Investigation of Correction Trajectory Considering Bone End-Plane Orientation and the Shortest Growth Path.

External fixators are widely used in orthopedics for the purposes of fracture reduction and bone deformity correction. Since there is nonlinear mapping between the joint and operation spaces of the external fixator, bone correction trajectories achieved by equally adjusting the length of the struts in the joint space are usually not the trajectories that clinicians expect. Based on two different adjustment strategies, a new strategy considering bone end-plane orientation and the shortest growth path is proposed to plan the position and orientation of the distal bone end, which is named joint adjustment for equal bone distraction. By proposing the inverse and forward kinematic solutions of an Ortho-SUV external fixator, correction trajectories with three different adjustment strategies are generated and compared, and the bone shapes for each strategy are modeled. The results obtained by comparative analysis indicate that a smooth and uniformly spaced linear trajectory can be acquired using the new adjustment strategy, which can avoid bone end interference and maintain an optimal distraction rate of 1.03 mm/day, with only a 3% error compared with 1 mm/day. The new strategy can perform multiplane corrections simultaneously and is beneficial for stimulating the growth of new bone tissue.