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.

An engineered periosteum for efficient delivery of rhBMP-2 and mesenchymal progenitor cells during bone regeneration.

During bone regeneration, the periosteum acts as a carrier for key regenerative cues, delivering osteochondroprogenitor cells and crucial growth factors to the injured bone. We developed a biocompatible, 3D polycaprolactone (PCL) melt electro-written membrane to act as a mimetic periosteum. Poly (ethyl acrylate) coating of the PCL membrane allowed functionalization, mediated by fibronectin and low dose recombinant human BMP-2 (rhBMP-2) (10-25 µg/ml), resulting in efficient, sustained osteoinduction in vitro. In vivo, rhBMP-2 functionalized mimetic periosteum demonstrated regenerative potential in the treatment of rat critical-size femoral defects with highly efficient healing and functional recovery (80%-93%). Mimetic periosteum has also proven to be efficient for cell delivery, as observed through the migration of transplanted periosteum-derived mesenchymal cells to the bone defect and their survival. Ultimately, mimetic periosteum demonstrated its ability to deliver key stem cells and morphogens to an injured site, exposing a therapeutic and translational potential in vivo when combined with unprecedentedly low rhBMP-2 doses.

In silico assessment of the bone regeneration potential of complex porous scaffolds.

Mechanical environment plays a crucial role in regulating bone regeneration in bone defects. Assessing the mechanobiological behavior of patient-specific orthopedic scaffolds in-silico could help guide optimal scaffold designs, as well as intra- and post-operative strategies to enhance bone regeneration and improve implant longevity. Additively manufactured porous scaffolds, and specifically triply periodic minimal surfaces (TPMS), have shown promising structural properties to act as bone substitutes, yet their ability to induce mechanobiologially-driven bone regeneration has not been elucidated. The aim of this study is to i) explore the bone regeneration potential of TPMS scaffolds made of different stiffness biocompatible materials, to ii) analyze the influence of pre-seeding the scaffolds and increasing the post-operative resting period, and to iii) assess the influence of patient-specific parameters, such as age and mechanosensitivity, on outcomes. To perform this study, an in silico model of a goat tibia is used. The bone ingrowth within the scaffold pores was simulated with a mechano-driven model of bone regeneration. Results showed that the scaffold's architectural properties affect cellular diffusion and strain distribution, resulting in variations in the regenerated bone volume and distribution. The softer material improved the bone ingrowth. An initial resting period improved the bone ingrowth but not enough to reach the scaffold's core. However, this was achieved with the implantation of a pre-seeded scaffold. Physiological parameters like age and health of the patient also influence the bone regeneration outcome, though to a lesser extent than the scaffold design. This analysis demonstrates the importance of the scaffold's geometry and its material, and highlights the potential of using mechanobiological patient-specific models in the design process for bone substitutes.

Additively manufactured lattice structures with controlled transverse isotropy for orthopedic porous implants.

Additively manufactured lattice structures enable the design of tissue scaffolds with tailored mechanical properties, which can be implemented in porous biomaterials. The adaptation of bone to physiological loads results in anisotropic bone tissue properties which are optimized for site-specific loads; therefore, some bone sites are stiffer and stronger along the principal load direction compared to other orientations. In this work, a semi-analytical model was developed for the design of transversely isotropic lattice structures that can mimic the anisotropy characteristics of different types of bone tissue. Several design possibilities were explored, and a particular unit cell, which was best suited for additive manufacturing was further analyzed. The design of the unit cell was parameterized and in-silico analysis was performed via Finite Element Analysis. The structures were manufactured additively in metal and tested under compressive loads in different orientations. Finite element analysis showed good correlation with the semi-analytical model, especially for elastic constants with low relative densities. The anisotropy measured experimentally showed a variable accuracy, highlighting the deviations from designs to additively manufactured parts. Overall, the proposed model enables to exploit the anisotropy of lattice structures to design lighter scaffolds with higher porosity and increased permeability by aligning the scaffold with the principal direction of the load.

Mechanical and morphological properties of parietal bone in patients with sagittal craniosynostosis.

