Abstract
Acquired adult flatfoot is a frequent deformity which implies multiple, complex and combined 3D modifications of the foot skeletal structure. The difficult thorough evaluation of the degree of severity pre-op and the corresponding assessment post-op can now be overcome by cone-beam (CBCT) technology, which can provide access to the 3D skeletal structure in weight-bearing. This study aims to report flatfoot deformities originally in 3D and in weight-bearing, with measurements taken using two different bone segmentation techniques. 21 such patients, with indication for surgical corrections, underwent CBCT (Carestream, US) while standing on one leg. From these scans, 3D models of each bone of the foot were reconstructed by using two different state-of-the-art segmentation tools: a semi-automatic (Mimics Innovation Suite, Materialise, Belgium), and an automatic (Bonelogic Ortho Foot and Ankle, Disior, Finland). From both reconstructed models, Principal Component Analysis was used to define anatomical reference frames, and original foot and ankle angles and other parameters were calculated mostly based on the longitudinal axis of the bones, in anatomical plane projections and in 3D. Both bone model reconstructions revealed a considerable valgus of the calcareous, plantarflexion and internal rotation of the talus, and typical Meary’s angles in the lateral and transverse plane projections. The mean difference from these angles between semi-automatic and automatic segmentations was larger than 3.5 degrees for only 3 of the 32 measurements, and a large number of these differences were not statistically significant. CBCT and the present techniques for bone shape reconstruction finally provide a novel and valuable 3D assessment of complex foot deformities in weight-bearing, eliminating previous limitations associated to unloaded feet and bidimensional measures. Corresponding measurements on the bone models from the two segmentation tools compared well. Other more representative measurements can be defined in the future using CBCT and these techniques.
Highlights
Acquired adult flatfoot, or pes planovalgus, is known to be a frequent deformity including valgus of the hindfoot, flattening of the medial longitudinal arch and abduction of the forefoot[1,2,3]
Cone-beam technology for computed tomography (CT) (CBCT) scans has overcome the critical traditional option between two-dimensional medical imaging under load from simple radiographs, and 3D scans in unloaded conditions of the traditional CT, i.e. where scans are collected with patients lying in supine position
A best possible software would support the user in accurately defining these 3D bone models, and at the same time would not require extensive manual work from an expert operator; for each different clinical or biomechanical application, a good compromise should be found between automation of the process and quality of the final result[35,36]
Summary
Pes planovalgus, is known to be a frequent deformity including valgus of the hindfoot, flattening of the medial longitudinal arch and abduction of the forefoot[1,2,3]. A best possible software would support the user in accurately defining these 3D bone models, and at the same time would not require extensive manual work from an expert operator; for each different clinical or biomechanical application, a good compromise should be found between automation of the process and quality of the final result[35,36] Among these software packages for 3D bone reconstruction, Mimics Innovation Suite (Materialise, Leuven, Belgium)—MIS— represents the state-of-the-art for fully supported semi-automatic segmentation of any bone structure, and on the other hand Bonelogic Ortho Foot and Ankle (Disior, Helsinki, Finland)—DIS—represents a most modern tool for fully automatic segmentation of foot bones. In 3D measures, this source of error is removed and the inclinations of the bones with respect to the ground plane can be objective, i.e. not dependent on foot positioning and on the operator[40,41]
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