Platelet-Rich Plasma for Patellar Tendinopathy: Letter to the Editor

Dear Editor: We first want to applaud Scott et al on their study ‘‘Platelet-Rich Plasma for Patellar Tendinopathy: A Randomized Controlled Trial of Leukocyte-Rich PRP or LeukocytePoor PRP Versus Saline. ’’ Patellar tendinopathy is one of the most difficult ailments that sports medicine professionals encounter, and this study is an excellent effort in advancing the care of these patients. It provides new insight and, frankly, calls into question the value of single platelet-rich plasma (PRP) injections for patellar tendinopathy. One important item that warrants additional discussion is the PRP classifications assigned in the subtitle: leukocyterich (LR) PRP versus leukocyte-poor (LP) PRP. Classifying and reporting PRP content is one of the great challenges facing orthobiologic research and should be carefully analyzed and discussed. The study appropriately adheres to standardized preparation methods, setting the device to 2% and 15% for the 2 PRP groups, referred to as LP and LR, respectively. However, the data reported in the study do not definitively establish that these classifications are accurate for all the injections administered in the trial. The PRP content testing was performed at 1 of the 3 sites and reported values for 12 of the 38 total PRP samples. While single-site reporting is a step in the right direction, leaving the majority of samples untested opens the possibility for variation in the other patients and potentially an inaccurate classification of the PRP. One example of the possible variation is that the PRP produced with the Angel device (Arthrex) at the 15% setting had a leukocyte fold change of 1.3 with a standard deviation of 0.6. Without the individual results, this standard deviation leaves the possibility that some of these PRP injections classified as LR were actually LP. The study refers to PRP produced at the 2% setting as LP, but this may be premature and should be considered in the context of other publications that have used the same setting. The trial classifies the 2% setting as LP based on 6 samples, which had leukocytes reduced to 0.6 of baseline. The remaining 13 injections considered to be LP were not analyzed. This is important to recognize because 2 previously published studies found that the 2% setting does not reduce leukocytes. Degen et al found that in 7 patients, the 2% setting increased leukocytes 2 times over baseline, but this was not significantly different from whole blood. No leukocyte reduction was reported in their study. Furthermore, work performed in our laboratory on 10 healthy subjects found that the 2% setting concentrated leukocytes 4.8 times (primarily driven by lymphocytes), which did reach statistical significance. Since multiple studies have shown that the 2% setting does not consistently reduce leukocytes (and in some cases actually concentrates them), the 13 untested injections in the work of Scott et al should not be assumed to be LP. The reason for these inconsistencies, despite identical preparation methods, is unclear. Individual patient variability is known to influence PRP content and may be a potential driver behind these observed differences in device output. Since we do not know the content of over two-thirds of the PRP used in this trial and the 2% setting does not always yield LP PRP, it could be premature to make a conclusion about LR versus LP PRP for patellar tendinopathy based on the results of this study. To do so may lead to an errant conclusion about the role of different types of PRP for tendinopathies. However, the study still contributes significantly by helping us understand the role of these 2 device settings in clinical practice. This continues to highlight the variable nature of PRP and orthobiologics. We certainly understand that reporting of cellular content for every patient is time-consuming and requires additional equipment and cost. Undoubtedly, this adds increased burden to orthobiologic studies, but given the variations present in the literature, it is necessary if we are to accurately classify, analyze, and understand biologic interventions. Again, we applaud Scott et al on their study and efforts to advance the clinical application of orthobiologics, but we want to ensure accurate interpretation of their results.