Relationship of Axial Alignment and Patient-Reported Outcomes in Patients with Total Ankle Arthroplasty under Weightbearing CT Scan

Abstract

Category: Ankle Arthritis Introduction/Purpose: Axial alignment (rotation) in total ankle replacement has come to surgeons' attention in recent publications. Unfortunately, most of the previously published data present information from non weight-bearing computed tomography (WBCT) scans or lack a correlation with patient-reported outcomes (PROs). To the author's knowledge, axial alignment is not completely understood in its current form and its relation to PROs. Therefore, our objective is to propose a standardization in measurements of axial alignment in prosthesis components under weight-bearing CT examination and to correlate it with patient-reported outcomes. Methods: After obtaining IRB approval, our prospectively collected surgical database was queried for patients undergoing Total Ankle Arthroplasty (TAA). Patients were included if they had preoperative weight-bearing X-rays, non-WBCT scan, pain evaluation (VAS pain score), preoperative functional scales (SF-36, SFMA, FAAOS, and FAAM) and underwent TAA using an Infinity Prosthesis with standard instrumentation. Patients were excluded if they had less than a one-year postoperative period, had revision surgery, or declined to participate. Twenty five patients met the inclusion/exclusion criteria. All patients were brought back to the clinic for weight-bearing CT scan, pain evaluation, repeat functional scales, and to sign informed consent for the specific needs of this study. Three fellowship-trained musculoskeletal radiologists realized all measurements in two time-frames (coronal, sagittal and axial alignment), separated for one month each. Cohen's inter and intraclass coefficients were calculated to estimate the amount of agreement that occurred by chance. Results: Average age was 64.5 years, Average BMI was 28. Good to excellent intraobserver reliability (ICC 0.891 , 0.750, 0.902 respectively) and good interobserver reliability (ICC 0.822) were reported. Component malrotation was seen in five patients (20%), defined as a relative axial rotation between components of 5 degrees or greater. There was a statistically significant correlation between coronal, sagittal and axial alignment measurements and FAAM scale (p<0.05). There was a positive trend in the association between malrotation and PROs, but this was not statistically significant (p=0.09). Conclusion: This is the first study to correlate axial component alignment in total ankle replacement with patient-reported outcomes. Success in TAA is in direct relationship with achieving neutral alignment at the ankle and hindfoot. Axial alignment is statistically correlated with PROs. There was a positive trend in the association between malrotation and PROs, however this study didn't show a statistical correlation.