Achilles Tendon Shear Wave Velocity Within a 1-Year Follow-Up After Non-Operatively Treated Rupture

The purpose of this study was to investigate changes in Achilles tendon (AT) shear wave velocity (SWV) during the first year after rupture. Additionally, we aimed to explore relationships between AT SWV and plantarflexion maximal voluntary torque (MVT), steps/day, patient-reported function, and tendon thickness. Participants (N = 27, 8 females, 41.5 ± 9.8 years) were measured for AT SWV at rest, accelerometer-monitored daily steps, and tendon thickness at 2-, 6-, and 12 months post-rupture. AT SWV was imaged from distal, middle, and proximal locations along the length of the tendon (ATdist, ATmid, ATprox). MVT was tested at 6- and 12 months. Achilles tendon total rupture score (ATRS) was inquired at 12 months. Pearson's correlation was used to assess the relationship between limb asymmetry (LSI, %) of ATmid SWV and the functional and structural outcomes. Linear mixed model was used to assess the effect of time, limb condition and imaging location on AT SWV. AT SWV LSI correlated with MVT LSI at 6- and 12 months after rupture (r = 0.500, p = 0.011; r = 0.653, p < 0.001, respectively). By 6 months, the injured tendon reached SWV level of the uninjured limb and at 12 months, ATprox SWV of the injured side was higher than the uninjured (mean difference 2.4 m × s⁻¹ (95% CI 0.9-3.7), p = 0.007. At 12 months, median ATRS was 91 points. Increase in SWV of the injured tendon may indicate an improvement in its material properties during recovery. This improvement may be associated with the ruptured tendon's ability to transfer loads and the muscle-tendon units' capacity to generate force.