Arrangement of joint distraction and hinge alignment during elbow dynamization using an arthrodiatasis fixator

For the arthrodiatasis technique, a unilaterally hinged fixator is used to treat a post-traumatic elbow. It provides immobilization, distraction, and dynamization to restore elbow functions. An ideal dynamization further necessitates the alignment of both elbow and fixator hinges. This is achieved by the manipulation of a guide pin and fixator joints during the intraoperative and postoperative periods. This study evaluates a method for manipulating the guide pin and fixator joints for elbow dynamization and determines whether the elbow distraction and dynamization are concurrent. Finite element models based on computed tomography images are developed. A detailed discussion about the design and release of fixator joints is given. The results show that at the distraction stage, the fixator-aided distraction causes the guide pin to shift towards the opposite side. Using this pin-shift effect, the fixator hinge can be shifted to align with the elbow hinge. The ideal value of the initial pin shift is about half the distance activated by the distractor. For ideal dynamization, the release of joints with at least 10 degrees of freedom (DOFs) is necessary to align the elbow and fixator hinges in the sagittal and coronal planes. If both the center locus and hinge jiggle of an articulating elbow are stable, however, only the DOF release of the fixator hinge is necessary after both elbow and fixator hinges are aligned. The distracting force results in the elastic deflection of the elbow-fixator-pin construct, inducing distraction loss and pin shift. The preparation for the pin shift and the estimation of both the center locus and hinge jiggle produces significantly better joint distraction and hinge alignment during elbow dynamization.