Purpose: For the parallel external fixator, there are some defects, such as uneven distraction rate, unbearable pain and uncontrollable movement trajectory in practical clinical applications. In order to solve the problems, a new deformity correction algorithm, which is used to calculate the elongation of the six struts, is developed. Meanwhile, the corresponding computer software for getting the electronic prescription is developed.
Methods: First, the trajectory of the moving bone is planned by Cartesian coordinate path control. Next, the prescription is obtained from the trajectory by the inverse pose solution algorithm. Finally, the genetic algorithm is utilized to optimize the achieved prescription. From the year of 2015 to 2018, twenty-three patients with complicated tibia deformity are treated by using parallel external fixator and the developed computer software. All patients have standing, patella-forward, full-length post-operative AP and lateral radiographs of the lower limbs with the complete proximal ring for getting the deformity parameters and frame parameters. These parameters are input into the computer software to calculate a daily prescription schedule for strut adjustment. Radiographs are taken regularly to determine the effects of recovery during the correction process.
Results: The mean time of follow-up is 18 months (range 11-40 months). All patients reach the requirements for deformity correction, and their symptoms and appearance are improved significantly. No cases of wound infections or complications occur, and no severe pain came as well during the correction process.
Conclusions: By using the computer-aided parallel external fixator for the correction of lower limb deformities, satisfactory outcomes can be achieved. Hence, this method greatly improved the treatment of these patients in a clinical application.
Keywords: Bone external fixator; Deformity correction; Genetic algorithm; Trajectory planning.