Introduction Elongation of the Achilles tendon after rupture is a frequent and overlooked complication. The Achilles Tendon Length Measure (ATLM) and the Achilles Tendon Resting Angle (ATRA) are indirect length measures using the resting angle of the ankle. Copenhagen Achilles Length Measure (CALM) is a direct ultrasound measure. Examination of the association of elongation to valid clinical measures of the length of the Achilles tendon are needed. The purpose was to examine the concurrent validity of ATLM and ATRA in relation to CALM within one year of rupture.
Materials and methods The study was performed as a validity study. Data were collected from patients included in a randomized controlled trial. Mixed linear regression, controlling for time after injury, age and gender, was performed investigating the three models (dependent-independent): CALM-ATRA, CALM-ATLM and ATRA-ATLM.
Results 130 patients were included (23 women, 107 men) mean age 41.8 years (SD 10.5). All three regression models demonstrated a statistical significant (p<0.01) linear relationship. For each degree ATRA increased, CALM increased with 0.39 mm. For each cm ATLM increased, CALM increased with 1.7 mm. For each cm ATLM increase, ATRA increase with 1,6 degrees.
Conclusion ATRA and ATLM were found to have a linear relationship to CALM and seems valid as surrogate measurements for the assessment of tendon elongation after an Achilles tendon rupture.