Towards a radiation free numerical modelling framework to predict spring assisted correction of scaphocephaly.

Sagittal Craniosynostosis (SC) is a congenital craniofacial malformation, involving premature sagittal suture ossification; spring-assisted cranioplasty (SAC) - insertion of metallic distractors for skull reshaping - is an established method for treating SC. Surgical outcomes are predictable using numerical modelling, however published methods rely on computed tomography (CT) scans availability, which are not routinely performed. We investigated a simplified method, based on radiation-free 3D stereophotogrammetry scans.Eight SAC patients (age 5.1 ± 0.4 months) with preoperative CT and 3D stereophotogrammetry scans were included. Information on osteotomies, spring model and post-operative spring opening were recorded. For each patient, two preoperative models (PREOP) were created: i) CT model and ii) S model, created by processing patient specific 3D surface scans using population averaged skin and skull thickness and suture locations. Each model was imported into ANSYS Mechanical (Analysis System Inc., Canonsburg, PA) to simulate spring expansion. Spring expansion and cranial index (CI - skull width over length) at times equivalent to immediate postop (POSTOP) and follow up (FU) were extracted and compared with in-vivo measurements.Overall expansion patterns were very similar for the 2 models at both POSTOP and FU. Both models had comparable outcomes when predicting spring expansion. Spring induced CI increase was similar, with a difference of 1.2%±0.8% for POSTOP and 1.6%±0.6% for FU.This work shows that a simplified model created from the head surface shape yields acceptable results in terms of spring expansion prediction. Further modelling refinements will allow the use of this predictive tool during preoperative planning.

Spring-assisted cranioplasty (SAC) ­insertion of metallic distractors helping skull reshaping ­ is a method for treating sagittal craniosynostosis, caused by premature sagittal suture closure. We present a method for predicting SAC outcomes, relying on radiation-free 3D stereophotogrammetry scans. Eight patients with preoperative CT and 3D stereophotogrammetry scans were recruited; results of spring expansion simulation were compared between models created using CT versus 3D scan data. Expansion patterns and extent of reshaping were very similar. This work proves that SAC preoperative planning can be carried out using non-ionising imaging. Further modelling refinements will allow clinical adoption of this predictive tool.

Initial UK series of endoscopic suturectomy with postoperative helmeting for craniosynostosis: early report of perioperative experience.

BACKGROUND: Endoscopic suturectomy with postoperative helmeting (ESCH) has emerged as a successful treatment for craniosynostosis, initially in North America. We report early outcomes from the first cohort of ESCH patients treated in the United Kingdom (UK). METHODS: Retrospective cohort study with electronic chart review. RESULTS: 18 consecutive patients from the first ESCH procedure in UK (May 2017) until January 2020 identified. 12 male and 6 female infantsd, with a mean age of 4.6 months (range 2.5-7.8 months) and weight of 6.8 kg (range 4.8-9.8 kg). Diagnoses were metopic (n = 8), unicoronal (n = 7), sagittal (n = 2) and multi-sutural (n = 1) synostoses. Median incision length was 3 cm (range 2-10 cm). 16/18 received no blood products, with 2 (both metopics) requiring transfusion (1 donor exposure). Mean operative time (including anaesthesia) was 96 min (range 40-127 min). Median length of hospital stay was 1 night. 1 surgical complication (superficial infection). All patients are currently undergoing helmet orthosis therapy. So far, no patients have required revisional or squint surgery. CONCLUSION: Early experience from the first UK cohort of ESCH suggests that this is a safe and well tolerated technique with low morbidity, transfusion and short hospital stay. Long-term results in terms of shape, cosmetic and developmental outcome are awaited.

Correlation between head shape and volumetric changes following spring-assisted posterior vault expansion.

