Towards collision detection in foot and ankle deformity correction using parallel external fixator: A novel analytical approach

Gradual correction using external fixator has been advocated as a minimally invasive so-lution for limb deformity and is widely used in the clinic. This treatment manner requires a long-term distraction process, which is guided by a preplanned correction path. How-ever, bone cross-section (BCS) collision and soft tissue (ST)-distraction rod (DR) collision may occur on the path and then affect the continuity of the process. Thus, collision detec-tion should be carried out before performing distraction. Existing detection solutions do not simultaneously consider these two types of collisions, and primarily target long-bone deformity. To solve these issues, taking more complex foot and ankle deformity as the re-search object, a novel analytical detection approach is proposed in this paper. By modelling the contours of BCS, ST, and DRs as convex envelope planes/bodies using different spatial line styles, the spatial posture relations of their boundaries can be reproduced on the cor-rection path, and collision detection can be transformed into the mathematical problem of calculating point-plane and point-line distances. Subsequently, two algorithms are pro-posed for BCS and ST-DR collision detections, and adjustment strategies are provided to resolve algorithm anomalies. Clinical case simulation proves the effectiveness and applica-bility of the approach. Since the detection is used for pre-distraction prediction rather than real-time monitoring, the correction path with potential collision risk can be re-planned before distraction, and finally, guarantees the safety of gradual correction.(c) 2022 Elsevier Inc. All rights reserved.