Standardizing Terminology, 3D Spatial Orientation, and Relative Positioning of the Foot and Ankle Bones: An Expert Consensus Task Force

Aims: Understanding of foot and ankle biomechanics is rapidly advancing as new technologies including weightbearing computed tomography and biplane fluoroscopy provide more detailed information about in vivo morphology and motion. While there is increased use of these technologies, commonly accepted foot bone axes or defined methodologies for calculating relationships between the bones are lacking. There is a growing interest in the orthopaedic community to develop standardized descriptors of 3D orientation and measurement for both research and clinical practice. Methods: A task force was established with representatives from three international societies. It consisted of orthopaedic surgeons and engineers with significant clinical and research expertise in foot and ankle. The task force aimed to establish important criteria for these standards, to determine relevant measures of importance, to review the literature, and when appropriate, develop new methodologies. Results: Relevant criteria established included: desired reliable automatic refence frame generation, low processing times, relevant joint motion, and ability to accommodate various pathologies. A literature review showed methodologies in use include identification of specific anatomical landmarks, fitting of geometric primitives to surface anatomy, and principal component analysis (PCA). Many published methods in the literature lacked automated methodology. Discussion: To achieve universal acceptance, the standards defined must be understandable, interpretable, and most importantly, reproducible. Reference definitions can be highly variable based on the shape of each individual bone. PCA is advantageous because it does not require user definitions however, may not represent the biomechanical joint axes. Identification of anatomic landmarks and/or fitting geometric primitives allows for better representation of bone morphology variations, but it is vital that methods established be automation-compatible because one of the main objectives is to improve accessability in analyzing 3D datasets. Ongoing work aims to evaluate existing and new proposed references with available clinical data to establish a scientifically grounded consensus.