Limited information is available on the effect of sagittal craniosynostosis (CS) on morphological and material properties of the parietal bone. Understanding these properties would not only provide an insight into bone response to surgical procedures but also improve the accuracy of computational models simulating these surgeries. The aim of the present study was to characterise the mechanical and microstructural properties of the cortical table and diploe in parietal bone of patients affected by sagittal CS. Twelve samples were collected from pediatric patients (11 males, and 1 female; age 5.2 ± 1.3 months) surgically treated for sagittal CS. Samples were imaged using micro-computed tomography (micro-CT); and mechanical properties were extracted by means of micro-CT based finite element modelling (micro-FE) of three-point bending test, calibrated using sample-specific experimental data. Reference point indentation (RPI) was used to validate the micro-FE output. Bone samples were classified based on their macrostructure as unilaminar or trilaminar (sandwich) structure. The elastic moduli obtained using RPI and micro-FE approaches for cortical tables (ERPI 3973.33 ± 268.45 MPa and Emicro-FE 3438.11 ± 387.38 MPa) in the sandwich structure and diploe (ERPI1958.17 ± 563.79 MPa and Emicro-FE 1960.66 ± 492.44 MPa) in unilaminar samples were in strong agreement (r = 0.86, p < .01). We found that the elastic modulus of cortical tables and diploe were correlated with bone mineral density. Changes in the microstructure and mechanical properties of bone specimens were found to be irrespective of patients' age. Although younger patients are reported to benefit more from surgical intervention as skull is more malleable, understanding the material properties is critical to better predict the surgical outcome in patients <1 year old since age-related changes were minimal.

Analytical model for the prediction of permeability of triply periodic minimal surfaces.

Triply periodic minimal surfaces (TPMS) are mathematically defined cellular structures whose geometry can be quickly adapted to target desired mechanical response (structural and fluid). This has made them desirable for a wide range of bioengineering applications; especially as bioinspired materials for bone replacement. The main objective of this study was to develop a novel analytical framework which would enable calculating permeability of TPMS structures based on the desired architecture, pore size and porosity. To achieve this, computer-aided designs of three TPMS structures (Fisher-Koch S, Gyroid and Schwarz P) were generated with varying cell size and porosity levels. Computational Fluid Dynamics (CFD) was used to calculate permeability for all models under laminar flow conditions. Permeability values were then used to fit an analytical model dependent on geometry parameters only. Results showed that permeability of the three architectures increased with porosity at different rates, highlighting the importance of pore distribution and architecture. The computed values of permeability fitted well with the suggested analytical model (R2>0.99, p<0.001). In conclusion, the novel analytical framework presented in the current study enables predicting permeability values of TPMS structures based on geometrical parameters within a difference <5%. This model, which could be combined with existing structural analytical models, could open new possibilities for the smart optimisation of TPMS structures for biomedical applications where structural and fluid flow properties need to be optimised.

Three-Dimensional Calvarial Growth in Spring-Assisted Cranioplasty for Correction of Sagittal Synostosis.

Spring-assisted cranioplasty (SAC) is a minimally invasive technique for treating sagittal synostosis in young infants. Yet, follow-up data on cranial growth in patients who have undergone SAC are lacking. This project aimed to understand how the cranial shape develops during the postoperative period, from spring insertion to removal. 3D head scans of 30 consecutive infants undergoing SAC for sagittal synostosis were acquired using a handheld scanner pre-operatively, immediately postoperatively, at follow-up and at spring removal; 3D scans of 41 age-matched control subjects were also acquired. Measurements of head length, width, height, circumference, and volume were taken for all subjects; cephalic index (CI) was calculated. Statistical shape modeling was used to compute 3D average head models of sagittal patients at the different time points. SAC was performed at a mean age of 5.2 months (range 3.3-8.0) and springs were removed 4.3 months later. CI increased significantly (P < 0.001) from pre-op (69.5% ±â€Š2.8%) to spring removal (74.4% ±â€Š3.9%), mainly due to the widening of head width, which became as wide as for age-matched controls; however, the CI of controls was not reached (82.3% ±â€Š6.8%). The springs did not constrain volume changes and allowed for natural growth. Population mean shapes showed that the bony prominences seen at the sites of spring engagement settle over time, and that springs affect the overall 3D head shape of the skull. In conclusion, results reaffirmed the effectiveness of SAC as a treatment method for nonsyndromic single suture sagittal synostosis.

Three-dimensional environment and vascularization induce osteogenic maturation of human adipose-derived stem cells comparable to that of bone-derived progenitors.

