Stem cells have emerged as a novel treatment method for tendon ill-conditions. The current evidence for stem cell therapy in tendon disorders have been systematically reviewed in this study.

A minimum of 5 cases in the randomised and non-randomised controlled trials, cohort studies and case series were searched in MEDLINE, CENTRAL, EMBASE, CINAHL, PEDro and SPORTDiscus. The grey literature databases and trial registries were also searched. Only the human studies were considered with no time and language restrictions limited to the search. For the possible eligible trials, all the references of included trials were thoroughly checked. The Cochrane risk of bias tool determined the risk of bias assessment for controlled trials and the Newcastle-Ottawa scale for the case series. The Oxford levels of evidence was used to assign the levels of evidence.          

Four published and three unpublished/pending trials were found for with a total of 79 patients. There was no unpublished data. The bone marrow-derived stem cells in rotator cuff repair surgery resulted from two trials. Lower retear rates were found when compared with historical controls or the literature. The allogenic adipose-derived stem cells to treat lateral epicondylar tendinopathy were also used in one trial. Enhanced Mayo Elbow Performance Index, Visual Analogue Pain scale and ultrasound findings after 1-year follow-up distinguished with baseline were revealed. After 5-year follow-up, ameliorated International Knee Documentation Committee, Knee injury and Osteoarthritis Outcome Score subscales and Tegner scores was found as result of bone marrow-derived stem cell-treated patellar tendinopathy. Mild adverse events (e.g., swelling, effusion) were noted in one trial. High risk of bias was observed for all trials. Only level 4 evidence was present.

For tendon disorders, no evidence (level 4) was found for the therapeutic use of stem cells. Currently, the use of stem cell therapy for tendon disorders in clinical practice is not suggested.