Differences in Recovery of Tendon Health Explained by Midportion Achilles Tendinopathy Subgroups: A 6-Month Follow-up.

OBJECTIVES: To (i) evaluate whether the defining characteristics of previously-reported Achilles tendinopathy subgroups were reproducible in a cohort with midportion Achilles tendinopathy and, (ii) compare recovery trajectories and outcomes. DESIGN: Prospective single cohort study METHODS: Participants (n=114, (Mean±SD) age 47±12, 57F) received the Silbernagel protocol and were evaluated at baseline, 8-, 16-, and 24 weeks. Subgroups were identified using mixture modeling. Main effects of group and time, and interaction effects were evaluated using linear mixed models for 23 outcome measures representing symptoms, lower extremity function, tendon structure, psychological factors, and patient-related factors. Recovery trajectories were reported descriptively to reflect clinically-meaningful change for outcomes. RESULTS: Activity-Dominant (n=34), Function-Dominant (n=38), Psychosocial-Dominant (n=27), and Structure-Dominant (n=15) subgroups were identified. There were significant effects of group and time for all primary outcome measures, except heel-rise limb symmetry index (LSI) and viscosity LSI. The Activity- and Function-Dominant subgroups achieved functional recovery despite persisting symptoms. The Psychosocial-Dominant subgroup reported the greatest impairments in symptom and foot and ankle-related quality of life at all timepoints. The Structure-Dominant subgroup experienced delayed improvement in symptoms and was the only subgroup to not achieve structural recovery. No subgroup met our criteria for complete recovery. CONCLUSION: The defining characteristics of Achilles tendinopathy subgroups were reproduced in a cohort with midportion Achilles tendinopathy. Activity- and Function-Dominant subgroups had superior outcomes compared to Psychosocial- and Structure-Dominant for symptomatic, functional, and structural recovery.