Joost Peerbooms

10 Chapter 1 PREFACE Musculoskeletal disorders are a major cause of pain and disability affecting hundreds of millions of people globally. An ageing population and prolonged life expectancy are expected to result in an increase in the number of patients suffering frommusculoskeletal disorders in the future, with significant social and economic impacts.¹ Over the years, surgical options for the treatment of musculoskeletal disorders have increased. More effective implants, surgical techniques, and post-operative rehabilitation programmes have led to an increase in the number of orthopaedic surgical procedures performed each year. However, many musculoskeletal conditions have a quite favourable natural history, with a reduction or complete disappearance of symptoms occurring over the course of weeks or months. Non-surgical treatment is important in reducing costs for patients and society as well as avoiding the risks of surgical interventions. The main tools for non-surgical treatments are pharmacological pain reduction with paracetamol or nonsteroidal anti-inflammatory drugs (NSAIDs), exercise therapy, and orthosis, among other techniques. 2 The effectiveness of these techniques has not been proven for all musculoskeletal conditions, and some may have no benefit over allowing the disorder to run its natural course. 3 Over the years, researchers have developed and promoted several techniques that have been claimed to stimulate or augment the repair of tissues, which may result in the improvement of symptoms. The basis for these techniques is the local injection of biological substances that are naturally produced in the patient’s body or cells (e.g., mesenchymal stem cells derived from bone marrow, adipose-derived mesenchymal cells, or growth factors). 4 The purpose of these techniques is to enhance biological repair processes. Among such ‘orthobiologic’ techniques, platelet-rich plasma (PRP) injection has received much attention and is the topic of this thesis. PLATELET-RICH PLASMA (PRP) What is PRP? To create a PRP preparation, the patient’s blood components (platelets, leukocytes, red blood cells, and plasma) must first be separated by centrifugation. The platelet-rich fraction must then be isolated. This yields PRP, which is a small volume of autologous blood plasma with a platelet concentration that is 5 to 10 times greater than normal. 5 The platelet granules contain hundreds of proteins called growth factors. The activation and subsequent degranulation of the platelets in PRP results in the release of these growth factors. 6,7 The basic growth factors that enhance the repair process include platelet-derived growth factor-AB (PDGF-AB), transforming growth factor ß1 (TGF-ß1), epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF). 7,8 When injected, these growth factors are thought to play an important role in cell proliferation,