Effect of joint angle positioning on shearwave speed and variability with ultrasound shearwave elastography in asymptomatic Achilles and patellar tendons.

This study investigated the impact of joint positioning on ultrasound shear wave elastography measurements in the Achilles and patellar tendons. Twenty-eight healthy adults underwent SWE assessment of shear wave speed (SWS) and coefficient of variation in SWS (CV-SWS) at three ankle positions (neutral, 10° plantar flexion, and 20° dorsiflexion) and two knee positions (90° flexion and full extension), at two academic sites. Participant positioning for ankle testing differed between sites (prone vs long-sitting)-while knee testing used consistent positioning. At the ankle, both joint and participant positioning significantly affected SWS. In the prone position, SWS was lower in neutral compared to dorsiflexed position (3.07 ± 1.13  m/s vs. 3.95 ± 1.03  m/s, p = 0.013). In long-sitting, SWS was lower in neutral compared to plantarflexed position (2.85 ± 0.53  m/s vs. 4.86 ± 1.92  m/s, p = 0.016); and SWS was higher in the plantarflexed position when participants were in long-sitting compared to prone (4.86 ± 1.92  m/s vs. 3.25 ± 1.13  m/s, p = 0.016). Participant positioning affected CV-SWS, with higher variability observed in prone compared to long-sitting in plantarflexed (29.3 ± 15.5 % vs 12.4 ± 9.12 %, p = 0.005) and neutral ankle angles (p = 0.03). At the knee, joint position significantly influenced SWS, with higher values in flexed versus extended positions (6.48 ± 3.1  m/s vs. 4.60 ± 2.3  m/s, p = 0.007). Extending the knee reduced CV-SWS compared to flexed position (14.5 ± 11.2 vs 19.2 ± 13.4, p = 0.044). In conclusion, joint position significantly affected SWS measurements in both the Achilles and patellar tendons, while participant positioning influenced measurement variability. Thus, standardizing joint and participant positioning is important to enhance the reliability of SWE assessments of tendon elasticity.