Subclinical Achilles tendon structural and pathology changes in asymptomatic amateur marathon runners: a correlational and multivariate MRI study

To investigate the morphological characteristics and pathological changes of the Achilles tendon in asymptomatic amateur marathon runners using high-resolution MRI and to identify the key demographic and running-related factors that influence these structural and pathology changes. Forty-eight asymptomatic amateur marathon runners (39 males, median age 38.0 years) underwent ankle 3.0T MRI. Quantitative parameters of the dominant leg’s Achilles tendon—including thickness, volume, cross-sectional area (CSA), and length—were measured. MRI findings suggestive of Achilles tendinopathy (mid portion/insertional), retrocalcaneal bursitis, superficial calcaneal bursitis, and paratendinopathy were recorded. Demographic data, running experience, monthly distance, running pace, and foot strike pattern were collected. Correlations were assessed using Pearson and Spearman correlation coefficients. Group differences were evaluated using t-tests and Mann-Whitney U tests, and multivariate binary logistic regression was performed to identify independently associated factors. MRI findings suggestive of retrocalcaneal bursitis (37.5%), insertional Achilles tendinopathy (31.2%), midportion Achilles tendinopathy (20.8%), and paratendinopathy (8.3%), with no superficial calcaneal bursitis detected. Running experience correlated positively with thickness, CSA, volume (all P < 0.05). Retrocalcaneal bursitis had a higher BMI (t = -3.176, P = 0.001) and longer running experience (t = -2.498, P = 0.012). Midportion and insertional Achilles tendinopathy had slower running paces (z = -2.526, P = 0.012 and z = -2.407, P = 0.016, respectively). Foot strike patterns varied among different Retrocalcaneal bursitis statuses ( x 2 = 6.146, P = 0.013). Volume was independently associated with midportion Achilles tendinopathy (OR = 1.001, 95% CI: 1.000–1.002, P = 0.045). BMI (OR = 1.956, 95% CI: 1.153–3.320, P = 0.013) and rearfoot strike pattern (OR = 0.236, 95% CI: 0.060–0.935, P = 0.040) were independently associated with retrocalcaneal bursitis. MRI-detected subclinical Achilles tendon abnormalities are prevalent in amateur marathon runners, with retrocalcaneal bursitis being the most common finding. BMI, foot strike pattern, and Achilles tendon volume were associated with different types of MRI abnormalities.