Background: The efficacy of platelet-rich plasma (PRP) for lateral epicondylitis has been demonstrated. However, the healing process monitored by repeated magnetic resonance imaging (MRI) is unclear. The purpose of this study was to evaluate sequential changes using MRI in patients with lateral epicondylitis treated by PRP injection at 6 follow-up visits over a 2-year period. Methods: Thirty patients who underwent PRP treatment for lateral epicondylitis and sequential MRI evaluation were prospectively enrolled. The MRI scores (ranging from 0 to 3) and clinical scores, including the visual analog scale (VAS) pain score and Patient-Rated Tennis Elbow Evaluation (PRTEE) score, were measured at baseline (before treatment) and 1, 3, 6, 12, 18, and 24 months after the procedure. Sequential changes in the MRI scores and clinical scores during the treatment period were evaluated. In addition, the associations between MRI scores and clinical scores were assessed. Results: The mean MRI score at baseline was 2.30, and the mean MRI scores at 1, 3, 6, 12, 18, and 24 months after the procedure were 1.97, 1.77, 1.13, 0.73, 0.60, and 0.33, respectively. Significant improvements in the MRI scores occurred by 3 months and continued over a period of 24 months. Regarding the clinical scores, the mean VAS pain scores were 72 at baseline, 48 at 1 month, 34 at 3 months, 28 at 6 months, 15 at 12 months, 14 at 18 months, and 11 at 24 months and the mean PRTEE scores were 56, 36, 26, 18, 8, 9, and 6, respectively. Significant improvements in the VAS pain score and PRTEE score occurred by 1 month and continued over a period of 12 months. There was little association between the MRI scores and clinical scores. Conclusions: Continuous tendon recovery assessed by MRI was found during a 2-year period after PRP treatment. Improvements in the MRI scores followed and continued longer than improvements assessed by the clinical scores.
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