Structure and Function of the Achilles Tendon and Plantarflexors 1 Year Following Achilles Tendon Rupture in the...

Achilles tendon rupture (ATR) is the most common tendon rupture affecting the lower limb. This study investigates Achilles tendon structure, strength and function 1 year or more after ATR.

This cross-sectional study recruited individuals ≥ 12 months post ATR. Structure was assessed using ultrasound tissue characterisation (UTC) including cross-sectional area (CSA), aligned fibrillar structure (AFS), disorganised fibrillar structure (DFS) and echo type percentage. Strength was measured using maximal voluntary isometric contraction (MVIC) plantarflexor testing and the calf raise test. Patient-reported outcomes included the Achilles tendon rupture score (ATRS), EQ-5D-5L and general practice physical activity questionnaire (GPPAQ). Achilles tendon resting angle (ATRA) was used as an indirect measure of tendon elongation. The relationship between outcomes and time since ATR was analysed using linear regression adjusting for age, sex, ethnicity and body mass index (BMI). Between limb comparisons were made using paired t-tests.

Sixty participants (mean age 55.2 years and 78.5% male) were assessed at a mean of 6.8 years post ATR. The affected tendon showed a 62% larger cross-sectional area, with 28.7 mm² (16%) DFS compared to 7.3 mm² (7%) on the nonaffected side (p < 0.001). Linear regression showed decreasing AFS with time postinjury (p = 0.04); no significant associations were found for CSA or DFS. Significant deficits were observed in plantarflexor strength and function, with MVIC and calf raise work 18% and 40% lower in the affected limb (p < 0.001). ATRA indicated tendon elongation in the affected limb of 6.7° (p < 0.001). Median ATRS was 83, EQ-5D index was 0.95 and VAS was 85; 93% were physically active based on the GPPAQ.

Significant structural and functional deficits persist years after ATR, including increased tendon size, fibre disorganisation, reduced strength and tendon elongation. ATRS scores were consistent with previous nonsurgical immobilisation protocol outcomes in the United Kingdom. Longitudinal studies are needed to understand the trajectory of recovery following ATR.