Abstract
Purpose
The purpose of this study was to assess the clinical outcomes over two years for total ankle arthroplasty (TAA) using Short Form-36, Foot Function Index and Ankle Osteoarthritis Scores, and to compare these with radiostereometric analysis longitudinal migration and inducible displacement results.
Method
Twenty patients undergoing TAA implanting the Mobility Total Ankle System (DePuy, Warsaw IN) were assessed at 3mth, 6mth, 1yr and 2yr followup periods by model-based radiostereometric analysis, MBRSA 3.2 (Medis specials, Leiden, The Netherlands), for longitudinal migration (LM) and inducible displacement (ID). The same subjects completed clinical outcome questionnaires at these followup periods for Short Form-36 (SF-36; Physical Component Scores (PCS) and Mental Component Scores (MCS)), Foot Function Index (FFI) and Ankle Osteoarthritis Scores (AOS). Descriptive statistics and Pearson correlations (alpha = 0.05) were calculated using Minitab 15 (Minitab Inc., State College PA).
Results
For the PCS of SF-36, FFI and AOS the scores were significantly different at 2 year followup when compared to preoperative values; p = 0.005, 0.0002 and 0.0003 respectively. The PCS on average increased with respect to pre-operative by 10 points (SD = +/−13), while the MCS on average did not change with respect to pre-operative (SD = +/− 12). The FFI on average decreased by 25 points with respect to pre-operative (SD = +/− 18) and AOS on average decreased by 23 points with respect to pre-operative (SD = +/− 21).
There were several correlations for the 2 yr results: AOS to FFI of r = 0.92 (p = 0.000); AOS to PCS of r = −0.67 (p = 0.005); AOS to MCS of r = −0.51 (p = 0.046); AOS to talar component ID of r = 0.70 (p = 0.004); AOS to the talar component LM of r = 0.62 (p = 0.046). PCS related better than MCS to both AOS and FFI.
The LM of the talar component and tibial component were not significantly correlated, r = 0.18 (p = 0.62). The ID of the talar component and tibial component were not significantly correlated, r = 0.48 (p = 0.07). The latter result may be too underpowered to determine a significant difference; due to the small sample size.
Conclusion
The outcome scores of AOS, FFI, SF-36 (PCS) and SF-36 (MCS) were correlated to each other. The strongest outcome score relationships were AOS to FFI, followed by AOS to SF-36 (PCS). The correlation of AOS to the talar component LM and ID suggests that the implant performance may be related to the stability of the talar component.