The aim of the study was to investigate whether different head shapes show different volumetric changes following spring-assisted posterior vault expansion (SA-PVE) and to investigate the influence of surgical and morphological parameters on SA-PVE. Preoperative three-dimensional skull models from patients who underwent SA-PVE were extracted from computed tomography scans. Patient head shape was described using statistical shape modelling (SSM) and principal component analysis (PCA). Preoperative and postoperative intracranial volume (ICV) and cranial index (CI) were calculated. Surgical and morphological parameters included skull bone thickness, number of springs, duration of spring insertion and type of osteotomy. In the analysis, 31 patients were included. SA-PVE resulted in a significant ICV increase (284.1 ± 171.6 cm3, p < 0.001) and a significant CI decrease (-2.9 ± 4.3%, p < 0.001). The first principal component was significantly correlated with change in ICV (Spearman ρ = 0.68, p < 0.001). Change in ICV was significantly correlated with skull bone thickness (ρ = -0.60, p < 0.001) and age at time of surgery (ρ = -0.60, p < 0.001). No correlations were found between the change in ICV and number of springs, duration of spring insertion and type of osteotomy. SA-PVE is effective for increasing the ICV and resolving raised intracranial pressure. Younger, brachycephalic patients benefit more from surgery in terms of ICV increase. Skull bone thickness seems to be a crucial factor and should be assessed to achieve optimal ICV increase. In contrast, insertion of more than two springs, duration of spring insertion or performing a fully cut through osteotomy do not seem to impact the ICV increase. When interpreting ICV increases, normal calvarial growth should be taken into account.

Validation of an in-silico modelling platform for outcome prediction in spring assisted posterior vault expansion.

BACKGROUND: Spring-Assisted Posterior Vault Expansion has been adopted at Great Ormond Street Hospital for Children, London, UK to treat raised intracranial pressure in patients affected by syndromic craniosynostosis, a congenital calvarial anomaly which causes premature fusion of skull sutures. This procedure aims at normalising head shape and augmenting intracranial volume by means of metallic springs which expand the back portion of the skull. The aim of this study is to create and validate a 3D numerical model able to predict the outcome of spring cranioplasty in patients affected by syndromic craniosynostosis, suitable for clinical adoption for preoperative surgical planning. METHODS: Retrospective spring expansion measurements retrieved from x-ray images of 50 patients were used to tune the skull viscoelastic properties for syndromic cases. Pre-operative computed tomography (CT) data relative to 14 patients were processed to extract patient-specific skull shape, replicate surgical cuts and simulate spring insertion. For each patient, the predicted finite element post-operative skull shape model was compared with the respective post-operative 3D CT data. FINDINGS: The comparison of the sagittal and transverse cross-sections of the simulated end-of-expansion calvaria and the post-operative skull shapes extracted from CT images showed a good shape matching for the whole population. The finite element model compared well in terms of post-operative intracranial volume prediction (R2 = 0.92, p < 0.0001). INTERPRETATION: These preliminary results show that Finite Element Modelling has great potential for outcome prediction of spring assisted posterior vault expansion. Further optimisation will make it suitable for clinical deployment.

Sporting activity after craniosynostosis surgery in children: a source of parental anxiety.

PURPOSE: Craniosynostosis correction involves major skull surgery in infancy-a potential source of worry for parents when their treated children begin involvement in sports. METHODS: Electronic multiple choice survey of parents of children who had undergone craniosynostosis surgery in infancy using 5-point Likert scales. RESULTS: Fifty-nine completed surveys were obtained from parents of children who had undergone previous craniosynostosis surgery. Mean age of children was 7.8 years (range 3 months to 22 years), with 36 non-syndromic and 23 syndromic cases. The most common surgery was fronto-orbital remodelling (18). Fifty-two of 59 were involved in athletic activity. The most intense sport type was non-contact in 23, light contact in 20, heavy contact in 4 and combat in 5. Participation level was school mandatory in 12, school club in 17, non-school sport club in 21 and regional representative in 2. One child had been advised to avoid sport by an external physician. Mean anxiety (1-5 Likert) increased with sport intensity: non-contact 1.7, light contact 2.2, heavy contact 3.5 and combat 3.6. Twenty-nine of 59 parents had been given specific advice by the Craniofacial Team regarding athletic activity, 28 of which found useful. Three sport-related head injuries were reported, none of which required hospitalisation. CONCLUSION: Little information exists regarding sports for children after craniosynostosis surgery. This study suggests that parental anxiety remains high, particularly for high impact/combat sports, and that parents would like more information from clinicians about the safety of post-operative sporting activities.

Computational modelling of patient specific spring assisted lambdoid craniosynostosis correction.

