soft tissue point located at the outer commissure of the left eye fissure.	Frontal
Exocanthion (right)	ex(r)	Right exocanthion, soft tissue point located at the outer commissure of the right eye fissure.	Frontal
Exocanthion (middle)	ex(m)	Soft tissue point automatically computed as the midpoint of the right exocanthion and left exocanthion.
Pupil reconstructed	p″	Pupil reconstructed point, midpoint between the endocanthi and pupils, located on the level of the exocanthi.	Frontal
Subnasale	sn	Subnasale, midpoint on the nasolabial soft tissue contour between the columella crest and the upper lip.	Lateral right
Plane		Description
Posterior nasal plane		A plane through landmarks ex(l), ex(r) and ch(m).
Lateral left nasal plane		A plane through landmarks en(l) and al(l) and perpendicular to the vertical plane.
Lateral right nasal plane		A plane through landmarks en(r) and al(r) and perpendicular to the vertical plane.
Median plane		The median (z) 3D Reference Plane is computed through the Pupil Reconstructed Point and as a plane perpendicular to the horizontal (x) and the vertical (y) 3D Reference Planes.
Upper nasal plane		A plane through landmark ex(m) and parallel to the horizontal plane.
Lower nasal plane		A plane through landmark sn and parallel to the horizontal plane.
Horizontal plane		The horizontal (x) 3D Reference Plane is automatically computed as a plane 6.6 degrees below the Cantion - Superaurale line, along the horizontal direction of the natural head position and through the Pupil Reconstructed Point translated 77.2mm more posteriorly.
Vertical plane		The vertical (y) 3D Reference Plane is computed as a plane perpendicular to the Horizontal (x) 3D Reference Plane and along the horizontal direction of the natural head position.

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• Fig. 2. 

  3D stereophotogrammetric photograph of the face. (a) Untextured 3D photograph with landmarks identified (red dots); (b) planes derived from the landmarks to outline the nasal area; (c) and (d) untextured cropped nose; (e) and (f) right and left halves of the untextured cropped nose.

Finally, only the nose was left and a virtual volume could be computed. To compare left and right volumes, the nose was divided into a left and right part using the cephalometric-based median plane (Table 1). The left and right volumes of the pre- and postoperative nose were then measured (mm³).

To determine intra- and inter-observer reliability, all measurements were performed twice by two observers (BL and TM), independently of each other, with a time interval (8 weeks for BL and 2 weeks for TM), so preventing memory effects.

Statistical analysis 

Means and standard deviations were calculated and comparisons were made between: the pre- and postoperative total volumes of the nose; the pre- and postoperative cleft side nasal volumes; the pre- and postoperative non-cleft side nasal volumes; the pre- and postoperative volumetric symmetry calculated by dividing the volume of the cleft side and the non-cleft side. A ratio of 1.00 means perfect symmetry.

Pre- and postoperative differences were analyzed using paired Student's t-tests with a p-value of 0.05 indicating statistically significant differences. Paired Student's t-tests were used to calculate the intra- and inter-observer reproducibility of the volumes for repeated measurements (mean difference) and to test for statistically significant differences. The measurement error was calculated as the standard deviation (SD) of the mean difference divided by √2. Reliability coefficients between first and second measurement were calculated as Pearson correlation coefficients. Statistical data analysis was performed with the SPSS software program, version 16.0 (SPSS Inc., Chicago, USA).

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Results 

Eight male and four female patients aged 13–40 years (median, 18 years) met the inclusion criteria and had various deformities of the nose (Table 2). Two patients had an isolated CL and 10 had a CLP. There were 8 left- and 4 right-sided clefts.

Table 2. Surgical characteristics for the 12 patients.

(A) Deviated columella; (B) depressed and deviated nasal tip; (C) wide nasal ala on the cleft side; (D) flat and v-shaped nostril.

