Impact of COVID-19 on patellar tendon properties over the first year after infection

This study aimed to examine the impact of infection severity and associated inactivity on patellar tendon health following COVID-19. Seventy participants were divided into three groups: moderate COVID-19 (n = 22), severe COVID-19 (n = 18), and control (n = 30). Four assessments were conducted over one-year for the COVID groups - between the 21st and 30th days (A21−30), 31 and 90 days (A31−90), 91 and 180 days (A91−180), and 181 and 360 days (A181−360) after the onset of symptoms for moderate or hospital discharge for severe. Maximal voluntary isometric knee extension contractions were performed, with simultaneous ultrasound imaging of patellar tendon length to calculate material and mechanical properties. Morphological properties (length and cross-sectional area) were obtained at rest. During one year, the severe group consistently had lower state of load on tendon (p < 0.002) and stress (p < 0.001) compared to the moderate and control groups, while strain in the first three months post-infection was comparable to the other groups (p > 0.256). A reduction in stiffness (p < 0.009) and Young’s modulus (p < 0.015) was observed during the same assessment period. Severe infection cases were associated with prolonged reductions in tendon load and stress. These findings suggest that systemic effects of infection and reduced activity levels may contribute to tendon adaptations.