Intraoperative Radiographic Assessment of Ankle Prosthesis Alignment

Abstract

Category: Ankle Arthritis Introduction/Purpose: In the last 2 decades, total ankle replacement (TAR) has gained greater acceptance as a treatment option for patients with end-stage ankle osteoarthritis. However, TAR still has a higher failure rate than either hip or knee replacements. One of the most common reasons for TAR failure is malalignment of the prosthesis component which accounts for 15% of all failures. The purpose of this study was to assess ankle prosthesis alignment using intraoperative fluoroscopy images and to compare the results with postoperative weightbearing radiographs. Methods: Sixty-eight primary TARs were performed using the Zimmer trabecular metal implant (37 men and 31 women, mean age of 67.7±8.2 years) from October 2012 to August 2017. Alpha and beta angles were used to assess the alignment of the tibial component in the coronal and sagittal plane, respectively. Gamma angle was used to assess the alignment of the talar component in the sagittal plane. All measurements were performed by two observers (ICC 0.787-0.984). One observer evaluated all images twice at a 6-week interval to determine the intraobserver reliability (ICC 0.858-0.986). Results: There were significant differences between intraoperative and postoperative assessment for all three angles. For the alpha angle, the mean absolute difference was 1.8º±1.5º with a range between 0º and 6º (p = 0.001). For the beta angle, the mean absolute difference was 2.1º±1.5º with a range between 0º and 7º (p = 0.034). For gamma angle, the mean absolute difference was 2.0º±1.5º with a range between 0º and 6º (p = 0.002). The Pearson coefficient for the alpha, beta, and gamma angle was 0.664 (p < 0.001), 0.852 (p < 0.001), and 0.928 (p < 0.001), respectively. Conclusion: In the present study, radiographic assessment of the prosthesis’ component alignment demonstrated significant differences up to 7 degrees. This can be partially explained by the lack of a standardized radiographic technique to obtain fluoroscopic images, difficult identification of anatomic landmarks for intraoperative measurements, and distortion of x-rays using fluoroscopy.