Knee osteoarthritis: hyaluronic acid, platelet-rich plasma or both in association?

INTRODUCTION: Bidirectional interactions between cells and fluidic surroundings regulate cellular functions and maintain tissue or organ architecture. Accordingly, the synovial fluid is the primary source of environmental signals and determines to a great extent the molecular interactions within the joint capsule, both in homeostasis and pathology. AREAS COVERED: We provided an update on hyaluronic acid (HA) and platelet-rich plasma (PRP) concepts necessary to build the rationale for creating a combined treatment. The information is based on a PubMed search using the terms 'platelet-rich plasma', 'hyaluronic acid', 'knee pathology', 'knee osteoarthritis' (OA). EXPERT OPINION: In OA, a deleterious fluidic microenvironment is established, with presence of HA fragments, catabolic enzymes and inflammatory molecules. The central concept underlying intra-articular injection is to modify deleterious fluidic microenvironments. PRP administration has shown pain remission and function improvement, but less than half of the patients showed clinically significant improvement. PRP exceeds HA, the comparator used in PRP clinical trials, albeit both HA and PRP alleviate symptoms in mild-to-moderate OA patients. Combining PRP and HA may benefit from their dissimilar biological mechanisms and help in controlling delivery and presentation of signaling molecules. Three armed randomized studies, using both HA and PRP as comparators, will provide information about the impact of this approach.