Numerical investigation of the relationship between pin deviations and joint coordinates of a unilateral external fixator

Background: Fracture correction is an important orthopedic operation, which can be performed using a unilateral external fixator. Regulating the rotational and translational joints of the fixator is usually necessary to correct complex deformities. However, pin deviations inevitably occur during surgery, and the fixator has its own limitations. Therefore, the relationship between fixator joint adjustment and pin deviations must be identified and discussed. Methods: The influence of pin deviation on the fixator joint adjustment was analyzed using the inverse kinematics method based on a 6-DOF unilateral external fixator. The effect of multiple pin deviations on fixator joint was also discussed. Findings: This study reveals that the single pin deviations in different axes affect different fixator joints. When multiple deviations occur simultaneously, the regulated quantity is equal to the sum of that of each deviation. Interpretation: Reasonable pin placement can reduce the joint adjustment values and prevent reaching limit values of fixator joint, which aids in expanding the application scope of the fixator. This research can also help reduce the duration of orthopedic surgeries, if the relationship between pin deviation and joint adjustment is known in advance.