Allan Ponniah

Three-dimensional image analysis of facial skeletal changes after monobloc and bipartition distraction.

Background: Both monobloc and facial bipartition distraction are important tools for correcting functional and aesthetic problems in patients with syndromic craniosynostosis. Three-dimensional computed tomographic reconstructions have become increasingly useful in planning and analyzing surgical results. This study measured the differential deformation of the facial skeleton following distraction osteogenesis with the rigid external distractor frame, looking especially at correction of the midface concavity. Correction of the midface concavity aims to not only improve the appearance but also increase the upper airway volume. Methods: Ten children with syndromic craniosynostoses were studied. Seven children with Crouzon syndrome underwent monobloc distraction and three with Apert syndrome underwent facial bipartition distraction using the rigid external distractor frame. The patients’ ages ranged from 4 months to 15 years. The medial advancement and the lateral advancement of the facial skeleton were compared by landmarking three-dimensional computed tomographic reconstructions using the sella turcica as the fixed point. To compare the shape of the monobloc segment from the preoperative to postoperative scans, a color map was generated. Results: Of the seven patients who underwent monobloc distraction, the mean medial advancement of the face was 4.9 mm greater than the lateral advancement. With the bipartition distraction, the mean central area advancement was 11.4 mm farther than the lateral aspect of the facial skeleton. Conclusions: Both monobloc and in particular the facial bipartition distraction differentially advance the central part of the face more than the lateral areas. This bending of the face appears to have both cosmetic and functional advantages.

Describing Crouzon and Pfeiffer syndrome based on principal component analysis

UNLABELLED Crouzon and Pfeiffer syndrome are syndromic craniosynostosis caused by specific mutations in the FGFR genes. Patients share the characteristics of a tall, flattened forehead, exorbitism, hypertelorism, maxillary hypoplasia and mandibular prognathism. Geometric morphometrics allows the identification of the global shape changes within and between the normal and syndromic population. METHODS Data from 27 Crouzon-Pfeiffer and 33 normal subjects were landmarked in order to compare both populations. With principal component analysis the variation within both groups was visualized and the vector of change was calculated. This model normalized a Crouzon-Pfeiffer skull and was compared to age-matched normative control data. RESULTS PCA defined a vector that described the shape changes between both populations. Movies showed how the normal skull transformed into a Crouzon-Pfeiffer phenotype and vice versa. Comparing these results to established age-matched normal control data confirmed that our model could normalize a Crouzon-Pfeiffer skull. CONCLUSIONS PCA was able to describe deformities associated with Crouzon-Pfeiffer syndrome and is a promising method to analyse variability in syndromic craniosynostosis. The virtual normalization of a Crouzon-Pfeiffer skull is useful to delineate the phenotypic changes required for correction, can help surgeons plan reconstructive surgery and is a potentially promising surgical outcome measure.

Large Scale 3D Morphable Models

We present large scale facial model (LSFM)—a 3D Morphable Model (3DMM) automatically constructed from 9663 distinct facial identities. To the best of our knowledge LSFM is the largest-scale Morphable Model ever constructed, containing statistical information from a huge variety of the human population. To build such a large model we introduce a novel fully automated and robust Morphable Model construction pipeline, informed by an evaluation of state-of-the-art dense correspondence techniques. The dataset that LSFM is trained on includes rich demographic information about each subject, allowing for the construction of not only a global 3DMM model but also models tailored for specific age, gender or ethnicity groups. We utilize the proposed model to perform age classification from 3D shape alone and to reconstruct noisy out-of-sample data in the low-dimensional model space. Furthermore, we perform a systematic analysis of the constructed 3DMM models that showcases their quality and descriptive power. The presented extensive qualitative and quantitative evaluations reveal that the proposed 3DMM achieves state-of-the-art results, outperforming existing models by a large margin. Finally, for the benefit of the research community, we make publicly available the source code of the proposed automatic 3DMM construction pipeline, as well as the constructed global 3DMM and a variety of bespoke models tailored by age, gender and ethnicity.

Planning surgical reconstruction in Treacher-Collins syndrome using virtual simulation.