Lambdoid craniosynostosis (LC) is a rare non-syndromic craniosynostosis characterised by fusion of the lambdoid sutures at the back of the head. Surgical correction including the spring assisted cranioplasty is the only option to correct the asymmetry at the skull in LC. However, the aesthetic outcome from spring assisted cranioplasty may remain suboptimal. The aim of this study is to develop a parametric finite element (FE) model of the LC skulls that could be used in the future to optimise spring surgery. The skull geometries from three different LC patients who underwent spring correction were reconstructed from the pre-operative computed tomography (CT) in Simpleware ScanIP. Initially, the skull growth between the pre-operative CT imaging and surgical intervention was simulated using MSC Marc. The osteotomies and spring implantation were performed to simulate the skull expansion due to the spring forces and skull growth between surgery and post-operative CT imaging in MSC Marc. Surface deviation between the FE models and post-operative skull models reconstructed from CT images changed between ± 5 mm over the skull geometries. Replicating spring assisted cranioplasty in LC patients allow to tune the parameters for surgical planning, which may help to improve outcomes in LC surgeries in the future.

Lack of association of cranial lacunae with intracranial hypertension in children with Crouzon syndrome and Apert syndrome: a 3D morphometric quantitative analysis.

PURPOSE: Cranial lacunae (foci of attenuated calvarial bone) are CT equivalents of "copper beating" seen on plain skull radiographs in children with craniosynostosis. The qualitative presence of copper beating has not been found to be useful for the diagnosis of intracranial hypertension (IH) in these patients. 3D morphometric analysis (3DMA) allows a more systematic and quantitative assessment of calvarial attenuation. We used 3DMA to examine the relationship between cranial lacunae and IH in children with Crouzon and Apert syndromic craniosynostosis. METHODS: Patients were divided into IH and non-IH groups defined on an intention-to-treat basis. Pre-operative CT scans were converted into 3D skull models and processed to quantify lacunae as a percentage of calvarium surface area (LCP). This was done on individual bone and whole skull basis. RESULTS: Eighteen consecutive children with Crouzon's syndrome and 17 with Apert syndrome were identified. Median age at CT scan was 135 days (range 6-1778). Of the 35 children, 21 required surgery for IH at median age of 364 days (range 38-1710). Of these 21 children, 14 had lacunae with mean LCP of 3% (0-28%). Of the 14 non-IH children, 8 had lacunae with mean LCP of 2% (0-8%). LCP was not significantly different between IH and non-IH groups. Parietal bones were most likely to show lacunae (IH 14/21, non-IH 9/14), followed by occipital (IH 8/21, non-IH 3/14), and frontal (IH 6/21, non-IH 2/14). CONCLUSION: Results suggest that cranial lacunae, measured using quantitative 3DMA, do not correlate with IH, in agreement with evidence from qualitative plain skull radiograph studies.

Intracranial Volume and Head Circumference in Children with Unoperated Syndromic Craniosynostosis.

BACKGROUND: When analyzing intracranial volume gain resulting from operative intervention in craniosynostosis, it is necessary to understand the underlying growth. The authors sought to create comprehensive intracranial volume and occipitofrontal circumference growth charts, as measured on unoperated craniosynostotic children, and aimed to investigate whether intracranial volume and occipitofrontal circumference could act as proxy measures for each other. METHODS: All preoperative Great Ormond Street Hospital patients with a diagnosis of Apert, Crouzon-Pfeiffer, or Saethre-Chotzen syndrome from the year 2004 onward were considered for this study. A control group of unaffected Great Ormond Street Hospital patients were also measured. Intracranial volume and occipitofrontal circumference were measured on the same scans. To study correlation between intracranial volume and occipitofrontal circumference, logarithmic fits were assessed. RESULTS: One hundred forty-seven craniosynostotic children with 221 preoperative scans were included (81 Apert, 81 Crouzon, 31 Pfeiffer, and 28 Saethre-Chotzen). The control group comprised 56 patients with 58 scans. Apert intracranial volume curves were significantly larger than those of other syndromes from 206 days onward; occipitofrontal circumference curves were not significantly different. The correlation coefficient between intracranial volume and occipitofrontal circumference was R = 0.87 for all syndromes combined and R = 0.91 for the control group. CONCLUSIONS: Apert syndrome children have a larger intracranial volume than children with other syndromic craniosynostotic conditions and unaffected children but maintain a similar occipitofrontal circumference. This study demonstrates high correlation between intracranial volume and occipitofrontal circumference with clinical care implications. The authors' reference growth curves can be used to monitor intracranial volume change over time and correct operative change for underlying growth.

