Three-dimensional computed tomography cephalometry of plagiocephaly: asymmetry and shape analysis.

OBJECTIVE: To investigate facial asymmetry associated with both deformational and synostotic plagiocephaly and to identify variables based on skeletal landmarks that distinguish the conditions and quantify severity. DESIGN: Retrospective, cross sectional. SETTING: Australian Craniofacial Unit, Adelaide. MAIN OUTCOME MEASURES: Proportional differences between bilateral distances and principal component (PC) analysis of the skeletal landmarks. PATIENTS: The three-dimensional positions of 78 osseous landmarks were determined from computed tomography (CT) scans of 21 patients with deformational plagiocephaly (DP), 20 patients with unilateral coronal synostosis (UCS), and 2 patients with unilateral lambdoid synostosis (ULS). RESULTS: For both DP and UCS, significant asymmetry was found for the orbital depths, mandibular lengths, maxillary depths, zygomatic arch lengths, lateral base of the parietal bone, and the angle between the anterior and the posterior cranial base projected onto the axial plane. The small sample size for ULS precluded definitive statistical statements but allowed some useful comparisons with the other conditions. The first three PC scores were able to distinguish among the three conditions and which side was affected. CONCLUSIONS: The asymmetry of the cranial base and facial structures, arising from localized abnormality or deformational forces in either the frontal or the occipital regions, can be quantified by a plethora of bilateral features or summarized by PC analysis.

Do Craniosynostosis syndrome phenotypes with both FGFR2 and TWIST mutations have a worse clinical outcome?

We present three cases with both FGFR2 mutations and novel TWIST sequence variants. The clinical outcome in this cohort is compared with that in individuals with a single mutation.

Validation of a finite element model of the human metacarpal.

Implant loosening and mechanical failure of components are frequently reported following metacarpophalangeal (MCP) joint replacement. Studies of the mechanical environment of the MCP implant-bone construct are rare. The objective of this study was to evaluate the predictive ability of a finite element model of the intact second human metacarpal to provide a validated baseline for further mechanical studies. A right index human metacarpal was subjected to torsion and combined axial/bending loading using strain gauge (SG) and 3D finite element (FE) analysis. Four different representations of bone material properties were considered. Regression analyses were performed comparing maximum and minimum principal surface strains taken from the SG and FE models. Regression slopes close to unity and high correlation coefficients were found when the diaphyseal cortical shell was modelled as anisotropic and cancellous bone properties were derived from quantitative computed tomography. The inclusion of anisotropy for cortical bone was strongly influential in producing high model validity whereas variation in methods of assigning stiffness to cancellous bone had only a minor influence. The validated FE model provides a tool for future investigations of current and novel MCP joint prostheses.

CT-determined intracranial volume for a normal population.

Intracranial volume comparisons of patients with craniosynostosis and normal have been contrary to expectations, leading to questioning of the validity of the current normal reference material. Computed tomography-determined intracranial volume is presented for a white normal population. Specifically, intracranial volumes for 157 subjects (82 female and 75 male) were measured from computed tomography data using the Cavalieri estimator: volume determination was based on measuring the area in each computed tomography section. Monomolecular and Gompertz models were applied to find curves of best fit to the intracranial volume as a function of the age. The best fit was obtained using the monomolecular model when the response variable was the logarithmically transformed intracranial volume, and the independent variable was the logarithm of the age from conception. For example, the mean (standard deviation) for male subjects at 1 year and 20 years were 1,125.6 (89.6) ml and 1,472.9 (117.2) ml, respectively, and for female subjects 1,024.9 (84.0) ml and 1,321.7 (108.3) ml, respectively. Although the shape and rate of increase of the female and male curves is similar, the female mean is 1.3 standard deviations below the male mean at 20 years. These curves were compared with the commonly referenced curves of Blinkov (1941), Lichtenberg (1960), and Dekaban (1977). Our male curve is substantially higher than these curves in the age range 8 months to 4 years. Our female curve, however, is approximately 1 standard deviation below Lichtenberg's curve from birth to 7 months. There are then only minor differences between our female curve and Lichtenberg's curve until his curve crosses ours at 41 months, where they significantly diverge from approximately 4.5 years. Our curves indicate that 95% of the final intracranial volume has been attained by 42 months for girls and 46 months for boys.

