Background There are many possible predisposing factors for Achilles tendon disorders suggested in the literature but their pathogenetic relevance is not proven in most cases. The asymmetric mechanical load distribution within the Achilles tendon during locomotion is frequently addressed as a major risk factor for Achilles tendon disorders. The spatial orientation of the subtalar joint axis (STA) may influence the Achilles tendon loading possibly leading to overload injuries.

Hypothesis There is a significant difference between the orientation of the STA in subjects with and without Achilles tendon pathologies.

Materials and methods 614 subtalar joint axes determined in 307 long-distance runners with and without Achilles tendon disorders were included. Achilles tendon disorders were defined as any Achilles tendon–related pain during or following running, existing for more than 2 weeks in the past. Motion analysis of the foot was performed using an ultrasonic pulse-echo-based measurement system. The orientation of the STA was expressed by two angles.

Results The mean inclination angle was 42±16° and the mean deviation angle was 11±23°. There was a significant difference (p=0.002) between the mean deviation angle measured in subjects with Achilles tendon pathologies (18±23°) and those without (10±23°).

Conclusions The results demonstrate a wide interindividual variability of the spatial orientation of the STA. In addition, the mean deviation angle in people with Achilles tendon pathologies is significantly more oblique than in people without. This finding indicates that the spatial orientation of the STA is related to the incidence of overuse injuries of the Achilles tendon in the investigated sample.