The Distal Free Achilles Tendon Is Longer in People with Tendinopathy than in Controls: A Retrospective Case-Control Study.

Objectives: The free Achilles tendon is defined as the region of tendon distal to the soleus which is "unbuttressed," i.e., unsupported by muscular tissue. We reasoned that a relative lack of distal buttressing could place the tendon at a greater risk for developing Achilles tendinopathy. Therefore, our primary goal was to compare the free Achilles tendon length between those with midportion or insertional Achilles tendinopathy and healthy controls.

Design: This is a retrospective case-control study. . Hospital in Vancouver, Canada. . 66 cases with Achilles tendinopathy (25 insertional, 41 midportion) consecutively drawn from a hospital database within a 5-year period and matched to 66 controls (without tendinopathy) based on sex, age, and weight. . Odds ratio of the risk of developing Achilles tendinopathy given the length of free tendon, defined anatomically on MRI, after adjustment for confounders.

Results: MRI-defined free Achilles tendon length is a statistically significant predictor of having midportion Achilles tendinopathy (odds ratio = 0.53, 95% confidence interval 1.13 to 2.07). Midportion Achilles tendinopathy cases had significantly longer free tendons ( = 51.2 mm,  = 26.9 mm) compared to controls ( = 40.8 mm,  = 20.0 mm), = 0.007. However, there was no significant difference between the free Achilles tendon lengths in insertional AT cases ( = 47.9 mm,  = 15.1 mm) and controls ( = 39.2 mm,  = 17.9 mm), = 0.158. Free Achilles tendon length was also correlated with the tendon thickness among those with Achilles tendinopathy,  = 0.25, and = 0.003.

Conclusions: The MRI-defined length of the free Achilles tendon is positively associated with the risk of midportion Achilles tendinopathy. A relative lack of distal muscular buttressing of the Achilles tendon may therefore influence the development of tendinopathy.