Side-to-side differences in Achilles tendon geometry and mechanical properties following achilles tendon rupture.

Background Recovery of tendon structure has been suggested to play a role in clinical success following Achilles tendon rupture. The purpose of this study was to identify side-to-side differences in tendon geometry and mechanical properties following Achilles tendon rupture and investigate the relationship of tendon structure with clinical outcomes. Methods Participants within 1 year post complete rupture were included. Tendon geometry and mechanical properties were quantified using B-mode ultrasound imaging and continuous shear wave elastography (cSWE). Clinical outcomes included the heel-rise test. Participant self-reported function was measured using the Achilles tendon Total Rupture Score, Foot and Ankle Outcome Score - quality of life subscale, and the Physical Activity Scale. Results Twenty participants [mean (SD) age: 42.7(13.6) years, 13 managed surgically] were included. Tendon thickness was greater on the ruptured side (p <0.001) [median (IQR) rupture: 1.38(1.21-1.56) cm, non-rupture: 0.49(0.40-0.52)]. Tendon length to the gastrocnemius was longer (p <0.001) on ruptured [22.8 (21.71-24.31) cm] than non-ruptured [21.66(20.74-23.62) cm] sides. Viscosity was lower on the ruptured side (p <0.001) [median (IQR) rupture: 37.7(30.6-43.3) Pa*s, non-rupture: 53.5(48.4-59.6) Pa*s]. Shear modulus was not different between sides. Tendon thickness (rho = 0.675, p = 0.002) and shear modulus (rho = -0.791, p = 0.001) related to total work on the heel-rise test. Conclusion Ultrasound imaging, including cSWE, can be used to detect side-to-side differences in tendon structure in individuals with Achilles tendon rupture and tendon structure relates to clinical performance. Level of evidence III b.