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.

Cranial bone structure in children with sagittal craniosynostosis: Relationship with surgical outcomes.

BACKGROUND: While spring-assisted cranioplasty has become a widespread technique to correct scaphocephaly in children with sagittal synostosis, predicting head shape changes induced by the gradual opening of the springs remains challenging. This study aimed to explore the role of cranial bone structure on surgical outcomes. METHODS: Patients with isolated sagittal synostosis undergoing spring-assisted cranioplasty at GOSH (London, UK) were recruited (n = 18, age: 3-8 months). Surgical outcome was assessed by the change in cephalic index measured on 3D head scans acquired before spring insertion and after their removal using a 3D handheld scanner. Parietal bone samples routinely discarded during spring-assisted cranioplasty were collected and scanned using micro-computed tomography. From visual assessment of such scans, bone structure was classified into one- or three-layered, the latter indicating the existence of a diploë cavity. Bone average thickness, volume fraction and surface density were computed and correlated with changes in cephalic index. RESULTS: Cephalic index increased for all patients (p < 0.001), but individual improvement varied. Although the patient age and treatment duration were not significantly correlated with changes in cephalic index, bone structural parameters were. The increase of cephalic index was smaller with increasing bone thickness (Pearson's r = -0.79, p < 0.001) and decreasing bone surface density (r = 0.77, p < 0.001), associated with the three-layered bone structure. CONCLUSIONS: Variation in parietal bone micro-structure was associated with the magnitude of head shape changes induced by spring-assisted cranioplasty. This suggests that bone structure analysis could be a valuable adjunct in designing surgical strategies that yield optimal patient-specific outcomes.

Statistical shape modelling to aid surgical planning: associations between surgical parameters and head shapes following spring-assisted cranioplasty.

PURPOSE: Spring-assisted cranioplasty is performed to correct the long and narrow head shape of children with sagittal synostosis. Such corrective surgery involves osteotomies and the placement of spring-like distractors, which gradually expand to widen the skull until removal about 4 months later. Due to its dynamic nature, associations between surgical parameters and post-operative 3D head shape features are difficult to comprehend. The current study aimed at applying population-based statistical shape modelling to gain insight into how the choice of surgical parameters such as craniotomy size and spring positioning affects post-surgical head shape. METHODS: Twenty consecutive patients with sagittal synostosis who underwent spring-assisted cranioplasty at Great Ormond Street Hospital for Children (London, UK) were prospectively recruited. Using a nonparametric statistical modelling technique based on mathematical currents, a 3D head shape template was computed from surface head scans of sagittal patients after spring removal. Partial least squares (PLS) regression was employed to quantify and visualise trends of localised head shape changes associated with the surgical parameters recorded during spring insertion: anterior-posterior and lateral craniotomy dimensions, anterior spring position and distance between anterior and posterior springs. RESULTS: Bivariate correlations between surgical parameters and corresponding PLS shape vectors demonstrated that anterior-posterior (Pearson's [Formula: see text]) and lateral craniotomy dimensions (Spearman's [Formula: see text]), as well as the position of the anterior spring ([Formula: see text]) and the distance between both springs ([Formula: see text]) on average had significant effects on head shapes at the time of spring removal. Such effects were visualised on 3D models. CONCLUSIONS: Population-based analysis of 3D post-operative medical images via computational statistical modelling tools allowed for detection of novel associations between surgical parameters and head shape features achieved following spring-assisted cranioplasty. The techniques described here could be extended to other cranio-maxillofacial procedures in order to assess post-operative outcomes and ultimately facilitate surgical decision making.

Three-dimensional surface scanners compared with standard anthropometric measurements for head shape.

