Analysis of constraints and requirements for the applicability of articulated external fixation

This research investigates the applicability of articulated external fixation to the ankle and elbow joint. Articulated external fixation is used for the clinical management of congenital or traumatic joint disorders, such as complex intra-articular fractures. In theory, external fixation provides stability to the reduced fracture site, and the fixator hinge enables early post-operative mobilization under load shielding of the articulation. However, current fixator designs and application techniques appear inadequate to reliably replicate quasi-physiologic joint kinematics.;Therefore, the present study investigates the kinematics of the elbow and ankle joints, focusing on the applicability of hinged external fixation. Constraints and requirements for the application of articulated external fixation, especially in regard to the positioning of the fixator hinge, are thoroughly analyzed. This research was approached in three steps: First, joint kinematics of the elbow and ankle were analyzed and represented in terms of screw displacement axis, generated from electromagnetic motion tracking source data. The results of this kinematic analysis were used to establish an optimal single hinge axis position for the application of articulated external fixation. Second, in a cadaveric study, a prototype articulated external fixator was applied with its hinge oriented along the optimized axis position, to determine how normal joint kinematics was influenced by the imposed fixator hinge. Finally, the fixator was applied in 16 distinct "off-axis"' positions to determine fixator induced extra resistance to joint motion as well as to quantify the motion of a simulated distal tibia fracture fragment in response to the imposed fixator. Furthermore, radiographs of the articulation, obtained along the optimal joint axis, were analyzed to establish landmarks for fluoroscope-based, intra-operative axis finding. The sensitivity of these landmarks toward joint "off-axis" alignment was then quantified to assess the accuracy of the axis-finding technique.;The results of this study comprehensively cover multiple aspects of the surgical technique of articulated external fixation to the ankle and elbow. This includes a thorough investigation of the theoretical basis for technique applicability, the establishment of an intra-operative application procedure, as well as novel fixator designs under considerations derived from the present research.