While human adipose-derived stem cells (hADSCs) are known to possess osteogenic differentiation potential, the bone tissues formed are generally considered rudimentary and immature compared with those made by bone-derived precursor cells such as human bone marrow-derived mesenchymal stem cells (hBMSCs) and less commonly studied human calvarium osteoprogenitor cells (hOPs). Traditional differentiation protocols have tended to focus on osteoinduction of hADSCs through the addition of osteogenic differentiation media or use of stimulatory bioactive scaffolds which have not resulted in mature bone formation. Here, we tested the hypothesis that by reproducing the physical as well as biochemical bone microenvironment through the use of three-dimensional (3D) culture and vascularization we could enhance osteogenic maturation in hADSCs. In addition to biomolecular characterization, we performed structural analysis through extracellular collagen alignment and mineral density in our bone tissue engineered samples to evaluate osteogenic maturation. We further compared bone formed by hADSCs, hBMSCs, and hOPs against mature human pediatric calvarial bone, yet not extensively investigated. Although bone generated by all three cell types was still less mature than native pediatric bone, a fibrin-based 3D microenvironment together with vascularization boosted osteogenic maturation of hADSC making it similar to that of bone-derived osteoprogenitors. This demonstrates the important role of vascularization and 3D culture in driving osteogenic maturation of cells easily available but constitutively less committed to this lineage and suggests a crucial avenue for recreating the bone microenvironment for tissue engineering of mature craniofacial bone tissues from pediatric hADSCs, as well as hBMSCs and hOPs.

A population-specific material model for sagittal craniosynostosis to predict surgical shape outcomes.

Sagittal craniosynostosis consists of premature fusion (ossification) of the sagittal suture during infancy, resulting in head deformity and brain growth restriction. Spring-assisted cranioplasty (SAC) entails skull incisions to free the fused suture and insertion of two springs (metallic distractors) to promote cranial reshaping. Although safe and effective, SAC outcomes remain uncertain. We aimed hereby to obtain and validate a skull material model for SAC outcome prediction. Computed tomography data relative to 18 patients were processed to simulate surgical cuts and spring location. A rescaling model for age matching was created using retrospective data and validated. Design of experiments was used to assess the effect of different material property parameters on the model output. Subsequent material optimization-using retrospective clinical spring measurements-was performed for nine patients. A population-derived material model was obtained and applied to the whole population. Results showed that bone Young's modulus and relaxation modulus had the largest effect on the model predictions: the use of the population-derived material model had a negligible effect on improving the prediction of on-table opening while significantly improved the prediction of spring kinematics at follow-up. The model was validated using on-table 3D scans for nine patients: the predicted head shape approximated within 2 mm the 3D scan model in 80% of the surface points, in 8 out of 9 patients. The accuracy and reliability of the developed computational model of SAC were increased using population data: this tool is now ready for prospective clinical application.

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.

Investigating the cause of late deformity following fronto-orbital remodelling for metopic synostosis using 3D CT imaging.

PURPOSE: Late deformity/indentation is well-recognised following fronto-orbital remodelling (FOR) for metopic synostosis. We hypothesise that if damage to temporalis muscle were a contributor, the thickness of soft tissue and bone in the affected area would be reduced. MATERIALS AND METHODS: Soft tissues and bone were separately segmented and reconstructed three-dimensionally from computed tomograms of 8 patients 1.5-18 years post-FOR performed at 16 ± 2 months for metopic synostosis and from 8 age-matched controls. Soft tissue (taken as proxy for temporalis muscle) and bone thickness overall and in the indented areas were computed. RESULTS: Post-FOR, three-dimensional soft tissue thickness maps demonstrated temporalis extending upwards but falling short of the indented area. Overall skull thickness increased with age post-FOR (logarithmic fit R2 = 0.71) and for controls (R2 = 0.90). Although immediately post-FOR the future indented area had a thickness of 98% of control, it decreased linearly to 64% 16 years later (Pearson's r = 0.84). CONCLUSION: These findings suggest that late post-FOR deformity/indentation is enhanced by limited upward extension (or retraction downwards) of temporalis muscle, while bone thickness in the affected area gradually decreases. This supports the hypothesis that aberrant re-attachment of the temporalis muscle makes a material contribution to late deformity following FOR for metopic synostosis.

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.

Results Following Adoption of a Modified Melbourne Technique of Total Scaphocephaly Correction.

The Melbourne technique was described in 2008 as a novel method for complete correction of scaphocephaly. Since 2015, it has become our operation of choice for children with sagittal synostosis who are too old at presentation for minimally invasive techniques. Our modifications were 2-position (initially supine then prone) technique and undertaking a formal fronto-orbital remodeling to correct forehead contour. Retrospective chart review was used to record demographics, blood transfusion frequency and volumes, operating time, length of stay, clinical outcome, and complications. Eleven underwent modified Melbourne procedure between July 2015 and March 2017; 9 of 11 were male. All had a diagnosis of nonsyndromic sagittal synostosis. Mean age at surgery was 29 months. Mean surgical time was 6 hours. All patients required blood transfusion with a mean volume transfused of 29 mL/kg (range 13-83 mL/kg). For those 5 patients where preoperative and postoperative measurements were available, there was an increase in mean cephalic index (CI) from 0.64 to 0.75. All postoperative patients had a CI of over 0.70. Three-dimensional shape analysis indicated head shape change addressing all phenotypic aspects of scaphocephaly. In the 5 patients in which analysis could be undertaken, the mean intracranial volume increased from 1481 cm preoperatively to 1671 cm postoperatively, a mean increase in intracranial volume of 14%. The postoperative intracranial volume was higher than preoperative in all 5 patients. There were 4 minor and no major complications. Modified Melbourne procedure is safe and effective for the treatment of severe scaphocephaly in sagittal synostosis.

