OBJECTIVES: To assess the associations between: (1) baseline patellar tendon stiffness and clinical outcome after exercise therapy in athletes with patellar tendinopathy and (2) the change in patellar tendon stiffness and clinical outcome during progressive tendon-loading exercise therapy and eccentric exercise therapy. DESIGN: Randomized controlled trial. METHODS: Athletes with patellar tendinopathy aged 18 to 35 years, playing tendon-loading sports at least 3 times per week were randomized in a 1:1 ratio between progressive tendon-loading exercise therapy and eccentric exercise therapy for 24 weeks. Patellar tendinopathy was diagnosed clinically, and confirmed by ultrasound. Patellar tendon stiffness (kilopascal, kPa) was assessed using shear-wave elastography. Clinical outcome was assessed using the validated Victorian Institute of Sports Assessment (VISA-P; range 0 to 100) questionnaire. Both were assessed at baseline, 12 and 24 week follow-up. Adjusted general linear, mixed-linear models and Generalized Estimating Equations were used. RESULTS: We included 76 athletes (58 men, mean age 24 + or- 4 years). No association was found between baseline stiffness and VISA-P after 24 weeks (p = 0.52). Decreased stiffness (adjusted mean difference = 10 kPa (95% CI 4 to 15) was significantly associated with improved clinical outcome at 12 weeks in all athletes (p = 0.02), and at both 12 and 24 weeks (p = 0.01) in athletes allocated to progressive tendon-loading exercise therapy. CONCLUSIONS: Patellar tendon stiffness, assessed with shear-wave elastography, is unsuitable to use as a single predictive measurement for clinical outcome. Decreasing stiffness during the course of exercise therapy is associated with improved clinical outcome in athletes recovering from patellar tendinopathy.

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