12 secondary open rhinoplasty procedures were performed (Table 2). Interdomal sutures were used in all patients. In two patients no further surgical procedures were performed. In the remaining 10 patients, one or two of the following surgical procedures were used in order to achieve more symmetry and increase the volume of the tip on the cleft side: a columellar strut was used in seven patients (five using septal cartilage and two using auricular cartilage), three patients underwent an alar wing graft (two using auricular cartilage, one using septal cartilage), a tip graft was performed in one patient (using septal cartilage) and a transcutaneous nasal bone osteotomy was performed in two patients.

No statistically significant differences (p<0.05) were found within and between observers for the measured volumes and symmetry (Table 3). The reliability coefficients for all volumes ranged from 0.96 to 1.00; duplicate measurement errors ranged from 55.68 to 147.40mm.

Table 3. Mean volume differences (mm³) with 95% confidence intervals and p-value, reliability coefficients (Pearson's correlation coefficient), and measurement error (mm³) within and between observers.

The volumes of the total nose pre- and postoperatively were computed. A mean volume increase of 1228.36mm³ was found (95% confidence interval (CI): 570.20–1886.52mm³). This increase was statistically significant (p=0.002). The pre- and postoperative volumes of the cleft and non-cleft side of the nose are shown in Table 4. A mean pre- and postoperative volume difference of 966.29mm³ was found for the cleft side, which was significant (95% CI: 437.43–1495.16mm³; p=0.002). For the non-cleft side the mean pre- and postoperative volume difference was 262.07mm³, which was not significant (95% CI: −47.40–571.54mm³; p=0.09). Almost all patients had an augmentation of the nasal volume as a result of the operation as is shown by the increase of volume on the cleft side (Table 4). Patients four and nine showed a decrease in volume.

Table 4. Pre- and postoperative volumes (mm³) of the cleft and the non-cleft side of the nose.

The results of the ratio cleft side to non-cleft side are given in Table 5. There was significant improvement of the symmetry (mean difference 0.03, 95% CI: 0.002–0.062; p=0.03).

Table 5. Pre- and postoperative ratio of the cleft and non-cleft side volume. A ratio of 1.00 means perfect symmetry. (*) Indicates improvement of symmetry.

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Discussion 

To the best of the authors’ knowledge, this is the first study to evaluate volumetric changes after rhinoplasty using 3D stereophotogrammetry in patients with clefts. Various methods to assess cleft-related facial deformities have been described¹. Traditionally studies comparing pre- and postoperative nasal changes in CL or CLP patients were limited to radiographs, anthropometry and 2D photogrammetry¹⁵. As summarized in the introduction, various 3D imaging techniques²⁶ have been developed to overcome the shortcomings of conventional 2D imaging.

During recent years, stereophotogrammetry has evolved. With the introduction of systems such as the 3dMDface™ System (3dMD LLC, Atlanta, USA), Di3D^TM (Dimensional Imaging, Glasgow, UK) and 3D-Sensoren FaceSCAN^3D (3D Shape GmbH, Erlangen, Germany), the applicability of 3D photographs in daily practice has become reality. 3D stereophotogrammetry is safe, non-invasive and able to capture superior quality ‘external surface’ photographs in less than 2ms. These characteristics make it ideal to collect the 3D data of faces, even in children or babies. After processing the data, an accurate digital model of the patient's face is created that can be used immediately in a clinical setting. Disadvantages of the system are the need for carefully controlled lighting conditions and the use of four to six high resolution cameras, making it a relatively non-portable system, while the cost of the setup can reach €50,000 or more.

The accuracy of these newly developed 3D imaging systems in recording facial morphologic features has recently been validated³⁰. Several recent studies have focused on determining the reproducibility of identifying landmarks by using various 3D modalities including 3D stereophotogrammetry², ⁴, ⁹, ¹², ¹⁹, ²², ³⁰, ³¹. The results of these studies indicate the 3dMD system to be accurate and precise for facial purposes. Furthermore, the small error in placing landmarks does not lead to statistically significant different volumetric or symmetry measurements, as is seen in the intra- and inter-observer validation (Table 3).