A novel soft tissue prediction methodology for orthognathic surgery based on probabilistic finite element modelling.

Repositioning of the maxilla in orthognathic surgery is carried out for functional and aesthetic purposes. Pre-surgical planning tools can predict 3D facial appearance by computing the response of the soft tissue to the changes to the underlying skeleton. The clinical use of commercial prediction software remains controversial, likely due to the deterministic nature of these computational predictions. A novel probabilistic finite element model (FEM) for the prediction of postoperative facial soft tissues is proposed in this paper. A probabilistic FEM was developed and validated on a cohort of eight patients who underwent maxillary repositioning and had pre- and postoperative cone beam computed tomography (CBCT) scans taken. Firstly, a variables correlation assessed various modelling parameters. Secondly, a design of experiments (DOE) provided a range of potential outcomes based on uniformly distributed input parameters, followed by an optimisation. Lastly, the second DOE iteration provided optimised predictions with a probability range. A range of 3D predictions was obtained using the probabilistic FEM and validated using reconstructed soft tissue surfaces from the postoperative CBCT data. The predictions in the nose and upper lip areas accurately include the true postoperative position, whereas the prediction under-estimates the position of the cheeks and lower lip. A probabilistic FEM has been developed and validated for the prediction of the facial appearance following orthognathic surgery. This method shows how inaccuracies in the modelling and uncertainties in executing surgical planning influence the soft tissue prediction and it provides a range of predictions including a minimum and maximum, which may be helpful for patients in understanding the impact of surgery on the face.

Spring assisted cranioplasty: A patient specific computational model.

Implantation of spring-like distractors in the treatment of sagittal craniosynostosis is a novel technique that has proven functionally and aesthetically effective in correcting skull deformities; however, final shape outcomes remain moderately unpredictable due to an incomplete understanding of the skull-distractor interaction. The aim of this study was to create a patient specific computational model of spring assisted cranioplasty (SAC) that can help predict the individual overall final head shape. Pre-operative computed tomography images of a SAC patient were processed to extract a 3D model of the infant skull anatomy and simulate spring implantation. The distractors were modeled based on mechanical experimental data. Viscoelastic bone properties from the literature were tuned using the specific patient procedural information recorded during surgery and from x-ray measurements at follow-up. The model accurately captured spring expansion on-table (within 9% of the measured values), as well as at first and second follow-ups (within 8% of the measured values). Comparison between immediate post-operative 3D head scanning and numerical results for this patient proved that the model could successfully predict the final overall head shape. This preliminary work showed the potential application of computational modeling to study SAC, to support pre-operative planning and guide novel distractor design.

Intracranial Volume Measurement: A Systematic Review and Comparison of Different Techniques.

The ability to calculate intracranial volume (ICV) from 3-dimensional imaging is a useful tool in a craniofacial team's armamentarium. Intracranial volume uses range from decision making to assessment. Various methods to calculate ICV exist including fully manual, semiautomatic, and fully automatic techniques and they are used with varying frequency in craniofacial centres globally.This study aimed to systematically analyze and compare ICV calculations across the 3 methods and provide information to allow the reader to utilize these processes in practice.Twenty-six computed tomography scans from Apert patients were used to compare ICV measurements calculated using the following techniques: fully manual segmentation with OsiriX (taken as the gold standard); semiautomatic segmentation using Simpleware ScanIP; and fully automatic segmentation using FSL neuroimaging software. In addition, to assess the effect that a reducing CT scan slice number had on ICV measurement, 13 scans were remeasured using half, quarter, and an eighth of the slices of the full scan.The manual and semiautomatic techniques had intraclass correlation coefficients of 0.997, and 0.993 respectively. Intracranial volume measurements using the semi- and fully automatic techniques showed high linear correlation with manual techniques (R = 0.993 and R = 0.995). The coefficients of determination for full scan versus half, quarter, and eighth scan were R = 0.98, 0.96, and 0.94 respectively.Similar ICV results can be obtained using manual, semiautomatic, or automatic techniques with decreasing amount of time required to perform each method. Command line code for the fully automatic method is provided.

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.