Short communication A technique for the quantification of the 3D connectivity of thin articulations in Bony sutures Asmaa Maloul a,b , Jeffrey Fialkov c,d , Seyed-Parsa Hojjat a,b , Cari M. Whyne a,b,c,n a Orthopaedic Biomechanics Lab, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada b Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada c Department of Surgery, University of Toronto, Toronto, Ontario, Canada d Division of Plastic Surgery, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada article info Article history: Accepted 21 November 2009 Keywords: Cranial sutures Facial sutures Micro-CT Connectivity abstract The anatomy and development of cranial and facial sutures have been studied in detail using histological sections, 2D radiographs and more recently CT imaging. However, little attention has been paid to evaluating and quantifying the connectivity of these thin cortical bone articulations. More recent technological advances such as micro-CT imaging has the potential to be used to provide quantitative measurements of 3D connectivity in bony articulations. This study presents a new technique for quantifying the connectivity of bony projections inside cranial and facial sutures using a combination of skeletonization, thinning algorithms and 3D intensity mapping. The technique is demonstrated in five sutures through semi-automated analysis and image processing of mCT scans. In the sagittal, coronal and frontozygomatic sutures an average bone connectivity of 6.6–11.6% was found with multiple bony projections providing an interlocking structure between adjacent bones. Much higher bone connectivity was present in the zygomaticotemporal and zygomaticomaxillary sutures (22.7–37.4%) with few bony projections. This method combining mCT scanning and image processing techniques was successfully used to quantify the connectivity of thin bone articulations and allowed detailed assessment of sutural fusion in 3D. The wider application of this technique may allow quantification of connectivity in other structures, in particular fracture healing of long bones. & 2009 Elsevier Ltd. All rights reserved. 1. Introduction Sutures are articulations in which the margins of adjacent bones are united by fibrous or bony tissue. They function to hold the bones of the skull together while allowing movement between cranial bones during childbirth. They also act as sites of bone growth and as mechanical stress absorbers. Articulations in thin bone structures in the human skeleton are understood to be fully fused by adulthood, with some structures achieving fusion up to the seventh decade (Rice, 2008). However, when suture growth is not appropriately regulated, sutures can fuse prematurely (craniosynostosis) resulting in craniofacial deformi- ties (Mao et al., 2003). Current clinical orthopaedic devices in use to modify skull growth and deformities apply forces to generate microscale bone strain in order to alter sutural growth patterns. Thus, characterizing the biomechanical behaviour of cranial and facial sutures is important for understanding how mechanical stimuli modulate sutural growth. The development, patency and structure of sutures in the craniofacial skeleton and cranial vault have been studied in detail (Furuya et al., 1984; Kokich, 1976; Latham and Burston, 1966; Persson et al., 1978; Todd and Lyon (1925)). Yet most of these studies were carried out in the early 1920s until the early 1980s. As such, they were largely based on results of gross inspection of external and internal surfaces, histological sections and 2D radiographs. Although the analytical methods used in these studies provided qualitative information about the fusion of the sutures, they did not provide quantitative measurements of their connectivity. More recently other methods of investigation have been used to study suture structure and development, including conventional CT, mCT and scanning electron microscopy (Anderson et al., 2006; Furuya et al., 1984). High resolution 3D medical imaging techniques such as micro- computed tomography have the potential to be used for studying the development of facial and cranial sutures. The interdigitation of adult sutures has been recognized by several investigators (Rice, 2008). However, the degree of connectivity through the full thickness of the suture has never been quantified. mCT can be ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Journal of Biomechanics 0021-9290/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbiomech.2009.11.024 n Correspondence to: 2075 Bayview Ave., Room UB-19, Toronto, Ontario, Canada M4 N3M5. Tel.: + 416 480 5056; fax: 416 480 5856. E-mail address: cari.whyne@sunnybrook.ca (C.Whyne). Journal of Biomechanics 43 (2010) 1227–1230