Nevertheless, several sources of error can be identified using this system. Firstly, an error might occur when the 3D photographs are reconstructed. The 3D hardware and software has limitations in the reconstruction of, for example, the nostrils, because of the complex anatomy and the inability of the cameras to capture dark holes perfectly. As a consequence, the nostrils are the regions of error. This error is expected to be of minimal influence for this study since special attention was given to positioning the patient in a standardized manner while acquiring the pre- and the postoperative 3D photographs. An alternative to minimize this problem is using a Cone Beam CT (CBCT) 3D reconstruction of the nose, however, because of the radiation side effect, CBCT is not applicable for longitudinal follow up, whereas 3D photographs are harmless. Secondly, surface matching of the pre- and postoperative 3D photographs can result in minimal errors. Recently, the authors’ group published a paper about the error of matching 3D photographs onto skin surfaces derived from CBCT data¹⁷.

The results of matching two different 3D photographs are even more reliable¹⁸. In this way, a mean registration error of less than 0.6mm is expected, which is clinical acceptable and valuable¹⁸. A third possible error lies in the definition of the midline. In this study the midline is dictated by the median plane, which is based on the pupil reconstructed point. This landmark is indicated as the middle of the inter-endocanthal line. Identification of landmarks can be difficult and may lead to a small error⁷, ⁹, ²⁷. Since one and the same midline plane was used for the pre- and postoperative 3D photographs the amount of volume increase as well as the symmetry ratio could not be affected.

For every patient the best operative technique was chosen by one experienced surgeon. The shape of the CL or CLP nose varied widely and as a consequence the surgical correction depended on the deformity of the nose and the wishes of the patient, making every rhinoplasty unique. Nevertheless, changes of the nasal region were obvious in all patients using the 3D photographs of the pre- and postoperative soft tissues (e.g. Fig. 1).

Since the main goal for surgery was to acquire more symmetry and tip projection, it was expected that the cleft side of the noses would increase in volume. In 10 out of 12 patients more volume was seen and measured on the cleft side. The results of the volumetric measurements were in accordance with the operative techniques performed. For example, alar wing volume increased in patients who acquired an alar wing graft. There was a decrease in volume of the complete nose in two patients. The decrease of volume in patient 4 was mostly caused by reduction of fibrous and connective tissue. Aside from this, there was no augmentation. In this patient the symmetry did not improve. In patient 9, both alar wings were mobilized and reinserted more medially in combination with a columellar strut and reduction of fibrous and connective tissue. This caused an overall reduction of volume and more symmetry. Patient 6 (Fig. 1) showed a decrease of volume on the non-cleft side that was attributed to the nasal osteotomy he underwent because of a deviation of the nasal bone to the non-cleft side. On the cleft side the volume increased partly because of a columellar strut and dome sutures. His nose became more symmetrical.

Although this study represents a small sample, significant statistical changes in the volume of the noses could be proved after 3 months of follow-up using 3D stereophotogrammetry. Student's t-test was used for statistical analysis because of the small group with paired data. Using this test, the mean difference in the pre- and postoperative data could be analyzed taking into account the within-subject variability.

The main purpose of this study was to investigate the applicability of 3D stereophotogrammetry to measure short-term changes in nasal volumes after operation. In future studies changes over a longer period of time will be assessed as postoperative swelling might influence short-term results. In this way, it will be possible to compare different operative techniques in patients with a CL or CLP deformed nose.

In conclusion, 3D stereophotogrammetry is a sensitive, quick and non-invasive method for capturing and evaluating the changes of the nose after rhinoplasty in CL or CLP patients.

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Funding 

This work was supported by a grant from the Dutch Technology Foundation (STW).

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Competing interests 

None declared.

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Ethical approval 

Not required.

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Financial interest in this study 

None.

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