Bilambdoid and posterior sagittal synostosis: the Mercedes Benz syndrome.

A consistent pattern of craniosynostosis in the sagittal and bilateral lambdoid sutures is described in three patients. The external cranial ridging associated with fusion of these sutures produces a characteristic triradiate, or "Mercedes Benz," appearance to the posterior skull. Locally marked growth restriction is evident in the posterior fossa with compensatory secondary expansion of the anterior fossa manifesting a degree of frontal bossing which mimics bicoronal synostosis. Although this appearance could lead to inadvertent surgery in the frontal region, attention to the occipital region with wide early suture excision and vault shaping is indicated.

Computer tomography determined intracranial volume of infants with deformational plagiocephaly: a useful "normal"?

Over the last 10 years, children with deformational (nonsynostotic) plagiocephaly have undergone computed tomography scans using the same protocols as children with lambdoid craniosynostosis because of their similarly distorted head shapes. These children are believed to have normal intracranial volume. Given the recent questioning of what is the normal range of intracranial volume in human populations, the authors have undertaken a comparison of the intracranial volume of children with deformational plagiocephaly and Lichtenberg's normal population (Lichtenberg R. Radiographie du crane de 226 enfants normaux de la naissance a 8 ans: Impressions digitiformes, capacite, angles et indices [thesis]. Paris: University of Paris, 1960). The intracranial volume was determined for 20 females and 46 males with deformational plagiocepahly ranging in age from 2.5 to 20.7 months using computed tomography scan data. Although no significant differences were found for the females, the authors found that the intracranial volume of the males with deformational plagiocephaly were significantly larger than Lichtenberg's population. The authors conclude that this is because Lichtenberg's data do not adequately reflect the normal range of intracranial volume for males ranging in age from 2.5 to 20.7 months, rather than gender differences associated with deformational plagiocephaly. Further, until a more suitable normal becomes available, the deformational (nonsynostotic) plagiocephaly data could be used as substitute normal reference material in the measured age range for assessment of the intracranial volumes of children with craniosynostosis.

Computer generated mandibular model: surgical role.

A life-size nylon model of a traumatized mandible was produced from CT scan data by the process of laser sintering. The model was used for pre-operative planning and for production of surgical aids in order to facilitate the restoration of a large bony defect. Vascularized iliac crest bone was harvested, titanium implants placed and the bone then grafted to the mandible.

Mandibular lengthening by distraction for airway obstruction in Treacher-Collins syndrome.

Mandibular lengthening by distraction was performed in a 6-year-old tracheostomy-dependent Treacher-Collins syndrome patient. Detailed preoperative imaging revealed an occluded retrotongue base pharyngeal airway, which, following mandibular distraction, became patent and permitted tracheostomy removal. Mandibular distraction as a technique must be targeted toward clinical problems--management of upper-airway obstruction may be one such scenario.

Craniofacial osseous landmark determination from stereo computer tomography reconstructions.

The accurate and reproducible determination of the three dimensional (3D) co-ordinate positions of anatomical landmarks from computer tomography (CT) images has been limited even though potentially the data have been available for several years. This paper describes a method of acquisition of osseous landmark positions using an off-line computing technique based on multiple stereo images of 3D CT reconstructions. The use of stereo pairs greatly enhances the consistent identification of osseous landmarks. Further, the technique is of particular value where access to the CT scanner is restricted due to heavy clinical demand and separate high quality graphics facilities are unavailable. Osseous landmark position data were determined for dried skulls and patients with craniofacial conditions. Accuracies of the order 1.7mm (median) were obtained. These results encourage the use of the technique for acquisition of landmark positions for the study of the craniofacial complex in three dimensions.