Three-dimensional (3D) surface imaging devices designed to capture and quantify craniofacial surface morphology are becoming more common in clinical environments. Such scanners overcome the limitations of two-dimensional photographs while avoiding the ionizing radiation of computed tomography. The purpose of this study was to compare standard anthropometric cranial measurements with measurements taken from images acquired with 3D surface scanners. Two 3D scanners of different cost were used to acquire head shape data from thirteen adult volunteers: M4D scan and Structure Sensor. Head circumference and cephalic index were measured directly on the patients as well as on 3D scans acquired with the two scanners. To compare head volume measurements with a gold standard, magnetic resonance imaging scans were used. Repeatability and accuracy of both devices were evaluated. Intra-rater repeatability for both scanners was excellent (intraclass correlation coefficients > 0.99, p < 0.001). Direct and digital measures of head circumference, cephalic index and head volume were strongly correlated (0.85 < r < 0.91, p < 0.001). Compared to direct measurements, accuracy was highest for M4D scan. Both 3D scanners provide reproducible data of head circumference, cephalic index and head volume and show a strong correlation with traditional measurements. However, care must be taken when using absolute values.

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.

Comparison of three-dimensional scanner systems for craniomaxillofacial imaging.

Two-dimensional photographs are the standard for assessing craniofacial surgery clinical outcomes despite lacking three-dimensional (3D) depth and shape. Therefore, 3D scanners have been gaining popularity in various fields of plastic and reconstructive surgery, including craniomaxillofacial surgery. Head shapes of eight adult volunteers were acquired using four 3D scanners: 1.5T Avanto MRI, Siemens; 3dMDface System, 3dMD Inc.; M4D Scan, Rodin4D; and Structure Sensor, Occipital Inc. Accuracy was evaluated as percentage of data within a range of 2 mm from the 3DMDface System reconstruction, by surface-to-surface root mean square (RMS) distances, and with facial distance maps. Precision was determined by RMS. Relative to the 3dMDface System, accuracy was the highest for M4D Scan (90% within 2 mm; RMS of 0.71 mm ± 0.28 mm), followed by Avanto MRI (86%; 1.11 mm ± 0.33 mm) and Structure Sensor (80%; 1.33 mm ± 0.46). M4D Scan and Structure Sensor precision were 0.50 ± 0.04 mm and 0.51 ± 0.03 mm, respectively. Clinical and technical requirements govern scanner choice; however, 3dMDface System and M4D Scan provide high-quality results. It is foreseeable that compact, handheld systems will become more popular in the near future.

Quantifying the effect of corrective surgery for trigonocephaly: A non-invasive, non-ionizing method using three-dimensional handheld scanning and statistical shape modelling.

Trigonocephaly in patients with metopic synostosis is corrected by fronto-orbital remodelling (FOR). The aim of this study was to quantitatively assess aesthetic outcomes of FOR by capturing 3D forehead scans of metopic patients pre- and post-operatively and comparing them with controls. Ten single-suture metopic patients undergoing FOR and 15 age-matched non-craniosynostotic controls were recruited at Great Ormond Street Hospital for Children (UK). Scans were acquired with a three-dimensional (3D) handheld camera and post-processed combining 3D imaging software. 3D scans were first used for cephalometric measurements. Statistical shape modelling was then used to compute the 3D mean head shapes of the three groups (FOR pre-op, post-op and controls). Head shape variations were described via principal component analysis (PCA). Cephalometric measurements showed that FOR significantly increased the forehead volume and improved trigonocephaly. This improvement was supported visually by pre- and post-operative computed mean 3D shapes and numerically by PCA (p < 0.001). Compared with controls, post-operative scans showed flatter foreheads (p < 0.001). In conclusion, 3D scanning followed by 3D statistical shape modelling enabled the 3D comparison of forehead shapes of metopic patients and non-craniosynostotic controls, and demonstrated that the adopted FOR technique was successful in correcting bitemporal narrowing but overcorrected the rounding of the forehead.

Evaluating the Efficacy of Monobloc Distraction in the Crouzon-Pfeiffer Craniofacial Deformity Using Geometric Morphometrics.

