Placebo Effect in the Treatment of Patellar Tendinopathy and Its Influencing Factors: Systematic Review With Meta-analysis and Meta Regression of Randomized Controlled Trials

Abstract

Background: The effectiveness of nonsurgical treatment of patellar tendinopathy is questioned due to the conflicting results of placebo-controlled randomized controlled trials (RCTs) in which placebo arms often show impressive results. Purpose: To quantify the magnitude of placebo effect of the different nonsurgical treatments of patellar tendinopathy. We also evaluated the influence of patients and treatments characteristics on the response to the placebo. Study Design: Systematic review; Level of evidence, 1. Methods: We searched PubMed, Web of Science, Embase, Scopus, Cochrane Library, and gray literature databases on May 10, 2023, with no time limitation. RCTs on nonoperative treatment of patellar tendinopathy, including a placebo control arm reporting the evolution of symptoms after placebo administration, were included. A single-arm meta-analysis was performed with the Victorian Institute of Sport Assessment-Patella (VISA-P) at mid-term follow-up (3-6 months) as the primary outcome. The VISA-P score at short-term (1-3 months) and long-term (6-12 months) follow-ups, as well as visual analog scale (VAS) for pain at all 3 time points were also analyzed. A subanalysis based on the type of placebo and a meta-regression were conducted to look for potential determinants of the placebo effect. Risk of bias and level of evidence were also analyzed using the revised tool for risk of bias in randomized trials and Grading of Recommendations Assessment, Development and Evaluation. Results: In total, 14 studies (251 patients) were included. VISA-P score at mid-term follow-up (3-6 months) showed statistically significant improvements of 13 of 100 points (P =.001). The change at short-term follow-up (1-3 months) was not statistically significant, whereas at long-term follow-up (6-12 months) it was 27 of 100 points (P