Background: Treacher-Collins syndrome is a rare autosomal dominant condition of varying phenotypic expression. The surgical correction in this syndrome is difficult, and the approach varies between craniofacial departments worldwide. The authors aimed to design standardized tools for planning orbitozygomatic and mandibular reconstruction in Treacher-Collins syndrome using geometric morphometrics. Methods: The Great Ormond Street Hospital database was retrospectively identified for patients with Treacher-Collins syndrome. Thirteen children (aged 2 to 15 years) who had suitable preoperative three-dimensional computed tomographic head scans were included. Six Treacher-Collins syndrome three-dimensional computed tomographic head scans were quantitatively compared using a template of 96 anatomically defined landmarks to 26 age-matched normal dry skulls. Results: Thin-plate spline videos illustrated the characteristic deformities of retromicrognathia and maxillary and orbitozygomatic hypoplasia in the Treacher-Collins syndrome population. Geometric morphometrics was used in the virtual reconstruction of the orbitozygomatic and mandibular region in Treacher-Collins syndrome patients. Intrarater and interrater reliability of the landmarks was acceptable and within a standard deviation of less than 1 mm on 97 percent and 100 percent of 10 repeated scans, respectively. Conclusions: Virtual normalization of the Treacher-Collins syndrome skull effectively describes characteristic skeletal deformities and provides a useful guide to surgical reconstruction. Size-matched stereolithographic templates derived from thin-plate spline warps can provide effective intraoperative templates for zygomatic and mandibular reconstruction in the Treacher-Collins syndrome patient. CLINICAL QUESTION/LEVEL OF EVIDENCE: Diagnostic, V.

Assessing the corrective effects of facial bipartition distraction in Apert syndrome using geometric morphometrics

UNLABELLED Apert syndrome is a congenital disorder characterized by craniosynostosis and midface hypoplasia. This study looks to identify to what extent bipartition distraction corrects the morphological abnormalities of this condition. Preoperative and postoperative three-dimensional computed tomography (3DCT) scans of 10 patients with Apert syndrome (12-21 years) were identified from the Great Ormond Street Hospital database. To analyse preoperative and postoperative scans, 98 landmarks and 13 normal skulls were used. Principal component analysis (PCA) was used to analyse patterns in the datasets. Within each group, eigenvectors were identified that demonstrated the aspects of the skull where most variations were found. The analysis allowed both global shape measurement and local proportions. Postoperative and normal scans both showed the same first three principal components. Warping from preoperative to postoperative illustrates midface advancement and inward rotation of the orbits. Postoperative to normal warps demonstrate some remaining differences. The reliability of the used land marks varied between 77% and 95% for the highly reproducible landmarks between the two observers. 95% versus 100% were at least acceptable reproducible landmarks. This study allows us to understand the way bipartition distraction corrects the abnormalities of the Apert skull. Analysing the surgical outcome of facial bipartition with geometric morphometrics shows that some major Apert characteristics are corrected. Using the data and the output of further studies, surgical procedures can be adapted in order to achieve a postoperative result closer to the normal population. LEVEL OF EVIDENCE Therapeutic clinical question Level IV.

Using principal component analysis to describe the Apert skull deformity and simulate its correction

Apert syndrome is an autosomal dominant condition caused by specific mutations leading to growth restriction, thought to originate in the anterior cranial base. This in turn results in the Apert skull. Geometric morphometrics and mathematical modelling techniques have been used to analyse complex shapes and are now being used in facial analysis at for example border controls, or in anthropologic and biologic studies. Using the latest advances in imaging technology and mathematical modelling we can create a virtual 3D image of what the normal skull may have looked like for each Apert

Monobloc distraction in an infant, using the rigid external distractor: Problems and solutions - A case report

INTRODUCTION Patients with craniofacial dysostosis frequently develop functional problems including raised intracranial pressure, ocular dysfunction, obstructive sleep apnoeas and failure to thrive. These functional problems can be treated by a number of different techniques. The monobloc frontofacial advancement has the ability to correct all of these functional problems in one procedure, but can be associated with high morbidity particularly in the young infant. AIM A case report of a 4-month-old infant with Pfeiffers syndrome and severe functional problems treated by monobloc osteotomy and distraction using the rigid external distractor is reported. The management, problems and complications encountered with this patient are discussed together with the role of monobloc distraction in the infant. Adaptation of the rigid external distraction (RED) technique using two titanium mesh sheets to prevent penetration of the skull by the cranial pins is described. CONCLUSIONS Monobloc frontofacial advancement in the very young can be successfully achieved using the RED frame, thus treating exophthalmus, raised intracranial pressure and upper airway problems in one operation. However, it may be associated with significant complications and should only be used for those extreme cases where the severity of the functional problems prevent treatment being delayed.

