Locomotor Function and Pain in Total Ankle Arthroplasty Patients at Six Months’ Follow-Up

CATEGORY: Ankle; Ankle Arthritis INTRODUCTION/PURPOSE: Outcomes following total ankle arthroplasty (TAA) are largely positive, with high levels of patient satisfaction, but residual pain has been identified in up to 60% of cases. While associations between implant kinematics and pain following TAA have been found in a study of walking gait, there have been no studies to date of pain and function during more challenging locomotor tasks. The purposes of this study were (1) to examine pre- to post-operative (6 months) changes in function along with comparisons to healthy controls, and (2) to determine how functional changes are related to pain. We hypothesized that following TAA, function would improve but would not match that of healthy controls. We further hypothesized that improvements in function would be related to reductions in pain. METHODS: Complete data sets were obtained for 11 TAA patients (age: 64.04 +- 9.26 y, height: 1.71 +- 0.07 m, body mass: 98.55+- 20.07 kg; 3 implant designs) and 15 age-matched control subjects (age: 63.14 +- 7.95 y, height: 1.68 +- 0.10 m, body mass: 75.57+- 13.66 kg). All procedures involving testing of human subjects were approved by the PSU HMC Institutional Review Board. Patients performed all tasks pre-operatively and six months post-operatively in a motion laboratory. Participants completed the RAND 36-Item Health Survey 1.0 (SF-36), whose global pain score was used in our analysis. Each patient and control participant performed three tasks to assess their locomotor function: Single-Leg Balance Test (SLBT); Timed Up-and-Go (TUG) Test, and Six- Minute Walk (6MW). Linear regression analysis incorporating covariates of change in pain (delta-pain) and BMI was performed to investigate how change in performance on these tests depended on these variables. RESULTS: For 6MW velocity (r = 0.653, p = 0.030), normalized 6MW velocity (r = 0.624, p = 0.040), and SLBT (r = 0.695, p = 0.018) pre-operative scores were correlated with post-operative function. TUG performance had a very weak correlation (r = 0.226, p = 0.504) and pain levels had a moderate correlation (r = 0.646, p = 0.032). Linear regression did not predict change in function from delta-pain alone, but when BMI and the interaction of BMI with delta-pain were included, moderate to good fits for change in function were obtained (Table 1). Improvements in pain (when accounting for BMI) accounted for the majority of improvement in average walking velocity, and up to half of the variation in improvement in TUG. CONCLUSION: This is the first study relating changes in locomotor function to changes in pain following TAA. Our first hypothesis that performance on the three tests would be improved over pre-operative function, but without reaching that of healthy controls, was supported. Contrary to our second hypothesis, we found that pain improvement assessed using the pain score from the SF-36 did not explain variation in observed improvements in function. When we included the interaction between pain and BMI in our models, 80% of the changes in 6MW average velocity was explained, and approximately 50% of TUG time change was explained.