Reliability of Cone Bean Weight-Bearing Measurements of the Postoperative Outcome of Total Ankle Arthroplasties and Inter-Method Reliability with Respect to the Weight Bearing x-rays

Abstract

Category: Ankle Arthritis; Ankle Introduction/Purpose: Postoperative evaluation of the total ankle arthroplasty (TAA) alignment is a fundamental step in measuring the surgical outcome. The current reference standard, weight-bearing x-ray (WBXR), is subject to technical bias. Weight-bearing cone beam computer tomography (WBCT) allows visualization of the complex three-dimensional (3D) structure of the foot under the influence of its deforming forces. A WBCT-based measurement system to assess postoperative outcomes has yet to be validated. The purpose of this study was (1) to measure the surgical outcome of TAA using semiautomatic generated models, (2) to evaluate the agreement levels between two raters, and (3) to evaluate the inter-method reliability with respect to WBXR. Methods: Fifty-five consecutive patients were retrospectively viewed. Two raters independently created a 3D model using dedicated software. Each rater measured six different measurements: α angle tibiotalar angle, hind foot angle (HFA), β angle, γ angle, and Φ angle using a semiautomatic 3D model and one measurement, the tibiatalar ratio (TTR) using WBCT on sagittal view. Measurements were repeated two months apart in the same independent fashion. Results were compared to standard weight- bearing x-rays. Consequently, interobserver, intraobserver, and intermethod agreements were calculated. Results: All seven measurements showed good to excellent interobserver and interobserver reliability. (ICC 0.85-0.95). The intermethod agreement showed good agreement for the γ angle (0.79) moderate agreement levels for the α angle, TTS angle, β angle, and TTR (ICC 0.68, 0.69, 0.70, 0.69 respectively), a poor agreement for the HFA angle (ICC 0.25), and a negative agreement for the φ angle (ICC -0.2). Conclusion: Postoperative analysis of TAA using WBCT demonstrated good to excellent interobserver and intraobserver agreement and can be reliably used. When compared to WBXR, moderate to good agreement was measured for the sagittal and coronal alignment of the components. A poor agreement was measured for the coronal alignment of the hindfoot, and a negative agreement was measured for the axial rotation angle, indicating that the intermethod comparison is unreliable.