Spring-assisted Cranioplasty for the Correction of Nonsyndromic Scaphocephaly: A Quantitative Analysis of 100 Consecutive Cases

Background: Spring-assisted cranioplasty has been proposed as an alternative to total calvarial remodeling for sagittal craniosynostosis. Advantages include its minimally invasive nature, and reduced morbidity and hospital stay. Potential drawbacks include the need for a second procedure for removal and the lack of published long-term follow-up. The authors present a single-institution experience of 100 consecutive cases using a novel spring design. Methods: All patients treated at the authors’ institution between April of 2010 and September of 2014 were evaluated retrospectively. Patients with isolated nonsyndromic sagittal craniosynostosis were included. Data were collected for operative time, anesthetic time, hospital stay, transfusion requirement, and complications in addition to cephalic index preoperatively and at 1 day, 3 weeks, and 6 months postoperatively. Results: One hundred patients were included. Mean cephalic index was 68 preoperatively, 71 at day 1, and 72 at 3 weeks and 6 months postoperatively. Nine patients required transfusion. Two patients developed a cerebrospinal fluid leak requiring intervention. One patient required early removal of springs because of infection. One patient had a wound dehiscence over the spring and one patient sustained a venous infarct with hemiplegia. Five patients required further calvarial remodeling surgery. Conclusions: The authors’ modified spring design and protocol represents an effective strategy in the management of single-suture sagittal craniosynostosis with reduced total operative time and blood loss compared with alternative treatment strategies. In patients referred within the first 6 months of birth, this technique has become the authors’ procedure of choice. In a minority of cases, especially in the older age groups, further remodeling surgery is required. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

A classification system to guide orbitozygomatic reconstruction in Treacher-Collins syndrome

We propose a classification system of the orbitozygomatic skeletal deformities seen in Treacher-Collins syndrome (TCS), a complex autosomal dominant disorder of craniofacial morphogenesis. The classification is designed both to characterize the degree of deformity and as a guide to the reconstructive planning. TCS results in varying degrees of retromicrognathia, maxillary hypoplasia and orbitozygomatic dysplasia. The severity of the soft tissue deformities generally parallel the underlying skeletal dysmorphology. The spectrum of mandibular deformity seen in Hemifacial Microsomia (HFM) was originally successfully classified by Pruzansky and since its introduction, the system or one of its variants has underpinned the management of the mandible and TMJ in this condition. The challenges in developing a coherent treatment philosophy for orbito-zygomatic dysplasia in TCS are very similar to those seen in treating the mandible in HFM. Both conditions present with varying degrees of skeletal hypoplasia which creates increasing challenges in providing additional bone stock for reconstruction. Both conditions present varying degrees of abnormality in both the shapeandposition of the affected skeletal elements and in both conditions there are functional problems related to the severity of the deformity. We have therefore applied the same concepts to devise a classification system to guide the craniofacial surgeon during orbitozygomatic reconstruction in TCS.

Assessment of spring cranioplasty biomechanics in sagittal craniosynostosis patients

OBJECTIVE Scaphocephaly secondary to sagittal craniosynostosis has been treated in recent years with spring-assisted cranioplasty, an innovative approach that leverages the use of metallic spring distractors to reshape the patient skull. In this study, a population of patients who had undergone spring cranioplasty for the correction of scaphocephaly at the Great Ormond Street Hospital for Children was retrospectively analyzed to systematically assess spring biomechanical performance and kinematics in relation to spring model, patient age, and outcomes over time. METHODS Data from 60 patients (49 males, mean age at surgery 5.2 ± 0.9 months) who had received 2 springs for the treatment of isolated sagittal craniosynostosis were analyzed. The opening distance of the springs at the time of insertion and removal was retrieved from the surgical notes and, during the implantation period, from planar radiographs obtained at 1 day postoperatively and at the 3-week follow-up. The force exerted by the spring to the patient skull at each time point was derived after mechanical testing of each spring model-3 devices with the same geometry but different wire thicknesses. Changes in the cephalic index between preoperatively and the 3-week follow-up were recorded. RESULTS Stiffer springs were implanted in older patients (p < 0.05) to achieve the same opening on-table as in younger patients, but this entailed significantly different-higher-forces exerted on the skull when combinations of stiffer springs were used (p < 0.001). After initial force differences between spring models, however, the devices all plateaued. Indeed, regardless of patient age or spring model, after 10 days from insertion, all the devices were open. CONCLUSIONS Results in this study provide biomechanical insights into spring-assisted cranioplasty and could help to improve spring design and follow-up strategy in the future.