BACKGROUND: Crouzon-Pfeiffer syndrome is caused by mutations predominantly in the FGFR2 gene leading to syndromic craniosynostosis and midfacial hypoplasia. Monobloc distraction aims to correct both functional and aesthetic disharmony as a result of midfacial hypoplasia. This study evaluates the corrective effects and effectiveness of monobloc distraction in Crouzon-Pfeiffer patients. METHODS: Preoperative and postoperative scans were collected from 20 Crouzon and two Pfeiffer patients aged 7 to 20 years. Fifty-six normal skulls were used as a control group. Geometric morphometrics using 52 frontofacial landmarks were used to analyze the normal skull and preoperative and postoperative patient skulls. Color maps were created to visualize differences among the average normal, preoperative, and postoperative Crouzon-Pfeiffer patients. RESULTS: In the studied patient population, monobloc distraction with the use of an external distractor advanced the upper half of the midface more than the lower half of the midface. There was an anteroinferior rotation in the monobloc segment. The zygomatic arch length improved on average to 88 and 90 percent of normal (right and left, respectively), whereas globe protrusion was corrected from 134 percent to 84 percent and from 131 percent to 87 percent of normal (right and left, respectively) in the studied patient population. Compared with a normal skull, the maxillary region remained retruded. CONCLUSIONS: The advancement achieved by monobloc distraction is effective in the upper half of the midface; the lower half of the midface is advanced but remains retruded in comparison with the normal population. The midface is rotated anteroinferiorly. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

Staged separation of craniopagus twins.

Craniopagus twins are rare and account for up to 6% of all conjoined twins. No hospital will encounter many such twins and the opportunity to develop expertise is limited. We have dealt with 2 such sets and illustrate our approach by reference to our most recent set. We believe that detailed imaging allows precise delineation of the anatomy and facilitates detailed planning of the surgery. When venous drainage from the 2 brains is connected, we believe that staged separation is preferable as gradual alteration of hemodynamics may be safer than a single-stage procedure.

Correcting the typical Apert face: combining bipartition with monobloc distraction.

BACKGROUND: Bipartition distraction is a novel procedure combining frontofacial bipartition and monobloc distraction. Apert syndrome and other syndromic craniofacial dysostoses are often characterized by hypertelorism, with a negative canthal axis and counterrotated orbits. Central midface hypoplasia can result in a biconcave face in both midsagittal and axial planes. Bipartition distraction can correct these facial abnormalities. METHODS: Twenty patients (19 Apert syndrome patients and one Pfeiffer syndrome patient, aged 1.6 to 21 years) underwent bipartition distraction. Severity of appearance was graded preoperatively and postoperatively as mild, moderate, or severe. Functional problems were documented by a multidisciplinary team. Central and lateral midface skeletal advancement were measured. Follow-up ranged from 15 months to 7 years. RESULTS: Bipartition distraction consistently produced more central than lateral facial advancement. Mean central advancement was 13.2 ± 5.9 mm at sella-nasion and 11.7 ± 5.4 mm at sella-A point. Lateral advancement was 4.7 ± 2.8 mm. Unbending the face improved aesthetic appearance. Airway function, eye exposure, and elevated intracranial pressure were improved. Complications included six temporary cerebrospinal fluid leaks (four needing a lumbar drain), five patients with postoperative seizures, five patients requiring Rigid External Distraction frame repositioning, one palatal fistula, one velopharyngeal incompetence, five pin-site infections, one abscess under frontal bone, three cases of sepsis, nine patients with worsened strabismus, two patients with enophthalmos, one patient with partial visual field loss, and three patients who required reintubation because of aspiration. CONCLUSIONS: : Bipartition distraction is an effective procedure with which to differentially advance the central face in Apert syndrome. It improves both function and aesthetics. CLINICAL QUESTION/LEVEL OF EVIDENCE: : Therapeutic, IV.

Complications of frontofacial advancement.

PURPOSE: The purpose of this study was to document the early and late complications associated with frontofacial distraction. METHOD: A systematic review of the literature on complications in craniofacial surgery and a review of records of patients undergoing frontofacial distraction at Great Ormond Street Hospital for Children over a 10-year period were conducted. RESULTS: Complications arising from frontofacial advancement are common. Mortality rates varied between 0 and 4.5 %. There has been a general decline in reported mortality rates with time, and the most recent series report mortalities of less than 1 %. The incidence of significant blood loss (greater than one blood volume) in patients undergoing monobloc osteotomy varied between 5.3 and 9.1 %. CSF leaks following monobloc distraction are common (incidence, 2-20 %). Most of these leaks settle spontaneously. The incidence of frontal bone flap necrosis requiring debridement and a subsequent cranioplasty varied between 3 and 20 %. CONCLUSIONS: The functional and aesthetic benefits of frontofacial distraction are well documented, but these advantages are associated with a significant complication rate. The potential benefits of frontofacial distraction need to be carefully weighed against the potential complications when deciding to recommend surgery.