Background Eccentric exercises have proven to be an effective management option and prevention strategy in tendon overuse injuries (a challenging sport pathology). However, till date, these exercise protocols are undifferentiated and certainly don't take subregional stress and strain differences, which have frequently been mentioned as important etiological factors, in account. Knowledge on these biomechanical parameters, obtained by in vivo experiments, could optimise the exercise protocols.

Objective The present experiment evaluates the feasibility of automatic, intensity-based, spatio-temporal elastic registration for non-invasive local strain measurement by speckle tracking on dynamic ultrasound movies.

Methods An isolated porcine patellar tendon (tendon length of 60 mm) with bone parts at each side was placed in a loading frame with an ultrasound transducer orientated along the long axis of the tendon. Ultrasound recordings were made while the tendon was cyclically loaded at two different velocities (1 mm/s and 2 mm/s) and three different displacements (1.5 mm, 3 mm and 5 mm). Afterwards a precalibrated strain-gauge extensometer was inserted in the central 2.5 cm of the tendon and the same loading scheme was applied while recording ultrasound movies. The movies were processed, based on non-rigid elastic registration and speckle tracking, and these results were compared with the extensometer data.

Results Ultrasound strain values were comparable to extensometer strain data in four measurements (a- velocity 1.0 mm/s, displacement 1.5 mm: 0.8% strain difference; b- velocity 1.0 mm/s, displacement 3.0 mm: 0.6% strain difference; c- velocity 1.0 mm/s displacement 5.0 mm: 0.7% strain difference; d- velocity 2.0 mm/s, displacement 1.5 mm: strain difference 0.1%) resulting in a mean strain difference of 0.55%. The measurements at velocity 2 mm/s and 3.00 and 5.00 mm displacement were left out because of poor tracking in these recordings due to more out of plane movement.

Conclusion It seems feasible to obtain comparable strain values between extensometer measurements and speckle tracking on non-invasive ultrasound recordings.