Application and comparison of techniques for three-dimensional analysis of craniofacial anomalies.

Traditionally, cephalometric analysis has been limited to data determined from two-dimensional (2-D) cephalograms. With imaging facilities such as CT and biplanar radiography now available, the natural extension has been towards the use of three-dimensional (3-D) coordinate positions of landmarks for comparative purposes. While these data have been potentially available for several years, the accurate and reproducible extraction of anatomic landmarks suitable for comparative purposes has been limited. This paper presents results of the application of traditional comparative techniques to well determined 3-D coordinate data acquired from biplanar radiography and CT for a patient with Treacher Collins syndrome and further provides a comparison with the technique of strain analysis, often referred to as finite element analysis, which has been applied recently to craniofacial data. Comparisons of distances and angles between landmarks, landmark coordinate positions, and strains of the patient relative to experimental reference standards reveal that the essential skeletal features of Treacher Collins syndrome have been identified and quantified by the analysis techniques. Further, a measure of the significance of the deviations has been determined by comparisons with the experimental reference standards.

Influence of alloy composition on the hardening of silver-tin dental amalgam.

The objective of the investigation was to examine the reactions of mercury with silver-tin alloys with compositions spanning the phase fields beta, (beta + gamma), gamma, and (gamma + Sn). The experimental methods employed include the application of light microscopy, scanning electron microscopy, and electron probe microanalysis. These techniques were used to investigate the mechanisms of reaction and to identify the nature and morphology of the reaction products formed on bulk specimens of the alloys. The progress and characteristics of the reactions that occur during hardening of amalgams prepared from powders of these alloys were monitored using a high-sensitivity dilatometer. These results were correlated with direct observations on the development of the microstructures. The reaction of mercury with the beta-phase alloy occurred rapidly and resulted in a very marked and rapid expansion during the initial stages of hardening. gamma-Phase alloys, on the other hand, reacted more slowly and contracted markedly during hardening. The behavior of amalgams made from alloys with compositions lying between these two extremes appeared to be explicable in terms of the characteristics of the separate phases from which they were constituted.

Microstructures of duplex (beta + gamma) silver-tin alloys.

The microstructures of (beta + gamma) silver-tin alloys are especially influenced by both homogenization temperature and subsequent heat treatment. When the alloy is cooled from homogenization temperatures above approximately 200 degrees C, lenticular regions of the ordered orthorhombic gamma phase precipitate from within the disordered h.c.p. beta phase on three structurally equivalent planes, (1210), (1120), and (2110), to form a Widmanstatten structure. When the duplex alloys were homogenized at temperatures below approximately 200 degrees C, where the beta/(beta + gamma) phase boundary is vertical, these structures were not observed.

Reaction of mercury with silver-tin dental amalgam alloy.

Electron diffraction evidence confirming the ordered orthorhombic crystal structure of the gamma phase of the silver-tin system has been obtained, and it has been established by optical metallography that an alloy with a composition corresponding to the dental amalgam alloy formula Ag3Sn (i.e., 26.85 wt % Sn) lies outside the single gamma phase field and in the duplex (gamma + Sn) phase field adjacent to it. Studies of the mechanism of the hardening reaction of single crystals of homogeneous gamma phase alloys with mercury were carried out using both scanning and transmission electron microscopy. Mercury attack occurred preferentially along well-defined planes in the single crystals. Using electron channeling and trace analysis techniques these planes of preferential attack were found to be [010] and [011], and from transmission electron microscopy of thin foils these were shown to be slip bands and deformation twins, respectively. In bicrystals of gamma phase material, preferential attack also occurred along grain boundaries. Similar preferential mercury attack, leading to the development of deep planar intrusions into the gamma phase material, was observed in an experimental dental amalgam prepared from a lathe-cut homogeneous gamma phase amalgam alloy. It is believed that the presence of such features would have important implications for the clinical performance of dental amalgam.