Is the Hip Keeping the Ankle Out of Work after Total Ankle Arthroplasty?

Submission Type: Total Ankle Arthroplasty Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Total ankle arthroplasty (TAA) outcomes include substantially improved gait speed and physical function scores. However, these outcomes remain deficient compared to age-associated norms in a large proportion of individuals after TAA. Of note, postoperative ankle energy production (i.e. power, work) during gait is also deficient and related to lower gait speed and physical function scores. These findings raise questions regarding if people after TAA have the capacity to generate greater ankle energy or rely on proximal joint (e.g. hip) energy during walking and more challenging daily functional tasks. Therefore, our purpose was to determine the energetic response of the ankle, knee, and hip during multiple functional tasks in people after TAA in comparison to healthy controls. Methods: Ten people after TAA (69.6±8.6 years, 5 female, 45.4±9.2 months post TAA) and five healthy control participants (66.8±8.3 years, 2 female) have completed this ongoing case-control study. Speeds were standardized and matched between groups during four functional tasks of increasing energy demand: normal walking, fast walking, standard step ascent (17 cm), and high step ascent (35 cm). A reliable biomechanical model was applied to collected motion capture and force plate data. Ankle, knee, and hip positive joint work (i.e. power across time) were derived to reflect the magnitude of propulsive energy at each joint during the gait cycle. Outcomes included ankle work and the ipsilateral proximal positive work ratio as ((hip+knee work) – ankle work) / total work, where larger values indicate a relatively greater contribution of hip and knee energy. Differences across tasks within the TAA group were analyzed with Friedman’s ANOVAs. Preliminary between-group differences were assessed descriptively. Results: TAA group ankle work increased as task demand increased from walking to stair ascent conditions (p < .01), but was lower than control values for each task (Figure 1). TAA group proximal positive work ratio increased across tasks (p = .03), and was higher than controls during each task. Specifically, proximal positive work ratio group differences of 5-9% during the walking conditions and 13-23% during stair ascent conditions indicated a greater reliance on hip and knee work in the TAA group. Conclusion: While ankle work increased as task demand increased, lower than normal ankle work appears to necessitate greater proximal joint work (e.g. hip) for task completion in people at least 3 years after TAA. The consequences, and potential adaptability, of this compensatory strategy deserve further attention to best guide postoperative interventions towards a realistic profile of joint performance to optimize mechanical efficiency, implant/joint integrity, and patient function long-term.