Axial Rotation Analysis in Total Ankle Arthroplasty Using Weight-Bearing Computer Tomography and Three-Dimensional Modeling

Abstract

Introduction/Purpose: Post-operative alignment is the most critical indicator for a successful total ankle arthroplasty (TAA). Total ankle malrotation is associated with an increased risk for polyethylene wear and medial gutter pain. Currently, there is no consensus on the correct way to measure the alignment of the tibial and talar component rotations in the axial plane. In the current study, the post-operative analysis system was assessed using weight-bearing computer tomography and a three- dimensional (3D) model. The purpose of the study was to assess the inter-observer and intra-observer agreement of this system. Methods: Four angles were measured by two raters independently in two separate readings: posterior tibial component rotation angle (PTIRA), posterior talar component rotation angle (PTARA), tibia talar component axial angle (TTAM), and tibial component to the second metatarsal angle (TMRA). Agreement analysis was quantified according to the interclass coefficient. Results: Sixty TAAs across 60 patients were evaluated. A good inter-observer agreement and intra-observer agreement when measuring the PTIRA, PTARA, and TTAM angles was observed along with an excellent inter-observer agreement and intra- observer agreement when measuring the TMRA angle. Conclusion: In conclusion, the current 3D model-based measurement system demonstrates good to excellent inter and intra- agreement. According to these results, 3D modelling can be reliably used to measure and assess the axial rotation of TAA components. Figure 3: Example case of how to measure the angles for assessing axial rotation of TAA and forefoot. 3 A) Posterior TIbial component Rotational Angle (PTIRA). The chosen slice is the one with the straightest posterior wall component of the tibia. The angle is measured on the following steps. First a reference is put on the posterior wall of the tibial component (blue horizontal line). Then the angle is measured starting from the center of the tibial axis (red dot explained on fig. 2), going to the fibular axis (medial part of the red line at the right of the draw), and finally ending 90° to the posterior reference line. 3 B) Posterior TAlar component Rotational Angle (PTARA). The chosen slice is the one with the straightest posterior wall component of the talus. For the angle measurement. The same steps as figure 3 A are followed with the talar component. 3 C) Talar component to 2nd Metatarsal Rotational Angle (TMRA): Defined as an intersection between a line parallel to the lateral border of the tibia component and a line perpendicular to the anatomical axis of the second metatarsal. This was measured using a 3D rendering tool