Reply to the letter by Dhillon and colleagues

Abstract

We would like to thank Prof. Dhillon and colleagues for the opportunity to revisit and explore some interesting and very controversial aspects of this innovative biological treatment approach. In a previous study [5] and in the subsequent analysis ‘‘platelet-rich plasma intra-articular knee injections for the treatment of degenerative cartilage lesions and osteoarthritis’’ [3] cited by Dhillon et al., we aimed to analyze our preliminary results with the use of intra-articular knee injections of platelet-rich plasma (PRP) as minimally invasive treatment for knee degenerative pathology. Our findings suggested the potential to reduce pain and improve both knee function and quality of life with short-term efficacy, especially in younger patients with chondral degenerative lesions or early osteoarthritis (OA). First of all, we would like to answer the observations made about the PRP preparation method. Our procedure involved a 150-ml venous blood sample, which was centrifuged twice to produce a 20-ml unit of PRP. The PRP was then divided into 4 small units of 5 ml each. All of the open procedures were performed in an A-class sterile hood. As correctly underlined, once prepared, the first PRP sample was injected within 4–6 h. The remaining samples were immediately stored at -30 C, in order to avoid the risks of bacterial proliferation and accumulation of pyrogenic cytokines, and towed after 3 and 6 weeks for the other cycle injections. We disagree with the doubts about the storing procedure. Freezing them gives us the time to proceed with the quality analysis. This has to be considered as an advantage, not a disadvantage, with respect to the open procedures for fresh PRP application. In fact, now in our clinical practice, we are also freezing the first sample; this delays the first injection but increases the safety procedure, ensuring a controlled not contaminated intraarticular delivery of the product. The alteration of the morphology and decrease in platelet functional properties, which includes degranulation of alpha-granules, after storing platelets in freezing conditions, is well known. On the contrary, there are no data on the effect of freezing on the clinical results of platelet injections and freeze-thawing is even one of the methods used for releasing intracellular GFs [2, 9]. Some studies, as well as some of our preliminary unpublished data, show a not significant influence of freezing on GF release, and frozen platelets have also been used by other authors [2, 8]. Regarding methods that increase the storage life of platelets in freezing conditions, such as the mentioned dimethylsulfoxide (DMSO), they involve further platelet manipulation and carry some risks, too (not excluding severe adverse events such as neurological toxicity), and removing it before patient administration also means losing cells and bioactive molecules [4]. Having freshly harvested PRP might preserve all the platelet functions better, but currently the data are still controversial and we cannot say that freeze-thawing adversely affects their properties to the point of impairing their clinical efficacy. Cellularity is another debated aspect of not secondary importance when evaluating PRP properties and the results obtained with its application. In fact, not only platelets but also leukocytes, monocytes, macrophages, and mast cells are contained in many platelet concentrates. Some authors define PRP as only platelets and attribute better results to leukocyte depletion, because of the deleterious effects of proteases and reactive oxygen released from white cells; G. Filardo E. Kon (&) M. Marcacci Biomechanics Laboratory–III Clinic, Rizzoli Orthopaedic Institute, Bologna, Italy e-mail: e.kon@biomec.ior.it