Achilles Tendon Resting Angle Relates to Tendon Length and Function

Area of Science:

• Orthopedics
• Biomechanics
• Musculoskeletal Imaging

Background:

• Achilles tendon rupture often results in long-term calf dysfunction due to tendon elongation.
• Achilles tendon resting angle (ATRA) is a potential surrogate for tendon length but requires validation.
• Ultrasound has not been used to validate ATRA against direct tendon length measurements.

Purpose of the Study:

• To validate the Achilles tendon resting angle (ATRA) as a measure of tendon elongation using ultrasound.
• To investigate the relationship between ATRA, tendon mechanical properties, and heel-rise test performance post-Achilles tendon rupture.

Main Methods:

• Participants with unilateral Achilles tendon rupture had ATRA measured in knee flexion and extension.
• Tendon elongation was quantified using extended field of view ultrasound imaging.
• Tendon mechanical properties were assessed using shear wave elastography; heel-rise test performance was also evaluated.

Main Results:

• Relative ATRA in both knee positions showed a moderate correlation with tendon elongation (P < .001).
• In individuals over one year post-rupture, relative ATRA with knee flexion correlated with shear modulus (P = .01) and heel-rise total work (P = .008).

Conclusions:

• Relative ATRA moderately predicts tendon elongation within the first year after Achilles tendon rupture.
• After one year, relative ATRA in knee flexion may be a superior indicator of tendon elongation, mechanical properties, and functional recovery.