BackgroundThere are controversies about platelet-rich plasma (PRP) as an established treatment option for rotator cuff (RC) tendinopathy. The purpose of the study was to find the relation of cellular component with clinical efficacy in RC tendinopathy and to find the composition of PRP in treating RC tendinopathy.MethodsA total 30 patients were recruited and divided into PRP and control groups. In the PRP group, 2 ml of PRP solution was injected to the hypoechoic lesion of degenerative supraspinatus via 22-gauge syringe with peppering technique. Patients in the control group were taught rotator cuff strengthening exercises. American Shoulder and Elbow Surgeons (ASES), Constant-Murley score, and numeric rating scale (NRS) were measured before, 6 weeks after, 12 weeks after, and 24 weeks after the procedure. PRP compositions were analyzed using the 1 ml of PRP solution.ResultsLinear regression analysis showed no significant difference of ASES and Constant-Murley scores between the groups at 6 weeks (P = 0.582 and 0.258) and at 12 weeks (P = 0.969 and 0.795) but showed a significant difference at 24 weeks (P = 0.050 and 0.048). Independent t test showed significant group difference of NRS at 6 weeks (P = 0.031) but not at 12 and 24 weeks (P = 0.147 and 0.935). 5.19 pg/ml in IL-1β and 61.79 μg/ml in TGF-β1 were acquired as cutoff values to predict meaningful improvement. The PRP subgroup above IL-1β or TGF-β1 cutoff value showed significant differences in all clinical outcomes compared with the exercise group while the PRP subgroup below the cutoff value showed no significant differences in linear regression analysis.ConclusionsOur study can help to find the optimal PRP condition and to enhance the effect of PRP on RC tendinopathy.Trial registrationAll the patients were registered in our Institutional Ethics Committee (approval number 2014-05-009).