Association Between T(2) (*) Relaxation Times Derived From Ultrashort Echo Time MRI and Symptoms During Exercise Therapy for Patellar Tendinopathy: A Large Prospective Study

BACKGROUND: Exercise therapy is considered preferential treatment for patellar tendinopathy (PT). However, there is conflicting evidence for structural patellar tendon adaptation in response to exercise therapy and its association with symptoms is weak. PURPOSE: To assess the association between 1) T(2) (*) relaxation times and symptom severity; 2) baseline T(2) (*) and clinical outcome; and 3) longitudinal T(2) (*) changes and clinical outcome in athletes with PT performing exercise therapy. STUDY TYPE: Randomized controlled clinical trial. SUBJECTS: Seventy‐six athletes (18–35 years) with clinically diagnosed and ultrasound‐confirmed PT. FIELD STRENGTH/SEQUENCE: 3D gradient echo sequence (3.0 T). ASSESSMENT: Patients were enrolled in a randomized trial of progressive tendon‐loading exercises (PTLE) versus eccentric exercise therapy (EET). Symptoms were assessed using the Victorian Institute of Sports Assessment (VISA‐P) questionnaire. 3D‐Ultrashort echo time (UTE)‐MRI was acquired at baseline, 12 and 24 weeks. Voxel‐wise T(2) (*) relaxation times were quantified using mono‐exponential and bi‐exponential models. T(2) (*) analysis was performed in three patellar tendon tissue compartments representing: aligned collagen, degenerative tissue, and interface. STATISTICAL TESTS: Adjusted general linear, mixed‐linear models, and generalized estimating equations. RESULTS: We included 76 patients with PT (58 men, mean age 24 ± 4 years); 38 in the PTLE‐group and 38 in the EET‐group, of which 57 subjects remained eligible for analysis. T(2) (*) relaxation times were significantly associated with VISA‐P in degenerative and interface tissues of the patellar tendon. No association was found between baseline T(2) (*) and VISA‐P after 24 weeks (P > 0.29). The estimated mean T(2) (*) in degenerative tissue decreased from 14 msec (95%CI: 12–16) at baseline to 13 msec (95%CI: 11–15) at 12 weeks and to 13 msec (95%CI: 10–15) at 24 weeks. The significant decrease in T(2) (*) from baseline to 24 weeks was associated with improved clinical outcome. DATA CONCLUSION: Tissue‐specific T(2) (*) relaxation times, identified with 3D‐UTE‐MRI, decreased significantly in athletes with patellar tendinopathy performing exercise therapy and this decrease was associated with improved clinical outcome. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 4